Contributed by James Craig Burley (craig@jcb-sc.com). Inspired by a first pass at translating g77-0.5.16/f/DOC that was contributed to Craig by David Ronis (ronis@onsager.chem.mcgill.ca).

## Short Contents

- Introduction
- GNU GENERAL PUBLIC LICENSE
- GNU Free Documentation License
- Contributors to GNU Fortran
- Funding Free Software
- 1 Funding GNU Fortran
- 2 Getting Started
- 3 What is GNU Fortran?
- 4 Compile Fortran, C, or Other Programs
- 5 GNU Fortran Command Options
- 6 News About GNU Fortran
- 7 User-visible Changes
- 8 The GNU Fortran Language
- 9 Other Dialects
- 10 The GNU Fortran Compiler
- 11 Other Compilers
- 12 Other Languages
- 13 Debugging and Interfacing
- 14 Collected Fortran Wisdom
- 15 Known Causes of Trouble with GNU Fortran
- 16 Open Questions
- 17 Reporting Bugs
- 18 How To Get Help with GNU Fortran
- 19 Adding Options
- 20 Projects
- 21 Front End
- 22 Diagnostics
- Keyword Index

## Table of Contents

- Introduction
- GNU GENERAL PUBLIC LICENSE
  - Preamble
  - How to Apply These Terms to Your New Programs
- GNU Free Documentation License
  - ADDENDUM: How to use this License for your documents
- Contributors to GNU Fortran
- Funding Free Software
- 1 Funding GNU Fortran
- 2 Getting Started
- 3 What is GNU Fortran?
- 4 Compile Fortran, C, or Other Programs
- 5 GNU Fortran Command Options
  - 5.1 Option Summary
  - 5.2 Options Controlling the Kind of Output
  - 5.3 Shorthand Options
  - 5.4 Options Controlling Fortran Dialect
  - 5.5 Options to Request or Suppress Warnings
  - 5.6 Options for Debugging Your Program or GNU Fortran
  - 5.7 Options That Control Optimization
  - 5.8 Options Controlling the Preprocessor
  - 5.9 Options for Directory Search
  - 5.10 Options for Code Generation Conventions
  - 5.11 Environment Variables Affecting GNU Fortran
- 6 News About GNU Fortran
- 7 User-visible Changes
- 8 The GNU Fortran Language
  - 8.1 Direction of Language Development
  - 8.2 ANSI FORTRAN 77 Standard Support
    - 8.2.1 No Passing External Assumed-length
    - 8.2.2 No Passing Dummy Assumed-length
    - 8.2.3 No Pathological Implied-DO
    - 8.2.4 No Useless Implied-DO
  - 8.3 Conformance
  - 8.4 Notation Used in This Chapter
  - 8.5 Fortran Terms and Concepts
    - 8.5.1 Syntactic Items
    - 8.5.2 Statements, Comments, and Lines
    - 8.5.3 Scope of Symbolic Names and Statement Labels
  - 8.6 Characters, Lines, and Execution Sequence
    - 8.6.1 GNU Fortran Character Set
    - 8.6.2 Lines
    - 8.6.3 Continuation Line
    - 8.6.4 Statements
    - 8.6.5 Statement Labels
    - 8.6.6 Order of Statements and Lines
    - 8.6.7 Including Source Text
    - 8.6.8 Cpp-style directives
  - 8.7 Data Types and Constants
    - 8.7.1 Data Types
      - 8.7.1.1 Double Notation
      - 8.7.1.2 Star Notation
      - 8.7.1.3 Kind Notation
    - 8.7.2 Constants
    - 8.7.3 Integer Type
    - 8.7.4 Character Type
  - 8.8 Expressions
    - 8.8.1 The `%LOC()` Construct
  - 8.9 Specification Statements
    - 8.9.1 `NAMELIST` Statement
    - 8.9.2 `DOUBLE COMPLEX` Statement
  - 8.10 Control Statements
    - 8.10.1 DO WHILE
    - 8.10.2 END DO
    - 8.10.3 Construct Names
    - 8.10.4 The `CYCLE` and `EXIT` Statements
  - 8.11 Functions and Subroutines
    - 8.11.1 The `%VAL()` Construct
    - 8.11.2 The `%REF()` Construct
    - 8.11.3 The `%DESCR()` Construct
    - 8.11.4 Generics and Specifics
    - 8.11.5 `REAL()` and `AIMAG()` of Complex
    - 8.11.6 `CMPLX()` of `DOUBLE PRECISION`
    - 8.11.7 MIL-STD 1753 Support
    - 8.11.8 f77/f2c Intrinsics
    - 8.11.9 Table of Intrinsic Functions
      - 8.11.9.1 Abort Intrinsic
      - 8.11.9.2 Abs Intrinsic
      - 8.11.9.3 Access Intrinsic
      - 8.11.9.4 AChar Intrinsic
      - 8.11.9.5 ACos Intrinsic
      - 8.11.9.6 AdjustL Intrinsic
      - 8.11.9.7 AdjustR Intrinsic
      - 8.11.9.8 AImag Intrinsic
      - 8.11.9.9 AInt Intrinsic
      - 8.11.9.10 Alarm Intrinsic
      - 8.11.9.11 All Intrinsic
      - 8.11.9.12 Allocated Intrinsic
      - 8.11.9.13 ALog Intrinsic
      - 8.11.9.14 ALog10 Intrinsic
      - 8.11.9.15 AMax0 Intrinsic
      - 8.11.9.16 AMax1 Intrinsic
      - 8.11.9.17 AMin0 Intrinsic
      - 8.11.9.18 AMin1 Intrinsic
      - 8.11.9.19 AMod Intrinsic
      - 8.11.9.20 And Intrinsic
      - 8.11.9.21 ANInt Intrinsic
      - 8.11.9.22 Any Intrinsic
      - 8.11.9.23 ASin Intrinsic
      - 8.11.9.24 Associated Intrinsic
      - 8.11.9.25 ATan Intrinsic
      - 8.11.9.26 ATan2 Intrinsic
      - 8.11.9.27 BesJ0 Intrinsic
      - 8.11.9.28 BesJ1 Intrinsic
      - 8.11.9.29 BesJN Intrinsic
      - 8.11.9.30 BesY0 Intrinsic
      - 8.11.9.31 BesY1 Intrinsic
      - 8.11.9.32 BesYN Intrinsic
      - 8.11.9.33 Bit_Size Intrinsic
      - 8.11.9.34 BTest Intrinsic
      - 8.11.9.35 CAbs Intrinsic
      - 8.11.9.36 CCos Intrinsic
      - 8.11.9.37 Ceiling Intrinsic
      - 8.11.9.38 CExp Intrinsic
      - 8.11.9.39 Char Intrinsic
      - 8.11.9.40 ChDir Intrinsic (subroutine)
      - 8.11.9.41 ChMod Intrinsic (subroutine)
      - 8.11.9.42 CLog Intrinsic
      - 8.11.9.43 Cmplx Intrinsic
      - 8.11.9.44 Complex Intrinsic
      - 8.11.9.45 Conjg Intrinsic
      - 8.11.9.46 Cos Intrinsic
      - 8.11.9.47 CosH Intrinsic
      - 8.11.9.48 Count Intrinsic
      - 8.11.9.49 CPU_Time Intrinsic
      - 8.11.9.50 CShift Intrinsic
      - 8.11.9.51 CSin Intrinsic
      - 8.11.9.52 CSqRt Intrinsic
      - 8.11.9.53 CTime Intrinsic (subroutine)
      - 8.11.9.54 CTime Intrinsic (function)
      - 8.11.9.55 DAbs Intrinsic
      - 8.11.9.56 DACos Intrinsic
      - 8.11.9.57 DASin Intrinsic
      - 8.11.9.58 DATan Intrinsic
      - 8.11.9.59 DATan2 Intrinsic
      - 8.11.9.60 Date_and_Time Intrinsic
      - 8.11.9.61 DbesJ0 Intrinsic
      - 8.11.9.62 DbesJ1 Intrinsic
      - 8.11.9.63 DbesJN Intrinsic
      - 8.11.9.64 DbesY0 Intrinsic
      - 8.11.9.65 DbesY1 Intrinsic
      - 8.11.9.66 DbesYN Intrinsic
      - 8.11.9.67 Dble Intrinsic
      - 8.11.9.68 DCos Intrinsic
      - 8.11.9.69 DCosH Intrinsic
      - 8.11.9.70 DDiM Intrinsic
      - 8.11.9.71 DErF Intrinsic
      - 8.11.9.72 DErFC Intrinsic
      - 8.11.9.73 DExp Intrinsic
      - 8.11.9.74 Digits Intrinsic
      - 8.11.9.75 DiM Intrinsic
      - 8.11.9.76 DInt Intrinsic
      - 8.11.9.77 DLog Intrinsic
      - 8.11.9.78 DLog10 Intrinsic
      - 8.11.9.79 DMax1 Intrinsic
      - 8.11.9.80 DMin1 Intrinsic
      - 8.11.9.81 DMod Intrinsic
      - 8.11.9.82 DNInt Intrinsic
      - 8.11.9.83 Dot_Product Intrinsic
      - 8.11.9.84 DProd Intrinsic
      - 8.11.9.85 DSign Intrinsic
      - 8.11.9.86 DSin Intrinsic
      - 8.11.9.87 DSinH Intrinsic
      - 8.11.9.88 DSqRt Intrinsic
      - 8.11.9.89 DTan Intrinsic
      - 8.11.9.90 DTanH Intrinsic
      - 8.11.9.91 DTime Intrinsic (subroutine)
      - 8.11.9.92 EOShift Intrinsic
      - 8.11.9.93 Epsilon Intrinsic
      - 8.11.9.94 ErF Intrinsic
      - 8.11.9.95 ErFC Intrinsic
      - 8.11.9.96 ETime Intrinsic (subroutine)
      - 8.11.9.97 ETime Intrinsic (function)
      - 8.11.9.98 Exit Intrinsic
      - 8.11.9.99 Exp Intrinsic
      - 8.11.9.100 Exponent Intrinsic
      - 8.11.9.101 FDate Intrinsic (subroutine)
      - 8.11.9.102 FDate Intrinsic (function)
      - 8.11.9.103 FGet Intrinsic (subroutine)
      - 8.11.9.104 FGetC Intrinsic (subroutine)
      - 8.11.9.105 Float Intrinsic
      - 8.11.9.106 Floor Intrinsic
      - 8.11.9.107 Flush Intrinsic
      - 8.11.9.108 FNum Intrinsic
      - 8.11.9.109 FPut Intrinsic (subroutine)
      - 8.11.9.110 FPutC Intrinsic (subroutine)
      - 8.11.9.111 Fraction Intrinsic
      - 8.11.9.112 FSeek Intrinsic
      - 8.11.9.113 FStat Intrinsic (subroutine)
      - 8.11.9.114 FStat Intrinsic (function)
      - 8.11.9.115 FTell Intrinsic (subroutine)
      - 8.11.9.116 FTell Intrinsic (function)
      - 8.11.9.117 GError Intrinsic
      - 8.11.9.118 GetArg Intrinsic
      - 8.11.9.119 GetCWD Intrinsic (subroutine)
      - 8.11.9.120 GetCWD Intrinsic (function)
      - 8.11.9.121 GetEnv Intrinsic
      - 8.11.9.122 GetGId Intrinsic
      - 8.11.9.123 GetLog Intrinsic
      - 8.11.9.124 GetPId Intrinsic
      - 8.11.9.125 GetUId Intrinsic
      - 8.11.9.126 GMTime Intrinsic
      - 8.11.9.127 HostNm Intrinsic (subroutine)
      - 8.11.9.128 HostNm Intrinsic (function)
      - 8.11.9.129 Huge Intrinsic
      - 8.11.9.130 IAbs Intrinsic
      - 8.11.9.131 IAChar Intrinsic
      - 8.11.9.132 IAnd Intrinsic
      - 8.11.9.133 IArgC Intrinsic
      - 8.11.9.134 IBClr Intrinsic
      - 8.11.9.135 IBits Intrinsic
      - 8.11.9.136 IBSet Intrinsic
      - 8.11.9.137 IChar Intrinsic
      - 8.11.9.138 IDate Intrinsic (UNIX)
      - 8.11.9.139 IDiM Intrinsic
      - 8.11.9.140 IDInt Intrinsic
      - 8.11.9.141 IDNInt Intrinsic
      - 8.11.9.142 IEOr Intrinsic
      - 8.11.9.143 IErrNo Intrinsic
      - 8.11.9.144 IFix Intrinsic
      - 8.11.9.145 Imag Intrinsic
      - 8.11.9.146 ImagPart Intrinsic
      - 8.11.9.147 Index Intrinsic
      - 8.11.9.148 Int Intrinsic
      - 8.11.9.149 Int2 Intrinsic
      - 8.11.9.150 Int8 Intrinsic
      - 8.11.9.151 IOr Intrinsic
      - 8.11.9.152 IRand Intrinsic
      - 8.11.9.153 IsaTty Intrinsic
      - 8.11.9.154 IShft Intrinsic
      - 8.11.9.155 IShftC Intrinsic
      - 8.11.9.156 ISign Intrinsic
      - 8.11.9.157 ITime Intrinsic
      - 8.11.9.158 Kill Intrinsic (subroutine)
      - 8.11.9.159 Kind Intrinsic
      - 8.11.9.160 LBound Intrinsic
      - 8.11.9.161 Len Intrinsic
      - 8.11.9.162 Len_Trim Intrinsic
      - 8.11.9.163 LGe Intrinsic
      - 8.11.9.164 LGt Intrinsic
      - 8.11.9.165 Link Intrinsic (subroutine)
      - 8.11.9.166 LLe Intrinsic
      - 8.11.9.167 LLt Intrinsic
      - 8.11.9.168 LnBlnk Intrinsic
      - 8.11.9.169 Loc Intrinsic
      - 8.11.9.170 Log Intrinsic
      - 8.11.9.171 Log10 Intrinsic
      - 8.11.9.172 Logical Intrinsic
      - 8.11.9.173 Long Intrinsic
      - 8.11.9.174 LShift Intrinsic
      - 8.11.9.175 LStat Intrinsic (subroutine)
      - 8.11.9.176 LStat Intrinsic (function)
      - 8.11.9.177 LTime Intrinsic
      - 8.11.9.178 MatMul Intrinsic
      - 8.11.9.179 Max Intrinsic
      - 8.11.9.180 Max0 Intrinsic
      - 8.11.9.181 Max1 Intrinsic
      - 8.11.9.182 MaxExponent Intrinsic
      - 8.11.9.183 MaxLoc Intrinsic
      - 8.11.9.184 MaxVal Intrinsic
      - 8.11.9.185 MClock Intrinsic
      - 8.11.9.186 MClock8 Intrinsic
      - 8.11.9.187 Merge Intrinsic
      - 8.11.9.188 Min Intrinsic
      - 8.11.9.189 Min0 Intrinsic
      - 8.11.9.190 Min1 Intrinsic
      - 8.11.9.191 MinExponent Intrinsic
      - 8.11.9.192 MinLoc Intrinsic
      - 8.11.9.193 MinVal Intrinsic
      - 8.11.9.194 Mod Intrinsic
      - 8.11.9.195 Modulo Intrinsic
      - 8.11.9.196 MvBits Intrinsic
      - 8.11.9.197 Nearest Intrinsic
      - 8.11.9.198 NInt Intrinsic
      - 8.11.9.199 Not Intrinsic
      - 8.11.9.200 Or Intrinsic
      - 8.11.9.201 Pack Intrinsic
      - 8.11.9.202 PError Intrinsic
      - 8.11.9.203 Precision Intrinsic
      - 8.11.9.204 Present Intrinsic
      - 8.11.9.205 Product Intrinsic
      - 8.11.9.206 Radix Intrinsic
      - 8.11.9.207 Rand Intrinsic
      - 8.11.9.208 Random_Number Intrinsic
      - 8.11.9.209 Random_Seed Intrinsic
      - 8.11.9.210 Range Intrinsic
      - 8.11.9.211 Real Intrinsic
      - 8.11.9.212 RealPart Intrinsic
      - 8.11.9.213 Rename Intrinsic (subroutine)
      - 8.11.9.214 Repeat Intrinsic
      - 8.11.9.215 Reshape Intrinsic
      - 8.11.9.216 RRSpacing Intrinsic
      - 8.11.9.217 RShift Intrinsic
      - 8.11.9.218 Scale Intrinsic
      - 8.11.9.219 Scan Intrinsic
      - 8.11.9.220 Second Intrinsic (function)
      - 8.11.9.221 Second Intrinsic (subroutine)
      - 8.11.9.222 Selected_Int_Kind Intrinsic
      - 8.11.9.223 Selected_Real_Kind Intrinsic
      - 8.11.9.224 Set_Exponent Intrinsic
      - 8.11.9.225 Shape Intrinsic
      - 8.11.9.226 Short Intrinsic
      - 8.11.9.227 Sign Intrinsic
      - 8.11.9.228 Signal Intrinsic (subroutine)
      - 8.11.9.229 Sin Intrinsic
      - 8.11.9.230 SinH Intrinsic
      - 8.11.9.231 Sleep Intrinsic
      - 8.11.9.232 Sngl Intrinsic
      - 8.11.9.233 Spacing Intrinsic
      - 8.11.9.234 Spread Intrinsic
      - 8.11.9.235 SqRt Intrinsic
      - 8.11.9.236 SRand Intrinsic
      - 8.11.9.237 Stat Intrinsic (subroutine)
      - 8.11.9.238 Stat Intrinsic (function)
      - 8.11.9.239 Sum Intrinsic
      - 8.11.9.240 SymLnk Intrinsic (subroutine)
      - 8.11.9.241 System Intrinsic (subroutine)
      - 8.11.9.242 System_Clock Intrinsic
      - 8.11.9.243 Tan Intrinsic
      - 8.11.9.244 TanH Intrinsic
      - 8.11.9.245 Time Intrinsic (UNIX)
      - 8.11.9.246 Time8 Intrinsic
      - 8.11.9.247 Tiny Intrinsic
      - 8.11.9.248 Transfer Intrinsic
      - 8.11.9.249 Transpose Intrinsic
      - 8.11.9.250 Trim Intrinsic
      - 8.11.9.251 TtyNam Intrinsic (subroutine)
      - 8.11.9.252 TtyNam Intrinsic (function)
      - 8.11.9.253 UBound Intrinsic
      - 8.11.9.254 UMask Intrinsic (subroutine)
      - 8.11.9.255 Unlink Intrinsic (subroutine)
      - 8.11.9.256 Unpack Intrinsic
      - 8.11.9.257 Verify Intrinsic
      - 8.11.9.258 XOr Intrinsic
      - 8.11.9.259 ZAbs Intrinsic
      - 8.11.9.260 ZCos Intrinsic
      - 8.11.9.261 ZExp Intrinsic
      - 8.11.9.262 ZLog Intrinsic
      - 8.11.9.263 ZSin Intrinsic
      - 8.11.9.264 ZSqRt Intrinsic
  - 8.12 Scope and Classes of Symbolic Names
    - 8.12.1 Underscores in Symbol Names
  - 8.13 I/O
  - 8.14 Fortran 90 Features
- 9 Other Dialects
  - 9.1 Source Form
    - 9.1.1 Carriage Returns
    - 9.1.2 Tabs
    - 9.1.3 Short Lines
    - 9.1.4 Long Lines
    - 9.1.5 Ampersand Continuation Line
  - 9.2 Trailing Comment
  - 9.3 Debug Line
  - 9.4 Dollar Signs in Symbol Names
  - 9.5 Case Sensitivity
  - 9.6 VXT Fortran
    - 9.6.1 Meaning of Double Quote
    - 9.6.2 Meaning of Exclamation Point in Column 6
  - 9.7 Fortran 90
  - 9.8 Pedantic Compilation
  - 9.9 Distensions
    - 9.9.1 Implicit Argument Conversion
    - 9.9.2 Ugly Assumed-Size Arrays
    - 9.9.3 Ugly Complex Part Extraction
    - 9.9.4 Ugly Null Arguments
    - 9.9.5 Ugly Conversion of Initializers
    - 9.9.6 Ugly Integer Conversions
    - 9.9.7 Ugly Assigned Labels
- 10 The GNU Fortran Compiler
  - 10.1 Compiler Limits
  - 10.2 Run-time Environment Limits
    - 10.2.1 Timer Wraparounds
    - 10.2.2 Year 2000 (Y2K) Problems
    - 10.2.3 Array Size
    - 10.2.4 Character-variable Length
    - 10.2.5 Year 10000 (Y10K) Problems
  - 10.3 Compiler Types
  - 10.4 Compiler Constants
  - 10.5 Compiler Intrinsics
    - 10.5.1 Intrinsic Groups
    - 10.5.2 Other Intrinsics
      - 10.5.2.1 ACosD Intrinsic
      - 10.5.2.2 AIMax0 Intrinsic
      - 10.5.2.3 AIMin0 Intrinsic
      - 10.5.2.4 AJMax0 Intrinsic
      - 10.5.2.5 AJMin0 Intrinsic
      - 10.5.2.6 ASinD Intrinsic
      - 10.5.2.7 ATan2D Intrinsic
      - 10.5.2.8 ATanD Intrinsic
      - 10.5.2.9 BITest Intrinsic
      - 10.5.2.10 BJTest Intrinsic
      - 10.5.2.11 CDAbs Intrinsic
      - 10.5.2.12 CDCos Intrinsic
      - 10.5.2.13 CDExp Intrinsic
      - 10.5.2.14 CDLog Intrinsic
      - 10.5.2.15 CDSin Intrinsic
      - 10.5.2.16 CDSqRt Intrinsic
      - 10.5.2.17 ChDir Intrinsic (function)
      - 10.5.2.18 ChMod Intrinsic (function)
      - 10.5.2.19 CosD Intrinsic
      - 10.5.2.20 DACosD Intrinsic
      - 10.5.2.21 DASinD Intrinsic
      - 10.5.2.22 DATan2D Intrinsic
      - 10.5.2.23 DATanD Intrinsic
      - 10.5.2.24 Date Intrinsic
      - 10.5.2.25 DbleQ Intrinsic
      - 10.5.2.26 DCmplx Intrinsic
      - 10.5.2.27 DConjg Intrinsic
      - 10.5.2.28 DCosD Intrinsic
      - 10.5.2.29 DFloat Intrinsic
      - 10.5.2.30 DFlotI Intrinsic
      - 10.5.2.31 DFlotJ Intrinsic
      - 10.5.2.32 DImag Intrinsic
      - 10.5.2.33 DReal Intrinsic
      - 10.5.2.34 DSinD Intrinsic
      - 10.5.2.35 DTanD Intrinsic
      - 10.5.2.36 DTime Intrinsic (function)
      - 10.5.2.37 FGet Intrinsic (function)
      - 10.5.2.38 FGetC Intrinsic (function)
      - 10.5.2.39 FloatI Intrinsic
      - 10.5.2.40 FloatJ Intrinsic
      - 10.5.2.41 FPut Intrinsic (function)
      - 10.5.2.42 FPutC Intrinsic (function)
      - 10.5.2.43 IDate Intrinsic (VXT)
      - 10.5.2.44 IIAbs Intrinsic
      - 10.5.2.45 IIAnd Intrinsic
      - 10.5.2.46 IIBClr Intrinsic
      - 10.5.2.47 IIBits Intrinsic
      - 10.5.2.48 IIBSet Intrinsic
      - 10.5.2.49 IIDiM Intrinsic
      - 10.5.2.50 IIDInt Intrinsic
      - 10.5.2.51 IIDNnt Intrinsic
      - 10.5.2.52 IIEOr Intrinsic
      - 10.5.2.53 IIFix Intrinsic
      - 10.5.2.54 IInt Intrinsic
      - 10.5.2.55 IIOr Intrinsic
      - 10.5.2.56 IIQint Intrinsic
      - 10.5.2.57 IIQNnt Intrinsic
      - 10.5.2.58 IIShftC Intrinsic
      - 10.5.2.59 IISign Intrinsic
      - 10.5.2.60 IMax0 Intrinsic
      - 10.5.2.61 IMax1 Intrinsic
      - 10.5.2.62 IMin0 Intrinsic
      - 10.5.2.63 IMin1 Intrinsic
      - 10.5.2.64 IMod Intrinsic
      - 10.5.2.65 INInt Intrinsic
      - 10.5.2.66 INot Intrinsic
      - 10.5.2.67 IZExt Intrinsic
      - 10.5.2.68 JIAbs Intrinsic
      - 10.5.2.69 JIAnd Intrinsic
      - 10.5.2.70 JIBClr Intrinsic
      - 10.5.2.71 JIBits Intrinsic
      - 10.5.2.72 JIBSet Intrinsic
      - 10.5.2.73 JIDiM Intrinsic
      - 10.5.2.74 JIDInt Intrinsic
      - 10.5.2.75 JIDNnt Intrinsic
      - 10.5.2.76 JIEOr Intrinsic
      - 10.5.2.77 JIFix Intrinsic
      - 10.5.2.78 JInt Intrinsic
      - 10.5.2.79 JIOr Intrinsic
      - 10.5.2.80 JIQint Intrinsic
      - 10.5.2.81 JIQNnt Intrinsic
      - 10.5.2.82 JIShft Intrinsic
      - 10.5.2.83 JIShftC Intrinsic
      - 10.5.2.84 JISign Intrinsic
      - 10.5.2.85 JMax0 Intrinsic
      - 10.5.2.86 JMax1 Intrinsic
      - 10.5.2.87 JMin0 Intrinsic
      - 10.5.2.88 JMin1 Intrinsic
      - 10.5.2.89 JMod Intrinsic
      - 10.5.2.90 JNInt Intrinsic
      - 10.5.2.91 JNot Intrinsic
      - 10.5.2.92 JZExt Intrinsic
      - 10.5.2.93 Kill Intrinsic (function)
      - 10.5.2.94 Link Intrinsic (function)
      - 10.5.2.95 QAbs Intrinsic
      - 10.5.2.96 QACos Intrinsic
      - 10.5.2.97 QACosD Intrinsic
      - 10.5.2.98 QASin Intrinsic
      - 10.5.2.99 QASinD Intrinsic
      - 10.5.2.100 QATan Intrinsic
      - 10.5.2.101 QATan2 Intrinsic
      - 10.5.2.102 QATan2D Intrinsic
      - 10.5.2.103 QATanD Intrinsic
      - 10.5.2.104 QCos Intrinsic
      - 10.5.2.105 QCosD Intrinsic
      - 10.5.2.106 QCosH Intrinsic
      - 10.5.2.107 QDiM Intrinsic
      - 10.5.2.108 QExp Intrinsic
      - 10.5.2.109 QExt Intrinsic
      - 10.5.2.110 QExtD Intrinsic
      - 10.5.2.111 QFloat Intrinsic
      - 10.5.2.112 QInt Intrinsic
      - 10.5.2.113 QLog Intrinsic
      - 10.5.2.114 QLog10 Intrinsic
      - 10.5.2.115 QMax1 Intrinsic
      - 10.5.2.116 QMin1 Intrinsic
      - 10.5.2.117 QMod Intrinsic
      - 10.5.2.118 QNInt Intrinsic
      - 10.5.2.119 QSin Intrinsic
      - 10.5.2.120 QSinD Intrinsic
      - 10.5.2.121 QSinH Intrinsic
      - 10.5.2.122 QSqRt Intrinsic
      - 10.5.2.123 QTan Intrinsic
      - 10.5.2.124 QTanD Intrinsic
      - 10.5.2.125 QTanH Intrinsic
      - 10.5.2.126 Rename Intrinsic (function)
      - 10.5.2.127 Secnds Intrinsic
      - 10.5.2.128 Signal Intrinsic (function)
      - 10.5.2.129 SinD Intrinsic
      - 10.5.2.130 SnglQ Intrinsic
      - 10.5.2.131 SymLnk Intrinsic (function)
      - 10.5.2.132 System Intrinsic (function)
      - 10.5.2.133 TanD Intrinsic
      - 10.5.2.134 Time Intrinsic (VXT)
      - 10.5.2.135 UMask Intrinsic (function)
      - 10.5.2.136 Unlink Intrinsic (function)
      - 10.5.2.137 ZExt Intrinsic
- 11 Other Compilers
  - 11.1 Dropping f2c Compatibility
  - 11.2 Compilers Other Than f2c
- 12 Other Languages
  - 12.1 Tools and advice for interoperating with C and C++
    - 12.1.1 C Interfacing Tools
    - 12.1.2 Accessing Type Information in C
    - 12.1.3 Generating Skeletons and Prototypes with f2c
    - 12.1.4 C++ Considerations
    - 12.1.5 Startup Code
- 13 Debugging and Interfacing
  - 13.1 Main Program Unit (PROGRAM)
  - 13.2 Procedures (SUBROUTINE and FUNCTION)
  - 13.3 Functions (FUNCTION and RETURN)
  - 13.4 Names
  - 13.5 Common Blocks (COMMON)
  - 13.6 Local Equivalence Areas (EQUIVALENCE)
  - 13.7 Complex Variables (COMPLEX)
  - 13.8 Arrays (DIMENSION)
  - 13.9 Adjustable Arrays (DIMENSION)
  - 13.10 Alternate Entry Points (ENTRY)
  - 13.11 Alternate Returns (SUBROUTINE and RETURN)
  - 13.12 Assigned Statement Labels (ASSIGN and GOTO)
  - 13.13 Run-time Library Errors
- 14 Collected Fortran Wisdom
  - 14.1 Advantages Over f2c
    - 14.1.1 Language Extensions
    - 14.1.2 Diagnostic Abilities
    - 14.1.3 Compiler Options
    - 14.1.4 Compiler Speed
    - 14.1.5 Program Speed
    - 14.1.6 Ease of Debugging
    - 14.1.7 Character and Hollerith Constants
  - 14.2 Block Data and Libraries
  - 14.3 Loops
  - 14.4 Working Programs
    - 14.4.1 Not My Type
    - 14.4.2 Variables Assumed To Be Zero
    - 14.4.3 Variables Assumed To Be Saved
    - 14.4.4 Unwanted Variables
    - 14.4.5 Unused Arguments
    - 14.4.6 Surprising Interpretations of Code
    - 14.4.7 Aliasing Assumed To Work
    - 14.4.8 Output Assumed To Flush
    - 14.4.9 Large File Unit Numbers
    - 14.4.10 Floating-point precision
    - 14.4.11 Inconsistent Calling Sequences
  - 14.5 Overly Convenient Command-line Options
  - 14.6 Faster Programs
    - 14.6.1 Aligned Data
    - 14.6.2 Prefer Automatic Uninitialized Variables
    - 14.6.3 Avoid f2c Compatibility
    - 14.6.4 Use Submodel Options
- 15 Known Causes of Trouble with GNU Fortran
  - 15.1 Bugs Not In GNU Fortran
    - 15.1.1 Signal 11 and Friends
    - 15.1.2 Cannot Link Fortran Programs
    - 15.1.3 Large Common Blocks
    - 15.1.4 Debugger Problems
    - 15.1.5 NeXTStep Problems
    - 15.1.6 Stack Overflow
    - 15.1.7 Nothing Happens
    - 15.1.8 Strange Behavior at Run Time
    - 15.1.9 Floating-point Errors
  - 15.2 Known Bugs In GNU Fortran
  - 15.3 Missing Features
    - 15.3.1 Better Source Model
    - 15.3.2 Fortran 90 Support
    - 15.3.3 Intrinsics in `PARAMETER` Statements
    - 15.3.4 Arbitrary Concatenation
    - 15.3.5 `SELECT CASE` on `CHARACTER` Type
    - 15.3.6 `RECURSIVE` Keyword
    - 15.3.7 Increasing Precision/Range
    - 15.3.8 Popular Non-standard Types
    - 15.3.9 Full Support for Compiler Types
    - 15.3.10 Array Bounds Expressions
    - 15.3.11 POINTER Statements
    - 15.3.12 Sensible Non-standard Constructs
    - 15.3.13 `READONLY` Keyword
    - 15.3.14 `FLUSH` Statement
    - 15.3.15 Expressions in `FORMAT` Statements
    - 15.3.16 Explicit Assembler Code
    - 15.3.17 Q Edit Descriptor
    - 15.3.18 Old-style PARAMETER Statements
    - 15.3.19 `TYPE` and `ACCEPT` I/O Statements
    - 15.3.20 `STRUCTURE`, `UNION`, `RECORD`, `MAP`
    - 15.3.21 `OPEN`, `CLOSE`, and `INQUIRE` Keywords
    - 15.3.22 `ENCODE` and `DECODE`
    - 15.3.23 `AUTOMATIC` Statement
    - 15.3.24 Suppressing Space Padding of Source Lines
    - 15.3.25 Fortran Preprocessor
    - 15.3.26 Bit Operations on Floating-point Data
    - 15.3.27 Really Ugly Character Assignments
    - 15.3.28 `POSIX` Standard
    - 15.3.29 Floating-point Exception Handling
    - 15.3.30 Nonportable Conversions
    - 15.3.31 Large Automatic Arrays
    - 15.3.32 Support for Threads
    - 15.3.33 Enabling Debug Lines
    - 15.3.34 Better Warnings
    - 15.3.35 Gracefully Handle Sensible Bad Code
    - 15.3.36 Non-standard Conversions
    - 15.3.37 Non-standard Intrinsics
    - 15.3.38 Modifying `DO` Variable
    - 15.3.39 Better Pedantic Compilation
    - 15.3.40 Warn About Implicit Conversions
    - 15.3.41 Invalid Use of Hollerith Constant
    - 15.3.42 Dummy Array Without Dimensioning Dummy
    - 15.3.43 Invalid FORMAT Specifiers
    - 15.3.44 Ambiguous Dialects
    - 15.3.45 Unused Labels
    - 15.3.46 Informational Messages
    - 15.3.47 Uninitialized Variables at Run Time
    - 15.3.48 Portable Unformatted Files
    - 15.3.49 Better List-directed I/O
    - 15.3.50 Default to Console I/O
    - 15.3.51 Labels Visible to Debugger
  - 15.4 Disappointments and Misunderstandings
    - 15.4.1 Mangling of Names in Source Code
    - 15.4.2 Multiple Definitions of External Names
    - 15.4.3 Limitation on Implicit Declarations
  - 15.5 Certain Changes We Don't Want to Make
    - 15.5.1 Backslash in Constants
    - 15.5.2 Initializing Before Specifying
    - 15.5.3 Context-Sensitive Intrinsicness
    - 15.5.4 Context-Sensitive Constants
    - 15.5.5 Equivalence Versus Equality
    - 15.5.6 Order of Side Effects
  - 15.6 Warning Messages and Error Messages
- 16 Open Questions
- 17 Reporting Bugs
  - 17.1 Have You Found a Bug?
  - 17.2 How to Report Bugs
- 18 How To Get Help with GNU Fortran
- 19 Adding Options
- 20 Projects
  - 20.1 Improve Efficiency
  - 20.2 Better Optimization
  - 20.3 Simplify Porting
  - 20.4 More Extensions
  - 20.5 Machine Model
  - 20.6 Internals Documentation
  - 20.7 Internals Improvements
  - 20.8 Better Diagnostics
- 21 Front End
  - 21.1 Overview of Sources
  - 21.2 Overview of Translation Process
    - 21.2.1 g77stripcard
    - 21.2.2 lex.c
    - 21.2.3 sta.c
    - 21.2.4 sti.c
    - 21.2.5 stq.c
    - 21.2.6 stb.c
    - 21.2.7 expr.c
    - 21.2.8 stc.c
    - 21.2.9 std.c
    - 21.2.10 ste.c
    - 21.2.11 Gotchas (Transforming)
      - 21.2.11.1 Multi-character Lexemes
      - 21.2.11.2 Space-padding Lexemes
      - 21.2.11.3 Bizarre Free-form Hollerith Constants
      - 21.2.11.4 Hollerith Constants
      - 21.2.11.5 Confusing Function Keyword
      - 21.2.11.6 Weird READ
    - 21.2.12 TBD (Transforming)
  - 21.3 Philosophy of Code Generation
  - 21.4 Two-pass Design
    - 21.4.1 Two-pass Code
    - 21.4.2 Why Two Passes
  - 21.5 Challenges Posed
  - 21.6 Transforming Statements
    - 21.6.1 Statements Needing Temporaries
    - 21.6.2 Transforming DO WHILE
    - 21.6.3 Transforming Iterative DO
    - 21.6.4 Transforming Block IF
    - 21.6.5 Transforming SELECT CASE
  - 21.7 Transforming Expressions
  - 21.8 Internal Naming Conventions
- 22 Diagnostics
  - 22.1 `CMPAMBIG`
  - 22.2 `EXPIMP`
  - 22.3 `INTGLOB`
  - 22.4 `LEX`
  - 22.5 `GLOBALS`
  - 22.6 `LINKFAIL`
  - 22.7 `Y2KBAD`
- Keyword Index

Next: Copying, Up: (DIR)

## Introduction

This manual documents how to run, install and port g77, as well as its new features and incompatibilities, and how to report bugs. It corresponds to the GCC-3.4.4 version of g77.

Next: GNU Free Documentation License, Previous: Top, Up: Top

## GNU GENERAL PUBLIC LICENSE

Version 2, June 1991

         Copyright © 1989, 1991 Free Software Foundation, Inc.
         59 Temple Place - Suite 330, Boston, MA  02111-1307, USA

         Everyone is permitted to copy and distribute verbatim copies
         of this license document, but changing it is not allowed.

### Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software—to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.

Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The “Program”, below, refers to any such program or work, and a “work based on the Program” means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term “modification”.) Each licensee is addressed as “you”.

   Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.

1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

   You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:
   1. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.
   2. You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.
   3. If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

   These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.

   Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

   In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:
   1. Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
   2. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
   3. Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)

   The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.

   If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
5. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.
6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.
7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

   If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

   It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

   This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.
9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

   Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and “any later version”, you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.

10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.
    NO WARRANTY
11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

END OF TERMS AND CONDITIONS

### How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.

         one line to give the program's name and a brief idea of what it does.
         Copyright (C) year  name of author

         This program is free software; you can redistribute it and/or modify
         it under the terms of the GNU General Public License as published by
         the Free Software Foundation; either version 2 of the License, or
         (at your option) any later version.

         This program is distributed in the hope that it will be useful,
         but WITHOUT ANY WARRANTY; without even the implied warranty of
         MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
         GNU General Public License for more details.

         You should have received a copy of the GNU General Public License
         along with this program; if not, write to the Free Software Foundation,
         Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

         Gnomovision version 69, Copyright (C) year name of author
         Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
         type `show w'.
         This is free software, and you are welcome to redistribute it
         under certain conditions; type `show c' for details.

The hypothetical commands show w and show c should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than show w and show c; they could even be mouse-clicks or menu items—whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names:

         Yoyodyne, Inc., hereby disclaims all copyright interest in the program
         `Gnomovision' (which makes passes at compilers) written by James Hacker.

         signature of Ty Coon, 1 April 1989
         Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.

Next: Contributors, Previous: Copying, Up: Top

## GNU Free Documentation License

Version 1.2, November 2002

         Copyright © 2000,2001,2002 Free Software Foundation, Inc.
         59 Temple Place, Suite 330, Boston, MA  02111-1307, USA

         Everyone is permitted to copy and distribute verbatim copies
         of this license document, but changing it is not allowed.

0. PREAMBLE

   The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

   This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

   We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONS

   This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

   A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

   A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

   The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

   The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

   A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.

   Examples of suitable formats for Transparent copies include plain ascii without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

   The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

   A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

   The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING

   You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

   You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY

   If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

   If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

   If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

   It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

   You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

   1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
   2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
   3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
   4. Preserve all the copyright notices of the Document.
   5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
   6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
   7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
   8. Include an unaltered copy of this License.
   9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
   10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
   11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
   12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
   13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
   14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
   15. Preserve any Warranty Disclaimers.

   If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

   You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

   You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

   The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

   You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

   The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

   In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”

6. COLLECTIONS OF DOCUMENTS

   You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

   You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

   A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

   If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION

   Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warrany Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

   If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION

   You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

10. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

### ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

           Copyright (C)  year  your name.
           Permission is granted to copy, distribute and/or modify this document
           under the terms of the GNU Free Documentation License, Version 1.2
           or any later version published by the Free Software Foundation;
           with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
           A copy of the license is included in the section entitled ``GNU
           Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

             with the Invariant Sections being list their titles, with
             the Front-Cover Texts being list, and with the Back-Cover Texts
             being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

Next: Funding, Previous: GNU Free Documentation License, Up: Top

## Contributors to GNU Fortran

In addition to James Craig Burley, who wrote the front end, many people have helped create and improve GNU Fortran.

- The packaging and compiler portions of GNU Fortran are based largely on the GCC compiler. See Contributors to GCC (Using the GNU Compiler Collection (GCC)), for more information.
- The run-time library used by GNU Fortran is a repackaged version of the `libf2c` library (combined from the `libF77` and `libI77` libraries) provided as part of f2c, available for free from `netlib` sites on the Internet.
- Cygnus Support and The Free Software Foundation contributed significant money and/or equipment to Craig's efforts.
- The following individuals served as alpha testers prior to g77's public release. This work consisted of testing, researching, sometimes debugging, and occasionally providing small amounts of code and fixes for g77, plus offering plenty of helpful advice to Craig:
  - Jonathan Corbet
  - Dr. Mark Fernyhough
  - Takafumi Hayashi (The University of Aizu)—takafumi@u-aizu.ac.jp
  - Kate Hedstrom
  - Michel Kern (INRIA and Rice University)—Michel.Kern@inria.fr
  - Dr. A. O. V. Le Blanc
  - Dave Love
  - Rick Lutowski
  - Toon Moene
  - Rick Niles
  - Derk Reefman
  - Wayne K. Schroll
  - Bill Thorson
  - Pedro A. M. Vazquez
  - Ian Watson
- Dave Love (d.love@dl.ac.uk) wrote the libU77 part of the run-time library.
- Scott Snyder (snyder@d0sgif.fnal.gov) provided the patch to add rudimentary support for `INTEGER*1`, `INTEGER*2`, and `LOGICAL*1`. This inspired Craig to add further support, even though the resulting support would still be incomplete. This support is believed to be completed at version 3.4 of gcc by Roger Sayle (roger@eyesopen.com).
- David Ronis (ronis@onsager.chem.mcgill.ca) inspired and encouraged Craig to rewrite the documentation in texinfo format by contributing a first pass at a translation of the old g77-0.5.16/f/DOC file.
- Toon Moene (toon@moene.indiv.nluug.nl) performed some analysis of generated code as part of an overall project to improve g77 code generation to at least be as good as f2c used in conjunction with gcc. So far, this has resulted in the three, somewhat experimental, options added by g77 to the gcc compiler and its back end.

  (These, in turn, had made their way into the `egcs` version of the compiler, and do not exist in gcc version 2.8 or versions of g77 based on that version of gcc.)

- John Carr (jfc@mit.edu) wrote the alias analysis improvements.
- Thanks to Mary Cortani and the staff at Craftwork Solutions (support@craftwork.com) for all of their support.
- Many other individuals have helped debug, test, and improve g77 over the past several years, and undoubtedly more people will be doing so in the future. If you have done so, and would like to see your name listed in the above list, please ask! The default is that people wish to remain anonymous.

Next: Funding GNU Fortran, Previous: Contributors, Up: Top

## Funding Free Software

If you want to have more free software a few years from now, it makes sense for you to help encourage people to contribute funds for its development. The most effective approach known is to encourage commercial redistributors to donate.

Users of free software systems can boost the pace of development by encouraging for-a-fee distributors to donate part of their selling price to free software developers—the Free Software Foundation, and others.

The way to convince distributors to do this is to demand it and expect it from them. So when you compare distributors, judge them partly by how much they give to free software development. Show distributors they must compete to be the one who gives the most.

To make this approach work, you must insist on numbers that you can compare, such as, “We will donate ten dollars to the Frobnitz project for each disk sold.” Don't be satisfied with a vague promise, such as “A portion of the profits are donated,” since it doesn't give a basis for comparison.

Even a precise fraction “of the profits from this disk” is not very meaningful, since creative accounting and unrelated business decisions can greatly alter what fraction of the sales price counts as profit. If the price you pay is $50, ten percent of the profit is probably less than a dollar; it might be a few cents, or nothing at all.

Some redistributors do development work themselves. This is useful too; but to keep everyone honest, you need to inquire how much they do, and what kind. Some kinds of development make much more long-term difference than others. For example, maintaining a separate version of a program contributes very little; maintaining the standard version of a program for the whole community contributes much. Easy new ports contribute little, since someone else would surely do them; difficult ports such as adding a new CPU to the GNU Compiler Collection contribute more; major new features or packages contribute the most.

By establishing the idea that supporting further development is “the proper thing to do” when distributing free software for a fee, we can assure a steady flow of resources into making more free software.

         Copyright © 1994 Free Software Foundation, Inc.
         Verbatim copying and redistribution of this section is permitted
         without royalty; alteration is not permitted.

Next: Getting Started, Previous: Funding, Up: Top

## 1 Funding GNU Fortran

James Craig Burley (craig@jcb-sc.com), the original author of g77, stopped working on it in September 1999 (He has a web page at http://world.std.com/%7Eburley/.)

GNU Fortran is currently maintained by Toon Moene (toon@moene.indiv.nluug.nl), with the help of countless other volunteers.

As with other GNU software, funding is important because it can pay for needed equipment, personnel, and so on.

The FSF provides information on the best way to fund ongoing development of GNU software (such as GNU Fortran) in documents such as the “GNUS Bulletin”. Email gnu@gnu.org for information on funding the FSF.

Another important way to support work on GNU Fortran is to volunteer to help out.

Email gcc@gcc.gnu.org to volunteer for this work.

However, we strongly expect that there will never be a version 0.6 of g77. Work on this compiler has stopped as of the release of GCC 3.1, except for bug fixing. g77 will be succeeded by g95 - see http://g95.sourceforge.net.

See Funding Free Software, for more information.

Next: What is GNU Fortran?, Previous: Funding GNU Fortran, Up: Top

## 2 Getting Started

If you don't need help getting started reading the portions of this manual that are most important to you, you should skip this portion of the manual.

If you are new to compilers, especially Fortran compilers, or new to how compilers are structured under UNIX and UNIX-like systems, you'll want to see What is GNU Fortran?.

If you are new to GNU compilers, or have used only one GNU compiler in the past and not had to delve into how it lets you manage various versions and configurations of gcc, you should see G77 and GCC.

Everyone except experienced g77 users should see Invoking G77.

If you're acquainted with previous versions of g77, you should see News About GNU Fortran. Further, if you've actually used previous versions of g77, especially if you've written or modified Fortran code to be compiled by previous versions of g77, you should see Changes.

If you intend to write or otherwise compile code that is not already strictly conforming ANSI FORTRAN 77—and this is probably everyone—you should see Language.

If you run into trouble getting Fortran code to compile, link, run, or work properly, you might find answers if you see Debugging and Interfacing, see Collected Fortran Wisdom, and see Trouble. You might also find that the problems you are encountering are bugs in g77—see Bugs, for information on reporting them, after reading the other material.

If you need further help with g77, or with freely redistributable software in general, see Service.

If you would like to help the g77 project, see Funding GNU Fortran, for information on helping financially, and see Projects, for information on helping in other ways.

If you're generally curious about the future of g77, see Projects. If you're curious about its past, see Contributors, and see Funding GNU Fortran.

To see a few of the questions maintainers of g77 have, and that you might be able to answer, see Open Questions.

Next: G77 and GCC, Previous: Getting Started, Up: Top

## 3 What is GNU Fortran?

GNU Fortran, or g77, is designed initially as a free replacement for, or alternative to, the UNIX f77 command. (Similarly, gcc is designed as a replacement for the UNIX cc command.)

g77 also is designed to fit in well with the other fine GNU compilers and tools.

Sometimes these design goals conflict—in such cases, resolution often is made in favor of fitting in well with Project GNU. These cases are usually identified in the appropriate sections of this manual.

As compilers, g77, gcc, and f77 share the following characteristics:

- They read a user's program, stored in a file and containing instructions written in the appropriate language (Fortran, C, and so on). This file contains source code.

- They translate the user's program into instructions a computer can carry out more quickly than it takes to translate the instructions in the first place. These instructions are called machine code—code designed to be efficiently translated and processed by a machine such as a computer. Humans usually aren't as good writing machine code as they are at writing Fortran or C, because it is easy to make tiny mistakes writing machine code. When writing Fortran or C, it is easy to make big mistakes.

- They provide information in the generated machine code that can make it easier to find bugs in the program (using a debugging tool, called a debugger, such as gdb).

- They locate and gather machine code already generated to perform actions requested by statements in the user's program. This machine code is organized into libraries and is located and gathered during the link phase of the compilation process. (Linking often is thought of as a separate step, because it can be directly invoked via the ld command. However, the g77 and gcc commands, as with most compiler commands, automatically perform the linking step by calling on ld directly, unless asked to not do so by the user.)

- They attempt to diagnose cases where the user's program contains incorrect usages of the language. The diagnostics produced by the compiler indicate the problem and the location in the user's source file where the problem was first noticed. The user can use this information to locate and fix the problem. (Sometimes an incorrect usage of the language leads to a situation where the compiler can no longer make any sense of what follows—while a human might be able to—and thus ends up complaining about many “problems” it encounters that, in fact, stem from just one problem, usually the first one reported.)

- They attempt to diagnose cases where the user's program contains a correct usage of the language, but instructs the computer to do something questionable. These diagnostics often are in the form of warnings, instead of the errors that indicate incorrect usage of the language.

How these actions are performed is generally under the control of the user. Using command-line options, the user can specify how persnickety the compiler is to be regarding the program (whether to diagnose questionable usage of the language), how much time to spend making the generated machine code run faster, and so on.

g77 consists of several components:

- A modified version of the gcc command, which also might be installed as the system's cc command. (In many cases, cc refers to the system's “native” C compiler, which might be a non-GNU compiler, or an older version of gcc considered more stable or that is used to build the operating system kernel.)

- The g77 command itself, which also might be installed as the system's f77 command.

- The `libg2c` run-time library. This library contains the machine code needed to support capabilities of the Fortran language that are not directly provided by the machine code generated by the g77 compilation phase.

  `libg2c` is just the unique name g77 gives to its version of `libf2c` to distinguish it from any copy of `libf2c` installed from f2c (or versions of g77 that built `libf2c` under that same name) on the system.

  The maintainer of `libf2c` currently is dmg@bell-labs.com.

- The compiler itself, internally named `f771`.

  Note that `f771` does not generate machine code directly—it generates assembly code that is a more readable form of machine code, leaving the conversion to actual machine code to an assembler, usually named as.

gcc is often thought of as “the C compiler” only, but it does more than that. Based on command-line options and the names given for files on the command line, gcc determines which actions to perform, including preprocessing, compiling (in a variety of possible languages), assembling, and linking.

For example, the command gcc foo.c drives the file foo.c through the preprocessor cpp, then the C compiler (internally named `cc1`), then the assembler (usually as), then the linker (ld), producing an executable program named a.out (on UNIX systems).

As another example, the command gcc foo.cc would do much the same as gcc foo.c, but instead of using the C compiler named `cc1`, gcc would use the C++ compiler (named `cc1plus`).

In a GNU Fortran installation, gcc recognizes Fortran source files by name just like it does C and C++ source files. It knows to use the Fortran compiler named `f771`, instead of `cc1` or `cc1plus`, to compile Fortran files.

Non-Fortran-related operation of gcc is generally unaffected by installing the GNU Fortran version of gcc. However, without the installed version of gcc being the GNU Fortran version, gcc will not be able to compile and link Fortran programs—and since g77 uses gcc to do most of the actual work, neither will g77!

The g77 command is essentially just a front-end for the gcc command. Fortran users will normally use g77 instead of gcc, because g77 knows how to specify the libraries needed to link with Fortran programs (`libg2c` and `lm`). g77 can still compile and link programs and source files written in other languages, just like gcc.

The command g77 -v is a quick way to display lots of version information for the various programs used to compile a typical preprocessed Fortran source file—this produces much more output than gcc -v currently does. (If it produces an error message near the end of the output—diagnostics from the linker, usually ld—you might have an out-of-date `libf2c` that improperly handles complex arithmetic.) In the output of this command, the line beginning GNU Fortran Front End identifies the version number of GNU Fortran; immediately preceding that line is a line identifying the version of gcc with which that version of g77 was built.

The `libf2c` library is distributed with GNU Fortran for the convenience of its users, but is not part of GNU Fortran. It contains the procedures needed by Fortran programs while they are running.

For example, while code generated by g77 is likely to do additions, subtractions, and multiplications in line—in the actual compiled code—it is not likely to do trigonometric functions this way.

Instead, operations like trigonometric functions are compiled by the `f771` compiler (invoked by g77 when compiling Fortran code) into machine code that, when run, calls on functions in `libg2c`, so `libg2c` must be linked with almost every useful program having any component compiled by GNU Fortran. (As mentioned above, the g77 command takes care of all this for you.)

The `f771` program represents most of what is unique to GNU Fortran. While much of the `libg2c` component comes from the `libf2c` component of f2c, a free Fortran-to-C converter distributed by Bellcore (AT&T), plus `libU77`, provided by Dave Love, and the g77 command is just a small front-end to gcc, `f771` is a combination of two rather large chunks of code.

One chunk is the so-called GNU Back End, or GBE, which knows how to generate fast code for a wide variety of processors. The same GBE is used by the C, C++, and Fortran compiler programs `cc1`, `cc1plus`, and `f771`, plus others. Often the GBE is referred to as the “gcc back end” or even just “gcc”—in this manual, the term GBE is used whenever the distinction is important.

The other chunk of `f771` is the majority of what is unique about GNU Fortran—the code that knows how to interpret Fortran programs to determine what they are intending to do, and then communicate that knowledge to the GBE for actual compilation of those programs. This chunk is called the Fortran Front End (FFE). The `cc1` and `cc1plus` programs have their own front ends, for the C and C++ languages, respectively. These fronts ends are responsible for diagnosing incorrect usage of their respective languages by the programs the process, and are responsible for most of the warnings about questionable constructs as well. (The GBE handles producing some warnings, like those concerning possible references to undefined variables.)

Because so much is shared among the compilers for various languages, much of the behavior and many of the user-selectable options for these compilers are similar. For example, diagnostics (error messages and warnings) are similar in appearance; command-line options like -Wall have generally similar effects; and the quality of generated code (in terms of speed and size) is roughly similar (since that work is done by the shared GBE).

Next: Invoking G77, Previous: What is GNU Fortran?, Up: Top

## 4 Compile Fortran, C, or Other Programs

A GNU Fortran installation includes a modified version of the gcc command.

In a non-Fortran installation, gcc recognizes C, C++, and Objective-C source files.

In a GNU Fortran installation, gcc also recognizes Fortran source files and accepts Fortran-specific command-line options, plus some command-line options that are designed to cater to Fortran users but apply to other languages as well.

See Programming Languages Supported by GCC (Using the GNU Compiler Collection (GCC)), for information on the way different languages are handled by the GCC compiler (gcc).

Also provided as part of GNU Fortran is the g77 command. The g77 command is designed to make compiling and linking Fortran programs somewhat easier than when using the gcc command for these tasks. It does this by analyzing the command line somewhat and changing it appropriately before submitting it to the gcc command.

Use the -v option with g77 to see what is going on—the first line of output is the invocation of the gcc command.

Next: News, Previous: G77 and GCC, Up: Top

## 5 GNU Fortran Command Options

The g77 command supports all the options supported by the gcc command. See GCC Command Options (Using the GNU Compiler Collection (GCC)), for information on the non-Fortran-specific aspects of the gcc command (and, therefore, the g77 command).

All gcc and g77 options are accepted both by g77 and by gcc (as well as any other drivers built at the same time, such as g++), since adding g77 to the gcc distribution enables acceptance of g77 options by all of the relevant drivers.

In some cases, options have positive and negative forms; the negative form of -ffoo would be -fno-foo. This manual documents only one of these two forms, whichever one is not the default.

Next: Overall Options, Up: Invoking G77

### 5.1 Option Summary

Here is a summary of all the options specific to GNU Fortran, grouped by type. Explanations are in the following sections.

Overall Options
  See Options Controlling the Kind of Output.

                -fversion  -fset-g77-defaults  -fno-silent

Shorthand Options
  See Shorthand Options.

                -ff66  -fno-f66  -ff77  -fno-f77  -fno-ugly

Fortran Language Options
  See Options Controlling Fortran Dialect.

                -ffree-form  -fno-fixed-form  -ff90
                -fvxt  -fdollar-ok  -fno-backslash
                -fno-ugly-args  -fno-ugly-assign  -fno-ugly-assumed
                -fugly-comma  -fugly-complex  -fugly-init  -fugly-logint
                -fonetrip  -ftypeless-boz
                -fintrin-case-initcap  -fintrin-case-upper
                -fintrin-case-lower  -fintrin-case-any
                -fmatch-case-initcap  -fmatch-case-upper
                -fmatch-case-lower  -fmatch-case-any
                -fsource-case-upper  -fsource-case-lower
                -fsource-case-preserve
                -fsymbol-case-initcap  -fsymbol-case-upper
                -fsymbol-case-lower  -fsymbol-case-any
                -fcase-strict-upper  -fcase-strict-lower
                -fcase-initcap  -fcase-upper  -fcase-lower  -fcase-preserve
                -ff2c-intrinsics-delete  -ff2c-intrinsics-hide
                -ff2c-intrinsics-disable  -ff2c-intrinsics-enable
                -fbadu77-intrinsics-delete  -fbadu77-intrinsics-hide
                -fbadu77-intrinsics-disable  -fbadu77-intrinsics-enable
                -ff90-intrinsics-delete  -ff90-intrinsics-hide
                -ff90-intrinsics-disable  -ff90-intrinsics-enable
                -fgnu-intrinsics-delete  -fgnu-intrinsics-hide
                -fgnu-intrinsics-disable  -fgnu-intrinsics-enable
                -fmil-intrinsics-delete  -fmil-intrinsics-hide
                -fmil-intrinsics-disable  -fmil-intrinsics-enable
                -funix-intrinsics-delete  -funix-intrinsics-hide
                -funix-intrinsics-disable  -funix-intrinsics-enable
                -fvxt-intrinsics-delete  -fvxt-intrinsics-hide
                -fvxt-intrinsics-disable  -fvxt-intrinsics-enable
                -ffixed-line-length-n  -ffixed-line-length-none

Warning Options
  See Options to Request or Suppress Warnings.

                -fsyntax-only  -pedantic  -pedantic-errors  -fpedantic
                -w  -Wno-globals  -Wimplicit  -Wunused  -Wuninitialized
                -Wall  -Wsurprising
                -Werror  -W

Debugging Options
  See Options for Debugging Your Program or GCC.

                -g

Optimization Options
  See Options that Control Optimization.

                -malign-double
                -ffloat-store  -fforce-mem  -fforce-addr  -fno-inline
                -ffast-math  -fstrength-reduce  -frerun-cse-after-loop
                -funsafe-math-optimizations -ffinite-math-only -fno-trapping-math
                -fexpensive-optimizations  -fdelayed-branch
                -fschedule-insns  -fschedule-insn2  -fcaller-saves
                -funroll-loops  -funroll-all-loops
                -fno-move-all-movables  -fno-reduce-all-givs
                -fno-rerun-loop-opt

Directory Options
  See Options for Directory Search.

                -Idir  -I-

Code Generation Options
  See Options for Code Generation Conventions.

                -fno-automatic  -finit-local-zero  -fno-f2c
                -ff2c-library  -fno-underscoring  -fno-ident
                -fpcc-struct-return  -freg-struct-return
                -fshort-double  -fno-common  -fpack-struct
                -fzeros  -fno-second-underscore
                -femulate-complex
                -falias-check  -fargument-alias
                -fargument-noalias  -fno-argument-noalias-global
                -fno-globals  -fflatten-arrays
                -fbounds-check  -ffortran-bounds-check

Next: Shorthand Options, Previous: Option Summary, Up: Invoking G77

### 5.2 Options Controlling the Kind of Output

Compilation can involve as many as four stages: preprocessing, code generation (often what is really meant by the term “compilation”), assembly, and linking, always in that order. The first three stages apply to an individual source file, and end by producing an object file; linking combines all the object files (those newly compiled, and those specified as input) into an executable file.

For any given input file, the file name suffix determines what kind of program is contained in the file—that is, the language in which the program is written is generally indicated by the suffix. Suffixes specific to GNU Fortran are listed below. See Options Controlling the Kind of Output (Using the GNU Compiler Collection (GCC)), for information on suffixes recognized by GCC.

file`.f`
file`.for`
file`.FOR`
  Fortran source code that should not be preprocessed.

  Such source code cannot contain any preprocessor directives, such as `#include`, `#define`, `#if`, and so on.

  You can force .f files to be preprocessed by cpp by using -x f77-cpp-input. See LEX.

file`.F`
file`.fpp`
file`.FPP`
  Fortran source code that must be preprocessed (by the C preprocessor cpp, which is part of GCC).

  Note that preprocessing is not extended to the contents of files included by the `INCLUDE` directive—the `#include` preprocessor directive must be used instead.

file`.r`
  Ratfor source code, which must be preprocessed by the ratfor command, which is available separately (as it is not yet part of the GNU Fortran distribution). A public domain version in C is at http://sepwww.stanford.edu/sep/prof/ratfor.shar.2.

UNIX users typically use the file.f and file.F nomenclature. Users of other operating systems, especially those that cannot distinguish upper-case letters from lower-case letters in their file names, typically use the file.for and file.fpp nomenclature.

Use of the preprocessor cpp allows use of C-like constructs such as `#define` and `#include`, but can lead to unexpected, even mistaken, results due to Fortran's source file format. It is recommended that use of the C preprocessor be limited to `#include` and, in conjunction with `#define`, only `#if` and related directives, thus avoiding in-line macro expansion entirely. This recommendation applies especially when using the traditional fixed source form. With free source form, fewer unexpected transformations are likely to happen, but use of constructs such as Hollerith and character constants can nevertheless present problems, especially when these are continued across multiple source lines. These problems result, primarily, from differences between the way such constants are interpreted by the C preprocessor and by a Fortran compiler.

Another example of a problem that results from using the C preprocessor is that a Fortran comment line that happens to contain any characters “interesting” to the C preprocessor, such as a backslash at the end of the line, is not recognized by the preprocessor as a comment line, so instead of being passed through “raw”, the line is edited according to the rules for the preprocessor. For example, the backslash at the end of the line is removed, along with the subsequent newline, resulting in the next line being effectively commented out—unfortunate if that line is a non-comment line of important code!

Note: The -traditional and -undef flags are supplied to cpp by default, to help avoid unpleasant surprises. See Options Controlling the Preprocessor (Using the GNU Compiler Collection (GCC)). This means that ANSI C preprocessor features (such as the # operator) aren't available, and only variables in the C reserved namespace (generally, names with a leading underscore) are liable to substitution by C predefines. Thus, if you want to do system-specific tests, use, for example, #ifdef __linux__ rather than #ifdef linux. Use the -v option to see exactly how the preprocessor is invoked.

Unfortunately, the -traditional flag will not avoid an error from anything that cpp sees as an unterminated C comment, such as:

         C Some Fortran compilers accept /* as starting
         C an inline comment.

See Trailing Comment.

The following options that affect overall processing are recognized by the g77 and gcc commands in a GNU Fortran installation:

`-fversion`
  Ensure that the g77 version of the compiler phase is reported, if run, and, starting in `egcs` version 1.1, that internal consistency checks in the f771 program are run.

  This option is supplied automatically when -v or --verbose is specified as a command-line option for g77 or gcc and when the resulting commands compile Fortran source files.

  In GCC 3.1, this is changed back to the behavior gcc displays for .c files.

`-fset-g77-defaults`
  Version info: This option was obsolete as of `egcs` version 1.1. The effect is instead achieved by the `lang_init_options` routine in gcc/gcc/f/com.c.

  Set up whatever gcc options are to apply to Fortran compilations, and avoid running internal consistency checks that might take some time.

  This option is supplied automatically when compiling Fortran code via the g77 or gcc command. The description of this option is provided so that users seeing it in the output of, say, g77 -v understand why it is there.

  Also, developers who run `f771` directly might want to specify it by hand to get the same defaults as they would running `f771` via g77 or gcc However, such developers should, after linking a new `f771` executable, invoke it without this option once, e.g. via `./f771 -quiet < /dev/null`, to ensure that they have not introduced any internal inconsistencies (such as in the table of intrinsics) before proceeding—g77 will crash with a diagnostic if it detects an inconsistency.

`-fno-silent`
  Print (to `stderr`) the names of the program units as they are compiled, in a form similar to that used by popular UNIX f77 implementations and f2c

See Options Controlling the Kind of Output (Using the GNU Compiler Collection (GCC)), for information on more options that control the overall operation of the gcc command (and, by extension, the g77 command).

Next: Fortran Dialect Options, Previous: Overall Options, Up: Invoking G77

### 5.3 Shorthand Options

The following options serve as “shorthand” for other options accepted by the compiler:

`-fugly`
  Note: This option is no longer supported. The information, below, is provided to aid in the conversion of old scripts.

  Specify that certain “ugly” constructs are to be quietly accepted. Same as:

                -fugly-args -fugly-assign -fugly-assumed
                -fugly-comma -fugly-complex -fugly-init
                -fugly-logint

  These constructs are considered inappropriate to use in new or well-maintained portable Fortran code, but widely used in old code. See Distensions, for more information.

`-fno-ugly`
  Specify that all “ugly” constructs are to be noisily rejected. Same as:

                -fno-ugly-args -fno-ugly-assign -fno-ugly-assumed
                -fno-ugly-comma -fno-ugly-complex -fno-ugly-init
                -fno-ugly-logint

  See Distensions, for more information.

`-ff66`
  Specify that the program is written in idiomatic FORTRAN 66. Same as -fonetrip -fugly-assumed.

  The -fno-f66 option is the inverse of -ff66. As such, it is the same as -fno-onetrip -fno-ugly-assumed.

  The meaning of this option is likely to be refined as future versions of g77 provide more compatibility with other existing and obsolete Fortran implementations.

`-ff77`
  Specify that the program is written in idiomatic UNIX FORTRAN 77 and/or the dialect accepted by the f2c product. Same as -fbackslash -fno-typeless-boz.

  The meaning of this option is likely to be refined as future versions of g77 provide more compatibility with other existing and obsolete Fortran implementations.

`-fno-f77`
  The -fno-f77 option is not the inverse of -ff77. It specifies that the program is not written in idiomatic UNIX FORTRAN 77 or f2c but in a more widely portable dialect. -fno-f77 is the same as -fno-backslash.

  The meaning of this option is likely to be refined as future versions of g77 provide more compatibility with other existing and obsolete Fortran implementations.

Next: Warning Options, Previous: Shorthand Options, Up: Invoking G77

### 5.4 Options Controlling Fortran Dialect

The following options control the dialect of Fortran that the compiler accepts:

`-ffree-form`
`-fno-fixed-form`
  Specify that the source file is written in free form (introduced in Fortran 90) instead of the more-traditional fixed form.

`-ff90`
  Allow certain Fortran-90 constructs.

  This option controls whether certain Fortran 90 constructs are recognized. (Other Fortran 90 constructs might or might not be recognized depending on other options such as -fvxt, -ff90-intrinsics-enable, and the current level of support for Fortran 90.)

  See Fortran 90, for more information.

`-fvxt`
  Specify the treatment of certain constructs that have different meanings depending on whether the code is written in GNU Fortran (based on FORTRAN 77 and akin to Fortran 90) or VXT Fortran (more like VAX FORTRAN).

  The default is -fno-vxt. -fvxt specifies that the VXT Fortran interpretations for those constructs are to be chosen.

  See VXT Fortran, for more information.

`-fdollar-ok`
  Allow $ as a valid character in a symbol name.

`-fno-backslash`
  Specify that \ is not to be specially interpreted in character and Hollerith constants a la C and many UNIX Fortran compilers.

  For example, with -fbackslash in effect, A\nB specifies three characters, with the second one being newline. With -fno-backslash, it specifies four characters, A, \, n, and B.

  Note that g77 implements a fairly general form of backslash processing that is incompatible with the narrower forms supported by some other compilers. For example, 'A\003B' is a three-character string in g77 whereas other compilers that support backslash might not support the three-octal-digit form, and thus treat that string as longer than three characters.

  See Backslash in Constants, for information on why -fbackslash is the default instead of -fno-backslash.

`-fno-ugly-args`
  Disallow passing Hollerith and typeless constants as actual arguments (for example, CALL FOO(4HABCD)).

  See Ugly Implicit Argument Conversion, for more information.

`-fugly-assign`
  Use the same storage for a given variable regardless of whether it is used to hold an assigned-statement label (as in ASSIGN 10 TO I) or used to hold numeric data (as in I = 3).

  See Ugly Assigned Labels, for more information.

`-fugly-assumed`
  Assume any dummy array with a final dimension specified as 1 is really an assumed-size array, as if * had been specified for the final dimension instead of 1.

  For example, DIMENSION X(1) is treated as if it had read DIMENSION X(*).

  See Ugly Assumed-Size Arrays, for more information.

`-fugly-comma`
  In an external-procedure invocation, treat a trailing comma in the argument list as specification of a trailing null argument, and treat an empty argument list as specification of a single null argument.

  For example, CALL FOO(,) is treated as CALL FOO(%VAL(0), %VAL(0)). That is, two null arguments are specified by the procedure call when -fugly-comma is in force. And F = FUNC() is treated as F = FUNC(%VAL(0)).

  The default behavior, -fno-ugly-comma, is to ignore a single trailing comma in an argument list. So, by default, CALL FOO(X,) is treated exactly the same as CALL FOO(X).

  See Ugly Null Arguments, for more information.

`-fugly-complex`
  Do not complain about REAL(expr) or AIMAG(expr) when expr is a `COMPLEX` type other than `COMPLEX(KIND=1)`—usually this is used to permit `COMPLEX(KIND=2)` (`DOUBLE COMPLEX`) operands.

  The -ff90 option controls the interpretation of this construct.

  See Ugly Complex Part Extraction, for more information.

`-fno-ugly-init`
  Disallow use of Hollerith and typeless constants as initial values (in `PARAMETER` and `DATA` statements), and use of character constants to initialize numeric types and vice versa.

  For example, DATA I/'F'/, CHRVAR/65/, J/4HABCD/ is disallowed by -fno-ugly-init.

  See Ugly Conversion of Initializers, for more information.

`-fugly-logint`
  Treat `INTEGER` and `LOGICAL` variables and expressions as potential stand-ins for each other.

  For example, automatic conversion between `INTEGER` and `LOGICAL` is enabled, for many contexts, via this option.

  See Ugly Integer Conversions, for more information.

`-fonetrip`
  Executable iterative `DO` loops are to be executed at least once each time they are reached.

  ANSI FORTRAN 77 and more recent versions of the Fortran standard specify that the body of an iterative `DO` loop is not executed if the number of iterations calculated from the parameters of the loop is less than 1. (For example, DO 10 I = 1, 0.) Such a loop is called a zero-trip loop.

  Prior to ANSI FORTRAN 77, many compilers implemented `DO` loops such that the body of a loop would be executed at least once, even if the iteration count was zero. Fortran code written assuming this behavior is said to require one-trip loops. For example, some code written to the FORTRAN 66 standard expects this behavior from its `DO` loops, although that standard did not specify this behavior.

  The -fonetrip option specifies that the source file(s) being compiled require one-trip loops.

  This option affects only those loops specified by the (iterative) `DO` statement and by implied-`DO` lists in I/O statements. Loops specified by implied-`DO` lists in `DATA` and specification (non-executable) statements are not affected.

`-ftypeless-boz`
  Specifies that prefix-radix non-decimal constants, such as Z'ABCD', are typeless instead of `INTEGER(KIND=1)`.

  You can test for yourself whether a particular compiler treats the prefix form as `INTEGER(KIND=1)` or typeless by running the following program:

                EQUIVALENCE (I, R)
                R = Z'ABCD1234'
                J = Z'ABCD1234'
                IF (J .EQ. I) PRINT *, 'Prefix form is TYPELESS'
                IF (J .NE. I) PRINT *, 'Prefix form is INTEGER'
                END

  Reports indicate that many compilers process this form as `INTEGER(KIND=1)`, though a few as typeless, and at least one based on a command-line option specifying some kind of compatibility.

`-fintrin-case-initcap`
`-fintrin-case-upper`
`-fintrin-case-lower`
`-fintrin-case-any`
  Specify expected case for intrinsic names. -fintrin-case-lower is the default.

`-fmatch-case-initcap`
`-fmatch-case-upper`
`-fmatch-case-lower`
`-fmatch-case-any`
  Specify expected case for keywords. -fmatch-case-lower is the default.

`-fsource-case-upper`
`-fsource-case-lower`
`-fsource-case-preserve`
  Specify whether source text other than character and Hollerith constants is to be translated to uppercase, to lowercase, or preserved as is. -fsource-case-lower is the default.

`-fsymbol-case-initcap`
`-fsymbol-case-upper`
`-fsymbol-case-lower`
`-fsymbol-case-any`
  Specify valid cases for user-defined symbol names. -fsymbol-case-any is the default.

`-fcase-strict-upper`
  Same as -fintrin-case-upper -fmatch-case-upper -fsource-case-preserve -fsymbol-case-upper. (Requires all pertinent source to be in uppercase.)

`-fcase-strict-lower`
  Same as -fintrin-case-lower -fmatch-case-lower -fsource-case-preserve -fsymbol-case-lower. (Requires all pertinent source to be in lowercase.)

`-fcase-initcap`
  Same as -fintrin-case-initcap -fmatch-case-initcap -fsource-case-preserve -fsymbol-case-initcap. (Requires all pertinent source to be in initial capitals, as in Print *,SqRt(Value).)

`-fcase-upper`
  Same as -fintrin-case-any -fmatch-case-any -fsource-case-upper -fsymbol-case-any. (Maps all pertinent source to uppercase.)

`-fcase-lower`
  Same as -fintrin-case-any -fmatch-case-any -fsource-case-lower -fsymbol-case-any. (Maps all pertinent source to lowercase.)

`-fcase-preserve`
  Same as -fintrin-case-any -fmatch-case-any -fsource-case-preserve -fsymbol-case-any. (Preserves all case in user-defined symbols, while allowing any-case matching of intrinsics and keywords. For example, call Foo(i,I) would pass two different variables named i and I to a procedure named Foo.)

`-fbadu77-intrinsics-delete`
`-fbadu77-intrinsics-hide`
`-fbadu77-intrinsics-disable`
`-fbadu77-intrinsics-enable`
  Specify status of UNIX intrinsics having inappropriate forms. -fbadu77-intrinsics-enable is the default. See Intrinsic Groups.

`-ff2c-intrinsics-delete`
`-ff2c-intrinsics-hide`
`-ff2c-intrinsics-disable`
`-ff2c-intrinsics-enable`
  Specify status of f2c-specific intrinsics. -ff2c-intrinsics-enable is the default. See Intrinsic Groups.

`-ff90-intrinsics-delete`
`-ff90-intrinsics-hide`
`-ff90-intrinsics-disable`
`-ff90-intrinsics-enable`
  Specify status of F90-specific intrinsics. -ff90-intrinsics-enable is the default. See Intrinsic Groups.

`-fgnu-intrinsics-delete`
`-fgnu-intrinsics-hide`
`-fgnu-intrinsics-disable`
`-fgnu-intrinsics-enable`
  Specify status of Digital's COMPLEX-related intrinsics. -fgnu-intrinsics-enable is the default. See Intrinsic Groups.

`-fmil-intrinsics-delete`
`-fmil-intrinsics-hide`
`-fmil-intrinsics-disable`
`-fmil-intrinsics-enable`
  Specify status of MIL-STD-1753-specific intrinsics. -fmil-intrinsics-enable is the default. See Intrinsic Groups.

`-funix-intrinsics-delete`
`-funix-intrinsics-hide`
`-funix-intrinsics-disable`
`-funix-intrinsics-enable`
  Specify status of UNIX intrinsics. -funix-intrinsics-enable is the default. See Intrinsic Groups.

`-fvxt-intrinsics-delete`
`-fvxt-intrinsics-hide`
`-fvxt-intrinsics-disable`
`-fvxt-intrinsics-enable`
  Specify status of VXT intrinsics. -fvxt-intrinsics-enable is the default. See Intrinsic Groups.

`-ffixed-line-length-`n
  Set column after which characters are ignored in typical fixed-form lines in the source file, and through which spaces are assumed (as if padded to that length) after the ends of short fixed-form lines.

  Popular values for n include 72 (the standard and the default), 80 (card image), and 132 (corresponds to “extended-source” options in some popular compilers). n may be none, meaning that the entire line is meaningful and that continued character constants never have implicit spaces appended to them to fill out the line. -ffixed-line-length-0 means the same thing as -ffixed-line-length-none.

  See Source Form, for more information.

Next: Debugging Options, Previous: Fortran Dialect Options, Up: Invoking G77

### 5.5 Options to Request or Suppress Warnings

Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there might have been an error.

You can request many specific warnings with options beginning -W, for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning -Wno- to turn off warnings; for example, -Wno-implicit. This manual lists only one of the two forms, whichever is not the default.

These options control the amount and kinds of warnings produced by GNU Fortran:

`-fsyntax-only`
  Check the code for syntax errors, but don't do anything beyond that.

`-pedantic`
  Issue warnings for uses of extensions to ANSI FORTRAN 77. -pedantic also applies to C-language constructs where they occur in GNU Fortran source files, such as use of \e in a character constant within a directive like #include.

  Valid ANSI FORTRAN 77 programs should compile properly with or without this option. However, without this option, certain GNU extensions and traditional Fortran features are supported as well. With this option, many of them are rejected.

  Some users try to use -pedantic to check programs for strict ANSI conformance. They soon find that it does not do quite what they want—it finds some non-ANSI practices, but not all. However, improvements to g77 in this area are welcome.

`-pedantic-errors`
  Like -pedantic, except that errors are produced rather than warnings.

`-fpedantic`
  Like -pedantic, but applies only to Fortran constructs.

`-w`
  Inhibit all warning messages.

`-Wno-globals`
  Inhibit warnings about use of a name as both a global name (a subroutine, function, or block data program unit, or a common block) and implicitly as the name of an intrinsic in a source file.

  Also inhibit warnings about inconsistent invocations and/or definitions of global procedures (function and subroutines). Such inconsistencies include different numbers of arguments and different types of arguments.

`-Wimplicit`
  Warn whenever a variable, array, or function is implicitly declared. Has an effect similar to using the `IMPLICIT NONE` statement in every program unit. (Some Fortran compilers provide this feature by an option named -u or /WARNINGS=DECLARATIONS.)

`-Wunused`
  Warn whenever a variable is unused aside from its declaration.

`-Wuninitialized`
  Warn whenever an automatic variable is used without first being initialized.

  These warnings are possible only in optimizing compilation, because they require data-flow information that is computed only when optimizing. If you don't specify -O, you simply won't get these warnings.

  These warnings occur only for variables that are candidates for register allocation. Therefore, they do not occur for a variable whose address is taken, or whose size is other than 1, 2, 4 or 8 bytes. Also, they do not occur for arrays, even when they are in registers.

  Note that there might be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data-flow analysis before the warnings are printed.

  These warnings are made optional because GNU Fortran is not smart enough to see all the reasons why the code might be correct despite appearing to have an error. Here is one example of how this can happen:

                SUBROUTINE DISPAT(J)
                IF (J.EQ.1) I=1
                IF (J.EQ.2) I=4
                IF (J.EQ.3) I=5
                CALL FOO(I)
                END

  If the value of `J` is always 1, 2 or 3, then `I` is always initialized, but GNU Fortran doesn't know this. Here is another common case:

                SUBROUTINE MAYBE(FLAG)
                LOGICAL FLAG
                IF (FLAG) VALUE = 9.4
                ...
                IF (FLAG) PRINT *, VALUE
                END

  This has no bug because `VALUE` is used only if it is set.

`-Wall`
  The -Wunused and -Wuninitialized options combined. These are all the options which pertain to usage that we recommend avoiding and that we believe is easy to avoid. (As more warnings are added to g77 some might be added to the list enabled by -Wall.)

The remaining -W... options are not implied by -Wall because they warn about constructions that we consider reasonable to use, on occasion, in clean programs.

`-Wsurprising`
  Warn about “suspicious” constructs that are interpreted by the compiler in a way that might well be surprising to someone reading the code. These differences can result in subtle, compiler-dependent (even machine-dependent) behavioral differences. The constructs warned about include:
  - Expressions having two arithmetic operators in a row, such as X*-Y. Such a construct is nonstandard, and can produce unexpected results in more complicated situations such as X**-Y*Z. g77 along with many other compilers, interprets this example differently than many programmers, and a few other compilers. Specifically, g77 interprets X**-Y*Z as (X**(-Y))*Z, while others might think it should be interpreted as X**(-(Y*Z)).

    A revealing example is the constant expression 2**-2*1., which g77 evaluates to .25, while others might evaluate it to 0., the difference resulting from the way precedence affects type promotion.

    (The -fpedantic option also warns about expressions having two arithmetic operators in a row.)

  - Expressions with a unary minus followed by an operand and then a binary operator other than plus or minus. For example, -2**2 produces a warning, because the precedence is -(2**2), yielding -4, not (-2)**2, which yields 4, and which might represent what a programmer expects.

    An example of an expression producing different results in a surprising way is -I*S, where I holds the value -2147483648 and S holds 0.5. On many systems, negating I results in the same value, not a positive number, because it is already the lower bound of what an `INTEGER(KIND=1)` variable can hold. So, the expression evaluates to a positive number, while the “expected” interpretation, (-I)*S, would evaluate to a negative number.

    Even cases such as -I*J produce warnings, even though, in most configurations and situations, there is no computational difference between the results of the two interpretations—the purpose of this warning is to warn about differing interpretations and encourage a better style of coding, not to identify only those places where bugs might exist in the user's code.

  - `DO` loops with `DO` variables that are not of integral type—that is, using `REAL` variables as loop control variables. Although such loops can be written to work in the “obvious” way, the way g77 is required by the Fortran standard to interpret such code is likely to be quite different from the way many programmers expect. (This is true of all `DO` loops, but the differences are pronounced for non-integral loop control variables.)

    See Loops, for more information.

`-Werror`
  Make all warnings into errors.

`-W`
  Turns on “extra warnings” and, if optimization is specified via -O, the -Wuninitialized option. (This might change in future versions of g77

  “Extra warnings” are issued for:

  - Unused parameters to a procedure (when -Wunused also is specified).
  - Overflows involving floating-point constants (not available for certain configurations).

See Options to Request or Suppress Warnings (Using the GNU Compiler Collection (GCC)), for information on more options offered by the GBE shared by g77 gcc and other GNU compilers.

Some of these have no effect when compiling programs written in Fortran:

`-Wcomment`
`-Wformat`
`-Wparentheses`
`-Wswitch`
`-Wswitch-default`
`-Wswitch-enum`
`-Wtraditional`
`-Wshadow`
`-Wid-clash-`len
`-Wlarger-than-`len
`-Wconversion`
`-Waggregate-return`
`-Wredundant-decls`
  These options all could have some relevant meaning for GNU Fortran programs, but are not yet supported.

Next: Optimize Options, Previous: Warning Options, Up: Invoking G77

### 5.6 Options for Debugging Your Program or GNU Fortran

GNU Fortran has various special options that are used for debugging either your program or g77

`-g`
  Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging information.

  A sample debugging session looks like this (note the use of the breakpoint):

                $ cat gdb.f
                      PROGRAM PROG
                      DIMENSION A(10)
                      DATA A /1.,2.,3.,4.,5.,6.,7.,8.,9.,10./
                      A(5) = 4.
                      PRINT*,A
                      END
                $ g77 -g -O gdb.f
                $ gdb a.out
                ...
                (gdb) break MAIN__
                Breakpoint 1 at 0x8048e96: file gdb.f, line 4.
                (gdb) run
                Starting program: /home/toon/g77-bugs/./a.out
                Breakpoint 1, MAIN__ () at gdb.f:4
                4             A(5) = 4.
                Current language:  auto; currently fortran
                (gdb) print a(5)
                $1 = 5
                (gdb) step
                5             PRINT*,A
                (gdb) print a(5)
                $2 = 4
                ...

  One could also add the setting of the breakpoint and the first run command to the file .gdbinit in the current directory, to simplify the debugging session.

See Options for Debugging Your Program or GCC (Using the GNU Compiler Collection (GCC)), for more information on debugging options.

Next: Preprocessor Options, Previous: Debugging Options, Up: Invoking G77

### 5.7 Options That Control Optimization

Most Fortran users will want to use no optimization when developing and testing programs, and use -O or -O2 when compiling programs for late-cycle testing and for production use. However, note that certain diagnostics—such as for uninitialized variables—depend on the flow analysis done by -O, i.e. you must use -O or -O2 to get such diagnostics.

The following flags have particular applicability when compiling Fortran programs:

`-malign-double`
  (Intel x86 architecture only.)

  Noticeably improves performance of g77 programs making heavy use of `REAL(KIND=2)` (`DOUBLE PRECISION`) data on some systems. In particular, systems using Pentium, Pentium Pro, 586, and 686 implementations of the i386 architecture execute programs faster when `REAL(KIND=2)` (`DOUBLE PRECISION`) data are aligned on 64-bit boundaries in memory.

  This option can, at least, make benchmark results more consistent across various system configurations, versions of the program, and data sets.

  Note: The warning in the gcc documentation about this option does not apply, generally speaking, to Fortran code compiled by g77

  See Aligned Data, for more information on alignment issues.

  Also also note: The negative form of -malign-double is -mno-align-double, not -benign-double.

`-ffloat-store`
  Might help a Fortran program that depends on exact IEEE conformance on some machines, but might slow down a program that doesn't.

  This option is effective when the floating-point unit is set to work in IEEE 854 `extended precision'—as it typically is on x86 and m68k GNU systems—rather than IEEE 754 double precision. -ffloat-store tries to remove the extra precision by spilling data from floating-point registers into memory and this typically involves a big performance hit. However, it doesn't affect intermediate results, so that it is only partially effective. `Excess precision' is avoided in code like:

                a = b + c
                d = a * e

  but not in code like:

                      d = (b + c) * e

  For another, potentially better, way of controlling the precision, see Floating-point precision.

`-fforce-mem`
`-fforce-addr`
  Might improve optimization of loops.

`-fno-inline`
  Don't compile statement functions inline. Might reduce the size of a program unit—which might be at expense of some speed (though it should compile faster). Note that if you are not optimizing, no functions can be expanded inline.

`-ffast-math`
  Might allow some programs designed to not be too dependent on IEEE behavior for floating-point to run faster, or die trying. Sets -funsafe-math-optimizations, -ffinite-math-only, and -fno-trapping-math.

`-funsafe-math-optimizations`
  Allow optimizations that may be give incorrect results for certain IEEE inputs.

`-ffinite-math-only`
  Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs.

  This option should never be turned on by any -O option since it can result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications.

  The default is -fno-finite-math-only.

`-fno-trapping-math`
  Allow the compiler to assume that floating-point arithmetic will not generate traps on any inputs. This is useful, for example, when running a program using IEEE "non-stop" floating-point arithmetic.

`-fstrength-reduce`
  Might make some loops run faster.

`-frerun-cse-after-loop`
`-fexpensive-optimizations`
`-fdelayed-branch`
`-fschedule-insns`
`-fschedule-insns2`
`-fcaller-saves`
  Might improve performance on some code.

`-funroll-loops`
  Typically improves performance on code using iterative `DO` loops by unrolling them and is probably generally appropriate for Fortran, though it is not turned on at any optimization level. Note that outer loop unrolling isn't done specifically; decisions about whether to unroll a loop are made on the basis of its instruction count.

  Also, no `loop discovery'1 is done, so only loops written with `DO` benefit from loop optimizations, including—but not limited to—unrolling. Loops written with `IF` and `GOTO` are not currently recognized as such. This option unrolls only iterative `DO` loops, not `DO WHILE` loops.

`-funroll-all-loops`
  Probably improves performance on code using `DO WHILE` loops by unrolling them in addition to iterative `DO` loops. In the absence of `DO WHILE`, this option is equivalent to -funroll-loops but possibly slower.
`-fno-move-all-movables`
`-fno-reduce-all-givs`
`-fno-rerun-loop-opt`
  In general, the optimizations enabled with these options will lead to faster code being generated by GNU Fortran; hence they are enabled by default when issuing the g77 command.

  -fmove-all-movables and -freduce-all-givs will enable loop optimization to move all loop-invariant index computations in nested loops over multi-rank array dummy arguments out of these loops.

  -frerun-loop-opt will move offset calculations resulting from the fact that Fortran arrays by default have a lower bound of 1 out of the loops.

  These three options are intended to be removed someday, once loop optimization is sufficiently advanced to perform all those transformations without help from these options.

See Options That Control Optimization (Using the GNU Compiler Collection (GCC)), for more information on options to optimize the generated machine code.

Next: Directory Options, Previous: Optimize Options, Up: Invoking G77

### 5.8 Options Controlling the Preprocessor

These options control the C preprocessor, which is run on each C source file before actual compilation.

See Options Controlling the Preprocessor (Using the GNU Compiler Collection (GCC)), for information on C preprocessor options.

Some of these options also affect how g77 processes the `INCLUDE` directive. Since this directive is processed even when preprocessing is not requested, it is not described in this section. See Options for Directory Search, for information on how g77 processes the `INCLUDE` directive.

However, the `INCLUDE` directive does not apply preprocessing to the contents of the included file itself.

Therefore, any file that contains preprocessor directives (such as `#include`, `#define`, and `#if`) must be included via the `#include` directive, not via the `INCLUDE` directive. Therefore, any file containing preprocessor directives, if included, is necessarily included by a file that itself contains preprocessor directives.

Next: Code Gen Options, Previous: Preprocessor Options, Up: Invoking G77

### 5.9 Options for Directory Search

These options affect how the cpp preprocessor searches for files specified via the `#include` directive. Therefore, when compiling Fortran programs, they are meaningful when the preprocessor is used.

Some of these options also affect how g77 searches for files specified via the `INCLUDE` directive, although files included by that directive are not, themselves, preprocessed. These options are:

`-I-`
`-I` dir
  These affect interpretation of the `INCLUDE` directive (as well as of the `#include` directive of the cpp preprocessor).

  Note that -I dir must be specified without any spaces between -I and the directory name—that is, -Ifoo/bar is valid, but -I foo/bar is rejected by the g77 compiler (though the preprocessor supports the latter form). Also note that the general behavior of -I and `INCLUDE` is pretty much the same as of -I with `#include` in the cpp preprocessor, with regard to looking for header.gcc files and other such things.

  See Options for Directory Search (Using the GNU Compiler Collection (GCC)), for information on the -I option.

Next: Environment Variables, Previous: Directory Options, Up: Invoking G77

### 5.10 Options for Code Generation Conventions

These machine-independent options control the interface conventions used in code generation.

Most of them have both positive and negative forms; the negative form of -ffoo would be -fno-foo. In the table below, only one of the forms is listed—the one which is not the default. You can figure out the other form by either removing no- or adding it.

`-fno-automatic`
  Treat each program unit as if the `SAVE` statement was specified for every local variable and array referenced in it. Does not affect common blocks. (Some Fortran compilers provide this option under the name -static.)

`-finit-local-zero`
  Specify that variables and arrays that are local to a program unit (not in a common block and not passed as an argument) are to be initialized to binary zeros.

  Since there is a run-time penalty for initialization of variables that are not given the `SAVE` attribute, it might be a good idea to also use -fno-automatic with -finit-local-zero.

`-fno-f2c`
  Do not generate code designed to be compatible with code generated by f2c use the GNU calling conventions instead.

  The f2c calling conventions require functions that return type `REAL(KIND=1)` to actually return the C type `double`, and functions that return type `COMPLEX` to return the values via an extra argument in the calling sequence that points to where to store the return value. Under the GNU calling conventions, such functions simply return their results as they would in GNU C—`REAL(KIND=1)` functions return the C type `float`, and `COMPLEX` functions return the GNU C type `complex` (or its `struct` equivalent).

  This does not affect the generation of code that interfaces with the `libg2c` library.

  However, because the `libg2c` library uses f2c calling conventions, g77 rejects attempts to pass intrinsics implemented by routines in this library as actual arguments when -fno-f2c is used, to avoid bugs when they are actually called by code expecting the GNU calling conventions to work.

  For example, INTRINSIC ABS;CALL FOO(ABS) is rejected when -fno-f2c is in force. (Future versions of the g77 run-time library might offer routines that provide GNU-callable versions of the routines that implement the f2c intrinsics that may be passed as actual arguments, so that valid programs need not be rejected when -fno-f2c is used.)

  Caution: If -fno-f2c is used when compiling any source file used in a program, it must be used when compiling all Fortran source files used in that program.

`-ff2c-library`
  Specify that use of `libg2c` (or the original `libf2c`) is required. This is the default for the current version of g77

  Currently it is not valid to specify -fno-f2c-library. This option is provided so users can specify it in shell scripts that build programs and libraries that require the `libf2c` library, even when being compiled by future versions of g77 that might otherwise default to generating code for an incompatible library.

`-fno-underscoring`
  Do not transform names of entities specified in the Fortran source file by appending underscores to them.

  With -funderscoring in effect, g77 appends two underscores to names with underscores and one underscore to external names with no underscores. (g77 also appends two underscores to internal names with underscores to avoid naming collisions with external names. The -fno-second-underscore option disables appending of the second underscore in all cases.)

  This is done to ensure compatibility with code produced by many UNIX Fortran compilers, including f2c which perform the same transformations.

  Use of -fno-underscoring is not recommended unless you are experimenting with issues such as integration of (GNU) Fortran into existing system environments (vis-a-vis existing libraries, tools, and so on).

  For example, with -funderscoring, and assuming other defaults like -fcase-lower and that j() and max_count() are external functions while my_var and lvar are local variables, a statement like

                I = J() + MAX_COUNT (MY_VAR, LVAR)

  is implemented as something akin to:

                i = j_() + max_count__(&my_var__, &lvar);

  With -fno-underscoring, the same statement is implemented as:

                i = j() + max_count(&my_var, &lvar);

  Use of -fno-underscoring allows direct specification of user-defined names while debugging and when interfacing g77 code with other languages.

  Note that just because the names match does not mean that the interface implemented by g77 for an external name matches the interface implemented by some other language for that same name. That is, getting code produced by g77 to link to code produced by some other compiler using this or any other method can be only a small part of the overall solution—getting the code generated by both compilers to agree on issues other than naming can require significant effort, and, unlike naming disagreements, linkers normally cannot detect disagreements in these other areas.

  Also, note that with -fno-underscoring, the lack of appended underscores introduces the very real possibility that a user-defined external name will conflict with a name in a system library, which could make finding unresolved-reference bugs quite difficult in some cases—they might occur at program run time, and show up only as buggy behavior at run time.

  In future versions of g77 we hope to improve naming and linking issues so that debugging always involves using the names as they appear in the source, even if the names as seen by the linker are mangled to prevent accidental linking between procedures with incompatible interfaces.

`-fno-second-underscore`
  Do not append a second underscore to names of entities specified in the Fortran source file.

  This option has no effect if -fno-underscoring is in effect.

  Otherwise, with this option, an external name such as MAX_COUNT is implemented as a reference to the link-time external symbol max_count_, instead of max_count__.

`-fno-ident`
  Ignore the #ident directive.

`-fzeros`
  Treat initial values of zero as if they were any other value.

  As of version 0.5.18, g77 normally treats `DATA` and other statements that are used to specify initial values of zero for variables and arrays as if no values were actually specified, in the sense that no diagnostics regarding multiple initializations are produced.

  This is done to speed up compiling of programs that initialize large arrays to zeros.

  Use -fzeros to revert to the simpler, slower behavior that can catch multiple initializations by keeping track of all initializations, zero or otherwise.

  Caution: Future versions of g77 might disregard this option (and its negative form, the default) or interpret it somewhat differently. The interpretation changes will affect only non-standard programs; standard-conforming programs should not be affected.

`-femulate-complex`
  Implement `COMPLEX` arithmetic via emulation, instead of using the facilities of the gcc back end that provide direct support of `complex` arithmetic.

  (gcc had some bugs in its back-end support for `complex` arithmetic, due primarily to the support not being completed as of version 2.8.1 and `egcs` 1.1.2.)

  Use -femulate-complex if you suspect code-generation bugs, or experience compiler crashes, that might result from g77 using the `COMPLEX` support in the gcc back end. If using that option fixes the bugs or crashes you are seeing, that indicates a likely g77 bugs (though, all compiler crashes are considered bugs), so, please report it. (Note that the known bugs, now believed fixed, produced compiler crashes rather than causing the generation of incorrect code.)

  Use of this option should not affect how Fortran code compiled by g77 works in terms of its interfaces to other code, e.g. that compiled by f2c

  As of GCC version 3.0, this option is not necessary anymore.

  Caution: Future versions of g77 might ignore both forms of this option.

`-falias-check`
`-fargument-alias`
`-fargument-noalias`
`-fno-argument-noalias-global`
  Version info: These options are not supported by versions of g77 based on gcc version 2.8.

  These options specify to what degree aliasing (overlap) is permitted between arguments (passed as pointers) and `COMMON` (external, or public) storage.

  The default for Fortran code, as mandated by the FORTRAN 77 and Fortran 90 standards, is -fargument-noalias-global. The default for code written in the C language family is -fargument-alias.

  Note that, on some systems, compiling with -fforce-addr in effect can produce more optimal code when the default aliasing options are in effect (and when optimization is enabled).

  See Aliasing Assumed To Work, for detailed information on the implications of compiling Fortran code that depends on the ability to alias dummy arguments.

`-fno-globals`
  Disable diagnostics about inter-procedural analysis problems, such as disagreements about the type of a function or a procedure's argument, that might cause a compiler crash when attempting to inline a reference to a procedure within a program unit. (The diagnostics themselves are still produced, but as warnings, unless -Wno-globals is specified, in which case no relevant diagnostics are produced.)

  Further, this option disables such inlining, to avoid compiler crashes resulting from incorrect code that would otherwise be diagnosed.

  As such, this option might be quite useful when compiling existing, “working” code that happens to have a few bugs that do not generally show themselves, but which g77 diagnoses.

  Use of this option therefore has the effect of instructing g77 to behave more like it did up through version 0.5.19.1, when it paid little or no attention to disagreements between program units about a procedure's type and argument information, and when it performed no inlining of procedures (except statement functions).

  Without this option, g77 defaults to performing the potentially inlining procedures as it started doing in version 0.5.20, but as of version 0.5.21, it also diagnoses disagreements that might cause such inlining to crash the compiler as (fatal) errors, and warns about similar disagreements that are currently believed to not likely to result in the compiler later crashing or producing incorrect code.

`-fflatten-arrays`
  Use back end's C-like constructs (pointer plus offset) instead of its `ARRAY_REF` construct to handle all array references.

  Note: This option is not supported. It is intended for use only by g77 developers, to evaluate code-generation issues. It might be removed at any time.

`-fbounds-check`
`-ffortran-bounds-check`
  Enable generation of run-time checks for array subscripts and substring start and end points against the (locally) declared minimum and maximum values.

  The current implementation uses the `libf2c` library routine `s_rnge` to print the diagnostic.

  However, whereas f2c generates a single check per reference for a multi-dimensional array, of the computed offset against the valid offset range (0 through the size of the array), g77 generates a single check per subscript expression. This catches some cases of potential bugs that f2c does not, such as references to below the beginning of an assumed-size array.

  g77 also generates checks for `CHARACTER` substring references, something f2c currently does not do.

  Use the new -ffortran-bounds-check option to specify bounds-checking for only the Fortran code you are compiling, not necessarily for code written in other languages.

  Note: To provide more detailed information on the offending subscript, g77 provides the `libg2c` run-time library routine `s_rnge` with somewhat differently-formatted information. Here's a sample diagnostic:

                Subscript out of range on file line 4, procedure rnge.f/bf.
                Attempt to access the -6-th element of variable b[subscript-2-of-2].
                Aborted

  The above message indicates that the offending source line is line 4 of the file rnge.f, within the program unit (or statement function) named bf. The offended array is named b. The offended array dimension is the second for a two-dimensional array, and the offending, computed subscript expression was -6.

  For a `CHARACTER` substring reference, the second line has this appearance:

                Attempt to access the 11-th element of variable a[start-substring].

  This indicates that the offended `CHARACTER` variable or array is named a, the offended substring position is the starting (leftmost) position, and the offending substring expression is 11.

  (Though the verbage of `s_rnge` is not ideal for the purpose of the g77 compiler, the above information should provide adequate diagnostic abilities to it users.)

See Options for Code Generation Conventions (Using the GNU Compiler Collection (GCC)), for information on more options offered by the GBE shared by g77 gcc and other GNU compilers.

Some of these do not work when compiling programs written in Fortran:

`-fpcc-struct-return`
`-freg-struct-return`
  You should not use these except strictly the same way as you used them to build the version of `libg2c` with which you will be linking all code compiled by g77 with the same option.

`-fshort-double`
  This probably either has no effect on Fortran programs, or makes them act loopy.

`-fno-common`
  Do not use this when compiling Fortran programs, or there will be Trouble.

`-fpack-struct`
  This probably will break any calls to the `libg2c` library, at the very least, even if it is built with the same option.

Previous: Code Gen Options, Up: Invoking G77

### 5.11 Environment Variables Affecting GNU Fortran

GNU Fortran currently does not make use of any environment variables to control its operation above and beyond those that affect the operation of gcc.

See Environment Variables Affecting GCC (Using the GNU Compiler Collection (GCC)), for information on environment variables.

Next: Changes, Previous: Invoking G77, Up: Top

## 6 News About GNU Fortran

`GCC` 3.4.x is the last edition of `GCC` to contain g77 - from `GCC` 4.0 onwards, use gfortran

Changes made to recent versions of GNU Fortran are listed below, with the most recent version first.

The changes are generally listed in order:

1. Code-generation and run-time-library bug-fixes
2. Compiler and run-time-library crashes involving valid code that have been fixed
3. New features
4. Fixes and enhancements to existing features
5. New diagnostics
6. Internal improvements
7. Miscellany

This order is not strict—for example, some items involve a combination of these elements.

Note that two variants of g77 are tracked below. The `egcs` variant is described vis-a-vis previous versions of `egcs` and/or an official FSF version, as appropriate. Note that all such variants are obsolete as of July 1999 - the information is retained here only for its historical value.

Therefore, `egcs` versions sometimes have multiple listings to help clarify how they differ from other versions, though this can make getting a complete picture of what a particular `egcs` version contains somewhat more difficult.

For information on bugs in the GCC-3.4.4 version of g77, see Known Bugs In GNU Fortran.

The following information was last updated on 2004-12-29:

### In `GCC` 3.4 versus `GCC` 3.3:

- Problem Reports fixed (in chronological order of submission):
  `8485`
    g77 doesn't accept INTEGER*8 constant in PARAMETER multiplication.
  `11918`
    (libf2c) isatty does not call f_init.
  `12317`
    Incorrect documentation for Fortran debugging features.
- Roger Sayle (roger@eyesopen.com) fixed the remaining problems with regard to the support of INTEGER*8, INTEGER*2 and INTEGER*1 as a fallout of fixing PR 8485.

### In `GCC` 3.3 versus `GCC` 3.2:

- Problem Reports fixed (in chronological order of submission):
  `1832`
    -list directed i/o overflow hangs, -fbounds-check doesn't detect
  `3924`
    g77 generates code which is rejected by GAS if COFF debugging info is requested
  `6286`
    Broken links on web pages
  `6367`
    (libf2c) multiple repeat counts confuse namelist read into array
  `6491`
    Logical operations error on logicals when using -fugly-logint
  `6742`
    Generation of C++ Prototype for FORTRAN and extern "C"
  `7113`
    Failure of g77.f-torture/execute/f90-intrinsic-bit.f -Os on irix6.5
  `7236`
    (libf2c) OPEN(...,RECL=nnn,...) without ACCESS='DIRECT' should assume a direct access file
  `7278`
    g77 "bug"; the executable misbehave (use of options -O2 -fno-automatic gave wrong results)
  `7384`
    (libf2c) DATE_AND_TIME milliseconds field inactive on Windows
  `7388`
    Incorrect output with 0-based array of characters
  `8587`
    Double complex zero ** double precision number -> NaN instead of zero
  `9038`
    -ffixed-line-length-none -x f77-cpp-input gives: Warning: unknown register name line-length-none
  `9263`
    ICE caused by invalid PARAMETER in implied DO loop
  `10197`
    Direct access files not unformatted by default
  `10726`
    Documentation for function IDATE Intrinsic (UNIX) is wrong [fixed in 3.3.1].
- Richard Henderson (rth@redhat.com) analyzed and improved the handling of (no-)aliasing information for dummy arguments and improved the optimization of induction variables in unrolled loops.

### In `GCC` 3.2 versus `GCC` 3.1:

- Problem Reports fixed (in chronological order of submission):
  `7681`
    ICE in compensate_edge, at reg-stack.c:2591
  `8308`
    gcc-3.x does not compile files with suffix .r (RATFOR) [Fixed in 3.2.1]
  `9258`
    [3.2/3.3/3.4 regression] ICE in compensate_edge, at reg-stack.c:2589

### In `GCC` 3.1 (formerly known as g77-0.5.27) versus `GCC` 3.0:

- Problem Reports fixed (in chronological order of submission):
  `947`
    Data statement initialization with subscript of kind INTEGER*2
  `3743`
    Reference to intrinsic `ISHFT' invalid
  `3807`
    Function BESJN(integer,double) problems
  `3957`
    g77 -pipe -xf77-cpp-input sends output to stdout
  `4279`
    g77 -h" gives bogus output
  `4730`
    ICE on valid input using CALL EXIT(%VAL(...))
  `4752`
    g77 -v -c -xf77-version /dev/null -xnone causes ice
  `4885`
    BACKSPACE example that doesn't work as of gcc/g77-3.0.x
  `5122`
    g77 rejects accepted use of INTEGER*2 as type of DATA statement loop index
  `5397`
    ICE on compiling source with 540 000 000 REAL array
  `5473`
    ICE on BESJN(integer*8,real)
  `5837`
    bug in loop unrolling
  `6106`
    sparc-sun-solaris2.7 gcc-3.1 extra g77 testsuite failures w/-m64
  `6138`
    Incorrect acces of integer*1 variables on PA
  `6304`
    Failure of LAPACK test dtest on irix6.5 with -mabi=64 -O2
- g77 now has its man page generated from the texinfo documentation, to guarantee that it remains up to date.
- g77 used to reject the following program on 32-bit targets:

                PROGRAM PROG
                DIMENSION A(140 000 000)
                END

  with the message:

                prog.f: In program `prog':
                prog.f:2:
                         DIMENSION A(140 000 000)
                                   ^
                Array `a' at (^) is too large to handle

  because 140 000 000 REALs is larger than the largest bit-extent that can be expressed in 32 bits. However, bit-sizes never play a role after offsets have been converted to byte addresses. Therefore this check has been removed, and the limit is now 2 Gbyte of memory (around 530 000 000 REALs). Note: On GNU/Linux systems one has to compile and link programs that occupy more than 1 Gbyte statically, i.e. `g77 -static ...`.

- Based on work done by Juergen Pfeifer (juergen.pfeifer@gmx.net) libf2c is now a shared library. One can still link in all objects with the program by specifying the -static option.
- Robert Anderson (rwa@alumni.princeton.edu) thought up a two line change that enables g77 to compile such code as:

                SUBROUTINE SUB(A, N)
                DIMENSION N(2)
                DIMENSION A(N(1),N(2))
                A(1,1) = 1.
                END

  Note the use of array elements in the bounds of the adjustable array A.

- George Helffrich (george@geo.titech.ac.jp) implemented a change in substring index checking (when specifying -fbounds-check) that permits the use of zero length substrings of the form `string(1:0)`.
- Based on code developed by Pedro Vazquez (vazquez@penelope.iqm.unicamp.br), the `libf2c` library is now able to read and write files larger than 2 Gbyte on 32-bit target machines, if the operating system supports this.

### In 0.5.26, `GCC` 3.0 versus `GCC` 2.95:

- When a REWIND was issued after a WRITE statement on an unformatted file, the implicit truncation was performed by copying the truncated file to /tmp and copying the result back. This has been fixed by using the `ftruncate` OS function. Thanks go to the GAMESS developers for bringing this to our attention.
- Using options -g, -ggdb or -gdwarf[-2] (where appropriate for your target) now also enables debugging information for COMMON BLOCK and EQUIVALENCE items to be emitted. Thanks go to Andrew Vaught (andy@xena.eas.asu.edu) and George Helffrich (george@geology.bristol.ac.uk) for fixing this longstanding problem.
- It is not necessary anymore to use the option -femulate-complex to compile Fortran code using COMPLEX arithmetic, even on 64-bit machines (like the Alpha). This will improve code generation.
- INTRINSIC arithmetic functions are now treated as routines that do not depend on anything but their argument(s). This enables further instruction scheduling, because it is known that they cannot read or modify arbitrary locations.
- Upgrade to `libf2c` as of 2000-12-05.

  This fixes a bug where a namelist containing initialization of LOGICAL items and a variable starting with T or F would be read incorrectly.

- The `TtyNam` intrinsics now set Name to all spaces (at run time) if the system has no `ttyname` implementation available.
- Upgrade to `libf2c` as of 1999-06-28.

  This fixes a bug whereby input to a `NAMELIST` read involving a repeat count, such as K(5)=10*3, was not properly handled by `libf2c`. The first item was written to K(5), but the remaining nine were written elsewhere (still within the array), not necessarily starting at K(6).

### In 0.5.25, `GCC` 2.95 (`EGCS` 1.2) versus `EGCS` 1.1.2:

- g77 no longer generates bad code for assignments, or other conversions, of `REAL` or `COMPLEX` constant expressions to type `INTEGER(KIND=2)` (often referred to as `INTEGER*8`).

  For example, INTEGER*8 J; J = 4E10 now works as documented.

- g77 no longer truncates `INTEGER(KIND=2)` (usually `INTEGER*8`) subscript expressions when evaluating array references on systems with pointers widers than `INTEGER(KIND=1)` (such as Alphas).
- g77 no longer generates bad code for an assignment to a `COMPLEX` variable or array that partially overlaps one or more of the sources of the same assignment (a very rare construction). It now assigns through a temporary, in cases where such partial overlap is deemed possible.
- `libg2c` (`libf2c`) no longer loses track of the file being worked on during a `BACKSPACE` operation.
- `libg2c` (`libf2c`) fixes a bug whereby input to a `NAMELIST` read involving a repeat count, such as K(5)=10*3, was not properly handled by `libf2c`. The first item was written to K(5), but the remaining nine were written elsewhere (still within the array), not necessarily starting at K(6).
- Automatic arrays now seem to be working on HP-UX systems.
- The `Date` intrinsic now returns the correct result on big-endian systems.
- Fix g77 so it no longer crashes when compiling I/O statements using keywords that define `INTEGER` values, such as IOSTAT=j, where j is other than default `INTEGER` (such as `INTEGER*2`). Instead, it issues a diagnostic.
- Fix g77 so it properly handles DATA A/rpt*val/, where rpt is not default `INTEGER`, such as `INTEGER*2`, instead of producing a spurious diagnostic. Also fix DATA (A(I),I=1,N), where N is not default `INTEGER` to work instead of crashing g77.
- The -ax option is now obeyed when compiling Fortran programs. (It is passed to the f771 driver.)
- The new -fbounds-check option causes g77 to compile run-time bounds checks of array subscripts, as well as of substring start and end points.
- `libg2c` now supports building as multilibbed library, which provides better support for systems that require options such as -mieee to work properly.
- Source file names with the suffixes .FOR and .FPP now are recognized by g77 as if they ended in .for and .fpp, respectively.
- The order of arguments to the subroutine forms of the `CTime`, `DTime`, `ETime`, and `TtyNam` intrinsics has been swapped. The argument serving as the returned value for the corresponding function forms now is the second argument, making these consistent with the other subroutine forms of `libU77` intrinsics.
- g77 now warns about a reference to an intrinsic that has an interface that is not Year 2000 (Y2K) compliant. Also, `libg2c` has been changed to increase the likelihood of catching references to the implementations of these intrinsics using the `EXTERNAL` mechanism (which would avoid the new warnings).

  See Year 2000 (Y2K) Problems, for more information.

- g77 now warns about a reference to a function when the corresponding subsequent function program unit disagrees with the reference concerning the type of the function.
- -fno-emulate-complex is now the default option. This should result in improved performance of code that uses the `COMPLEX` data type.

- The -malign-double option now reliably aligns all double-precision variables and arrays on Intel x86 targets.
- Even without the -malign-double option, g77 reliably aligns local double-precision variables that are not in `EQUIVALENCE` areas and not `SAVE`'d.
- g77 now open-codes (“inlines”) division of `COMPLEX` operands instead of generating a run-time call to the `libf2c` routines `c_div` or `z_div`, unless the -Os option is specified.
- g77 no longer generates code to maintain `errno`, a C-language concept, when performing operations such as the `SqRt` intrinsic.
- g77 developers can temporarily use the -fflatten-arrays option to compare how the compiler handles code generation using C-like constructs as compared to the Fortran-like method constructs normally used.
- A substantial portion of the g77 front end's code-generation component was rewritten. It now generates code using facilities more robustly supported by the gcc back end. One effect of this rewrite is that some codes no longer produce a spurious “label lab used before containing binding contour” message.
- Support for the -fugly option has been removed.
- Improve documentation and indexing, including information on Year 2000 (Y2K) compliance, and providing more information on internals of the front end.
- Upgrade to `libf2c` as of 1999-05-10.

### In 0.5.24 versus 0.5.23:

There is no g77 version 0.5.24 at this time, or planned. 0.5.24 is the version number designated for bug fixes and, perhaps, some new features added, to 0.5.23. Version 0.5.23 requires gcc 2.8.1, as 0.5.24 was planned to require.

Due to `EGCS` becoming `GCC` (which is now an acronym for “GNU Compiler Collection”), and `EGCS` 1.2 becoming officially designated `GCC` 2.95, there seems to be no need for an actual 0.5.24 release.

To reduce the confusion already resulting from use of 0.5.24 to designate g77 versions within `EGCS` versions 1.0 and 1.1, as well as in versions of g77 documentation and notices during that period, “mainline” g77 version numbering resumes at 0.5.25 with `GCC` 2.95 (`EGCS` 1.2), skipping over 0.5.24 as a placeholder version number.

To repeat, there is no g77 0.5.24, but there is now a 0.5.25. Please remain calm and return to your keypunch units.

### In `EGCS` 1.1.2 versus `EGCS` 1.1.1:

- Fix the `IDate` intrinsic (VXT) (in `libg2c`) so the returned year is in the documented, non-Y2K-compliant range of 0-99, instead of being returned as 100 in the year 2000.

  See IDate Intrinsic (VXT), for more information.

- Fix the `Date_and_Time` intrinsic (in `libg2c`) to return the milliseconds value properly in Values(8).
- Fix the `LStat` intrinsic (in `libg2c`) to return device-ID information properly in SArray(7).
- Improve documentation.

### In `EGCS` 1.1.1 versus `EGCS` 1.1:

- Fix `libg2c` so it performs an implicit `ENDFILE` operation (as appropriate) whenever a `REWIND` is done.

  (This bug was introduced in 0.5.23 and `egcs` 1.1 in g77's version of `libf2c`.)

- Fix `libg2c` so it no longer crashes with a spurious diagnostic upon doing any I/O following a direct formatted write.

  (This bug was introduced in 0.5.23 and `egcs` 1.1 in g77's version of `libf2c`.)

- Fix g77 so it no longer crashes compiling references to the `Rand` intrinsic on some systems.
- Fix g77 portion of installation process so it works better on some systems (those with shells requiring else true clauses on `if` constructs for the completion code to be set properly).

### In `EGCS` 1.1 versus `EGCS` 1.0.3:

- Fix bugs in the `libU77` intrinsic `HostNm` that wrote one byte beyond the end of its `CHARACTER` argument, and in the `libU77` intrinsics `GMTime` and `LTime` that overwrote their arguments.
- Assumed arrays with negative bounds (such as REAL A(-1:*)) no longer elicit spurious diagnostics from g77, even on systems with pointers having different sizes than integers.

  This bug is not known to have existed in any recent version of gcc. It was introduced in an early release of `egcs`.

- Valid combinations of `EXTERNAL`, passing that external as a dummy argument without explicitly giving it a type, and, in a subsequent program unit, referencing that external as an external function with a different type no longer crash g77.
- `CASE DEFAULT` no longer crashes g77.
- The -Wunused option no longer issues a spurious warning about the “master” procedure generated by g77 for procedures containing `ENTRY` statements.
- Support FORMAT(I<expr>) when expr is a compile-time constant `INTEGER` expression.
- Fix g77 -g option so procedures that use `ENTRY` can be stepped through, line by line, in gdb.
- Allow any `REAL` argument to intrinsics `Second` and `CPU_Time`.
- Use `tempnam`, if available, to open scratch files (as in OPEN(STATUS='SCRATCH')) so that the `TMPDIR` environment variable, if present, is used.
- g77's version of `libf2c` separates out the setting of global state (such as command-line arguments and signal handling) from main.o into distinct, new library archive members.

  This should make it easier to write portable applications that have their own (non-Fortran) `main()` routine properly set up the `libf2c` environment, even when `libf2c` (now `libg2c`) is a shared library.

- g77 no longer installs the f77 command and f77.1 man page in the /usr or /usr/local hierarchy, even if the f77-install-ok file exists in the source or build directory. See the installation documentation for more information.
- g77 no longer installs the libf2c.a library and f2c.h include file in the /usr or /usr/local hierarchy, even if the f2c-install-ok or f2c-exists-ok files exist in the source or build directory. See the installation documentation for more information.
- The libf2c.a library produced by g77 has been renamed to libg2c.a. It is installed only in the gcc “private” directory hierarchy, gcc-lib. This allows system administrators and users to choose which version of the `libf2c` library from `netlib` they wish to use on a case-by-case basis. See the installation documentation for more information.
- The f2c.h include (header) file produced by g77 has been renamed to g2c.h. It is installed only in the gcc “private” directory hierarchy, gcc-lib. This allows system administrators and users to choose which version of the include file from `netlib` they wish to use on a case-by-case basis. See the installation documentation for more information.
- The g77 command now expects the run-time library to be named `libg2c.a` instead of `libf2c.a`, to ensure that a version other than the one built and installed as part of the same g77 version is picked up.
- During the configuration and build process, g77 creates subdirectories it needs only as it needs them. Other cleaning up of the configuration and build process has been performed as well.
- `install-info` now used to update the directory of Info documentation to contain an entry for g77 (during installation).
- Some diagnostics have been changed from warnings to errors, to prevent inadvertent use of the resulting, probably buggy, programs. These mostly include diagnostics about use of unsupported features in the `OPEN`, `INQUIRE`, `READ`, and `WRITE` statements, and about truncations of various sorts of constants.
- Improve compilation of `FORMAT` expressions so that a null byte is appended to the last operand if it is a constant. This provides a cleaner run-time diagnostic as provided by `libf2c` for statements like PRINT '(I1', 42.
- Improve documentation and indexing.
- The upgrade to `libf2c` as of 1998-06-18 should fix a variety of problems, including those involving some uses of the `T` format specifier, and perhaps some build (porting) problems as well.

### In `EGCS` 1.1 versus g77 0.5.23:

- Fix a code-generation bug that afflicted Intel x86 targets when -O2 was specified compiling, for example, an old version of the `DNRM2` routine.

  The x87 coprocessor stack was being mismanaged in cases involving assigned `GOTO` and `ASSIGN`.

- g77 no longer produces incorrect code and initial values for `EQUIVALENCE` and `COMMON` aggregates that, due to “unnatural” ordering of members vis-a-vis their types, require initial padding.
- Fix g77 crash compiling code containing the construct CMPLX(0.) or similar.
- g77 no longer crashes when compiling code containing specification statements such as INTEGER(KIND=7) PTR.
- g77 no longer crashes when compiling code such as J = SIGNAL(1, 2).
- g77 now treats %LOC(expr) and LOC(expr) as “ordinary” expressions when they are used as arguments in procedure calls. This change applies only to global (filewide) analysis, making it consistent with how g77 actually generates code for these cases.

  Previously, g77 treated these expressions as denoting special “pointer” arguments for the purposes of filewide analysis.

- Fix g77 crash (or apparently infinite run-time) when compiling certain complicated expressions involving `COMPLEX` arithmetic (especially multiplication).

- Align static double-precision variables and arrays on Intel x86 targets regardless of whether -malign-double is specified.

  Generally, this affects only local variables and arrays having the `SAVE` attribute or given initial values via `DATA`.

- The g77 driver now ensures that -lg2c is specified in the link phase prior to any occurrence of -lm. This prevents accidentally linking to a routine in the SunOS4 -lm library when the generated code wants to link to the one in `libf2c` (`libg2c`).
- g77 emits more debugging information when -g is used.

  This new information allows, for example, `which __g77_length_a` to be used in gdb to determine the type of the phantom length argument supplied with `CHARACTER` variables.

  This information pertains to internally-generated type, variable, and other information, not to the longstanding deficiencies vis-a-vis `COMMON` and `EQUIVALENCE`.

- The F90 `Date_and_Time` intrinsic now is supported.
- The F90 `System_Clock` intrinsic allows the optional arguments (except for the `Count` argument) to be omitted.
- Upgrade to `libf2c` as of 1998-06-18.
- Improve documentation and indexing.

### In 0.5.23 versus 0.5.22:

- This release contains several regressions against version 0.5.22 of g77, due to using the “vanilla” gcc back end instead of patching it to fix a few bugs and improve performance in a few cases.

  Features that have been dropped from this version of g77 due to their being implemented via g77-specific patches to the gcc back end in previous releases include:

  - Support for `__restrict__` keyword, the options -fargument-alias, -fargument-noalias, and -fargument-noalias-global, and the corresponding alias-analysis code.

    (`egcs` has the alias-analysis code, but not the `__restrict__` keyword. `egcs` g77 users benefit from the alias-analysis code despite the lack of the `__restrict__` keyword, which is a C-language construct.)

  - Support for the GNU compiler options -fmove-all-movables, -freduce-all-givs, and -frerun-loop-opt.

    (`egcs` supports these options. g77 users of `egcs` benefit from them even if they are not explicitly specified, because the defaults are optimized for g77 users.)

  - Support for the -W option warning about integer division by zero.
  - The Intel x86-specific option -malign-double applying to stack-allocated data as well as statically-allocate data.

  Note that the gcc/f/gbe/ subdirectory has been removed from this distribution as a result of g77 no longer including patches for the gcc back end.

- Fix bugs in the `libU77` intrinsic `HostNm` that wrote one byte beyond the end of its `CHARACTER` argument, and in the `libU77` intrinsics `GMTime` and `LTime` that overwrote their arguments.
- Support gcc version 2.8, and remove support for prior versions of gcc.

- Remove support for the --driver option, as g77 now does all the driving, just like gcc.
- `CASE DEFAULT` no longer crashes g77.
- Valid combinations of `EXTERNAL`, passing that external as a dummy argument without explicitly giving it a type, and, in a subsequent program unit, referencing that external as an external function with a different type no longer crash g77.
- g77 no longer installs the f77 command and f77.1 man page in the /usr or /usr/local hierarchy, even if the f77-install-ok file exists in the source or build directory. See the installation documentation for more information.
- g77 no longer installs the libf2c.a library and f2c.h include file in the /usr or /usr/local hierarchy, even if the f2c-install-ok or f2c-exists-ok files exist in the source or build directory. See the installation documentation for more information.
- The libf2c.a library produced by g77 has been renamed to libg2c.a. It is installed only in the gcc “private” directory hierarchy, gcc-lib. This allows system administrators and users to choose which version of the `libf2c` library from `netlib` they wish to use on a case-by-case basis. See the installation documentation for more information.
- The f2c.h include (header) file produced by g77 has been renamed to g2c.h. It is installed only in the gcc “private” directory hierarchy, gcc-lib. This allows system administrators and users to choose which version of the include file from `netlib` they wish to use on a case-by-case basis. See the installation documentation for more information.
- The g77 command now expects the run-time library to be named `libg2c.a` instead of `libf2c.a`, to ensure that a version other than the one built and installed as part of the same g77 version is picked up.
- The -Wunused option no longer issues a spurious warning about the “master” procedure generated by g77 for procedures containing `ENTRY` statements.
- g77's version of `libf2c` separates out the setting of global state (such as command-line arguments and signal handling) from main.o into distinct, new library archive members.

  This should make it easier to write portable applications that have their own (non-Fortran) `main()` routine properly set up the `libf2c` environment, even when `libf2c` (now `libg2c`) is a shared library.

- During the configuration and build process, g77 creates subdirectories it needs only as it needs them, thus avoiding unnecessary creation of, for example, stage1/f/runtime when doing a non-bootstrap build. Other cleaning up of the configuration and build process has been performed as well.
- `install-info` now used to update the directory of Info documentation to contain an entry for g77 (during installation).
- Some diagnostics have been changed from warnings to errors, to prevent inadvertent use of the resulting, probably buggy, programs. These mostly include diagnostics about use of unsupported features in the `OPEN`, `INQUIRE`, `READ`, and `WRITE` statements, and about truncations of various sorts of constants.
- Improve documentation and indexing.
- Upgrade to `libf2c` as of 1998-04-20.

  This should fix a variety of problems, including those involving some uses of the `T` format specifier, and perhaps some build (porting) problems as well.

### In 0.5.22 versus 0.5.21:

- Fix code generation for iterative `DO` loops that have one or more references to the iteration variable, or to aliases of it, in their control expressions. For example, DO 10 J=2,J now is compiled correctly.

- Fix a code-generation bug that afflicted Intel x86 targets when -O2 was specified compiling, for example, an old version of the `DNRM2` routine.

  The x87 coprocessor stack was being mismanaged in cases involving assigned `GOTO` and `ASSIGN`.

- Fix `DTime` intrinsic so as not to truncate results to integer values (on some systems).
- Fix `Signal` intrinsic so it offers portable support for 64-bit systems (such as Digital Alphas running GNU/Linux).
- Fix run-time crash involving `NAMELIST` on 64-bit machines such as Alphas.
- Fix g77 version of `libf2c` so it no longer produces a spurious I/O recursion diagnostic at run time when an I/O operation (such as READ *,I) is interrupted in a manner that causes the program to be terminated via the `f_exit` routine (such as via `C-c`).
- Fix g77 crash triggered by `CASE` statement with an omitted lower or upper bound.
- Fix g77 crash compiling references to `CPU_Time` intrinsic.
- Fix g77 crash (or apparently infinite run-time) when compiling certain complicated expressions involving `COMPLEX` arithmetic (especially multiplication).
- Fix g77 crash on statements such as PRINT *, (REAL(Z(I)),I=1,2), where Z is `DOUBLE COMPLEX`.
- Fix a g++ crash.
- Support FORMAT(I<expr>) when expr is a compile-time constant `INTEGER` expression.
- Fix g77 -g option so procedures that use `ENTRY` can be stepped through, line by line, in gdb.
- Fix a profiling-related bug in gcc back end for Intel x86 architecture.
- Allow any `REAL` argument to intrinsics `Second` and `CPU_Time`.
- Allow any numeric argument to intrinsics `Int2` and `Int8`.
- Use `tempnam`, if available, to open scratch files (as in OPEN(STATUS='SCRATCH')) so that the `TMPDIR` environment variable, if present, is used.
- Rename the gcc keyword `restrict` to `__restrict__`, to avoid rejecting valid, existing, C programs. Support for `restrict` is now more like support for `complex`.
- Fix -fpedantic to not reject procedure invocations such as I=J() and CALL FOO().
- Fix -fugly-comma to affect invocations of only external procedures. Restore rejection of gratuitous trailing omitted arguments to intrinsics, as in I=MAX(3,4,,).
- Fix compiler so it accepts -fgnu-intrinsics-* and -fbadu77-intrinsics-* options.
- Improve diagnostic messages from `libf2c` so it is more likely that the printing of the active format string is limited to the string, with no trailing garbage being printed.

  (Unlike f2c, g77 did not append a null byte to its compiled form of every format string specified via a `FORMAT` statement. However, f2c would exhibit the problem anyway for a statement like PRINT '(I)garbage', 1 by printing (I)garbage as the format string.)

- Improve compilation of `FORMAT` expressions so that a null byte is appended to the last operand if it is a constant. This provides a cleaner run-time diagnostic as provided by `libf2c` for statements like PRINT '(I1', 42.
- Fix various crashes involving code with diagnosed errors.
- Fix cross-compilation bug when configuring `libf2c`.
- Improve diagnostics.
- Improve documentation and indexing.
- Upgrade to `libf2c` as of 1997-09-23. This fixes a formatted-I/O bug that afflicted 64-bit systems with 32-bit integers (such as Digital Alpha running GNU/Linux).

### In `EGCS` 1.0.2 versus `EGCS` 1.0.1:

- Fix g77 crash triggered by `CASE` statement with an omitted lower or upper bound.
- Fix g77 crash on statements such as PRINT *, (REAL(Z(I)),I=1,2), where Z is `DOUBLE COMPLEX`.

- Fix -fPIC (such as compiling for ELF targets) on the Intel x86 architecture target so invalid assembler code is no longer produced.
- Fix -fpedantic to not reject procedure invocations such as I=J() and CALL FOO().
- Fix -fugly-comma to affect invocations of only external procedures. Restore rejection of gratuitous trailing omitted arguments to intrinsics, as in I=MAX(3,4,,).
- Fix compiler so it accepts -fgnu-intrinsics-* and -fbadu77-intrinsics-* options.

### In `EGCS` 1.0.1 versus `EGCS` 1.0:

- Fix run-time crash involving `NAMELIST` on 64-bit machines such as Alphas.

### In `EGCS` 1.0 versus g77 0.5.21:

- Version 1.0 of `egcs` contains several regressions against version 0.5.21 of g77, due to using the “vanilla” gcc back end instead of patching it to fix a few bugs and improve performance in a few cases.

  Features that have been dropped from this version of g77 due to their being implemented via g77-specific patches to the gcc back end in previous releases include:

  - Support for the C-language `restrict` keyword.
  - Support for the -W option warning about integer division by zero.
  - The Intel x86-specific option -malign-double applying to stack-allocated data as well as statically-allocate data.

  Note that the gcc/f/gbe/ subdirectory has been removed from this distribution as a result of g77 being fully integrated with the `egcs` variant of the gcc back end.

- Fix code generation for iterative `DO` loops that have one or more references to the iteration variable, or to aliases of it, in their control expressions. For example, DO 10 J=2,J now is compiled correctly.
- Fix `DTime` intrinsic so as not to truncate results to integer values (on some systems).
- Some Fortran code, miscompiled by g77 built on gcc version 2.8.1 on m68k-next-nextstep3 configurations when using the -O2 option, is now compiled correctly. It is believed that a C function known to miscompile on that configuration when using the -O2 -funroll-loops options also is now compiled correctly.
- Remove support for non-`egcs` versions of gcc.

- Remove support for the --driver option, as g77 now does all the driving, just like gcc.
- Allow any numeric argument to intrinsics `Int2` and `Int8`.
- Improve diagnostic messages from `libf2c` so it is more likely that the printing of the active format string is limited to the string, with no trailing garbage being printed.

  (Unlike f2c, g77 did not append a null byte to its compiled form of every format string specified via a `FORMAT` statement. However, `f2c` would exhibit the problem anyway for a statement like PRINT '(I)garbage', 1 by printing (I)garbage as the format string.)

- Upgrade to `libf2c` as of 1997-09-23. This fixes a formatted-I/O bug that afflicted 64-bit systems with 32-bit integers (such as Digital Alpha running GNU/Linux).

### In 0.5.21:

- Fix a code-generation bug introduced by 0.5.20 caused by loop unrolling (by specifying -funroll-loops or similar). This bug afflicted all code compiled by version 2.7.2.2.f.2 of gcc (C, C++, Fortran, and so on).
- Fix a code-generation bug manifested when combining local `EQUIVALENCE` with a `DATA` statement that follows the first executable statement (or is treated as an executable-context statement as a result of using the -fpedantic option).
- Fix a compiler crash that occurred when an integer division by a constant zero is detected. Instead, when the -W option is specified, the gcc back end issues a warning about such a case. This bug afflicted all code compiled by version 2.7.2.2.f.2 of gcc (C, C++, Fortran, and so on).
- Fix a compiler crash that occurred in some cases of procedure inlining. (Such cases became more frequent in 0.5.20.)
- Fix a compiler crash resulting from using `DATA` or similar to initialize a `COMPLEX` variable or array to zero.
- Fix compiler crashes involving use of `AND`, `OR`, or `XOR` intrinsics.
- Fix compiler bug triggered when using a `COMMON` or `EQUIVALENCE` variable as the target of an `ASSIGN` or assigned-`GOTO` statement.
- Fix compiler crashes due to using the name of a some non-standard intrinsics (such as `FTell` or `FPutC`) as such and as the name of a procedure or common block. Such dual use of a name in a program is allowed by the standard.
- Place automatic arrays on the stack, even if `SAVE` or the -fno-automatic option is in effect. This avoids a compiler crash in some cases.
- The -malign-double option now reliably aligns `DOUBLE PRECISION` optimally on Pentium and Pentium Pro architectures (586 and 686 in gcc).
- New option -Wno-globals disables warnings about “suspicious” use of a name both as a global name and as the implicit name of an intrinsic, and warnings about disagreements over the number or natures of arguments passed to global procedures, or the natures of the procedures themselves.

  The default is to issue such warnings, which are new as of this version of g77.

- New option -fno-globals disables diagnostics about potentially fatal disagreements analysis problems, such as disagreements over the number or natures of arguments passed to global procedures, or the natures of those procedures themselves.

  The default is to issue such diagnostics and flag the compilation as unsuccessful. With this option, the diagnostics are issued as warnings, or, if -Wno-globals is specified, are not issued at all.

  This option also disables inlining of global procedures, to avoid compiler crashes resulting from coding errors that these diagnostics normally would identify.

- Diagnose cases where a reference to a procedure disagrees with the type of that procedure, or where disagreements about the number or nature of arguments exist. This avoids a compiler crash.
- Fix parsing bug whereby g77 rejected a second initialization specification immediately following the first's closing / without an intervening comma in a `DATA` statement, and the second specification was an implied-DO list.
- Improve performance of the gcc back end so certain complicated expressions involving `COMPLEX` arithmetic (especially multiplication) don't appear to take forever to compile.
- Fix a couple of profiling-related bugs in gcc back end.
- Integrate GNU Ada's (GNAT's) changes to the back end, which consist almost entirely of bug fixes. These fixes are circa version 3.10p of GNAT.
- Include some other gcc fixes that seem useful in g77's version of gcc. (See gcc/ChangeLog for details—compare it to that file in the vanilla `gcc-2.7.2.3.tar.gz` distribution.)
- Fix `libU77` routines that accept file and other names to strip trailing blanks from them, for consistency with other implementations. Blanks may be forcibly appended to such names by appending a single null character (CHAR(0)) to the significant trailing blanks.
- Fix `CHMOD` intrinsic to work with file names that have embedded blanks, commas, and so on.
- Fix `SIGNAL` intrinsic so it accepts an optional third `Status` argument.
- Fix `IDATE()` intrinsic subroutine (VXT form) so it accepts arguments in the correct order. Documentation fixed accordingly, and for `GMTIME()` and `LTIME()` as well.
- Make many changes to `libU77` intrinsics to support existing code more directly.

  Such changes include allowing both subroutine and function forms of many routines, changing `MCLOCK()` and `TIME()` to return `INTEGER(KIND=1)` values, introducing `MCLOCK8()` and `TIME8()` to return `INTEGER(KIND=2)` values, and placing functions that are intended to perform side effects in a new intrinsic group, `badu77`.

- Improve `libU77` so it is more portable.
- Add options -fbadu77-intrinsics-delete, -fbadu77-intrinsics-hide, and so on.
- Fix crashes involving diagnosed or invalid code.
- g77 and gcc now do a somewhat better job detecting and diagnosing arrays that are too large to handle before these cause diagnostics during the assembler or linker phase, a compiler crash, or generation of incorrect code.
- Make some fixes to alias analysis code.
- Add support for `restrict` keyword in gcc front end.
- Support gcc version 2.7.2.3 (modified by g77 into version 2.7.2.3.f.1), and remove support for prior versions of gcc.
- Incorporate GNAT's patches to the gcc back end into g77's, so GNAT users do not need to apply GNAT's patches to build both GNAT and g77 from the same source tree.
- Modify make rules and related code so that generation of Info documentation doesn't require compilation using gcc. Now, any ANSI C compiler should be adequate to produce the g77 documentation (in particular, the tables of intrinsics) from scratch.
- Add `INT2` and `INT8` intrinsics.
- Add `CPU_TIME` intrinsic.
- Add `ALARM` intrinsic.
- `CTIME` intrinsic now accepts any `INTEGER` argument, not just `INTEGER(KIND=2)`.
- Warn when explicit type declaration disagrees with the type of an intrinsic invocation.
- Support *f771 entry in gcc specs file.
- Fix typo in make rule g77-cross, used only for cross-compiling.
- Fix `libf2c` build procedure to re-archive library if previous attempt to archive was interrupted.
- Change gcc to unroll loops only during the last invocation (of as many as two invocations) of loop optimization.
- Improve handling of -fno-f2c so that code that attempts to pass an intrinsic as an actual argument, such as CALL FOO(ABS), is rejected due to the fact that the run-time-library routine is, effectively, compiled with -ff2c in effect.
- Fix g77 driver to recognize -fsyntax-only as an option that inhibits linking, just like -c or -S, and to recognize and properly handle the -nostdlib, -M, -MM, -nodefaultlibs, and -Xlinker options.
- Upgrade to `libf2c` as of 1997-08-16.
- Modify `libf2c` to consistently and clearly diagnose recursive I/O (at run time).
- g77 driver now prints version information (such as produced by `g77 -v`) to `stderr` instead of `stdout`.
- The .r suffix now designates a Ratfor source file, to be preprocessed via the ratfor command, available separately.
- Fix some aspects of how gcc determines what kind of system is being configured and what kinds are supported. For example, GNU Linux/Alpha ELF systems now are directly supported.
- Improve diagnostics.
- Improve documentation and indexing.
- Include all pertinent files for `libf2c` that come from `netlib.bell-labs.com`; give any such files that aren't quite accurate in g77's version of `libf2c` the suffix .netlib.
- Reserve `INTEGER(KIND=0)` for future use.

### In 0.5.20:

- The -fno-typeless-boz option is now the default.

  This option specifies that non-decimal-radix constants using the prefixed-radix form (such as Z'1234') are to be interpreted as `INTEGER(KIND=1)` constants. Specify -ftypeless-boz to cause such constants to be interpreted as typeless.

  (Version 0.5.19 introduced -fno-typeless-boz and its inverse.)

  See Options Controlling Fortran Dialect, for information on the -ftypeless-boz option.

- Options -ff90-intrinsics-enable and -fvxt-intrinsics-enable now are the defaults.

  Some programs might use names that clash with intrinsic names defined (and now enabled) by these options or by the new `libU77` intrinsics. Users of such programs might need to compile them differently (using, for example, -ff90-intrinsics-disable) or, better yet, insert appropriate `EXTERNAL` statements specifying that these names are not intended to be names of intrinsics.

- The `ALWAYS_FLUSH` macro is no longer defined when building `libf2c`, which should result in improved I/O performance, especially over NFS.

  Note: If you have code that depends on the behavior of `libf2c` when built with `ALWAYS_FLUSH` defined, you will have to modify `libf2c` accordingly before building it from this and future versions of g77.

  See Output Assumed To Flush, for more information.

- Dave Love's implementation of `libU77` has been added to the version of `libf2c` distributed with and built as part of g77. g77 now knows about the routines in this library as intrinsics.
- New option -fvxt specifies that the source file is written in VXT Fortran, instead of GNU Fortran.

  See VXT Fortran, for more information on the constructs recognized when the -fvxt option is specified.

- The -fvxt-not-f90 option has been deleted, along with its inverse, -ff90-not-vxt.

  If you used one of these deleted options, you should re-read the pertinent documentation to determine which options, if any, are appropriate for compiling your code with this version of g77.

  See Other Dialects, for more information.

- The -fugly option now issues a warning, as it likely will be removed in a future version.

  (Enabling all the -fugly-* options is unlikely to be feasible, or sensible, in the future, so users should learn to specify only those -fugly-* options they really need for a particular source file.)

- The -fugly-assumed option, introduced in version 0.5.19, has been changed to better accommodate old and new code.

  See Ugly Assumed-Size Arrays, for more information.

- Make a number of fixes to the g77 front end and the gcc back end to better support Alpha (AXP) machines. This includes providing at least one bug-fix to the gcc back end for Alphas.
- Related to supporting Alpha (AXP) machines, the `LOC()` intrinsic and `%LOC()` construct now return values of `INTEGER(KIND=0)` type, as defined by the GNU Fortran language.

  This type is wide enough (holds the same number of bits) as the character-pointer type on the machine.

  On most machines, this won't make a difference, whereas, on Alphas and other systems with 64-bit pointers, the `INTEGER(KIND=0)` type is equivalent to `INTEGER(KIND=2)` (often referred to as `INTEGER*8`) instead of the more common `INTEGER(KIND=1)` (often referred to as `INTEGER*4`).

- Emulate `COMPLEX` arithmetic in the g77 front end, to avoid bugs in `complex` support in the gcc back end. New option -fno-emulate-complex causes g77 to revert the 0.5.19 behavior.
- Fix bug whereby REAL A(1), for example, caused a compiler crash if -fugly-assumed was in effect and A was a local (automatic) array. That case is no longer affected by the new handling of -fugly-assumed.
- Fix g77 command driver so that g77 -o foo.f no longer deletes foo.f before issuing other diagnostics, and so the -x option is properly handled.
- Enable inlining of subroutines and functions by the gcc back end. This works as it does for gcc itself—program units may be inlined for invocations that follow them in the same program unit, as long as the appropriate compile-time options are specified.
- Dummy arguments are no longer assumed to potentially alias (overlap) other dummy arguments or `COMMON` areas when any of these are defined (assigned to) by Fortran code.

  This can result in faster and/or smaller programs when compiling with optimization enabled, though on some systems this effect is observed only when -fforce-addr also is specified.

  New options -falias-check, -fargument-alias, -fargument-noalias, and -fno-argument-noalias-global control the way g77 handles potential aliasing.

  See Aliasing Assumed To Work, for detailed information on why the new defaults might result in some programs no longer working the way they did when compiled by previous versions of g77.

- The `CONJG()` and `DCONJG()` intrinsics now are compiled in-line.
- The bug-fix for 0.5.19.1 has been re-done. The g77 compiler has been changed back to assume `libf2c` has no aliasing problems in its implementations of the `COMPLEX` (and `DOUBLE COMPLEX`) intrinsics. The `libf2c` has been changed to have no such problems.

  As a result, 0.5.20 is expected to offer improved performance over 0.5.19.1, perhaps as good as 0.5.19 in most or all cases, due to this change alone.

  Note: This change requires version 0.5.20 of `libf2c`, at least, when linking code produced by any versions of g77 other than 0.5.19.1. Use g77 -v to determine the version numbers of the `libF77`, `libI77`, and `libU77` components of the `libf2c` library. (If these version numbers are not printed—in particular, if the linker complains about unresolved references to names like g77__fvers__—that strongly suggests your installation has an obsolete version of `libf2c`.)

- New option -fugly-assign specifies that the same memory locations are to be used to hold the values assigned by both statements I = 3 and ASSIGN 10 TO I, for example. (Normally, g77 uses a separate memory location to hold assigned statement labels.)

  See Ugly Assigned Labels, for more information.

- `FORMAT` and `ENTRY` statements now are allowed to precede `IMPLICIT NONE` statements.
- Produce diagnostic for unsupported `SELECT CASE` on `CHARACTER` type, instead of crashing, at compile time.
- Fix crashes involving diagnosed or invalid code.
- Change approach to building `libf2c` archive (libf2c.a) so that members are added to it only when truly necessary, so the user that installs an already-built g77 doesn't need to have write access to the build tree (whereas the user doing the build might not have access to install new software on the system).
- Support gcc version 2.7.2.2 (modified by g77 into version 2.7.2.2.f.2), and remove support for prior versions of gcc.
- Upgrade to `libf2c` as of 1997-02-08, and fix up some of the build procedures.
- Improve general build procedures for g77, fixing minor bugs (such as deletion of any file named f771 in the parent directory of `gcc/`).
- Enable full support of `INTEGER(KIND=2)` (often referred to as `INTEGER*8`) available in `libf2c` and f2c.h so that f2c users may make full use of its features via the g77 version of f2c.h and the `INTEGER(KIND=2)` support routines in the g77 version of `libf2c`.
- Improve g77 driver and `libf2c` so that g77 -v yields version information on the library.
- The `SNGL` and `FLOAT` intrinsics now are specific intrinsics, instead of synonyms for the generic intrinsic `REAL`.
- New intrinsics have been added. These are `REALPART`, `IMAGPART`, `COMPLEX`, `LONG`, and `SHORT`.
- A new group of intrinsics, `gnu`, has been added to contain the new `REALPART`, `IMAGPART`, and `COMPLEX` intrinsics. An old group, `dcp`, has been removed.
- Complain about industry-wide ambiguous references REAL(expr) and AIMAG(expr), where expr is `DOUBLE COMPLEX` (or any complex type other than `COMPLEX`), unless -ff90 option specifies Fortran 90 interpretation or new -fugly-complex option, in conjunction with -fnot-f90, specifies f2c interpretation.
- Make improvements to diagnostics.
- Speed up compiler a bit.
- Improvements to documentation and indexing, including a new chapter containing information on one, later more, diagnostics that users are directed to pull up automatically via a message in the diagnostic itself.

  (Hence the menu item `M` for the node `Diagnostics` in the top-level menu of the Info documentation.)

### In previous versions:

Information on previous versions is archived in gcc/gcc/f/news.texi following the test of the `DOC-OLDNEWS` macro.

Next: Language, Previous: News, Up: Top

## 7 User-visible Changes

This chapter describes changes to g77 that are visible to the programmers who actually write and maintain Fortran code they compile with g77. Information on changes to installation procedures, changes to the documentation, and bug fixes is not provided here, unless it is likely to affect how users use g77. See News About GNU Fortran, for information on such changes to g77.

Note that two variants of g77 are tracked below. The `egcs` variant is described vis-a-vis previous versions of `egcs` and/or an official FSF version, as appropriate. Note that all such variants are obsolete as of July 1999 - the information is retained here only for its historical value.

Therefore, `egcs` versions sometimes have multiple listings to help clarify how they differ from other versions, though this can make getting a complete picture of what a particular `egcs` version contains somewhat more difficult.

For information on bugs in the GCC-3.4.4 version of g77, see Known Bugs In GNU Fortran.

The following information was last updated on 2004-12-29:

### In `GCC` 3.4 versus `GCC` 3.3:

- Problem Reports fixed (in chronological order of submission):
  `8485`
    g77 doesn't accept INTEGER*8 constant in PARAMETER multiplication.
  `11918`
    (libf2c) isatty does not call f_init.
  `12317`
    Incorrect documentation for Fortran debugging features.
- Roger Sayle (roger@eyesopen.com) fixed the remaining problems with regard to the support of INTEGER*8, INTEGER*2 and INTEGER*1 as a fallout of fixing PR 8485.

### In `GCC` 3.3 versus `GCC` 3.2:

- Problem Reports fixed (in chronological order of submission):
  `1832`
    -list directed i/o overflow hangs, -fbounds-check doesn't detect
  `3924`
    g77 generates code which is rejected by GAS if COFF debugging info is requested
  `6286`
    Broken links on web pages
  `6367`
    (libf2c) multiple repeat counts confuse namelist read into array
  `6491`
    Logical operations error on logicals when using -fugly-logint
  `6742`
    Generation of C++ Prototype for FORTRAN and extern "C"
  `7113`
    Failure of g77.f-torture/execute/f90-intrinsic-bit.f -Os on irix6.5
  `7236`
    (libf2c) OPEN(...,RECL=nnn,...) without ACCESS='DIRECT' should assume a direct access file
  `7278`
    g77 "bug"; the executable misbehave (use of options -O2 -fno-automatic gave wrong results)
  `7384`
    (libf2c) DATE_AND_TIME milliseconds field inactive on Windows
  `7388`
    Incorrect output with 0-based array of characters
  `8587`
    Double complex zero ** double precision number -> NaN instead of zero
  `9038`
    -ffixed-line-length-none -x f77-cpp-input gives: Warning: unknown register name line-length-none
  `9263`
    ICE caused by invalid PARAMETER in implied DO loop
  `10197`
    Direct access files not unformatted by default
  `10726`
    Documentation for function IDATE Intrinsic (UNIX) is wrong [fixed in 3.3.1].
- Richard Henderson (rth@redhat.com) analyzed and improved the handling of (no-)aliasing information for dummy arguments and improved the optimization of induction variables in unrolled loops.

### In `GCC` 3.2 versus `GCC` 3.1:

- Problem Reports fixed (in chronological order of submission):
  `7681`
    ICE in compensate_edge, at reg-stack.c:2591
  `8308`
    gcc-3.x does not compile files with suffix .r (RATFOR) [Fixed in 3.2.1]
  `9258`
    [3.2/3.3/3.4 regression] ICE in compensate_edge, at reg-stack.c:2589

### In `GCC` 3.1 (formerly known as g77-0.5.27) versus `GCC` 3.0:

- Problem Reports fixed (in chronological order of submission):
  `947`
    Data statement initialization with subscript of kind INTEGER*2
  `3743`
    Reference to intrinsic `ISHFT' invalid
  `3807`
    Function BESJN(integer,double) problems
  `3957`
    g77 -pipe -xf77-cpp-input sends output to stdout
  `4279`
    g77 -h" gives bogus output
  `4730`
    ICE on valid input using CALL EXIT(%VAL(...))
  `4752`
    g77 -v -c -xf77-version /dev/null -xnone causes ice
  `4885`
    BACKSPACE example that doesn't work as of gcc/g77-3.0.x
  `5122`
    g77 rejects accepted use of INTEGER*2 as type of DATA statement loop index
  `5397`
    ICE on compiling source with 540 000 000 REAL array
  `5473`
    ICE on BESJN(integer*8,real)
  `5837`
    bug in loop unrolling
  `6106`
    sparc-sun-solaris2.7 gcc-3.1 extra g77 testsuite failures w/-m64
  `6138`
    Incorrect acces of integer*1 variables on PA
  `6304`
    Failure of LAPACK test dtest on irix6.5 with -mabi=64 -O2
- g77 now has its man page generated from the texinfo documentation, to guarantee that it remains up to date.
- g77 used to reject the following program on 32-bit targets:

                PROGRAM PROG
                DIMENSION A(140 000 000)
                END

  with the message:

                prog.f: In program `prog':
                prog.f:2:
                         DIMENSION A(140 000 000)
                                   ^
                Array `a' at (^) is too large to handle

  because 140 000 000 REALs is larger than the largest bit-extent that can be expressed in 32 bits. However, bit-sizes never play a role after offsets have been converted to byte addresses. Therefore this check has been removed, and the limit is now 2 Gbyte of memory (around 530 000 000 REALs). Note: On GNU/Linux systems one has to compile and link programs that occupy more than 1 Gbyte statically, i.e. `g77 -static ...`.

- Based on work done by Juergen Pfeifer (juergen.pfeifer@gmx.net) libf2c is now a shared library. One can still link in all objects with the program by specifying the -static option.
- Robert Anderson (rwa@alumni.princeton.edu) thought up a two line change that enables g77 to compile such code as:

                SUBROUTINE SUB(A, N)
                DIMENSION N(2)
                DIMENSION A(N(1),N(2))
                A(1,1) = 1.
                END

  Note the use of array elements in the bounds of the adjustable array A.

- George Helffrich (george@geo.titech.ac.jp) implemented a change in substring index checking (when specifying -fbounds-check) that permits the use of zero length substrings of the form `string(1:0)`.
- Based on code developed by Pedro Vazquez (vazquez@penelope.iqm.unicamp.br), the `libf2c` library is now able to read and write files larger than 2 Gbyte on 32-bit target machines, if the operating system supports this.

### In 0.5.26, `GCC` 3.0 versus `GCC` 2.95:

- When a REWIND was issued after a WRITE statement on an unformatted file, the implicit truncation was performed by copying the truncated file to /tmp and copying the result back. This has been fixed by using the `ftruncate` OS function. Thanks go to the GAMESS developers for bringing this to our attention.
- Using options -g, -ggdb or -gdwarf[-2] (where appropriate for your target) now also enables debugging information for COMMON BLOCK and EQUIVALENCE items to be emitted. Thanks go to Andrew Vaught (andy@xena.eas.asu.edu) and George Helffrich (george@geology.bristol.ac.uk) for fixing this longstanding problem.
- It is not necessary anymore to use the option -femulate-complex to compile Fortran code using COMPLEX arithmetic, even on 64-bit machines (like the Alpha). This will improve code generation.
- INTRINSIC arithmetic functions are now treated as routines that do not depend on anything but their argument(s). This enables further instruction scheduling, because it is known that they cannot read or modify arbitrary locations.

### In 0.5.25, `GCC` 2.95 (`EGCS` 1.2) versus `EGCS` 1.1.2:

- The new -fbounds-check option causes g77 to compile run-time bounds checks of array subscripts, as well as of substring start and end points.
- `libg2c` now supports building as multilibbed library, which provides better support for systems that require options such as -mieee to work properly.
- Source file names with the suffixes .FOR and .FPP now are recognized by g77 as if they ended in .for and .fpp, respectively.
- The order of arguments to the subroutine forms of the `CTime`, `DTime`, `ETime`, and `TtyNam` intrinsics has been swapped. The argument serving as the returned value for the corresponding function forms now is the second argument, making these consistent with the other subroutine forms of `libU77` intrinsics.
- g77 now warns about a reference to an intrinsic that has an interface that is not Year 2000 (Y2K) compliant. Also, `libg2c` has been changed to increase the likelihood of catching references to the implementations of these intrinsics using the `EXTERNAL` mechanism (which would avoid the new warnings).

  See Year 2000 (Y2K) Problems, for more information.

- -fno-emulate-complex is now the default option. This should result in improved performance of code that uses the `COMPLEX` data type.

- The -malign-double option now reliably aligns all double-precision variables and arrays on Intel x86 targets.
- g77 no longer generates code to maintain `errno`, a C-language concept, when performing operations such as the `SqRt` intrinsic.
- Support for the -fugly option has been removed.

### In 0.5.24 versus 0.5.23:

There is no g77 version 0.5.24 at this time, or planned. 0.5.24 is the version number designated for bug fixes and, perhaps, some new features added, to 0.5.23. Version 0.5.23 requires gcc 2.8.1, as 0.5.24 was planned to require.

Due to `EGCS` becoming `GCC` (which is now an acronym for “GNU Compiler Collection”), and `EGCS` 1.2 becoming officially designated `GCC` 2.95, there seems to be no need for an actual 0.5.24 release.

To reduce the confusion already resulting from use of 0.5.24 to designate g77 versions within `EGCS` versions 1.0 and 1.1, as well as in versions of g77 documentation and notices during that period, “mainline” g77 version numbering resumes at 0.5.25 with `GCC` 2.95 (`EGCS` 1.2), skipping over 0.5.24 as a placeholder version number.

To repeat, there is no g77 0.5.24, but there is now a 0.5.25. Please remain calm and return to your keypunch units.

### In `EGCS` 1.1.2 versus `EGCS` 1.1.1:

### In `EGCS` 1.1.1 versus `EGCS` 1.1:

### In `EGCS` 1.1 versus `EGCS` 1.0.3:

- Support FORMAT(I<expr>) when expr is a compile-time constant `INTEGER` expression.
- Fix g77 -g option so procedures that use `ENTRY` can be stepped through, line by line, in gdb.
- Allow any `REAL` argument to intrinsics `Second` and `CPU_Time`.
- Use `tempnam`, if available, to open scratch files (as in OPEN(STATUS='SCRATCH')) so that the `TMPDIR` environment variable, if present, is used.
- g77's version of `libf2c` separates out the setting of global state (such as command-line arguments and signal handling) from main.o into distinct, new library archive members.

  This should make it easier to write portable applications that have their own (non-Fortran) `main()` routine properly set up the `libf2c` environment, even when `libf2c` (now `libg2c`) is a shared library.

- The g77 command now expects the run-time library to be named `libg2c.a` instead of `libf2c.a`, to ensure that a version other than the one built and installed as part of the same g77 version is picked up.
- Some diagnostics have been changed from warnings to errors, to prevent inadvertent use of the resulting, probably buggy, programs. These mostly include diagnostics about use of unsupported features in the `OPEN`, `INQUIRE`, `READ`, and `WRITE` statements, and about truncations of various sorts of constants.

### In `EGCS` 1.1 versus g77 0.5.23:

- g77 now treats %LOC(expr) and LOC(expr) as “ordinary” expressions when they are used as arguments in procedure calls. This change applies only to global (filewide) analysis, making it consistent with how g77 actually generates code for these cases.

  Previously, g77 treated these expressions as denoting special “pointer” arguments for the purposes of filewide analysis.

- Align static double-precision variables and arrays on Intel x86 targets regardless of whether -malign-double is specified.

  Generally, this affects only local variables and arrays having the `SAVE` attribute or given initial values via `DATA`.

- The g77 driver now ensures that -lg2c is specified in the link phase prior to any occurrence of -lm. This prevents accidentally linking to a routine in the SunOS4 -lm library when the generated code wants to link to the one in `libf2c` (`libg2c`).
- g77 emits more debugging information when -g is used.

  This new information allows, for example, `which __g77_length_a` to be used in gdb to determine the type of the phantom length argument supplied with `CHARACTER` variables.

  This information pertains to internally-generated type, variable, and other information, not to the longstanding deficiencies vis-a-vis `COMMON` and `EQUIVALENCE`.

- The F90 `Date_and_Time` intrinsic now is supported.
- The F90 `System_Clock` intrinsic allows the optional arguments (except for the `Count` argument) to be omitted.

### In 0.5.23 versus 0.5.22:

- This release contains several regressions against version 0.5.22 of g77, due to using the “vanilla” gcc back end instead of patching it to fix a few bugs and improve performance in a few cases.

  Features that have been dropped from this version of g77 due to their being implemented via g77-specific patches to the gcc back end in previous releases include:

  - Support for `__restrict__` keyword, the options -fargument-alias, -fargument-noalias, and -fargument-noalias-global, and the corresponding alias-analysis code.

    (`egcs` has the alias-analysis code, but not the `__restrict__` keyword. `egcs` g77 users benefit from the alias-analysis code despite the lack of the `__restrict__` keyword, which is a C-language construct.)

  - Support for the GNU compiler options -fmove-all-movables, -freduce-all-givs, and -frerun-loop-opt.

    (`egcs` supports these options. g77 users of `egcs` benefit from them even if they are not explicitly specified, because the defaults are optimized for g77 users.)

  - Support for the -W option warning about integer division by zero.
  - The Intel x86-specific option -malign-double applying to stack-allocated data as well as statically-allocate data.
- Support gcc version 2.8, and remove support for prior versions of gcc.

- Remove support for the --driver option, as g77 now does all the driving, just like gcc.
- The g77 command now expects the run-time library to be named `libg2c.a` instead of `libf2c.a`, to ensure that a version other than the one built and installed as part of the same g77 version is picked up.
- g77's version of `libf2c` separates out the setting of global state (such as command-line arguments and signal handling) from main.o into distinct, new library archive members.

  This should make it easier to write portable applications that have their own (non-Fortran) `main()` routine properly set up the `libf2c` environment, even when `libf2c` (now `libg2c`) is a shared library.

- Some diagnostics have been changed from warnings to errors, to prevent inadvertent use of the resulting, probably buggy, programs. These mostly include diagnostics about use of unsupported features in the `OPEN`, `INQUIRE`, `READ`, and `WRITE` statements, and about truncations of various sorts of constants.

### In 0.5.22 versus 0.5.21:

- Fix `Signal` intrinsic so it offers portable support for 64-bit systems (such as Digital Alphas running GNU/Linux).
- Support FORMAT(I<expr>) when expr is a compile-time constant `INTEGER` expression.
- Fix g77 -g option so procedures that use `ENTRY` can be stepped through, line by line, in gdb.
- Allow any `REAL` argument to intrinsics `Second` and `CPU_Time`.
- Allow any numeric argument to intrinsics `Int2` and `Int8`.
- Use `tempnam`, if available, to open scratch files (as in OPEN(STATUS='SCRATCH')) so that the `TMPDIR` environment variable, if present, is used.
- Rename the gcc keyword `restrict` to `__restrict__`, to avoid rejecting valid, existing, C programs. Support for `restrict` is now more like support for `complex`.
- Fix -fugly-comma to affect invocations of only external procedures. Restore rejection of gratuitous trailing omitted arguments to intrinsics, as in I=MAX(3,4,,).
- Fix compiler so it accepts -fgnu-intrinsics-* and -fbadu77-intrinsics-* options.

### In `EGCS` 1.0.2 versus `EGCS` 1.0.1:

- Fix compiler so it accepts -fgnu-intrinsics-* and -fbadu77-intrinsics-* options.

### In `EGCS` 1.0.1 versus `EGCS` 1.0:

### In `EGCS` 1.0 versus g77 0.5.21:

- Version 1.0 of `egcs` contains several regressions against version 0.5.21 of g77, due to using the “vanilla” gcc back end instead of patching it to fix a few bugs and improve performance in a few cases.

  Features that have been dropped from this version of g77 due to their being implemented via g77-specific patches to the gcc back end in previous releases include:

  - Support for the C-language `restrict` keyword.
  - Support for the -W option warning about integer division by zero.
  - The Intel x86-specific option -malign-double applying to stack-allocated data as well as statically-allocate data.

- Remove support for the --driver option, as g77 now does all the driving, just like gcc.
- Allow any numeric argument to intrinsics `Int2` and `Int8`.

### In 0.5.21:

- When the -W option is specified, gcc, g77, and other GNU compilers that incorporate the gcc back end as modified by g77, issue a warning about integer division by constant zero.
- New option -Wno-globals disables warnings about “suspicious” use of a name both as a global name and as the implicit name of an intrinsic, and warnings about disagreements over the number or natures of arguments passed to global procedures, or the natures of the procedures themselves.

  The default is to issue such warnings, which are new as of this version of g77.

- New option -fno-globals disables diagnostics about potentially fatal disagreements analysis problems, such as disagreements over the number or natures of arguments passed to global procedures, or the natures of those procedures themselves.

  The default is to issue such diagnostics and flag the compilation as unsuccessful. With this option, the diagnostics are issued as warnings, or, if -Wno-globals is specified, are not issued at all.

  This option also disables inlining of global procedures, to avoid compiler crashes resulting from coding errors that these diagnostics normally would identify.

- Fix `libU77` routines that accept file and other names to strip trailing blanks from them, for consistency with other implementations. Blanks may be forcibly appended to such names by appending a single null character (CHAR(0)) to the significant trailing blanks.
- Fix `CHMOD` intrinsic to work with file names that have embedded blanks, commas, and so on.
- Fix `SIGNAL` intrinsic so it accepts an optional third `Status` argument.
- Make many changes to `libU77` intrinsics to support existing code more directly.

  Such changes include allowing both subroutine and function forms of many routines, changing `MCLOCK()` and `TIME()` to return `INTEGER(KIND=1)` values, introducing `MCLOCK8()` and `TIME8()` to return `INTEGER(KIND=2)` values, and placing functions that are intended to perform side effects in a new intrinsic group, `badu77`.

- Add options -fbadu77-intrinsics-delete, -fbadu77-intrinsics-hide, and so on.
- Add `INT2` and `INT8` intrinsics.
- Add `CPU_TIME` intrinsic.
- Add `ALARM` intrinsic.
- `CTIME` intrinsic now accepts any `INTEGER` argument, not just `INTEGER(KIND=2)`.
- g77 driver now prints version information (such as produced by `g77 -v`) to `stderr` instead of `stdout`.
- The .r suffix now designates a Ratfor source file, to be preprocessed via the ratfor command, available separately.

### In 0.5.20:

- The -fno-typeless-boz option is now the default.

  This option specifies that non-decimal-radix constants using the prefixed-radix form (such as Z'1234') are to be interpreted as `INTEGER(KIND=1)` constants. Specify -ftypeless-boz to cause such constants to be interpreted as typeless.

  (Version 0.5.19 introduced -fno-typeless-boz and its inverse.)

  See Options Controlling Fortran Dialect, for information on the -ftypeless-boz option.

- Options -ff90-intrinsics-enable and -fvxt-intrinsics-enable now are the defaults.

  Some programs might use names that clash with intrinsic names defined (and now enabled) by these options or by the new `libU77` intrinsics. Users of such programs might need to compile them differently (using, for example, -ff90-intrinsics-disable) or, better yet, insert appropriate `EXTERNAL` statements specifying that these names are not intended to be names of intrinsics.

- The `ALWAYS_FLUSH` macro is no longer defined when building `libf2c`, which should result in improved I/O performance, especially over NFS.

  Note: If you have code that depends on the behavior of `libf2c` when built with `ALWAYS_FLUSH` defined, you will have to modify `libf2c` accordingly before building it from this and future versions of g77.

  See Output Assumed To Flush, for more information.

- Dave Love's implementation of `libU77` has been added to the version of `libf2c` distributed with and built as part of g77. g77 now knows about the routines in this library as intrinsics.
- New option -fvxt specifies that the source file is written in VXT Fortran, instead of GNU Fortran.

  See VXT Fortran, for more information on the constructs recognized when the -fvxt option is specified.

- The -fvxt-not-f90 option has been deleted, along with its inverse, -ff90-not-vxt.

  If you used one of these deleted options, you should re-read the pertinent documentation to determine which options, if any, are appropriate for compiling your code with this version of g77.

  See Other Dialects, for more information.

- The -fugly option now issues a warning, as it likely will be removed in a future version.

  (Enabling all the -fugly-* options is unlikely to be feasible, or sensible, in the future, so users should learn to specify only those -fugly-* options they really need for a particular source file.)

- The -fugly-assumed option, introduced in version 0.5.19, has been changed to better accommodate old and new code.

  See Ugly Assumed-Size Arrays, for more information.

- Related to supporting Alpha (AXP) machines, the `LOC()` intrinsic and `%LOC()` construct now return values of `INTEGER(KIND=0)` type, as defined by the GNU Fortran language.

  This type is wide enough (holds the same number of bits) as the character-pointer type on the machine.

  On most machines, this won't make a difference, whereas, on Alphas and other systems with 64-bit pointers, the `INTEGER(KIND=0)` type is equivalent to `INTEGER(KIND=2)` (often referred to as `INTEGER*8`) instead of the more common `INTEGER(KIND=1)` (often referred to as `INTEGER*4`).

- Emulate `COMPLEX` arithmetic in the g77 front end, to avoid bugs in `complex` support in the gcc back end. New option -fno-emulate-complex causes g77 to revert the 0.5.19 behavior.
- Dummy arguments are no longer assumed to potentially alias (overlap) other dummy arguments or `COMMON` areas when any of these are defined (assigned to) by Fortran code.

  This can result in faster and/or smaller programs when compiling with optimization enabled, though on some systems this effect is observed only when -fforce-addr also is specified.

  New options -falias-check, -fargument-alias, -fargument-noalias, and -fno-argument-noalias-global control the way g77 handles potential aliasing.

  See Aliasing Assumed To Work, for detailed information on why the new defaults might result in some programs no longer working the way they did when compiled by previous versions of g77.

- New option -fugly-assign specifies that the same memory locations are to be used to hold the values assigned by both statements I = 3 and ASSIGN 10 TO I, for example. (Normally, g77 uses a separate memory location to hold assigned statement labels.)

  See Ugly Assigned Labels, for more information.

- `FORMAT` and `ENTRY` statements now are allowed to precede `IMPLICIT NONE` statements.
- Enable full support of `INTEGER(KIND=2)` (often referred to as `INTEGER*8`) available in `libf2c` and f2c.h so that f2c users may make full use of its features via the g77 version of f2c.h and the `INTEGER(KIND=2)` support routines in the g77 version of `libf2c`.
- Improve g77 driver and `libf2c` so that g77 -v yields version information on the library.
- The `SNGL` and `FLOAT` intrinsics now are specific intrinsics, instead of synonyms for the generic intrinsic `REAL`.
- New intrinsics have been added. These are `REALPART`, `IMAGPART`, `COMPLEX`, `LONG`, and `SHORT`.
- A new group of intrinsics, `gnu`, has been added to contain the new `REALPART`, `IMAGPART`, and `COMPLEX` intrinsics. An old group, `dcp`, has been removed.
- Complain about industry-wide ambiguous references REAL(expr) and AIMAG(expr), where expr is `DOUBLE COMPLEX` (or any complex type other than `COMPLEX`), unless -ff90 option specifies Fortran 90 interpretation or new -fugly-complex option, in conjunction with -fnot-f90, specifies f2c interpretation.

### In previous versions:

Information on previous versions is archived in gcc/gcc/f/news.texi following the test of the `DOC-OLDNEWS` macro.

Next: Compiler, Previous: Changes, Up: Top

## 8 The GNU Fortran Language

GNU Fortran supports a variety of extensions to, and dialects of, the Fortran language. Its primary base is the ANSI FORTRAN 77 standard, currently available on the network at http://www.fortran.com/fortran/F77_std/rjcnf0001.html or as monolithic text at http://www.fortran.com/fortran/F77_std/f77_std.html. It offers some extensions that are popular among users of UNIX f77 and f2c compilers, some that are popular among users of other compilers (such as Digital products), some that are popular among users of the newer Fortran 90 standard, and some that are introduced by GNU Fortran.

(If you need a text on Fortran, a few freely available electronic references have pointers from http://www.fortran.com/F/books.html. There is a `cooperative net project', User Notes on Fortran Programming at ftp://vms.huji.ac.il/fortran/ and mirrors elsewhere; some of this material might not apply specifically to g77.)

Part of what defines a particular implementation of a Fortran system, such as g77, is the particular characteristics of how it supports types, constants, and so on. Much of this is left up to the implementation by the various Fortran standards and accepted practice in the industry.

The GNU Fortran language is described below. Much of the material is organized along the same lines as the ANSI FORTRAN 77 standard itself.

See Other Dialects, for information on features g77 supports that are not part of the GNU Fortran language.

Note: This portion of the documentation definitely needs a lot of work!

Relationship to the ANSI FORTRAN 77 standard:

Extensions to the ANSI FORTRAN 77 standard:

Next: Standard Support, Up: Language

### 8.1 Direction of Language Development

The purpose of the following description of the GNU Fortran language is to promote wide portability of GNU Fortran programs.

GNU Fortran is an evolving language, due to the fact that g77 itself is in beta test. Some current features of the language might later be redefined as dialects of Fortran supported by g77 when better ways to express these features are added to g77, for example. Such features would still be supported by g77, but would be available only when one or more command-line options were used.

The GNU Fortran language is distinct from the GNU Fortran compilation system (g77).

For example, g77 supports various dialects of Fortran—in a sense, these are languages other than GNU Fortran—though its primary purpose is to support the GNU Fortran language, which also is described in its documentation and by its implementation.

On the other hand, non-GNU compilers might offer support for the GNU Fortran language, and are encouraged to do so.

Currently, the GNU Fortran language is a fairly fuzzy object. It represents something of a cross between what g77 accepts when compiling using the prevailing defaults and what this document describes as being part of the language.

Future versions of g77 are expected to clarify the definition of the language in the documentation. Often, this will mean adding new features to the language, in the form of both new documentation and new support in g77. However, it might occasionally mean removing a feature from the language itself to “dialect” status. In such a case, the documentation would be adjusted to reflect the change, and g77 itself would likely be changed to require one or more command-line options to continue supporting the feature.

The development of the GNU Fortran language is intended to strike a balance between:

- Serving as a mostly-upwards-compatible language from the de facto UNIX Fortran dialect as supported by f77.
- Offering new, well-designed language features. Attributes of such features include not making existing code any harder to read (for those who might be unaware that the new features are not in use) and not making state-of-the-art compilers take longer to issue diagnostics, among others.
- Supporting existing, well-written code without gratuitously rejecting non-standard constructs, regardless of the origin of the code (its dialect).
- Offering default behavior and command-line options to reduce and, where reasonable, eliminate the need for programmers to make any modifications to code that already works in existing production environments.
- Diagnosing constructs that have different meanings in different systems, languages, and dialects, while offering clear, less ambiguous ways to express each of the different meanings so programmers can change their code appropriately.

One of the biggest practical challenges for the developers of the GNU Fortran language is meeting the sometimes contradictory demands of the above items.

For example, a feature might be widely used in one popular environment, but the exact same code that utilizes that feature might not work as expected—perhaps it might mean something entirely different—in another popular environment.

Traditionally, Fortran compilers—even portable ones—have solved this problem by simply offering the appropriate feature to users of the respective systems. This approach treats users of various Fortran systems and dialects as remote “islands”, or camps, of programmers, and assume that these camps rarely come into contact with each other (or, especially, with each other's code).

Project GNU takes a radically different approach to software and language design, in that it assumes that users of GNU software do not necessarily care what kind of underlying system they are using, regardless of whether they are using software (at the user-interface level) or writing it (for example, writing Fortran or C code).

As such, GNU users rarely need consider just what kind of underlying hardware (or, in many cases, operating system) they are using at any particular time. They can use and write software designed for a general-purpose, widely portable, heterogeneous environment—the GNU environment.

In line with this philosophy, GNU Fortran must evolve into a product that is widely ported and portable not only in the sense that it can be successfully built, installed, and run by users, but in the larger sense that its users can use it in the same way, and expect largely the same behaviors from it, regardless of the kind of system they are using at any particular time.

This approach constrains the solutions g77 can use to resolve conflicts between various camps of Fortran users. If these two camps disagree about what a particular construct should mean, g77 cannot simply be changed to treat that particular construct as having one meaning without comment (such as a warning), lest the users expecting it to have the other meaning are unpleasantly surprised that their code misbehaves when executed.

The use of the ASCII backslash character in character constants is an excellent (and still somewhat unresolved) example of this kind of controversy. See Backslash in Constants. Other examples are likely to arise in the future, as g77 developers strive to improve its ability to accept an ever-wider variety of existing Fortran code without requiring significant modifications to said code.

Development of GNU Fortran is further constrained by the desire to avoid requiring programmers to change their code. This is important because it allows programmers, administrators, and others to more faithfully evaluate and validate g77 (as an overall product and as new versions are distributed) without having to support multiple versions of their programs so that they continue to work the same way on their existing systems (non-GNU perhaps, but possibly also earlier versions of g77).

Next: Conformance, Previous: Direction of Language Development, Up: Language

### 8.2 ANSI FORTRAN 77 Standard Support

GNU Fortran supports ANSI FORTRAN 77 with the following caveats. In summary, the only ANSI FORTRAN 77 features g77 doesn't support are those that are probably rarely used in actual code, some of which are explicitly disallowed by the Fortran 90 standard.

Next: No Passing Dummy Assumed-length, Up: Standard Support

#### 8.2.1 No Passing External Assumed-length

g77 disallows passing of an external procedure as an actual argument if the procedure's type is declared `CHARACTER*(*)`. For example:

         CHARACTER*(*) CFUNC
         EXTERNAL CFUNC
         CALL FOO(CFUNC)
         END

It isn't clear whether the standard considers this conforming.

Next: No Pathological Implied-DO, Previous: No Passing External Assumed-length, Up: Standard Support

#### 8.2.2 No Passing Dummy Assumed-length

g77 disallows passing of a dummy procedure as an actual argument if the procedure's type is declared `CHARACTER*(*)`.

         SUBROUTINE BAR(CFUNC)
         CHARACTER*(*) CFUNC
         EXTERNAL CFUNC
         CALL FOO(CFUNC)
         END

It isn't clear whether the standard considers this conforming.

Next: No Useless Implied-DO, Previous: No Passing Dummy Assumed-length, Up: Standard Support

#### 8.2.3 No Pathological Implied-DO

The `DO` variable for an implied-`DO` construct in a `DATA` statement may not be used as the `DO` variable for an outer implied-`DO` construct. For example, this fragment is disallowed by g77:

         DATA ((A(I, I), I= 1, 10), I= 1, 10) /.../

This also is disallowed by Fortran 90, as it offers no additional capabilities and would have a variety of possible meanings.

Note that it is very unlikely that any production Fortran code tries to use this unsupported construct.

Previous: No Pathological Implied-DO, Up: Standard Support

#### 8.2.4 No Useless Implied-DO

An array element initializer in an implied-`DO` construct in a `DATA` statement must contain at least one reference to the `DO` variables of each outer implied-`DO` construct. For example, this fragment is disallowed by g77:

         DATA (A, I= 1, 1) /1./

This also is disallowed by Fortran 90, as FORTRAN 77's more permissive requirements offer no additional capabilities. However, g77 doesn't necessarily diagnose all cases where this requirement is not met.

Note that it is very unlikely that any production Fortran code tries to use this unsupported construct.

Next: Notation Used, Previous: Standard Support, Up: Language

### 8.3 Conformance

(The following information augments or overrides the information in Section 1.4 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 1 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

The definition of the GNU Fortran language is akin to that of the ANSI FORTRAN 77 language in that it does not generally require conforming implementations to diagnose cases where programs do not conform to the language.

However, g77 as a compiler is being developed in a way that is intended to enable it to diagnose such cases in an easy-to-understand manner.

A program that conforms to the GNU Fortran language should, when compiled, linked, and executed using a properly installed g77 system, perform as described by the GNU Fortran language definition. Reasons for different behavior include, among others:

- Use of resources (memory—heap, stack, and so on; disk space; CPU time; etc.) exceeds those of the system.
- Range and/or precision of calculations required by the program exceeds that of the system.
- Excessive reliance on behaviors that are system-dependent (non-portable Fortran code).
- Bugs in the program.
- Bug in g77.
- Bugs in the system.

Despite these “loopholes”, the availability of a clear specification of the language of programs submitted to g77, as this document is intended to provide, is considered an important aspect of providing a robust, clean, predictable Fortran implementation.

The definition of the GNU Fortran language, while having no special legal status, can therefore be viewed as a sort of contract, or agreement. This agreement says, in essence, “if you write a program in this language, and run it in an environment (such as a g77 system) that supports this language, the program should behave in a largely predictable way”.

Next: Terms and Concepts, Previous: Conformance, Up: Language

### 8.4 Notation Used in This Chapter

(The following information augments or overrides the information in Section 1.5 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 1 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

In this chapter, “must” denotes a requirement, “may” denotes permission, and “must not” and “may not” denote prohibition. Terms such as “might”, “should”, and “can” generally add little or nothing in the way of weight to the GNU Fortran language itself, but are used to explain or illustrate the language.

For example:

         “The FROBNITZ statement must precede all executable
         statements in a program unit, and may not specify any dummy
         arguments.  It may specify local or common variables and arrays.
         Its use should be limited to portions of the program designed to
         be non-portable and system-specific, because it might cause the
         containing program unit to behave quite differently on different
         systems.”

Insofar as the GNU Fortran language is specified, the requirements and permissions denoted by the above sample statement are limited to the placement of the statement and the kinds of things it may specify. The rest of the statement—the content regarding non-portable portions of the program and the differing behavior of program units containing the `FROBNITZ` statement—does not pertain the GNU Fortran language itself. That content offers advice and warnings about the `FROBNITZ` statement.

Remember: The GNU Fortran language definition specifies both what constitutes a valid GNU Fortran program and how, given such a program, a valid GNU Fortran implementation is to interpret that program.

It is not incumbent upon a valid GNU Fortran implementation to behave in any particular way, any consistent way, or any predictable way when it is asked to interpret input that is not a valid GNU Fortran program.

Such input is said to have undefined behavior when interpreted by a valid GNU Fortran implementation, though an implementation may choose to specify behaviors for some cases of inputs that are not valid GNU Fortran programs.

Other notation used herein is that of the GNU texinfo format, which is used to generate printed hardcopy, on-line hypertext (Info), and on-line HTML versions, all from a single source document. This notation is used as follows:

- Keywords defined by the GNU Fortran language are shown in uppercase, as in: `COMMON`, `INTEGER`, and `BLOCK DATA`.

  Note that, in practice, many Fortran programs are written in lowercase—uppercase is used in this manual as a means to readily distinguish keywords and sample Fortran-related text from the prose in this document.

- Portions of actual sample program, input, or output text look like this: Actual program text.

  Generally, uppercase is used for all Fortran-specific and Fortran-related text, though this does not always include literal text within Fortran code.

  For example: PRINT *, 'My name is Bob'.

- A metasyntactic variable—that is, a name used in this document to serve as a placeholder for whatever text is used by the user or programmer—appears as shown in the following example:

  “The `INTEGER` ivar statement specifies that ivar is a variable or array of type `INTEGER`.”

  In the above example, any valid text may be substituted for the metasyntactic variable ivar to make the statement apply to a specific instance, as long as the same text is substituted for both occurrences of ivar.

- Ellipses (“...”) are used to indicate further text that is either unimportant or expanded upon further, elsewhere.
- Names of data types are in the style of Fortran 90, in most cases.

  See Kind Notation, for information on the relationship between Fortran 90 nomenclature (such as `INTEGER(KIND=1)`) and the more traditional, less portably concise nomenclature (such as `INTEGER*4`).

Next: Characters Lines Sequence, Previous: Notation Used, Up: Language

### 8.5 Fortran Terms and Concepts

(The following information augments or overrides the information in Chapter 2 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 2 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

Next: Statements Comments Lines, Up: Terms and Concepts

#### 8.5.1 Syntactic Items

(Corresponds to Section 2.2 of ANSI X3.9-1978 FORTRAN 77.)

In GNU Fortran, a symbolic name is at least one character long, and has no arbitrary upper limit on length. However, names of entities requiring external linkage (such as external functions, external subroutines, and `COMMON` areas) might be restricted to some arbitrary length by the system. Such a restriction is no more constrained than that of one through six characters.

Underscores (_) are accepted in symbol names after the first character (which must be a letter).

Next: Scope of Names and Labels, Previous: Syntactic Items, Up: Terms and Concepts

#### 8.5.2 Statements, Comments, and Lines

(Corresponds to Section 2.3 of ANSI X3.9-1978 FORTRAN 77.)

Use of an exclamation point (!) to begin a trailing comment (a comment that extends to the end of the same source line) is permitted under the following conditions:

- The exclamation point does not appear in column 6. Otherwise, it is treated as an indicator of a continuation line.
- The exclamation point appears outside a character or Hollerith constant. Otherwise, the exclamation point is considered part of the constant.
- The exclamation point appears to the left of any other possible trailing comment. That is, a trailing comment may contain exclamation points in their commentary text.

Use of a semicolon (;) as a statement separator is permitted under the following conditions:

- The semicolon appears outside a character or Hollerith constant. Otherwise, the semicolon is considered part of the constant.
- The semicolon appears to the left of a trailing comment. Otherwise, the semicolon is considered part of that comment.
- Neither a logical `IF` statement nor a non-construct `WHERE` statement (a Fortran 90 feature) may be followed (in the same, possibly continued, line) by a semicolon used as a statement separator.

  This restriction avoids the confusion that can result when reading a line such as:

                IF (VALIDP) CALL FOO; CALL BAR

  Some readers might think the CALL BAR is executed only if VALIDP is `.TRUE.`, while others might assume its execution is unconditional.

  (At present, g77 does not diagnose code that violates this restriction.)

Previous: Statements Comments Lines, Up: Terms and Concepts

#### 8.5.3 Scope of Symbolic Names and Statement Labels

(Corresponds to Section 2.9 of ANSI X3.9-1978 FORTRAN 77.)

Included in the list of entities that have a scope of a program unit are construct names (a Fortran 90 feature). See Construct Names, for more information.

Next: Data Types and Constants, Previous: Terms and Concepts, Up: Language

### 8.6 Characters, Lines, and Execution Sequence

(The following information augments or overrides the information in Chapter 3 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 3 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

Next: Lines, Up: Characters Lines Sequence

#### 8.6.1 GNU Fortran Character Set

(Corresponds to Section 3.1 of ANSI X3.9-1978 FORTRAN 77.)

Letters include uppercase letters (the twenty-six characters of the English alphabet) and lowercase letters (their lowercase equivalent). Generally, lowercase letters may be used in place of uppercase letters, though in character and Hollerith constants, they are distinct.

Special characters include:

- Semicolon (;)
- Exclamation point (!)
- Double quote (")
- Backslash (\)
- Question mark (?)
- Hash mark (#)
- Ampersand (&)
- Percent sign (%)
- Underscore (_)
- Open angle (<)
- Close angle (>)
- The FORTRAN 77 special characters (<SPC>, =, +, -, *, /, (, ), ,, ., $, ', and :)

Note that this document refers to <SPC> as space, while X3.9-1978 FORTRAN 77 refers to it as blank.

Next: Continuation Line, Previous: Character Set, Up: Characters Lines Sequence

#### 8.6.2 Lines

(Corresponds to Section 3.2 of ANSI X3.9-1978 FORTRAN 77.)

The way a Fortran compiler views source files depends entirely on the implementation choices made for the compiler, since those choices are explicitly left to the implementation by the published Fortran standards.

The GNU Fortran language mandates a view applicable to UNIX-like text files—files that are made up of an arbitrary number of lines, each with an arbitrary number of characters (sometimes called stream-based files).

This view does not apply to types of files that are specified as having a particular number of characters on every single line (sometimes referred to as record-based files).

Because a “line in a program unit is a sequence of 72 characters”, to quote X3.9-1978, the GNU Fortran language specifies that a stream-based text file is translated to GNU Fortran lines as follows:

- A newline in the file is the character that represents the end of a line of text to the underlying system. For example, on ASCII-based systems, a newline is the <NL> character, which has ASCII value 10 (decimal).
- Each newline in the file serves to end the line of text that precedes it (and that does not contain a newline).
- The end-of-file marker (`EOF`) also serves to end the line of text that precedes it (and that does not contain a newline).
- Any line of text that is shorter than 72 characters is padded to that length with spaces (called “blanks” in the standard).
- Any line of text that is longer than 72 characters is truncated to that length, but the truncated remainder must consist entirely of spaces.
- Characters other than newline and the GNU Fortran character set are invalid.

For the purposes of the remainder of this description of the GNU Fortran language, the translation described above has already taken place, unless otherwise specified.

The result of the above translation is that the source file appears, in terms of the remainder of this description of the GNU Fortran language, as if it had an arbitrary number of 72-character lines, each character being among the GNU Fortran character set.

For example, if the source file itself has two newlines in a row, the second newline becomes, after the above translation, a single line containing 72 spaces.

Next: Statements, Previous: Lines, Up: Characters Lines Sequence

#### 8.6.3 Continuation Line

(Corresponds to Section 3.2.3 of ANSI X3.9-1978 FORTRAN 77.)

A continuation line is any line that both

- Contains a continuation character, and
- Contains only spaces in columns 1 through 5

A continuation character is any character of the GNU Fortran character set other than space (<SPC>) or zero (0) in column 6, or a digit (0 through 9) in column 7 through 72 of a line that has only spaces to the left of that digit.

The continuation character is ignored as far as the content of the statement is concerned.

The GNU Fortran language places no limit on the number of continuation lines in a statement. In practice, the limit depends on a variety of factors, such as available memory, statement content, and so on, but no GNU Fortran system may impose an arbitrary limit.

Next: Statement Labels, Previous: Continuation Line, Up: Characters Lines Sequence

#### 8.6.4 Statements

(Corresponds to Section 3.3 of ANSI X3.9-1978 FORTRAN 77.)

Statements may be written using an arbitrary number of continuation lines.

Statements may be separated using the semicolon (;), except that the logical `IF` and non-construct `WHERE` statements may not be separated from subsequent statements using only a semicolon as statement separator.

The `END PROGRAM`, `END SUBROUTINE`, `END FUNCTION`, and `END BLOCK DATA` statements are alternatives to the `END` statement. These alternatives may be written as normal statements—they are not subject to the restrictions of the `END` statement.

However, no statement other than `END` may have an initial line that appears to be an `END` statement—even `END PROGRAM`, for example, must not be written as:

               END
              &PROGRAM

Next: Order, Previous: Statements, Up: Characters Lines Sequence

#### 8.6.5 Statement Labels

(Corresponds to Section 3.4 of ANSI X3.9-1978 FORTRAN 77.)

A statement separated from its predecessor via a semicolon may be labeled as follows:

- The semicolon is followed by the label for the statement, which in turn follows the label.
- The label must be no more than five digits in length.
- The first digit of the label for the statement is not the first non-space character on a line. Otherwise, that character is treated as a continuation character.

A statement may have only one label defined for it.

Next: INCLUDE, Previous: Statement Labels, Up: Characters Lines Sequence

#### 8.6.6 Order of Statements and Lines

(Corresponds to Section 3.5 of ANSI X3.9-1978 FORTRAN 77.)

Generally, `DATA` statements may precede executable statements. However, specification statements pertaining to any entities initialized by a `DATA` statement must precede that `DATA` statement. For example, after DATA I/1/, INTEGER I is not permitted, but INTEGER J is permitted.

The last line of a program unit may be an `END` statement, or may be:

- An `END PROGRAM` statement, if the program unit is a main program.
- An `END SUBROUTINE` statement, if the program unit is a subroutine.
- An `END FUNCTION` statement, if the program unit is a function.
- An `END BLOCK DATA` statement, if the program unit is a block data.

Next: Cpp-style directives, Previous: Order, Up: Characters Lines Sequence

#### 8.6.7 Including Source Text

Additional source text may be included in the processing of the source file via the `INCLUDE` directive:

         INCLUDE filename

The source text to be included is identified by filename, which is a literal GNU Fortran character constant. The meaning and interpretation of filename depends on the implementation, but typically is a filename.

(g77 treats it as a filename that it searches for in the current directory and/or directories specified via the -I command-line option.)

The effect of the `INCLUDE` directive is as if the included text directly replaced the directive in the source file prior to interpretation of the program. Included text may itself use `INCLUDE`. The depth of nested `INCLUDE` references depends on the implementation, but typically is a positive integer.

This virtual replacement treats the statements and `INCLUDE` directives in the included text as syntactically distinct from those in the including text.

Therefore, the first non-comment line of the included text must not be a continuation line. The included text must therefore have, after the non-comment lines, either an initial line (statement), an `INCLUDE` directive, or nothing (the end of the included text).

Similarly, the including text may end the `INCLUDE` directive with a semicolon or the end of the line, but it cannot follow an `INCLUDE` directive at the end of its line with a continuation line. Thus, the last statement in an included text may not be continued.

Any statements between two `INCLUDE` directives on the same line are treated as if they appeared in between the respective included texts. For example:

         INCLUDE 'A'; PRINT *, 'B'; INCLUDE 'C'; END PROGRAM

If the text included by INCLUDE 'A' constitutes a PRINT *, 'A' statement and the text included by INCLUDE 'C' constitutes a PRINT *, 'C' statement, then the output of the above sample program would be

         A
         B
         C

(with suitable allowances for how an implementation defines its handling of output).

Included text must not include itself directly or indirectly, regardless of whether the filename used to reference the text is the same.

Note that `INCLUDE` is not a statement. As such, it is neither a non-executable or executable statement. However, if the text it includes constitutes one or more executable statements, then the placement of `INCLUDE` is subject to effectively the same restrictions as those on executable statements.

An `INCLUDE` directive may be continued across multiple lines as if it were a statement. This permits long names to be used for filename.

Previous: INCLUDE, Up: Characters Lines Sequence

#### 8.6.8 Cpp-style directives

`cpp` output-style `#` directives (see C Preprocessor Output (The C Preprocessor)) are recognized by the compiler even when the preprocessor isn't run on the input (as it is when compiling .F files). (Note the distinction between these cpp `#` output directives and `#line` input directives.)

Next: Expressions, Previous: Characters Lines Sequence, Up: Language

### 8.7 Data Types and Constants

(The following information augments or overrides the information in Chapter 4 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 4 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

To more concisely express the appropriate types for entities, this document uses the more concise Fortran 90 nomenclature such as `INTEGER(KIND=1)` instead of the more traditional, but less portably concise, byte-size-based nomenclature such as `INTEGER*4`, wherever reasonable.

When referring to generic types—in contexts where the specific precision and range of a type are not important—this document uses the generic type names `INTEGER`, `LOGICAL`, `REAL`, `COMPLEX`, and `CHARACTER`.

In some cases, the context requires specification of a particular type. This document uses the KIND= notation to accomplish this throughout, sometimes supplying the more traditional notation for clarification, though the traditional notation might not work the same way on all GNU Fortran implementations.

Use of KIND= makes this document more concise because g77 is able to define values for KIND= that have the same meanings on all systems, due to the way the Fortran 90 standard specifies these values are to be used.

(In particular, that standard permits an implementation to arbitrarily assign nonnegative values. There are four distinct sets of assignments: one to the `CHARACTER` type; one to the `INTEGER` type; one to the `LOGICAL` type; and the fourth to both the `REAL` and `COMPLEX` types. Implementations are free to assign these values in any order, leave gaps in the ordering of assignments, and assign more than one value to a representation.)

This makes KIND= values superior to the values used in non-standard statements such as INTEGER*4, because the meanings of the values in those statements vary from machine to machine, compiler to compiler, even operating system to operating system.

However, use of KIND= is not generally recommended when writing portable code (unless, for example, the code is going to be compiled only via g77, which is a widely ported compiler). GNU Fortran does not yet have adequate language constructs to permit use of KIND= in a fashion that would make the code portable to Fortran 90 implementations; and, this construct is known to not be accepted by many popular FORTRAN 77 implementations, so it cannot be used in code that is to be ported to those.

The distinction here is that this document is able to use specific values for KIND= to concisely document the types of various operations and operands.

A Fortran program should use the FORTRAN 77 designations for the appropriate GNU Fortran types—such as `INTEGER` for `INTEGER(KIND=1)`, `REAL` for `REAL(KIND=1)`, and `DOUBLE COMPLEX` for `COMPLEX(KIND=2)`—and, where no such designations exist, make use of appropriate techniques (preprocessor macros, parameters, and so on) to specify the types in a fashion that may be easily adjusted to suit each particular implementation to which the program is ported. (These types generally won't need to be adjusted for ports of g77.)

Further details regarding GNU Fortran data types and constants are provided below.

Next: Constants, Up: Data Types and Constants

#### 8.7.1 Data Types

(Corresponds to Section 4.1 of ANSI X3.9-1978 FORTRAN 77.)

GNU Fortran supports these types:

1. Integer (generic type `INTEGER`)
2. Real (generic type `REAL`)
3. Double precision
4. Complex (generic type `COMPLEX`)
5. Logical (generic type `LOGICAL`)
6. Character (generic type `CHARACTER`)
7. Double Complex

(The types numbered 1 through 6 above are standard FORTRAN 77 types.)

The generic types shown above are referred to in this document using only their generic type names. Such references usually indicate that any specific type (kind) of that generic type is valid.

For example, a context described in this document as accepting the `COMPLEX` type also is likely to accept the `DOUBLE COMPLEX` type.

The GNU Fortran language supports three ways to specify a specific kind of a generic type.

Next: Star Notation, Up: Types

##### 8.7.1.1 Double Notation

The GNU Fortran language supports two uses of the keyword `DOUBLE` to specify a specific kind of type:

- `DOUBLE PRECISION`, equivalent to `REAL(KIND=2)`
- `DOUBLE COMPLEX`, equivalent to `COMPLEX(KIND=2)`

Use one of the above forms where a type name is valid.

While use of this notation is popular, it doesn't scale well in a language or dialect rich in intrinsic types, as is the case for the GNU Fortran language (especially planned future versions of it).

After all, one rarely sees type names such as DOUBLE INTEGER, QUADRUPLE REAL, or QUARTER INTEGER. Instead, `INTEGER*8`, `REAL*16`, and `INTEGER*1` often are substituted for these, respectively, even though they do not always have the same meanings on all systems. (And, the fact that DOUBLE REAL does not exist as such is an inconsistency.)

Therefore, this document uses “double notation” only on occasion for the benefit of those readers who are accustomed to it.

Next: Kind Notation, Previous: Double Notation, Up: Types

##### 8.7.1.2 Star Notation

The following notation specifies the storage size for a type:

         generic-type*n

generic-type must be a generic type—one of `INTEGER`, `REAL`, `COMPLEX`, `LOGICAL`, or `CHARACTER`. n must be one or more digits comprising a decimal integer number greater than zero.

Use the above form where a type name is valid.

The *n notation specifies that the amount of storage occupied by variables and array elements of that type is n times the storage occupied by a `CHARACTER*1` variable.

This notation might indicate a different degree of precision and/or range for such variables and array elements, and the functions that return values of types using this notation. It does not limit the precision or range of values of that type in any particular way—use explicit code to do that.

Further, the GNU Fortran language requires no particular values for n to be supported by an implementation via the *n notation. g77 supports `INTEGER*1` (as `INTEGER(KIND=3)`) on all systems, for example, but not all implementations are required to do so, and g77 is known to not support `REAL*1` on most (or all) systems.

As a result, except for generic-type of `CHARACTER`, uses of this notation should be limited to isolated portions of a program that are intended to handle system-specific tasks and are expected to be non-portable.

(Standard FORTRAN 77 supports the *n notation for only `CHARACTER`, where it signifies not only the amount of storage occupied, but the number of characters in entities of that type. However, almost all Fortran compilers have supported this notation for generic types, though with a variety of meanings for n.)

Specifications of types using the *n notation always are interpreted as specifications of the appropriate types described in this document using the KIND=n notation, described below.

While use of this notation is popular, it doesn't serve well in the context of a widely portable dialect of Fortran, such as the GNU Fortran language.

For example, even on one particular machine, two or more popular Fortran compilers might well disagree on the size of a type declared `INTEGER*2` or `REAL*16`. Certainly there is known to be disagreement over such things among Fortran compilers on different systems.

Further, this notation offers no elegant way to specify sizes that are not even multiples of the “byte size” typically designated by `INTEGER*1`. Use of “absurd” values (such as `INTEGER*1000`) would certainly be possible, but would perhaps be stretching the original intent of this notation beyond the breaking point in terms of widespread readability of documentation and code making use of it.

Therefore, this document uses “star notation” only on occasion for the benefit of those readers who are accustomed to it.

Previous: Star Notation, Up: Types

##### 8.7.1.3 Kind Notation

The following notation specifies the kind-type selector of a type:

         generic-type(KIND=n)

Use the above form where a type name is valid.

generic-type must be a generic type—one of `INTEGER`, `REAL`, `COMPLEX`, `LOGICAL`, or `CHARACTER`. n must be an integer initialization expression that is a positive, nonzero value.

Programmers are discouraged from writing these values directly into their code. Future versions of the GNU Fortran language will offer facilities that will make the writing of code portable to g77 and Fortran 90 implementations simpler.

However, writing code that ports to existing FORTRAN 77 implementations depends on avoiding the KIND= construct.

The KIND= construct is thus useful in the context of GNU Fortran for two reasons:

- It provides a means to specify a type in a fashion that is portable across all GNU Fortran implementations (though not other FORTRAN 77 and Fortran 90 implementations).
- It provides a sort of Rosetta stone for this document to use to concisely describe the types of various operations and operands.

The values of n in the GNU Fortran language are assigned using a scheme that:

- Attempts to maximize the ability of readers of this document to quickly familiarize themselves with assignments for popular types
- Provides a unique value for each specific desired meaning
- Provides a means to automatically assign new values so they have a “natural” relationship to existing values, if appropriate, or, if no such relationship exists, will not interfere with future values assigned on the basis of such relationships
- Avoids using values that are similar to values used in the existing, popular *n notation, to prevent readers from expecting that these implied correspondences work on all GNU Fortran implementations

The assignment system accomplishes this by assigning to each “fundamental meaning” of a specific type a unique prime number. Combinations of fundamental meanings—for example, a type that is two times the size of some other type—are assigned values of n that are the products of the values for those fundamental meanings.

A prime value of n is never given more than one fundamental meaning, to avoid situations where some code or system cannot reasonably provide those meanings in the form of a single type.

The values of n assigned so far are:

`KIND=0`
  This value is reserved for future use.

  The planned future use is for this value to designate, explicitly, context-sensitive kind-type selection. For example, the expression 1D0 * 0.1_0 would be equivalent to 1D0 * 0.1D0.

`KIND=1`
  This corresponds to the default types for `REAL`, `INTEGER`, `LOGICAL`, `COMPLEX`, and `CHARACTER`, as appropriate.

  These are the “default” types described in the Fortran 90 standard, though that standard does not assign any particular KIND= value to these types.

  (Typically, these are `REAL*4`, `INTEGER*4`, `LOGICAL*4`, and `COMPLEX*8`.)

`KIND=2`
  This corresponds to types that occupy twice as much storage as the default types. `REAL(KIND=2)` is `DOUBLE PRECISION` (typically `REAL*8`), `COMPLEX(KIND=2)` is `DOUBLE COMPLEX` (typically `COMPLEX*16`),

  These are the “double precision” types described in the Fortran 90 standard, though that standard does not assign any particular KIND= value to these types.

  n of 4 thus corresponds to types that occupy four times as much storage as the default types, n of 8 to types that occupy eight times as much storage, and so on.

  The `INTEGER(KIND=2)` and `LOGICAL(KIND=2)` types are not necessarily supported by every GNU Fortran implementation.

`KIND=3`
  This corresponds to types that occupy as much storage as the default `CHARACTER` type, which is the same effective type as `CHARACTER(KIND=1)` (making that type effectively the same as `CHARACTER(KIND=3)`).

  (Typically, these are `INTEGER*1` and `LOGICAL*1`.)

  n of 6 thus corresponds to types that occupy twice as much storage as the n=3 types, n of 12 to types that occupy four times as much storage, and so on.

  These are not necessarily supported by every GNU Fortran implementation.

`KIND=5`
  This corresponds to types that occupy half the storage as the default (n=1) types.

  (Typically, these are `INTEGER*2` and `LOGICAL*2`.)

  n of 25 thus corresponds to types that occupy one-quarter as much storage as the default types.

  These are not necessarily supported by every GNU Fortran implementation.

`KIND=7`
  This is valid only as `INTEGER(KIND=7)` and denotes the `INTEGER` type that has the smallest storage size that holds a pointer on the system.

  A pointer representable by this type is capable of uniquely addressing a `CHARACTER*1` variable, array, array element, or substring.

  (Typically this is equivalent to `INTEGER*4` or, on 64-bit systems, `INTEGER*8`. In a compatible C implementation, it typically would be the same size and semantics of the C type `void *`.)

Note that these are proposed correspondences and might change in future versions of g77—avoid writing code depending on them while g77, and therefore the GNU Fortran language it defines, is in beta testing.

Values not specified in the above list are reserved to future versions of the GNU Fortran language.

Implementation-dependent meanings will be assigned new, unique prime numbers so as to not interfere with other implementation-dependent meanings, and offer the possibility of increasing the portability of code depending on such types by offering support for them in other GNU Fortran implementations.

Other meanings that might be given unique values are:

- Types that make use of only half their storage size for representing precision and range.

  For example, some compilers offer options that cause `INTEGER` types to occupy the amount of storage that would be needed for `INTEGER(KIND=2)` types, but the range remains that of `INTEGER(KIND=1)`.

- The IEEE single floating-point type.
- Types with a specific bit pattern (endianness), such as the little-endian form of `INTEGER(KIND=1)`. These could permit, conceptually, use of portable code and implementations on data files written by existing systems.

Future prime numbers should be given meanings in as incremental a fashion as possible, to allow for flexibility and expressiveness in combining types.

For example, instead of defining a prime number for little-endian IEEE doubles, one prime number might be assigned the meaning “little-endian”, another the meaning “IEEE double”, and the value of n for a little-endian IEEE double would thus naturally be the product of those two respective assigned values. (It could even be reasonable to have IEEE values result from the products of prime values denoting exponent and fraction sizes and meanings, hidden bit usage, availability and representations of special values such as subnormals, infinities, and Not-A-Numbers (NaNs), and so on.)

This assignment mechanism, while not inherently required for future versions of the GNU Fortran language, is worth using because it could ease management of the “space” of supported types much easier in the long run.

The above approach suggests a mechanism for specifying inheritance of intrinsic (built-in) types for an entire, widely portable product line. It is certainly reasonable that, unlike programmers of other languages offering inheritance mechanisms that employ verbose names for classes and subclasses, along with graphical browsers to elucidate the relationships, Fortran programmers would employ a mechanism that works by multiplying prime numbers together and finding the prime factors of such products.

Most of the advantages for the above scheme have been explained above. One disadvantage is that it could lead to the defining, by the GNU Fortran language, of some fairly large prime numbers. This could lead to the GNU Fortran language being declared “munitions” by the United States Department of Defense.

Next: Integer Type, Previous: Types, Up: Data Types and Constants

#### 8.7.2 Constants

(Corresponds to Section 4.2 of ANSI X3.9-1978 FORTRAN 77.)

A typeless constant has one of the following forms:

         'binary-digits'B
         'octal-digits'O
         'hexadecimal-digits'Z
         'hexadecimal-digits'X

binary-digits, octal-digits, and hexadecimal-digits are nonempty strings of characters in the set 01, 01234567, and 0123456789ABCDEFabcdef, respectively. (The value for A (and a) is 10, for B and b is 11, and so on.)

A prefix-radix constant, such as Z'ABCD', can optionally be treated as typeless. See Options Controlling Fortran Dialect, for information on the -ftypeless-boz option.

Typeless constants have values that depend on the context in which they are used.

All other constants, called typed constants, are interpreted—converted to internal form—according to their inherent type. Thus, context is never a determining factor for the type, and hence the interpretation, of a typed constant. (All constants in the ANSI FORTRAN 77 language are typed constants.)

For example, 1 is always type `INTEGER(KIND=1)` in GNU Fortran (called default INTEGER in Fortran 90), 9.435784839284958 is always type `REAL(KIND=1)` (even if the additional precision specified is lost, and even when used in a `REAL(KIND=2)` context), 1E0 is always type `REAL(KIND=2)`, and 1D0 is always type `REAL(KIND=2)`.

Next: Character Type, Previous: Constants, Up: Data Types and Constants

#### 8.7.3 Integer Type

(Corresponds to Section 4.3 of ANSI X3.9-1978 FORTRAN 77.)

An integer constant also may have one of the following forms:

         B'binary-digits'
         O'octal-digits'
         Z'hexadecimal-digits'
         X'hexadecimal-digits'

binary-digits, octal-digits, and hexadecimal-digits are nonempty strings of characters in the set 01, 01234567, and 0123456789ABCDEFabcdef, respectively. (The value for A (and a) is 10, for B and b is 11, and so on.)

Previous: Integer Type, Up: Data Types and Constants

#### 8.7.4 Character Type

(Corresponds to Section 4.8 of ANSI X3.9-1978 FORTRAN 77.)

A character constant may be delimited by a pair of double quotes (") instead of apostrophes. In this case, an apostrophe within the constant represents a single apostrophe, while a double quote is represented in the source text of the constant by two consecutive double quotes with no intervening spaces.

A character constant may be empty (have a length of zero).

A character constant may include a substring specification, The value of such a constant is the value of the substring—for example, the value of 'hello'(3:5) is the same as the value of 'llo'.

Next: Specification Statements, Previous: Data Types and Constants, Up: Language

### 8.8 Expressions

(The following information augments or overrides the information in Chapter 6 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 6 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

Up: Expressions

#### 8.8.1 The `%LOC()` Construct

         %LOC(arg)

The `%LOC()` construct is an expression that yields the value of the location of its argument, arg, in memory. The size of the type of the expression depends on the system—typically, it is equivalent to either `INTEGER(KIND=1)` or `INTEGER(KIND=2)`, though it is actually type `INTEGER(KIND=7)`.

The argument to `%LOC()` must be suitable as the left-hand side of an assignment statement. That is, it may not be a general expression involving operators such as addition, subtraction, and so on, nor may it be a constant.

Use of `%LOC()` is recommended only for code that is accessing facilities outside of GNU Fortran, such as operating system or windowing facilities. It is best to constrain such uses to isolated portions of a program—portions that deal specifically and exclusively with low-level, system-dependent facilities. Such portions might well provide a portable interface for use by the program as a whole, but are themselves not portable, and should be thoroughly tested each time they are rebuilt using a new compiler or version of a compiler.

Do not depend on `%LOC()` returning a pointer that can be safely used to define (change) the argument. While this might work in some circumstances, it is hard to predict whether it will continue to work when a program (that works using this unsafe behavior) is recompiled using different command-line options or a different version of g77.

Generally, `%LOC()` is safe when used as an argument to a procedure that makes use of the value of the corresponding dummy argument only during its activation, and only when such use is restricted to referencing (reading) the value of the argument to `%LOC()`.

Implementation Note: Currently, g77 passes arguments (those not passed using a construct such as `%VAL()`) by reference or descriptor, depending on the type of the actual argument. Thus, given INTEGER I, CALL FOO(I) would seem to mean the same thing as CALL FOO(%VAL(%LOC(I))), and in fact might compile to identical code.

However, CALL FOO(%VAL(%LOC(I))) emphatically means “pass, by value, the address of I in memory”. While CALL FOO(I) might use that same approach in a particular version of g77, another version or compiler might choose a different implementation, such as copy-in/copy-out, to effect the desired behavior—and which will therefore not necessarily compile to the same code as would CALL FOO(%VAL(%LOC(I))) using the same version or compiler.

See Debugging and Interfacing, for detailed information on how this particular version of g77 implements various constructs.

Next: Control Statements, Previous: Expressions, Up: Language

### 8.9 Specification Statements

(The following information augments or overrides the information in Chapter 8 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 8 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

Next: DOUBLE COMPLEX, Up: Specification Statements

#### 8.9.1 `NAMELIST` Statement

The `NAMELIST` statement, and related I/O constructs, are supported by the GNU Fortran language in essentially the same way as they are by f2c.

This follows Fortran 90 with the restriction that on `NAMELIST` input, subscripts must have the form

         subscript [ : subscript [ : stride]]

i.e.

         &xx x(1:3,8:10:2)=1,2,3,4,5,6/

is allowed, but not, say,

         &xx x(:3,8::2)=1,2,3,4,5,6/

As an extension of the Fortran 90 form, `$` and `$END` may be used in place of `&` and `/` in `NAMELIST` input, so that

         $&xx x(1:3,8:10:2)=1,2,3,4,5,6 $end

could be used instead of the example above.

Previous: NAMELIST, Up: Specification Statements

#### 8.9.2 `DOUBLE COMPLEX` Statement

`DOUBLE COMPLEX` is a type-statement (and type) that specifies the type `COMPLEX(KIND=2)` in GNU Fortran.

Next: Functions and Subroutines, Previous: Specification Statements, Up: Language

### 8.10 Control Statements

(The following information augments or overrides the information in Chapter 11 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 11 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

Next: END DO, Up: Control Statements

#### 8.10.1 DO WHILE

The `DO WHILE` statement, a feature of both the MIL-STD 1753 and Fortran 90 standards, is provided by the GNU Fortran language. The Fortran 90 “do forever” statement comprising just `DO` is also supported.

Next: Construct Names, Previous: DO WHILE, Up: Control Statements

#### 8.10.2 END DO

The `END DO` statement is provided by the GNU Fortran language.

This statement is used in one of two ways:

- The Fortran 90 meaning, in which it specifies the termination point of a single `DO` loop started with a `DO` statement that specifies no termination label.
- The MIL-STD 1753 meaning, in which it specifies the termination point of one or more `DO` loops, all of which start with a `DO` statement that specify the label defined for the `END DO` statement.

  This kind of `END DO` statement is merely a synonym for `CONTINUE`, except it is permitted only when the statement is labeled and a target of one or more labeled `DO` loops.

  It is expected that this use of `END DO` will be removed from the GNU Fortran language in the future, though it is likely that it will long be supported by g77 as a dialect form.

Next: CYCLE and EXIT, Previous: END DO, Up: Control Statements

#### 8.10.3 Construct Names

The GNU Fortran language supports construct names as defined by the Fortran 90 standard. These names are local to the program unit and are defined as follows:

         construct-name: block-statement

Here, construct-name is the construct name itself; its definition is connoted by the single colon (:); and block-statement is an `IF`, `DO`, or `SELECT CASE` statement that begins a block.

A block that is given a construct name must also specify the same construct name in its termination statement:

         END block construct-name

Here, block must be `IF`, `DO`, or `SELECT`, as appropriate.

Previous: Construct Names, Up: Control Statements

#### 8.10.4 The `CYCLE` and `EXIT` Statements

The `CYCLE` and `EXIT` statements specify that the remaining statements in the current iteration of a particular active (enclosing) `DO` loop are to be skipped.

`CYCLE` specifies that these statements are skipped, but the `END DO` statement that marks the end of the `DO` loop be executed—that is, the next iteration, if any, is to be started. If the statement marking the end of the `DO` loop is not `END DO`—in other words, if the loop is not a block `DO`—the `CYCLE` statement does not execute that statement, but does start the next iteration (if any).

`EXIT` specifies that the loop specified by the `DO` construct is terminated.

The `DO` loop affected by `CYCLE` and `EXIT` is the innermost enclosing `DO` loop when the following forms are used:

         CYCLE
         EXIT

Otherwise, the following forms specify the construct name of the pertinent `DO` loop:

         CYCLE construct-name
         EXIT construct-name

`CYCLE` and `EXIT` can be viewed as glorified `GO TO` statements. However, they cannot be easily thought of as `GO TO` statements in obscure cases involving FORTRAN 77 loops. For example:

               DO 10 I = 1, 5
               DO 10 J = 1, 5
                  IF (J .EQ. 5) EXIT
               DO 10 K = 1, 5
                  IF (K .EQ. 3) CYCLE
         10    PRINT *, 'I=', I, ' J=', J, ' K=', K
         20    CONTINUE

In particular, neither the `EXIT` nor `CYCLE` statements above are equivalent to a `GO TO` statement to either label 10 or 20.

To understand the effect of `CYCLE` and `EXIT` in the above fragment, it is helpful to first translate it to its equivalent using only block `DO` loops:

               DO I = 1, 5
                  DO J = 1, 5
                     IF (J .EQ. 5) EXIT
                     DO K = 1, 5
                        IF (K .EQ. 3) CYCLE
         10             PRINT *, 'I=', I, ' J=', J, ' K=', K
                     END DO
                  END DO
               END DO
         20    CONTINUE

Adding new labels allows translation of `CYCLE` and `EXIT` to `GO TO` so they may be more easily understood by programmers accustomed to FORTRAN coding:

               DO I = 1, 5
                  DO J = 1, 5
                     IF (J .EQ. 5) GOTO 18
                     DO K = 1, 5
                        IF (K .EQ. 3) GO TO 12
         10             PRINT *, 'I=', I, ' J=', J, ' K=', K
         12          END DO
                  END DO
         18    END DO
         20    CONTINUE

Thus, the `CYCLE` statement in the innermost loop skips over the `PRINT` statement as it begins the next iteration of the loop, while the `EXIT` statement in the middle loop ends that loop but not the outermost loop.

Next: Scope and Classes of Names, Previous: Control Statements, Up: Language

### 8.11 Functions and Subroutines

(The following information augments or overrides the information in Chapter 15 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 15 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

Next: %REF(), Up: Functions and Subroutines

#### 8.11.1 The `%VAL()` Construct

         %VAL(arg)

The `%VAL()` construct specifies that an argument, arg, is to be passed by value, instead of by reference or descriptor.

`%VAL()` is restricted to actual arguments in invocations of external procedures.

Use of `%VAL()` is recommended only for code that is accessing facilities outside of GNU Fortran, such as operating system or windowing facilities. It is best to constrain such uses to isolated portions of a program—portions the deal specifically and exclusively with low-level, system-dependent facilities. Such portions might well provide a portable interface for use by the program as a whole, but are themselves not portable, and should be thoroughly tested each time they are rebuilt using a new compiler or version of a compiler.

Implementation Note: Currently, g77 passes all arguments either by reference or by descriptor.

Thus, use of `%VAL()` tends to be restricted to cases where the called procedure is written in a language other than Fortran that supports call-by-value semantics. (C is an example of such a language.)

See Procedures (SUBROUTINE and FUNCTION), for detailed information on how this particular version of g77 passes arguments to procedures.

Next: %DESCR(), Previous: %VAL(), Up: Functions and Subroutines

#### 8.11.2 The `%REF()` Construct

         %REF(arg)

The `%REF()` construct specifies that an argument, arg, is to be passed by reference, instead of by value or descriptor.

`%REF()` is restricted to actual arguments in invocations of external procedures.

Use of `%REF()` is recommended only for code that is accessing facilities outside of GNU Fortran, such as operating system or windowing facilities. It is best to constrain such uses to isolated portions of a program—portions the deal specifically and exclusively with low-level, system-dependent facilities. Such portions might well provide a portable interface for use by the program as a whole, but are themselves not portable, and should be thoroughly tested each time they are rebuilt using a new compiler or version of a compiler.

Do not depend on `%REF()` supplying a pointer to the procedure being invoked. While that is a likely implementation choice, other implementation choices are available that preserve Fortran pass-by-reference semantics without passing a pointer to the argument, arg. (For example, a copy-in/copy-out implementation.)

Implementation Note: Currently, g77 passes all arguments (other than variables and arrays of type `CHARACTER`) by reference. Future versions of, or dialects supported by, g77 might not pass `CHARACTER` functions by reference.

Thus, use of `%REF()` tends to be restricted to cases where arg is type `CHARACTER` but the called procedure accesses it via a means other than the method used for Fortran `CHARACTER` arguments.

See Procedures (SUBROUTINE and FUNCTION), for detailed information on how this particular version of g77 passes arguments to procedures.

Next: Generics and Specifics, Previous: %REF(), Up: Functions and Subroutines

#### 8.11.3 The `%DESCR()` Construct

         %DESCR(arg)

The `%DESCR()` construct specifies that an argument, arg, is to be passed by descriptor, instead of by value or reference.

`%DESCR()` is restricted to actual arguments in invocations of external procedures.

Use of `%DESCR()` is recommended only for code that is accessing facilities outside of GNU Fortran, such as operating system or windowing facilities. It is best to constrain such uses to isolated portions of a program—portions the deal specifically and exclusively with low-level, system-dependent facilities. Such portions might well provide a portable interface for use by the program as a whole, but are themselves not portable, and should be thoroughly tested each time they are rebuilt using a new compiler or version of a compiler.

Do not depend on `%DESCR()` supplying a pointer and/or a length passed by value to the procedure being invoked. While that is a likely implementation choice, other implementation choices are available that preserve the pass-by-reference semantics without passing a pointer to the argument, arg. (For example, a copy-in/copy-out implementation.) And, future versions of g77 might change the way descriptors are implemented, such as passing a single argument pointing to a record containing the pointer/length information instead of passing that same information via two arguments as it currently does.

Implementation Note: Currently, g77 passes all variables and arrays of type `CHARACTER` by descriptor. Future versions of, or dialects supported by, g77 might pass `CHARACTER` functions by descriptor as well.

Thus, use of `%DESCR()` tends to be restricted to cases where arg is not type `CHARACTER` but the called procedure accesses it via a means similar to the method used for Fortran `CHARACTER` arguments.

See Procedures (SUBROUTINE and FUNCTION), for detailed information on how this particular version of g77 passes arguments to procedures.

Next: REAL() and AIMAG() of Complex, Previous: %DESCR(), Up: Functions and Subroutines

#### 8.11.4 Generics and Specifics

The ANSI FORTRAN 77 language defines generic and specific intrinsics. In short, the distinctions are:

- Specific intrinsics have specific types for their arguments and a specific return type.
- Generic intrinsics are treated, on a case-by-case basis in the program's source code, as one of several possible specific intrinsics.

  Typically, a generic intrinsic has a return type that is determined by the type of one or more of its arguments.

The GNU Fortran language generalizes these concepts somewhat, especially by providing intrinsic subroutines and generic intrinsics that are treated as either a specific intrinsic subroutine or a specific intrinsic function (e.g. `SECOND`).

However, GNU Fortran avoids generalizing this concept to the point where existing code would be accepted as meaning something possibly different than what was intended.

For example, `ABS` is a generic intrinsic, so all working code written using `ABS` of an `INTEGER` argument expects an `INTEGER` return value. Similarly, all such code expects that `ABS` of an `INTEGER*2` argument returns an `INTEGER*2` return value.

Yet, `IABS` is a specific intrinsic that accepts only an `INTEGER(KIND=1)` argument. Code that passes something other than an `INTEGER(KIND=1)` argument to `IABS` is not valid GNU Fortran code, because it is not clear what the author intended.

For example, if J is `INTEGER(KIND=6)`, IABS(J) is not defined by the GNU Fortran language, because the programmer might have used that construct to mean any of the following, subtly different, things:

- Convert J to `INTEGER(KIND=1)` first (as if IABS(INT(J)) had been written).
- Convert the result of the intrinsic to `INTEGER(KIND=1)` (as if INT(ABS(J)) had been written).
- No conversion (as if ABS(J) had been written).

The distinctions matter especially when types and values wider than `INTEGER(KIND=1)` (such as `INTEGER(KIND=2)`), or when operations performing more “arithmetic” than absolute-value, are involved.

The following sample program is not a valid GNU Fortran program, but might be accepted by other compilers. If so, the output is likely to be revealing in terms of how a given compiler treats intrinsics (that normally are specific) when they are given arguments that do not conform to their stated requirements:

               PROGRAM JCB002
         C Version 1:
         C Modified 1999-02-15 (Burley) to delete my email address.
         C Modified 1997-05-21 (Burley) to accommodate compilers that implement
         C INT(I1-I2) as INT(I1)-INT(I2) given INTEGER*2 I1,I2.
         C
         C Version 0:
         C Written by James Craig Burley 1997-02-20.
         C
         C Purpose:
         C Determine how compilers handle non-standard IDIM
         C on INTEGER*2 operands, which presumably can be
         C extrapolated into understanding how the compiler
         C generally treats specific intrinsics that are passed
         C arguments not of the correct types.
         C
         C If your compiler implements INTEGER*2 and INTEGER
         C as the same type, change all INTEGER*2 below to
         C INTEGER*1.
         C
               INTEGER*2 I0, I4
               INTEGER I1, I2, I3
               INTEGER*2 ISMALL, ILARGE
               INTEGER*2 ITOOLG, ITWO
               INTEGER*2 ITMP
               LOGICAL L2, L3, L4
         C
         C Find smallest INTEGER*2 number.
         C
               ISMALL=0
          10   I0 = ISMALL-1
               IF ((I0 .GE. ISMALL) .OR. (I0+1 .NE. ISMALL)) GOTO 20
               ISMALL = I0
               GOTO 10
          20   CONTINUE
         C
         C Find largest INTEGER*2 number.
         C
               ILARGE=0
          30   I0 = ILARGE+1
               IF ((I0 .LE. ILARGE) .OR. (I0-1 .NE. ILARGE)) GOTO 40
               ILARGE = I0
               GOTO 30
          40   CONTINUE
         C
         C Multiplying by two adds stress to the situation.
         C
               ITWO = 2
         C
         C Need a number that, added to -2, is too wide to fit in I*2.
         C
               ITOOLG = ISMALL
         C
         C Use IDIM the straightforward way.
         C
               I1 = IDIM (ILARGE, ISMALL) * ITWO + ITOOLG
         C
         C Calculate result for first interpretation.
         C
               I2 = (INT (ILARGE) - INT (ISMALL)) * ITWO + ITOOLG
         C
         C Calculate result for second interpretation.
         C
               ITMP = ILARGE - ISMALL
               I3 = (INT (ITMP)) * ITWO + ITOOLG
         C
         C Calculate result for third interpretation.
         C
               I4 = (ILARGE - ISMALL) * ITWO + ITOOLG
         C
         C Print results.
         C
               PRINT *, 'ILARGE=', ILARGE
               PRINT *, 'ITWO=', ITWO
               PRINT *, 'ITOOLG=', ITOOLG
               PRINT *, 'ISMALL=', ISMALL
               PRINT *, 'I1=', I1
               PRINT *, 'I2=', I2
               PRINT *, 'I3=', I3
               PRINT *, 'I4=', I4
               PRINT *
               L2 = (I1 .EQ. I2)
               L3 = (I1 .EQ. I3)
               L4 = (I1 .EQ. I4)
               IF (L2 .AND. .NOT.L3 .AND. .NOT.L4) THEN
                  PRINT *, 'Interp 1: IDIM(I*2,I*2) => IDIM(INT(I*2),INT(I*2))'
                  STOP
               END IF
               IF (L3 .AND. .NOT.L2 .AND. .NOT.L4) THEN
                  PRINT *, 'Interp 2: IDIM(I*2,I*2) => INT(DIM(I*2,I*2))'
                  STOP
               END IF
               IF (L4 .AND. .NOT.L2 .AND. .NOT.L3) THEN
                  PRINT *, 'Interp 3: IDIM(I*2,I*2) => DIM(I*2,I*2)'
                  STOP
               END IF
               PRINT *, 'Results need careful analysis.'
               END

No future version of the GNU Fortran language will likely permit specific intrinsic invocations with wrong-typed arguments (such as `IDIM` in the above example), since it has been determined that disagreements exist among many production compilers on the interpretation of such invocations. These disagreements strongly suggest that Fortran programmers, and certainly existing Fortran programs, disagree about the meaning of such invocations.

The first version of `JCB002` didn't accommodate some compilers' treatment of INT(I1-I2) where I1 and I2 are `INTEGER*2`. In such a case, these compilers apparently convert both operands to `INTEGER*4` and then do an `INTEGER*4` subtraction, instead of doing an `INTEGER*2` subtraction on the original values in I1 and I2.

However, the results of the careful analyses done on the outputs of programs compiled by these various compilers show that they all implement either Interp 1 or Interp 2 above.

Specifically, it is believed that the new version of `JCB002` above will confirm that:

- Digital Semiconductor (“DEC”) Alpha OSF/1, HP-UX 10.0.1, AIX 3.2.5 f77 compilers all implement Interp 1.
- IRIX 5.3 f77 compiler implements Interp 2.
- Solaris 2.5, SunOS 4.1.3, DECstation ULTRIX 4.3, and IRIX 6.1 f77 compilers all implement Interp 3.

If you get different results than the above for the stated compilers, or have results for other compilers that might be worth adding to the above list, please let us know the details (compiler product, version, machine, results, and so on).

Next: CMPLX() of DOUBLE PRECISION, Previous: Generics and Specifics, Up: Functions and Subroutines

#### 8.11.5 `REAL()` and `AIMAG()` of Complex

The GNU Fortran language disallows `REAL(`expr`)` and `AIMAG(`expr`)`, where expr is any `COMPLEX` type other than `COMPLEX(KIND=1)`, except when they are used in the following way:

         REAL(REAL(expr))
         REAL(AIMAG(expr))

The above forms explicitly specify that the desired effect is to convert the real or imaginary part of expr, which might be some `REAL` type other than `REAL(KIND=1)`, to type `REAL(KIND=1)`, and have that serve as the value of the expression.

The GNU Fortran language offers clearly named intrinsics to extract the real and imaginary parts of a complex entity without any conversion:

         REALPART(expr)
         IMAGPART(expr)

To express the above using typical extended FORTRAN 77, use the following constructs (when expr is `COMPLEX(KIND=2)`):

         DBLE(expr)
         DIMAG(expr)

The FORTRAN 77 language offers no way to explicitly specify the real and imaginary parts of a complex expression of arbitrary type, apparently as a result of requiring support for only one `COMPLEX` type (`COMPLEX(KIND=1)`). The concepts of converting an expression to type `REAL(KIND=1)` and of extracting the real part of a complex expression were thus “smooshed” by FORTRAN 77 into a single intrinsic, since they happened to have the exact same effect in that language (due to having only one `COMPLEX` type).

Note: When -ff90 is in effect, g77 treats REAL(expr), where expr is of type `COMPLEX`, as REALPART(expr), whereas with -fugly-complex -fno-f90 in effect, it is treated as REAL(REALPART(expr)).

See Ugly Complex Part Extraction, for more information.

Next: MIL-STD 1753, Previous: REAL() and AIMAG() of Complex, Up: Functions and Subroutines

#### 8.11.6 `CMPLX()` of `DOUBLE PRECISION`

In accordance with Fortran 90 and at least some (perhaps all) other compilers, the GNU Fortran language defines `CMPLX()` as always returning a result that is type `COMPLEX(KIND=1)`.

This means CMPLX(D1,D2), where D1 and D2 are `REAL(KIND=2)` (`DOUBLE PRECISION`), is treated as:

         CMPLX(SNGL(D1), SNGL(D2))

(It was necessary for Fortran 90 to specify this behavior for `DOUBLE PRECISION` arguments, since that is the behavior mandated by FORTRAN 77.)

The GNU Fortran language also provides the `DCMPLX()` intrinsic, which is provided by some FORTRAN 77 compilers to construct a `DOUBLE COMPLEX` entity from of `DOUBLE PRECISION` operands. However, this solution does not scale well when more `COMPLEX` types (having various precisions and ranges) are offered by Fortran implementations.

Fortran 90 extends the `CMPLX()` intrinsic by adding an extra argument used to specify the desired kind of complex result. However, this solution is somewhat awkward to use, and g77 currently does not support it.

The GNU Fortran language provides a simple way to build a complex value out of two numbers, with the precise type of the value determined by the types of the two numbers (via the usual type-promotion mechanism):

         COMPLEX(real, imag)

When real and imag are the same `REAL` types, `COMPLEX()` performs no conversion other than to put them together to form a complex result of the same (complex version of real) type.

See Complex Intrinsic, for more information.

Next: f77/f2c Intrinsics, Previous: CMPLX() of DOUBLE PRECISION, Up: Functions and Subroutines

#### 8.11.7 MIL-STD 1753 Support

The GNU Fortran language includes the MIL-STD 1753 intrinsics `BTEST`, `IAND`, `IBCLR`, `IBITS`, `IBSET`, `IEOR`, `IOR`, `ISHFT`, `ISHFTC`, `MVBITS`, and `NOT`.

Next: Table of Intrinsic Functions, Previous: MIL-STD 1753, Up: Functions and Subroutines

#### 8.11.8 f77/f2c Intrinsics

The bit-manipulation intrinsics supported by traditional f77 and by f2c are available in the GNU Fortran language. These include `AND`, `LSHIFT`, `OR`, `RSHIFT`, and `XOR`.

Also supported are the intrinsics `CDABS`, `CDCOS`, `CDEXP`, `CDLOG`, `CDSIN`, `CDSQRT`, `DCMPLX`, `DCONJG`, `DFLOAT`, `DIMAG`, `DREAL`, and `IMAG`, `ZABS`, `ZCOS`, `ZEXP`, `ZLOG`, `ZSIN`, and `ZSQRT`.

Previous: f77/f2c Intrinsics, Up: Functions and Subroutines

#### 8.11.9 Table of Intrinsic Functions

(Corresponds to Section 15.10 of ANSI X3.9-1978 FORTRAN 77.)

The GNU Fortran language adds various functions, subroutines, types, and arguments to the set of intrinsic functions in ANSI FORTRAN 77. The complete set of intrinsics supported by the GNU Fortran language is described below.

Note that a name is not treated as that of an intrinsic if it is specified in an `EXTERNAL` statement in the same program unit; if a command-line option is used to disable the groups to which the intrinsic belongs; or if the intrinsic is not named in an `INTRINSIC` statement and a command-line option is used to hide the groups to which the intrinsic belongs.

So, it is recommended that any reference in a program unit to an intrinsic procedure that is not a standard FORTRAN 77 intrinsic be accompanied by an appropriate `INTRINSIC` statement in that program unit. This sort of defensive programming makes it more likely that an implementation will issue a diagnostic rather than generate incorrect code for such a reference.

The terminology used below is based on that of the Fortran 90 standard, so that the text may be more concise and accurate:

- `OPTIONAL` means the argument may be omitted.
- A-1, A-2, ..., A-n means more than one argument (generally named A) may be specified.
- scalar means the argument must not be an array (must be a variable or array element, or perhaps a constant if expressions are permitted).
- DIMENSION(4) means the argument must be an array having 4 elements.
- `INTENT(IN)` means the argument must be an expression (such as a constant or a variable that is defined upon invocation of the intrinsic).
- `INTENT(OUT)` means the argument must be definable by the invocation of the intrinsic (that is, must not be a constant nor an expression involving operators other than array reference and substring reference).
- `INTENT(INOUT)` means the argument must be defined prior to, and definable by, invocation of the intrinsic (a combination of the requirements of `INTENT(IN)` and `INTENT(OUT)`.
- See Kind Notation, for an explanation of `KIND`.

Next: Abs Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.1 Abort Intrinsic

         CALL Abort()

Intrinsic groups: `unix`.

Description:

Prints a message and potentially causes a core dump via `abort(3)`.

Next: Access Intrinsic, Previous: Abort Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.2 Abs Intrinsic

         Abs(A)

Abs: `INTEGER` or `REAL` function. The exact type depends on that of argument A—if A is `COMPLEX`, this function's type is `REAL` with the same KIND= value as the type of A. Otherwise, this function's type is the same as that of A.

A: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the absolute value of A.

If A is type `COMPLEX`, the absolute value is computed as:

         SQRT(REALPART(A)**2+IMAGPART(A)**2)

Otherwise, it is computed by negating A if it is negative, or returning A.

See Sign Intrinsic, for how to explicitly compute the positive or negative form of the absolute value of an expression.

Next: AChar Intrinsic, Previous: Abs Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.3 Access Intrinsic

         Access(Name, Mode)

Access: `INTEGER(KIND=1)` function.

Name: `CHARACTER`; scalar; INTENT(IN).

Mode: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Checks file Name for accessibility in the mode specified by Mode and returns 0 if the file is accessible in that mode, otherwise an error code if the file is inaccessible or Mode is invalid. See `access(2)`. A null character (CHAR(0)) marks the end of the name in Name—otherwise, trailing blanks in Name are ignored. Mode may be a concatenation of any of the following characters:

r
  Read permission
w
  Write permission
x
  Execute permission
`SPC`
  Existence

Next: ACos Intrinsic, Previous: Access Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.4 AChar Intrinsic

         AChar(I)

AChar: `CHARACTER*1` function.

I: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `f90`.

Description:

Returns the ASCII character corresponding to the code specified by I.

See IAChar Intrinsic, for the inverse of this function.

See Char Intrinsic, for the function corresponding to the system's native character set.

Next: AdjustL Intrinsic, Previous: AChar Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.5 ACos Intrinsic

         ACos(X)

ACos: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the arc-cosine (inverse cosine) of X in radians.

See Cos Intrinsic, for the inverse of this function.

Next: AdjustR Intrinsic, Previous: ACos Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.6 AdjustL Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL AdjustL to use this name for an external procedure.

Next: AImag Intrinsic, Previous: AdjustL Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.7 AdjustR Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL AdjustR to use this name for an external procedure.

Next: AInt Intrinsic, Previous: AdjustR Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.8 AImag Intrinsic

         AImag(Z)

AImag: `REAL` function. This intrinsic is valid when argument Z is `COMPLEX(KIND=1)`. When Z is any other `COMPLEX` type, this intrinsic is valid only when used as the argument to `REAL()`, as explained below.

Z: `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the (possibly converted) imaginary part of Z.

Use of `AIMAG()` with an argument of a type other than `COMPLEX(KIND=1)` is restricted to the following case:

         REAL(AIMAG(Z))

This expression converts the imaginary part of Z to `REAL(KIND=1)`.

See REAL() and AIMAG() of Complex, for more information.

Next: Alarm Intrinsic, Previous: AImag Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.9 AInt Intrinsic

         AInt(A)

AInt: `REAL` function, the KIND= value of the type being that of argument A.

A: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns A with the fractional portion of its magnitude truncated and its sign preserved. (Also called “truncation towards zero”.)

See ANInt Intrinsic, for how to round to nearest whole number.

See Int Intrinsic, for how to truncate and then convert number to `INTEGER`.

Next: All Intrinsic, Previous: AInt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.10 Alarm Intrinsic

         CALL Alarm(Seconds, Handler, Status)

Seconds: `INTEGER`; scalar; INTENT(IN).

Handler: Signal handler (`INTEGER FUNCTION` or `SUBROUTINE`) or dummy/global `INTEGER(KIND=1)` scalar.

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Causes external subroutine Handler to be executed after a delay of Seconds seconds by using `alarm(1)` to set up a signal and `signal(2)` to catch it. If Status is supplied, it will be returned with the number of seconds remaining until any previously scheduled alarm was due to be delivered, or zero if there was no previously scheduled alarm. See Signal Intrinsic (subroutine).

Next: Allocated Intrinsic, Previous: Alarm Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.11 All Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL All to use this name for an external procedure.

Next: ALog Intrinsic, Previous: All Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.12 Allocated Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Allocated to use this name for an external procedure.

Next: ALog10 Intrinsic, Previous: Allocated Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.13 ALog Intrinsic

         ALog(X)

ALog: `REAL(KIND=1)` function.

X: `REAL(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `LOG()` that is specific to one type for X. See Log Intrinsic.

Next: AMax0 Intrinsic, Previous: ALog Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.14 ALog10 Intrinsic

         ALog10(X)

ALog10: `REAL(KIND=1)` function.

X: `REAL(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `LOG10()` that is specific to one type for X. See Log10 Intrinsic.

Next: AMax1 Intrinsic, Previous: ALog10 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.15 AMax0 Intrinsic

         AMax0(A-1, A-2, ..., A-n)

AMax0: `REAL(KIND=1)` function.

A: `INTEGER(KIND=1)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MAX()` that is specific to one type for A and a different return type. See Max Intrinsic.

Next: AMin0 Intrinsic, Previous: AMax0 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.16 AMax1 Intrinsic

         AMax1(A-1, A-2, ..., A-n)

AMax1: `REAL(KIND=1)` function.

A: `REAL(KIND=1)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MAX()` that is specific to one type for A. See Max Intrinsic.

Next: AMin1 Intrinsic, Previous: AMax1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.17 AMin0 Intrinsic

         AMin0(A-1, A-2, ..., A-n)

AMin0: `REAL(KIND=1)` function.

A: `INTEGER(KIND=1)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MIN()` that is specific to one type for A and a different return type. See Min Intrinsic.

Next: AMod Intrinsic, Previous: AMin0 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.18 AMin1 Intrinsic

         AMin1(A-1, A-2, ..., A-n)

AMin1: `REAL(KIND=1)` function.

A: `REAL(KIND=1)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MIN()` that is specific to one type for A. See Min Intrinsic.

Next: And Intrinsic, Previous: AMin1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.19 AMod Intrinsic

         AMod(A, P)

AMod: `REAL(KIND=1)` function.

A: `REAL(KIND=1)`; scalar; INTENT(IN).

P: `REAL(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MOD()` that is specific to one type for A. See Mod Intrinsic.

Next: ANInt Intrinsic, Previous: AMod Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.20 And Intrinsic

         And(I, J)

And: `INTEGER` or `LOGICAL` function, the exact type being the result of cross-promoting the types of all the arguments.

I: `INTEGER` or `LOGICAL`; scalar; INTENT(IN).

J: `INTEGER` or `LOGICAL`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Returns value resulting from boolean AND of pair of bits in each of I and J.

Next: Any Intrinsic, Previous: And Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.21 ANInt Intrinsic

         ANInt(A)

ANInt: `REAL` function, the KIND= value of the type being that of argument A.

A: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns A with the fractional portion of its magnitude eliminated by rounding to the nearest whole number and with its sign preserved.

A fractional portion exactly equal to .5 is rounded to the whole number that is larger in magnitude. (Also called “Fortran round”.)

See AInt Intrinsic, for how to truncate to whole number.

See NInt Intrinsic, for how to round and then convert number to `INTEGER`.

Next: ASin Intrinsic, Previous: ANInt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.22 Any Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Any to use this name for an external procedure.

Next: Associated Intrinsic, Previous: Any Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.23 ASin Intrinsic

         ASin(X)

ASin: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the arc-sine (inverse sine) of X in radians.

See Sin Intrinsic, for the inverse of this function.

Next: ATan Intrinsic, Previous: ASin Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.24 Associated Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Associated to use this name for an external procedure.

Next: ATan2 Intrinsic, Previous: Associated Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.25 ATan Intrinsic

         ATan(X)

ATan: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the arc-tangent (inverse tangent) of X in radians.

See Tan Intrinsic, for the inverse of this function.

Next: BesJ0 Intrinsic, Previous: ATan Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.26 ATan2 Intrinsic

         ATan2(Y, X)

ATan2: `REAL` function, the exact type being the result of cross-promoting the types of all the arguments.

Y: `REAL`; scalar; INTENT(IN).

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the arc-tangent (inverse tangent) of the complex number (Y, X) in radians.

See Tan Intrinsic, for the inverse of this function.

Next: BesJ1 Intrinsic, Previous: ATan2 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.27 BesJ0 Intrinsic

         BesJ0(X)

BesJ0: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Calculates the Bessel function of the first kind of order 0 of X. See `bessel(3m)`, on whose implementation the function depends.

Next: BesJN Intrinsic, Previous: BesJ0 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.28 BesJ1 Intrinsic

         BesJ1(X)

BesJ1: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Calculates the Bessel function of the first kind of order 1 of X. See `bessel(3m)`, on whose implementation the function depends.

Next: BesY0 Intrinsic, Previous: BesJ1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.29 BesJN Intrinsic

         BesJN(N, X)

BesJN: `REAL` function, the KIND= value of the type being that of argument X.

N: `INTEGER` not wider than the default kind; scalar; INTENT(IN).

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Calculates the Bessel function of the first kind of order N of X. See `bessel(3m)`, on whose implementation the function depends.

Next: BesY1 Intrinsic, Previous: BesJN Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.30 BesY0 Intrinsic

         BesY0(X)

BesY0: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Calculates the Bessel function of the second kind of order 0 of X. See `bessel(3m)`, on whose implementation the function depends.

Next: BesYN Intrinsic, Previous: BesY0 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.31 BesY1 Intrinsic

         BesY1(X)

BesY1: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Calculates the Bessel function of the second kind of order 1 of X. See `bessel(3m)`, on whose implementation the function depends.

Next: Bit_Size Intrinsic, Previous: BesY1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.32 BesYN Intrinsic

         BesYN(N, X)

BesYN: `REAL` function, the KIND= value of the type being that of argument X.

N: `INTEGER` not wider than the default kind; scalar; INTENT(IN).

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Calculates the Bessel function of the second kind of order N of X. See `bessel(3m)`, on whose implementation the function depends.

Next: BTest Intrinsic, Previous: BesYN Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.33 Bit_Size Intrinsic

         Bit_Size(I)

Bit_Size: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar.

Intrinsic groups: `f90`.

Description:

Returns the number of bits (integer precision plus sign bit) represented by the type for I.

See BTest Intrinsic, for how to test the value of a bit in a variable or array.

See IBSet Intrinsic, for how to set a bit in a variable to 1.

See IBClr Intrinsic, for how to set a bit in a variable to 0.

Next: CAbs Intrinsic, Previous: Bit_Size Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.34 BTest Intrinsic

         BTest(I, Pos)

BTest: `LOGICAL(KIND=1)` function.

I: `INTEGER`; scalar; INTENT(IN).

Pos: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Returns `.TRUE.` if bit Pos in I is 1, `.FALSE.` otherwise.

(Bit 0 is the low-order (rightmost) bit, adding the value or 1, to the number if set to 1; bit 1 is the next-higher-order bit, adding or 2; bit 2 adds or 4; and so on.)

See Bit_Size Intrinsic, for how to obtain the number of bits in a type. The leftmost bit of I is BIT_SIZE(I-1).

Next: CCos Intrinsic, Previous: BTest Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.35 CAbs Intrinsic

         CAbs(A)

CAbs: `REAL(KIND=1)` function.

A: `COMPLEX(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `ABS()` that is specific to one type for A. See Abs Intrinsic.

Next: Ceiling Intrinsic, Previous: CAbs Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.36 CCos Intrinsic

         CCos(X)

CCos: `COMPLEX(KIND=1)` function.

X: `COMPLEX(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `COS()` that is specific to one type for X. See Cos Intrinsic.

Next: CExp Intrinsic, Previous: CCos Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.37 Ceiling Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Ceiling to use this name for an external procedure.

Next: Char Intrinsic, Previous: Ceiling Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.38 CExp Intrinsic

         CExp(X)

CExp: `COMPLEX(KIND=1)` function.

X: `COMPLEX(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `EXP()` that is specific to one type for X. See Exp Intrinsic.

Next: ChDir Intrinsic (subroutine), Previous: CExp Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.39 Char Intrinsic

         Char(I)

Char: `CHARACTER*1` function.

I: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the character corresponding to the code specified by I, using the system's native character set.

Because the system's native character set is used, the correspondence between character and their codes is not necessarily the same between GNU Fortran implementations.

Note that no intrinsic exists to convert a numerical value to a printable character string. For example, there is no intrinsic that, given an `INTEGER` or `REAL` argument with the value 154, returns the `CHARACTER` result '154'.

Instead, you can use internal-file I/O to do this kind of conversion. For example:

         INTEGER VALUE
         CHARACTER*10 STRING
         VALUE = 154
         WRITE (STRING, '(I10)'), VALUE
         PRINT *, STRING
         END

The above program, when run, prints:

                 154

See IChar Intrinsic, for the inverse of the `CHAR` function.

See AChar Intrinsic, for the function corresponding to the ASCII character set.

Next: ChMod Intrinsic (subroutine), Previous: Char Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.40 ChDir Intrinsic (subroutine)

         CALL ChDir(Dir, Status)

Dir: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Sets the current working directory to be Dir. If the Status argument is supplied, it contains 0 on success or a nonzero error code otherwise upon return. See `chdir(3)`.

Caution: Using this routine during I/O to a unit connected with a non-absolute file name can cause subsequent I/O on such a unit to fail because the I/O library might reopen files by name.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See ChDir Intrinsic (function).

Next: CLog Intrinsic, Previous: ChDir Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.41 ChMod Intrinsic (subroutine)

         CALL ChMod(Name, Mode, Status)

Name: `CHARACTER`; scalar; INTENT(IN).

Mode: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Changes the access mode of file Name according to the specification Mode, which is given in the format of `chmod(1)`. A null character (CHAR(0)) marks the end of the name in Name—otherwise, trailing blanks in Name are ignored. Currently, Name must not contain the single quote character.

If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return.

Note that this currently works by actually invoking `/bin/chmod` (or the `chmod` found when the library was configured) and so might fail in some circumstances and will, anyway, be slow.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See ChMod Intrinsic (function).

Next: Cmplx Intrinsic, Previous: ChMod Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.42 CLog Intrinsic

         CLog(X)

CLog: `COMPLEX(KIND=1)` function.

X: `COMPLEX(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `LOG()` that is specific to one type for X. See Log Intrinsic.

Next: Complex Intrinsic, Previous: CLog Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.43 Cmplx Intrinsic

         Cmplx(X, Y)

Cmplx: `COMPLEX(KIND=1)` function.

X: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Y: `INTEGER` or `REAL`; OPTIONAL (must be omitted if X is `COMPLEX`); scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

If X is not type `COMPLEX`, constructs a value of type `COMPLEX(KIND=1)` from the real and imaginary values specified by X and Y, respectively. If Y is omitted, 0. is assumed.

If X is type `COMPLEX`, converts it to type `COMPLEX(KIND=1)`.

See Complex Intrinsic, for information on easily constructing a `COMPLEX` value of arbitrary precision from `REAL` arguments.

Next: Conjg Intrinsic, Previous: Cmplx Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.44 Complex Intrinsic

         Complex(Real, Imag)

Complex: `COMPLEX` function, the exact type being the result of cross-promoting the types of all the arguments.

Real: `INTEGER` or `REAL`; scalar; INTENT(IN).

Imag: `INTEGER` or `REAL`; scalar; INTENT(IN).

Intrinsic groups: `gnu`.

Description:

Returns a `COMPLEX` value that has Real and Imag as its real and imaginary parts, respectively.

If Real and Imag are the same type, and that type is not `INTEGER`, no data conversion is performed, and the type of the resulting value has the same kind value as the types of Real and Imag.

If Real and Imag are not the same type, the usual type-promotion rules are applied to both, converting either or both to the appropriate `REAL` type. The type of the resulting value has the same kind value as the type to which both Real and Imag were converted, in this case.

If Real and Imag are both `INTEGER`, they are both converted to `REAL(KIND=1)`, and the result of the `COMPLEX()` invocation is type `COMPLEX(KIND=1)`.

Note: The way to do this in standard Fortran 90 is too hairy to describe here, but it is important to note that CMPLX(D1,D2) returns a `COMPLEX(KIND=1)` result even if D1 and D2 are type `REAL(KIND=2)`. Hence the availability of `COMPLEX()` in GNU Fortran.

Next: Cos Intrinsic, Previous: Complex Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.45 Conjg Intrinsic

         Conjg(Z)

Conjg: `COMPLEX` function, the KIND= value of the type being that of argument Z.

Z: `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the complex conjugate:

         COMPLEX(REALPART(Z), -IMAGPART(Z))

Next: CosH Intrinsic, Previous: Conjg Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.46 Cos Intrinsic

         Cos(X)

Cos: `REAL` or `COMPLEX` function, the exact type being that of argument X.

X: `REAL` or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the cosine of X, an angle measured in radians.

See ACos Intrinsic, for the inverse of this function.

Next: Count Intrinsic, Previous: Cos Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.47 CosH Intrinsic

         CosH(X)

CosH: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the hyperbolic cosine of X.

Next: CPU_Time Intrinsic, Previous: CosH Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.48 Count Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Count to use this name for an external procedure.

Next: CShift Intrinsic, Previous: Count Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.49 CPU_Time Intrinsic

         CALL CPU_Time(Seconds)

Seconds: `REAL`; scalar; INTENT(OUT).

Intrinsic groups: `f90`.

Description:

Returns in Seconds the current value of the system time. This implementation of the Fortran 95 intrinsic is just an alias for `second` See Second Intrinsic (subroutine).

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wraparounds) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

Next: CSin Intrinsic, Previous: CPU_Time Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.50 CShift Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL CShift to use this name for an external procedure.

Next: CSqRt Intrinsic, Previous: CShift Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.51 CSin Intrinsic

         CSin(X)

CSin: `COMPLEX(KIND=1)` function.

X: `COMPLEX(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `SIN()` that is specific to one type for X. See Sin Intrinsic.

Next: CTime Intrinsic (subroutine), Previous: CSin Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.52 CSqRt Intrinsic

         CSqRt(X)

CSqRt: `COMPLEX(KIND=1)` function.

X: `COMPLEX(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `SQRT()` that is specific to one type for X. See SqRt Intrinsic.

Next: CTime Intrinsic (function), Previous: CSqRt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.53 CTime Intrinsic (subroutine)

         CALL CTime(STime, Result)

STime: `INTEGER`; scalar; INTENT(IN).

Result: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Converts STime, a system time value, such as returned by `TIME8()`, to a string of the form Sat Aug 19 18:13:14 1995, and returns that string in Result.

See Time8 Intrinsic.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine.

For information on other intrinsics with the same name: See CTime Intrinsic (function).

Next: DAbs Intrinsic, Previous: CTime Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.54 CTime Intrinsic (function)

         CTime(STime)

CTime: `CHARACTER*(*)` function.

STime: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Converts STime, a system time value, such as returned by `TIME8()`, to a string of the form Sat Aug 19 18:13:14 1995, and returns that string as the function value.

See Time8 Intrinsic.

For information on other intrinsics with the same name: See CTime Intrinsic (subroutine).

Next: DACos Intrinsic, Previous: CTime Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.55 DAbs Intrinsic

         DAbs(A)

DAbs: `REAL(KIND=2)` function.

A: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `ABS()` that is specific to one type for A. See Abs Intrinsic.

Next: DASin Intrinsic, Previous: DAbs Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.56 DACos Intrinsic

         DACos(X)

DACos: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `ACOS()` that is specific to one type for X. See ACos Intrinsic.

Next: DATan Intrinsic, Previous: DACos Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.57 DASin Intrinsic

         DASin(X)

DASin: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `ASIN()` that is specific to one type for X. See ASin Intrinsic.

Next: DATan2 Intrinsic, Previous: DASin Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.58 DATan Intrinsic

         DATan(X)

DATan: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `ATAN()` that is specific to one type for X. See ATan Intrinsic.

Next: Date_and_Time Intrinsic, Previous: DATan Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.59 DATan2 Intrinsic

         DATan2(Y, X)

DATan2: `REAL(KIND=2)` function.

Y: `REAL(KIND=2)`; scalar; INTENT(IN).

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `ATAN2()` that is specific to one type for Y and X. See ATan2 Intrinsic.

Next: DbesJ0 Intrinsic, Previous: DATan2 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.60 Date_and_Time Intrinsic

         CALL Date_and_Time(Date, Time, Zone, Values)

Date: `CHARACTER`; scalar; INTENT(OUT).

Time: `CHARACTER`; OPTIONAL; scalar; INTENT(OUT).

Zone: `CHARACTER`; OPTIONAL; scalar; INTENT(OUT).

Values: `INTEGER(KIND=1)`; OPTIONAL; DIMENSION(8); INTENT(OUT).

Intrinsic groups: `f90`.

Description:

Returns:

Date
  The date in the form ccyymmdd: century, year, month and day;
Time
  The time in the form hhmmss.ss: hours, minutes, seconds and milliseconds;
Zone
  The difference between local time and UTC (GMT) in the form Shhmm: sign, hours and minutes, e.g. -0500 (winter in New York);
Values
  The year, month of the year, day of the month, time difference in minutes from UTC, hour of the day, minutes of the hour, seconds of the minute, and milliseconds of the second in successive values of the array.

Programs making use of this intrinsic might not be Year 10000 (Y10K) compliant. For example, the date might appear, to such programs, to wrap around (change from a larger value to a smaller one) as of the Year 10000.

On systems where a millisecond timer isn't available, the millisecond value is returned as zero.

Next: DbesJ1 Intrinsic, Previous: Date_and_Time Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.61 DbesJ0 Intrinsic

         DbesJ0(X)

DbesJ0: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `BESJ0()` that is specific to one type for X. See BesJ0 Intrinsic.

Next: DbesJN Intrinsic, Previous: DbesJ0 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.62 DbesJ1 Intrinsic

         DbesJ1(X)

DbesJ1: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `BESJ1()` that is specific to one type for X. See BesJ1 Intrinsic.

Next: DbesY0 Intrinsic, Previous: DbesJ1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.63 DbesJN Intrinsic

         DbesJN(N, X)

DbesJN: `REAL(KIND=2)` function.

N: `INTEGER` not wider than the default kind; scalar; INTENT(IN).

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `BESJN()` that is specific to one type for X. See BesJN Intrinsic.

Next: DbesY1 Intrinsic, Previous: DbesJN Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.64 DbesY0 Intrinsic

         DbesY0(X)

DbesY0: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `BESY0()` that is specific to one type for X. See BesY0 Intrinsic.

Next: DbesYN Intrinsic, Previous: DbesY0 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.65 DbesY1 Intrinsic

         DbesY1(X)

DbesY1: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `BESY1()` that is specific to one type for X. See BesY1 Intrinsic.

Next: Dble Intrinsic, Previous: DbesY1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.66 DbesYN Intrinsic

         DbesYN(N, X)

DbesYN: `REAL(KIND=2)` function.

N: `INTEGER` not wider than the default kind; scalar; INTENT(IN).

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `BESYN()` that is specific to one type for X. See BesYN Intrinsic.

Next: DCos Intrinsic, Previous: DbesYN Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.67 Dble Intrinsic

         Dble(A)

Dble: `REAL(KIND=2)` function.

A: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns A converted to double precision (`REAL(KIND=2)`). If A is `COMPLEX`, the real part of A is used for the conversion and the imaginary part disregarded.

See Sngl Intrinsic, for the function that converts to single precision.

See Int Intrinsic, for the function that converts to `INTEGER`.

See Complex Intrinsic, for the function that converts to `COMPLEX`.

Next: DCosH Intrinsic, Previous: Dble Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.68 DCos Intrinsic

         DCos(X)

DCos: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `COS()` that is specific to one type for X. See Cos Intrinsic.

Next: DDiM Intrinsic, Previous: DCos Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.69 DCosH Intrinsic

         DCosH(X)

DCosH: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `COSH()` that is specific to one type for X. See CosH Intrinsic.

Next: DErF Intrinsic, Previous: DCosH Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.70 DDiM Intrinsic

         DDiM(X, Y)

DDiM: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Y: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `DIM()` that is specific to one type for X and Y. See DiM Intrinsic.

Next: DErFC Intrinsic, Previous: DDiM Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.71 DErF Intrinsic

         DErF(X)

DErF: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `ERF()` that is specific to one type for X. See ErF Intrinsic.

Next: DExp Intrinsic, Previous: DErF Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.72 DErFC Intrinsic

         DErFC(X)

DErFC: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `ERFC()` that is specific to one type for X. See ErFC Intrinsic.

Next: Digits Intrinsic, Previous: DErFC Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.73 DExp Intrinsic

         DExp(X)

DExp: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `EXP()` that is specific to one type for X. See Exp Intrinsic.

Next: DiM Intrinsic, Previous: DExp Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.74 Digits Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Digits to use this name for an external procedure.

Next: DInt Intrinsic, Previous: Digits Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.75 DiM Intrinsic

         DiM(X, Y)

DiM: `INTEGER` or `REAL` function, the exact type being the result of cross-promoting the types of all the arguments.

X: `INTEGER` or `REAL`; scalar; INTENT(IN).

Y: `INTEGER` or `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns X-Y if X is greater than Y; otherwise returns zero.

Next: DLog Intrinsic, Previous: DiM Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.76 DInt Intrinsic

         DInt(A)

DInt: `REAL(KIND=2)` function.

A: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `AINT()` that is specific to one type for A. See AInt Intrinsic.

Next: DLog10 Intrinsic, Previous: DInt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.77 DLog Intrinsic

         DLog(X)

DLog: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `LOG()` that is specific to one type for X. See Log Intrinsic.

Next: DMax1 Intrinsic, Previous: DLog Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.78 DLog10 Intrinsic

         DLog10(X)

DLog10: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `LOG10()` that is specific to one type for X. See Log10 Intrinsic.

Next: DMin1 Intrinsic, Previous: DLog10 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.79 DMax1 Intrinsic

         DMax1(A-1, A-2, ..., A-n)

DMax1: `REAL(KIND=2)` function.

A: `REAL(KIND=2)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MAX()` that is specific to one type for A. See Max Intrinsic.

Next: DMod Intrinsic, Previous: DMax1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.80 DMin1 Intrinsic

         DMin1(A-1, A-2, ..., A-n)

DMin1: `REAL(KIND=2)` function.

A: `REAL(KIND=2)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MIN()` that is specific to one type for A. See Min Intrinsic.

Next: DNInt Intrinsic, Previous: DMin1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.81 DMod Intrinsic

         DMod(A, P)

DMod: `REAL(KIND=2)` function.

A: `REAL(KIND=2)`; scalar; INTENT(IN).

P: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MOD()` that is specific to one type for A. See Mod Intrinsic.

Next: Dot_Product Intrinsic, Previous: DMod Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.82 DNInt Intrinsic

         DNInt(A)

DNInt: `REAL(KIND=2)` function.

A: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `ANINT()` that is specific to one type for A. See ANInt Intrinsic.

Next: DProd Intrinsic, Previous: DNInt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.83 Dot_Product Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Dot_Product to use this name for an external procedure.

Next: DSign Intrinsic, Previous: Dot_Product Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.84 DProd Intrinsic

         DProd(X, Y)

DProd: `REAL(KIND=2)` function.

X: `REAL(KIND=1)`; scalar; INTENT(IN).

Y: `REAL(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns DBLE(X)*DBLE(Y).

Next: DSin Intrinsic, Previous: DProd Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.85 DSign Intrinsic

         DSign(A, B)

DSign: `REAL(KIND=2)` function.

A: `REAL(KIND=2)`; scalar; INTENT(IN).

B: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `SIGN()` that is specific to one type for A and B. See Sign Intrinsic.

Next: DSinH Intrinsic, Previous: DSign Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.86 DSin Intrinsic

         DSin(X)

DSin: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `SIN()` that is specific to one type for X. See Sin Intrinsic.

Next: DSqRt Intrinsic, Previous: DSin Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.87 DSinH Intrinsic

         DSinH(X)

DSinH: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `SINH()` that is specific to one type for X. See SinH Intrinsic.

Next: DTan Intrinsic, Previous: DSinH Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.88 DSqRt Intrinsic

         DSqRt(X)

DSqRt: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `SQRT()` that is specific to one type for X. See SqRt Intrinsic.

Next: DTanH Intrinsic, Previous: DSqRt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.89 DTan Intrinsic

         DTan(X)

DTan: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `TAN()` that is specific to one type for X. See Tan Intrinsic.

Next: DTime Intrinsic (subroutine), Previous: DTan Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.90 DTanH Intrinsic

         DTanH(X)

DTanH: `REAL(KIND=2)` function.

X: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `TANH()` that is specific to one type for X. See TanH Intrinsic.

Next: EOShift Intrinsic, Previous: DTanH Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.91 DTime Intrinsic (subroutine)

         CALL DTime(TArray, Result)

TArray: `REAL(KIND=1)`; DIMENSION(2); INTENT(OUT).

Result: `REAL(KIND=1)`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Initially, return the number of seconds of runtime since the start of the process's execution in Result, and the user and system components of this in TArray(1) and TArray(2) respectively. The value of Result is equal to TArray(1) + TArray(2).

Subsequent invocations of DTIME() set values based on accumulations since the previous invocation.

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wraparounds) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine.

For information on other intrinsics with the same name: See DTime Intrinsic (function).

Next: Epsilon Intrinsic, Previous: DTime Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.92 EOShift Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL EOShift to use this name for an external procedure.

Next: ErF Intrinsic, Previous: EOShift Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.93 Epsilon Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Epsilon to use this name for an external procedure.

Next: ErFC Intrinsic, Previous: Epsilon Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.94 ErF Intrinsic

         ErF(X)

ErF: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns the error function of X. See `erf(3m)`, which provides the implementation.

Next: ETime Intrinsic (subroutine), Previous: ErF Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.95 ErFC Intrinsic

         ErFC(X)

ErFC: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns the complementary error function of X: ERFC(R) = 1 - ERF(R) (except that the result might be more accurate than explicitly evaluating that formulae would give). See `erfc(3m)`, which provides the implementation.

Next: ETime Intrinsic (function), Previous: ErFC Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.96 ETime Intrinsic (subroutine)

         CALL ETime(TArray, Result)

TArray: `REAL(KIND=1)`; DIMENSION(2); INTENT(OUT).

Result: `REAL(KIND=1)`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Return the number of seconds of runtime since the start of the process's execution in Result, and the user and system components of this in TArray(1) and TArray(2) respectively. The value of Result is equal to TArray(1) + TArray(2).

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wraparounds) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine.

For information on other intrinsics with the same name: See ETime Intrinsic (function).

Next: Exit Intrinsic, Previous: ETime Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.97 ETime Intrinsic (function)

         ETime(TArray)

ETime: `REAL(KIND=1)` function.

TArray: `REAL(KIND=1)`; DIMENSION(2); INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Return the number of seconds of runtime since the start of the process's execution as the function value, and the user and system components of this in TArray(1) and TArray(2) respectively. The functions' value is equal to TArray(1) + TArray(2).

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wraparounds) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

For information on other intrinsics with the same name: See ETime Intrinsic (subroutine).

Next: Exp Intrinsic, Previous: ETime Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.98 Exit Intrinsic

         CALL Exit(Status)

Status: `INTEGER` not wider than the default kind; OPTIONAL; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Exit the program with status Status after closing open Fortran I/O units and otherwise behaving as `exit(2)`. If Status is omitted the canonical `success' value will be returned to the system.

Next: Exponent Intrinsic, Previous: Exit Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.99 Exp Intrinsic

         Exp(X)

Exp: `REAL` or `COMPLEX` function, the exact type being that of argument X.

X: `REAL` or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns e**X, where e is approximately 2.7182818.

See Log Intrinsic, for the inverse of this function.

Next: FDate Intrinsic (subroutine), Previous: Exp Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.100 Exponent Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Exponent to use this name for an external procedure.

Next: FDate Intrinsic (function), Previous: Exponent Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.101 FDate Intrinsic (subroutine)

         CALL FDate(Date)

Date: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Returns the current date (using the same format as `CTIME()`) in Date.

Equivalent to:

         CALL CTIME(Date, TIME8())

Programs making use of this intrinsic might not be Year 10000 (Y10K) compliant. For example, the date might appear, to such programs, to wrap around (change from a larger value to a smaller one) as of the Year 10000.

See CTime Intrinsic (subroutine).

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine.

For information on other intrinsics with the same name: See FDate Intrinsic (function).

Next: FGet Intrinsic (subroutine), Previous: FDate Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.102 FDate Intrinsic (function)

         FDate()

FDate: `CHARACTER*(*)` function.

Intrinsic groups: `unix`.

Description:

Returns the current date (using the same format as `CTIME()`).

Equivalent to:

         CTIME(TIME8())

Programs making use of this intrinsic might not be Year 10000 (Y10K) compliant. For example, the date might appear, to such programs, to wrap around (change from a larger value to a smaller one) as of the Year 10000.

See CTime Intrinsic (function).

For information on other intrinsics with the same name: See FDate Intrinsic (subroutine).

Next: FGetC Intrinsic (subroutine), Previous: FDate Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.103 FGet Intrinsic (subroutine)

         CALL FGet(C, Status)

C: `CHARACTER`; scalar; INTENT(OUT).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Reads a single character into C in stream mode from unit 5 (by-passing normal formatted output) using `getc(3)`. Returns in Status 0 on success, −1 on end-of-file, and the error code from `ferror(3)` otherwise.

Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

For information on other intrinsics with the same name: See FGet Intrinsic (function).

Next: Float Intrinsic, Previous: FGet Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.104 FGetC Intrinsic (subroutine)

         CALL FGetC(Unit, C, Status)

Unit: `INTEGER`; scalar; INTENT(IN).

C: `CHARACTER`; scalar; INTENT(OUT).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Reads a single character into C in stream mode from unit Unit (by-passing normal formatted output) using `getc(3)`. Returns in Status 0 on success, −1 on end-of-file, and the error code from `ferror(3)` otherwise.

Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

For information on other intrinsics with the same name: See FGetC Intrinsic (function).

Next: Floor Intrinsic, Previous: FGetC Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.105 Float Intrinsic

         Float(A)

Float: `REAL(KIND=1)` function.

A: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `REAL()` that is specific to one type for A. See Real Intrinsic.

Next: Flush Intrinsic, Previous: Float Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.106 Floor Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Floor to use this name for an external procedure.

Next: FNum Intrinsic, Previous: Floor Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.107 Flush Intrinsic

         CALL Flush(Unit)

Unit: `INTEGER`; OPTIONAL; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Flushes Fortran unit(s) currently open for output. Without the optional argument, all such units are flushed, otherwise just the unit specified by Unit.

Some non-GNU implementations of Fortran provide this intrinsic as a library procedure that might or might not support the (optional) Unit argument.

Next: FPut Intrinsic (subroutine), Previous: Flush Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.108 FNum Intrinsic

         FNum(Unit)

FNum: `INTEGER(KIND=1)` function.

Unit: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns the Unix file descriptor number corresponding to the open Fortran I/O unit Unit. This could be passed to an interface to C I/O routines.

Next: FPutC Intrinsic (subroutine), Previous: FNum Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.109 FPut Intrinsic (subroutine)

         CALL FPut(C, Status)

C: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Writes the single character C in stream mode to unit 6 (by-passing normal formatted output) using `putc(3)`. Returns in Status 0 on success, the error code from `ferror(3)` otherwise.

Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

For information on other intrinsics with the same name: See FPut Intrinsic (function).

Next: Fraction Intrinsic, Previous: FPut Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.110 FPutC Intrinsic (subroutine)

         CALL FPutC(Unit, C, Status)

Unit: `INTEGER`; scalar; INTENT(IN).

C: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Writes the single character Unit in stream mode to unit 6 (by-passing normal formatted output) using `putc(3)`. Returns in C 0 on success, the error code from `ferror(3)` otherwise.

Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

For information on other intrinsics with the same name: See FPutC Intrinsic (function).

Next: FSeek Intrinsic, Previous: FPutC Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.111 Fraction Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Fraction to use this name for an external procedure.

Next: FStat Intrinsic (subroutine), Previous: Fraction Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.112 FSeek Intrinsic

         CALL FSeek(Unit, Offset, Whence, ErrLab)

Unit: `INTEGER`; scalar; INTENT(IN).

Offset: `INTEGER`; scalar; INTENT(IN).

Whence: `INTEGER`; scalar; INTENT(IN).

ErrLab: *label, where label is the label of an executable statement; OPTIONAL.

Intrinsic groups: `unix`.

Description:

Attempts to move Fortran unit Unit to the specified Offset: absolute offset if Whence=0; relative to the current offset if Whence=1; relative to the end of the file if Whence=2. It branches to label ErrLab if Unit is not open or if the call otherwise fails.

Next: FStat Intrinsic (function), Previous: FSeek Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.113 FStat Intrinsic (subroutine)

         CALL FStat(Unit, SArray, Status)

Unit: `INTEGER`; scalar; INTENT(IN).

SArray: `INTEGER(KIND=1)`; DIMENSION(13); INTENT(OUT).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Obtains data about the file open on Fortran I/O unit Unit and places them in the array SArray. The values in this array are extracted from the `stat` structure as returned by `fstat(2)` q.v., as follows:

1. Device ID
2. Inode number
3. File mode
4. Number of links
5. Owner's uid
6. Owner's gid
7. ID of device containing directory entry for file (0 if not available)
8. File size (bytes)
9. Last access time
10. Last modification time
11. Last file status change time
12. Preferred I/O block size (-1 if not available)
13. Number of blocks allocated (-1 if not available)

Not all these elements are relevant on all systems. If an element is not relevant, it is returned as 0.

If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See FStat Intrinsic (function).

Next: FTell Intrinsic (subroutine), Previous: FStat Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.114 FStat Intrinsic (function)

         FStat(Unit, SArray)

FStat: `INTEGER(KIND=1)` function.

Unit: `INTEGER`; scalar; INTENT(IN).

SArray: `INTEGER(KIND=1)`; DIMENSION(13); INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Obtains data about the file open on Fortran I/O unit Unit and places them in the array SArray. The values in this array are extracted from the `stat` structure as returned by `fstat(2)` q.v., as follows:

1. Device ID
2. Inode number
3. File mode
4. Number of links
5. Owner's uid
6. Owner's gid
7. ID of device containing directory entry for file (0 if not available)
8. File size (bytes)
9. Last access time
10. Last modification time
11. Last file status change time
12. Preferred I/O block size (-1 if not available)
13. Number of blocks allocated (-1 if not available)

Not all these elements are relevant on all systems. If an element is not relevant, it is returned as 0.

Returns 0 on success or a nonzero error code.

For information on other intrinsics with the same name: See FStat Intrinsic (subroutine).

Next: FTell Intrinsic (function), Previous: FStat Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.115 FTell Intrinsic (subroutine)

         CALL FTell(Unit, Offset)

Unit: `INTEGER`; scalar; INTENT(IN).

Offset: `INTEGER(KIND=1)`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Sets Offset to the current offset of Fortran unit Unit (or to −1 if Unit is not open).

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine.

For information on other intrinsics with the same name: See FTell Intrinsic (function).

Next: GError Intrinsic, Previous: FTell Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.116 FTell Intrinsic (function)

         FTell(Unit)

FTell: `INTEGER(KIND=1)` function.

Unit: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns the current offset of Fortran unit Unit (or −1 if Unit is not open).

For information on other intrinsics with the same name: See FTell Intrinsic (subroutine).

Next: GetArg Intrinsic, Previous: FTell Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.117 GError Intrinsic

         CALL GError(Message)

Message: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Returns the system error message corresponding to the last system error (C `errno`).

Next: GetCWD Intrinsic (subroutine), Previous: GError Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.118 GetArg Intrinsic

         CALL GetArg(Pos, Value)

Pos: `INTEGER` not wider than the default kind; scalar; INTENT(IN).

Value: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Sets Value to the Pos-th command-line argument (or to all blanks if there are fewer than Value command-line arguments); `CALL GETARG(0,` value`)` sets value to the name of the program (on systems that support this feature).

See IArgC Intrinsic, for information on how to get the number of arguments.

Next: GetCWD Intrinsic (function), Previous: GetArg Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.119 GetCWD Intrinsic (subroutine)

         CALL GetCWD(Name, Status)

Name: `CHARACTER`; scalar; INTENT(OUT).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Places the current working directory in Name. If the Status argument is supplied, it contains 0 success or a nonzero error code upon return (`ENOSYS` if the system does not provide `getcwd(3)` or `getwd(3)`).

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See GetCWD Intrinsic (function).

Next: GetEnv Intrinsic, Previous: GetCWD Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.120 GetCWD Intrinsic (function)

         GetCWD(Name)

GetCWD: `INTEGER(KIND=1)` function.

Name: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Places the current working directory in Name. Returns 0 on success, otherwise a nonzero error code (`ENOSYS` if the system does not provide `getcwd(3)` or `getwd(3)`).

For information on other intrinsics with the same name: See GetCWD Intrinsic (subroutine).

Next: GetGId Intrinsic, Previous: GetCWD Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.121 GetEnv Intrinsic

         CALL GetEnv(Name, Value)

Name: `CHARACTER`; scalar; INTENT(IN).

Value: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Sets Value to the value of environment variable given by the value of Name (`$name` in shell terms) or to blanks if `$name` has not been set. A null character (CHAR(0)) marks the end of the name in Name—otherwise, trailing blanks in Name are ignored.

Next: GetLog Intrinsic, Previous: GetEnv Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.122 GetGId Intrinsic

         GetGId()

GetGId: `INTEGER(KIND=1)` function.

Intrinsic groups: `unix`.

Description:

Returns the group id for the current process.

Next: GetPId Intrinsic, Previous: GetGId Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.123 GetLog Intrinsic

         CALL GetLog(Login)

Login: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Returns the login name for the process in Login.

Caution: On some systems, the `getlogin(3)` function, which this intrinsic calls at run time, is either not implemented or returns a null pointer. In the latter case, this intrinsic returns blanks in Login.

Next: GetUId Intrinsic, Previous: GetLog Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.124 GetPId Intrinsic

         GetPId()

GetPId: `INTEGER(KIND=1)` function.

Intrinsic groups: `unix`.

Description:

Returns the process id for the current process.

Next: GMTime Intrinsic, Previous: GetPId Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.125 GetUId Intrinsic

         GetUId()

GetUId: `INTEGER(KIND=1)` function.

Intrinsic groups: `unix`.

Description:

Returns the user id for the current process.

Next: HostNm Intrinsic (subroutine), Previous: GetUId Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.126 GMTime Intrinsic

         CALL GMTime(STime, TArray)

STime: `INTEGER(KIND=1)`; scalar; INTENT(IN).

TArray: `INTEGER(KIND=1)`; DIMENSION(9); INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Given a system time value STime, fills TArray with values extracted from it appropriate to the GMT time zone using `gmtime(3)`.

The array elements are as follows:

1. Seconds after the minute, range 0–59 or 0–61 to allow for leap seconds
2. Minutes after the hour, range 0–59
3. Hours past midnight, range 0–23
4. Day of month, range 0–31
5. Number of months since January, range 0–12
6. Years since 1900
7. Number of days since Sunday, range 0–6
8. Days since January 1
9. Daylight savings indicator: positive if daylight savings is in effect, zero if not, and negative if the information isn't available.

Next: HostNm Intrinsic (function), Previous: GMTime Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.127 HostNm Intrinsic (subroutine)

         CALL HostNm(Name, Status)

Name: `CHARACTER`; scalar; INTENT(OUT).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Fills Name with the system's host name returned by `gethostname(2)`. If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return (`ENOSYS` if the system does not provide `gethostname(2)`).

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

On some systems (specifically SCO) it might be necessary to link the “socket” library if you call this routine. Typically this means adding -lg2c -lsocket -lm to the `g77` command line when linking the program.

For information on other intrinsics with the same name: See HostNm Intrinsic (function).

Next: Huge Intrinsic, Previous: HostNm Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.128 HostNm Intrinsic (function)

         HostNm(Name)

HostNm: `INTEGER(KIND=1)` function.

Name: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Fills Name with the system's host name returned by `gethostname(2)`, returning 0 on success or a nonzero error code (`ENOSYS` if the system does not provide `gethostname(2)`).

On some systems (specifically SCO) it might be necessary to link the “socket” library if you call this routine. Typically this means adding -lg2c -lsocket -lm to the `g77` command line when linking the program.

For information on other intrinsics with the same name: See HostNm Intrinsic (subroutine).

Next: IAbs Intrinsic, Previous: HostNm Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.129 Huge Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Huge to use this name for an external procedure.

Next: IAChar Intrinsic, Previous: Huge Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.130 IAbs Intrinsic

         IAbs(A)

IAbs: `INTEGER(KIND=1)` function.

A: `INTEGER(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `ABS()` that is specific to one type for A. See Abs Intrinsic.

Next: IAnd Intrinsic, Previous: IAbs Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.131 IAChar Intrinsic

         IAChar(C)

IAChar: `INTEGER(KIND=1)` function.

C: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `f90`.

Description:

Returns the code for the ASCII character in the first character position of C.

See AChar Intrinsic, for the inverse of this function.

See IChar Intrinsic, for the function corresponding to the system's native character set.

Next: IArgC Intrinsic, Previous: IAChar Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.132 IAnd Intrinsic

         IAnd(I, J)

IAnd: `INTEGER` function, the exact type being the result of cross-promoting the types of all the arguments.

I: `INTEGER`; scalar; INTENT(IN).

J: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Returns value resulting from boolean AND of pair of bits in each of I and J.

Next: IBClr Intrinsic, Previous: IAnd Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.133 IArgC Intrinsic

         IArgC()

IArgC: `INTEGER(KIND=1)` function.

Intrinsic groups: `unix`.

Description:

Returns the number of command-line arguments.

This count does not include the specification of the program name itself.

Next: IBits Intrinsic, Previous: IArgC Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.134 IBClr Intrinsic

         IBClr(I, Pos)

IBClr: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar; INTENT(IN).

Pos: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Returns the value of I with bit Pos cleared (set to zero). See BTest Intrinsic, for information on bit positions.

Next: IBSet Intrinsic, Previous: IBClr Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.135 IBits Intrinsic

         IBits(I, Pos, Len)

IBits: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar; INTENT(IN).

Pos: `INTEGER`; scalar; INTENT(IN).

Len: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Extracts a subfield of length Len from I, starting from bit position Pos and extending left for Len bits. The result is right-justified and the remaining bits are zeroed. The value of Pos+Len must be less than or equal to the value BIT_SIZE(I). See Bit_Size Intrinsic.

Next: IChar Intrinsic, Previous: IBits Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.136 IBSet Intrinsic

         IBSet(I, Pos)

IBSet: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar; INTENT(IN).

Pos: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Returns the value of I with bit Pos set (to one). See BTest Intrinsic, for information on bit positions.

Next: IDate Intrinsic (UNIX), Previous: IBSet Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.137 IChar Intrinsic

         IChar(C)

IChar: `INTEGER(KIND=1)` function.

C: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the code for the character in the first character position of C.

Because the system's native character set is used, the correspondence between character and their codes is not necessarily the same between GNU Fortran implementations.

Note that no intrinsic exists to convert a printable character string to a numerical value. For example, there is no intrinsic that, given the `CHARACTER` value '154', returns an `INTEGER` or `REAL` value with the value 154.

Instead, you can use internal-file I/O to do this kind of conversion. For example:

         INTEGER VALUE
         CHARACTER*10 STRING
         STRING = '154'
         READ (STRING, '(I10)'), VALUE
         PRINT *, VALUE
         END

The above program, when run, prints:

          154

See Char Intrinsic, for the inverse of the `ICHAR` function.

See IAChar Intrinsic, for the function corresponding to the ASCII character set.

Next: IDiM Intrinsic, Previous: IChar Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.138 IDate Intrinsic (UNIX)

         CALL IDate(TArray)

TArray: `INTEGER(KIND=1)`; DIMENSION(3); INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Fills TArray with the numerical values at the current local time. The day (in the range 1–31), month (in the range 1–12), and year appear in elements 1, 2, and 3 of TArray, respectively. The year has four significant digits.

Programs making use of this intrinsic might not be Year 10000 (Y10K) compliant. For example, the date might appear, to such programs, to wrap around (change from a larger value to a smaller one) as of the Year 10000.

For information on other intrinsics with the same name: See IDate Intrinsic (VXT).

Next: IDInt Intrinsic, Previous: IDate Intrinsic (UNIX), Up: Table of Intrinsic Functions

##### 8.11.9.139 IDiM Intrinsic

         IDiM(X, Y)

IDiM: `INTEGER(KIND=1)` function.

X: `INTEGER(KIND=1)`; scalar; INTENT(IN).

Y: `INTEGER(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `DIM()` that is specific to one type for X and Y. See DiM Intrinsic.

Next: IDNInt Intrinsic, Previous: IDiM Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.140 IDInt Intrinsic

         IDInt(A)

IDInt: `INTEGER(KIND=1)` function.

A: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `INT()` that is specific to one type for A. See Int Intrinsic.

Next: IEOr Intrinsic, Previous: IDInt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.141 IDNInt Intrinsic

         IDNInt(A)

IDNInt: `INTEGER(KIND=1)` function.

A: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `NINT()` that is specific to one type for A. See NInt Intrinsic.

Next: IErrNo Intrinsic, Previous: IDNInt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.142 IEOr Intrinsic

         IEOr(I, J)

IEOr: `INTEGER` function, the exact type being the result of cross-promoting the types of all the arguments.

I: `INTEGER`; scalar; INTENT(IN).

J: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Returns value resulting from boolean exclusive-OR of pair of bits in each of I and J.

Next: IFix Intrinsic, Previous: IEOr Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.143 IErrNo Intrinsic

         IErrNo()

IErrNo: `INTEGER(KIND=1)` function.

Intrinsic groups: `unix`.

Description:

Returns the last system error number (corresponding to the C `errno`).

Next: Imag Intrinsic, Previous: IErrNo Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.144 IFix Intrinsic

         IFix(A)

IFix: `INTEGER(KIND=1)` function.

A: `REAL(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `INT()` that is specific to one type for A. See Int Intrinsic.

Next: ImagPart Intrinsic, Previous: IFix Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.145 Imag Intrinsic

         Imag(Z)

Imag: `REAL` function, the KIND= value of the type being that of argument Z.

Z: `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

The imaginary part of Z is returned, without conversion.

Note: The way to do this in standard Fortran 90 is AIMAG(Z). However, when, for example, Z is `DOUBLE COMPLEX`, AIMAG(Z) means something different for some compilers that are not true Fortran 90 compilers but offer some extensions standardized by Fortran 90 (such as the `DOUBLE COMPLEX` type, also known as `COMPLEX(KIND=2)`).

The advantage of `IMAG()` is that, while not necessarily more or less portable than `AIMAG()`, it is more likely to cause a compiler that doesn't support it to produce a diagnostic than generate incorrect code.

See REAL() and AIMAG() of Complex, for more information.

Next: Index Intrinsic, Previous: Imag Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.146 ImagPart Intrinsic

         ImagPart(Z)

ImagPart: `REAL` function, the KIND= value of the type being that of argument Z.

Z: `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: `gnu`.

Description:

The imaginary part of Z is returned, without conversion.

Note: The way to do this in standard Fortran 90 is AIMAG(Z). However, when, for example, Z is `DOUBLE COMPLEX`, AIMAG(Z) means something different for some compilers that are not true Fortran 90 compilers but offer some extensions standardized by Fortran 90 (such as the `DOUBLE COMPLEX` type, also known as `COMPLEX(KIND=2)`).

The advantage of `IMAGPART()` is that, while not necessarily more or less portable than `AIMAG()`, it is more likely to cause a compiler that doesn't support it to produce a diagnostic than generate incorrect code.

See REAL() and AIMAG() of Complex, for more information.

Next: Int Intrinsic, Previous: ImagPart Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.147 Index Intrinsic

         Index(String, Substring)

Index: `INTEGER(KIND=1)` function.

String: `CHARACTER`; scalar; INTENT(IN).

Substring: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the position of the start of the first occurrence of string Substring as a substring in String, counting from one. If Substring doesn't occur in String, zero is returned.

Next: Int2 Intrinsic, Previous: Index Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.148 Int Intrinsic

         Int(A)

Int: `INTEGER(KIND=1)` function.

A: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns A with the fractional portion of its magnitude truncated and its sign preserved, converted to type `INTEGER(KIND=1)`.

If A is type `COMPLEX`, its real part is truncated and converted, and its imaginary part is disregarded.

See NInt Intrinsic, for how to convert, rounded to nearest whole number.

See AInt Intrinsic, for how to truncate to whole number without converting.

Next: Int8 Intrinsic, Previous: Int Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.149 Int2 Intrinsic

         Int2(A)

Int2: `INTEGER(KIND=6)` function.

A: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: `gnu`.

Description:

Returns A with the fractional portion of its magnitude truncated and its sign preserved, converted to type `INTEGER(KIND=6)`.

If A is type `COMPLEX`, its real part is truncated and converted, and its imaginary part is disregarded.

See Int Intrinsic.

The precise meaning of this intrinsic might change in a future version of the GNU Fortran language, as more is learned about how it is used.

Next: IOr Intrinsic, Previous: Int2 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.150 Int8 Intrinsic

         Int8(A)

Int8: `INTEGER(KIND=2)` function.

A: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: `gnu`.

Description:

Returns A with the fractional portion of its magnitude truncated and its sign preserved, converted to type `INTEGER(KIND=2)`.

If A is type `COMPLEX`, its real part is truncated and converted, and its imaginary part is disregarded.

See Int Intrinsic.

The precise meaning of this intrinsic might change in a future version of the GNU Fortran language, as more is learned about how it is used.

Next: IRand Intrinsic, Previous: Int8 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.151 IOr Intrinsic

         IOr(I, J)

IOr: `INTEGER` function, the exact type being the result of cross-promoting the types of all the arguments.

I: `INTEGER`; scalar; INTENT(IN).

J: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Returns value resulting from boolean OR of pair of bits in each of I and J.

Next: IsaTty Intrinsic, Previous: IOr Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.152 IRand Intrinsic

         IRand(Flag)

IRand: `INTEGER(KIND=1)` function.

Flag: `INTEGER`; OPTIONAL; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns a uniform quasi-random number up to a system-dependent limit. If Flag is 0, the next number in sequence is returned; if Flag is 1, the generator is restarted by calling the UNIX function srand(0); if Flag has any other value, it is used as a new seed with `srand()`.

See SRand Intrinsic.

Note: As typically implemented (by the routine of the same name in the C library), this random number generator is a very poor one, though the BSD and GNU libraries provide a much better implementation than the `traditional' one. On a different system you almost certainly want to use something better.

Next: IShft Intrinsic, Previous: IRand Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.153 IsaTty Intrinsic

         IsaTty(Unit)

IsaTty: `LOGICAL(KIND=1)` function.

Unit: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns `.TRUE.` if and only if the Fortran I/O unit specified by Unit is connected to a terminal device. See `isatty(3)`.

Next: IShftC Intrinsic, Previous: IsaTty Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.154 IShft Intrinsic

         IShft(I, Shift)

IShft: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar; INTENT(IN).

Shift: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

All bits representing I are shifted Shift places. Shift.GT.0 indicates a left shift, Shift.EQ.0 indicates no shift and Shift.LT.0 indicates a right shift. If the absolute value of the shift count is greater than BIT_SIZE(I), the result is undefined. Bits shifted out from the left end or the right end are lost. Zeros are shifted in from the opposite end.

See IShftC Intrinsic, for the circular-shift equivalent.

Next: ISign Intrinsic, Previous: IShft Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.155 IShftC Intrinsic

         IShftC(I, Shift, Size)

IShftC: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar; INTENT(IN).

Shift: `INTEGER`; scalar; INTENT(IN).

Size: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

The rightmost Size bits of the argument I are shifted circularly Shift places, i.e. the bits shifted out of one end are shifted into the opposite end. No bits are lost. The unshifted bits of the result are the same as the unshifted bits of I. The absolute value of the argument Shift must be less than or equal to Size. The value of Size must be greater than or equal to one and less than or equal to BIT_SIZE(I).

See IShft Intrinsic, for the logical shift equivalent.

Next: ITime Intrinsic, Previous: IShftC Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.156 ISign Intrinsic

         ISign(A, B)

ISign: `INTEGER(KIND=1)` function.

A: `INTEGER(KIND=1)`; scalar; INTENT(IN).

B: `INTEGER(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `SIGN()` that is specific to one type for A and B. See Sign Intrinsic.

Next: Kill Intrinsic (subroutine), Previous: ISign Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.157 ITime Intrinsic

         CALL ITime(TArray)

TArray: `INTEGER(KIND=1)`; DIMENSION(3); INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Returns the current local time hour, minutes, and seconds in elements 1, 2, and 3 of TArray, respectively.

Next: Kind Intrinsic, Previous: ITime Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.158 Kill Intrinsic (subroutine)

         CALL Kill(Pid, Signal, Status)

Pid: `INTEGER`; scalar; INTENT(IN).

Signal: `INTEGER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Sends the signal specified by Signal to the process Pid. If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return. See `kill(2)`.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See Kill Intrinsic (function).

Next: LBound Intrinsic, Previous: Kill Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.159 Kind Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Kind to use this name for an external procedure.

Next: Len Intrinsic, Previous: Kind Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.160 LBound Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL LBound to use this name for an external procedure.

Next: Len_Trim Intrinsic, Previous: LBound Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.161 Len Intrinsic

         Len(String)

Len: `INTEGER(KIND=1)` function.

String: `CHARACTER`; scalar.

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the length of String.

If String is an array, the length of an element of String is returned.

Note that String need not be defined when this intrinsic is invoked, since only the length, not the content, of String is needed.

See Bit_Size Intrinsic, for the function that determines the size of its argument in bits.

Next: LGe Intrinsic, Previous: Len Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.162 Len_Trim Intrinsic

         Len_Trim(String)

Len_Trim: `INTEGER(KIND=1)` function.

String: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `f90`.

Description:

Returns the index of the last non-blank character in String. `LNBLNK` and `LEN_TRIM` are equivalent.

Next: LGt Intrinsic, Previous: Len_Trim Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.163 LGe Intrinsic

         LGe(String_A, String_B)

LGe: `LOGICAL(KIND=1)` function.

String_A: `CHARACTER`; scalar; INTENT(IN).

String_B: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns .TRUE. if String_A.GE.String_B, .FALSE. otherwise. String_A and String_B are interpreted as containing ASCII character codes. If either value contains a character not in the ASCII character set, the result is processor dependent.

If the String_A and String_B are not the same length, the shorter is compared as if spaces were appended to it to form a value that has the same length as the longer.

The lexical comparison intrinsics `LGe`, `LGt`, `LLe`, and `LLt` differ from the corresponding intrinsic operators `.GE.`, `.GT.`, `.LE.`, `.LT.`. Because the ASCII collating sequence is assumed, the following expressions always return .TRUE.:

         LGE ('0', ' ')
         LGE ('A', '0')
         LGE ('a', 'A')

The following related expressions do not always return .TRUE., as they are not necessarily evaluated assuming the arguments use ASCII encoding:

         '0' .GE. ' '
         'A' .GE. '0'
         'a' .GE. 'A'

The same difference exists between `LGt` and `.GT.`; between `LLe` and `.LE.`; and between `LLt` and `.LT.`.

Next: Link Intrinsic (subroutine), Previous: LGe Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.164 LGt Intrinsic

         LGt(String_A, String_B)

LGt: `LOGICAL(KIND=1)` function.

String_A: `CHARACTER`; scalar; INTENT(IN).

String_B: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns .TRUE. if String_A.GT.String_B, .FALSE. otherwise. String_A and String_B are interpreted as containing ASCII character codes. If either value contains a character not in the ASCII character set, the result is processor dependent.

If the String_A and String_B are not the same length, the shorter is compared as if spaces were appended to it to form a value that has the same length as the longer.

See LGe Intrinsic, for information on the distinction between the `LGT` intrinsic and the `.GT.` operator.

Next: LLe Intrinsic, Previous: LGt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.165 Link Intrinsic (subroutine)

         CALL Link(Path1, Path2, Status)

Path1: `CHARACTER`; scalar; INTENT(IN).

Path2: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Makes a (hard) link from file Path1 to Path2. A null character (CHAR(0)) marks the end of the names in Path1 and Path2—otherwise, trailing blanks in Path1 and Path2 are ignored. If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return. See `link(2)`.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See Link Intrinsic (function).

Next: LLt Intrinsic, Previous: Link Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.166 LLe Intrinsic

         LLe(String_A, String_B)

LLe: `LOGICAL(KIND=1)` function.

String_A: `CHARACTER`; scalar; INTENT(IN).

String_B: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns .TRUE. if String_A.LE.String_B, .FALSE. otherwise. String_A and String_B are interpreted as containing ASCII character codes. If either value contains a character not in the ASCII character set, the result is processor dependent.

If the String_A and String_B are not the same length, the shorter is compared as if spaces were appended to it to form a value that has the same length as the longer.

See LGe Intrinsic, for information on the distinction between the `LLE` intrinsic and the `.LE.` operator.

Next: LnBlnk Intrinsic, Previous: LLe Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.167 LLt Intrinsic

         LLt(String_A, String_B)

LLt: `LOGICAL(KIND=1)` function.

String_A: `CHARACTER`; scalar; INTENT(IN).

String_B: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns .TRUE. if String_A.LT.String_B, .FALSE. otherwise. String_A and String_B are interpreted as containing ASCII character codes. If either value contains a character not in the ASCII character set, the result is processor dependent.

If the String_A and String_B are not the same length, the shorter is compared as if spaces were appended to it to form a value that has the same length as the longer.

See LGe Intrinsic, for information on the distinction between the `LLT` intrinsic and the `.LT.` operator.

Next: Loc Intrinsic, Previous: LLt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.168 LnBlnk Intrinsic

         LnBlnk(String)

LnBlnk: `INTEGER(KIND=1)` function.

String: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns the index of the last non-blank character in String. `LNBLNK` and `LEN_TRIM` are equivalent.

Next: Log Intrinsic, Previous: LnBlnk Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.169 Loc Intrinsic

         Loc(Entity)

Loc: `INTEGER(KIND=7)` function.

Entity: Any type; cannot be a constant or expression.

Intrinsic groups: `unix`.

Description:

The `LOC()` intrinsic works the same way as the `%LOC()` construct. See The `%LOC()` Construct, for more information.

Next: Log10 Intrinsic, Previous: Loc Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.170 Log Intrinsic

         Log(X)

Log: `REAL` or `COMPLEX` function, the exact type being that of argument X.

X: `REAL` or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the natural logarithm of X, which must be greater than zero or, if type `COMPLEX`, must not be zero.

See Exp Intrinsic, for the inverse of this function.

See Log10 Intrinsic, for the `common' (base-10) logarithm function.

Next: Logical Intrinsic, Previous: Log Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.171 Log10 Intrinsic

         Log10(X)

Log10: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the common logarithm (base 10) of X, which must be greater than zero.

The inverse of this function is 10. ** LOG10(X).

See Log Intrinsic, for the natural logarithm function.

Next: Long Intrinsic, Previous: Log10 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.172 Logical Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Logical to use this name for an external procedure.

Next: LShift Intrinsic, Previous: Logical Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.173 Long Intrinsic

         Long(A)

Long: `INTEGER(KIND=1)` function.

A: `INTEGER(KIND=6)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Archaic form of `INT()` that is specific to one type for A. See Int Intrinsic.

The precise meaning of this intrinsic might change in a future version of the GNU Fortran language, as more is learned about how it is used.

Next: LStat Intrinsic (subroutine), Previous: Long Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.174 LShift Intrinsic

         LShift(I, Shift)

LShift: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar; INTENT(IN).

Shift: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Returns I shifted to the left Shift bits.

Although similar to the expression I*(2**Shift), there are important differences. For example, the sign of the result is not necessarily the same as the sign of I.

Currently this intrinsic is defined assuming the underlying representation of I is as a two's-complement integer. It is unclear at this point whether that definition will apply when a different representation is involved.

See LShift Intrinsic, for the inverse of this function.

See IShft Intrinsic, for information on a more widely available left-shifting intrinsic that is also more precisely defined.

Next: LStat Intrinsic (function), Previous: LShift Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.175 LStat Intrinsic (subroutine)

         CALL LStat(File, SArray, Status)

File: `CHARACTER`; scalar; INTENT(IN).

SArray: `INTEGER(KIND=1)`; DIMENSION(13); INTENT(OUT).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Obtains data about the given file File and places them in the array SArray. A null character (CHAR(0)) marks the end of the name in File—otherwise, trailing blanks in File are ignored. If File is a symbolic link it returns data on the link itself, so the routine is available only on systems that support symbolic links. The values in this array are extracted from the `stat` structure as returned by `fstat(2)` q.v., as follows:

1. Device ID
2. Inode number
3. File mode
4. Number of links
5. Owner's uid
6. Owner's gid
7. ID of device containing directory entry for file (0 if not available)
8. File size (bytes)
9. Last access time
10. Last modification time
11. Last file status change time
12. Preferred I/O block size (-1 if not available)
13. Number of blocks allocated (-1 if not available)

Not all these elements are relevant on all systems. If an element is not relevant, it is returned as 0.

If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return (`ENOSYS` if the system does not provide `lstat(2)`).

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See LStat Intrinsic (function).

Next: LTime Intrinsic, Previous: LStat Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.176 LStat Intrinsic (function)

         LStat(File, SArray)

LStat: `INTEGER(KIND=1)` function.

File: `CHARACTER`; scalar; INTENT(IN).

SArray: `INTEGER(KIND=1)`; DIMENSION(13); INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Obtains data about the given file File and places them in the array SArray. A null character (CHAR(0)) marks the end of the name in File—otherwise, trailing blanks in File are ignored. If File is a symbolic link it returns data on the link itself, so the routine is available only on systems that support symbolic links. The values in this array are extracted from the `stat` structure as returned by `fstat(2)` q.v., as follows:

1. Device ID
2. Inode number
3. File mode
4. Number of links
5. Owner's uid
6. Owner's gid
7. ID of device containing directory entry for file (0 if not available)
8. File size (bytes)
9. Last access time
10. Last modification time
11. Last file status change time
12. Preferred I/O block size (-1 if not available)
13. Number of blocks allocated (-1 if not available)

Not all these elements are relevant on all systems. If an element is not relevant, it is returned as 0.

Returns 0 on success or a nonzero error code (`ENOSYS` if the system does not provide `lstat(2)`).

For information on other intrinsics with the same name: See LStat Intrinsic (subroutine).

Next: MatMul Intrinsic, Previous: LStat Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.177 LTime Intrinsic

         CALL LTime(STime, TArray)

STime: `INTEGER(KIND=1)`; scalar; INTENT(IN).

TArray: `INTEGER(KIND=1)`; DIMENSION(9); INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Given a system time value STime, fills TArray with values extracted from it appropriate to the GMT time zone using `localtime(3)`.

The array elements are as follows:

1. Seconds after the minute, range 0–59 or 0–61 to allow for leap seconds
2. Minutes after the hour, range 0–59
3. Hours past midnight, range 0–23
4. Day of month, range 0–31
5. Number of months since January, range 0–12
6. Years since 1900
7. Number of days since Sunday, range 0–6
8. Days since January 1
9. Daylight savings indicator: positive if daylight savings is in effect, zero if not, and negative if the information isn't available.

Next: Max Intrinsic, Previous: LTime Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.178 MatMul Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL MatMul to use this name for an external procedure.

Next: Max0 Intrinsic, Previous: MatMul Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.179 Max Intrinsic

         Max(A-1, A-2, ..., A-n)

Max: `INTEGER` or `REAL` function, the exact type being the result of cross-promoting the types of all the arguments.

A: `INTEGER` or `REAL`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the argument with the largest value.

See Min Intrinsic, for the opposite function.

Next: Max1 Intrinsic, Previous: Max Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.180 Max0 Intrinsic

         Max0(A-1, A-2, ..., A-n)

Max0: `INTEGER(KIND=1)` function.

A: `INTEGER(KIND=1)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MAX()` that is specific to one type for A. See Max Intrinsic.

Next: MaxExponent Intrinsic, Previous: Max0 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.181 Max1 Intrinsic

         Max1(A-1, A-2, ..., A-n)

Max1: `INTEGER(KIND=1)` function.

A: `REAL(KIND=1)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MAX()` that is specific to one type for A and a different return type. See Max Intrinsic.

Next: MaxLoc Intrinsic, Previous: Max1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.182 MaxExponent Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL MaxExponent to use this name for an external procedure.

Next: MaxVal Intrinsic, Previous: MaxExponent Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.183 MaxLoc Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL MaxLoc to use this name for an external procedure.

Next: MClock Intrinsic, Previous: MaxLoc Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.184 MaxVal Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL MaxVal to use this name for an external procedure.

Next: MClock8 Intrinsic, Previous: MaxVal Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.185 MClock Intrinsic

         MClock()

MClock: `INTEGER(KIND=1)` function.

Intrinsic groups: `unix`.

Description:

Returns the number of clock ticks since the start of the process. Supported on systems with `clock(3)` (q.v.).

This intrinsic is not fully portable, such as to systems with 32-bit `INTEGER` types but supporting times wider than 32 bits. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

See MClock8 Intrinsic, for information on a similar intrinsic that might be portable to more GNU Fortran implementations, though to fewer Fortran compilers.

If the system does not support `clock(3)`, -1 is returned.

Next: Merge Intrinsic, Previous: MClock Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.186 MClock8 Intrinsic

         MClock8()

MClock8: `INTEGER(KIND=2)` function.

Intrinsic groups: `unix`.

Description:

Returns the number of clock ticks since the start of the process. Supported on systems with `clock(3)` (q.v.).

Warning: this intrinsic does not increase the range of the timing values over that returned by `clock(3)`. On a system with a 32-bit `clock(3)`, `MCLOCK8` will return a 32-bit value, even though converted to an INTEGER(KIND=2) value. That means overflows of the 32-bit value can still occur. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

No Fortran implementations other than GNU Fortran are known to support this intrinsic at the time of this writing. See MClock Intrinsic, for information on a similar intrinsic that might be portable to more Fortran compilers, though to fewer GNU Fortran implementations.

If the system does not support `clock(3)`, -1 is returned.

Next: Min Intrinsic, Previous: MClock8 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.187 Merge Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Merge to use this name for an external procedure.

Next: Min0 Intrinsic, Previous: Merge Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.188 Min Intrinsic

         Min(A-1, A-2, ..., A-n)

Min: `INTEGER` or `REAL` function, the exact type being the result of cross-promoting the types of all the arguments.

A: `INTEGER` or `REAL`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the argument with the smallest value.

See Max Intrinsic, for the opposite function.

Next: Min1 Intrinsic, Previous: Min Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.189 Min0 Intrinsic

         Min0(A-1, A-2, ..., A-n)

Min0: `INTEGER(KIND=1)` function.

A: `INTEGER(KIND=1)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MIN()` that is specific to one type for A. See Min Intrinsic.

Next: MinExponent Intrinsic, Previous: Min0 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.190 Min1 Intrinsic

         Min1(A-1, A-2, ..., A-n)

Min1: `INTEGER(KIND=1)` function.

A: `REAL(KIND=1)`; at least two such arguments must be provided; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `MIN()` that is specific to one type for A and a different return type. See Min Intrinsic.

Next: MinLoc Intrinsic, Previous: Min1 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.191 MinExponent Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL MinExponent to use this name for an external procedure.

Next: MinVal Intrinsic, Previous: MinExponent Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.192 MinLoc Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL MinLoc to use this name for an external procedure.

Next: Mod Intrinsic, Previous: MinLoc Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.193 MinVal Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL MinVal to use this name for an external procedure.

Next: Modulo Intrinsic, Previous: MinVal Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.194 Mod Intrinsic

         Mod(A, P)

Mod: `INTEGER` or `REAL` function, the exact type being the result of cross-promoting the types of all the arguments.

A: `INTEGER` or `REAL`; scalar; INTENT(IN).

P: `INTEGER` or `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns remainder calculated as:

         A - (INT(A / P) * P)

P must not be zero.

Next: MvBits Intrinsic, Previous: Mod Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.195 Modulo Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Modulo to use this name for an external procedure.

Next: Nearest Intrinsic, Previous: Modulo Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.196 MvBits Intrinsic

         CALL MvBits(From, FromPos, Len, TO, ToPos)

From: `INTEGER`; scalar; INTENT(IN).

FromPos: `INTEGER`; scalar; INTENT(IN).

Len: `INTEGER`; scalar; INTENT(IN).

TO: `INTEGER` with same KIND= value as for From; scalar; INTENT(INOUT).

ToPos: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Moves Len bits from positions FromPos through FromPos+Len-1 of From to positions ToPos through FromPos+Len-1 of TO. The portion of argument TO not affected by the movement of bits is unchanged. Arguments From and TO are permitted to be the same numeric storage unit. The values of FromPos+Len and ToPos+Len must be less than or equal to BIT_SIZE(From).

Next: NInt Intrinsic, Previous: MvBits Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.197 Nearest Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Nearest to use this name for an external procedure.

Next: Not Intrinsic, Previous: Nearest Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.198 NInt Intrinsic

         NInt(A)

NInt: `INTEGER(KIND=1)` function.

A: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns A with the fractional portion of its magnitude eliminated by rounding to the nearest whole number and with its sign preserved, converted to type `INTEGER(KIND=1)`.

If A is type `COMPLEX`, its real part is rounded and converted.

A fractional portion exactly equal to .5 is rounded to the whole number that is larger in magnitude. (Also called “Fortran round”.)

See Int Intrinsic, for how to convert, truncate to whole number.

See ANInt Intrinsic, for how to round to nearest whole number without converting.

Next: Or Intrinsic, Previous: NInt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.199 Not Intrinsic

         Not(I)

Not: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `mil`, `f90`, `vxt`.

Description:

Returns value resulting from boolean NOT of each bit in I.

Next: Pack Intrinsic, Previous: Not Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.200 Or Intrinsic

         Or(I, J)

Or: `INTEGER` or `LOGICAL` function, the exact type being the result of cross-promoting the types of all the arguments.

I: `INTEGER` or `LOGICAL`; scalar; INTENT(IN).

J: `INTEGER` or `LOGICAL`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Returns value resulting from boolean OR of pair of bits in each of I and J.

Next: PError Intrinsic, Previous: Or Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.201 Pack Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Pack to use this name for an external procedure.

Next: Precision Intrinsic, Previous: Pack Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.202 PError Intrinsic

         CALL PError(String)

String: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Prints (on the C `stderr` stream) a newline-terminated error message corresponding to the last system error. This is prefixed by String, a colon and a space. See `perror(3)`.

Next: Present Intrinsic, Previous: PError Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.203 Precision Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Precision to use this name for an external procedure.

Next: Product Intrinsic, Previous: Precision Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.204 Present Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Present to use this name for an external procedure.

Next: Radix Intrinsic, Previous: Present Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.205 Product Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Product to use this name for an external procedure.

Next: Rand Intrinsic, Previous: Product Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.206 Radix Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Radix to use this name for an external procedure.

Next: Random_Number Intrinsic, Previous: Radix Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.207 Rand Intrinsic

         Rand(Flag)

Rand: `REAL(KIND=1)` function.

Flag: `INTEGER`; OPTIONAL; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns a uniform quasi-random number between 0 and 1. If Flag is 0, the next number in sequence is returned; if Flag is 1, the generator is restarted by calling srand(0); if Flag has any other value, it is used as a new seed with `srand`.

See SRand Intrinsic.

Note: As typically implemented (by the routine of the same name in the C library), this random number generator is a very poor one, though the BSD and GNU libraries provide a much better implementation than the `traditional' one. On a different system you almost certainly want to use something better.

Next: Random_Seed Intrinsic, Previous: Rand Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.208 Random_Number Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Random_Number to use this name for an external procedure.

Next: Range Intrinsic, Previous: Random_Number Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.209 Random_Seed Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Random_Seed to use this name for an external procedure.

Next: Real Intrinsic, Previous: Random_Seed Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.210 Range Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Range to use this name for an external procedure.

Next: RealPart Intrinsic, Previous: Range Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.211 Real Intrinsic

         Real(A)

Real: `REAL` function. The exact type is REAL(KIND=1) when argument A is any type other than `COMPLEX`, or when it is `COMPLEX(KIND=1)`. When A is any `COMPLEX` type other than `COMPLEX(KIND=1)`, this intrinsic is valid only when used as the argument to `REAL()`, as explained below.

A: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Converts A to `REAL(KIND=1)`.

Use of `REAL()` with a `COMPLEX` argument (other than `COMPLEX(KIND=1)`) is restricted to the following case:

         REAL(REAL(A))

This expression converts the real part of A to `REAL(KIND=1)`.

See RealPart Intrinsic, for information on a GNU Fortran intrinsic that extracts the real part of an arbitrary `COMPLEX` value.

See REAL() and AIMAG() of Complex, for more information.

Next: Rename Intrinsic (subroutine), Previous: Real Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.212 RealPart Intrinsic

         RealPart(Z)

RealPart: `REAL` function, the KIND= value of the type being that of argument Z.

Z: `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: `gnu`.

Description:

The real part of Z is returned, without conversion.

Note: The way to do this in standard Fortran 90 is REAL(Z). However, when, for example, Z is `COMPLEX(KIND=2)`, REAL(Z) means something different for some compilers that are not true Fortran 90 compilers but offer some extensions standardized by Fortran 90 (such as the `DOUBLE COMPLEX` type, also known as `COMPLEX(KIND=2)`).

The advantage of `REALPART()` is that, while not necessarily more or less portable than `REAL()`, it is more likely to cause a compiler that doesn't support it to produce a diagnostic than generate incorrect code.

See REAL() and AIMAG() of Complex, for more information.

Next: Repeat Intrinsic, Previous: RealPart Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.213 Rename Intrinsic (subroutine)

         CALL Rename(Path1, Path2, Status)

Path1: `CHARACTER`; scalar; INTENT(IN).

Path2: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Renames the file Path1 to Path2. A null character (CHAR(0)) marks the end of the names in Path1 and Path2—otherwise, trailing blanks in Path1 and Path2 are ignored. See `rename(2)`. If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See Rename Intrinsic (function).

Next: Reshape Intrinsic, Previous: Rename Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.214 Repeat Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Repeat to use this name for an external procedure.

Next: RRSpacing Intrinsic, Previous: Repeat Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.215 Reshape Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Reshape to use this name for an external procedure.

Next: RShift Intrinsic, Previous: Reshape Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.216 RRSpacing Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL RRSpacing to use this name for an external procedure.

Next: Scale Intrinsic, Previous: RRSpacing Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.217 RShift Intrinsic

         RShift(I, Shift)

RShift: `INTEGER` function, the KIND= value of the type being that of argument I.

I: `INTEGER`; scalar; INTENT(IN).

Shift: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Returns I shifted to the right Shift bits.

Although similar to the expression I/(2**Shift), there are important differences. For example, the sign of the result is undefined.

Currently this intrinsic is defined assuming the underlying representation of I is as a two's-complement integer. It is unclear at this point whether that definition will apply when a different representation is involved.

See RShift Intrinsic, for the inverse of this function.

See IShft Intrinsic, for information on a more widely available right-shifting intrinsic that is also more precisely defined.

Next: Scan Intrinsic, Previous: RShift Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.218 Scale Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Scale to use this name for an external procedure.

Next: Second Intrinsic (function), Previous: Scale Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.219 Scan Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Scan to use this name for an external procedure.

Next: Second Intrinsic (subroutine), Previous: Scan Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.220 Second Intrinsic (function)

         Second()

Second: `REAL(KIND=1)` function.

Intrinsic groups: `unix`.

Description:

Returns the process's runtime in seconds—the same value as the UNIX function `etime` returns.

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wraparounds) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

For information on other intrinsics with the same name: See Second Intrinsic (subroutine).

Next: Selected_Int_Kind Intrinsic, Previous: Second Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.221 Second Intrinsic (subroutine)

         CALL Second(Seconds)

Seconds: `REAL`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Returns the process's runtime in seconds in Seconds—the same value as the UNIX function `etime` returns.

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wraparounds) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

This routine is known from Cray Fortran. See CPU_Time Intrinsic, for a standard equivalent.

For information on other intrinsics with the same name: See Second Intrinsic (function).

Next: Selected_Real_Kind Intrinsic, Previous: Second Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.222 Selected_Int_Kind Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Selected_Int_Kind to use this name for an external procedure.

Next: Set_Exponent Intrinsic, Previous: Selected_Int_Kind Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.223 Selected_Real_Kind Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Selected_Real_Kind to use this name for an external procedure.

Next: Shape Intrinsic, Previous: Selected_Real_Kind Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.224 Set_Exponent Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Set_Exponent to use this name for an external procedure.

Next: Short Intrinsic, Previous: Set_Exponent Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.225 Shape Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Shape to use this name for an external procedure.

Next: Sign Intrinsic, Previous: Shape Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.226 Short Intrinsic

         Short(A)

Short: `INTEGER(KIND=6)` function.

A: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns A with the fractional portion of its magnitude truncated and its sign preserved, converted to type `INTEGER(KIND=6)`.

If A is type `COMPLEX`, its real part is truncated and converted, and its imaginary part is disregarded.

See Int Intrinsic.

The precise meaning of this intrinsic might change in a future version of the GNU Fortran language, as more is learned about how it is used.

Next: Signal Intrinsic (subroutine), Previous: Short Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.227 Sign Intrinsic

         Sign(A, B)

Sign: `INTEGER` or `REAL` function, the exact type being the result of cross-promoting the types of all the arguments.

A: `INTEGER` or `REAL`; scalar; INTENT(IN).

B: `INTEGER` or `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns ABS(A)*s, where s is +1 if B.GE.0, -1 otherwise.

See Abs Intrinsic, for the function that returns the magnitude of a value.

Next: Sin Intrinsic, Previous: Sign Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.228 Signal Intrinsic (subroutine)

         CALL Signal(Number, Handler, Status)

Number: `INTEGER`; scalar; INTENT(IN).

Handler: Signal handler (`INTEGER FUNCTION` or `SUBROUTINE`) or dummy/global `INTEGER(KIND=1)` scalar.

Status: `INTEGER(KIND=7)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

If Handler is a an `EXTERNAL` routine, arranges for it to be invoked with a single integer argument (of system-dependent length) when signal Number occurs. If Handler is an integer, it can be used to turn off handling of signal Number or revert to its default action. See `signal(2)`.

Note that Handler will be called using C conventions, so the value of its argument in Fortran terms Fortran terms is obtained by applying `%LOC()` (or `LOC()`) to it.

The value returned by `signal(2)` is written to Status, if that argument is supplied. Otherwise the return value is ignored.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

Warning: Use of the `libf2c` run-time library function signal_ directly (such as via EXTERNAL SIGNAL) requires use of the `%VAL()` construct to pass an `INTEGER` value (such as SIG_IGN or SIG_DFL) for the Handler argument.

However, while CALL SIGNAL(signum, %VAL(SIG_IGN)) works when SIGNAL is treated as an external procedure (and resolves, at link time, to `libf2c`'s signal_ routine), this construct is not valid when SIGNAL is recognized as the intrinsic of that name.

Therefore, for maximum portability and reliability, code such references to the SIGNAL facility as follows:

         INTRINSIC SIGNAL
         ...
         CALL SIGNAL(signum, SIG_IGN)

`g77` will compile such a call correctly, while other compilers will generally either do so as well or reject the INTRINSIC SIGNAL statement via a diagnostic, allowing you to take appropriate action.

For information on other intrinsics with the same name: See Signal Intrinsic (function).

Next: SinH Intrinsic, Previous: Signal Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.229 Sin Intrinsic

         Sin(X)

Sin: `REAL` or `COMPLEX` function, the exact type being that of argument X.

X: `REAL` or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the sine of X, an angle measured in radians.

See ASin Intrinsic, for the inverse of this function.

Next: Sleep Intrinsic, Previous: Sin Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.230 SinH Intrinsic

         SinH(X)

SinH: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the hyperbolic sine of X.

Next: Sngl Intrinsic, Previous: SinH Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.231 Sleep Intrinsic

         CALL Sleep(Seconds)

Seconds: `INTEGER(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Causes the process to pause for Seconds seconds. See `sleep(2)`.

Next: Spacing Intrinsic, Previous: Sleep Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.232 Sngl Intrinsic

         Sngl(A)

Sngl: `REAL(KIND=1)` function.

A: `REAL(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Archaic form of `REAL()` that is specific to one type for A. See Real Intrinsic.

Next: Spread Intrinsic, Previous: Sngl Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.233 Spacing Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Spacing to use this name for an external procedure.

Next: SqRt Intrinsic, Previous: Spacing Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.234 Spread Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Spread to use this name for an external procedure.

Next: SRand Intrinsic, Previous: Spread Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.235 SqRt Intrinsic

         SqRt(X)

SqRt: `REAL` or `COMPLEX` function, the exact type being that of argument X.

X: `REAL` or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the square root of X, which must not be negative.

To calculate and represent the square root of a negative number, complex arithmetic must be used. For example, SQRT(COMPLEX(X)).

The inverse of this function is SQRT(X) * SQRT(X).

Next: Stat Intrinsic (subroutine), Previous: SqRt Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.236 SRand Intrinsic

         CALL SRand(Seed)

Seed: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Reinitializes the generator with the seed in Seed. See IRand Intrinsic. See Rand Intrinsic.

Next: Stat Intrinsic (function), Previous: SRand Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.237 Stat Intrinsic (subroutine)

         CALL Stat(File, SArray, Status)

File: `CHARACTER`; scalar; INTENT(IN).

SArray: `INTEGER(KIND=1)`; DIMENSION(13); INTENT(OUT).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Obtains data about the given file File and places them in the array SArray. A null character (CHAR(0)) marks the end of the name in File—otherwise, trailing blanks in File are ignored. The values in this array are extracted from the `stat` structure as returned by `fstat(2)` q.v., as follows:

1. Device ID
2. Inode number
3. File mode
4. Number of links
5. Owner's uid
6. Owner's gid
7. ID of device containing directory entry for file (0 if not available)
8. File size (bytes)
9. Last access time
10. Last modification time
11. Last file status change time
12. Preferred I/O block size (-1 if not available)
13. Number of blocks allocated (-1 if not available)

Not all these elements are relevant on all systems. If an element is not relevant, it is returned as 0.

If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See Stat Intrinsic (function).

Next: Sum Intrinsic, Previous: Stat Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.238 Stat Intrinsic (function)

         Stat(File, SArray)

Stat: `INTEGER(KIND=1)` function.

File: `CHARACTER`; scalar; INTENT(IN).

SArray: `INTEGER(KIND=1)`; DIMENSION(13); INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Obtains data about the given file File and places them in the array SArray. A null character (CHAR(0)) marks the end of the name in File—otherwise, trailing blanks in File are ignored. The values in this array are extracted from the `stat` structure as returned by `fstat(2)` q.v., as follows:

1. Device ID
2. Inode number
3. File mode
4. Number of links
5. Owner's uid
6. Owner's gid
7. ID of device containing directory entry for file (0 if not available)
8. File size (bytes)
9. Last access time
10. Last modification time
11. Last file status change time
12. Preferred I/O block size (-1 if not available)
13. Number of blocks allocated (-1 if not available)

Not all these elements are relevant on all systems. If an element is not relevant, it is returned as 0.

Returns 0 on success or a nonzero error code.

For information on other intrinsics with the same name: See Stat Intrinsic (subroutine).

Next: SymLnk Intrinsic (subroutine), Previous: Stat Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.239 Sum Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Sum to use this name for an external procedure.

Next: System Intrinsic (subroutine), Previous: Sum Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.240 SymLnk Intrinsic (subroutine)

         CALL SymLnk(Path1, Path2, Status)

Path1: `CHARACTER`; scalar; INTENT(IN).

Path2: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Makes a symbolic link from file Path1 to Path2. A null character (CHAR(0)) marks the end of the names in Path1 and Path2—otherwise, trailing blanks in Path1 and Path2 are ignored. If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return (`ENOSYS` if the system does not provide `symlink(2)`).

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See SymLnk Intrinsic (function).

Next: System_Clock Intrinsic, Previous: SymLnk Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.241 System Intrinsic (subroutine)

         CALL System(Command, Status)

Command: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Passes the command Command to a shell (see `system(3)`). If argument Status is present, it contains the value returned by `system(3)`, presumably 0 if the shell command succeeded. Note that which shell is used to invoke the command is system-dependent and environment-dependent.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See System Intrinsic (function).

Next: Tan Intrinsic, Previous: System Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.242 System_Clock Intrinsic

         CALL System_Clock(Count, Rate, Max)

Count: `INTEGER(KIND=1)`; scalar; INTENT(OUT).

Rate: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Max: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `f90`.

Description:

Returns in Count the current value of the system clock; this is the value returned by the UNIX function `times(2)` in this implementation, but isn't in general. Rate is the number of clock ticks per second and Max is the maximum value this can take, which isn't very useful in this implementation since it's just the maximum C `unsigned int` value.

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wraparounds) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

Next: TanH Intrinsic, Previous: System_Clock Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.243 Tan Intrinsic

         Tan(X)

Tan: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the tangent of X, an angle measured in radians.

See ATan Intrinsic, for the inverse of this function.

Next: Time Intrinsic (UNIX), Previous: Tan Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.244 TanH Intrinsic

         TanH(X)

TanH: `REAL` function, the KIND= value of the type being that of argument X.

X: `REAL`; scalar; INTENT(IN).

Intrinsic groups: (standard FORTRAN 77).

Description:

Returns the hyperbolic tangent of X.

Next: Time8 Intrinsic, Previous: TanH Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.245 Time Intrinsic (UNIX)

         Time()

Time: `INTEGER(KIND=1)` function.

Intrinsic groups: `unix`.

Description:

Returns the current time encoded as an integer (in the manner of the UNIX function `time(3)`). This value is suitable for passing to `CTIME`, `GMTIME`, and `LTIME`.

This intrinsic is not fully portable, such as to systems with 32-bit `INTEGER` types but supporting times wider than 32 bits. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

See Time8 Intrinsic, for information on a similar intrinsic that might be portable to more GNU Fortran implementations, though to fewer Fortran compilers.

For information on other intrinsics with the same name: See Time Intrinsic (VXT).

Next: Tiny Intrinsic, Previous: Time Intrinsic (UNIX), Up: Table of Intrinsic Functions

##### 8.11.9.246 Time8 Intrinsic

         Time8()

Time8: `INTEGER(KIND=2)` function.

Intrinsic groups: `unix`.

Description:

Returns the current time encoded as a long integer (in the manner of the UNIX function `time(3)`). This value is suitable for passing to `CTIME`, `GMTIME`, and `LTIME`.

Warning: this intrinsic does not increase the range of the timing values over that returned by `time(3)`. On a system with a 32-bit `time(3)`, `TIME8` will return a 32-bit value, even though converted to an INTEGER(KIND=2) value. That means overflows of the 32-bit value can still occur. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

No Fortran implementations other than GNU Fortran are known to support this intrinsic at the time of this writing. See Time Intrinsic (UNIX), for information on a similar intrinsic that might be portable to more Fortran compilers, though to fewer GNU Fortran implementations.

Next: Transfer Intrinsic, Previous: Time8 Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.247 Tiny Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Tiny to use this name for an external procedure.

Next: Transpose Intrinsic, Previous: Tiny Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.248 Transfer Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Transfer to use this name for an external procedure.

Next: Trim Intrinsic, Previous: Transfer Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.249 Transpose Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Transpose to use this name for an external procedure.

Next: TtyNam Intrinsic (subroutine), Previous: Transpose Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.250 Trim Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Trim to use this name for an external procedure.

Next: TtyNam Intrinsic (function), Previous: Trim Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.251 TtyNam Intrinsic (subroutine)

         CALL TtyNam(Unit, Name)

Unit: `INTEGER`; scalar; INTENT(IN).

Name: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Sets Name to the name of the terminal device open on logical unit Unit or to a blank string if Unit is not connected to a terminal.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine.

For information on other intrinsics with the same name: See TtyNam Intrinsic (function).

Next: UBound Intrinsic, Previous: TtyNam Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.252 TtyNam Intrinsic (function)

         TtyNam(Unit)

TtyNam: `CHARACTER*(*)` function.

Unit: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `unix`.

Description:

Returns the name of the terminal device open on logical unit Unit or a blank string if Unit is not connected to a terminal.

For information on other intrinsics with the same name: See TtyNam Intrinsic (subroutine).

Next: UMask Intrinsic (subroutine), Previous: TtyNam Intrinsic (function), Up: Table of Intrinsic Functions

##### 8.11.9.253 UBound Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL UBound to use this name for an external procedure.

Next: Unlink Intrinsic (subroutine), Previous: UBound Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.254 UMask Intrinsic (subroutine)

         CALL UMask(Mask, Old)

Mask: `INTEGER`; scalar; INTENT(IN).

Old: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Sets the file creation mask to Mask and returns the old value in argument Old if it is supplied. See `umask(2)`.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine.

For information on other intrinsics with the same name: See UMask Intrinsic (function).

Next: Unpack Intrinsic, Previous: UMask Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.255 Unlink Intrinsic (subroutine)

         CALL Unlink(File, Status)

File: `CHARACTER`; scalar; INTENT(IN).

Status: `INTEGER(KIND=1)`; OPTIONAL; scalar; INTENT(OUT).

Intrinsic groups: `unix`.

Description:

Unlink the file File. A null character (CHAR(0)) marks the end of the name in File—otherwise, trailing blanks in File are ignored. If the Status argument is supplied, it contains 0 on success or a nonzero error code upon return. See `unlink(2)`.

Some non-GNU implementations of Fortran provide this intrinsic as only a function, not as a subroutine, or do not support the (optional) Status argument.

For information on other intrinsics with the same name: See Unlink Intrinsic (function).

Next: Verify Intrinsic, Previous: Unlink Intrinsic (subroutine), Up: Table of Intrinsic Functions

##### 8.11.9.256 Unpack Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Unpack to use this name for an external procedure.

Next: XOr Intrinsic, Previous: Unpack Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.257 Verify Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL Verify to use this name for an external procedure.

Next: ZAbs Intrinsic, Previous: Verify Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.258 XOr Intrinsic

         XOr(I, J)

XOr: `INTEGER` or `LOGICAL` function, the exact type being the result of cross-promoting the types of all the arguments.

I: `INTEGER` or `LOGICAL`; scalar; INTENT(IN).

J: `INTEGER` or `LOGICAL`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Returns value resulting from boolean exclusive-OR of pair of bits in each of I and J.

Next: ZCos Intrinsic, Previous: XOr Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.259 ZAbs Intrinsic

         ZAbs(A)

ZAbs: `REAL(KIND=2)` function.

A: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Archaic form of `ABS()` that is specific to one type for A. See Abs Intrinsic.

Next: ZExp Intrinsic, Previous: ZAbs Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.260 ZCos Intrinsic

         ZCos(X)

ZCos: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Archaic form of `COS()` that is specific to one type for X. See Cos Intrinsic.

Next: ZLog Intrinsic, Previous: ZCos Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.261 ZExp Intrinsic

         ZExp(X)

ZExp: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Archaic form of `EXP()` that is specific to one type for X. See Exp Intrinsic.

Next: ZSin Intrinsic, Previous: ZExp Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.262 ZLog Intrinsic

         ZLog(X)

ZLog: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Archaic form of `LOG()` that is specific to one type for X. See Log Intrinsic.

Next: ZSqRt Intrinsic, Previous: ZLog Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.263 ZSin Intrinsic

         ZSin(X)

ZSin: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Archaic form of `SIN()` that is specific to one type for X. See Sin Intrinsic.

Previous: ZSin Intrinsic, Up: Table of Intrinsic Functions

##### 8.11.9.264 ZSqRt Intrinsic

         ZSqRt(X)

ZSqRt: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`.

Description:

Archaic form of `SQRT()` that is specific to one type for X. See SqRt Intrinsic.

Next: I/O, Previous: Functions and Subroutines, Up: Language

### 8.12 Scope and Classes of Symbolic Names

(The following information augments or overrides the information in Chapter 18 of ANSI X3.9-1978 FORTRAN 77 in specifying the GNU Fortran language. Chapter 18 of that document otherwise serves as the basis for the relevant aspects of GNU Fortran.)

Up: Scope and Classes of Names

#### 8.12.1 Underscores in Symbol Names

Underscores (_) are accepted in symbol names after the first character (which must be a letter).

Next: Fortran 90 Features, Previous: Scope and Classes of Names, Up: Language

### 8.13 I/O

A dollar sign at the end of an output format specification suppresses the newline at the end of the output.

Edit descriptors in `FORMAT` statements may contain compile-time `INTEGER` constant expressions in angle brackets, such as

         10    FORMAT (I<WIDTH>)

The `OPEN` specifier `NAME=` is equivalent to `FILE=`.

These Fortran 90 features are supported:

- The `O` and `Z` edit descriptors are supported for I/O of integers in octal and hexadecimal formats, respectively.
- The `FILE=` specifier may be omitted in an `OPEN` statement if `STATUS='SCRATCH'` is supplied. The `STATUS='REPLACE'` specifier is supported.

Previous: I/O, Up: Language

### 8.14 Fortran 90 Features

For convenience this section collects a list (probably incomplete) of the Fortran 90 features supported by the GNU Fortran language, even if they are documented elsewhere. See Characters, Lines, and Execution Sequence, for information on additional fixed source form lexical issues. Further, the free source form is supported through the -ffree-form option. Other Fortran 90 features can be turned on by the -ff90 option; see Fortran 90. For information on the Fortran 90 intrinsics available, see Table of Intrinsic Functions.

Automatic arrays in procedures
Character assignments
  In character assignments, the variable being assigned may occur on the right hand side of the assignment.
Character strings
  Strings may have zero length and substrings of character constants are permitted. Character constants may be enclosed in double quotes (`"`) as well as single quotes. See Character Type.
Construct names
  (Symbolic tags on blocks.) See Construct Names.
`CYCLE` and `EXIT`
  See The `CYCLE` and `EXIT` Statements.
`DOUBLE COMPLEX`
  See `DOUBLE COMPLEX` Statement.
`DO WHILE`
  See DO WHILE.
`END` decoration
  See Statements.
`END DO`
  See END DO.
`KIND`
`IMPLICIT NONE`
`INCLUDE` statements
  See INCLUDE.
List-directed and namelist I/O on internal files
Binary, octal and hexadecimal constants
  These are supported more generally than required by Fortran 90. See Integer Type.
O and Z edit descriptors
`NAMELIST`
  See NAMELIST.
`OPEN` specifiers
  `STATUS='REPLACE'` is supported. The `FILE=` specifier may be omitted in an `OPEN` statement if `STATUS='SCRATCH'` is supplied.
`FORMAT` edit descriptors
  The `Z` edit descriptor is supported.
Relational operators
  The operators `<`, `<=`, `==`, `/=`, `>` and `>=` may be used instead of `.LT.`, `.LE.`, `.EQ.`, `.NE.`, `.GT.` and `.GE.` respectively.
`SELECT CASE`
  Not fully implemented. See `SELECT CASE` on `CHARACTER` Type.
Specification statements
  A limited subset of the Fortran 90 syntax and semantics for variable declarations is supported, including `KIND`. See Kind Notation. (`KIND` is of limited usefulness in the absence of the `KIND`-related intrinsics, since these intrinsics permit writing more widely portable code.) An example of supported `KIND` usage is:

                INTEGER (KIND=1) :: FOO=1, BAR=2
                CHARACTER (LEN=3) FOO

  `PARAMETER` and `DIMENSION` attributes aren't supported.

Next: Other Compilers, Previous: Compiler, Up: Top

## 9 Other Dialects

GNU Fortran supports a variety of features that are not considered part of the GNU Fortran language itself, but are representative of various dialects of Fortran that g77 supports in whole or in part.

Any of the features listed below might be disallowed by g77 unless some command-line option is specified. Currently, some of the features are accepted using the default invocation of g77, but that might change in the future.

Note: This portion of the documentation definitely needs a lot of work!

Next: Trailing Comment, Up: Other Dialects

### 9.1 Source Form

GNU Fortran accepts programs written in either fixed form or free form.

Fixed form corresponds to ANSI FORTRAN 77 (plus popular extensions, such as allowing tabs) and Fortran 90's fixed form.

Free form corresponds to Fortran 90's free form (though possibly not entirely up-to-date, and without complaining about some things that for which Fortran 90 requires diagnostics, such as the spaces in the constant in R = 3 . 1).

The way a Fortran compiler views source files depends entirely on the implementation choices made for the compiler, since those choices are explicitly left to the implementation by the published Fortran standards. GNU Fortran currently tries to be somewhat like a few popular compilers (f2c, Digital (“DEC”) Fortran, and so on).

This section describes how g77 interprets source lines.

Next: Tabs, Up: Source Form

#### 9.1.1 Carriage Returns

Carriage returns (\r) in source lines are ignored. This is somewhat different from f2c, which seems to treat them as spaces outside character/Hollerith constants, and encodes them as \r inside such constants.

Next: Short Lines, Previous: Carriage Returns, Up: Source Form

#### 9.1.2 Tabs

A source line with a <TAB> character anywhere in it is treated as entirely significant—however long it is—instead of ending in column 72 (for fixed-form source) or 132 (for free-form source). This also is different from f2c, which encodes tabs as \t (the ASCII <TAB> character) inside character and Hollerith constants, but nevertheless seems to treat the column position as if it had been affected by the canonical tab positioning.

g77 effectively translates tabs to the appropriate number of spaces (a la the default for the UNIX expand command) before doing any other processing, other than (currently) noting whether a tab was found on a line and using this information to decide how to interpret the length of the line and continued constants.

Next: Long Lines, Previous: Tabs, Up: Source Form

#### 9.1.3 Short Lines

Source lines shorter than the applicable fixed-form length are treated as if they were padded with spaces to that length. (None of this is relevant to source files written in free form.)

This affects only continued character and Hollerith constants, and is a different interpretation than provided by some other popular compilers (although a bit more consistent with the traditional punched-card basis of Fortran and the way the Fortran standard expressed fixed source form).

g77 might someday offer an option to warn about cases where differences might be seen as a result of this treatment, and perhaps an option to specify the alternate behavior as well.

Note that this padding cannot apply to lines that are effectively of infinite length—such lines are specified using command-line options like -ffixed-line-length-none, for example.

Next: Ampersands, Previous: Short Lines, Up: Source Form

#### 9.1.4 Long Lines

Source lines longer than the applicable length are truncated to that length. Currently, g77 does not warn if the truncated characters are not spaces, to accommodate existing code written for systems that treated truncated text as commentary (especially in columns 73 through 80).

See Options Controlling Fortran Dialect, for information on the -ffixed-line-length-n option, which can be used to set the line length applicable to fixed-form source files.

Previous: Long Lines, Up: Source Form

#### 9.1.5 Ampersand Continuation Line

A & in column 1 of fixed-form source denotes an arbitrary-length continuation line, imitating the behavior of f2c.

Next: Debug Line, Previous: Source Form, Up: Other Dialects

### 9.2 Trailing Comment

g77 supports use of /* to start a trailing comment. In the GNU Fortran language, ! is used for this purpose.

/* is not in the GNU Fortran language because the use of /* in a program might suggest to some readers that a block, not trailing, comment is started (and thus ended by */, not end of line), since that is the meaning of /* in C.

Also, such readers might think they can use // to start a trailing comment as an alternative to /*, but // already denotes concatenation, and such a “comment” might actually result in a program that compiles without error (though it would likely behave incorrectly).

Next: Dollar Signs, Previous: Trailing Comment, Up: Other Dialects

### 9.3 Debug Line

Use of D or d as the first character (column 1) of a source line denotes a debug line.

In turn, a debug line is treated as either a comment line or a normal line, depending on whether debug lines are enabled.

When treated as a comment line, a line beginning with D or d is treated as if it the first character was C or c, respectively. When treated as a normal line, such a line is treated as if the first character was <SPC> (space).

(Currently, g77 provides no means for treating debug lines as normal lines.)

Next: Case Sensitivity, Previous: Debug Line, Up: Other Dialects

### 9.4 Dollar Signs in Symbol Names

Dollar signs ($) are allowed in symbol names (after the first character) when the -fdollar-ok option is specified.

Next: VXT Fortran, Previous: Dollar Signs, Up: Other Dialects

### 9.5 Case Sensitivity

GNU Fortran offers the programmer way too much flexibility in deciding how source files are to be treated vis-a-vis uppercase and lowercase characters. There are 66 useful settings that affect case sensitivity, plus 10 settings that are nearly useless, with the remaining 116 settings being either redundant or useless.

None of these settings have any effect on the contents of comments (the text after a c or C in Column 1, for example) or of character or Hollerith constants. Note that things like the E in the statement CALL FOO(3.2E10) and the TO in ASSIGN 10 TO LAB are considered built-in keywords, and so are affected by these settings.

Low-level switches are identified in this section as follows:

- A Source Case Conversion:
  - 0 Preserve (see Note 1)
  - 1 Convert to Upper Case
  - 2 Convert to Lower Case
- B Built-in Keyword Matching:
  - 0 Match Any Case (per-character basis)
  - 1 Match Upper Case Only
  - 2 Match Lower Case Only
  - 3 Match InitialCaps Only (see tables for spellings)
- C Built-in Intrinsic Matching:
  - 0 Match Any Case (per-character basis)
  - 1 Match Upper Case Only
  - 2 Match Lower Case Only
  - 3 Match InitialCaps Only (see tables for spellings)
- D User-defined Symbol Possibilities (warnings only):
  - 0 Allow Any Case (per-character basis)
  - 1 Allow Upper Case Only
  - 2 Allow Lower Case Only
  - 3 Allow InitialCaps Only (see Note 2)

Note 1: g77 eventually will support `NAMELIST` in a manner that is consistent with these source switches—in the sense that input will be expected to meet the same requirements as source code in terms of matching symbol names and keywords (for the exponent letters).

Currently, however, `NAMELIST` is supported by `libg2c`, which uppercases `NAMELIST` input and symbol names for matching. This means not only that `NAMELIST` output currently shows symbol (and keyword) names in uppercase even if lower-case source conversion (option A2) is selected, but that `NAMELIST` cannot be adequately supported when source case preservation (option A0) is selected.

If A0 is selected, a warning message will be output for each `NAMELIST` statement to this effect. The behavior of the program is undefined at run time if two or more symbol names appear in a given `NAMELIST` such that the names are identical when converted to upper case (e.g. NAMELIST /X/ VAR, Var, var). For complete and total elegance, perhaps there should be a warning when option A2 is selected, since the output of NAMELIST is currently in uppercase but will someday be lowercase (when a `libg77` is written), but that seems to be overkill for a product in beta test.

Note 2: Rules for InitialCaps names are:

- Must be a single uppercase letter, or
- Must start with an uppercase letter and contain at least one lowercase letter.

So A, Ab, ABc, AbC, and Abc are valid InitialCaps names, but AB, A2, and ABC are not. Note that most, but not all, built-in names meet these requirements—the exceptions are some of the two-letter format specifiers, such as `BN` and `BZ`.

Here are the names of the corresponding command-line options:

         A0: -fsource-case-preserve
         A1: -fsource-case-upper
         A2: -fsource-case-lower

         B0: -fmatch-case-any
         B1: -fmatch-case-upper
         B2: -fmatch-case-lower
         B3: -fmatch-case-initcap

         C0: -fintrin-case-any
         C1: -fintrin-case-upper
         C2: -fintrin-case-lower
         C3: -fintrin-case-initcap

         D0: -fsymbol-case-any
         D1: -fsymbol-case-upper
         D2: -fsymbol-case-lower
         D3: -fsymbol-case-initcap

Useful combinations of the above settings, along with abbreviated option names that set some of these combinations all at once:

          1: A0--  B0---  C0---  D0---    -fcase-preserve
          2: A0--  B0---  C0---  D-1--
          3: A0--  B0---  C0---  D--2-
          4: A0--  B0---  C0---  D---3
          5: A0--  B0---  C-1--  D0---
          6: A0--  B0---  C-1--  D-1--
          7: A0--  B0---  C-1--  D--2-
          8: A0--  B0---  C-1--  D---3
          9: A0--  B0---  C--2-  D0---
         10: A0--  B0---  C--2-  D-1--
         11: A0--  B0---  C--2-  D--2-
         12: A0--  B0---  C--2-  D---3
         13: A0--  B0---  C---3  D0---
         14: A0--  B0---  C---3  D-1--
         15: A0--  B0---  C---3  D--2-
         16: A0--  B0---  C---3  D---3
         17: A0--  B-1--  C0---  D0---
         18: A0--  B-1--  C0---  D-1--
         19: A0--  B-1--  C0---  D--2-
         20: A0--  B-1--  C0---  D---3
         21: A0--  B-1--  C-1--  D0---
         22: A0--  B-1--  C-1--  D-1--    -fcase-strict-upper
         23: A0--  B-1--  C-1--  D--2-
         24: A0--  B-1--  C-1--  D---3
         25: A0--  B-1--  C--2-  D0---
         26: A0--  B-1--  C--2-  D-1--
         27: A0--  B-1--  C--2-  D--2-
         28: A0--  B-1--  C--2-  D---3
         29: A0--  B-1--  C---3  D0---
         30: A0--  B-1--  C---3  D-1--
         31: A0--  B-1--  C---3  D--2-
         32: A0--  B-1--  C---3  D---3
         33: A0--  B--2-  C0---  D0---
         34: A0--  B--2-  C0---  D-1--
         35: A0--  B--2-  C0---  D--2-
         36: A0--  B--2-  C0---  D---3
         37: A0--  B--2-  C-1--  D0---
         38: A0--  B--2-  C-1--  D-1--
         39: A0--  B--2-  C-1--  D--2-
         40: A0--  B--2-  C-1--  D---3
         41: A0--  B--2-  C--2-  D0---
         42: A0--  B--2-  C--2-  D-1--
         43: A0--  B--2-  C--2-  D--2-    -fcase-strict-lower
         44: A0--  B--2-  C--2-  D---3
         45: A0--  B--2-  C---3  D0---
         46: A0--  B--2-  C---3  D-1--
         47: A0--  B--2-  C---3  D--2-
         48: A0--  B--2-  C---3  D---3
         49: A0--  B---3  C0---  D0---
         50: A0--  B---3  C0---  D-1--
         51: A0--  B---3  C0---  D--2-
         52: A0--  B---3  C0---  D---3
         53: A0--  B---3  C-1--  D0---
         54: A0--  B---3  C-1--  D-1--
         55: A0--  B---3  C-1--  D--2-
         56: A0--  B---3  C-1--  D---3
         57: A0--  B---3  C--2-  D0---
         58: A0--  B---3  C--2-  D-1--
         59: A0--  B---3  C--2-  D--2-
         60: A0--  B---3  C--2-  D---3
         61: A0--  B---3  C---3  D0---
         62: A0--  B---3  C---3  D-1--
         63: A0--  B---3  C---3  D--2-
         64: A0--  B---3  C---3  D---3    -fcase-initcap
         65: A-1-  B01--  C01--  D01--    -fcase-upper
         66: A--2  B0-2-  C0-2-  D0-2-    -fcase-lower

Number 22 is the “strict” ANSI FORTRAN 77 model wherein all input (except comments, character constants, and Hollerith strings) must be entered in uppercase. Use -fcase-strict-upper to specify this combination.

Number 43 is like Number 22 except all input must be lowercase. Use -fcase-strict-lower to specify this combination.

Number 65 is the “classic” ANSI FORTRAN 77 model as implemented on many non-UNIX machines whereby all the source is translated to uppercase. Use -fcase-upper to specify this combination.

Number 66 is the “canonical” UNIX model whereby all the source is translated to lowercase. Use -fcase-lower to specify this combination.

There are a few nearly useless combinations:

         67: A-1-  B01--  C01--  D--2-
         68: A-1-  B01--  C01--  D---3
         69: A-1-  B01--  C--23  D01--
         70: A-1-  B01--  C--23  D--2-
         71: A-1-  B01--  C--23  D---3
         72: A--2  B01--  C0-2-  D-1--
         73: A--2  B01--  C0-2-  D---3
         74: A--2  B01--  C-1-3  D0-2-
         75: A--2  B01--  C-1-3  D-1--
         76: A--2  B01--  C-1-3  D---3

The above allow some programs to be compiled but with restrictions that make most useful programs impossible: Numbers 67 and 72 warn about any user-defined symbol names (such as SUBROUTINE FOO); Numbers 68 and 73 warn about any user-defined symbol names longer than one character that don't have at least one non-alphabetic character after the first; Numbers 69 and 74 disallow any references to intrinsics; and Numbers 70, 71, 75, and 76 are combinations of the restrictions in 67+69, 68+69, 72+74, and 73+74, respectively.

All redundant combinations are shown in the above tables anyplace where more than one setting is shown for a low-level switch. For example, B0-2- means either setting 0 or 2 is valid for switch B. The “proper” setting in such a case is the one that copies the setting of switch A—any other setting might slightly reduce the speed of the compiler, though possibly to an unmeasurable extent.

All remaining combinations are useless in that they prevent successful compilation of non-null source files (source files with something other than comments).

Next: Fortran 90, Previous: Case Sensitivity, Up: Other Dialects

### 9.6 VXT Fortran

g77 supports certain constructs that have different meanings in VXT Fortran than they do in the GNU Fortran language.

Generally, this manual uses the invented term VXT Fortran to refer VAX FORTRAN (circa v4). That compiler offered many popular features, though not necessarily those that are specific to the VAX processor architecture, the VMS operating system, or Digital Equipment Corporation's Fortran product line. (VAX and VMS probably are trademarks of Digital Equipment Corporation.)

An extension offered by a Digital Fortran product that also is offered by several other Fortran products for different kinds of systems is probably going to be considered for inclusion in g77 someday, and is considered a VXT Fortran feature.

The -fvxt option generally specifies that, where the meaning of a construct is ambiguous (means one thing in GNU Fortran and another in VXT Fortran), the VXT Fortran meaning is to be assumed.

Next: Exclamation Point, Up: VXT Fortran

#### 9.6.1 Meaning of Double Quote

g77 treats double-quote (") as beginning an octal constant of `INTEGER(KIND=1)` type when the -fvxt option is specified. The form of this octal constant is

         "octal-digits

where octal-digits is a nonempty string of characters in the set 01234567.

For example, the -fvxt option permits this:

         PRINT *, "20
         END

The above program would print the value 16.

See Integer Type, for information on the preferred construct for integer constants specified using GNU Fortran's octal notation.

(In the GNU Fortran language, the double-quote character (") delimits a character constant just as does apostrophe ('). There is no way to allow both constructs in the general case, since statements like PRINT *,"2000 !comment?" would be ambiguous.)

Previous: Double Quote Meaning, Up: VXT Fortran

#### 9.6.2 Meaning of Exclamation Point in Column 6

g77 treats an exclamation point (!) in column 6 of a fixed-form source file as a continuation character rather than as the beginning of a comment (as it does in any other column) when the -fvxt option is specified.

The following program, when run, prints a message indicating whether it is interpreted according to GNU Fortran (and Fortran 90) rules or VXT Fortran rules:

         C234567  (This line begins in column 1.)
               I = 0
              !1
               IF (I.EQ.0) PRINT *, ' I am a VXT Fortran program'
               IF (I.EQ.1) PRINT *, ' I am a Fortran 90 program'
               IF (I.LT.0 .OR. I.GT.1) PRINT *, ' I am a HAL 9000 computer'
               END

(In the GNU Fortran and Fortran 90 languages, exclamation point is a valid character and, unlike space (<SPC>) or zero (0), marks a line as a continuation line when it appears in column 6.)

Next: Pedantic Compilation, Previous: VXT Fortran, Up: Other Dialects

### 9.7 Fortran 90

The GNU Fortran language includes a number of features that are part of Fortran 90, even when the -ff90 option is not specified. The features enabled by -ff90 are intended to be those that, when -ff90 is not specified, would have another meaning to g77—usually meaning something invalid in the GNU Fortran language.

So, the purpose of -ff90 is not to specify whether g77 is to gratuitously reject Fortran 90 constructs. The -pedantic option specified with -fno-f90 is intended to do that, although its implementation is certainly incomplete at this point.

When -ff90 is specified:

- The type of REAL(expr) and AIMAG(expr), where expr is `COMPLEX` type, is the same type as the real part of expr.

  For example, assuming Z is type `COMPLEX(KIND=2)`, REAL(Z) would return a value of type `REAL(KIND=2)`, not of type `REAL(KIND=1)`, since -ff90 is specified.

Next: Distensions, Previous: Fortran 90, Up: Other Dialects

### 9.8 Pedantic Compilation

The -fpedantic command-line option specifies that g77 is to warn about code that is not standard-conforming. This is useful for finding some extensions g77 accepts that other compilers might not accept. (Note that the -pedantic and -pedantic-errors options always imply -fpedantic.)

With -fno-f90 in force, ANSI FORTRAN 77 is used as the standard for conforming code. With -ff90 in force, Fortran 90 is used.

The constructs for which g77 issues diagnostics when -fpedantic and -fno-f90 are in force are:

- Automatic arrays, as in

                SUBROUTINE X(N)
                REAL A(N)
                ...

  where A is not listed in any `ENTRY` statement, and thus is not a dummy argument.

- The commas in READ (5), I and WRITE (10), J.

  These commas are disallowed by FORTRAN 77, but, while strictly superfluous, are syntactically elegant, especially given that commas are required in statements such as READ 99, I and PRINT *, J. Many compilers permit the superfluous commas for this reason.

- `DOUBLE COMPLEX`, either explicitly or implicitly.

  An explicit use of this type is via a `DOUBLE COMPLEX` or `IMPLICIT DOUBLE COMPLEX` statement, for examples.

  An example of an implicit use is the expression C*D, where C is `COMPLEX(KIND=1)` and D is `DOUBLE PRECISION`. This expression is prohibited by ANSI FORTRAN 77 because the rules of promotion would suggest that it produce a `DOUBLE COMPLEX` result—a type not provided for by that standard.

- Automatic conversion of numeric expressions to `INTEGER(KIND=1)` in contexts such as:
  - Array-reference indexes.
  - Alternate-return values.
  - Computed `GOTO`.
  - `FORMAT` run-time expressions (not yet supported).
  - Dimension lists in specification statements.
  - Numbers for I/O statements (such as READ (UNIT=3.2), I)
  - Sizes of `CHARACTER` entities in specification statements.
  - Kind types in specification entities (a Fortran 90 feature).
  - Initial, terminal, and incrementation parameters for implied-`DO` constructs in `DATA` statements.
- Automatic conversion of `LOGICAL` expressions to `INTEGER` in contexts such as arithmetic `IF` (where `COMPLEX` expressions are disallowed anyway).
- Zero-size array dimensions, as in:

                INTEGER I(10,20,4:2)

- Zero-length `CHARACTER` entities, as in:

                PRINT *, ''

- Substring operators applied to character constants and named constants, as in:

                PRINT *, 'hello'(3:5)

- Null arguments passed to statement function, as in:

                PRINT *, FOO(,3)

- Disagreement among program units regarding whether a given `COMMON` area is `SAVE`d (for targets where program units in a single source file are “glued” together as they typically are for UNIX development environments).
- Disagreement among program units regarding the size of a named `COMMON` block.
- Specification statements following first `DATA` statement.

  (In the GNU Fortran language, DATA I/1/ may be followed by INTEGER J, but not INTEGER I. The -fpedantic option disallows both of these.)

- Semicolon as statement separator, as in:

                CALL FOO; CALL BAR

- Use of & in column 1 of fixed-form source (to indicate continuation).
- Use of `CHARACTER` constants to initialize numeric entities, and vice versa.
- Expressions having two arithmetic operators in a row, such as X*-Y.

If -fpedantic is specified along with -ff90, the following constructs result in diagnostics:

- Use of semicolon as a statement separator on a line that has an `INCLUDE` directive.

Previous: Pedantic Compilation, Up: Other Dialects

### 9.9 Distensions

The -fugly-* command-line options determine whether certain features supported by VAX FORTRAN and other such compilers, but considered too ugly to be in code that can be changed to use safer and/or more portable constructs, are accepted. These are humorously referred to as “distensions”, extensions that just plain look ugly in the harsh light of day.

Next: Ugly Assumed-Size Arrays, Up: Distensions

#### 9.9.1 Implicit Argument Conversion

The -fno-ugly-args option disables passing typeless and Hollerith constants as actual arguments in procedure invocations. For example:

         CALL FOO(4HABCD)
         CALL BAR('123'O)

These constructs can be too easily used to create non-portable code, but are not considered as “ugly” as others. Further, they are widely used in existing Fortran source code in ways that often are quite portable. Therefore, they are enabled by default.

Next: Ugly Null Arguments, Previous: Ugly Implicit Argument Conversion, Up: Distensions

#### 9.9.2 Ugly Assumed-Size Arrays

The -fugly-assumed option enables the treatment of any array with a final dimension specified as 1 as an assumed-size array, as if * had been specified instead.

For example, DIMENSION X(1) is treated as if it had read DIMENSION X(*) if X is listed as a dummy argument in a preceding `SUBROUTINE`, `FUNCTION`, or `ENTRY` statement in the same program unit.

Use an explicit lower bound to avoid this interpretation. For example, DIMENSION X(1:1) is never treated as if it had read DIMENSION X(*) or DIMENSION X(1:*). Nor is DIMENSION X(2-1) affected by this option, since that kind of expression is unlikely to have been intended to designate an assumed-size array.

This option is used to prevent warnings being issued about apparent out-of-bounds reference such as X(2) = 99.

It also prevents the array from being used in contexts that disallow assumed-size arrays, such as PRINT *,X. In such cases, a diagnostic is generated and the source file is not compiled.

The construct affected by this option is used only in old code that pre-exists the widespread acceptance of adjustable and assumed-size arrays in the Fortran community.

Note: This option does not affect how DIMENSION X(1) is treated if X is listed as a dummy argument only after the `DIMENSION` statement (presumably in an `ENTRY` statement). For example, -fugly-assumed has no effect on the following program unit:

         SUBROUTINE X
         REAL A(1)
         RETURN
         ENTRY Y(A)
         PRINT *, A
         END

Next: Ugly Conversion of Initializers, Previous: Ugly Null Arguments, Up: Distensions

#### 9.9.3 Ugly Complex Part Extraction

The -fugly-complex option enables use of the `REAL()` and `AIMAG()` intrinsics with arguments that are `COMPLEX` types other than `COMPLEX(KIND=1)`.

With -ff90 in effect, these intrinsics return the unconverted real and imaginary parts (respectively) of their argument.

With -fno-f90 in effect, these intrinsics convert the real and imaginary parts to `REAL(KIND=1)`, and return the result of that conversion.

Due to this ambiguity, the GNU Fortran language defines these constructs as invalid, except in the specific case where they are entirely and solely passed as an argument to an invocation of the `REAL()` intrinsic. For example,

         REAL(REAL(Z))

is permitted even when Z is `COMPLEX(KIND=2)` and -fno-ugly-complex is in effect, because the meaning is clear.

g77 enforces this restriction, unless -fugly-complex is specified, in which case the appropriate interpretation is chosen and no diagnostic is issued.

See CMPAMBIG, for information on how to cope with existing code with unclear expectations of `REAL()` and `AIMAG()` with `COMPLEX(KIND=2)` arguments.

See RealPart Intrinsic, for information on the `REALPART()` intrinsic, used to extract the real part of a complex expression without conversion. See ImagPart Intrinsic, for information on the `IMAGPART()` intrinsic, used to extract the imaginary part of a complex expression without conversion.

Next: Ugly Complex Part Extraction, Previous: Ugly Assumed-Size Arrays, Up: Distensions

#### 9.9.4 Ugly Null Arguments

The -fugly-comma option enables use of a single trailing comma to mean “pass an extra trailing null argument” in a list of actual arguments to an external procedure, and use of an empty list of arguments to such a procedure to mean “pass a single null argument”.

(Null arguments often are used in some procedure-calling schemes to indicate omitted arguments.)

For example, CALL FOO(,) means “pass two null arguments”, rather than “pass one null argument”. Also, CALL BAR() means “pass one null argument”.

This construct is considered “ugly” because it does not provide an elegant way to pass a single null argument that is syntactically distinct from passing no arguments. That is, this construct changes the meaning of code that makes no use of the construct.

So, with -fugly-comma in force, CALL FOO() and I = JFUNC() pass a single null argument, instead of passing no arguments as required by the Fortran 77 and 90 standards.

Note: Many systems gracefully allow the case where a procedure call passes one extra argument that the called procedure does not expect.

So, in practice, there might be no difference in the behavior of a program that does CALL FOO() or I = JFUNC() and is compiled with -fugly-comma in force as compared to its behavior when compiled with the default, -fno-ugly-comma, in force, assuming FOO and JFUNC do not expect any arguments to be passed.

Next: Ugly Integer Conversions, Previous: Ugly Complex Part Extraction, Up: Distensions

#### 9.9.5 Ugly Conversion of Initializers

The constructs disabled by -fno-ugly-init are:

- Use of Hollerith and typeless constants in contexts where they set initial (compile-time) values for variables, arrays, and named constants—that is, `DATA` and `PARAMETER` statements, plus type-declaration statements specifying initial values.

  Here are some sample initializations that are disabled by the -fno-ugly-init option:

                PARAMETER (VAL='9A304FFE'X)
                REAL*8 STRING/8HOUTPUT00/
                DATA VAR/4HABCD/

- In the same contexts as above, use of character constants to initialize numeric items and vice versa (one constant per item).

  Here are more sample initializations that are disabled by the -fno-ugly-init option:

                INTEGER IA
                CHARACTER BELL
                PARAMETER (IA = 'A')
                PARAMETER (BELL = 7)

- Use of Hollerith and typeless constants on the right-hand side of assignment statements to numeric types, and in other contexts (such as passing arguments in invocations of intrinsic procedures and statement functions) that are treated as assignments to known types (the dummy arguments, in these cases).

  Here are sample statements that are disabled by the -fno-ugly-init option:

                IVAR = 4HABCD
                PRINT *, IMAX0(2HAB, 2HBA)

The above constructs, when used, can tend to result in non-portable code. But, they are widely used in existing Fortran code in ways that often are quite portable. Therefore, they are enabled by default.

Next: Ugly Assigned Labels, Previous: Ugly Conversion of Initializers, Up: Distensions

#### 9.9.6 Ugly Integer Conversions

The constructs enabled via -fugly-logint are:

- Automatic conversion between `INTEGER` and `LOGICAL` as dictated by context (typically implies nonportable dependencies on how a particular implementation encodes `.TRUE.` and `.FALSE.`).
- Use of a `LOGICAL` variable in `ASSIGN` and assigned-`GOTO` statements.

The above constructs are disabled by default because use of them tends to lead to non-portable code. Even existing Fortran code that uses that often turns out to be non-portable, if not outright buggy.

Some of this is due to differences among implementations as far as how `.TRUE.` and `.FALSE.` are encoded as `INTEGER` values—Fortran code that assumes a particular coding is likely to use one of the above constructs, and is also likely to not work correctly on implementations using different encodings.

See Equivalence Versus Equality, for more information.

Previous: Ugly Integer Conversions, Up: Distensions

#### 9.9.7 Ugly Assigned Labels

The -fugly-assign option forces g77 to use the same storage for assigned labels as it would for a normal assignment to the same variable.

For example, consider the following code fragment:

         I = 3
         ASSIGN 10 TO I

Normally, for portability and improved diagnostics, g77 reserves distinct storage for a “sibling” of I, used only for `ASSIGN` statements to that variable (along with the corresponding assigned-`GOTO` and assigned-`FORMAT`-I/O statements that reference the variable).

However, some code (that violates the ANSI FORTRAN 77 standard) attempts to copy assigned labels among variables involved with `ASSIGN` statements, as in:

         ASSIGN 10 TO I
         ISTATE(5) = I
         ...
         J = ISTATE(ICUR)
         GOTO J

Such code doesn't work under g77 unless -fugly-assign is specified on the command-line, ensuring that the value of `I` referenced in the second line is whatever value g77 uses to designate statement label 10, so the value may be copied into the ISTATE array, later retrieved into a variable of the appropriate type (J), and used as the target of an assigned-`GOTO` statement.

Note: To avoid subtle program bugs, when -fugly-assign is specified, g77 requires the type of variables specified in assigned-label contexts must be the same type returned by `%LOC()`. On many systems, this type is effectively the same as `INTEGER(KIND=1)`, while, on others, it is effectively the same as `INTEGER(KIND=2)`.

Do not depend on g77 actually writing valid pointers to these variables, however. While g77 currently chooses that implementation, it might be changed in the future.

See Assigned Statement Labels (ASSIGN and GOTO), for implementation details on assigned-statement labels.

Next: Other Dialects, Previous: Language, Up: Top

## 10 The GNU Fortran Compiler

The GNU Fortran compiler, g77, supports programs written in the GNU Fortran language and in some other dialects of Fortran.

Some aspects of how g77 works are universal regardless of dialect, and yet are not properly part of the GNU Fortran language itself. These are described below.

Note: This portion of the documentation definitely needs a lot of work!

Next: Run-time Environment Limits, Up: Compiler

### 10.1 Compiler Limits

g77, as with GNU tools in general, imposes few arbitrary restrictions on lengths of identifiers, number of continuation lines, number of external symbols in a program, and so on.

For example, some other Fortran compiler have an option (such as -Nl x) to increase the limit on the number of continuation lines. Also, some Fortran compilation systems have an option (such as -Nx x) to increase the limit on the number of external symbols.

g77, gcc, and GNU ld (the GNU linker) have no equivalent options, since they do not impose arbitrary limits in these areas.

g77 does currently limit the number of dimensions in an array to the same degree as do the Fortran standards—seven (7). This restriction might be lifted in a future version.

Next: Compiler Types, Previous: Compiler Limits, Up: Compiler

### 10.2 Run-time Environment Limits

As a portable Fortran implementation, g77 offers its users direct access to, and otherwise depends upon, the underlying facilities of the system used to build g77, the system on which g77 itself is used to compile programs, and the system on which the g77-compiled program is actually run. (For most users, the three systems are of the same type—combination of operating environment and hardware—often the same physical system.)

The run-time environment for a particular system inevitably imposes some limits on a program's use of various system facilities. These limits vary from system to system.

Even when such limits might be well beyond the possibility of being encountered on a particular system, the g77 run-time environment has certain built-in limits, usually, but not always, stemming from intrinsics with inherently limited interfaces.

Currently, the g77 run-time environment does not generally offer a less-limiting environment by augmenting the underlying system's own environment.

Therefore, code written in the GNU Fortran language, while syntactically and semantically portable, might nevertheless make non-portable assumptions about the run-time environment—assumptions that prove to be false for some particular environments.

The GNU Fortran language, the g77 compiler and run-time environment, and the g77 documentation do not yet offer comprehensive portable work-arounds for such limits, though programmers should be able to find their own in specific instances.

Not all of the limitations are described in this document. Some of the known limitations include:

Next: Year 2000 (Y2K) Problems, Up: Run-time Environment Limits

#### 10.2.1 Timer Wraparounds

Intrinsics that return values computed from system timers, whether elapsed (wall-clock) timers, process CPU timers, or other kinds of timers, are prone to experiencing wrap-around errors (or returning wrapped-around values from successive calls) due to insufficient ranges offered by the underlying system's timers.

Some of the symptoms of such behaviors include apparently negative time being computed for a duration, an extremely short amount of time being computed for a long duration, and an extremely long amount of time being computed for a short duration.

See the following for intrinsics known to have potential problems in these areas on at least some systems: CPU_Time Intrinsic, DTime Intrinsic (function), DTime Intrinsic (subroutine), ETime Intrinsic (function), ETime Intrinsic (subroutine), MClock Intrinsic, MClock8 Intrinsic, Secnds Intrinsic, Second Intrinsic (function), Second Intrinsic (subroutine), System_Clock Intrinsic, Time Intrinsic (UNIX), Time Intrinsic (VXT), Time8 Intrinsic.

Next: Array Size, Previous: Timer Wraparounds, Up: Run-time Environment Limits

#### 10.2.2 Year 2000 (Y2K) Problems

While the g77 compiler itself is believed to be Year-2000 (Y2K) compliant, some intrinsics are not, and, potentially, some underlying systems are not, perhaps rendering some Y2K-compliant intrinsics non-compliant when used on those particular systems.

Fortran code that uses non-Y2K-compliant intrinsics (listed below) is, itself, almost certainly not compliant, and should be modified to use Y2K-compliant intrinsics instead.

Fortran code that uses no non-Y2K-compliant intrinsics, but which currently is running on a non-Y2K-compliant system, can be made more Y2K compliant by compiling and linking it for use on a new Y2K-compliant system, such as a new version of an old, non-Y2K-compliant, system.

Currently, information on Y2K and related issues is being maintained at http://www.gnu.org/software/year2000-list.html.

See the following for intrinsics known to have potential problems in these areas on at least some systems: Date Intrinsic, IDate Intrinsic (VXT).

The `libg2c` library shipped with any g77 that warns about invocation of a non-Y2K-compliant intrinsic has renamed the `EXTERNAL` procedure names of those intrinsics. This is done so that the `libg2c` implementations of these intrinsics cannot be directly linked to as `EXTERNAL` names (which normally would avoid the non-Y2K-intrinsic warning).

The renamed forms of the `EXTERNAL` names of these renamed procedures may be linked to by appending the string _y2kbug to the name of the procedure in the source code. For example:

         CHARACTER*20 STR
         INTEGER YY, MM, DD
         EXTERNAL DATE_Y2KBUG, VXTIDATE_Y2KBUG
         CALL DATE_Y2KBUG (STR)
         CALL VXTIDATE_Y2KBUG (MM, DD, YY)

(Note that the `EXTERNAL` statement is not actually required, since the modified names are not recognized as intrinsics by the current version of g77. But it is shown in this specific case, for purposes of illustration.)

The renaming of `EXTERNAL` procedure names of these intrinsics causes unresolved references at link time. For example, EXTERNAL DATE; CALL DATE(STR) is normally compiled by g77 as, in C, date_(&str, 20);. This, in turn, links to the `date_` procedure in the `libE77` portion of `libg2c`, which purposely calls a nonexistent procedure named `G77_date_y2kbuggy_0`. The resulting link-time error is designed, via this name, to encourage the programmer to look up the index entries to this portion of the g77 documentation.

Generally, we recommend that the `EXTERNAL` method of invoking procedures in `libg2c` not be used. When used, some of the correctness checking normally performed by g77 is skipped.

In particular, it is probably better to use the `INTRINSIC` method of invoking non-Y2K-compliant procedures, so anyone compiling the code can quickly notice the potential Y2K problems (via the warnings printing by g77) without having to even look at the code itself.

If there are problems linking `libg2c` to code compiled by g77 that involve the string y2kbug, and these are not explained above, that probably indicates that a version of `libg2c` older than g77 is being linked to, or that the new library is being linked to code compiled by an older version of g77.

That's because, as of the version that warns about non-Y2K-compliant intrinsic invocation, g77 references the `libg2c` implementations of those intrinsics using new names, containing the string y2kbug.

So, linking newly-compiled code (invoking one of the intrinsics in question) to an old library might yield an unresolved reference to `G77_date_y2kbug_0`. (The old library calls it `G77_date_0`.)

Similarly, linking previously-compiled code to a new library might yield an unresolved reference to `G77_vxtidate_0`. (The new library calls it `G77_vxtidate_y2kbug_0`.)

The proper fix for the above problems is to obtain the latest release of g77 and related products (including `libg2c`) and install them on all systems, then recompile, relink, and install (as appropriate) all existing Fortran programs.

(Normally, this sort of renaming is steadfastly avoided. In this case, however, it seems more important to highlight potential Y2K problems than to ease the transition of potentially non-Y2K-compliant code to new versions of g77 and `libg2c`.)

Next: Character-variable Length, Previous: Year 2000 (Y2K) Problems, Up: Run-time Environment Limits

#### 10.2.3 Array Size

Currently, g77 uses the default `INTEGER` type for array indexes, which limits the sizes of single-dimension arrays on systems offering a larger address space than can be addressed by that type. (That g77 puts all arrays in memory could be considered another limitation—it could use large temporary files—but that decision is left to the programmer as an implementation choice by most Fortran implementations.)

It is not yet clear whether this limitation never, sometimes, or always applies to the sizes of multiple-dimension arrays as a whole.

For example, on a system with 64-bit addresses and 32-bit default `INTEGER`, an array with a size greater than can be addressed by a 32-bit offset can be declared using multiple dimensions. Such an array is therefore larger than a single-dimension array can be, on the same system.

Whether large multiple-dimension arrays are reliably supported depends mostly on the gcc back end (code generator) used by g77, and has not yet been fully investigated.

Next: Year 10000 (Y10K) Problems, Previous: Array Size, Up: Run-time Environment Limits

#### 10.2.4 Character-variable Length

Currently, g77 uses the default `INTEGER` type for the lengths of `CHARACTER` variables and array elements.

This means that, for example, a system with a 64-bit address space and a 32-bit default `INTEGER` type does not, under g77, support a `CHARACTER*`n declaration where n is greater than 2147483647.

Previous: Character-variable Length, Up: Run-time Environment Limits

#### 10.2.5 Year 10000 (Y10K) Problems

Most intrinsics returning, or computing values based on, date information are prone to Year-10000 (Y10K) problems, due to supporting only 4 digits for the year.

See the following for examples: FDate Intrinsic (function), FDate Intrinsic (subroutine), IDate Intrinsic (UNIX), Time Intrinsic (VXT), Date_and_Time Intrinsic.

Next: Compiler Constants, Previous: Run-time Environment Limits, Up: Compiler

### 10.3 Compiler Types

Fortran implementations have a fair amount of freedom given them by the standard as far as how much storage space is used and how much precision and range is offered by the various types such as `LOGICAL(KIND=1)`, `INTEGER(KIND=1)`, `REAL(KIND=1)`, `REAL(KIND=2)`, `COMPLEX(KIND=1)`, and `CHARACTER`. Further, many compilers offer so-called *n notation, but the interpretation of n varies across compilers and target architectures.

The standard requires that `LOGICAL(KIND=1)`, `INTEGER(KIND=1)`, and `REAL(KIND=1)` occupy the same amount of storage space, and that `COMPLEX(KIND=1)` and `REAL(KIND=2)` take twice as much storage space as `REAL(KIND=1)`. Further, it requires that `COMPLEX(KIND=1)` entities be ordered such that when a `COMPLEX(KIND=1)` variable is storage-associated (such as via `EQUIVALENCE`) with a two-element `REAL(KIND=1)` array named R, R(1) corresponds to the real element and R(2) to the imaginary element of the `COMPLEX(KIND=1)` variable.

(Few requirements as to precision or ranges of any of these are placed on the implementation, nor is the relationship of storage sizes of these types to the `CHARACTER` type specified, by the standard.)

g77 follows the above requirements, warning when compiling a program requires placement of items in memory that contradict the requirements of the target architecture. (For example, a program can require placement of a `REAL(KIND=2)` on a boundary that is not an even multiple of its size, but still an even multiple of the size of a `REAL(KIND=1)` variable. On some target architectures, using the canonical mapping of Fortran types to underlying architectural types, such placement is prohibited by the machine definition or the Application Binary Interface (ABI) in force for the configuration defined for building gcc and g77. g77 warns about such situations when it encounters them.)

g77 follows consistent rules for configuring the mapping between Fortran types, including the *n notation, and the underlying architectural types as accessed by a similarly-configured applicable version of the gcc compiler. These rules offer a widely portable, consistent Fortran/C environment, although they might well conflict with the expectations of users of Fortran compilers designed and written for particular architectures.

These rules are based on the configuration that is in force for the version of gcc built in the same release as g77 (and which was therefore used to build both the g77 compiler components and the `libg2c` run-time library):

`REAL(KIND=1)`
  Same as `float` type.

`REAL(KIND=2)`
  Same as whatever floating-point type that is twice the size of a `float`—usually, this is a `double`.

`INTEGER(KIND=1)`
  Same as an integral type that is occupies the same amount of memory storage as `float`—usually, this is either an `int` or a `long int`.

`LOGICAL(KIND=1)`
  Same gcc type as `INTEGER(KIND=1)`.

`INTEGER(KIND=2)`
  Twice the size, and usually nearly twice the range, as `INTEGER(KIND=1)`—usually, this is either a `long int` or a `long long int`.

`LOGICAL(KIND=2)`
  Same gcc type as `INTEGER(KIND=2)`.

`INTEGER(KIND=3)`
  Same gcc type as signed `char`.

`LOGICAL(KIND=3)`
  Same gcc type as `INTEGER(KIND=3)`.

`INTEGER(KIND=6)`
  Twice the size, and usually nearly twice the range, as `INTEGER(KIND=3)`—usually, this is a `short`.

`LOGICAL(KIND=6)`
  Same gcc type as `INTEGER(KIND=6)`.

`COMPLEX(KIND=1)`
  Two `REAL(KIND=1)` scalars (one for the real part followed by one for the imaginary part).

`COMPLEX(KIND=2)`
  Two `REAL(KIND=2)` scalars.

numeric-type`*`n
  (Where numeric-type is any type other than `CHARACTER`.) Same as whatever gcc type occupies n times the storage space of a gcc `char` item.

`DOUBLE PRECISION`
  Same as `REAL(KIND=2)`.

`DOUBLE COMPLEX`
  Same as `COMPLEX(KIND=2)`.

Note that the above are proposed correspondences and might change in future versions of g77—avoid writing code depending on them.

Other types supported by g77 are derived from gcc types such as `char`, `short`, `int`, `long int`, `long long int`, `long double`, and so on. That is, whatever types gcc already supports, g77 supports now or probably will support in a future version. The rules for the numeric-type*n notation apply to these types, and new values for numeric-type(KIND=n) will be assigned in a way that encourages clarity, consistency, and portability.

Next: Compiler Intrinsics, Previous: Compiler Types, Up: Compiler

### 10.4 Compiler Constants

g77 strictly assigns types to all constants not documented as “typeless” (typeless constants including '1'Z, for example). Many other Fortran compilers attempt to assign types to typed constants based on their context. This results in hard-to-find bugs, nonportable code, and is not in the spirit (though it strictly follows the letter) of the 77 and 90 standards.

g77 might offer, in a future release, explicit constructs by which a wider variety of typeless constants may be specified, and/or user-requested warnings indicating places where g77 might differ from how other compilers assign types to constants.

See Context-Sensitive Constants, for more information on this issue.

Previous: Compiler Constants, Up: Compiler

### 10.5 Compiler Intrinsics

g77 offers an ever-widening set of intrinsics. Currently these all are procedures (functions and subroutines).

Some of these intrinsics are unimplemented, but their names reserved to reduce future problems with existing code as they are implemented. Others are implemented as part of the GNU Fortran language, while yet others are provided for compatibility with other dialects of Fortran but are not part of the GNU Fortran language.

To manage these distinctions, g77 provides intrinsic groups, a facility that is simply an extension of the intrinsic groups provided by the GNU Fortran language.

Next: Other Intrinsics, Up: Compiler Intrinsics

#### 10.5.1 Intrinsic Groups

A given specific intrinsic belongs in one or more groups. Each group is deleted, disabled, hidden, or enabled by default or a command-line option. The meaning of each term follows.

Deleted
  No intrinsics are recognized as belonging to that group.

Disabled
  Intrinsics are recognized as belonging to the group, but references to them (other than via the `INTRINSIC` statement) are disallowed through that group.

Hidden
  Intrinsics in that group are recognized and enabled (if implemented) only if the first mention of the actual name of an intrinsic in a program unit is in an `INTRINSIC` statement.

Enabled
  Intrinsics in that group are recognized and enabled (if implemented).

The distinction between deleting and disabling a group is illustrated by the following example. Assume intrinsic FOO belongs only to group FGR. If group FGR is deleted, the following program unit will successfully compile, because FOO() will be seen as a reference to an external function named FOO:

         PRINT *, FOO()
         END

If group FGR is disabled, compiling the above program will produce diagnostics, either because the FOO intrinsic is improperly invoked or, if properly invoked, it is not enabled. To change the above program so it references an external function FOO instead of the disabled FOO intrinsic, add the following line to the top:

         EXTERNAL FOO

So, deleting a group tells g77 to pretend as though the intrinsics in that group do not exist at all, whereas disabling it tells g77 to recognize them as (disabled) intrinsics in intrinsic-like contexts.

Hiding a group is like enabling it, but the intrinsic must be first named in an `INTRINSIC` statement to be considered a reference to the intrinsic rather than to an external procedure. This might be the “safest” way to treat a new group of intrinsics when compiling old code, because it allows the old code to be generally written as if those new intrinsics never existed, but to be changed to use them by inserting `INTRINSIC` statements in the appropriate places. However, it should be the goal of development to use `EXTERNAL` for all names of external procedures that might be intrinsic names.

If an intrinsic is in more than one group, it is enabled if any of its containing groups are enabled; if not so enabled, it is hidden if any of its containing groups are hidden; if not so hidden, it is disabled if any of its containing groups are disabled; if not so disabled, it is deleted. This extra complication is necessary because some intrinsics, such as `IBITS`, belong to more than one group, and hence should be enabled if any of the groups to which they belong are enabled, and so on.

The groups are:

`badu77`
  UNIX intrinsics having inappropriate forms (usually functions that have intended side effects).

`gnu`
  Intrinsics the GNU Fortran language supports that are extensions to the Fortran standards (77 and 90).

`f2c`
  Intrinsics supported by AT&T's f2c converter and/or `libf2c`.

`f90`
  Fortran 90 intrinsics.

`mil`
  MIL-STD 1753 intrinsics (`MVBITS`, `IAND`, `BTEST`, and so on).

`unix`
  UNIX intrinsics (`IARGC`, `EXIT`, `ERF`, and so on).

`vxt`
  VAX/VMS FORTRAN (current as of v4) intrinsics.

Previous: Intrinsic Groups, Up: Compiler Intrinsics

#### 10.5.2 Other Intrinsics

g77 supports intrinsics other than those in the GNU Fortran language proper. This set of intrinsics is described below.

Next: AIMax0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.1 ACosD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL ACosD to use this name for an external procedure.

Next: AIMin0 Intrinsic, Previous: ACosD Intrinsic, Up: Other Intrinsics

##### 10.5.2.2 AIMax0 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL AIMax0 to use this name for an external procedure.

Next: AJMax0 Intrinsic, Previous: AIMax0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.3 AIMin0 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL AIMin0 to use this name for an external procedure.

Next: AJMin0 Intrinsic, Previous: AIMin0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.4 AJMax0 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL AJMax0 to use this name for an external procedure.

Next: ASinD Intrinsic, Previous: AJMax0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.5 AJMin0 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL AJMin0 to use this name for an external procedure.

Next: ATan2D Intrinsic, Previous: AJMin0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.6 ASinD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL ASinD to use this name for an external procedure.

Next: ATanD Intrinsic, Previous: ASinD Intrinsic, Up: Other Intrinsics

##### 10.5.2.7 ATan2D Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL ATan2D to use this name for an external procedure.

Next: BITest Intrinsic, Previous: ATan2D Intrinsic, Up: Other Intrinsics

##### 10.5.2.8 ATanD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL ATanD to use this name for an external procedure.

Next: BJTest Intrinsic, Previous: ATanD Intrinsic, Up: Other Intrinsics

##### 10.5.2.9 BITest Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL BITest to use this name for an external procedure.

Next: CDAbs Intrinsic, Previous: BITest Intrinsic, Up: Other Intrinsics

##### 10.5.2.10 BJTest Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL BJTest to use this name for an external procedure.

Next: CDCos Intrinsic, Previous: BJTest Intrinsic, Up: Other Intrinsics

##### 10.5.2.11 CDAbs Intrinsic

         CDAbs(A)

CDAbs: `REAL(KIND=2)` function.

A: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `ABS()` that is specific to one type for A. See Abs Intrinsic.

Next: CDExp Intrinsic, Previous: CDAbs Intrinsic, Up: Other Intrinsics

##### 10.5.2.12 CDCos Intrinsic

         CDCos(X)

CDCos: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `COS()` that is specific to one type for X. See Cos Intrinsic.

Next: CDLog Intrinsic, Previous: CDCos Intrinsic, Up: Other Intrinsics

##### 10.5.2.13 CDExp Intrinsic

         CDExp(X)

CDExp: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `EXP()` that is specific to one type for X. See Exp Intrinsic.

Next: CDSin Intrinsic, Previous: CDExp Intrinsic, Up: Other Intrinsics

##### 10.5.2.14 CDLog Intrinsic

         CDLog(X)

CDLog: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `LOG()` that is specific to one type for X. See Log Intrinsic.

Next: CDSqRt Intrinsic, Previous: CDLog Intrinsic, Up: Other Intrinsics

##### 10.5.2.15 CDSin Intrinsic

         CDSin(X)

CDSin: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `SIN()` that is specific to one type for X. See Sin Intrinsic.

Next: ChDir Intrinsic (function), Previous: CDSin Intrinsic, Up: Other Intrinsics

##### 10.5.2.16 CDSqRt Intrinsic

         CDSqRt(X)

CDSqRt: `COMPLEX(KIND=2)` function.

X: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `SQRT()` that is specific to one type for X. See SqRt Intrinsic.

Next: ChMod Intrinsic (function), Previous: CDSqRt Intrinsic, Up: Other Intrinsics

##### 10.5.2.17 ChDir Intrinsic (function)

         ChDir(Dir)

ChDir: `INTEGER(KIND=1)` function.

Dir: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Sets the current working directory to be Dir. Returns 0 on success or a nonzero error code. See `chdir(3)`.

Caution: Using this routine during I/O to a unit connected with a non-absolute file name can cause subsequent I/O on such a unit to fail because the I/O library might reopen files by name.

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See ChDir Intrinsic (subroutine).

Next: CosD Intrinsic, Previous: ChDir Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.18 ChMod Intrinsic (function)

         ChMod(Name, Mode)

ChMod: `INTEGER(KIND=1)` function.

Name: `CHARACTER`; scalar; INTENT(IN).

Mode: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Changes the access mode of file Name according to the specification Mode, which is given in the format of `chmod(1)`. A null character (CHAR(0)) marks the end of the name in Name—otherwise, trailing blanks in Name are ignored. Currently, Name must not contain the single quote character.

Returns 0 on success or a nonzero error code otherwise.

Note that this currently works by actually invoking `/bin/chmod` (or the `chmod` found when the library was configured) and so might fail in some circumstances and will, anyway, be slow.

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See ChMod Intrinsic (subroutine).

Next: DACosD Intrinsic, Previous: ChMod Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.19 CosD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL CosD to use this name for an external procedure.

Next: DASinD Intrinsic, Previous: CosD Intrinsic, Up: Other Intrinsics

##### 10.5.2.20 DACosD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DACosD to use this name for an external procedure.

Next: DATan2D Intrinsic, Previous: DACosD Intrinsic, Up: Other Intrinsics

##### 10.5.2.21 DASinD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DASinD to use this name for an external procedure.

Next: DATanD Intrinsic, Previous: DASinD Intrinsic, Up: Other Intrinsics

##### 10.5.2.22 DATan2D Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DATan2D to use this name for an external procedure.

Next: Date Intrinsic, Previous: DATan2D Intrinsic, Up: Other Intrinsics

##### 10.5.2.23 DATanD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DATanD to use this name for an external procedure.

Next: DbleQ Intrinsic, Previous: DATanD Intrinsic, Up: Other Intrinsics

##### 10.5.2.24 Date Intrinsic

         CALL Date(Date)

Date: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `vxt`.

Description:

Returns Date in the form dd-mmm-yy, representing the numeric day of the month dd, a three-character abbreviation of the month name mmm and the last two digits of the year yy, e.g. 25-Nov-96.

This intrinsic is not recommended, due to the year 2000 approaching. Therefore, programs making use of this intrinsic might not be Year 2000 (Y2K) compliant. See CTime Intrinsic (subroutine), for information on obtaining more digits for the current (or any) date.

Next: DCmplx Intrinsic, Previous: Date Intrinsic, Up: Other Intrinsics

##### 10.5.2.25 DbleQ Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DbleQ to use this name for an external procedure.

Next: DConjg Intrinsic, Previous: DbleQ Intrinsic, Up: Other Intrinsics

##### 10.5.2.26 DCmplx Intrinsic

         DCmplx(X, Y)

DCmplx: `COMPLEX(KIND=2)` function.

X: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Y: `INTEGER` or `REAL`; OPTIONAL (must be omitted if X is `COMPLEX`); scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

If X is not type `COMPLEX`, constructs a value of type `COMPLEX(KIND=2)` from the real and imaginary values specified by X and Y, respectively. If Y is omitted, 0D0 is assumed.

If X is type `COMPLEX`, converts it to type `COMPLEX(KIND=2)`.

Although this intrinsic is not standard Fortran, it is a popular extension offered by many compilers that support `DOUBLE COMPLEX`, since it offers the easiest way to convert to `DOUBLE COMPLEX` without using Fortran 90 features (such as the KIND= argument to the `CMPLX()` intrinsic).

(CMPLX(0D0, 0D0) returns a single-precision `COMPLEX` result, as required by standard FORTRAN 77. That's why so many compilers provide `DCMPLX()`, since DCMPLX(0D0, 0D0) returns a `DOUBLE COMPLEX` result. Still, `DCMPLX()` converts even `REAL*16` arguments to their `REAL*8` equivalents in most dialects of Fortran, so neither it nor `CMPLX()` allow easy construction of arbitrary-precision values without potentially forcing a conversion involving extending or reducing precision. GNU Fortran provides such an intrinsic, called `COMPLEX()`.)

See Complex Intrinsic, for information on easily constructing a `COMPLEX` value of arbitrary precision from `REAL` arguments.

Next: DCosD Intrinsic, Previous: DCmplx Intrinsic, Up: Other Intrinsics

##### 10.5.2.27 DConjg Intrinsic

         DConjg(Z)

DConjg: `COMPLEX(KIND=2)` function.

Z: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `CONJG()` that is specific to one type for Z. See Conjg Intrinsic.

Next: DFloat Intrinsic, Previous: DConjg Intrinsic, Up: Other Intrinsics

##### 10.5.2.28 DCosD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DCosD to use this name for an external procedure.

Next: DFlotI Intrinsic, Previous: DCosD Intrinsic, Up: Other Intrinsics

##### 10.5.2.29 DFloat Intrinsic

         DFloat(A)

DFloat: `REAL(KIND=2)` function.

A: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `REAL()` that is specific to one type for A. See Real Intrinsic.

Next: DFlotJ Intrinsic, Previous: DFloat Intrinsic, Up: Other Intrinsics

##### 10.5.2.30 DFlotI Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DFlotI to use this name for an external procedure.

Next: DImag Intrinsic, Previous: DFlotI Intrinsic, Up: Other Intrinsics

##### 10.5.2.31 DFlotJ Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DFlotJ to use this name for an external procedure.

Next: DReal Intrinsic, Previous: DFlotJ Intrinsic, Up: Other Intrinsics

##### 10.5.2.32 DImag Intrinsic

         DImag(Z)

DImag: `REAL(KIND=2)` function.

Z: `COMPLEX(KIND=2)`; scalar; INTENT(IN).

Intrinsic groups: `f2c`, `vxt`.

Description:

Archaic form of `AIMAG()` that is specific to one type for Z. See AImag Intrinsic.

Next: DSinD Intrinsic, Previous: DImag Intrinsic, Up: Other Intrinsics

##### 10.5.2.33 DReal Intrinsic

         DReal(A)

DReal: `REAL(KIND=2)` function.

A: `INTEGER`, `REAL`, or `COMPLEX`; scalar; INTENT(IN).

Intrinsic groups: `vxt`.

Description:

Converts A to `REAL(KIND=2)`.

If A is type `COMPLEX`, its real part is converted (if necessary) to `REAL(KIND=2)`, and its imaginary part is disregarded.

Although this intrinsic is not standard Fortran, it is a popular extension offered by many compilers that support `DOUBLE COMPLEX`, since it offers the easiest way to extract the real part of a `DOUBLE COMPLEX` value without using the Fortran 90 `REAL()` intrinsic in a way that produces a return value inconsistent with the way many FORTRAN 77 compilers handle `REAL()` of a `DOUBLE COMPLEX` value.

See RealPart Intrinsic, for information on a GNU Fortran intrinsic that avoids these areas of confusion.

See Dble Intrinsic, for information on the standard FORTRAN 77 replacement for `DREAL()`.

See REAL() and AIMAG() of Complex, for more information on this issue.

Next: DTanD Intrinsic, Previous: DReal Intrinsic, Up: Other Intrinsics

##### 10.5.2.34 DSinD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DSinD to use this name for an external procedure.

Next: DTime Intrinsic (function), Previous: DSinD Intrinsic, Up: Other Intrinsics

##### 10.5.2.35 DTanD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL DTanD to use this name for an external procedure.

Next: FGet Intrinsic (function), Previous: DTanD Intrinsic, Up: Other Intrinsics

##### 10.5.2.36 DTime Intrinsic (function)

         DTime(TArray)

DTime: `REAL(KIND=1)` function.

TArray: `REAL(KIND=1)`; DIMENSION(2); INTENT(OUT).

Intrinsic groups: `badu77`.

Description:

Initially, return the number of seconds of runtime since the start of the process's execution as the function value, and the user and system components of this in TArray(1) and TArray(2) respectively. The functions' value is equal to TArray(1) + TArray(2).

Subsequent invocations of DTIME() return values accumulated since the previous invocation.

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wraparounds) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See DTime Intrinsic (subroutine).

Next: FGetC Intrinsic (function), Previous: DTime Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.37 FGet Intrinsic (function)

         FGet(C)

FGet: `INTEGER(KIND=1)` function.

C: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `badu77`.

Description:

Reads a single character into C in stream mode from unit 5 (by-passing normal formatted input) using `getc(3)`. Returns 0 on success, −1 on end-of-file, and the error code from `ferror(3)` otherwise.

Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

For information on other intrinsics with the same name: See FGet Intrinsic (subroutine).

Next: FloatI Intrinsic, Previous: FGet Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.38 FGetC Intrinsic (function)

         FGetC(Unit, C)

FGetC: `INTEGER(KIND=1)` function.

Unit: `INTEGER`; scalar; INTENT(IN).

C: `CHARACTER`; scalar; INTENT(OUT).

Intrinsic groups: `badu77`.

Description:

Reads a single character into C in stream mode from unit Unit (by-passing normal formatted output) using `getc(3)`. Returns 0 on success, −1 on end-of-file, and the error code from `ferror(3)` otherwise.

Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

For information on other intrinsics with the same name: See FGetC Intrinsic (subroutine).

Next: FloatJ Intrinsic, Previous: FGetC Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.39 FloatI Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL FloatI to use this name for an external procedure.

Next: FPut Intrinsic (function), Previous: FloatI Intrinsic, Up: Other Intrinsics

##### 10.5.2.40 FloatJ Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL FloatJ to use this name for an external procedure.

Next: FPutC Intrinsic (function), Previous: FloatJ Intrinsic, Up: Other Intrinsics

##### 10.5.2.41 FPut Intrinsic (function)

         FPut(C)

FPut: `INTEGER(KIND=1)` function.

C: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Writes the single character C in stream mode to unit 6 (by-passing normal formatted output) using `getc(3)`. Returns 0 on success, the error code from `ferror(3)` otherwise.

Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

For information on other intrinsics with the same name: See FPut Intrinsic (subroutine).

Next: IDate Intrinsic (VXT), Previous: FPut Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.42 FPutC Intrinsic (function)

         FPutC(Unit, C)

FPutC: `INTEGER(KIND=1)` function.

Unit: `INTEGER`; scalar; INTENT(IN).

C: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Writes the single character C in stream mode to unit Unit (by-passing normal formatted output) using `putc(3)`. Returns 0 on success, the error code from `ferror(3)` otherwise.

Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

For information on other intrinsics with the same name: See FPutC Intrinsic (subroutine).

Next: IIAbs Intrinsic, Previous: FPutC Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.43 IDate Intrinsic (VXT)

         CALL IDate(M, D, Y)

M: `INTEGER(KIND=1)`; scalar; INTENT(OUT).

D: `INTEGER(KIND=1)`; scalar; INTENT(OUT).

Y: `INTEGER(KIND=1)`; scalar; INTENT(OUT).

Intrinsic groups: `vxt`.

Description:

Returns the numerical values of the current local time. The month (in the range 1–12) is returned in M, the day (in the range 1–31) in D, and the year in Y (in the range 0–99).

This intrinsic is not recommended, due to the fact that its return value for year wraps around century boundaries (change from a larger value to a smaller one). Therefore, programs making use of this intrinsic, for instance, might not be Year 2000 (Y2K) compliant. For example, the date might appear, to such programs, to wrap around as of the Year 2000.

See IDate Intrinsic (UNIX), for information on obtaining more digits for the current date.

For information on other intrinsics with the same name: See IDate Intrinsic (UNIX).

Next: IIAnd Intrinsic, Previous: IDate Intrinsic (VXT), Up: Other Intrinsics

##### 10.5.2.44 IIAbs Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIAbs to use this name for an external procedure.

Next: IIBClr Intrinsic, Previous: IIAbs Intrinsic, Up: Other Intrinsics

##### 10.5.2.45 IIAnd Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIAnd to use this name for an external procedure.

Next: IIBits Intrinsic, Previous: IIAnd Intrinsic, Up: Other Intrinsics

##### 10.5.2.46 IIBClr Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIBClr to use this name for an external procedure.

Next: IIBSet Intrinsic, Previous: IIBClr Intrinsic, Up: Other Intrinsics

##### 10.5.2.47 IIBits Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIBits to use this name for an external procedure.

Next: IIDiM Intrinsic, Previous: IIBits Intrinsic, Up: Other Intrinsics

##### 10.5.2.48 IIBSet Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIBSet to use this name for an external procedure.

Next: IIDInt Intrinsic, Previous: IIBSet Intrinsic, Up: Other Intrinsics

##### 10.5.2.49 IIDiM Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIDiM to use this name for an external procedure.

Next: IIDNnt Intrinsic, Previous: IIDiM Intrinsic, Up: Other Intrinsics

##### 10.5.2.50 IIDInt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIDInt to use this name for an external procedure.

Next: IIEOr Intrinsic, Previous: IIDInt Intrinsic, Up: Other Intrinsics

##### 10.5.2.51 IIDNnt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIDNnt to use this name for an external procedure.

Next: IIFix Intrinsic, Previous: IIDNnt Intrinsic, Up: Other Intrinsics

##### 10.5.2.52 IIEOr Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIEOr to use this name for an external procedure.

Next: IInt Intrinsic, Previous: IIEOr Intrinsic, Up: Other Intrinsics

##### 10.5.2.53 IIFix Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIFix to use this name for an external procedure.

Next: IIOr Intrinsic, Previous: IIFix Intrinsic, Up: Other Intrinsics

##### 10.5.2.54 IInt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IInt to use this name for an external procedure.

Next: IIQint Intrinsic, Previous: IInt Intrinsic, Up: Other Intrinsics

##### 10.5.2.55 IIOr Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIOr to use this name for an external procedure.

Next: IIQNnt Intrinsic, Previous: IIOr Intrinsic, Up: Other Intrinsics

##### 10.5.2.56 IIQint Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIQint to use this name for an external procedure.

Next: IIShftC Intrinsic, Previous: IIQint Intrinsic, Up: Other Intrinsics

##### 10.5.2.57 IIQNnt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIQNnt to use this name for an external procedure.

Next: IISign Intrinsic, Previous: IIQNnt Intrinsic, Up: Other Intrinsics

##### 10.5.2.58 IIShftC Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IIShftC to use this name for an external procedure.

Next: IMax0 Intrinsic, Previous: IIShftC Intrinsic, Up: Other Intrinsics

##### 10.5.2.59 IISign Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IISign to use this name for an external procedure.

Next: IMax1 Intrinsic, Previous: IISign Intrinsic, Up: Other Intrinsics

##### 10.5.2.60 IMax0 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IMax0 to use this name for an external procedure.

Next: IMin0 Intrinsic, Previous: IMax0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.61 IMax1 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IMax1 to use this name for an external procedure.

Next: IMin1 Intrinsic, Previous: IMax1 Intrinsic, Up: Other Intrinsics

##### 10.5.2.62 IMin0 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IMin0 to use this name for an external procedure.

Next: IMod Intrinsic, Previous: IMin0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.63 IMin1 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IMin1 to use this name for an external procedure.

Next: INInt Intrinsic, Previous: IMin1 Intrinsic, Up: Other Intrinsics

##### 10.5.2.64 IMod Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IMod to use this name for an external procedure.

Next: INot Intrinsic, Previous: IMod Intrinsic, Up: Other Intrinsics

##### 10.5.2.65 INInt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL INInt to use this name for an external procedure.

Next: IZExt Intrinsic, Previous: INInt Intrinsic, Up: Other Intrinsics

##### 10.5.2.66 INot Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL INot to use this name for an external procedure.

Next: JIAbs Intrinsic, Previous: INot Intrinsic, Up: Other Intrinsics

##### 10.5.2.67 IZExt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL IZExt to use this name for an external procedure.

Next: JIAnd Intrinsic, Previous: IZExt Intrinsic, Up: Other Intrinsics

##### 10.5.2.68 JIAbs Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIAbs to use this name for an external procedure.

Next: JIBClr Intrinsic, Previous: JIAbs Intrinsic, Up: Other Intrinsics

##### 10.5.2.69 JIAnd Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIAnd to use this name for an external procedure.

Next: JIBits Intrinsic, Previous: JIAnd Intrinsic, Up: Other Intrinsics

##### 10.5.2.70 JIBClr Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIBClr to use this name for an external procedure.

Next: JIBSet Intrinsic, Previous: JIBClr Intrinsic, Up: Other Intrinsics

##### 10.5.2.71 JIBits Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIBits to use this name for an external procedure.

Next: JIDiM Intrinsic, Previous: JIBits Intrinsic, Up: Other Intrinsics

##### 10.5.2.72 JIBSet Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIBSet to use this name for an external procedure.

Next: JIDInt Intrinsic, Previous: JIBSet Intrinsic, Up: Other Intrinsics

##### 10.5.2.73 JIDiM Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIDiM to use this name for an external procedure.

Next: JIDNnt Intrinsic, Previous: JIDiM Intrinsic, Up: Other Intrinsics

##### 10.5.2.74 JIDInt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIDInt to use this name for an external procedure.

Next: JIEOr Intrinsic, Previous: JIDInt Intrinsic, Up: Other Intrinsics

##### 10.5.2.75 JIDNnt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIDNnt to use this name for an external procedure.

Next: JIFix Intrinsic, Previous: JIDNnt Intrinsic, Up: Other Intrinsics

##### 10.5.2.76 JIEOr Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIEOr to use this name for an external procedure.

Next: JInt Intrinsic, Previous: JIEOr Intrinsic, Up: Other Intrinsics

##### 10.5.2.77 JIFix Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIFix to use this name for an external procedure.

Next: JIOr Intrinsic, Previous: JIFix Intrinsic, Up: Other Intrinsics

##### 10.5.2.78 JInt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JInt to use this name for an external procedure.

Next: JIQint Intrinsic, Previous: JInt Intrinsic, Up: Other Intrinsics

##### 10.5.2.79 JIOr Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIOr to use this name for an external procedure.

Next: JIQNnt Intrinsic, Previous: JIOr Intrinsic, Up: Other Intrinsics

##### 10.5.2.80 JIQint Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIQint to use this name for an external procedure.

Next: JIShft Intrinsic, Previous: JIQint Intrinsic, Up: Other Intrinsics

##### 10.5.2.81 JIQNnt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIQNnt to use this name for an external procedure.

Next: JIShftC Intrinsic, Previous: JIQNnt Intrinsic, Up: Other Intrinsics

##### 10.5.2.82 JIShft Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIShft to use this name for an external procedure.

Next: JISign Intrinsic, Previous: JIShft Intrinsic, Up: Other Intrinsics

##### 10.5.2.83 JIShftC Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JIShftC to use this name for an external procedure.

Next: JMax0 Intrinsic, Previous: JIShftC Intrinsic, Up: Other Intrinsics

##### 10.5.2.84 JISign Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JISign to use this name for an external procedure.

Next: JMax1 Intrinsic, Previous: JISign Intrinsic, Up: Other Intrinsics

##### 10.5.2.85 JMax0 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JMax0 to use this name for an external procedure.

Next: JMin0 Intrinsic, Previous: JMax0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.86 JMax1 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JMax1 to use this name for an external procedure.

Next: JMin1 Intrinsic, Previous: JMax1 Intrinsic, Up: Other Intrinsics

##### 10.5.2.87 JMin0 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JMin0 to use this name for an external procedure.

Next: JMod Intrinsic, Previous: JMin0 Intrinsic, Up: Other Intrinsics

##### 10.5.2.88 JMin1 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JMin1 to use this name for an external procedure.

Next: JNInt Intrinsic, Previous: JMin1 Intrinsic, Up: Other Intrinsics

##### 10.5.2.89 JMod Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JMod to use this name for an external procedure.

Next: JNot Intrinsic, Previous: JMod Intrinsic, Up: Other Intrinsics

##### 10.5.2.90 JNInt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JNInt to use this name for an external procedure.

Next: JZExt Intrinsic, Previous: JNInt Intrinsic, Up: Other Intrinsics

##### 10.5.2.91 JNot Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JNot to use this name for an external procedure.

Next: Kill Intrinsic (function), Previous: JNot Intrinsic, Up: Other Intrinsics

##### 10.5.2.92 JZExt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL JZExt to use this name for an external procedure.

Next: Link Intrinsic (function), Previous: JZExt Intrinsic, Up: Other Intrinsics

##### 10.5.2.93 Kill Intrinsic (function)

         Kill(Pid, Signal)

Kill: `INTEGER(KIND=1)` function.

Pid: `INTEGER`; scalar; INTENT(IN).

Signal: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Sends the signal specified by Signal to the process Pid. Returns 0 on success or a nonzero error code. See `kill(2)`.

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See Kill Intrinsic (subroutine).

Next: QAbs Intrinsic, Previous: Kill Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.94 Link Intrinsic (function)

         Link(Path1, Path2)

Link: `INTEGER(KIND=1)` function.

Path1: `CHARACTER`; scalar; INTENT(IN).

Path2: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Makes a (hard) link from file Path1 to Path2. A null character (CHAR(0)) marks the end of the names in Path1 and Path2—otherwise, trailing blanks in Path1 and Path2 are ignored. Returns 0 on success or a nonzero error code. See `link(2)`.

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See Link Intrinsic (subroutine).

Next: QACos Intrinsic, Previous: Link Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.95 QAbs Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QAbs to use this name for an external procedure.

Next: QACosD Intrinsic, Previous: QAbs Intrinsic, Up: Other Intrinsics

##### 10.5.2.96 QACos Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QACos to use this name for an external procedure.

Next: QASin Intrinsic, Previous: QACos Intrinsic, Up: Other Intrinsics

##### 10.5.2.97 QACosD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QACosD to use this name for an external procedure.

Next: QASinD Intrinsic, Previous: QACosD Intrinsic, Up: Other Intrinsics

##### 10.5.2.98 QASin Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QASin to use this name for an external procedure.

Next: QATan Intrinsic, Previous: QASin Intrinsic, Up: Other Intrinsics

##### 10.5.2.99 QASinD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QASinD to use this name for an external procedure.

Next: QATan2 Intrinsic, Previous: QASinD Intrinsic, Up: Other Intrinsics

##### 10.5.2.100 QATan Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QATan to use this name for an external procedure.

Next: QATan2D Intrinsic, Previous: QATan Intrinsic, Up: Other Intrinsics

##### 10.5.2.101 QATan2 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QATan2 to use this name for an external procedure.

Next: QATanD Intrinsic, Previous: QATan2 Intrinsic, Up: Other Intrinsics

##### 10.5.2.102 QATan2D Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QATan2D to use this name for an external procedure.

Next: QCos Intrinsic, Previous: QATan2D Intrinsic, Up: Other Intrinsics

##### 10.5.2.103 QATanD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QATanD to use this name for an external procedure.

Next: QCosD Intrinsic, Previous: QATanD Intrinsic, Up: Other Intrinsics

##### 10.5.2.104 QCos Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QCos to use this name for an external procedure.

Next: QCosH Intrinsic, Previous: QCos Intrinsic, Up: Other Intrinsics

##### 10.5.2.105 QCosD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QCosD to use this name for an external procedure.

Next: QDiM Intrinsic, Previous: QCosD Intrinsic, Up: Other Intrinsics

##### 10.5.2.106 QCosH Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QCosH to use this name for an external procedure.

Next: QExp Intrinsic, Previous: QCosH Intrinsic, Up: Other Intrinsics

##### 10.5.2.107 QDiM Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QDiM to use this name for an external procedure.

Next: QExt Intrinsic, Previous: QDiM Intrinsic, Up: Other Intrinsics

##### 10.5.2.108 QExp Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QExp to use this name for an external procedure.

Next: QExtD Intrinsic, Previous: QExp Intrinsic, Up: Other Intrinsics

##### 10.5.2.109 QExt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QExt to use this name for an external procedure.

Next: QFloat Intrinsic, Previous: QExt Intrinsic, Up: Other Intrinsics

##### 10.5.2.110 QExtD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QExtD to use this name for an external procedure.

Next: QInt Intrinsic, Previous: QExtD Intrinsic, Up: Other Intrinsics

##### 10.5.2.111 QFloat Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QFloat to use this name for an external procedure.

Next: QLog Intrinsic, Previous: QFloat Intrinsic, Up: Other Intrinsics

##### 10.5.2.112 QInt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QInt to use this name for an external procedure.

Next: QLog10 Intrinsic, Previous: QInt Intrinsic, Up: Other Intrinsics

##### 10.5.2.113 QLog Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QLog to use this name for an external procedure.

Next: QMax1 Intrinsic, Previous: QLog Intrinsic, Up: Other Intrinsics

##### 10.5.2.114 QLog10 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QLog10 to use this name for an external procedure.

Next: QMin1 Intrinsic, Previous: QLog10 Intrinsic, Up: Other Intrinsics

##### 10.5.2.115 QMax1 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QMax1 to use this name for an external procedure.

Next: QMod Intrinsic, Previous: QMax1 Intrinsic, Up: Other Intrinsics

##### 10.5.2.116 QMin1 Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QMin1 to use this name for an external procedure.

Next: QNInt Intrinsic, Previous: QMin1 Intrinsic, Up: Other Intrinsics

##### 10.5.2.117 QMod Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QMod to use this name for an external procedure.

Next: QSin Intrinsic, Previous: QMod Intrinsic, Up: Other Intrinsics

##### 10.5.2.118 QNInt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QNInt to use this name for an external procedure.

Next: QSinD Intrinsic, Previous: QNInt Intrinsic, Up: Other Intrinsics

##### 10.5.2.119 QSin Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QSin to use this name for an external procedure.

Next: QSinH Intrinsic, Previous: QSin Intrinsic, Up: Other Intrinsics

##### 10.5.2.120 QSinD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QSinD to use this name for an external procedure.

Next: QSqRt Intrinsic, Previous: QSinD Intrinsic, Up: Other Intrinsics

##### 10.5.2.121 QSinH Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QSinH to use this name for an external procedure.

Next: QTan Intrinsic, Previous: QSinH Intrinsic, Up: Other Intrinsics

##### 10.5.2.122 QSqRt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QSqRt to use this name for an external procedure.

Next: QTanD Intrinsic, Previous: QSqRt Intrinsic, Up: Other Intrinsics

##### 10.5.2.123 QTan Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QTan to use this name for an external procedure.

Next: QTanH Intrinsic, Previous: QTan Intrinsic, Up: Other Intrinsics

##### 10.5.2.124 QTanD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QTanD to use this name for an external procedure.

Next: Rename Intrinsic (function), Previous: QTanD Intrinsic, Up: Other Intrinsics

##### 10.5.2.125 QTanH Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL QTanH to use this name for an external procedure.

Next: Secnds Intrinsic, Previous: QTanH Intrinsic, Up: Other Intrinsics

##### 10.5.2.126 Rename Intrinsic (function)

         Rename(Path1, Path2)

Rename: `INTEGER(KIND=1)` function.

Path1: `CHARACTER`; scalar; INTENT(IN).

Path2: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Renames the file Path1 to Path2. A null character (CHAR(0)) marks the end of the names in Path1 and Path2—otherwise, trailing blanks in Path1 and Path2 are ignored. See `rename(2)`. Returns 0 on success or a nonzero error code.

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See Rename Intrinsic (subroutine).

Next: Signal Intrinsic (function), Previous: Rename Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.127 Secnds Intrinsic

         Secnds(T)

Secnds: `REAL(KIND=1)` function.

T: `REAL(KIND=1)`; scalar; INTENT(IN).

Intrinsic groups: `vxt`.

Description:

Returns the local time in seconds since midnight minus the value T.

This values returned by this intrinsic become numerically less than previous values (they wrap around) during a single run of the compiler program, under normal circumstances (such as running through the midnight hour).

Next: SinD Intrinsic, Previous: Secnds Intrinsic, Up: Other Intrinsics

##### 10.5.2.128 Signal Intrinsic (function)

         Signal(Number, Handler)

Signal: `INTEGER(KIND=7)` function.

Number: `INTEGER`; scalar; INTENT(IN).

Handler: Signal handler (`INTEGER FUNCTION` or `SUBROUTINE`) or dummy/global `INTEGER(KIND=1)` scalar.

Intrinsic groups: `badu77`.

Description:

If Handler is a an `EXTERNAL` routine, arranges for it to be invoked with a single integer argument (of system-dependent length) when signal Number occurs. If Handler is an integer, it can be used to turn off handling of signal Number or revert to its default action. See `signal(2)`.

Note that Handler will be called using C conventions, so the value of its argument in Fortran terms is obtained by applying `%LOC()` (or `LOC()`) to it.

The value returned by `signal(2)` is returned.

Due to the side effects performed by this intrinsic, the function form is not recommended.

Warning: If the returned value is stored in an `INTEGER(KIND=1)` (default `INTEGER`) argument, truncation of the original return value occurs on some systems (such as Alphas, which have 64-bit pointers but 32-bit default integers), with no warning issued by `g77` under normal circumstances.

Therefore, the following code fragment might silently fail on some systems:

         INTEGER RTN
         EXTERNAL MYHNDL
         RTN = SIGNAL(signum, MYHNDL)
         ...
         ! Restore original handler:
         RTN = SIGNAL(signum, RTN)

The reason for the failure is that RTN might not hold all the information on the original handler for the signal, thus restoring an invalid handler. This bug could manifest itself as a spurious run-time failure at an arbitrary point later during the program's execution, for example.

Warning: Use of the `libf2c` run-time library function signal_ directly (such as via EXTERNAL SIGNAL) requires use of the `%VAL()` construct to pass an `INTEGER` value (such as SIG_IGN or SIG_DFL) for the Handler argument.

However, while RTN = SIGNAL(signum, %VAL(SIG_IGN)) works when SIGNAL is treated as an external procedure (and resolves, at link time, to `libf2c`'s signal_ routine), this construct is not valid when SIGNAL is recognized as the intrinsic of that name.

Therefore, for maximum portability and reliability, code such references to the SIGNAL facility as follows:

         INTRINSIC SIGNAL
         ...
         RTN = SIGNAL(signum, SIG_IGN)

`g77` will compile such a call correctly, while other compilers will generally either do so as well or reject the INTRINSIC SIGNAL statement via a diagnostic, allowing you to take appropriate action.

For information on other intrinsics with the same name: See Signal Intrinsic (subroutine).

Next: SnglQ Intrinsic, Previous: Signal Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.129 SinD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL SinD to use this name for an external procedure.

Next: SymLnk Intrinsic (function), Previous: SinD Intrinsic, Up: Other Intrinsics

##### 10.5.2.130 SnglQ Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL SnglQ to use this name for an external procedure.

Next: System Intrinsic (function), Previous: SnglQ Intrinsic, Up: Other Intrinsics

##### 10.5.2.131 SymLnk Intrinsic (function)

         SymLnk(Path1, Path2)

SymLnk: `INTEGER(KIND=1)` function.

Path1: `CHARACTER`; scalar; INTENT(IN).

Path2: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Makes a symbolic link from file Path1 to Path2. A null character (CHAR(0)) marks the end of the names in Path1 and Path2—otherwise, trailing blanks in Path1 and Path2 are ignored. Returns 0 on success or a nonzero error code (`ENOSYS` if the system does not provide `symlink(2)`).

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See SymLnk Intrinsic (subroutine).

Next: TanD Intrinsic, Previous: SymLnk Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.132 System Intrinsic (function)

         System(Command)

System: `INTEGER(KIND=1)` function.

Command: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Passes the command Command to a shell (see `system(3)`). Returns the value returned by `system(3)`, presumably 0 if the shell command succeeded. Note that which shell is used to invoke the command is system-dependent and environment-dependent.

Due to the side effects performed by this intrinsic, the function form is not recommended. However, the function form can be valid in cases where the actual side effects performed by the call are unimportant to the application.

For example, on a UNIX system, SAME = SYSTEM('cmp a b') does not perform any side effects likely to be important to the program, so the programmer would not care if the actual system call (and invocation of `cmp`) was optimized away in a situation where the return value could be determined otherwise, or was not actually needed (SAME not actually referenced after the sample assignment statement).

For information on other intrinsics with the same name: See System Intrinsic (subroutine).

Next: Time Intrinsic (VXT), Previous: System Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.133 TanD Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL TanD to use this name for an external procedure.

Next: UMask Intrinsic (function), Previous: TanD Intrinsic, Up: Other Intrinsics

##### 10.5.2.134 Time Intrinsic (VXT)

         CALL Time(Time)

Time: `CHARACTER*8`; scalar; INTENT(OUT).

Intrinsic groups: `vxt`.

Description:

Returns in Time a character representation of the current time as obtained from `ctime(3)`.

Programs making use of this intrinsic might not be Year 10000 (Y10K) compliant. For example, the date might appear, to such programs, to wrap around (change from a larger value to a smaller one) as of the Year 10000.

See FDate Intrinsic (subroutine), for an equivalent routine.

For information on other intrinsics with the same name: See Time Intrinsic (UNIX).

Next: Unlink Intrinsic (function), Previous: Time Intrinsic (VXT), Up: Other Intrinsics

##### 10.5.2.135 UMask Intrinsic (function)

         UMask(Mask)

UMask: `INTEGER(KIND=1)` function.

Mask: `INTEGER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Sets the file creation mask to Mask and returns the old value. See `umask(2)`.

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See UMask Intrinsic (subroutine).

Next: ZExt Intrinsic, Previous: UMask Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.136 Unlink Intrinsic (function)

         Unlink(File)

Unlink: `INTEGER(KIND=1)` function.

File: `CHARACTER`; scalar; INTENT(IN).

Intrinsic groups: `badu77`.

Description:

Unlink the file File. A null character (CHAR(0)) marks the end of the name in File—otherwise, trailing blanks in File are ignored. Returns 0 on success or a nonzero error code. See `unlink(2)`.

Due to the side effects performed by this intrinsic, the function form is not recommended.

For information on other intrinsics with the same name: See Unlink Intrinsic (subroutine).

Previous: Unlink Intrinsic (function), Up: Other Intrinsics

##### 10.5.2.137 ZExt Intrinsic

This intrinsic is not yet implemented. The name is, however, reserved as an intrinsic. Use EXTERNAL ZExt to use this name for an external procedure.

Next: Other Languages, Previous: Other Dialects, Up: Top

## 11 Other Compilers

An individual Fortran source file can be compiled to an object (*.o) file instead of to the final program executable. This allows several portions of a program to be compiled at different times and linked together whenever a new version of the program is needed. However, it introduces the issue of object compatibility across the various object files (and libraries, or *.a files) that are linked together to produce any particular executable file.

Object compatibility is an issue when combining, in one program, Fortran code compiled by more than one compiler (or more than one configuration of a compiler). If the compilers disagree on how to transform the names of procedures, there will normally be errors when linking such programs. Worse, if the compilers agree on naming, but disagree on issues like how to pass parameters, return arguments, and lay out `COMMON` areas, the earliest detected errors might be the incorrect results produced by the program (and that assumes these errors are detected, which is not always the case).

Normally, g77 generates code that is object-compatible with code generated by a version of f2c configured (with, for example, f2c.h definitions) to be generally compatible with g77 as built by gcc. (Normally, f2c will, by default, conform to the appropriate configuration, but it is possible that older or perhaps even newer versions of f2c, or versions having certain configuration changes to f2c internals, will produce object files that are incompatible with g77.)

For example, a Fortran string subroutine argument will become two arguments on the C side: a `char *` and an `int` length.

Much of this compatibility results from the fact that g77 uses the same run-time library, `libf2c`, used by f2c, though g77 gives its version the name `libg2c` so as to avoid conflicts when linking, installing them in the same directories, and so on.

Other compilers might or might not generate code that is object-compatible with `libg2c` and current g77, and some might offer such compatibility only when explicitly selected via a command-line option to the compiler.

Note: This portion of the documentation definitely needs a lot of work!

Next: Compilers Other Than f2c, Up: Other Compilers

### 11.1 Dropping f2c Compatibility

Specifying -fno-f2c allows g77 to generate, in some cases, faster code, by not needing to allow to the possibility of linking with code compiled by f2c.

For example, this affects how `REAL(KIND=1)`, `COMPLEX(KIND=1)`, and `COMPLEX(KIND=2)` functions are called. With -fno-f2c, they are compiled as returning the appropriate gcc type (`float`, `__complex__ float`, `__complex__ double`, in many configurations).

With -ff2c in force, they are compiled differently (with perhaps slower run-time performance) to accommodate the restrictions inherent in f2c's use of K&R C as an intermediate language—`REAL(KIND=1)` functions return C's `double` type, while `COMPLEX` functions return `void` and use an extra argument pointing to a place for the functions to return their values.

It is possible that, in some cases, leaving -ff2c in force might produce faster code than using -fno-f2c. Feel free to experiment, but remember to experiment with changing the way entire programs and their Fortran libraries are compiled at a time, since this sort of experimentation affects the interface of code generated for a Fortran source file—that is, it affects object compatibility.

Note that f2c compatibility is a fairly static target to achieve, though not necessarily perfectly so, since, like g77, it is still being improved. However, specifying -fno-f2c causes g77 to generate code that will probably be incompatible with code generated by future versions of g77 when the same option is in force. You should make sure you are always able to recompile complete programs from source code when upgrading to new versions of g77 or f2c, especially when using options such as -fno-f2c.

Therefore, if you are using g77 to compile libraries and other object files for possible future use and you don't want to require recompilation for future use with subsequent versions of g77, you might want to stick with f2c compatibility for now, and carefully watch for any announcements about changes to the f2c/`libf2c` interface that might affect existing programs (thus requiring recompilation).

It is probable that a future version of g77 will not, by default, generate object files compatible with f2c, and that version probably would no longer use `libf2c`. If you expect to depend on this compatibility in the long term, use the options -ff2c -ff2c-library when compiling all of the applicable code. This should cause future versions of g77 either to produce compatible code (at the expense of the availability of some features and performance), or at the very least, to produce diagnostics.

(The library g77 produces will no longer be named libg2c when it is no longer generally compatible with libf2c. It will likely be referred to, and, if installed as a distinct library, named `libg77`, or some other as-yet-unused name.)

Previous: Dropping f2c Compatibility, Up: Other Compilers

### 11.2 Compilers Other Than f2c

On systems with Fortran compilers other than f2c and g77, code compiled by g77 is not expected to work well with code compiled by the native compiler. (This is true for f2c-compiled objects as well.) Libraries compiled with the native compiler probably will have to be recompiled with g77 to be used with g77-compiled code.

Reasons for such incompatibilities include:

- There might be differences in the way names of Fortran procedures are translated for use in the system's object-file format. For example, the statement CALL FOO might be compiled by g77 to call a procedure the linker ld sees given the name _foo_, while the apparently corresponding statement SUBROUTINE FOO might be compiled by the native compiler to define the linker-visible name _foo, or _FOO_, and so on.
- There might be subtle type mismatches which cause subroutine arguments and function return values to get corrupted.

  This is why simply getting g77 to transform procedure names the same way a native compiler does is not usually a good idea—unless some effort has been made to ensure that, aside from the way the two compilers transform procedure names, everything else about the way they generate code for procedure interfaces is identical.

- Native compilers use libraries of private I/O routines which will not be available at link time unless you have the native compiler—and you would have to explicitly ask for them.

  For example, on the Sun you would have to add -L/usr/lang/SCx.x -lF77 -lV77 to the link command.

Next: Debugging and Interfacing, Previous: Other Compilers, Up: Top

## 12 Other Languages

Note: This portion of the documentation definitely needs a lot of work!

Up: Other Languages

### 12.1 Tools and advice for interoperating with C and C++

The following discussion assumes that you are running g77 in f2c compatibility mode, i.e. not using -fno-f2c. It provides some advice about quick and simple techniques for linking Fortran and C (or C++), the most common requirement. For the full story consult the description of code generation. See Debugging and Interfacing.

When linking Fortran and C, it's usually best to use g77 to do the linking so that the correct libraries are included (including the maths one). If you're linking with C++ you will want to add -lstdc++, -lg++ or whatever. If you need to use another driver program (or ld directly), you can find out what linkage options g77 passes by running g77 -v.

Next: C Access to Type Information, Up: Interoperating with C and C++

#### 12.1.1 C Interfacing Tools

Even if you don't actually use it as a compiler, f2c from ftp://ftp.netlib.org/f2c/src, can be a useful tool when you're interfacing (linking) Fortran and C. See Generating Skeletons and Prototypes with f2c.

To use f2c for this purpose you only need retrieve and build the src directory from the distribution, consult the README instructions there for machine-specifics, and install the f2c program on your path.

Something else that might be useful is cfortran.h from ftp://zebra.desy.de/cfortran. This is a fairly general tool which can be used to generate interfaces for calling in both directions between Fortran and C. It can be used in f2c mode with g77—consult its documentation for details.

Next: f2c Skeletons and Prototypes, Previous: C Interfacing Tools, Up: Interoperating with C and C++

#### 12.1.2 Accessing Type Information in C

Generally, C code written to link with g77 code—calling and/or being called from Fortran—should #include <g2c.h> to define the C versions of the Fortran types. Don't assume Fortran `INTEGER` types correspond to C `int`s, for instance; instead, declare them as `integer`, a type defined by g2c.h. g2c.h is installed where gcc will find it by default, assuming you use a copy of gcc compatible with g77, probably built at the same time as g77.

Next: C++ Considerations, Previous: C Access to Type Information, Up: Interoperating with C and C++

#### 12.1.3 Generating Skeletons and Prototypes with f2c

A simple and foolproof way to write g77-callable C routines—e.g. to interface with an existing library—is to write a file (named, for example, fred.f) of dummy Fortran skeletons comprising just the declaration of the routine(s) and dummy arguments plus `END` statements. Then run f2c on file fred.f to produce fred.c into which you can edit useful code, confident the calling sequence is correct, at least. (There are some errors otherwise commonly made in generating C interfaces with f2c conventions, such as not using `doublereal` as the return type of a `REAL` `FUNCTION`.)

f2c also can help with calling Fortran from C, using its -P option to generate C prototypes appropriate for calling the Fortran.2 If the Fortran code containing any routines to be called from C is in file joe.f, use the command `f2c -P joe.f` to generate the file joe.P containing prototype information. `#include` this in the C which has to call the Fortran routines to make sure you get it right.

See Arrays (DIMENSION), for information on the differences between the way Fortran (including compilers like g77) and C handle arrays.

Next: Startup Code, Previous: f2c Skeletons and Prototypes, Up: Interoperating with C and C++

#### 12.1.4 C++ Considerations

f2c can be used to generate suitable code for compilation with a C++ system using the -C++ option. The important thing about linking g77-compiled code with C++ is that the prototypes for the g77 routines must specify C linkage to avoid name mangling. So, use an extern "C" declaration. f2c's -C++ option will not take care of this when generating skeletons or prototype files as above, however, it will avoid clashes with C++ reserved words in addition to those in C.

Previous: C++ Considerations, Up: Interoperating with C and C++

#### 12.1.5 Startup Code

Unlike with some runtime systems, it shouldn't be necessary (unless there are bugs) to use a Fortran main program unit to ensure the runtime—specifically the I/O system—is initialized.

However, to use the g77 intrinsics `GETARG` and `IARGC`, either the `main` routine from the libg2c library must be used, or the `f_setarg` routine (new as of `egcs` version 1.1 and g77 version 0.5.23) must be called with the appropriate `argc` and `argv` arguments prior to the program calling `GETARG` or `IARGC`.

To provide more flexibility for mixed-language programming involving g77 while allowing for shared libraries, as of `egcs` version 1.1 and g77 version 0.5.23, g77's `main` routine in `libg2c` does the following, in order:

1. Calls `f_setarg` with the incoming `argc` and `argv` arguments, in the same order as for `main` itself.

   This sets up the command-line environment for `GETARG` and `IARGC`.

2. Calls `f_setsig` (with no arguments).

   This sets up the signaling and exception environment.

3. Calls `f_init` (with no arguments).

   This initializes the I/O environment, though that should not be necessary, as all I/O functions in `libf2c` are believed to call `f_init` automatically, if necessary.

   (A future version of g77 might skip this explicit step, to speed up normal exit of a program.)

4. Arranges for `f_exit` to be called (with no arguments) when the program exits.

   This ensures that the I/O environment is properly shut down before the program exits normally. Otherwise, output buffers might not be fully flushed, scratch files might not be deleted, and so on.

   The simple way `main` does this is to call `f_exit` itself after calling `MAIN__` (in the next step).

   However, this does not catch the cases where the program might call `exit` directly, instead of using the `EXIT` intrinsic (implemented as `exit_` in `libf2c`).

   So, `main` attempts to use the operating environment's `onexit` or `atexit` facility, if available, to cause `f_exit` to be called automatically upon any invocation of `exit`.

5. Calls `MAIN__` (with no arguments).

   This starts executing the Fortran main program unit for the application. (Both g77 and f2c currently compile a main program unit so that its global name is `MAIN__`.)

6. If no `onexit` or `atexit` is provided by the system, calls `f_exit`.
7. Calls `exit` with a zero argument, to signal a successful program termination.
8. Returns a zero value to the caller, to signal a successful program termination, in case `exit` doesn't exit on the system.

All of the above names are C `extern` names, i.e. not mangled.

When using the `main` procedure provided by g77 without a Fortran main program unit, you need to provide `MAIN__` as the entry point for your C code. (Make sure you link the object file that defines that entry point with the rest of your program.)

To provide your own `main` procedure in place of g77's, make sure you specify the object file defining that procedure before -lg2c on the g77 command line. Since the -lg2c option is implicitly provided, this is usually straightforward. (Use the --verbose option to see how and where g77 implicitly adds -lg2c in a command line that will link the program. Feel free to specify -lg2c explicitly, as appropriate.)

However, when providing your own `main`, make sure you perform the appropriate tasks in the appropriate order. For example, if your `main` does not call `f_setarg`, make sure the rest of your application does not call `GETARG` or `IARGC`.

And, if your `main` fails to ensure that `f_exit` is called upon program exit, some files might end up incompletely written, some scratch files might be left lying around, and some existing files being written might be left with old data not properly truncated at the end.

Note that, generally, the g77 operating environment does not depend on a procedure named `MAIN__` actually being called prior to any other g77-compiled code. That is, `MAIN__` does not, itself, set up any important operating-environment characteristics upon which other code might depend. This might change in future versions of g77, with appropriate notification in the release notes.

For more information, consult the source code for the above routines. These are in gcc/libf2c/libF77/, named main.c, setarg.c, setsig.c, getarg_.c, and iargc_.c.

Also, the file gcc/gcc/f/com.c contains the code g77 uses to open-code (inline) references to `IARGC`.

Next: Collected Fortran Wisdom, Previous: Other Languages, Up: Top

## 13 Debugging and Interfacing

GNU Fortran currently generates code that is object-compatible with the f2c converter. Also, it avoids limitations in the current GBE, such as the inability to generate a procedure with multiple entry points, by generating code that is structured differently (in terms of procedure names, scopes, arguments, and so on) than might be expected.

As a result, writing code in other languages that calls on, is called by, or shares in-memory data with g77-compiled code generally requires some understanding of the way g77 compiles code for various constructs.

Similarly, using a debugger to debug g77-compiled code, even if that debugger supports native Fortran debugging, generally requires this sort of information.

This section describes some of the basic information on how g77 compiles code for constructs involving interfaces to other languages and to debuggers.

Caution: Much or all of this information pertains to only the current release of g77, sometimes even to using certain compiler options with g77 (such as -fno-f2c). Do not write code that depends on this information without clearly marking said code as nonportable and subject to review for every new release of g77. This information is provided primarily to make debugging of code generated by this particular release of g77 easier for the user, and partly to make writing (generally nonportable) interface code easier. Both of these activities require tracking changes in new version of g77 as they are installed, because new versions can change the behaviors described in this section.

Next: Procedures, Up: Debugging and Interfacing

### 13.1 Main Program Unit (PROGRAM)

When g77 compiles a main program unit, it gives it the public procedure name `MAIN__`. The `libg2c` library has the actual `main()` procedure as is typical of C-based environments, and it is this procedure that performs some initial start-up activity and then calls `MAIN__`.

Generally, g77 and `libg2c` are designed so that you need not include a main program unit written in Fortran in your program—it can be written in C or some other language. Especially for I/O handling, this is the case, although g77 version 0.5.16 includes a bug fix for `libg2c` that solved a problem with using the `OPEN` statement as the first Fortran I/O activity in a program without a Fortran main program unit.

However, if you don't intend to use g77 (or f2c) to compile your main program unit—that is, if you intend to compile a `main()` procedure using some other language—you should carefully examine the code for `main()` in `libg2c`, found in the source file gcc/libf2c/libF77/main.c, to see what kinds of things might need to be done by your `main()` in order to provide the Fortran environment your Fortran code is expecting.

For example, `libg2c`'s `main()` sets up the information used by the `IARGC` and `GETARG` intrinsics. Bypassing `libg2c`'s `main()` without providing a substitute for this activity would mean that invoking `IARGC` and `GETARG` would produce undefined results.

When debugging, one implication of the fact that `main()`, which is the place where the debugged program “starts” from the debugger's point of view, is in `libg2c` is that you won't be starting your Fortran program at a point you recognize as your Fortran code.

The standard way to get around this problem is to set a break point (a one-time, or temporary, break point will do) at the entrance to `MAIN__`, and then run the program. A convenient way to do so is to add the gdb command

         tbreak MAIN__

to the file .gdbinit in the directory in which you're debugging (using gdb).

After doing this, the debugger will see the current execution point of the program as at the beginning of the main program unit of your program.

Of course, if you really want to set a break point at some other place in your program and just start the program running, without first breaking at `MAIN__`, that should work fine.

Next: Functions, Previous: Main Program Unit, Up: Debugging and Interfacing

### 13.2 Procedures (SUBROUTINE and FUNCTION)

Currently, g77 passes arguments via reference—specifically, by passing a pointer to the location in memory of a variable, array, array element, a temporary location that holds the result of evaluating an expression, or a temporary or permanent location that holds the value of a constant.

Procedures that accept `CHARACTER` arguments are implemented by g77 so that each `CHARACTER` argument has two actual arguments.

The first argument occupies the expected position in the argument list and has the user-specified name. This argument is a pointer to an array of characters, passed by the caller.

The second argument is appended to the end of the user-specified calling sequence and is named __g77_length_x, where x is the user-specified name. This argument is of the C type `ftnlen` (see gcc/libf2c/g2c.h.in for information on that type) and is the number of characters the caller has allocated in the array pointed to by the first argument.

A procedure will ignore the length argument if X is not declared `CHARACTER*(*)`, because for other declarations, it knows the length. Not all callers necessarily “know” this, however, which is why they all pass the extra argument.

The contents of the `CHARACTER` argument are specified by the address passed in the first argument (named after it). The procedure can read or write these contents as appropriate.

When more than one `CHARACTER` argument is present in the argument list, the length arguments are appended in the order the original arguments appear. So CALL FOO('HI','THERE') is implemented in C as foo("hi","there",2,5);, ignoring the fact that g77 does not provide the trailing null bytes on the constant strings (f2c does provide them, but they are unnecessary in a Fortran environment, and you should not expect them to be there).

Note that the above information applies to `CHARACTER` variables and arrays only. It does not apply to external `CHARACTER` functions or to intrinsic `CHARACTER` functions. That is, no second length argument is passed to FOO in this case:

         CHARACTER X
         EXTERNAL X
         CALL FOO(X)

Nor does FOO expect such an argument in this case:

         SUBROUTINE FOO(X)
         CHARACTER X
         EXTERNAL X

Because of this implementation detail, if a program has a bug such that there is disagreement as to whether an argument is a procedure, and the type of the argument is `CHARACTER`, subtle symptoms might appear.

Next: Names, Previous: Procedures, Up: Debugging and Interfacing

### 13.3 Functions (FUNCTION and RETURN)

g77 handles in a special way functions that return the following types:

- `CHARACTER`
- `COMPLEX`
- `REAL(KIND=1)`

For `CHARACTER`, g77 implements a subroutine (a C function returning `void`) with two arguments prepended: __g77_result, which the caller passes as a pointer to a `char` array expected to hold the return value, and __g77_length, which the caller passes as an `ftnlen` value specifying the length of the return value as declared in the calling program. For `CHARACTER*(*)`, the called function uses __g77_length to determine the size of the array that __g77_result points to; otherwise, it ignores that argument.

For `COMPLEX`, when -ff2c is in force, g77 implements a subroutine with one argument prepended: __g77_result, which the caller passes as a pointer to a variable of the type of the function. The called function writes the return value into this variable instead of returning it as a function value. When -fno-f2c is in force, g77 implements a `COMPLEX` function as gcc's __complex__ float or __complex__ double function (or an emulation thereof, when -femulate-complex is in effect), returning the result of the function in the same way as gcc would.

For `REAL(KIND=1)`, when -ff2c is in force, g77 implements a function that actually returns `REAL(KIND=2)` (typically C's `double` type). When -fno-f2c is in force, `REAL(KIND=1)` functions return `float`.

Next: Common Blocks, Previous: Functions, Up: Debugging and Interfacing

### 13.4 Names

Fortran permits each implementation to decide how to represent names as far as how they're seen in other contexts, such as debuggers and when interfacing to other languages, and especially as far as how casing is handled.

External names—names of entities that are public, or “accessible”, to all modules in a program—normally have an underscore (_) appended by g77, to generate code that is compatible with f2c. External names include names of Fortran things like common blocks, external procedures (subroutines and functions, but not including statement functions, which are internal procedures), and entry point names.

However, use of the -fno-underscoring option disables this kind of transformation of external names (though inhibiting the transformation certainly improves the chances of colliding with incompatible externals written in other languages—but that might be intentional.

When -funderscoring is in force, any name (external or local) that already has at least one underscore in it is implemented by g77 by appending two underscores. (This second underscore can be disabled via the -fno-second-underscore option.) External names are changed this way for f2c compatibility. Local names are changed this way to avoid collisions with external names that are different in the source code—f2c does the same thing, but there's no compatibility issue there except for user expectations while debugging.

For example:

         Max_Cost = 0

Here, a user would, in the debugger, refer to this variable using the name max_cost__ (or MAX_COST__ or Max_Cost__, as described below). (We hope to improve g77 in this regard in the future—don't write scripts depending on this behavior! Also, consider experimenting with the -fno-underscoring option to try out debugging without having to massage names by hand like this.)

g77 provides a number of command-line options that allow the user to control how case mapping is handled for source files. The default is the traditional UNIX model for Fortran compilers—names are mapped to lower case. Other command-line options can be specified to map names to upper case, or to leave them exactly as written in the source file.

For example:

         Foo = 9.436

Here, it is normally the case that the variable assigned will be named foo. This would be the name to enter when using a debugger to access the variable.

However, depending on the command-line options specified, the name implemented by g77 might instead be FOO or even Foo, thus affecting how debugging is done.

Also:

         Call Foo

This would normally call a procedure that, if it were in a separate C program, be defined starting with the line:

         void foo_()

However, g77 command-line options could be used to change the casing of names, resulting in the name FOO_ or Foo_ being given to the procedure instead of foo_, and the -fno-underscoring option could be used to inhibit the appending of the underscore to the name.

Next: Local Equivalence Areas, Previous: Names, Up: Debugging and Interfacing

### 13.5 Common Blocks (COMMON)

g77 names and lays out `COMMON` areas the same way f2c does, for compatibility with f2c.

Next: Complex Variables, Previous: Common Blocks, Up: Debugging and Interfacing

### 13.6 Local Equivalence Areas (EQUIVALENCE)

g77 treats storage-associated areas involving a `COMMON` block as explained in the section on common blocks.

A local `EQUIVALENCE` area is a collection of variables and arrays connected to each other in any way via `EQUIVALENCE`, none of which are listed in a `COMMON` statement.

(Note: g77 version 0.5.18 and earlier chose the name for x using a different method when more than one name was in the list of names of entities placed at the beginning of the array. Though the documentation specified that the first name listed in the `EQUIVALENCE` statements was chosen for x, g77 in fact chose the name using a method that was so complicated, it seemed easier to change it to an alphabetical sort than to describe the previous method in the documentation.)

Next: Arrays, Previous: Local Equivalence Areas, Up: Debugging and Interfacing

### 13.7 Complex Variables (COMPLEX)

As of 0.5.20, g77 defaults to handling `COMPLEX` types (and related intrinsics, constants, functions, and so on) in a manner that makes direct debugging involving these types in Fortran language mode difficult.

Essentially, g77 implements these types using an internal construct similar to C's `struct`, at least as seen by the gcc back end.

Currently, the back end, when outputting debugging info with the compiled code for the assembler to digest, does not detect these `struct` types as being substitutes for Fortran complex. As a result, the Fortran language modes of debuggers such as gdb see these types as C `struct` types, which they might or might not support.

Until this is fixed, switch to C language mode to work with entities of `COMPLEX` type and then switch back to Fortran language mode afterward. (In gdb, this is accomplished via set lang c and either set lang fortran or set lang auto.)

Next: Adjustable Arrays, Previous: Complex Variables, Up: Debugging and Interfacing

### 13.8 Arrays (DIMENSION)

Fortran uses “column-major ordering” in its arrays. This differs from other languages, such as C, which use “row-major ordering”. The difference is that, with Fortran, array elements adjacent to each other in memory differ in the first subscript instead of the last; A(5,10,20) immediately follows A(4,10,20), whereas with row-major ordering it would follow A(5,10,19).

This consideration affects not only interfacing with and debugging Fortran code, it can greatly affect how code is designed and written, especially when code speed and size is a concern.

Fortran also differs from C, a popular language for interfacing and to support directly in debuggers, in the way arrays are treated. In C, arrays are single-dimensional and have interesting relationships to pointers, neither of which is true for Fortran. As a result, dealing with Fortran arrays from within an environment limited to C concepts can be challenging.

For example, accessing the array element A(5,10,20) is easy enough in Fortran (use A(5,10,20)), but in C some difficult machinations are needed. First, C would treat the A array as a single-dimension array. Second, C does not understand low bounds for arrays as does Fortran. Third, C assumes a low bound of zero (0), while Fortran defaults to a low bound of one (1) and can supports an arbitrary low bound. Therefore, calculations must be done to determine what the C equivalent of A(5,10,20) would be, and these calculations require knowing the dimensions of A.

For DIMENSION A(2:11,21,0:29), the calculation of the offset of A(5,10,20) would be:

           (5-2)
         + (10-1)*(11-2+1)
         + (20-0)*(11-2+1)*(21-1+1)
         = 4293

So the C equivalent in this case would be a[4293].

When using a debugger directly on Fortran code, the C equivalent might not work, because some debuggers cannot understand the notion of low bounds other than zero. However, unlike f2c, g77 does inform the GBE that a multi-dimensional array (like A in the above example) is really multi-dimensional, rather than a single-dimensional array, so at least the dimensionality of the array is preserved.

Debuggers that understand Fortran should have no trouble with nonzero low bounds, but for non-Fortran debuggers, especially C debuggers, the above example might have a C equivalent of a[4305]. This calculation is arrived at by eliminating the subtraction of the lower bound in the first parenthesized expression on each line—that is, for (5-2) substitute (5), for (10-1) substitute (10), and for (20-0) substitute (20). Actually, the implication of this can be that the expression *(&a[2][1][0] + 4293) works fine, but that a[20][10][5] produces the equivalent of *(&a[0][0][0] + 4305) because of the missing lower bounds.

Come to think of it, perhaps the behavior is due to the debugger internally compensating for the lower bounds by offsetting the base address of a, leaving &a set lower, in this case, than &a[2][1][0] (the address of its first element as identified by subscripts equal to the corresponding lower bounds).

You know, maybe nobody really needs to use arrays.

Next: Alternate Entry Points, Previous: Arrays, Up: Debugging and Interfacing

### 13.9 Adjustable Arrays (DIMENSION)

Adjustable and automatic arrays in Fortran require the implementation (in this case, the g77 compiler) to “memorize” the expressions that dimension the arrays each time the procedure is invoked. This is so that subsequent changes to variables used in those expressions, made during execution of the procedure, do not have any effect on the dimensions of those arrays.

For example:

         REAL ARRAY(5)
         DATA ARRAY/5*2/
         CALL X(ARRAY, 5)
         END
         SUBROUTINE X(A, N)
         DIMENSION A(N)
         N = 20
         PRINT *, N, A
         END

Here, the implementation should, when running the program, print something like:

         20   2.  2.  2.  2.  2.

Note that this shows that while the value of N was successfully changed, the size of the A array remained at 5 elements.

To support this, g77 generates code that executes before any user code (and before the internally generated computed `GOTO` to handle alternate entry points, as described below) that evaluates each (nonconstant) expression in the list of subscripts for an array, and saves the result of each such evaluation to be used when determining the size of the array (instead of re-evaluating the expressions).

So, in the above example, when X is first invoked, code is executed that copies the value of N to a temporary. And that same temporary serves as the actual high bound for the single dimension of the A array (the low bound being the constant 1). Since the user program cannot (legitimately) change the value of the temporary during execution of the procedure, the size of the array remains constant during each invocation.

For alternate entry points, the code g77 generates takes into account the possibility that a dummy adjustable array is not actually passed to the actual entry point being invoked at that time. In that case, the public procedure implementing the entry point passes to the master private procedure implementing all the code for the entry points a `NULL` pointer where a pointer to that adjustable array would be expected. The g77-generated code doesn't attempt to evaluate any of the expressions in the subscripts for an array if the pointer to that array is `NULL` at run time in such cases. (Don't depend on this particular implementation by writing code that purposely passes `NULL` pointers where the callee expects adjustable arrays, even if you know the callee won't reference the arrays—nor should you pass `NULL` pointers for any dummy arguments used in calculating the bounds of such arrays or leave undefined any values used for that purpose in COMMON—because the way g77 implements these things might change in the future!)

Next: Alternate Returns, Previous: Adjustable Arrays, Up: Debugging and Interfacing

### 13.10 Alternate Entry Points (ENTRY)

The GBE does not understand the general concept of alternate entry points as Fortran provides via the ENTRY statement. g77 gets around this by using an approach to compiling procedures having at least one `ENTRY` statement that is almost identical to the approach used by f2c. (An alternate approach could be used that would probably generate faster, but larger, code that would also be a bit easier to debug.)

Information on how g77 implements `ENTRY` is provided for those trying to debug such code. The choice of implementation seems unlikely to affect code (compiled in other languages) that interfaces to such code.

g77 compiles exactly one public procedure for the primary entry point of a procedure plus each `ENTRY` point it specifies, as usual. That is, in terms of the public interface, there is no difference between

         SUBROUTINE X
         END
         SUBROUTINE Y
         END

and:

         SUBROUTINE X
         ENTRY Y
         END

The difference between the above two cases lies in the code compiled for the X and Y procedures themselves, plus the fact that, for the second case, an extra internal procedure is compiled.

For every Fortran procedure with at least one `ENTRY` statement, g77 compiles an extra procedure named __g77_masterfun_x, where x is the name of the primary entry point (which, in the above case, using the standard compiler options, would be x_ in C).

This extra procedure is compiled as a private procedure—that is, a procedure not accessible by name to separately compiled modules. It contains all the code in the program unit, including the code for the primary entry point plus for every entry point. (The code for each public procedure is quite short, and explained later.)

The extra procedure has some other interesting characteristics.

The argument list for this procedure is invented by g77. It contains a single integer argument named __g77_which_entrypoint, passed by value (as in Fortran's %VAL() intrinsic), specifying the entry point index—0 for the primary entry point, 1 for the first entry point (the first `ENTRY` statement encountered), 2 for the second entry point, and so on.

It also contains, for functions returning `CHARACTER` and (when -ff2c is in effect) `COMPLEX` functions, and for functions returning different types among the `ENTRY` statements (e.g. REAL FUNCTION R() containing ENTRY I()), an argument named __g77_result that is expected at run time to contain a pointer to where to store the result of the entry point. For `CHARACTER` functions, this storage area is an array of the appropriate number of characters; for `COMPLEX` functions, it is the appropriate area for the return type; for multiple-return-type functions, it is a union of all the supported return types (which cannot include `CHARACTER`, since combining `CHARACTER` and non-`CHARACTER` return types via `ENTRY` in a single function is not supported by g77).

For `CHARACTER` functions, the __g77_result argument is followed by yet another argument named __g77_length that, at run time, specifies the caller's expected length of the returned value. Note that only `CHARACTER*(*)` functions and entry points actually make use of this argument, even though it is always passed by all callers of public `CHARACTER` functions (since the caller does not generally know whether such a function is `CHARACTER*(*)` or whether there are any other callers that don't have that information).

The rest of the argument list is the union of all the arguments specified for all the entry points (in their usual forms, e.g. `CHARACTER` arguments have extra length arguments, all appended at the end of this list). This is considered the “master list” of arguments.

The code for this procedure has, before the code for the first executable statement, code much like that for the following Fortran statement:

                GOTO (100000,100001,100002), __g77_which_entrypoint
         100000 ...code for primary entry point...
         100001 ...code immediately following first ENTRY statement...
         100002 ...code immediately following second ENTRY statement...

(Note that invalid Fortran statement labels and variable names are used in the above example to highlight the fact that it represents code generated by the g77 internals, not code to be written by the user.)

It is this code that, when the procedure is called, picks which entry point to start executing.

Getting back to the public procedures (x and Y in the original example), those procedures are fairly simple. Their interfaces are just like they would be if they were self-contained procedures (without `ENTRY`), of course, since that is what the callers expect. Their code consists of simply calling the private procedure, described above, with the appropriate extra arguments (the entry point index, and perhaps a pointer to a multiple-type- return variable, local to the public procedure, that contains all the supported returnable non-character types). For arguments that are not listed for a given entry point that are listed for other entry points, and therefore that are in the “master list” for the private procedure, null pointers (in C, the `NULL` macro) are passed. Also, for entry points that are part of a multiple-type- returning function, code is compiled after the call of the private procedure to extract from the multi-type union the appropriate result, depending on the type of the entry point in question, returning that result to the original caller.

When debugging a procedure containing alternate entry points, you can either set a break point on the public procedure itself (e.g. a break point on X or Y) or on the private procedure that contains most of the pertinent code (e.g. __g77_masterfun_x). If you do the former, you should use the debugger's command to “step into” the called procedure to get to the actual code; with the latter approach, the break point leaves you right at the actual code, skipping over the public entry point and its call to the private procedure (unless you have set a break point there as well, of course).

Further, the list of dummy arguments that is visible when the private procedure is active is going to be the expanded version of the list for whichever particular entry point is active, as explained above, and the way in which return values are handled might well be different from how they would be handled for an equivalent single-entry function.

Next: Assigned Statement Labels, Previous: Alternate Entry Points, Up: Debugging and Interfacing

### 13.11 Alternate Returns (SUBROUTINE and RETURN)

Subroutines with alternate returns (e.g. SUBROUTINE X(*) and CALL X(*50)) are implemented by g77 as functions returning the C `int` type. The actual alternate-return arguments are omitted from the calling sequence. Instead, the caller uses the return value to do a rough equivalent of the Fortran computed-`GOTO` statement, as in GOTO (50), X() in the example above (where X is quietly declared as an `INTEGER(KIND=1)` function), and the callee just returns whatever integer is specified in the `RETURN` statement for the subroutine For example, RETURN 1 is implemented as X = 1 followed by RETURN in C, and RETURN by itself is X = 0 and RETURN).

Next: Run-time Library Errors, Previous: Alternate Returns, Up: Debugging and Interfacing

### 13.12 Assigned Statement Labels (ASSIGN and GOTO)

For portability to machines where a pointer (such as to a label, which is how g77 implements `ASSIGN` and its relatives, the assigned-`GOTO` and assigned-`FORMAT`-I/O statements) is wider (bitwise) than an `INTEGER(KIND=1)`, g77 uses a different memory location to hold the `ASSIGN`ed value of a variable than it does the numerical value in that variable, unless the variable is wide enough (can hold enough bits).

In particular, while g77 implements

         I = 10

as, in C notation, i = 10;, it implements

         ASSIGN 10 TO I

as, in GNU's extended C notation (for the label syntax), __g77_ASSIGN_I = &&L10; (where L10 is just a massaging of the Fortran label 10 to make the syntax C-like; g77 doesn't actually generate the name L10 or any other name like that, since debuggers cannot access labels anyway).

While this currently means that an `ASSIGN` statement does not overwrite the numeric contents of its target variable, do not write any code depending on this feature. g77 has already changed this implementation across versions and might do so in the future. This information is provided only to make debugging Fortran programs compiled with the current version of g77 somewhat easier. If there's no debugger-visible variable named __g77_ASSIGN_I in a program unit that does ASSIGN 10 TO I, that probably means g77 has decided it can store the pointer to the label directly into I itself.

See Ugly Assigned Labels, for information on a command-line option to force g77 to use the same storage for both normal and assigned-label uses of a variable.

Previous: Assigned Statement Labels, Up: Debugging and Interfacing

### 13.13 Run-time Library Errors

The `libg2c` library currently has the following table to relate error code numbers, returned in `IOSTAT=` variables, to messages. This information should, in future versions of this document, be expanded upon to include detailed descriptions of each message.

In line with good coding practices, any of the numbers in the list below should not be directly written into Fortran code you write. Instead, make a separate `INCLUDE` file that defines `PARAMETER` names for them, and use those in your code, so you can more easily change the actual numbers in the future.

The information below is culled from the definition of `F_err` in f/runtime/libI77/err.c in the g77 source tree.

         100: "error in format"
         101: "illegal unit number"
         102: "formatted io not allowed"
         103: "unformatted io not allowed"
         104: "direct io not allowed"
         105: "sequential io not allowed"
         106: "can't backspace file"
         107: "null file name"
         108: "can't stat file"
         109: "unit not connected"
         110: "off end of record"
         111: "truncation failed in endfile"
         112: "incomprehensible list input"
         113: "out of free space"
         114: "unit not connected"
         115: "read unexpected character"
         116: "bad logical input field"
         117: "bad variable type"
         118: "bad namelist name"
         119: "variable not in namelist"
         120: "no end record"
         121: "variable count incorrect"
         122: "subscript for scalar variable"
         123: "invalid array section"
         124: "substring out of bounds"
         125: "subscript out of bounds"
         126: "can't read file"
         127: "can't write file"
         128: "'new' file exists"
         129: "can't append to file"
         130: "non-positive record number"
         131: "I/O started while already doing I/O"

Next: Trouble, Previous: Debugging and Interfacing, Up: Top

## 14 Collected Fortran Wisdom

Most users of g77 can be divided into two camps:

- Those writing new Fortran code to be compiled by g77.
- Those using g77 to compile existing, “legacy” code.

Users writing new code generally understand most of the necessary aspects of Fortran to write “mainstream” code, but often need help deciding how to handle problems, such as the construction of libraries containing `BLOCK DATA`.

Users dealing with “legacy” code sometimes don't have much experience with Fortran, but believe that the code they're compiling already works when compiled by other compilers (and might not understand why, as is sometimes the case, it doesn't work when compiled by g77).

The following information is designed to help users do a better job coping with existing, “legacy” Fortran code, and with writing new code as well.

Next: Block Data and Libraries, Up: Collected Fortran Wisdom

### 14.1 Advantages Over f2c

Without f2c, g77 would have taken much longer to do and probably not been as good for quite a while. Sometimes people who notice how much g77 depends on, and documents encouragement to use, f2c ask why g77 was created if f2c already existed.

This section gives some basic answers to these questions, though it is not intended to be comprehensive.

Next: Diagnostic Abilities, Up: Advantages Over f2c

#### 14.1.1 Language Extensions

g77 offers several extensions to FORTRAN 77 language that f2c doesn't:

- Automatic arrays
- `CYCLE` and `EXIT`
- Construct names
- `SELECT CASE`
- `KIND=` and `LEN=` notation
- Semicolon as statement separator
- Constant expressions in `FORMAT` statements (such as FORMAT(I<J>), where J is a `PARAMETER` named constant)
- `MvBits` intrinsic
- `libU77` (Unix-compatibility) library, with routines known to compiler as intrinsics (so they work even when compiler options are used to change the interfaces used by Fortran routines)

g77 also implements iterative `DO` loops so that they work even in the presence of certain “extreme” inputs, unlike f2c. See Loops.

However, f2c offers a few that g77 doesn't, such as:

- Intrinsics in `PARAMETER` statements
- Array bounds expressions (such as REAL M(N(2)))
- `AUTOMATIC` statement

It is expected that g77 will offer some or all of these missing features at some time in the future.

Next: Compiler Options, Previous: Language Extensions, Up: Advantages Over f2c

#### 14.1.2 Diagnostic Abilities

g77 offers better diagnosis of problems in `FORMAT` statements. f2c doesn't, for example, emit any diagnostic for FORMAT(XZFAJG10324), leaving that to be diagnosed, at run time, by the `libf2c` run-time library.

Next: Compiler Speed, Previous: Diagnostic Abilities, Up: Advantages Over f2c

#### 14.1.3 Compiler Options

g77 offers compiler options that f2c doesn't, most of which are designed to more easily accommodate legacy code:

- Two that control the automatic appending of extra underscores to external names
- One that allows dollar signs ($) in symbol names
- A variety that control acceptance of various “ugly” constructs
- Several that specify acceptable use of upper and lower case in the source code
- Many that enable, disable, delete, or hide groups of intrinsics
- One to specify the length of fixed-form source lines (normally 72)
- One to specify the the source code is written in Fortran-90-style free-form

However, f2c offers a few that g77 doesn't, like an option to have `REAL` default to `REAL*8`. It is expected that g77 will offer all of the missing options pertinent to being a Fortran compiler at some time in the future.

Next: Program Speed, Previous: Compiler Options, Up: Advantages Over f2c

#### 14.1.4 Compiler Speed

Saving the steps of writing and then rereading C code is a big reason why g77 should be able to compile code much faster than using f2c in conjunction with the equivalent invocation of gcc.

However, due to g77's youth, lots of self-checking is still being performed. As a result, this improvement is as yet unrealized (though the potential seems to be there for quite a big speedup in the future). It is possible that, as of version 0.5.18, g77 is noticeably faster compiling many Fortran source files than using f2c in conjunction with gcc.

Next: Ease of Debugging, Previous: Compiler Speed, Up: Advantages Over f2c

#### 14.1.5 Program Speed

g77 has the potential to better optimize code than f2c, even when gcc is used to compile the output of f2c, because f2c must necessarily translate Fortran into a somewhat lower-level language (C) that cannot preserve all the information that is potentially useful for optimization, while g77 can gather, preserve, and transmit that information directly to the GBE.

For example, g77 implements `ASSIGN` and assigned `GOTO` using direct assignment of pointers to labels and direct jumps to labels, whereas f2c maps the assigned labels to integer values and then uses a C `switch` statement to encode the assigned `GOTO` statements.

However, as is typical, theory and reality don't quite match, at least not in all cases, so it is still the case that f2c plus gcc can generate code that is faster than g77.

Version 0.5.18 of g77 offered default settings and options, via patches to the gcc back end, that allow for better program speed, though some of these improvements also affected the performance of programs translated by f2c and then compiled by g77's version of gcc.

Version 0.5.20 of g77 offers further performance improvements, at least one of which (alias analysis) is not generally applicable to f2c (though f2c could presumably be changed to also take advantage of this new capability of the gcc back end, assuming this is made available in an upcoming release of gcc).

Next: Character and Hollerith Constants, Previous: Program Speed, Up: Advantages Over f2c

#### 14.1.6 Ease of Debugging

Because g77 compiles directly to assembler code like gcc, instead of translating to an intermediate language (C) as does f2c, support for debugging can be better for g77 than f2c.

However, although g77 might be somewhat more “native” in terms of debugging support than f2c plus gcc, there still are a lot of things “not quite right”. Many of the important ones should be resolved in the near future.

For example, g77 doesn't have to worry about reserved names like f2c does. Given FOR = WHILE, f2c must necessarily translate this to something other than for = while;, because C reserves those words.

However, g77 does still uses things like an extra level of indirection for `ENTRY`-laden procedures—in this case, because the back end doesn't yet support multiple entry points.

Another example is that, given

         COMMON A, B
         EQUIVALENCE (B, C)

the g77 user should be able to access the variables directly, by name, without having to traverse C-like structures and unions, while f2c is unlikely to ever offer this ability (due to limitations in the C language).

Yet another example is arrays. g77 represents them to the debugger using the same “dimensionality” as in the source code, while f2c must necessarily convert them all to one-dimensional arrays to fit into the confines of the C language. However, the level of support offered by debuggers for interactive Fortran-style access to arrays as compiled by g77 can vary widely. In some cases, it can actually be an advantage that f2c converts everything to widely supported C semantics.

In fairness, g77 could do many of the things f2c does to get things working at least as well as f2c—for now, the developers prefer making g77 work the way they think it is supposed to, and finding help improving the other products (the back end of gcc; gdb; and so on) to get things working properly.

Previous: Ease of Debugging, Up: Advantages Over f2c

#### 14.1.7 Character and Hollerith Constants

To avoid the extensive hassle that would be needed to avoid this, f2c uses C character constants to encode character and Hollerith constants. That means a constant like 'HELLO' is translated to "hello" in C, which further means that an extra null byte is present at the end of the constant. This null byte is superfluous.

g77 does not generate such null bytes. This represents significant savings of resources, such as on systems where /dev/null or /dev/zero represent bottlenecks in the systems' performance, because g77 simply asks for fewer zeros from the operating system than f2c. (Avoiding spurious use of zero bytes, each byte typically have eight zero bits, also reduces the liabilities in case Microsoft's rumored patent on the digits 0 and 1 is upheld.)

Next: Loops, Previous: Advantages Over f2c, Up: Collected Fortran Wisdom

### 14.2 Block Data and Libraries

To ensure that block data program units are linked, especially a concern when they are put into libraries, give each one a name (as in BLOCK DATA FOO) and make sure there is an EXTERNAL FOO statement in every program unit that uses any common block initialized by the corresponding `BLOCK DATA`. g77 currently compiles a `BLOCK DATA` as if it were a `SUBROUTINE`, that is, it generates an actual procedure having the appropriate name. The procedure does nothing but return immediately if it happens to be called. For EXTERNAL FOO, where FOO is not otherwise referenced in the same program unit, g77 assumes there exists a BLOCK DATA FOO in the program and ensures that by generating a reference to it so the linker will make sure it is present. (Specifically, g77 outputs in the data section a static pointer to the external name FOO.)

The implementation g77 currently uses to make this work is one of the few things not compatible with f2c as currently shipped. f2c currently does nothing with EXTERNAL FOO except issue a warning that FOO is not otherwise referenced, and, for BLOCK DATA FOO, f2c doesn't generate a dummy procedure with the name FOO. The upshot is that you shouldn't mix f2c and g77 in this particular case. If you use f2c to compile BLOCK DATA FOO, then any g77-compiled program unit that says EXTERNAL FOO will result in an unresolved reference when linked. If you do the opposite, then FOO might not be linked in under various circumstances (such as when FOO is in a library, or you're using a “clever” linker—so clever, it produces a broken program with little or no warning by omitting initializations of global data because they are contained in unreferenced procedures).

The changes you make to your code to make g77 handle this situation, however, appear to be a widely portable way to handle it. That is, many systems permit it (as they should, since the FORTRAN 77 standard permits EXTERNAL FOO when FOO is a block data program unit), and of the ones that might not link BLOCK DATA FOO under some circumstances, most of them appear to do so once EXTERNAL FOO is present in the appropriate program units.

Here is the recommended approach to modifying a program containing a program unit such as the following:

         BLOCK DATA FOO
         COMMON /VARS/ X, Y, Z
         DATA X, Y, Z / 3., 4., 5. /
         END

If the above program unit might be placed in a library module, then ensure that every program unit in every program that references that particular `COMMON` area uses the `EXTERNAL` statement to force the area to be initialized.

For example, change a program unit that starts with

         INTEGER FUNCTION CURX()
         COMMON /VARS/ X, Y, Z
         CURX = X
         END

so that it uses the `EXTERNAL` statement, as in:

         INTEGER FUNCTION CURX()
         COMMON /VARS/ X, Y, Z
         EXTERNAL FOO
         CURX = X
         END

That way, CURX is compiled by g77 (and many other compilers) so that the linker knows it must include FOO, the `BLOCK DATA` program unit that sets the initial values for the variables in VAR, in the executable program.

Next: Working Programs, Previous: Block Data and Libraries, Up: Collected Fortran Wisdom

### 14.3 Loops

The meaning of a `DO` loop in Fortran is precisely specified in the Fortran standard...and is quite different from what many programmers might expect.

In particular, Fortran iterative `DO` loops are implemented as if the number of trips through the loop is calculated before the loop is entered.

The number of trips for a loop is calculated from the start, end, and increment values specified in a statement such as:

         DO iter = start, end, increment

The trip count is evaluated using a fairly simple formula based on the three values following the = in the statement, and it is that trip count that is effectively decremented during each iteration of the loop. If, at the beginning of an iteration of the loop, the trip count is zero or negative, the loop terminates. The per-loop-iteration modifications to iter are not related to determining whether to terminate the loop.

There are two important things to remember about the trip count:

- It can be negative, in which case it is treated as if it was zero—meaning the loop is not executed at all.
- The type used to calculate the trip count is the same type as iter, but the final calculation, and thus the type of the trip count itself, always is `INTEGER(KIND=1)`.

These two items mean that there are loops that cannot be written in straightforward fashion using the Fortran `DO`.

For example, on a system with the canonical 32-bit two's-complement implementation of `INTEGER(KIND=1)`, the following loop will not work:

         DO I = -2000000000, 2000000000

Although the start and end values are well within the range of `INTEGER(KIND=1)`, the trip count is not. The expected trip count is 40000000001, which is outside the range of `INTEGER(KIND=1)` on many systems.

Instead, the above loop should be constructed this way:

         I = -2000000000
         DO
           IF (I .GT. 2000000000) EXIT
           ...
           I = I + 1
         END DO

The simple `DO` construct and the `EXIT` statement (used to leave the innermost loop) are F90 features that g77 supports.

Some Fortran compilers have buggy implementations of `DO`, in that they don't follow the standard. They implement `DO` as a straightforward translation to what, in C, would be a `for` statement. Instead of creating a temporary variable to hold the trip count as calculated at run time, these compilers use the iteration variable iter to control whether the loop continues at each iteration.

The bug in such an implementation shows up when the trip count is within the range of the type of iter, but the magnitude of ABS(end) + ABS(incr) exceeds that range. For example:

         DO I = 2147483600, 2147483647

A loop started by the above statement will work as implemented by g77, but the use, by some compilers, of a more C-like implementation akin to

         for (i = 2147483600; i <= 2147483647; ++i)

produces a loop that does not terminate, because i can never be greater than 2147483647, since incrementing it beyond that value overflows i, setting it to -2147483648. This is a large, negative number that still is less than 2147483647.

Another example of unexpected behavior of `DO` involves using a nonintegral iteration variable iter, that is, a `REAL` variable. Consider the following program:

               DATA BEGIN, END, STEP /.1, .31, .007/
               DO 10 R = BEGIN, END, STEP
                  IF (R .GT. END) PRINT *, R, ' .GT. ', END, '!!'
                  PRINT *,R
         10    CONTINUE
               PRINT *,'LAST = ',R
               IF (R .LE. END) PRINT *, R, ' .LE. ', END, '!!'
               END

A C-like view of `DO` would hold that the two “exclamatory” `PRINT` statements are never executed. However, this is the output of running the above program as compiled by g77 on a GNU/Linux ix86 system:

          .100000001
          .107000001
          .114
          .120999999
          ...
          .289000005
          .296000004
          .303000003
         LAST =   .310000002
          .310000002 .LE.   .310000002!!

Note that one of the two checks in the program turned up an apparent violation of the programmer's expectation—yet, the loop is correctly implemented by g77, in that it has 30 iterations. This trip count of 30 is correct when evaluated using the floating-point representations for the begin, end, and incr values (.1, .31, .007) on GNU/Linux ix86 are used. On other systems, an apparently more accurate trip count of 31 might result, but, nevertheless, g77 is faithfully following the Fortran standard, and the result is not what the author of the sample program above apparently expected. (Such other systems might, for different values in the `DATA` statement, violate the other programmer's expectation, for example.)

Due to this combination of imprecise representation of floating-point values and the often-misunderstood interpretation of `DO` by standard-conforming compilers such as g77, use of `DO` loops with `REAL` iteration variables is not recommended. Such use can be caught by specifying -Wsurprising. See Warning Options, for more information on this option.

Next: Overly Convenient Options, Previous: Loops, Up: Collected Fortran Wisdom

### 14.4 Working Programs

Getting Fortran programs to work in the first place can be quite a challenge—even when the programs already work on other systems, or when using other compilers.

g77 offers some facilities that might be useful for tracking down bugs in such programs.

Next: Variables Assumed To Be Zero, Up: Working Programs

#### 14.4.1 Not My Type

A fruitful source of bugs in Fortran source code is use, or mis-use, of Fortran's implicit-typing feature, whereby the type of a variable, array, or function is determined by the first character of its name.

Simple cases of this include statements like LOGX=9.227, without a statement such as REAL LOGX. In this case, LOGX is implicitly given `INTEGER(KIND=1)` type, with the result of the assignment being that it is given the value 9.

More involved cases include a function that is defined starting with a statement like DOUBLE PRECISION FUNCTION IPS(...). Any caller of this function that does not also declare IPS as type `DOUBLE PRECISION` (or, in GNU Fortran, `REAL(KIND=2)`) is likely to assume it returns `INTEGER`, or some other type, leading to invalid results or even program crashes.

The -Wimplicit option might catch failures to properly specify the types of variables, arrays, and functions in the code.

However, in code that makes heavy use of Fortran's implicit-typing facility, this option might produce so many warnings about cases that are working, it would be hard to find the one or two that represent bugs. This is why so many experienced Fortran programmers strongly recommend widespread use of the `IMPLICIT NONE` statement, despite it not being standard FORTRAN 77, to completely turn off implicit typing. (g77 supports `IMPLICIT NONE`, as do almost all FORTRAN 77 compilers.)

Note that -Wimplicit catches only implicit typing of names. It does not catch implicit typing of expressions such as X**(2/3). Such expressions can be buggy as well—in fact, X**(2/3) is equivalent to X**0, due to the way Fortran expressions are given types and then evaluated. (In this particular case, the programmer probably wanted X**(2./3.).)

Next: Variables Assumed To Be Saved, Previous: Not My Type, Up: Working Programs

#### 14.4.2 Variables Assumed To Be Zero

Many Fortran programs were developed on systems that provided automatic initialization of all, or some, variables and arrays to zero. As a result, many of these programs depend, sometimes inadvertently, on this behavior, though to do so violates the Fortran standards.

You can ask g77 for this behavior by specifying the -finit-local-zero option when compiling Fortran code. (You might want to specify -fno-automatic as well, to avoid code-size inflation for non-optimized compilations.)

Note that a program that works better when compiled with the -finit-local-zero option is almost certainly depending on a particular system's, or compiler's, tendency to initialize some variables to zero. It might be worthwhile finding such cases and fixing them, using techniques such as compiling with the -O -Wuninitialized options using g77.

Next: Unwanted Variables, Previous: Variables Assumed To Be Zero, Up: Working Programs

#### 14.4.3 Variables Assumed To Be Saved

Many Fortran programs were developed on systems that saved the values of all, or some, variables and arrays across procedure calls. As a result, many of these programs depend, sometimes inadvertently, on being able to assign a value to a variable, perform a `RETURN` to a calling procedure, and, upon subsequent invocation, reference the previously assigned variable to obtain the value.

They expect this despite not using the `SAVE` statement to specify that the value in a variable is expected to survive procedure returns and calls. Depending on variables and arrays to retain values across procedure calls without using `SAVE` to require it violates the Fortran standards.

You can ask g77 to assume `SAVE` is specified for all relevant (local) variables and arrays by using the -fno-automatic option.

Note that a program that works better when compiled with the -fno-automatic option is almost certainly depending on not having to use the `SAVE` statement as required by the Fortran standard. It might be worthwhile finding such cases and fixing them, using techniques such as compiling with the -O -Wuninitialized options using g77.

Next: Unused Arguments, Previous: Variables Assumed To Be Saved, Up: Working Programs

#### 14.4.4 Unwanted Variables

The -Wunused option can find bugs involving implicit typing, sometimes more easily than using -Wimplicit in code that makes heavy use of implicit typing. An unused variable or array might indicate that the spelling for its declaration is different from that of its intended uses.

Other than cases involving typos, unused variables rarely indicate actual bugs in a program. However, investigating such cases thoroughly has, on occasion, led to the discovery of code that had not been completely written—where the programmer wrote declarations as needed for the whole algorithm, wrote some or even most of the code for that algorithm, then got distracted and forgot that the job was not complete.

Next: Surprising Interpretations of Code, Previous: Unwanted Variables, Up: Working Programs

#### 14.4.5 Unused Arguments

As with unused variables, It is possible that unused arguments to a procedure might indicate a bug. Compile with -W -Wunused option to catch cases of unused arguments.

Note that -W also enables warnings regarding overflow of floating-point constants under certain circumstances.

Next: Aliasing Assumed To Work, Previous: Unused Arguments, Up: Working Programs

#### 14.4.6 Surprising Interpretations of Code

The -Wsurprising option can help find bugs involving expression evaluation or in the way `DO` loops with non-integral iteration variables are handled. Cases found by this option might indicate a difference of interpretation between the author of the code involved, and a standard-conforming compiler such as g77. Such a difference might produce actual bugs.

In any case, changing the code to explicitly do what the programmer might have expected it to do, so g77 and other compilers are more likely to follow the programmer's expectations, might be worthwhile, especially if such changes make the program work better.

Next: Output Assumed To Flush, Previous: Surprising Interpretations of Code, Up: Working Programs

#### 14.4.7 Aliasing Assumed To Work

The -falias-check, -fargument-alias, -fargument-noalias, and -fno-argument-noalias-global options, introduced in version 0.5.20 and g77's version 2.7.2.2.f.2 of gcc, were withdrawn as of g77 version 0.5.23 due to their not being supported by gcc version 2.8.

These options control the assumptions regarding aliasing (overlapping) of writes and reads to main memory (core) made by the gcc back end.

The information below still is useful, but applies to only those versions of g77 that support the alias analysis implied by support for these options.

These options are effective only when compiling with -O (specifying any level other than -O0) or with -falias-check.

The default for Fortran code is -fargument-noalias-global. (The default for C code and code written in other C-based languages is -fargument-alias. These defaults apply regardless of whether you use g77 or gcc to compile your code.)

Note that, on some systems, compiling with -fforce-addr in effect can produce more optimal code when the default aliasing options are in effect (and when optimization is enabled).

If your program is not working when compiled with optimization, it is possible it is violating the Fortran standards (77 and 90) by relying on the ability to “safely” modify variables and arrays that are aliased, via procedure calls, to other variables and arrays, without using `EQUIVALENCE` to explicitly set up this kind of aliasing.

(The FORTRAN 77 standard's prohibition of this sort of overlap, generally referred to therein as “storage association”, appears in Sections 15.9.3.6. This prohibition allows implementations, such as g77, to, for example, implement the passing of procedures and even values in `COMMON` via copy operations into local, perhaps more efficiently accessed temporaries at entry to a procedure, and, where appropriate, via copy operations back out to their original locations in memory at exit from that procedure, without having to take into consideration the order in which the local copies are updated by the code, among other things.)

To test this hypothesis, try compiling your program with the -fargument-alias option, which causes the compiler to revert to assumptions essentially the same as made by versions of g77 prior to 0.5.20.

If the program works using this option, that strongly suggests that the bug is in your program. Finding and fixing the bug(s) should result in a program that is more standard-conforming and that can be compiled by g77 in a way that results in a faster executable.

(You might want to try compiling with -fargument-noalias, a kind of half-way point, to see if the problem is limited to aliasing between dummy arguments and `COMMON` variables—this option assumes that such aliasing is not done, while still allowing aliasing among dummy arguments.)

An example of aliasing that is invalid according to the standards is shown in the following program, which might not produce the expected results when executed:

         I = 1
         CALL FOO(I, I)
         PRINT *, I
         END

         SUBROUTINE FOO(J, K)
         J = J + K
         K = J * K
         PRINT *, J, K
         END

The above program attempts to use the temporary aliasing of the J and K arguments in FOO to effect a pathological behavior—the simultaneous changing of the values of both J and K when either one of them is written.

The programmer likely expects the program to print these values:

         2  4
         4

However, since the program is not standard-conforming, an implementation's behavior when running it is undefined, because subroutine FOO modifies at least one of the arguments, and they are aliased with each other. (Even if one of the assignment statements was deleted, the program would still violate these rules. This kind of on-the-fly aliasing is permitted by the standard only when none of the aliased items are defined, or written, while the aliasing is in effect.)

As a practical example, an optimizing compiler might schedule the J = part of the second line of FOO after the reading of J and K for the J * K expression, resulting in the following output:

         2  2
         2

Essentially, compilers are promised (by the standard and, therefore, by programmers who write code they claim to be standard-conforming) that if they cannot detect aliasing via static analysis of a single program unit's `EQUIVALENCE` and `COMMON` statements, no such aliasing exists. In such cases, compilers are free to assume that an assignment to one variable will not change the value of another variable, allowing it to avoid generating code to re-read the value of the other variable, to re-schedule reads and writes, and so on, to produce a faster executable.

The same promise holds true for arrays (as seen by the called procedure)—an element of one dummy array cannot be aliased with, or overlap, any element of another dummy array or be in a `COMMON` area known to the procedure.

(These restrictions apply only when the procedure defines, or writes to, one of the aliased variables or arrays.)

Unfortunately, there is no way to find all possible cases of violations of the prohibitions against aliasing in Fortran code. Static analysis is certainly imperfect, as is run-time analysis, since neither can catch all violations. (Static analysis can catch all likely violations, and some that might never actually happen, while run-time analysis can catch only those violations that actually happen during a particular run. Neither approach can cope with programs mixing Fortran code with routines written in other languages, however.)

Currently, g77 provides neither static nor run-time facilities to detect any cases of this problem, although other products might. Run-time facilities are more likely to be offered by future versions of g77, though patches improving g77 so that it provides either form of detection are welcome.

Next: Large File Unit Numbers, Previous: Aliasing Assumed To Work, Up: Working Programs

#### 14.4.8 Output Assumed To Flush

For several versions prior to 0.5.20, g77 configured its version of the `libf2c` run-time library so that one of its configuration macros, `ALWAYS_FLUSH`, was defined.

This was done as a result of a belief that many programs expected output to be flushed to the operating system (under UNIX, via the `fflush()` library call) with the result that errors, such as disk full, would be immediately flagged via the relevant `ERR=` and `IOSTAT=` mechanism.

Because of the adverse effects this approach had on the performance of many programs, g77 no longer configures `libf2c` (now named `libg2c` in its g77 incarnation) to always flush output.

If your program depends on this behavior, either insert the appropriate CALL FLUSH statements, or modify the sources to the `libg2c`, rebuild and reinstall g77, and relink your programs with the modified library.

(Ideally, `libg2c` would offer the choice at run-time, so that a compile-time option to g77 or f2c could result in generating the appropriate calls to flushing or non-flushing library routines.)

Some Fortran programs require output (writes) to be flushed to the operating system (under UNIX, via the `fflush()` library call) so that errors, such as disk full, are immediately flagged via the relevant `ERR=` and `IOSTAT=` mechanism, instead of such errors being flagged later as subsequent writes occur, forcing the previously written data to disk, or when the file is closed.

Essentially, the difference can be viewed as synchronous error reporting (immediate flagging of errors during writes) versus asynchronous, or, more precisely, buffered error reporting (detection of errors might be delayed).

`libg2c` supports flagging write errors immediately when it is built with the `ALWAYS_FLUSH` macro defined. This results in a `libg2c` that runs slower, sometimes quite a bit slower, under certain circumstances—for example, accessing files via the networked file system NFS—but the effect can be more reliable, robust file I/O.

If you know that Fortran programs requiring this level of precision of error reporting are to be compiled using the version of g77 you are building, you might wish to modify the g77 source tree so that the version of `libg2c` is built with the `ALWAYS_FLUSH` macro defined, enabling this behavior.

To do this, find this line in gcc/libf2c/f2c.h in your g77 source tree:

         /* #define ALWAYS_FLUSH */

Remove the leading /* , so the line begins with #define, and the trailing */.

Then build or rebuild g77 as appropriate.

Next: Floating-point precision, Previous: Output Assumed To Flush, Up: Working Programs

#### 14.4.9 Large File Unit Numbers

If your program crashes at run time with a message including the text illegal unit number, that probably is a message from the run-time library, `libg2c`.

The message means that your program has attempted to use a file unit number that is out of the range accepted by `libg2c`. Normally, this range is 0 through 99, and the high end of the range is controlled by a `libg2c` source-file macro named `MXUNIT`.

If you can easily change your program to use unit numbers in the range 0 through 99, you should do so.

As distributed, whether as part of f2c or g77, `libf2c` accepts file unit numbers only in the range 0 through 99. For example, a statement such as WRITE (UNIT=100) causes a run-time crash in `libf2c`, because the unit number, 100, is out of range.

If you know that Fortran programs at your installation require the use of unit numbers higher than 99, you can change the value of the `MXUNIT` macro, which represents the maximum unit number, to an appropriately higher value.

To do this, edit the file gcc/libf2c/libI77/fio.h in your g77 source tree, changing the following line:

         #define MXUNIT 100

Change the line so that the value of `MXUNIT` is defined to be at least one greater than the maximum unit number used by the Fortran programs on your system.

(For example, a program that does WRITE (UNIT=255) would require `MXUNIT` set to at least 256 to avoid crashing.)

Then build or rebuild g77 as appropriate.

Note: Changing this macro has no effect on other limits your system might place on the number of files open at the same time. That is, the macro might allow a program to do WRITE (UNIT=100), but the library and operating system underlying `libf2c` might disallow it if many other files have already been opened (via `OPEN` or implicitly via `READ`, `WRITE`, and so on). Information on how to increase these other limits should be found in your system's documentation.

Next: Inconsistent Calling Sequences, Previous: Large File Unit Numbers, Up: Working Programs

#### 14.4.10 Floating-point precision

If your program depends on exact IEEE 754 floating-point handling it may help on some systems—specifically x86 or m68k hardware—to use the -ffloat-store option or to reset the precision flag on the floating-point unit. See Optimize Options.

However, it might be better simply to put the FPU into double precision mode and not take the performance hit of -ffloat-store. On x86 and m68k GNU systems you can do this with a technique similar to that for turning on floating-point exceptions (see Floating-point Exception Handling). The control word could be set to double precision by some code like this one:

         #include <fpu_control.h>
         {
           fpu_control_t cw = (_FPU_DEFAULT & ~_FPU_EXTENDED) | _FPU_DOUBLE;
           _FPU_SETCW(cw);
         }

(It is not clear whether this has any effect on the operation of the GNU maths library, but we have no evidence of it causing trouble.)

Some targets (such as the Alpha) may need special options for full IEEE conformance. See Hardware Models and Configurations (Using the GNU Compiler Collection (GCC)).

Previous: Floating-point precision, Up: Working Programs

#### 14.4.11 Inconsistent Calling Sequences

Code containing inconsistent calling sequences in the same file is normally rejected—see GLOBALS. (Use, say, ftnchek to ensure consistency across source files. See Generating Skeletons and Prototypes with f2c.)

Mysterious errors, which may appear to be code generation problems, can appear specifically on the x86 architecture with some such inconsistencies. On x86 hardware, floating-point return values of functions are placed on the floating-point unit's register stack, not the normal stack. Thus calling a `REAL` or `DOUBLE PRECISION` `FUNCTION` as some other sort of procedure, or vice versa, scrambles the floating-point stack. This may break unrelated code executed later. Similarly if, say, external C routines are written incorrectly.

Next: Faster Programs, Previous: Working Programs, Up: Collected Fortran Wisdom

### 14.5 Overly Convenient Command-line Options

These options should be used only as a quick-and-dirty way to determine how well your program will run under different compilation models without having to change the source. Some are more problematic than others, depending on how portable and maintainable you want the program to be (and, of course, whether you are allowed to change it at all is crucial).

You should not continue to use these command-line options to compile a given program, but rather should make changes to the source code:

`-finit-local-zero`
  (This option specifies that any uninitialized local variables and arrays have default initialization to binary zeros.)

  Many other compilers do this automatically, which means lots of Fortran code developed with those compilers depends on it.

  It is safer (and probably would produce a faster program) to find the variables and arrays that need such initialization and provide it explicitly via `DATA`, so that -finit-local-zero is not needed.

  Consider using -Wuninitialized (which requires -O) to find likely candidates, but do not specify -finit-local-zero or -fno-automatic, or this technique won't work.

`-fno-automatic`
  (This option specifies that all local variables and arrays are to be treated as if they were named in `SAVE` statements.)

  Many other compilers do this automatically, which means lots of Fortran code developed with those compilers depends on it.

  The effect of this is that all non-automatic variables and arrays are made static, that is, not placed on the stack or in heap storage. This might cause a buggy program to appear to work better. If so, rather than relying on this command-line option (and hoping all compilers provide the equivalent one), add `SAVE` statements to some or all program unit sources, as appropriate. Consider using -Wuninitialized (which requires -O) to find likely candidates, but do not specify -finit-local-zero or -fno-automatic, or this technique won't work.

  The default is -fautomatic, which tells g77 to try and put variables and arrays on the stack (or in fast registers) where possible and reasonable. This tends to make programs faster.

  Note: Automatic variables and arrays are not affected by this option. These are variables and arrays that are necessarily automatic, either due to explicit statements, or due to the way they are declared. Examples include local variables and arrays not given the `SAVE` attribute in procedures declared `RECURSIVE`, and local arrays declared with non-constant bounds (automatic arrays). Currently, g77 supports only automatic arrays, not `RECURSIVE` procedures or other means of explicitly specifying that variables or arrays are automatic.

`-f` group`-intrinsics-hide`
  Change the source code to use `EXTERNAL` for any external procedure that might be the name of an intrinsic. It is easy to find these using -f group-intrinsics-disable.

Previous: Overly Convenient Options, Up: Collected Fortran Wisdom

### 14.6 Faster Programs

Aside from the usual gcc options, such as -O, -ffast-math, and so on, consider trying some of the following approaches to speed up your program (once you get it working).

Next: Prefer Automatic Uninitialized Variables, Up: Faster Programs

#### 14.6.1 Aligned Data

On some systems, such as those with Pentium Pro CPUs, programs that make heavy use of `REAL(KIND=2)` (`DOUBLE PRECISION`) might run much slower than possible due to the compiler not aligning these 64-bit values to 64-bit boundaries in memory. (The effect also is present, though to a lesser extent, on the 586 (Pentium) architecture.)

The Intel x86 architecture generally ensures that these programs will work on all its implementations, but particular implementations (such as Pentium Pro) perform better with more strict alignment. (Such behavior isn't unique to the Intel x86 architecture.) Other architectures might demand 64-bit alignment of 64-bit data.

There are a variety of approaches to use to address this problem:

- Order your `COMMON` and `EQUIVALENCE` areas such that the variables and arrays with the widest alignment guidelines come first.

  For example, on most systems, this would mean placing `COMPLEX(KIND=2)`, `REAL(KIND=2)`, and `INTEGER(KIND=2)` entities first, followed by `REAL(KIND=1)`, `INTEGER(KIND=1)`, and `LOGICAL(KIND=1)` entities, then `INTEGER(KIND=6)` entities, and finally `CHARACTER` and `INTEGER(KIND=3)` entities.

  The reason to use such placement is it makes it more likely that your data will be aligned properly, without requiring you to do detailed analysis of each aggregate (`COMMON` and `EQUIVALENCE`) area.

  Specifically, on systems where the above guidelines are appropriate, placing `CHARACTER` entities before `REAL(KIND=2)` entities can work just as well, but only if the number of bytes occupied by the `CHARACTER` entities is divisible by the recommended alignment for `REAL(KIND=2)`.

  By ordering the placement of entities in aggregate areas according to the simple guidelines above, you avoid having to carefully count the number of bytes occupied by each entity to determine whether the actual alignment of each subsequent entity meets the alignment guidelines for the type of that entity.

  If you don't ensure correct alignment of `COMMON` elements, the compiler may be forced by some systems to violate the Fortran semantics by adding padding to get `DOUBLE PRECISION` data properly aligned. If the unfortunate practice is employed of overlaying different types of data in the `COMMON` block, the different variants of this block may become misaligned with respect to each other. Even if your platform doesn't require strict alignment, `COMMON` should be laid out as above for portability. (Unfortunately the FORTRAN 77 standard didn't anticipate this possible requirement, which is compiler-independent on a given platform.)

- Use the (x86-specific) -malign-double option when compiling programs for the Pentium and Pentium Pro architectures (called 586 and 686 in the gcc configuration subsystem). The warning about this in the gcc manual isn't generally relevant to Fortran, but using it will force `COMMON` to be padded if necessary to align `DOUBLE PRECISION` data.

  When `DOUBLE PRECISION` data is forcibly aligned in `COMMON` by g77 due to specifying -malign-double, g77 issues a warning about the need to insert padding.

  In this case, each and every program unit that uses the same `COMMON` area must specify the same layout of variables and their types for that area and be compiled with -malign-double as well. g77 will issue warnings in each case, but as long as every program unit using that area is compiled with the same warnings, the resulting object files should work when linked together unless the program makes additional assumptions about `COMMON` area layouts that are outside the scope of the FORTRAN 77 standard, or uses `EQUIVALENCE` or different layouts in ways that assume no padding is ever inserted by the compiler.

- Ensure that crt0.o or crt1.o on your system guarantees a 64-bit aligned stack for `main()`. The recent one from GNU (`glibc2`) will do this on x86 systems, but we don't know of any other x86 setups where it will be right. Read your system's documentation to determine if it is appropriate to upgrade to a more recent version to obtain the optimal alignment.

Progress is being made on making this work “out of the box” on future versions of g77, gcc, and some of the relevant operating systems (such as GNU/Linux).

Next: Avoid f2c Compatibility, Previous: Aligned Data, Up: Faster Programs

#### 14.6.2 Prefer Automatic Uninitialized Variables

If you're using -fno-automatic already, you probably should change your code to allow compilation with -fautomatic (the default), to allow the program to run faster.

Similarly, you should be able to use -fno-init-local-zero (the default) instead of -finit-local-zero. This is because it is rare that every variable affected by these options in a given program actually needs to be so affected.

For example, -fno-automatic, which effectively `SAVE`s every local non-automatic variable and array, affects even things like `DO` iteration variables, which rarely need to be `SAVE`d, and this often reduces run-time performances. Similarly, -fno-init-local-zero forces such variables to be initialized to zero—when `SAVE`d (such as when -fno-automatic), this by itself generally affects only startup time for a program, but when not `SAVE`d, it can slow down the procedure every time it is called.

See Overly Convenient Command-Line Options, for information on the -fno-automatic and -finit-local-zero options and how to convert their use into selective changes in your own code.

Next: Use Submodel Options, Previous: Prefer Automatic Uninitialized Variables, Up: Faster Programs

#### 14.6.3 Avoid f2c Compatibility

If you aren't linking with any code compiled using f2c, try using the -fno-f2c option when compiling all the code in your program. (Note that `libf2c` is not an example of code that is compiled using f2c—it is compiled by a C compiler, typically gcc.)

Previous: Avoid f2c Compatibility, Up: Faster Programs

#### 14.6.4 Use Submodel Options

Using an appropriate -m option to generate specific code for your CPU may be worthwhile, though it may mean the executable won't run on other versions of the CPU that don't support the same instruction set. See Hardware Models and Configurations (Using the GNU Compiler Collection (GCC)). For instance on an x86 system the compiler might have been built—as shown by g77 -v—for the target i386-pc-linux-gnu, i.e. an i386 CPU. In that case to generate code best optimized for a Pentium you could use the option -march=pentium.

For recent CPUs that don't have explicit support in the released version of gcc, it might still be possible to get improvements with certain -m options.

-fomit-frame-pointer can help performance on x86 systems and others. It will, however, inhibit debugging on the systems on which it is not turned on anyway by -O.

Next: Open Questions, Previous: Collected Fortran Wisdom, Up: Top

## 15 Known Causes of Trouble with GNU Fortran

This section describes known problems that affect users of GNU Fortran. Most of these are not GNU Fortran bugs per se—if they were, we would fix them. But the result for a user might be like the result of a bug.

Some of these problems are due to bugs in other software, some are missing features that are too much work to add, and some are places where people's opinions differ as to what is best.

(Note that some of this portion of the manual is lifted directly from the gcc manual, with minor modifications to tailor it to users of g77. Anytime a bug seems to have more to do with the gcc portion of g77, see Known Causes of Trouble with GCC (Using the GNU Compiler Collection (GCC)).)

Next: Known Bugs, Up: Trouble

### 15.1 Bugs Not In GNU Fortran

These are bugs to which the maintainers often have to reply, “but that isn't a bug in g77...”. Some of these already are fixed in new versions of other software; some still need to be fixed; some are problems with how g77 is installed or is being used; some are the result of bad hardware that causes software to misbehave in sometimes bizarre ways; some just cannot be addressed at this time until more is known about the problem.

Please don't re-report these bugs to the g77 maintainers—if you must remind someone how important it is to you that the problem be fixed, talk to the people responsible for the other products identified below, but preferably only after you've tried the latest versions of those products. The g77 maintainers have their hands full working on just fixing and improving g77, without serving as a clearinghouse for all bugs that happen to affect g77 users.

See Collected Fortran Wisdom, for information on behavior of Fortran programs, and the programs that compile them, that might be thought to indicate bugs.

Next: Cannot Link Fortran Programs, Up: But-bugs

#### 15.1.1 Signal 11 and Friends

A whole variety of strange behaviors can occur when the software, or the way you are using the software, stresses the hardware in a way that triggers hardware bugs. This might seem hard to believe, but it happens frequently enough that there exist documents explaining in detail what the various causes of the problems are, what typical symptoms look like, and so on.

Generally these problems are referred to in this document as “signal 11” crashes, because the Linux kernel, running on the most popular hardware (the Intel x86 line), often stresses the hardware more than other popular operating systems. When hardware problems do occur under GNU/Linux on x86 systems, these often manifest themselves as “signal 11” problems, as illustrated by the following diagnostic:

         sh# g77 myprog.f
         gcc: Internal compiler error: program f771 got fatal signal 11
         sh#

It is very important to remember that the above message is not the only one that indicates a hardware problem, nor does it always indicate a hardware problem.

In particular, on systems other than those running the Linux kernel, the message might appear somewhat or very different, as it will if the error manifests itself while running a program other than the g77 compiler. For example, it will appear somewhat different when running your program, when running Emacs, and so on.

How to cope with such problems is well beyond the scope of this manual.

However, users of Linux-based systems (such as GNU/Linux) should review http://www.bitwizard.nl/sig11/, a source of detailed information on diagnosing hardware problems, by recognizing their common symptoms.

Users of other operating systems and hardware might find this reference useful as well. If you know of similar material for another hardware/software combination, please let us know so we can consider including a reference to it in future versions of this manual.

Next: Large Common Blocks, Previous: Signal 11 and Friends, Up: But-bugs

#### 15.1.2 Cannot Link Fortran Programs

On some systems, perhaps just those with out-of-date (shared?) libraries, unresolved-reference errors happen when linking g77-compiled programs (which should be done using g77).

If this happens to you, try appending -lc to the command you use to link the program, e.g. g77 foo.f -lc. g77 already specifies -lg2c -lm when it calls the linker, but it cannot also specify -lc because not all systems have a file named libc.a.

It is unclear at this point whether there are legitimately installed systems where -lg2c -lm is insufficient to resolve code produced by g77.

If your program doesn't link due to unresolved references to names like _main, make sure you're using the g77 command to do the link, since this command ensures that the necessary libraries are loaded by specifying -lg2c -lm when it invokes the gcc command to do the actual link. (Use the -v option to discover more about what actually happens when you use the g77 and gcc commands.)

Also, try specifying -lc as the last item on the g77 command line, in case that helps.

Next: Debugger Problems, Previous: Cannot Link Fortran Programs, Up: But-bugs

#### 15.1.3 Large Common Blocks

On some older GNU/Linux systems, programs with common blocks larger than 16MB cannot be linked without some kind of error message being produced.

This is a bug in older versions of ld, fixed in more recent versions of `binutils`, such as version 2.6.

Next: NeXTStep Problems, Previous: Large Common Blocks, Up: But-bugs

#### 15.1.4 Debugger Problems

There are some known problems when using gdb on code compiled by g77. Inadequate investigation as of the release of 0.5.16 results in not knowing which products are the culprit, but gdb-4.14 definitely crashes when, for example, an attempt is made to print the contents of a `COMPLEX(KIND=2)` dummy array, on at least some GNU/Linux machines, plus some others. Attempts to access assumed-size arrays are also known to crash recent versions of gdb. (gdb's Fortran support was done for a different compiler and isn't properly compatible with g77.)

Next: Stack Overflow, Previous: Debugger Problems, Up: But-bugs

#### 15.1.5 NeXTStep Problems

Developers of Fortran code on NeXTStep (all architectures) have to watch out for the following problem when writing programs with large, statically allocated (i.e. non-stack based) data structures (common blocks, saved arrays).

Due to the way the native loader (/bin/ld) lays out data structures in virtual memory, it is very easy to create an executable wherein the __DATA segment overlaps (has addresses in common) with the UNIX STACK segment.

This leads to all sorts of trouble, from the executable simply not executing, to bus errors. The NeXTStep command line tool ebadexec points to the problem as follows:

         % /bin/ebadexec a.out
         /bin/ebadexec: __LINKEDIT segment (truncated address = 0x3de000
         rounded size = 0x2a000) of executable file: a.out overlaps with UNIX
         STACK segment (truncated address = 0x400000 rounded size =
         0x3c00000) of executable file: a.out

(In the above case, it is the __LINKEDIT segment that overlaps the stack segment.)

This can be cured by assigning the __DATA segment (virtual) addresses beyond the stack segment. A conservative estimate for this is from address 6000000 (hexadecimal) onwards—this has always worked for me [Toon Moene]:

         % g77 -segaddr __DATA 6000000 test.f
         % ebadexec a.out
         ebadexec: file: a.out appears to be executable
         %

Browsing through gcc/gcc/f/Makefile.in, you will find that the `f771` program itself also has to be linked with these flags—it has large statically allocated data structures. (Version 0.5.18 reduces this somewhat, but probably not enough.)

(The above item was contributed by Toon Moene (toon@moene.indiv.nluug.nl).)

Next: Nothing Happens, Previous: NeXTStep Problems, Up: But-bugs

#### 15.1.6 Stack Overflow

g77 code might fail at runtime (probably with a “segmentation violation”) due to overflowing the stack. This happens most often on systems with an environment that provides substantially more heap space (for use when arbitrarily allocating and freeing memory) than stack space.

Often this can be cured by increasing or removing your shell's limit on stack usage, typically using `limit stacksize` (in csh and derivatives) or `ulimit -s` (in sh and derivatives).

Increasing the allowed stack size might, however, require changing some operating system or system configuration parameters.

You might be able to work around the problem by compiling with the -fno-automatic option to reduce stack usage, probably at the expense of speed.

g77, on most machines, puts many variables and arrays on the stack where possible, and can be configured (by changing `FFECOM_sizeMAXSTACKITEM` in gcc/gcc/f/com.c) to force smaller-sized entities into static storage (saving on stack space) or permit larger-sized entities to be put on the stack (which can improve run-time performance, as it presents more opportunities for the GBE to optimize the generated code).

Note: Putting more variables and arrays on the stack might cause problems due to system-dependent limits on stack size. Also, the value of `FFECOM_sizeMAXSTACKITEM` has no effect on automatic variables and arrays. See But-bugs, for more information. Note: While `libg2c` places a limit on the range of Fortran file-unit numbers, the underlying library and operating system might impose different kinds of limits. For example, some systems limit the number of files simultaneously open by a running program. Information on how to increase these limits should be found in your system's documentation.

However, if your program uses large automatic arrays (for example, has declarations like REAL A(N) where A is a local array and N is a dummy or `COMMON` variable that can have a large value), neither use of -fno-automatic, nor changing the cut-off point for g77 for using the stack, will solve the problem by changing the placement of these large arrays, as they are necessarily automatic.

g77 currently provides no means to specify that automatic arrays are to be allocated on the heap instead of the stack. So, other than increasing the stack size, your best bet is to change your source code to avoid large automatic arrays. Methods for doing this currently are outside the scope of this document.

(Note: If your system puts stack and heap space in the same memory area, such that they are effectively combined, then a stack overflow probably indicates a program that is either simply too large for the system, or buggy.)

Next: Strange Behavior at Run Time, Previous: Stack Overflow, Up: But-bugs

#### 15.1.7 Nothing Happens

It is occasionally reported that a “simple” program, such as a “Hello, World!” program, does nothing when it is run, even though the compiler reported no errors, despite the program containing nothing other than a simple `PRINT` statement.

This most often happens because the program has been compiled and linked on a UNIX system and named test, though other names can lead to similarly unexpected run-time behavior on various systems.

Essentially this problem boils down to giving your program a name that is already known to the shell you are using to identify some other program, which the shell continues to execute instead of your program when you invoke it via, for example:

         sh# test
         sh#

Under UNIX and many other system, a simple command name invokes a searching mechanism that might well not choose the program located in the current working directory if there is another alternative (such as the test command commonly installed on UNIX systems).

The reliable way to invoke a program you just linked in the current directory under UNIX is to specify it using an explicit pathname, as in:

         sh# ./test
          Hello, World!
         sh#

Users who encounter this problem should take the time to read up on how their shell searches for commands, how to set their search path, and so on. The relevant UNIX commands to learn about include man, info (on GNU systems), setenv (or set and env), which, and find.

Next: Floating-point Errors, Previous: Nothing Happens, Up: But-bugs

#### 15.1.8 Strange Behavior at Run Time

g77 code might fail at runtime with “segmentation violation”, “bus error”, or even something as subtle as a procedure call overwriting a variable or array element that it is not supposed to touch.

These can be symptoms of a wide variety of actual bugs that occurred earlier during the program's run, but manifested themselves as visible problems some time later.

Overflowing the bounds of an array—usually by writing beyond the end of it—is one of two kinds of bug that often occurs in Fortran code. (Compile your code with the -fbounds-check option to catch many of these kinds of errors at program run time.)

The other kind of bug is a mismatch between the actual arguments passed to a procedure and the dummy arguments as declared by that procedure.

Both of these kinds of bugs, and some others as well, can be difficult to track down, because the bug can change its behavior, or even appear to not occur, when using a debugger.

That is, these bugs can be quite sensitive to data, including data representing the placement of other data in memory (that is, pointers, such as the placement of stack frames in memory).

g77 now offers the ability to catch and report some of these problems at compile, link, or run time, such as by generating code to detect references to beyond the bounds of most arrays (except assumed-size arrays), and checking for agreement between calling and called procedures. Future improvements are likely to be made in the procedure-mismatch area, at least.

In the meantime, finding and fixing the programming bugs that lead to these behaviors is, ultimately, the user's responsibility, as difficult as that task can sometimes be.

One runtime problem that has been observed might have a simple solution. If a formatted `WRITE` produces an endless stream of spaces, check that your program is linked against the correct version of the C library. The configuration process takes care to account for your system's normal libc not being ANSI-standard, which will otherwise cause this behavior. If your system's default library is ANSI-standard and you subsequently link against a non-ANSI one, there might be problems such as this one.

Specifically, on Solaris2 systems, avoid picking up the `BSD` library from /usr/ucblib.

Previous: Strange Behavior at Run Time, Up: But-bugs

#### 15.1.9 Floating-point Errors

Some programs appear to produce inconsistent floating-point results compiled by g77 versus by other compilers.

Often the reason for this behavior is the fact that floating-point values are represented on almost all Fortran systems by approximations, and these approximations are inexact even for apparently simple values like 0.1, 0.2, 0.3, 0.4, 0.6, 0.7, 0.8, 0.9, 1.1, and so on. Most Fortran systems, including all current ports of g77, use binary arithmetic to represent these approximations.

Therefore, the exact value of any floating-point approximation as manipulated by g77-compiled code is representable by adding some combination of the values 1.0, 0.5, 0.25, 0.125, and so on (just keep dividing by two) through the precision of the fraction (typically around 23 bits for `REAL(KIND=1)`, 52 for `REAL(KIND=2)`), then multiplying the sum by a integral power of two (in Fortran, by 2**N) that typically is between -127 and +128 for `REAL(KIND=1)` and -1023 and +1024 for `REAL(KIND=2)`, then multiplying by -1 if the number is negative.

So, a value like 0.2 is exactly represented in decimal—since it is a fraction, 2/10, with a denominator that is compatible with the base of the number system (base 10). However, 2/10 cannot be represented by any finite number of sums of any of 1.0, 0.5, 0.25, and so on, so 0.2 cannot be exactly represented in binary notation.

(On the other hand, decimal notation can represent any binary number in a finite number of digits. Decimal notation cannot do so with ternary, or base-3, notation, which would represent floating-point numbers as sums of any of 1/1, 1/3, 1/9, and so on. After all, no finite number of decimal digits can exactly represent 1/3. Fortunately, few systems use ternary notation.)

Moreover, differences in the way run-time I/O libraries convert between these approximations and the decimal representation often used by programmers and the programs they write can result in apparent differences between results that do not actually exist, or exist to such a small degree that they usually are not worth worrying about.

For example, consider the following program:

         PRINT *, 0.2
         END

When compiled by g77, the above program might output 0.20000003, while another compiler might produce a executable that outputs 0.2.

This particular difference is due to the fact that, currently, conversion of floating-point values by the `libg2c` library, used by g77, handles only double-precision values.

Since 0.2 in the program is a single-precision value, it is converted to double precision (still in binary notation) before being converted back to decimal. The conversion to binary appends binary zero digits to the original value—which, again, is an inexact approximation of 0.2—resulting in an approximation that is much less exact than is connoted by the use of double precision.

(The appending of binary zero digits has essentially the same effect as taking a particular decimal approximation of 1/3, such as 0.3333333, and appending decimal zeros to it, producing 0.33333330000000000. Treating the resulting decimal approximation as if it really had 18 or so digits of valid precision would make it seem a very poor approximation of 1/3.)

As a result of converting the single-precision approximation to double precision by appending binary zeros, the conversion of the resulting double-precision value to decimal produces what looks like an incorrect result, when in fact the result is inexact, and is probably no less inaccurate or imprecise an approximation of 0.2 than is produced by other compilers that happen to output the converted value as “exactly” 0.2. (Some compilers behave in a way that can make them appear to retain more accuracy across a conversion of a single-precision constant to double precision. See Context-Sensitive Constants, to see why this practice is illusory and even dangerous.)

Note that a more exact approximation of the constant is computed when the program is changed to specify a double-precision constant:

         PRINT *, 0.2D0
         END

Future versions of g77 and/or `libg2c` might convert single-precision values directly to decimal, instead of converting them to double precision first. This would tend to result in output that is more consistent with that produced by some other Fortran implementations.

A useful source of information on floating-point computation is David Goldberg, `What Every Computer Scientist Should Know About Floating-Point Arithmetic', Computing Surveys, 23, March 1991, pp. 5-48. An online version is available at http://docs.sun.com/.

Information related to the IEEE 754 floating-point standard can be found at http://grouper.ieee.org/groups/754/ and http://http.cs.berkeley.edu/%7Ewkahan/ieee754status/; see also slides from the short course referenced from http://http.cs.berkeley.edu/%7Efateman/.

The supplement to the PostScript-formatted Goldberg document, referenced above, is available in HTML format. See `Differences Among IEEE 754 Implementations' by Doug Priest. This document explores some of the issues surrounding computing of extended (80-bit) results on processors such as the x86, especially when those results are arbitrarily truncated to 32-bit or 64-bit values by the compiler as “spills”.

(Note: g77 specifically, and gcc generally, does arbitrarily truncate 80-bit results during spills as of this writing. It is not yet clear whether a future version of the GNU compiler suite will offer 80-bit spills as an option, or perhaps even as the default behavior.)

The GNU C library provides routines for controlling the FPU, and other documentation about this.

See Floating-point precision, regarding IEEE 754 conformance.

Next: Missing Features, Previous: But-bugs, Up: Trouble

### 15.2 Known Bugs In GNU Fortran

This section identifies bugs that `g77` users might run into in the GCC-3.4.4 version of `g77`. This includes bugs that are actually in the `gcc` back end (GBE) or in `libf2c`, because those sets of code are at least somewhat under the control of (and necessarily intertwined with) `g77`, so it isn't worth separating them out.

For information on bugs in other versions of `g77`, see News About GNU Fortran. There, lists of bugs fixed in various versions of `g77` can help determine what bugs existed in prior versions.

The following information was last updated on 2004-05-18:

- `g77` fails to warn about use of a “live” iterative-DO variable as an implied-DO variable in a `WRITE` or `PRINT` statement (although it does warn about this in a `READ` statement).
- Something about `g77`'s straightforward handling of label references and definitions sometimes prevents the GBE from unrolling loops. Until this is solved, try inserting or removing `CONTINUE` statements as the terminal statement, using the `END DO` form instead, and so on.
- Some confusion in diagnostics concerning failing `INCLUDE` statements from within `INCLUDE`'d or `#include`'d files.

- `g77` assumes that `INTEGER(KIND=1)` constants range from -2**31 to 2**31-1 (the range for two's-complement 32-bit values), instead of determining their range from the actual range of the type for the configuration (and, someday, for the constant).

  Further, it generally doesn't implement the handling of constants very well in that it makes assumptions about the configuration that it no longer makes regarding variables (types).

  Included with this item is the fact that `g77` doesn't recognize that, on IEEE-754/854-compliant systems, 0./0. should produce a NaN and no warning instead of the value 0. and a warning.

- `g77` uses way too much memory and CPU time to process large aggregate areas having any initialized elements.

  For example, REAL A(1000000) followed by DATA A(1)/1/ takes up way too much time and space, including the size of the generated assembler file.

  Version 0.5.18 improves cases like this—specifically, cases of sparse initialization that leave large, contiguous areas uninitialized—significantly. However, even with the improvements, these cases still require too much memory and CPU time.

  (Version 0.5.18 also improves cases where the initial values are zero to a much greater degree, so if the above example ends with DATA A(1)/0/, the compile-time performance will be about as good as it will ever get, aside from unrelated improvements to the compiler.)

  Note that `g77` does display a warning message to notify the user before the compiler appears to hang. A warning message is issued when `g77` sees code that provides initial values (e.g. via `DATA`) to an aggregate area (`COMMON` or `EQUIVALENCE`, or even a large enough array or `CHARACTER` variable) that is large enough to increase `g77`'s compile time by roughly a factor of 10.

  This size currently is quite small, since `g77` currently has a known bug requiring too much memory and time to handle such cases. In gcc/gcc/f/data.c, the macro `FFEDATA_sizeTOO_BIG_INIT_` is defined to the minimum size for the warning to appear. The size is specified in storage units, which can be bytes, words, or whatever, on a case-by-case basis.

  After changing this macro definition, you must (of course) rebuild and reinstall `g77` for the change to take effect.

  Note that, as of version 0.5.18, improvements have reduced the scope of the problem for sparse initialization of large arrays, especially those with large, contiguous uninitialized areas. However, the warning is issued at a point prior to when `g77` knows whether the initialization is sparse, and delaying the warning could mean it is produced too late to be helpful.

  Therefore, the macro definition should not be adjusted to reflect sparse cases. Instead, adjust it to generate the warning when densely initialized arrays begin to cause responses noticeably slower than linear performance would suggest.

- When debugging, after starting up the debugger but before being able to see the source code for the main program unit, the user must currently set a breakpoint at `MAIN__` (or `MAIN___` or `MAIN_` if `MAIN__` doesn't exist) and run the program until it hits the breakpoint. At that point, the main program unit is activated and about to execute its first executable statement, but that's the state in which the debugger should start up, as is the case for languages like C.

- Debugging `g77`-compiled code using debuggers other than `gdb` is likely not to work.

  Getting `g77` and `gdb` to work together is a known problem—getting `g77` to work properly with other debuggers, for which source code often is unavailable to `g77` developers, seems like a much larger, unknown problem, and is a lower priority than making `g77` and `gdb` work together properly.

  On the other hand, information about problems other debuggers have with `g77` output might make it easier to properly fix `g77`, and perhaps even improve `gdb`, so it is definitely welcome. Such information might even lead to all relevant products working together properly sooner.

- `g77` doesn't work perfectly on 64-bit configurations such as the Digital Semiconductor (“DEC”) Alpha.

  This problem is largely resolved as of version 0.5.23.

- `g77` currently inserts needless padding for things like COMMON A,IPAD where A is `CHARACTER*1` and IPAD is `INTEGER(KIND=1)` on machines like x86, because the back end insists that IPAD be aligned to a 4-byte boundary, but the processor has no such requirement (though it is usually good for performance).

  The `gcc` back end needs to provide a wider array of specifications of alignment requirements and preferences for targets, and front ends like `g77` should take advantage of this when it becomes available.

- The `libf2c` routines that perform some run-time arithmetic on `COMPLEX` operands were modified circa version 0.5.20 of `g77` to work properly even in the presence of aliased operands.

  While the `g77` and `netlib` versions of `libf2c` differ on how this is accomplished, the main differences are that we believe the `g77` version works properly even in the presence of partially aliased operands.

  However, these modifications have reduced performance on targets such as x86, due to the extra copies of operands involved.

Next: Disappointments, Previous: Known Bugs, Up: Trouble

### 15.3 Missing Features

This section lists features we know are missing from g77, and which we want to add someday. (There is no priority implied in the ordering below.)

GNU Fortran language:

GNU Fortran dialects:

New facilities:

Better diagnostics:

Run-time facilities:

Debugging:

Next: Fortran 90 Support, Up: Missing Features

#### 15.3.1 Better Source Model

g77 needs to provide, as the default source-line model, a “pure visual” mode, where the interpretation of a source program in this mode can be accurately determined by a user looking at a traditionally displayed rendition of the program (assuming the user knows whether the program is fixed or free form).

The design should assume the user cannot tell tabs from spaces and cannot see trailing spaces on lines, but has canonical tab stops and, for fixed-form source, has the ability to always know exactly where column 72 is (since the Fortran standard itself requires this for fixed-form source).

This would change the default treatment of fixed-form source to not treat lines with tabs as if they were infinitely long—instead, they would end at column 72 just as if the tabs were replaced by spaces in the canonical way.

As part of this, provide common alternate models (Digital, f2c, and so on) via command-line options. This includes allowing arbitrarily long lines for free-form source as well as fixed-form source and providing various limits and diagnostics as appropriate.

Also, g77 should offer, perhaps even default to, warnings when characters beyond the last valid column are anything other than spaces. This would mean code with “sequence numbers” in columns 73 through 80 would be rejected, and there's a lot of that kind of code around, but one of the most frequent bugs encountered by new users is accidentally writing fixed-form source code into and beyond column 73. So, maybe the users of old code would be able to more easily handle having to specify, say, a -Wno-col73to80 option.

Next: Intrinsics in PARAMETER Statements, Previous: Better Source Model, Up: Missing Features

#### 15.3.2 Fortran 90 Support

g77 does not support many of the features that distinguish Fortran 90 (and, now, Fortran 95) from ANSI FORTRAN 77.

Some Fortran 90 features are supported, because they make sense to offer even to die-hard users of F77. For example, many of them codify various ways F77 has been extended to meet users' needs during its tenure, so g77 might as well offer them as the primary way to meet those same needs, even if it offers compatibility with one or more of the ways those needs were met by other F77 compilers in the industry.

Still, many important F90 features are not supported, because no attempt has been made to research each and every feature and assess its viability in g77. In the meantime, users who need those features must use Fortran 90 compilers anyway, and the best approach to adding some F90 features to GNU Fortran might well be to fund a comprehensive project to create GNU Fortran 95.

Next: Arbitrary Concatenation, Previous: Fortran 90 Support, Up: Missing Features

#### 15.3.3 Intrinsics in `PARAMETER` Statements

g77 doesn't allow intrinsics in `PARAMETER` statements.

Related to this, g77 doesn't allow non-integral exponentiation in `PARAMETER` statements, such as PARAMETER (R=2**.25). It is unlikely g77 will ever support this feature, as doing it properly requires complete emulation of a target computer's floating-point facilities when building g77 as a cross-compiler. But, if the gcc back end is enhanced to provide such a facility, g77 will likely use that facility in implementing this feature soon afterwards.

Next: SELECT CASE on CHARACTER Type, Previous: Intrinsics in PARAMETER Statements, Up: Missing Features

#### 15.3.4 Arbitrary Concatenation

g77 doesn't support arbitrary operands for concatenation in contexts where run-time allocation is required. For example:

         SUBROUTINE X(A)
         CHARACTER*(*) A
         CALL FOO(A // 'suffix')

Next: RECURSIVE Keyword, Previous: Arbitrary Concatenation, Up: Missing Features

#### 15.3.5 `SELECT CASE` on `CHARACTER` Type

Character-type selector/cases for `SELECT CASE` currently are not supported.

Next: Popular Non-standard Types, Previous: SELECT CASE on CHARACTER Type, Up: Missing Features

#### 15.3.6 `RECURSIVE` Keyword

g77 doesn't support the `RECURSIVE` keyword that F90 compilers do. Nor does it provide any means for compiling procedures designed to do recursion.

All recursive code can be rewritten to not use recursion, but the result is not pretty.

Next: Enabling Debug Lines, Previous: Support for Threads, Up: Missing Features

#### 15.3.7 Increasing Precision/Range

Some compilers, such as f2c, have an option (-r8, -qrealsize=8 or similar) that provides automatic treatment of `REAL` entities such that they have twice the storage size, and a corresponding increase in the range and precision, of what would normally be the `REAL(KIND=1)` (default `REAL`) type. (This affects `COMPLEX` the same way.)

They also typically offer another option (-i8) to increase `INTEGER` entities so they are twice as large (with roughly twice as much range).

(There are potential pitfalls in using these options.)

g77 does not yet offer any option that performs these kinds of transformations. Part of the problem is the lack of detailed specifications regarding exactly how these options affect the interpretation of constants, intrinsics, and so on.

Until g77 addresses this need, programmers could improve the portability of their code by modifying it to not require compile-time options to produce correct results. Some free tools are available which may help, specifically in Toolpack (which one would expect to be sound) and the fortran section of the Netlib repository.

Use of preprocessors can provide a fairly portable means to work around the lack of widely portable methods in the Fortran language itself (though increasing acceptance of Fortran 90 would alleviate this problem).

Next: Full Support for Compiler Types, Previous: RECURSIVE Keyword, Up: Missing Features

#### 15.3.8 Popular Non-standard Types

g77 doesn't fully support `INTEGER*2`, `LOGICAL*1`, and similar. In the meantime, version 0.5.18 provides rudimentary support for them.

Next: Array Bounds Expressions, Previous: Popular Non-standard Types, Up: Missing Features

#### 15.3.9 Full Support for Compiler Types

g77 doesn't support `INTEGER`, `REAL`, and `COMPLEX` equivalents for all applicable back-end-supported types (`char`, `short int`, `int`, `long int`, `long long int`, and `long double`). This means providing intrinsic support, and maybe constant support (using F90 syntax) as well, and, for most machines will result in automatic support of `INTEGER*1`, `INTEGER*2`, `INTEGER*8`, maybe even `REAL*16`, and so on.

Next: POINTER Statements, Previous: Full Support for Compiler Types, Up: Missing Features

#### 15.3.10 Array Bounds Expressions

g77 doesn't support more general expressions to dimension arrays, such as array element references, function references, etc.

For example, g77 currently does not accept the following:

         SUBROUTINE X(M, N)
         INTEGER N(10), M(N(2), N(1))

Next: Sensible Non-standard Constructs, Previous: Array Bounds Expressions, Up: Missing Features

#### 15.3.11 POINTER Statements

g77 doesn't support pointers or allocatable objects (other than automatic arrays). This set of features is probably considered just behind intrinsics in `PARAMETER` statements on the list of large, important things to add to g77.

In the meantime, consider using the `INTEGER(KIND=7)` declaration to specify that a variable must be able to hold a pointer. This construct is not portable to other non-GNU compilers, but it is portable to all machines GNU Fortran supports when g77 is used.

See Functions and Subroutines, for information on `%VAL()`, `%REF()`, and `%DESCR()` constructs, which are useful for passing pointers to procedures written in languages other than Fortran.

Next: READONLY Keyword, Previous: POINTER Statements, Up: Missing Features

#### 15.3.12 Sensible Non-standard Constructs

g77 rejects things other compilers accept, like INTRINSIC SQRT,SQRT. As time permits in the future, some of these things that are easy for humans to read and write and unlikely to be intended to mean something else will be accepted by g77 (though -fpedantic should trigger warnings about such non-standard constructs).

Until g77 no longer gratuitously rejects sensible code, you might as well fix your code to be more standard-conforming and portable.

The kind of case that is important to except from the recommendation to change your code is one where following good coding rules would force you to write non-standard code that nevertheless has a clear meaning.

For example, when writing an `INCLUDE` file that defines a common block, it might be appropriate to include a `SAVE` statement for the common block (such as SAVE /CBLOCK/), so that variables defined in the common block retain their values even when all procedures declaring the common block become inactive (return to their callers).

However, putting `SAVE` statements in an `INCLUDE` file would prevent otherwise standard-conforming code from also specifying the `SAVE` statement, by itself, to indicate that all local variables and arrays are to have the `SAVE` attribute.

For this reason, g77 already has been changed to allow this combination, because although the general problem of gratuitously rejecting unambiguous and “safe” constructs still exists in g77, this particular construct was deemed useful enough that it was worth fixing g77 for just this case.

So, while there is no need to change your code to avoid using this particular construct, there might be other, equally appropriate but non-standard constructs, that you shouldn't have to stop using just because g77 (or any other compiler) gratuitously rejects it.

Until the general problem is solved, if you have any such construct you believe is worthwhile using (e.g. not just an arbitrary, redundant specification of an attribute), please submit a bug report with an explanation, so we can consider fixing g77 just for cases like yours.

Next: FLUSH Statement, Previous: Sensible Non-standard Constructs, Up: Missing Features

#### 15.3.13 `READONLY` Keyword

Support for `READONLY`, in `OPEN` statements, requires `libg2c` support, to make sure that CLOSE(...,STATUS='DELETE') does not delete a file opened on a unit with the `READONLY` keyword, and perhaps to trigger a fatal diagnostic if a `WRITE` or `PRINT` to such a unit is attempted.

Note: It is not sufficient for g77 and `libg2c` (its version of `libf2c`) to assume that `READONLY` does not need some kind of explicit support at run time, due to UNIX systems not (generally) needing it. g77 is not just a UNIX-based compiler!

Further, mounting of non-UNIX filesystems on UNIX systems (such as via NFS) might require proper `READONLY` support.

(Similar issues might be involved with supporting the `SHARED` keyword.)

Next: Expressions in FORMAT Statements, Previous: READONLY Keyword, Up: Missing Features

#### 15.3.14 `FLUSH` Statement

g77 could perhaps use a `FLUSH` statement that does what CALL FLUSH does, but that supports * as the unit designator (same unit as for `PRINT`) and accepts `ERR=` and/or `IOSTAT=` specifiers.

Next: Explicit Assembler Code, Previous: FLUSH Statement, Up: Missing Features

#### 15.3.15 Expressions in `FORMAT` Statements

g77 doesn't support FORMAT(I<J>) and the like. Supporting this requires a significant redesign or replacement of `libg2c`.

However, g77 does support this construct when the expression is constant (as of version 0.5.22). For example:

               PARAMETER (IWIDTH = 12)
         10    FORMAT (I<IWIDTH>)

Otherwise, at least for output (`PRINT` and `WRITE`), Fortran code making use of this feature can be rewritten to avoid it by constructing the `FORMAT` string in a `CHARACTER` variable or array, then using that variable or array in place of the `FORMAT` statement label to do the original `PRINT` or `WRITE`.

Many uses of this feature on input can be rewritten this way as well, but not all can. For example, this can be rewritten:

               READ 20, I
         20    FORMAT (I<J>)

However, this cannot, in general, be rewritten, especially when `ERR=` and `END=` constructs are employed:

               READ 30, J, I
         30    FORMAT (I<J>)

Next: Q Edit Descriptor, Previous: Expressions in FORMAT Statements, Up: Missing Features

#### 15.3.16 Explicit Assembler Code

g77 needs to provide some way, a la gcc, for g77 code to specify explicit assembler code.

Next: Old-style PARAMETER Statements, Previous: Explicit Assembler Code, Up: Missing Features

#### 15.3.17 Q Edit Descriptor

The `Q` edit descriptor in `FORMAT`s isn't supported. (This is meant to get the number of characters remaining in an input record.) Supporting this requires a significant redesign or replacement of `libg2c`.

A workaround might be using internal I/O or the stream-based intrinsics. See FGetC Intrinsic (subroutine).

Next: TYPE and ACCEPT I/O Statements, Previous: Q Edit Descriptor, Up: Missing Features

#### 15.3.18 Old-style PARAMETER Statements

g77 doesn't accept PARAMETER I=1. Supporting this obsolete form of the `PARAMETER` statement would not be particularly hard, as most of the parsing code is already in place and working.

Until time/money is spent implementing it, you might as well fix your code to use the standard form, PARAMETER (I=1) (possibly needing INTEGER I preceding the `PARAMETER` statement as well, otherwise, in the obsolete form of `PARAMETER`, the type of the variable is set from the type of the constant being assigned to it).

Next: STRUCTURE UNION RECORD MAP, Previous: Old-style PARAMETER Statements, Up: Missing Features

#### 15.3.19 `TYPE` and `ACCEPT` I/O Statements

g77 doesn't support the I/O statements `TYPE` and `ACCEPT`. These are common extensions that should be easy to support, but also are fairly easy to work around in user code.

Generally, any TYPE fmt,list I/O statement can be replaced by PRINT fmt,list. And, any ACCEPT fmt,list statement can be replaced by READ fmt,list.

Next: OPEN CLOSE and INQUIRE Keywords, Previous: TYPE and ACCEPT I/O Statements, Up: Missing Features

#### 15.3.20 `STRUCTURE`, `UNION`, `RECORD`, `MAP`

g77 doesn't support `STRUCTURE`, `UNION`, `RECORD`, `MAP`. This set of extensions is quite a bit lower on the list of large, important things to add to g77, partly because it requires a great deal of work either upgrading or replacing `libg2c`.

Next: ENCODE and DECODE, Previous: STRUCTURE UNION RECORD MAP, Up: Missing Features

#### 15.3.21 `OPEN`, `CLOSE`, and `INQUIRE` Keywords

g77 doesn't have support for keywords such as `DISP='DELETE'` in the `OPEN`, `CLOSE`, and `INQUIRE` statements. These extensions are easy to add to g77 itself, but require much more work on `libg2c`.

g77 doesn't support `FORM='PRINT'` or an equivalent to translate the traditional `carriage control' characters in column 1 of output to use backspaces, carriage returns and the like. However programs exist to translate them in output files (or standard output). These are typically called either fpr or asa. You can get a version of asa from ftp://sunsite.unc.edu/pub/Linux/devel/lang/fortran for GNU systems which will probably build easily on other systems. Alternatively, fpr is in BSD distributions in various archive sites.

Next: AUTOMATIC Statement, Previous: OPEN CLOSE and INQUIRE Keywords, Up: Missing Features

#### 15.3.22 `ENCODE` and `DECODE`

g77 doesn't support `ENCODE` or `DECODE`.

These statements are best replaced by READ and WRITE statements involving internal files (CHARACTER variables and arrays).

For example, replace a code fragment like

               INTEGER*1 LINE(80)
         ...
               DECODE (80, 9000, LINE) A, B, C
         ...
         9000  FORMAT (1X, 3(F10.5))

with:

               CHARACTER*80 LINE
         ...
               READ (UNIT=LINE, FMT=9000) A, B, C
         ...
         9000  FORMAT (1X, 3(F10.5))

Similarly, replace a code fragment like

               INTEGER*1 LINE(80)
         ...
               ENCODE (80, 9000, LINE) A, B, C
         ...
         9000  FORMAT (1X, 'OUTPUT IS ', 3(F10.5))

with:

               CHARACTER*80 LINE
         ...
               WRITE (UNIT=LINE, FMT=9000) A, B, C
         ...
         9000  FORMAT (1X, 'OUTPUT IS ', 3(F10.5))

It is entirely possible that `ENCODE` and `DECODE` will be supported by a future version of g77.

Next: Suppressing Space Padding, Previous: ENCODE and DECODE, Up: Missing Features

#### 15.3.23 `AUTOMATIC` Statement

g77 doesn't support the `AUTOMATIC` statement that f2c does.

`AUTOMATIC` would identify a variable or array as not being `SAVE`'d, which is normally the default, but which would be especially useful for code that, generally, needed to be compiled with the -fno-automatic option.

`AUTOMATIC` also would serve as a hint to the compiler that placing the variable or array—even a very large array–on the stack is acceptable.

`AUTOMATIC` would not, by itself, designate the containing procedure as recursive.

`AUTOMATIC` should work syntactically like `SAVE`, in that `AUTOMATIC` with no variables listed should apply to all pertinent variables and arrays (which would not include common blocks or their members).

Variables and arrays denoted as `AUTOMATIC` would not be permitted to be initialized via `DATA` or other specification of any initial values, requiring explicit initialization, such as via assignment statements.

Perhaps `UNSAVE` and `STATIC`, as strict semantic opposites to `SAVE` and `AUTOMATIC`, should be provided as well.

Next: Fortran Preprocessor, Previous: AUTOMATIC Statement, Up: Missing Features

#### 15.3.24 Suppressing Space Padding of Source Lines

g77 should offer VXT-Fortran-style suppression of virtual spaces at the end of a source line if an appropriate command-line option is specified.

This affects cases where a character constant is continued onto the next line in a fixed-form source file, as in the following example:

         10    PRINT *,'HOW MANY
              1 SPACES?'

g77, and many other compilers, virtually extend the continued line through column 72 with spaces that become part of the character constant, but Digital Fortran normally didn't, leaving only one space between MANY and SPACES? in the output of the above statement.

Fairly recently, at least one version of Digital Fortran was enhanced to provide the other behavior when a command-line option is specified, apparently due to demand from readers of the USENET group comp.lang.fortran to offer conformance to this widespread practice in the industry. g77 should return the favor by offering conformance to Digital's approach to handling the above example.

Next: Bit Operations on Floating-point Data, Previous: Suppressing Space Padding, Up: Missing Features

#### 15.3.25 Fortran Preprocessor

g77 should offer a preprocessor designed specifically for Fortran to replace cpp -traditional. There are several out there worth evaluating, at least.

Such a preprocessor would recognize Hollerith constants, properly parse comments and character constants, and so on. It might also recognize, process, and thus preprocess files included via the `INCLUDE` directive.

Next: Really Ugly Character Assignments, Previous: Fortran Preprocessor, Up: Missing Features

#### 15.3.26 Bit Operations on Floating-point Data

g77 does not allow `REAL` and other non-integral types for arguments to intrinsics like `And`, `Or`, and `Shift`.

For example, this program is rejected by g77, because the intrinsic `Iand` does not accept `REAL` arguments:

         DATA A/7.54/, B/9.112/
         PRINT *, IAND(A, B)
         END

Next: POSIX Standard, Previous: Bit Operations on Floating-point Data, Up: Missing Features

#### 15.3.27 Really Ugly Character Assignments

An option such as -fugly-char should be provided to allow

         REAL*8 A1
         DATA A1 / '12345678' /

and:

         REAL*8 A1
         A1 = 'ABCDEFGH'

Next: Floating-point Exception Handling, Previous: Really Ugly Character Assignments, Up: Missing Features

#### 15.3.28 `POSIX` Standard

g77 should support the POSIX standard for Fortran.

Next: Nonportable Conversions, Previous: POSIX Standard, Up: Missing Features

#### 15.3.29 Floating-point Exception Handling

The gcc backend and, consequently, g77, currently provides no general control over whether or not floating-point exceptions are trapped or ignored. (Ignoring them typically results in NaN values being propagated in systems that conform to IEEE 754.) The behavior is normally inherited from the system-dependent startup code, though some targets, such as the Alpha, have code generation options which change the behavior.

Most systems provide some C-callable mechanism to change this; this can be invoked at startup using gcc's `constructor` attribute. For example, just compiling and linking the following C code with your program will turn on exception trapping for the “common” exceptions on a GNU system using glibc 2.2 or newer:

         #define _GNU_SOURCE 1
         #include <fenv.h>
         static void __attribute__ ((constructor))
         trapfpe ()
         {
           /* Enable some exceptions.  At startup all exceptions are masked.  */

           feenableexcept (FE_INVALID|FE_DIVBYZERO|FE_OVERFLOW);
         }

A convenient trick is to compile this something like:

         gcc -o libtrapfpe.a trapfpe.c

and then use it by adding -trapfpe to the g77 command line when linking.

Next: Large Automatic Arrays, Previous: Floating-point Exception Handling, Up: Missing Features

#### 15.3.30 Nonportable Conversions

g77 doesn't accept some particularly nonportable, silent data-type conversions such as `LOGICAL` to `REAL` (as in A=.FALSE., where A is type `REAL`), that other compilers might quietly accept.

Some of these conversions are accepted by g77 when the -fugly-logint option is specified. Perhaps it should accept more or all of them.

Next: Support for Threads, Previous: Nonportable Conversions, Up: Missing Features

#### 15.3.31 Large Automatic Arrays

Currently, automatic arrays always are allocated on the stack. For situations where the stack cannot be made large enough, g77 should offer a compiler option that specifies allocation of automatic arrays in heap storage.

Next: Increasing Precision/Range, Previous: Large Automatic Arrays, Up: Missing Features

#### 15.3.32 Support for Threads

Neither the code produced by g77 nor the `libg2c` library are thread-safe, nor does g77 have support for parallel processing (other than the instruction-level parallelism available on some processors). A package such as PVM might help here.

Next: Better Warnings, Previous: Increasing Precision/Range, Up: Missing Features

#### 15.3.33 Enabling Debug Lines

An option such as -fdebug-lines should be provided to turn fixed-form lines beginning with D to be treated as if they began with a space, instead of as if they began with a C (as comment lines).

Next: Gracefully Handle Sensible Bad Code, Previous: Enabling Debug Lines, Up: Missing Features

#### 15.3.34 Better Warnings

Because of how g77 generates code via the back end, it doesn't always provide warnings the user wants. Consider:

         PROGRAM X
         PRINT *, A
         END

Currently, the above is not flagged as a case of using an uninitialized variable, because g77 generates a run-time library call that looks, to the GBE, like it might actually modify A at run time. (And, in fact, depending on the previous run-time library call, it would!)

Fixing this requires one of the following:

- Switch to new library, `libg77`, that provides a more “clean” interface, vis-a-vis input, output, and modified arguments, so the GBE can tell what's going on.

  This would provide a pretty big performance improvement, at least theoretically, and, ultimately, in practice, for some types of code.

- Have g77 pass a pointer to a temporary containing a copy of A, instead of to A itself. The GBE would then complain about the copy operation involving a potentially uninitialized variable.

  This might also provide a performance boost for some code, because A might then end up living in a register, which could help with inner loops.

- Have g77 use a GBE construct similar to `ADDR_EXPR` but with extra information on the fact that the item pointed to won't be modified (a la `const` in C).

  Probably the best solution for now, but not quite trivial to implement in the general case.

Next: Non-standard Conversions, Previous: Better Warnings, Up: Missing Features

#### 15.3.35 Gracefully Handle Sensible Bad Code

g77 generally should continue processing for warnings and recoverable (user) errors whenever possible—that is, it shouldn't gratuitously make bad or useless code.

For example:

         INTRINSIC ZABS
         CALL FOO(ZABS)
         END

When compiling the above with -ff2c-intrinsics-disable, g77 should indeed complain about passing `ZABS`, but it still should compile, instead of rejecting the entire `CALL` statement. (Some of this is related to improving the compiler internals to improve how statements are analyzed.)

Next: Non-standard Intrinsics, Previous: Gracefully Handle Sensible Bad Code, Up: Missing Features

#### 15.3.36 Non-standard Conversions

-Wconversion and related should flag places where non-standard conversions are found. Perhaps much of this would be part of -Wugly*.

Next: Modifying DO Variable, Previous: Non-standard Conversions, Up: Missing Features

#### 15.3.37 Non-standard Intrinsics

g77 needs a new option, like -Wintrinsics, to warn about use of non-standard intrinsics without explicit `INTRINSIC` statements for them. This would help find code that might fail silently when ported to another compiler.

Next: Better Pedantic Compilation, Previous: Non-standard Intrinsics, Up: Missing Features

#### 15.3.38 Modifying `DO` Variable

g77 should warn about modifying `DO` variables via `EQUIVALENCE`. (The internal information gathered to produce this warning might also be useful in setting the internal “doiter” flag for a variable or even array reference within a loop, since that might produce faster code someday.)

For example, this code is invalid, so g77 should warn about the invalid assignment to NOTHER:

         EQUIVALENCE (I, NOTHER)
         DO I = 1, 100
            IF (I.EQ. 10) NOTHER = 20
         END DO

Next: Warn About Implicit Conversions, Previous: Modifying DO Variable, Up: Missing Features

#### 15.3.39 Better Pedantic Compilation

g77 needs to support -fpedantic more thoroughly, and use it only to generate warnings instead of rejecting constructs outright. Have it warn: if a variable that dimensions an array is not a dummy or placed explicitly in `COMMON` (F77 does not allow it to be placed in `COMMON` via `EQUIVALENCE`); if specification statements follow statement-function-definition statements; about all sorts of syntactic extensions.

Next: Invalid Use of Hollerith Constant, Previous: Better Pedantic Compilation, Up: Missing Features

#### 15.3.40 Warn About Implicit Conversions

g77 needs a -Wpromotions option to warn if source code appears to expect automatic, silent, and somewhat dangerous compiler-assisted conversion of `REAL(KIND=1)` constants to `REAL(KIND=2)` based on context.

For example, it would warn about cases like this:

         DOUBLE PRECISION FOO
         PARAMETER (TZPHI = 9.435784839284958)
         FOO = TZPHI * 3D0

Next: Dummy Array Without Dimensioning Dummy, Previous: Warn About Implicit Conversions, Up: Missing Features

#### 15.3.41 Invalid Use of Hollerith Constant

g77 should disallow statements like RETURN 2HAB, which are invalid in both source forms (unlike RETURN (2HAB), which probably still makes no sense but at least can be reliably parsed). Fixed-form processing rejects it, but not free-form, except in a way that is a bit difficult to understand.

Next: Invalid FORMAT Specifiers, Previous: Invalid Use of Hollerith Constant, Up: Missing Features

#### 15.3.42 Dummy Array Without Dimensioning Dummy

g77 should complain when a list of dummy arguments containing an adjustable dummy array does not also contain every variable listed in the dimension list of the adjustable array.

Currently, g77 does complain about a variable that dimensions an array but doesn't appear in any dummy list or `COMMON` area, but this needs to be extended to catch cases where it doesn't appear in every dummy list that also lists any arrays it dimensions.

For example, g77 should warn about the entry point ALT below, since it includes ARRAY but not ISIZE in its list of arguments:

         SUBROUTINE PRIMARY(ARRAY, ISIZE)
         REAL ARRAY(ISIZE)
         ENTRY ALT(ARRAY)

Next: Ambiguous Dialects, Previous: Dummy Array Without Dimensioning Dummy, Up: Missing Features

#### 15.3.43 Invalid FORMAT Specifiers

g77 should check `FORMAT` specifiers for validity as it does `FORMAT` statements.

For example, a diagnostic would be produced for:

         PRINT 'HI THERE!'  !User meant PRINT *, 'HI THERE!'

Next: Unused Labels, Previous: Invalid FORMAT Specifiers, Up: Missing Features

#### 15.3.44 Ambiguous Dialects

g77 needs a set of options such as -Wugly*, -Wautomatic, -Wvxt, -Wf90, and so on. These would warn about places in the user's source where ambiguities are found, helpful in resolving ambiguities in the program's dialect or dialects.

Next: Informational Messages, Previous: Ambiguous Dialects, Up: Missing Features

#### 15.3.45 Unused Labels

g77 should warn about unused labels when -Wunused is in effect.

Next: Uninitialized Variables at Run Time, Previous: Unused Labels, Up: Missing Features

#### 15.3.46 Informational Messages

g77 needs an option to suppress information messages (notes). -w does this but also suppresses warnings. The default should be to suppress info messages.

Perhaps info messages should simply be eliminated.

Next: Portable Unformatted Files, Previous: Informational Messages, Up: Missing Features

#### 15.3.47 Uninitialized Variables at Run Time

g77 needs an option to initialize everything (not otherwise explicitly initialized) to “weird” (machine-dependent) values, e.g. NaNs, bad (non-`NULL`) pointers, and largest-magnitude integers, would help track down references to some kinds of uninitialized variables at run time.

Note that use of the options -O -Wuninitialized can catch many such bugs at compile time.

Next: Better List-directed I/O, Previous: Uninitialized Variables at Run Time, Up: Missing Features

#### 15.3.48 Portable Unformatted Files

g77 has no facility for exchanging unformatted files with systems using different number formats—even differing only in endianness (byte order)—or written by other compilers. Some compilers provide facilities at least for doing byte-swapping during unformatted I/O.

It is unrealistic to expect to cope with exchanging unformatted files with arbitrary other compiler runtimes, but the g77 runtime should at least be able to read files written by g77 on systems with different number formats, particularly if they differ only in byte order.

In case you do need to write a program to translate to or from g77 (`libf2c`) unformatted files, they are written as follows:

Sequential
  Unformatted sequential records consist of
  1. A number giving the length of the record contents;
  2. the length of record contents again (for backspace).

  The record length is of C type `long`; this means that it is 8 bytes on 64-bit systems such as Alpha GNU/Linux and 4 bytes on other systems, such as x86 GNU/Linux. Consequently such files cannot be exchanged between 64-bit and 32-bit systems, even with the same basic number format.

Direct access
  Unformatted direct access files form a byte stream of length records*recl bytes, where records is the maximum record number (`REC=`records) written and recl is the record length in bytes specified in the `OPEN` statement (`RECL=`recl). Data appear in the records as determined by the relevant `WRITE` statement. Dummy records with arbitrary contents appear in the file in place of records which haven't been written.

Thus for exchanging a sequential or direct access unformatted file between big- and little-endian 32-bit systems using IEEE 754 floating point it would be sufficient to reverse the bytes in consecutive words in the file if, and only if, only `REAL*4`, `COMPLEX`, `INTEGER*4` and/or `LOGICAL*4` data have been written to it by g77.

If necessary, it is possible to do byte-oriented i/o with g77's `FGETC` and `FPUTC` intrinsics. Byte-swapping can be done in Fortran by equivalencing larger sized variables to an `INTEGER*1` array or a set of scalars.

If you need to exchange binary data between arbitrary system and compiler variations, we recommend using a portable binary format with Fortran bindings, such as NCSA's HDF (http://hdf.ncsa.uiuc.edu/) or PACT's PDB3 (http://www.llnl.gov/def_sci/pact/pact_homepage.html). (Unlike, say, CDF or XDR, HDF-like systems write in the native number formats and only incur overhead when they are read on a system with a different format.) A future g77 runtime library should use such techniques.

Next: Default to Console I/O, Previous: Portable Unformatted Files, Up: Missing Features

#### 15.3.49 Better List-directed I/O

Values output using list-directed I/O (PRINT *, R, D) should be written with a field width, precision, and so on appropriate for the type (precision) of each value.

(Currently, no distinction is made between single-precision and double-precision values by `libf2c`.)

It is likely this item will require the `libg77` project to be undertaken.

In the meantime, use of formatted I/O is recommended. While it might be of little consolation, g77 does support FORMAT(F<WIDTH>.4), for example, as long as WIDTH is defined as a named constant (via `PARAMETER`). That at least allows some compile-time specification of the precision of a data type, perhaps controlled by preprocessing directives.

Next: Labels Visible to Debugger, Previous: Better List-directed I/O, Up: Missing Features

#### 15.3.50 Default to Console I/O

The default I/O units, specified by READ fmt, READ (UNIT=*), WRITE (UNIT=*), and PRINT fmt, should not be units 5 (input) and 6 (output), but, rather, unit numbers not normally available for use in statements such as `OPEN` and `CLOSE`.

Changing this would allow a program to connect units 5 and 6 to files via `OPEN`, but still use READ (UNIT=*) and PRINT to do I/O to the “console”.

This change probably requires the `libg77` project.

Previous: Default to Console I/O, Up: Missing Features

#### 15.3.51 Labels Visible to Debugger

g77 should output debugging information for statements labels, for use by debuggers that know how to support them. Same with weirder things like construct names. It is not yet known if any debug formats or debuggers support these.

Next: Non-bugs, Previous: Missing Features, Up: Trouble

### 15.4 Disappointments and Misunderstandings

These problems are perhaps regrettable, but we don't know any practical way around them for now.

Next: Multiple Definitions of External Names, Up: Disappointments

#### 15.4.1 Mangling of Names in Source Code

The current external-interface design, which includes naming of external procedures, COMMON blocks, and the library interface, has various usability problems, including things like adding underscores where not really necessary (and preventing easier inter-language operability) and yet not providing complete namespace freedom for user C code linked with Fortran apps (due to the naming of functions in the library, among other things).

Project GNU should at least get all this “right” for systems it fully controls, such as the Hurd, and provide defaults and options for compatibility with existing systems and interoperability with popular existing compilers.

Next: Limitation on Implicit Declarations, Previous: Mangling of Names, Up: Disappointments

#### 15.4.2 Multiple Definitions of External Names

g77 doesn't allow a common block and an external procedure or `BLOCK DATA` to have the same name. Some systems allow this, but g77 does not, to be compatible with f2c.

g77 could special-case the way it handles `BLOCK DATA`, since it is not compatible with f2c in this particular area (necessarily, since g77 offers an important feature here), but it is likely that such special-casing would be very annoying to people with programs that use EXTERNAL FOO, with no other mention of FOO in the same program unit, to refer to external procedures, since the result would be that g77 would treat these references as requests to force-load BLOCK DATA program units.

In that case, if g77 modified names of `BLOCK DATA` so they could have the same names as `COMMON`, users would find that their programs wouldn't link because the FOO procedure didn't have its name translated the same way.

(Strictly speaking, g77 could emit a null-but-externally-satisfying definition of FOO with its name transformed as if it had been a `BLOCK DATA`, but that probably invites more trouble than it's worth.)

Previous: Multiple Definitions of External Names, Up: Disappointments

#### 15.4.3 Limitation on Implicit Declarations

g77 disallows `IMPLICIT CHARACTER*(*)`. This is not standard-conforming.

Next: Warnings and Errors, Previous: Disappointments, Up: Trouble

### 15.5 Certain Changes We Don't Want to Make

This section lists changes that people frequently request, but which we do not make because we think GNU Fortran is better without them.

Next: Initializing Before Specifying, Up: Non-bugs

#### 15.5.1 Backslash in Constants

In the opinion of many experienced Fortran users, -fno-backslash should be the default, not -fbackslash, as currently set by g77.

First of all, you can always specify -fno-backslash to turn off this processing.

Despite not being within the spirit (though apparently within the letter) of the ANSI FORTRAN 77 standard, g77 defaults to -fbackslash because that is what most UNIX f77 commands default to, and apparently lots of code depends on this feature.

This is a particularly troubling issue. The use of a C construct in the midst of Fortran code is bad enough, worse when it makes existing Fortran programs stop working (as happens when programs written for non-UNIX systems are ported to UNIX systems with compilers that provide the -fbackslash feature as the default—sometimes with no option to turn it off).

The author of GNU Fortran wished, for reasons of linguistic purity, to make -fno-backslash the default for GNU Fortran and thus require users of UNIX f77 and f2c to specify -fbackslash to get the UNIX behavior.

However, the realization that g77 is intended as a replacement for UNIX f77, caused the author to choose to make g77 as compatible with f77 as feasible, which meant making -fbackslash the default.

The primary focus on compatibility is at the source-code level, and the question became “What will users expect a replacement for f77 to do, by default?” Although at least one UNIX f77 does not provide -fbackslash as a default, it appears that the majority of them do, which suggests that the majority of code that is compiled by UNIX f77 compilers expects -fbackslash to be the default.

It is probably the case that more code exists that would not work with -fbackslash in force than code that requires it be in force.

However, most of that code is not being compiled with f77, and when it is, new build procedures (shell scripts, makefiles, and so on) must be set up anyway so that they work under UNIX. That makes a much more natural and safe opportunity for non-UNIX users to adapt their build procedures for g77's default of -fbackslash than would exist for the majority of UNIX f77 users who would have to modify existing, working build procedures to explicitly specify -fbackslash if that was not the default.

One suggestion has been to configure the default for -fbackslash (and perhaps other options as well) based on the configuration of g77.

This is technically quite straightforward, but will be avoided even in cases where not configuring defaults to be dependent on a particular configuration greatly inconveniences some users of legacy code.

Many users appreciate the GNU compilers because they provide an environment that is uniform across machines. These users would be inconvenienced if the compiler treated things like the format of the source code differently on certain machines.

Occasionally users write programs intended only for a particular machine type. On these occasions, the users would benefit if the GNU Fortran compiler were to support by default the same dialect as the other compilers on that machine. But such applications are rare. And users writing a program to run on more than one type of machine cannot possibly benefit from this kind of compatibility. (This is consistent with the design goals for gcc. To change them for g77, you must first change them for gcc. Do not ask the maintainers of g77 to do this for you, or to disassociate g77 from the widely understood, if not widely agreed-upon, goals for GNU compilers in general.)

This is why GNU Fortran does and will treat backslashes in the same fashion on all types of machines (by default). See Direction of Language Development, for more information on this overall philosophy guiding the development of the GNU Fortran language.

Of course, users strongly concerned about portability should indicate explicitly in their build procedures which options are expected by their source code, or write source code that has as few such expectations as possible.

For example, avoid writing code that depends on backslash (\) being interpreted either way in particular, such as by starting a program unit with:

         CHARACTER BACKSL
         PARAMETER (BACKSL = '\\')

Then, use concatenation of BACKSL anyplace a backslash is desired. In this way, users can write programs which have the same meaning in many Fortran dialects.

(However, this technique does not work for Hollerith constants—which is just as well, since the only generally portable uses for Hollerith constants are in places where character constants can and should be used instead, for readability.)

Next: Context-Sensitive Intrinsicness, Previous: Backslash in Constants, Up: Non-bugs

#### 15.5.2 Initializing Before Specifying

g77 does not allow DATA VAR/1/ to appear in the source code before COMMON VAR, DIMENSION VAR(10), INTEGER VAR, and so on. In general, g77 requires initialization of a variable or array to be specified after all other specifications of attributes (type, size, placement, and so on) of that variable or array are specified (though confirmation of data type is permitted).

It is possible g77 will someday allow all of this, even though it is not allowed by the FORTRAN 77 standard.

Then again, maybe it is better to have g77 always require placement of `DATA` so that it can possibly immediately write constants to the output file, thus saving time and space.

That is, DATA A/1000000*1/ should perhaps always be immediately writable to canonical assembler, unless it's already known to be in a `COMMON` area following as-yet-uninitialized stuff, and to do this it cannot be followed by COMMON A.

Next: Context-Sensitive Constants, Previous: Initializing Before Specifying, Up: Non-bugs

#### 15.5.3 Context-Sensitive Intrinsicness

g77 treats procedure references to possible intrinsic names as always enabling their intrinsic nature, regardless of whether the form of the reference is valid for that intrinsic.

For example, CALL SQRT is interpreted by g77 as an invalid reference to the `SQRT` intrinsic function, because the reference is a subroutine invocation.

First, g77 recognizes the statement CALL SQRT as a reference to a procedure named SQRT, not to a variable with that name (as it would for a statement such as V = SQRT).

Next, g77 establishes that, in the program unit being compiled, `SQRT` is an intrinsic—not a subroutine that happens to have the same name as an intrinsic (as would be the case if, for example, EXTERNAL SQRT was present).

Finally, g77 recognizes that the form of the reference is invalid for that particular intrinsic. That is, it recognizes that it is invalid for an intrinsic function, such as `SQRT`, to be invoked as a subroutine.

At that point, g77 issues a diagnostic.

Some users claim that it is “obvious” that CALL SQRT references an external subroutine of their own, not an intrinsic function.

However, g77 knows about intrinsic subroutines, not just functions, and is able to support both having the same names, for example.

As a result of this, g77 rejects calls to intrinsics that are not subroutines, and function invocations of intrinsics that are not functions, just as it (and most compilers) rejects invocations of intrinsics with the wrong number (or types) of arguments.

So, use the EXTERNAL SQRT statement in a program unit that calls a user-written subroutine named SQRT.

Next: Equivalence Versus Equality, Previous: Context-Sensitive Intrinsicness, Up: Non-bugs

#### 15.5.4 Context-Sensitive Constants

g77 does not use context to determine the types of constants or named constants (`PARAMETER`), except for (non-standard) typeless constants such as '123'O.

For example, consider the following statement:

         PRINT *, 9.435784839284958 * 2D0

g77 will interpret the (truncated) constant 9.435784839284958 as a `REAL(KIND=1)`, not `REAL(KIND=2)`, constant, because the suffix `D0` is not specified.

As a result, the output of the above statement when compiled by g77 will appear to have “less precision” than when compiled by other compilers.

In these and other cases, some compilers detect the fact that a single-precision constant is used in a double-precision context and therefore interpret the single-precision constant as if it was explicitly specified as a double-precision constant. (This has the effect of appending decimal, not binary, zeros to the fractional part of the number—producing different computational results.)

The reason this misfeature is dangerous is that a slight, apparently innocuous change to the source code can change the computational results. Consider:

         REAL ALMOST, CLOSE
         DOUBLE PRECISION FIVE
         PARAMETER (ALMOST = 5.000000000001)
         FIVE = 5
         CLOSE = 5.000000000001
         PRINT *, 5.000000000001 - FIVE
         PRINT *, ALMOST - FIVE
         PRINT *, CLOSE - FIVE
         END

Running the above program should result in the same value being printed three times. With g77 as the compiler, it does.

However, compiled by many other compilers, running the above program would print two or three distinct values, because in two or three of the statements, the constant 5.000000000001, which on most systems is exactly equal to 5. when interpreted as a single-precision constant, is instead interpreted as a double-precision constant, preserving the represented precision. However, this “clever” promotion of type does not extend to variables or, in some compilers, to named constants.

Since programmers often are encouraged to replace manifest constants or permanently-assigned variables with named constants (`PARAMETER` in Fortran), and might need to replace some constants with variables having the same values for pertinent portions of code, it is important that compilers treat code so modified in the same way so that the results of such programs are the same. g77 helps in this regard by treating constants just the same as variables in terms of determining their types in a context-independent way.

Still, there is a lot of existing Fortran code that has been written to depend on the way other compilers freely interpret constants' types based on context, so anything g77 can do to help flag cases of this in such code could be very helpful.

Next: Order of Side Effects, Previous: Context-Sensitive Constants, Up: Non-bugs

#### 15.5.5 Equivalence Versus Equality

Use of `.EQ.` and `.NE.` on `LOGICAL` operands is not supported, except via -fugly-logint, which is not recommended except for legacy code (where the behavior expected by the code is assumed).

Legacy code should be changed, as resources permit, to use `.EQV.` and `.NEQV.` instead, as these are permitted by the various Fortran standards.

New code should never be written expecting `.EQ.` or `.NE.` to work if either of its operands is `LOGICAL`.

The problem with supporting this “feature” is that there is unlikely to be consensus on how it works, as illustrated by the following sample program:

         LOGICAL L,M,N
         DATA L,M,N /3*.FALSE./
         IF (L.AND.M.EQ.N) PRINT *,'L.AND.M.EQ.N'
         END

The issue raised by the above sample program is: what is the precedence of `.EQ.` (and `.NE.`) when applied to `LOGICAL` operands?

Some programmers will argue that it is the same as the precedence for `.EQ.` when applied to numeric (such as `INTEGER`) operands. By this interpretation, the subexpression M.EQ.N must be evaluated first in the above program, resulting in a program that, when run, does not execute the `PRINT` statement.

Other programmers will argue that the precedence is the same as the precedence for `.EQV.`, which is restricted by the standards to `LOGICAL` operands. By this interpretation, the subexpression L.AND.M must be evaluated first, resulting in a program that does execute the `PRINT` statement.

Assigning arbitrary semantic interpretations to syntactic expressions that might legitimately have more than one “obvious” interpretation is generally unwise.

The creators of the various Fortran standards have done a good job in this case, requiring a distinct set of operators (which have their own distinct precedence) to compare `LOGICAL` operands. This requirement results in expression syntax with more certain precedence (without requiring substantial context), making it easier for programmers to read existing code. g77 will avoid muddying up elements of the Fortran language that were well-designed in the first place.

(Ask C programmers about the precedence of expressions such as (a) & (b) and (a) - (b)—they cannot even tell you, without knowing more context, whether the & and - operators are infix (binary) or unary!)

Most dangerous of all is the fact that, even assuming consensus on its meaning, an expression like L.AND.M.EQ.N, if it is the result of a typographical error, doesn't look like it has such a typo. Even experienced Fortran programmers would not likely notice that L.AND.M.EQV.N was, in fact, intended.

So, this is a prime example of a circumstance in which a quality compiler diagnoses the code, instead of leaving it up to someone debugging it to know to turn on special compiler options that might diagnose it.

Previous: Equivalence Versus Equality, Up: Non-bugs

#### 15.5.6 Order of Side Effects

g77 does not necessarily produce code that, when run, performs side effects (such as those performed by function invocations) in the same order as in some other compiler—or even in the same order as another version, port, or invocation (using different command-line options) of g77.

It is never safe to depend on the order of evaluation of side effects. For example, an expression like this may very well behave differently from one compiler to another:

         J = IFUNC() - IFUNC()

There is no guarantee that IFUNC will be evaluated in any particular order. Either invocation might happen first. If IFUNC returns 5 the first time it is invoked, and returns 12 the second time, J might end up with the value 7, or it might end up with -7.

Generally, in Fortran, procedures with side-effects intended to be visible to the caller are best designed as subroutines, not functions. Examples of such side-effects include:

- The generation of random numbers that are intended to influence return values.
- Performing I/O (other than internal I/O to local variables).
- Updating information in common blocks.

An example of a side-effect that is not intended to be visible to the caller is a function that maintains a cache of recently calculated results, intended solely to speed repeated invocations of the function with identical arguments. Such a function can be safely used in expressions, because if the compiler optimizes away one or more calls to the function, operation of the program is unaffected (aside from being speeded up).

Previous: Non-bugs, Up: Trouble

### 15.6 Warning Messages and Error Messages

The GNU compiler can produce two kinds of diagnostics: errors and warnings. Each kind has a different purpose:

- Errors report problems that make it impossible to compile your program. GNU Fortran reports errors with the source file name, line number, and column within the line where the problem is apparent.
- Warnings report other unusual conditions in your code that might indicate a problem, although compilation can (and does) proceed. Warning messages also report the source file name, line number, and column information, but include the text warning: to distinguish them from error messages.

Warnings might indicate danger points where you should check to make sure that your program really does what you intend; or the use of obsolete features; or the use of nonstandard features of GNU Fortran. Many warnings are issued only if you ask for them, with one of the -W options (for instance, -Wall requests a variety of useful warnings).

Note: Currently, the text of the line and a pointer to the column is printed in most g77 diagnostics.

See Options to Request or Suppress Warnings, for more detail on these and related command-line options.

Next: Bugs, Previous: Trouble, Up: Top

## 16 Open Questions

Please consider offering useful answers to these questions!

- `LOC()` and other intrinsics are probably somewhat misclassified. Is the a need for more precise classification of intrinsics, and if so, what are the appropriate groupings? Is there a need to individually enable/disable/delete/hide intrinsics from the command line?

Next: Service, Previous: Open Questions, Up: Top

## 17 Reporting Bugs

Your bug reports play an essential role in making GNU Fortran reliable.

When you encounter a problem, the first thing to do is to see if it is already known. See Trouble. If it isn't known, then you should report the problem.

See Known Causes of Trouble with GNU Fortran, for information on problems we already know about.

See How To Get Help with GNU Fortran, for information on where to ask for help.

Next: Bug Reporting, Up: Bugs

### 17.1 Have You Found a Bug?

If you are not sure whether you have found a bug, here are some guidelines:

- If the compiler gets a fatal signal, for any input whatever, that is a compiler bug. Reliable compilers never crash—they just remain obsolete.

- If the compiler produces invalid assembly code, for any input whatever, that is a compiler bug, unless the compiler reports errors (not just warnings) which would ordinarily prevent the assembler from being run.

- If the compiler produces valid assembly code that does not correctly execute the input source code, that is a compiler bug.

  However, you must double-check to make sure, because you might have run into an incompatibility between GNU Fortran and traditional Fortran. These incompatibilities might be considered bugs, but they are inescapable consequences of valuable features.

  Or you might have a program whose behavior is undefined, which happened by chance to give the desired results with another Fortran compiler. It is best to check the relevant Fortran standard thoroughly if it is possible that the program indeed does something undefined.

  After you have localized the error to a single source line, it should be easy to check for these things. If your program is correct and well defined, you have found a compiler bug.

  It might help if, in your submission, you identified the specific language in the relevant Fortran standard that specifies the desired behavior, if it isn't likely to be obvious and agreed-upon by all Fortran users.

- If the compiler produces an error message for valid input, that is a compiler bug.

- If the compiler does not produce an error message for invalid input, that is a compiler bug. However, you should note that your idea of “invalid input” might be someone else's idea of “an extension” or “support for traditional practice”.
- If you are an experienced user of Fortran compilers, your suggestions for improvement of GNU Fortran are welcome in any case.

Many, perhaps most, bug reports against g77 turn out to be bugs in the user's code. While we find such bug reports educational, they sometimes take a considerable amount of time to track down or at least respond to—time we could be spending making g77, not some user's code, better.

Some steps you can take to verify that the bug is not certainly in the code you're compiling with g77:

- Compile your code using the g77 options -W -Wall -O. These options enable many useful warning; the -O option enables flow analysis that enables the uninitialized-variable warning.

  If you investigate the warnings and find evidence of possible bugs in your code, fix them first and retry g77.

- Compile your code using the g77 options -finit-local-zero, -fno-automatic, -ffloat-store, and various combinations thereof.

  If your code works with any of these combinations, that is not proof that the bug isn't in g77—a g77 bug exposed by your code might simply be avoided, or have a different, more subtle effect, when different options are used—but it can be a strong indicator that your code is making unwarranted assumptions about the Fortran dialect and/or underlying machine it is being compiled and run on.

  See Overly Convenient Command-Line Options, for information on the -fno-automatic and -finit-local-zero options and how to convert their use into selective changes in your own code.

- Validate your code with ftnchek or a similar code-checking tool. ftnchek can be found at ftp://ftp.netlib.org/fortran or ftp://ftp.dsm.fordham.edu.

  Here are some sample Makefile rules using ftnchek “project” files to do cross-file checking and sfmakedepend (from ftp://ahab.rutgers.edu/pub/perl/sfmakedepend) to maintain dependencies automatically. These assume the use of GNU make.

                # Dummy suffix for ftnchek targets:
                .SUFFIXES: .chek
                .PHONY: chekall

                # How to compile .f files (for implicit rule):
                FC = g77
                # Assume `include' directory:
                FFLAGS = -Iinclude -g -O -Wall

                # Flags for ftnchek:
                CHEK1 = -array=0 -include=includes -noarray
                CHEK2 = -nonovice -usage=1 -notruncation
                CHEKFLAGS = $(CHEK1) $(CHEK2)

                # Run ftnchek with all the .prj files except the one corresponding
                # to the target's root:
                %.chek : %.f ; \
                  ftnchek $(filter-out $*.prj,$(PRJS)) $(CHEKFLAGS) \
                    -noextern -library $<

                # Derive a project file from a source file:
                %.prj : %.f ; \
                  ftnchek $(CHEKFLAGS) -noextern -project -library $<

                # The list of objects is assumed to be in variable OBJS.
                # Sources corresponding to the objects:
                SRCS = $(OBJS:%.o=%.f)
                # ftnchek project files:
                PRJS = $(OBJS:%.o=%.prj)

                # Build the program
                prog: $(OBJS) ; \
                  $(FC) -o $ $(OBJS)

                chekall: $(PRJS) ; \
                  ftnchek $(CHEKFLAGS) $(PRJS)

                prjs: $(PRJS)

                # For Emacs M-x find-tag:
                TAGS: $(SRCS) ; \
                  etags $(SRCS)

                # Rebuild dependencies:
                depend: ; \
                  sfmakedepend -I $(PLTLIBDIR) -I includes -a prj $(SRCS1)

- Try your code out using other Fortran compilers, such as f2c. If it does not work on at least one other compiler (assuming the compiler supports the features the code needs), that is a strong indicator of a bug in the code.

  However, even if your code works on many compilers except g77, that does not mean the bug is in g77. It might mean the bug is in your code, and that g77 simply exposes it more readily than other compilers.

Previous: Bug Criteria, Up: Bugs

### 17.2 How to Report Bugs

Bugs should be reported to our bug database. Please refer to http://gcc.gnu.org/bugs.html for up-to-date instructions how to submit bug reports. Copies of this file in HTML (bugs.html) and plain text (BUGS) are also part of GCC releases.

Next: Adding Options, Previous: Bugs, Up: Top

## 18 How To Get Help with GNU Fortran

If you need help installing, using or changing GNU Fortran, there are two ways to find it:

- Look in the service directory for someone who might help you for a fee. The service directory is found in the file named SERVICE in the GCC distribution.
- Send a message to gcc-help@gcc.gnu.org.

Next: Projects, Previous: Service, Up: Top

## 19 Adding Options

To add a new command-line option to g77, first decide what kind of option you wish to add. Search the g77 and gcc documentation for one or more options that is most closely like the one you want to add (in terms of what kind of effect it has, and so on) to help clarify its nature.

- Fortran options are options that apply only when compiling Fortran programs. They are accepted by g77 and gcc, but they apply only when compiling Fortran programs.
- Compiler options are options that apply when compiling most any kind of program.

Fortran options are listed in the file gcc/gcc/f/lang-options.h, which is used during the build of gcc to build a list of all options that are accepted by at least one language's compiler. This list goes into the `documented_lang_options` array in gcc/toplev.c, which uses this array to determine whether a particular option should be offered to the linked-in front end for processing by calling `lang_option_decode`, which, for g77, is in gcc/gcc/f/com.c and just calls `ffe_decode_option`.

If the linked-in front end “rejects” a particular option passed to it, toplev.c just ignores the option, because some language's compiler is willing to accept it.

This allows commands like gcc -fno-asm foo.c bar.f to work, even though Fortran compilation does not currently support the -fno-asm option; even though the `f771` version of `lang_decode_option` rejects -fno-asm, toplev.c doesn't produce a diagnostic because some other language (C) does accept it.

This also means that commands like g77 -fno-asm foo.f yield no diagnostics, despite the fact that no phase of the command was able to recognize and process -fno-asm—perhaps a warning about this would be helpful if it were possible.

Code that processes Fortran options is found in gcc/gcc/f/top.c, function `ffe_decode_option`. This code needs to check positive and negative forms of each option.

The defaults for Fortran options are set in their global definitions, also found in gcc/gcc/f/top.c. Many of these defaults are actually macros defined in gcc/gcc/f/target.h, since they might be machine-specific. However, since, in practice, GNU compilers should behave the same way on all configurations (especially when it comes to language constructs), the practice of setting defaults in target.h is likely to be deprecated and, ultimately, stopped in future versions of g77.

Accessor macros for Fortran options, used by code in the g77 FFE, are defined in gcc/gcc/f/top.h.

Compiler options are listed in gcc/toplev.c in the array `f_options`. An option not listed in `lang_options` is looked up in `f_options` and handled from there.

The defaults for compiler options are set in the global definitions for the corresponding variables, some of which are in gcc/toplev.c.

You can set different defaults for Fortran-oriented or Fortran-reticent compiler options by changing the source code of g77 and rebuilding. How to do this depends on the version of g77:

`G77 0.5.24 (EGCS 1.1)`
`G77 0.5.25 (EGCS 1.2 - which became GCC 2.95)`
  Change the `lang_init_options` routine in gcc/gcc/f/com.c.

  (Note that these versions of g77 perform internal consistency checking automatically when the -fversion option is specified.)

`G77 0.5.23`
`G77 0.5.24 (EGCS 1.0)`
  Change the way `f771` handles the -fset-g77-defaults option, which is always provided as the first option when called by g77 or gcc.

  This code is in `ffe_decode_options` in gcc/gcc/f/top.c. Have it change just the variables that you want to default to a different setting for Fortran compiles compared to compiles of other languages.

  The -fset-g77-defaults option is passed to `f771` automatically because of the specification information kept in gcc/gcc/f/lang-specs.h. This file tells the gcc command how to recognize, in this case, Fortran source files (those to be preprocessed, and those that are not), and further, how to invoke the appropriate programs (including `f771`) to process those source files.

  It is in gcc/gcc/f/lang-specs.h that -fset-g77-defaults, -fversion, and other options are passed, as appropriate, even when the user has not explicitly specified them. Other “internal” options such as -quiet also are passed via this mechanism.

Next: Front End, Previous: Adding Options, Up: Top

## 20 Projects

If you want to contribute to g77 by doing research, design, specification, documentation, coding, or testing, the following information should give you some ideas.

Next: Better Optimization, Up: Projects

### 20.1 Improve Efficiency

Don't bother doing any performance analysis until most of the following items are taken care of, because there's no question they represent serious space/time problems, although some of them show up only given certain kinds of (popular) input.

- Improve `malloc` package and its uses to specify more info about memory pools and, where feasible, use obstacks to implement them.
- Skip over uninitialized portions of aggregate areas (arrays, `COMMON` areas, `EQUIVALENCE` areas) so zeros need not be output. This would reduce memory usage for large initialized aggregate areas, even ones with only one initialized element.

  As of version 0.5.18, a portion of this item has already been accomplished.

- Prescan the statement (in sta.c) so that the nature of the statement is determined as much as possible by looking entirely at its form, and not looking at any context (previous statements, including types of symbols). This would allow ripping out of the statement-confirmation, symbol retraction/confirmation, and diagnostic inhibition mechanisms. Plus, it would result in much-improved diagnostics. For example, CALL some-intrinsic(...), where the intrinsic is not a subroutine intrinsic, would result actual error instead of the unimplemented-statement catch-all.
- Throughout g77, don't pass line/column pairs where a simple `ffewhere` type, which points to the error as much as is desired by the configuration, will do, and don't pass `ffelexToken` types where a simple `ffewhere` type will do. Then, allow new default configuration of `ffewhere` such that the source line text is not preserved, and leave it to things like Emacs' next-error function to point to them (now that next-error supports column, or, perhaps, character-offset, numbers). The change in calling sequences should improve performance somewhat, as should not having to save source lines. (Whether this whole item will improve performance is questionable, but it should improve maintainability.)
- Handle DATA (A(I),I=1,1000000)/1000000*2/ more efficiently, especially as regards the assembly output. Some of this might require improving the back end, but lots of improvement in space/time required in g77 itself can be fairly easily obtained without touching the back end. Maybe type-conversion, where necessary, can be speeded up as well in cases like the one shown (converting the 2 into 2.).
- If analysis shows it to be worthwhile, optimize lex.c.
- Consider redesigning lex.c to not need any feedback during tokenization, by keeping track of enough parse state on its own.

Next: Simplify Porting, Previous: Efficiency, Up: Projects

### 20.2 Better Optimization

Much of this work should be put off until after g77 has all the features necessary for its widespread acceptance as a useful F77 compiler. However, perhaps this work can be done in parallel during the feature-adding work.

- Do the equivalent of the trick of putting extern inline in front of every function definition in `libg2c` and #include'ing the resulting file in f2c+gcc—that is, inline all run-time-library functions that are at all worth inlining. (Some of this has already been done, such as for integral exponentiation.)
- When doing CHAR_VAR = CHAR_FUNC(...), and it's clear that types line up and CHAR_VAR is addressable or not a `VAR_DECL`, make CHAR_VAR, not a temporary, be the receiver for CHAR_FUNC. (This is now done for `COMPLEX` variables.)
- Design and implement Fortran-specific optimizations that don't really belong in the back end, or where the front end needs to give the back end more info than it currently does.
- Design and implement a new run-time library interface, with the code going into `libgcc` so no special linking is required to link Fortran programs using standard language features. This library would speed up lots of things, from I/O (using precompiled formats, doing just one, or, at most, very few, calls for arrays or array sections, and so on) to general computing (array/section implementations of various intrinsics, implementation of commonly performed loops that aren't likely to be optimally compiled otherwise, etc.).

  Among the important things the library would do are:

  - Be a one-stop-shop-type library, hence shareable and usable by all, in that what are now library-build-time options in `libg2c` would be moved at least to the g77 compile phase, if not to finer grains (such as choosing how list-directed I/O formatting is done by default at `OPEN` time, for preconnected units via options or even statements in the main program unit, maybe even on a per-I/O basis with appropriate pragma-like devices).
- Probably requiring the new library design, change interface to normally have `COMPLEX` functions return their values in the way gcc would if they were declared `__complex__ float`, rather than using the mechanism currently used by `CHARACTER` functions (whereby the functions are compiled as returning void and their first arg is a pointer to where to store the result). (Don't append underscores to external names for `COMPLEX` functions in some cases once g77 uses gcc rather than f2c calling conventions.)
- Do something useful with `doiter` references where possible. For example, CALL FOO(I) cannot modify I if within a `DO` loop that uses I as the iteration variable, and the back end might find that info useful in determining whether it needs to read I back into a register after the call. (It normally has to do that, unless it knows FOO never modifies its passed-by-reference argument, which is rarely the case for Fortran-77 code.)

Next: More Extensions, Previous: Better Optimization, Up: Projects

### 20.3 Simplify Porting

Making g77 easier to configure, port, build, and install, either as a single-system compiler or as a cross-compiler, would be very useful.

- A new library (replacing `libg2c`) should improve portability as well as produce more optimal code. Further, g77 and the new library should conspire to simplify naming of externals, such as by removing unnecessarily added underscores, and to reduce/eliminate the possibility of naming conflicts, while making debugger more straightforward.

  Also, it should make multi-language applications more feasible, such as by providing Fortran intrinsics that get Fortran unit numbers given C `FILE *` descriptors.

- Possibly related to a new library, g77 should produce the equivalent of a gcc main(argc, argv) function when it compiles a main program unit, instead of compiling something that must be called by a library implementation of `main()`.

  This would do many useful things such as provide more flexibility in terms of setting up exception handling, not requiring programmers to start their debugging sessions with `breakpoint MAIN__` followed by `run`, and so on.

- The GBE needs to understand the difference between alignment requirements and desires. For example, on Intel x86 machines, g77 currently imposes overly strict alignment requirements, due to the back end, but it would be useful for Fortran and C programmers to be able to override these recommendations as long as they don't violate the actual processor requirements.

Next: Machine Model, Previous: Simplify Porting, Up: Projects

### 20.4 More Extensions

These extensions are not the sort of things users ask for “by name”, but they might improve the usability of g77, and Fortran in general, in the long run. Some of these items really pertain to improving g77 internals so that some popular extensions can be more easily supported.

- Look through all the documentation on the GNU Fortran language, dialects, compiler, missing features, bugs, and so on. Many mentions of incomplete or missing features are sprinkled throughout. It is not worth repeating them here.
- Consider adding a `NUMERIC` type to designate typeless numeric constants, named and unnamed. The idea is to provide a forward-looking, effective replacement for things like the old-style `PARAMETER` statement when people really need typelessness in a maintainable, portable, clearly documented way. Maybe `TYPELESS` would include `CHARACTER`, `POINTER`, and whatever else might come along. (This is not really a call for polymorphism per se, just an ability to express limited, syntactic polymorphism.)
- Support OPEN(...,KEY=(...),...).
- Support arbitrary file unit numbers, instead of limiting them to 0 through MXUNIT-1. (This is a `libg2c` issue.)
- OPEN(NOSPANBLOCKS,...) is treated as OPEN(UNIT=NOSPANBLOCKS,...), so a later `UNIT=` in the first example is invalid. Make sure this is what users of this feature would expect.
- Currently g77 disallows READ(1'10) since it is an obnoxious syntax, but supporting it might be pretty easy if needed. More details are needed, such as whether general expressions separated by an apostrophe are supported, or maybe the record number can be a general expression, and so on.
- Support `STRUCTURE`, `UNION`, `MAP`, and `RECORD` fully. Currently there is no support at all for `%FILL` in `STRUCTURE` and related syntax, whereas the rest of the stuff has at least some parsing support. This requires either major changes to `libg2c` or its replacement.
- F90 and g77 probably disagree about label scoping relative to `INTERFACE` and `END INTERFACE`, and their contained procedure interface bodies (blocks?).
- `ENTRY` doesn't support F90 `RESULT()` yet, since that was added after S8.112.
- Empty-statement handling (10 ;;CONTINUE;;) probably isn't consistent with the final form of the standard (it was vague at S8.112).
- It seems to be an “open” question whether a file, immediately after being `OPEN`ed,is positioned at the beginning, the end, or wherever—it might be nice to offer an option of opening to “undefined” status, requiring an explicit absolute-positioning operation to be performed before any other (besides `CLOSE`) to assist in making applications port to systems (some IBM?) that `OPEN` to the end of a file or some such thing.

Next: Internals Documentation, Previous: More Extensions, Up: Projects

### 20.5 Machine Model

This items pertain to generalizing g77's view of the machine model to more fully accept whatever the GBE provides it via its configuration.

- Switch to using `REAL_VALUE_TYPE` to represent floating-point constants exclusively so the target float format need not be required. This means changing the way g77 handles initialization of aggregate areas having more than one type, such as `REAL` and `INTEGER`, because currently it initializes them as if they were arrays of `char` and uses the bit patterns of the constants of the various types in them to determine what to stuff in elements of the arrays.
- Rely more and more on back-end info and capabilities, especially in the area of constants (where having the g77 front-end's IL just store the appropriate tree nodes containing constants might be best).
- Suite of C and Fortran programs that a user/administrator can run on a machine to help determine the configuration for g77 before building and help determine if the compiler works (especially with whatever libraries are installed) after building.

Next: Internals Improvements, Previous: Machine Model, Up: Projects

### 20.6 Internals Documentation

Better info on how g77 works and how to port it is needed.

See Front End, which contains some information on g77 internals.

Next: Better Diagnostics, Previous: Internals Documentation, Up: Projects

### 20.7 Internals Improvements

Some more items that would make g77 more reliable and easier to maintain:

- Generally make expression handling focus more on critical syntax stuff, leaving semantics to callers. For example, anything a caller can check, semantically, let it do so, rather than having expr.c do it. (Exceptions might include things like diagnosing FOO(I--K:)=BAR where FOO is a `PARAMETER`—if it seems important to preserve the left-to-right-in-source order of production of diagnostics.)
- Come up with better naming conventions for -D to establish requirements to achieve desired implementation dialect via proj.h.
- Clean up used tokens and `ffewhere`s in `ffeglobal_terminate_1`.
- Replace sta.c `outpooldisp` mechanism with `malloc_pool_use`.
- Check for `opANY` in more places in com.c, std.c, and ste.c, and get rid of the opCONVERT(opANY) kludge (after determining if there is indeed no real need for it).
- Utility to read and check bad.def messages and their references in the code, to make sure calls are consistent with message templates.
- Search and fix &ffe... and similar so that ffe...ptr... macros are available instead (a good argument for wishing this could have written all this stuff in C++, perhaps). On the other hand, it's questionable whether this sort of improvement is really necessary, given the availability of tools such as Emacs and Perl, which make finding any address-taking of structure members easy enough?
- Some modules truly export the member names of their structures (and the structures themselves), maybe fix this, and fix other modules that just appear to as well (by appending _, though it'd be ugly and probably not worth the time).
- Implement C macros RETURNS(value) and SETS(something,value) in proj.h and use them throughout g77 source code (especially in the definitions of access macros in .h files) so they can be tailored to catch code writing into a RETURNS() or reading from a SETS().
- Decorate throughout with `const` and other such stuff.
- All F90 notational derivations in the source code are still based on the S8.112 version of the draft standard. Probably should update to the official standard, or put documentation of the rules as used in the code...uh...in the code.
- Some `ffebld_new` calls (those outside of ffeexpr.c or inside but invoked via paths not involving `ffeexpr_lhs` or `ffeexpr_rhs`) might be creating things in improper pools, leading to such things staying around too long or (doubtful, but possible and dangerous) not long enough.
- Some `ffebld_list_new` (or whatever) calls might not be matched by `ffebld_list_bottom` (or whatever) calls, which might someday matter. (It definitely is not a problem just yet.)
- Probably not doing clean things when we fail to `EQUIVALENCE` something due to alignment/mismatch or other problems—they end up without `ffestorag` objects, so maybe the backend (and other parts of the front end) can notice that and handle like an `opANY` (do what it wants, just don't complain or crash). Most of this seems to have been addressed by now, but a code review wouldn't hurt.

Previous: Internals Improvements, Up: Projects

### 20.8 Better Diagnostics

These are things users might not ask about, or that need to be looked into, before worrying about. Also here are items that involve reducing unnecessary diagnostic clutter.

- When `FUNCTION` and `ENTRY` point types disagree (`CHARACTER` lengths, type classes, and so on), `ANY`-ize the offending `ENTRY` point and any new dummies it specifies.
- Speed up and improve error handling for data when repeat-count is specified. For example, don't output 20 unnecessary messages after the first necessary one for:

                INTEGER X(20)
                CONTINUE
                DATA (X(I), J= 1, 20) /20*5/
                END

  (The `CONTINUE` statement ensures the `DATA` statement is processed in the context of executable, not specification, statements.)

Next: Diagnostics, Previous: Projects, Up: Top

## 21 Front End

This chapter describes some aspects of the design and implementation of the `g77` front end.

To find about things that are “To Be Determined” or “To Be Done”, search for the string TBD. If you want to help by working on one or more of these items, email gcc@gcc.gnu.org. If you're planning to do more than just research issues and offer comments, see http://gcc.gnu.org/contribute.html for steps you might need to take first.

Next: Overview of Translation Process, Up: Front End

### 21.1 Overview of Sources

The current directory layout includes the following:

srcdir/gcc/
  Non-g77 files in gcc
srcdir/gcc/f/
  GNU Fortran front end sources
srcdir/libf2c/
  `libg2c` configuration and `g2c.h` file generation
srcdir/libf2c/libF77/
  General support and math portion of `libg2c`
srcdir/libf2c/libI77/
  I/O portion of `libg2c`
srcdir/libf2c/libU77/
  Additional interfaces to Unix `libc` for `libg2c`

Components of note in `g77` are described below.

f/ as a whole contains the source for `g77`, while libf2c/ contains a portion of the separate program `f2c`. Note that the `libf2c` code is not part of the program `g77`, just distributed with it.

f/ contains text files that document the Fortran compiler, source files for the GNU Fortran Front End (FFE), and some other stuff. The `g77` compiler code is placed in f/ because it, along with its contents, is designed to be a subdirectory of a `gcc` source directory, gcc/, which is structured so that language-specific front ends can be “dropped in” as subdirectories. The C++ front end (`g++`), is an example of this—it resides in the cp/ subdirectory. Note that the C front end (also referred to as `gcc`) is an exception to this, as its source files reside in the gcc/ directory itself.

libf2c/ contains the run-time libraries for the `f2c` program, also used by `g77`. These libraries normally referred to collectively as `libf2c`. When built as part of `g77`, `libf2c` is installed under the name `libg2c` to avoid conflict with any existing version of `libf2c`, and thus is often referred to as `libg2c` when the `g77` version is specifically being referred to.

The `netlib` version of `libf2c/` contains two distinct libraries, `libF77` and `libI77`, each in their own subdirectories. In `g77`, this distinction is not made, beyond maintaining the subdirectory structure in the source-code tree.

libf2c/ is not part of the program `g77`, just distributed with it. It contains files not present in the official (`netlib`) version of `libf2c`, and also contains some minor changes made from `libf2c`, to fix some bugs, and to facilitate automatic configuration, building, and installation of `libf2c` (as `libg2c`) for use by `g77` users. See libf2c/README for more information, including licensing conditions governing distribution of programs containing code from `libg2c`.

`libg2c`, `g77`'s version of `libf2c`, adds Dave Love's implementation of `libU77`, in the libf2c/libU77/ directory. This library is distributed under the GNU Library General Public License (LGPL)—see the file libf2c/libU77/COPYING.LIB for more information, as this license governs distribution conditions for programs containing code from this portion of the library.

Files of note in f/ and libf2c/ are described below:

f/BUGS
  Lists some important bugs known to be in g77. Or use Info (or GNU Emacs Info mode) to read the “Actual Bugs” node of the `g77` documentation:

                info -f f/g77.info -n "Actual Bugs"

f/ChangeLog
  Lists recent changes to `g77` internals.
libf2c/ChangeLog
  Lists recent changes to `libg2c` internals.
f/NEWS
  Contains the per-release changes. These include the user-visible changes described in the node “Changes” in the `g77` documentation, plus internal changes of import. Or use:

                info -f f/g77.info -n News

f/g77.info*
  The `g77` documentation, in Info format, produced by building `g77`.

  All users of `g77` (not just installers) should read this, using the `more` command if neither the `info` command, nor GNU Emacs (with its Info mode), are available, or if users aren't yet accustomed to using these tools. All of these files are readable as “plain text” files, though they're easier to navigate using Info readers such as `info` and GNU Emacs Info mode.

If you want to explore the FFE code, which lives entirely in f/, here are a few clues. The file g77spec.c contains the `g77`-specific source code for the `g77` command only—this just forms a variant of the `gcc` command, so, just as the `gcc` command itself does not contain the C front end, the `g77` command does not contain the Fortran front end (FFE). The FFE code ends up in an executable named f771, which does the actual compiling, so it contains the FFE plus the `gcc` back end (GBE), the latter to do most of the optimization, and the code generation.

The file parse.c is the source file for `yyparse()`, which is invoked by the GBE to start the compilation process, for f771.

The file top.c contains the top-level FFE function `ffe_file` and it (along with top.h) define all ffe_[a-z].*, ffe[A-Z].*, and FFE_[A-Za-z].* symbols.

The file fini.c is a `main()` program that is used when building the FFE to generate C header and source files for recognizing keywords. The files malloc.c and malloc.h comprise a memory manager that defines all malloc_[a-z].*, malloc[A-Z].*, and MALLOC_[A-Za-z].* symbols.

All other modules named xyz are comprised of all files named xyz*.ext and define all ffe xyz_[a-z].*, ffe xyz[A-Z].*, and FFE XYZ_[A-Za-z].* symbols. If you understand all this, congratulations—it's easier for me to remember how it works than to type in these regular expressions. But it does make it easy to find where a symbol is defined. For example, the symbol ffexyz_set_something would be defined in xyz.h and implemented there (if it's a macro) or in xyz.c.

The “porting” files of note currently are:

proj.h
  This defines the “language” used by all the other source files, the language being Standard C plus some useful things like `ARRAY_SIZE` and such.
target.c
target.h
  These describe the target machine in terms of what data types are supported, how they are denoted (to what C type does an `INTEGER*8` map, for example), how to convert between them, and so on. Over time, versions of `g77` rely less on this file and more on run-time configuration based on GBE info in com.c.
com.c
com.h
  These are the primary interface to the GBE.
ste.c
ste.h
  This contains code for implementing recognized executable statements in the GBE.
src.c
src.h
  These contain information on the format(s) of source files (such as whether they are never to be processed as case-insensitive with regard to Fortran keywords).

If you want to debug the f771 executable, for example if it crashes, note that the global variables `lineno` and `input_filename` are usually set to reflect the current line being read by the lexer during the first-pass analysis of a program unit and to reflect the current line being processed during the second-pass compilation of a program unit.

If an invocation of the function `ffestd_exec_end` is on the stack, the compiler is in the second pass, otherwise it is in the first.

(This information might help you reduce a test case and/or work around a bug in `g77` until a fix is available.)

Next: Philosophy of Code Generation, Previous: Overview of Sources, Up: Front End

### 21.2 Overview of Translation Process

The order of phases translating source code to the form accepted by the GBE is:

1. Stripping punched-card sources (g77stripcard.c)
2. Lexing (lex.c)
3. Stand-alone statement identification (sta.c)
4. INCLUDE handling (sti.c)
5. Order-dependent statement identification (stq.c)
6. Parsing (stb.c and expr.c)
7. Constructing (stc.c)
8. Collecting (std.c)
9. Expanding (ste.c)

To get a rough idea of how a particularly twisted Fortran statement gets treated by the passes, consider:

               FORMAT(I2 4H)=(J/
              &   I3)

The job of lex.c is to know enough about Fortran syntax rules to break the statement up into distinct lexemes without requiring any feedback from subsequent phases:

         `FORMAT'
         `('
         `I24H'
         `)'
         `='
         `('
         `J'
         `/'
         `I3'
         `)'

The job of sta.c is to figure out the kind of statement, or, at least, statement form, that sequence of lexemes represent.

The sooner it can do this (in terms of using the smallest number of lexemes, starting with the first for each statement), the better, because that leaves diagnostics for problems beyond the recognition of the statement form to subsequent phases, which can usually better describe the nature of the problem.

In this case, the = at “level zero” (not nested within parentheses) tells sta.c that this is an assignment-form, not `FORMAT`, statement.

An assignment-form statement might be a statement-function definition or an executable assignment statement.

To make that determination, sta.c looks at the first two lexemes.

Since the second lexeme is (, the first must represent an array for this to be an assignment statement, else it's a statement function.

Either way, sta.c hands off the statement to stq.c (via sti.c, which expands INCLUDE files). stq.c figures out what a statement that is, on its own, ambiguous, must actually be based on the context established by previous statements.

So, stq.c watches the statement stream for executable statements, END statements, and so on, so it knows whether A(B)=C is (intended as) a statement-function definition or an assignment statement.

After establishing the context-aware statement info, stq.c passes the original sample statement on to stb.c (either its statement-function parser or its assignment-statement parser).

stb.c forms a statement-specific record containing the pertinent information. That information includes a source expression and, for an assignment statement, a destination expression. Expressions are parsed by expr.c.

This record is passed to stc.c, which copes with the implications of the statement within the context established by previous statements.

For example, if it's the first statement in the file or after an `END` statement, stc.c recognizes that, first of all, a main program unit is now being lexed (and tells that to std.c before telling it about the current statement).

stc.c attaches whatever information it can, usually derived from the context established by the preceding statements, and passes the information to std.c.

std.c saves this information away, since the GBE cannot cope with information that might be incomplete at this stage.

For example, I3 might later be determined to be an argument to an alternate `ENTRY` point.

When std.c is told about the end of an external (top-level) program unit, it passes all the information it has saved away on statements in that program unit to ste.c.

ste.c “expands” each statement, in sequence, by constructing the appropriate GBE information and calling the appropriate GBE routines.

Details on the transformational phases follow. Keep in mind that Fortran numbering is used, so the first character on a line is column 1, decimal numbering is used, and so on.

Next: lex.c, Up: Overview of Translation Process

#### 21.2.1 g77stripcard

The `g77stripcard` program handles removing content beyond column 72 (adjustable via a command-line option), optionally warning about that content being something other than trailing whitespace or Fortran commentary.

This program is needed because `lex.c` doesn't pay attention to maximum line lengths at all, to make it easier to maintain, as well as faster (for sources that don't depend on the maximum column length vis-a-vis trailing non-blank non-commentary content).

Just how this program will be run—whether automatically for old source (perhaps as the default for .f files?)—is not yet determined.

In the meantime, it might as well be implemented as a typical UNIX pipe.

It should accept a -fline-length-n option, with the default line length set to 72.

When the text it strips off the end of a line is not blank (not spaces and tabs), it should insert an additional comment line (beginning with !, so it works for both fixed-form and free-form files) containing the text, following the stripped line. The inserted comment should have a prefix of some kind, TBD, that distinguishes the comment as representing stripped text. Users could use that to `sed` out such lines, if they wished—it seems silly to provide a command-line option to delete information when it can be so easily filtered out by another program.

(This inserted comment should be designed to “fit in” well with whatever the Fortran community is using these days for preprocessor, translator, and other such products, like OpenMP. What that's all about, and how `g77` can elegantly fit its special comment conventions into it all, is TBD as well. We don't want to reinvent the wheel here, but if there turn out to be too many conflicting conventions, we might have to invent one that looks nothing like the others, but which offers their host products a better infrastructure in which to fit and coexist peacefully.)

`g77stripcard` probably shouldn't do any tab expansion or other fancy stuff. People can use `expand` or other pre-filtering if they like. The idea here is to keep each stage quite simple, while providing excellent performance for “normal” code.

(Code with junk beyond column 73 is not really “normal”, as it comes from a card-punch heritage, and will be increasingly hard for tomorrow's Fortran programmers to read.)

Next: sta.c, Previous: g77stripcard, Up: Overview of Translation Process

#### 21.2.2 lex.c

To help make the lexer simple, fast, and easy to maintain, while also having `g77` generally encourage Fortran programmers to write simple, maintainable, portable code by maximizing the performance of compiling that kind of code:

- There'll be just one lexer, for both fixed-form and free-form source.
- It'll care about the form only when handling the first 7 columns of text, stuff like spaces between strings of alphanumerics, and how lines are continued.

  Some other distinctions will be handled by subsequent phases, so at least one of them will have to know which form is involved.

  For example, I = 2 . 4 is acceptable in fixed form, and works in free form as well given the implementation `g77` presently uses. But the standard requires a diagnostic for it in free form, so the parser has to be able to recognize that the lexemes aren't contiguous (information the lexer does have to provide) and that free-form source is being parsed, so it can provide the diagnostic.

  The `g77` lexer doesn't try to gather 2 . 4 into a single lexeme. Otherwise, it'd have to know a whole lot more about how to parse Fortran, or subsequent phases (mainly parsing) would have two paths through lots of critical code—one to handle the lexeme 2, ., and 4 in sequence, another to handle the lexeme 2.4.

- It won't worry about line lengths (beyond the first 7 columns for fixed-form source).

  That is, once it starts parsing the “statement” part of a line (column 7 for fixed-form, column 1 for free-form), it'll keep going until it finds a newline, rather than ignoring everything past a particular column (72 or 132).

  The implication here is that there shouldn't be anything past that last column, other than whitespace or commentary, because users using typical editors (or viewing output as typically printed) won't necessarily know just where the last column is.

  Code that has “garbage” beyond the last column (almost certainly only fixed-form code with a punched-card legacy, such as code using columns 73-80 for “sequence numbers”) will have to be run through `g77stripcard` first.

  Also, keeping track of the maximum column position while also watching out for the end of a line and while reading from a file just makes things slower. Since a file must be read, and watching for the end of the line is necessary (unless the typical input file was preprocessed to include the necessary number of trailing spaces), dropping the tracking of the maximum column position is the only way to reduce the complexity of the pertinent code while maintaining high performance.

- ASCII encoding is assumed for the input file.

  Code written in other character sets will have to be converted first.

- Tabs (ASCII code 9) will be converted to spaces via the straightforward approach.

  Specifically, a tab is converted to between one and eight spaces as necessary to reach column n, where dividing (n - 1) by eight results in a remainder of zero.

  That saves having to pass most source files through `expand`.

- Linefeeds (ASCII code 10) mark the ends of lines.
- A carriage return (ASCII code 13) is accept if it immediately precedes a linefeed, in which case it is ignored.

  Otherwise, it is rejected (with a diagnostic).

- Any other characters other than the above that are not part of the GNU Fortran Character Set (see Character Set) are rejected with a diagnostic.

  This includes backspaces, form feeds, and the like.

  (It might make sense to allow a form feed in column 1 as long as that's the only character on a line. It certainly wouldn't seem to cost much in terms of performance.)

- The end of the input stream (EOF) ends the current line.
- The distinction between uppercase and lowercase letters will be preserved.

  It will be up to subsequent phases to decide to fold case.

  Current plans are to permit any casing for Fortran (reserved) keywords while preserving casing for user-defined names. (This might not be made the default for .f files, though.)

  Preserving case seems necessary to provide more direct access to facilities outside of `g77`, such as to C or Pascal code.

  Names of intrinsics will probably be matchable in any case,

  (How external SiN; r = sin(x) would be handled is TBD. I think old `g77` might already handle that pretty elegantly, but whether we can cope with allowing the same fragment to reference a different procedure, even with the same interface, via s = SiN(r), needs to be determined. If it can't, we need to make sure that when code introduces a user-defined name, any intrinsic matching that name using a case-insensitive comparison is “turned off”.)

- Backslashes in `CHARACTER` and Hollerith constants are not allowed.

  This avoids the confusion introduced by some Fortran compiler vendors providing C-like interpretation of backslashes, while others provide straight-through interpretation.

  Some kind of lexical construct (TBD) will be provided to allow flagging of a `CHARACTER` (but probably not a Hollerith) constant that permits backslashes. It'll necessarily be a prefix, such as:

                PRINT *, C'This line has a backspace \b here.'
                PRINT *, F'This line has a straight backslash \ here.'

  Further, command-line options might be provided to specify that one prefix or the other is to be assumed as the default for `CHARACTER` constants.

  However, it seems more helpful for `g77` to provide a program that converts prefix all constants (or just those containing backslashes) with the desired designation, so printouts of code can be read without knowing the compile-time options used when compiling it.

  If such a program is provided (let's name it `g77slash` for now), then a command-line option to `g77` should not be provided. (Though, given that it'll be easy to implement, it might be hard to resist user requests for it “to compile faster than if we have to invoke another filter”.)

  This program would take a command-line option to specify the default interpretation of slashes, affecting which prefix it uses for constants.

  `g77slash` probably should automatically convert Hollerith constants that contain slashes to the appropriate `CHARACTER` constants. Then `g77` wouldn't have to define a prefix syntax for Hollerith constants specifying whether they want C-style or straight-through backslashes.

- To allow for form-neutral INCLUDE files without requiring them to be preprocessed, the fixed-form lexer should offer an extension (if possible) allowing a trailing & to be ignored, especially if after column 72, as it would be using the traditional Unix Fortran source model (which ignores everything after column 72).

The above implements nearly exactly what is specified by Character Set, and Lines, except it also provides automatic conversion of tabs and ignoring of newline-related carriage returns, as well as accommodating form-neutral INCLUDE files.

It also implements the “pure visual” model, by which is meant that a user viewing his code in a typical text editor (assuming it's not preprocessed via `g77stripcard` or similar) doesn't need any special knowledge of whether spaces on the screen are really tabs, whether lines end immediately after the last visible non-space character or after a number of spaces and tabs that follow it, or whether the last line in the file is ended by a newline.

Most editors don't make these distinctions, the ANSI FORTRAN 77 standard doesn't require them to, and it permits a standard-conforming compiler to define a method for transforming source code to “standard form” however it wants.

So, GNU Fortran defines it such that users have the best chance of having the code be interpreted the way it looks on the screen of the typical editor.

(Fancy editors should never be required to correctly read code written in classic two-dimensional-plaintext form. By correct reading I mean ability to read it, book-like, without mistaking text ignored by the compiler for program code and vice versa, and without having to count beyond the first several columns. The vague meaning of ASCII TAB, among other things, complicates this somewhat, but as long as “everyone”, including the editor, other tools, and printer, agrees about the every-eighth-column convention, the GNU Fortran “pure visual” model meets these requirements. Any language or user-visible source form requiring special tagging of tabs, the ends of lines after spaces/tabs, and so on, fails to meet this fairly straightforward specification. Fortunately, Fortran itself does not mandate such a failure, though most vendor-supplied defaults for their Fortran compilers do fail to meet this specification for readability.)

Further, this model provides a clean interface to whatever preprocessors or code-generators are used to produce input to this phase of `g77`. Mainly, they need not worry about long lines.

Next: sti.c, Previous: lex.c, Up: Overview of Translation Process

#### 21.2.3 sta.c

Next: stq.c, Previous: sta.c, Up: Overview of Translation Process

#### 21.2.4 sti.c

Next: stb.c, Previous: sti.c, Up: Overview of Translation Process

#### 21.2.5 stq.c

Next: expr.c, Previous: stq.c, Up: Overview of Translation Process

#### 21.2.6 stb.c

Next: stc.c, Previous: stb.c, Up: Overview of Translation Process

#### 21.2.7 expr.c

Next: std.c, Previous: expr.c, Up: Overview of Translation Process

#### 21.2.8 stc.c

Next: ste.c, Previous: stc.c, Up: Overview of Translation Process

#### 21.2.9 std.c

Next: Gotchas (Transforming), Previous: std.c, Up: Overview of Translation Process

#### 21.2.10 ste.c

Next: TBD (Transforming), Previous: ste.c, Up: Overview of Translation Process

#### 21.2.11 Gotchas (Transforming)

This section is not about transforming “gotchas” into something else. It is about the weirder aspects of transforming Fortran, however that's defined, into a more modern, canonical form.

##### 21.2.11.1 Multi-character Lexemes

Each lexeme carries with it a pointer to where it appears in the source.

To provide the ability for diagnostics to point to column numbers, in addition to line numbers and names, lexemes that represent more than one (significant) character in the source code need, generally, to provide pointers to where each character appears in the source.

This provides the ability to properly identify the precise location of the problem in code like

         SUBROUTINE X
         END
         BLOCK DATA X
         END

which, in fixed-form source, would result in single lexemes consisting of the strings SUBROUTINEX and BLOCKDATAX. (The problem is that X is defined twice, so a pointer to the X in the second definition, as well as a follow-up pointer to the corresponding pointer in the first, would be preferable to pointing to the beginnings of the statements.)

This need also arises when parsing (and diagnosing) `FORMAT` statements.

Further, it arises when diagnosing `FMT=` specifiers that contain constants (or partial constants, or even propagated constants!) in I/O statements, as in:

         PRINT '(I2, 3HAB)', J

(A pointer to the beginning of the prematurely-terminated Hollerith constant, and/or to the close parenthese, is preferable to a pointer to the open-parenthese or the apostrophe that precedes it.)

Multi-character lexemes, which would seem to naturally include at least digit strings, alphanumeric strings, `CHARACTER` constants, and Hollerith constants, therefore need to provide location information on each character. (Maybe Hollerith constants don't, but it's unnecessary to except them.)

The question then arises, what about other multi-character lexemes, such as ** and //, and Fortran 90's (/, /), ::, and so on?

Turns out there's a need to identify the location of the second character of these two-character lexemes. For example, in I(/J) = K, the slash needs to be diagnosed as the problem, not the open parenthese. Similarly, it is preferable to diagnose the second slash in I = J // K rather than the first, given the implicit typing rules, which would result in the compiler disallowing the attempted concatenation of two integers. (Though, since that's more of a semantic issue, it's not that much preferable.)

Even sequences that could be parsed as digit strings could use location info, for example, to diagnose the 9 in the octal constant O'129'. (This probably will be parsed as a character string, to be consistent with the parsing of Z'129A'.)

To avoid the hassle of recording the location of the second character, while also preserving the general rule that each significant character is distinctly pointed to by the lexeme that contains it, it's best to simply not have any fixed-size lexemes larger than one character.

This new design is expected to make checking for two * lexemes in a row much easier than the old design, so this is not much of a sacrifice. It probably makes the lexer much easier to implement than it makes the parser harder.

##### 21.2.11.2 Space-padding Lexemes

Certain lexemes need to be padded with virtual spaces when the end of the line (or file) is encountered.

This is necessary in fixed form, to handle lines that don't extend to column 72, assuming that's the line length in effect.

##### 21.2.11.3 Bizarre Free-form Hollerith Constants

Last I checked, the Fortran 90 standard actually required the compiler to silently accept something like

         FORMAT ( 1 2   Htwelve chars )

as a valid `FORMAT` statement specifying a twelve-character Hollerith constant.

The implication here is that, since the new lexer is a zero-feedback one, it won't know that the special case of a `FORMAT` statement being parsed requires apparently distinct lexemes 1 and 2 to be treated as a single lexeme.

(This is a horrible misfeature of the Fortran 90 language. It's one of many such misfeatures that almost make me want to not support them, and forge ahead with designing a new “GNU Fortran” language that has the features, but not the misfeatures, of Fortran 90, and provide utility programs to do the conversion automatically.)

So, the lexer must gather distinct chunks of decimal strings into a single lexeme in contexts where a single decimal lexeme might start a Hollerith constant.

(Which probably means it might as well do that all the time for all multi-character lexemes, even in free-form mode, leaving it to subsequent phases to pull them apart as they see fit.)

Compare the treatment of this to how

         CHARACTER * 4 5 HEY

and

         CHARACTER * 12 HEY

must be treated—the former must be diagnosed, due to the separation between lexemes, the latter must be accepted as a proper declaration.

##### 21.2.11.4 Hollerith Constants

Recognizing a Hollerith constant—specifically, that an H or h after a digit string begins such a constant—requires some knowledge of context.

Hollerith constants (such as 2HAB) can appear after:

- (
- ,
- =
- +, -, /
- *, except as noted below

Hollerith constants don't appear after:

- CHARACTER*, which can be treated generally as any * that is the second lexeme of a statement

##### 21.2.11.5 Confusing Function Keyword

While

         REAL FUNCTION FOO ()

must be a `FUNCTION` statement and

         REAL FUNCTION FOO (5)

must be a type-definition statement,

         REAL FUNCTION FOO (names)

where names is a comma-separated list of names, can be one or the other.

The only way to disambiguate that statement (short of mandating free-form source or a short maximum length for name for external procedures) is based on the context of the statement.

In particular, the statement is known to be within an already-started program unit (but not at the outer level of the `CONTAINS` block), it is a type-declaration statement.

Otherwise, the statement is a `FUNCTION` statement, in that it begins a function program unit (external, or, within `CONTAINS`, nested).

##### 21.2.11.6 Weird READ

The statement

         READ (N)

is equivalent to either

         READ (UNIT=(N))

or

         READ (FMT=(N))

depending on which would be valid in context.

Specifically, if N is type `INTEGER`, READ (FMT=(N)) would not be valid, because parentheses may not be used around N, whereas they may around it in READ (UNIT=(N)).

Further, if N is type `CHARACTER`, the opposite is true—READ (UNIT=(N)) is not valid, but READ (FMT=(N)) is.

Strictly speaking, if anything follows

         READ (N)

in the statement, whether the first lexeme after the close parenthese is a comma could be used to disambiguate the two cases, without looking at the type of N, because the comma is required for the READ (FMT=(N)) interpretation and disallowed for the READ (UNIT=(N)) interpretation.

However, in practice, many Fortran compilers allow the comma for the READ (UNIT=(N)) interpretation anyway (in that they generally allow a leading comma before an I/O list in an I/O statement), and much code takes advantage of this allowance.

(This is quite a reasonable allowance, since the juxtaposition of a comma-separated list immediately after an I/O control-specification list, which is also comma-separated, without an intervening comma, looks sufficiently “wrong” to programmers that they can't resist the itch to insert the comma. READ (I, J), K, L simply looks cleaner than READ (I, J) K, L.)

So, type-based disambiguation is needed unless strict adherence to the standard is always assumed, and we're not going to assume that.

Previous: Gotchas (Transforming), Up: Overview of Translation Process

#### 21.2.12 TBD (Transforming)

Continue researching gotchas, designing the transformational process, and implementing it.

Specific issues to resolve:

- Just where should (if it was implemented) `USE` processing take place?

  This gets into the whole issue of how `g77` should handle the concept of modules. I think GNAT already takes on this issue, but don't know more than that. Jim Giles has written extensively on `comp.lang.fortran` about his opinions on module handling, as have others. Jim's views should be taken into account.

  Actually, Richard M. Stallman (RMS) also has written up some guidelines for implementing such things, but I'm not sure where I read them. Perhaps the old gcc2@cygnus.com list.

  If someone could dig references to these up and get them to me, that would be much appreciated! Even though modules are not on the short-term list for implementation, it'd be helpful to know now how to avoid making them harder to implement them later.

- Should the `g77` command become just a script that invokes all the various preprocessing that might be needed, thus making it seem slower than necessary for legacy code that people are unwilling to convert, or should we provide a separate script for that, thus encouraging people to convert their code once and for all?

  At least, a separate script to behave as old `g77` did, perhaps named `g77old`, might ease the transition, as might a corresponding one that converts source codes named `g77oldnew`.

  These scripts would take all the pertinent options `g77` used to take and run the appropriate filters, passing the results to `g77` or just making new sources out of them (in a subdirectory, leaving the user to do the dirty deed of moving or copying them over the old sources).

- Do other Fortran compilers provide a prefix syntax to govern the treatment of backslashes in `CHARACTER` (or Hollerith) constants?

  Knowing what other compilers provide would help.

- Is it okay to drop support for the -fintrin-case-initcap, -fmatch-case-initcap, -fsymbol-case-initcap, and -fcase-initcap options?

  I've asked info-gnu-fortran@gnu.org for input on this. Not having to support these makes it easier to write the new front end, and might also avoid complicated its design.

  The consensus to date (1999-11-17) has been to drop this support. Can't recall anybody saying they're using it, in fact.

Next: Two-pass Design, Previous: Overview of Translation Process, Up: Front End

### 21.3 Philosophy of Code Generation

Don't poke the bear.

The `g77` front end generates code via the `gcc` back end.

The `gcc` back end (GBE) is a large, complex labyrinth of intricate code written in a combination of the C language and specialized languages internal to `gcc`.

While the code that implements the GBE is written in a combination of languages, the GBE itself is, to the front end for a language like Fortran, best viewed as a compiler that compiles its own, unique, language.

The GBE's “source”, then, is written in this language, which consists primarily of a combination of calls to GBE functions and tree nodes (which are, themselves, created by calling GBE functions).

So, the `g77` generates code by, in effect, translating the Fortran code it reads into a form “written” in the “language” of the `gcc` back end.

This language will heretofore be referred to as GBEL, for GNU Back End Language.

GBEL is an evolving language, not fully specified in any published form as of this writing. It offers many facilities, but its “core” facilities are those that corresponding most directly to those needed to support `gcc` (compiling code written in GNU C).

The `g77` Fortran Front End (FFE) is designed and implemented to navigate the currents and eddies of ongoing GBEL and `gcc` development while also delivering on the potential of an integrated FFE (as compared to using a converter like `f2c` and feeding the output into `gcc`).

Goals of the FFE's code-generation strategy include:

- High likelihood of generation of correct code, or, failing that, producing a fatal diagnostic or crashing.
- Generation of highly optimized code, as directed by the user via GBE-specific (versus `g77`-specific) constructs, such as command-line options.
- Fast overall (FFE plus GBE) compilation.
- Preservation of source-level debugging information.

The strategies historically, and currently, used by the FFE to achieve these goals include:

- Use of GBEL constructs that most faithfully encapsulate the semantics of Fortran.
- Avoidance of GBEL constructs that are so rarely used, or limited to use in specialized situations not related to Fortran, that their reliability and performance has not yet been established as sufficient for use by the FFE.
- Flexible design, to readily accommodate changes to specific code-generation strategies, perhaps governed by command-line options.

“Don't poke the bear” somewhat summarizes the above strategies. The GBE is the bear. The FFE is designed and implemented to avoid poking it in ways that are likely to just annoy it. The FFE usually either tackles it head-on, or avoids treating it in ways dissimilar to how the `gcc` front end treats it.

For example, the FFE uses the native array facility in the back end instead of the lower-level pointer-arithmetic facility used by `gcc` when compiling `f2c` output). Theoretically, this presents more opportunities for optimization, faster compile times, and the production of more faithful debugging information. These benefits were not, however, immediately realized, mainly because `gcc` itself makes little or no use of the native array facility.

Complex arithmetic is a case study of the evolution of this strategy. When originally implemented, the GBEL had just evolved its own native complex-arithmetic facility, so the FFE took advantage of that.

When porting `g77` to 64-bit systems, it was discovered that the GBE didn't really implement its native complex-arithmetic facility properly.

The short-term solution was to rewrite the FFE to instead use the lower-level facilities that'd be used by `gcc`-compiled code (assuming that code, itself, didn't use the native complex type provided, as an extension, by `gcc`), since these were known to work, and, in any case, if shown to not work, would likely be rapidly fixed (since they'd likely not work for vanilla C code in similar circumstances).

However, the rewrite accommodated the original, native approach as well by offering a command-line option to select it over the emulated approach. This allowed users, and especially GBE maintainers, to try out fixes to complex-arithmetic support in the GBE while `g77` continued to default to compiling more code correctly, albeit producing (typically) slower executables.

As of April 1999, it appeared that the last few bugs in the GBE's support of its native complex-arithmetic facility were worked out. The FFE was changed back to default to using that native facility, leaving emulation as an option.

Later during the release cycle (which was called EGCS 1.2, but soon became GCC 2.95), bugs in the native facility were found. Reactions among various people included “the last thing we should do is change the default back”, “we must change the default back”, and “let's figure out whether we can narrow down the bugs to few enough cases to allow the now-months-long-tested default to remain the same”. The latter viewpoint won that particular time. The bugs exposed other concerns regarding ABI compliance when the ABI specified treatment of complex data as different from treatment of what Fortran and GNU C consider the equivalent aggregation (structure) of real (or float) pairs.

Other Fortran constructs—arrays, character strings, complex division, `COMMON` and `EQUIVALENCE` aggregates, and so on—involve issues similar to those pertaining to complex arithmetic.

So, it is possible that the history of how the FFE handled complex arithmetic will be repeated, probably in modified form (and hopefully over shorter timeframes), for some of these other facilities.

Next: Challenges Posed, Previous: Philosophy of Code Generation, Up: Front End

### 21.4 Two-pass Design

The FFE does not tell the GBE anything about a program unit until after the last statement in that unit has been parsed. (A program unit is a Fortran concept that corresponds, in the C world, mostly closely to functions definitions in ISO C. That is, a program unit in Fortran is like a top-level function in C. Nested functions, found among the extensions offered by GNU C, correspond roughly to Fortran's statement functions.)

So, while parsing the code in a program unit, the FFE saves up all the information on statements, expressions, names, and so on, until it has seen the last statement.

At that point, the FFE revisits the saved information (in what amounts to a second pass over the program unit) to perform the actual translation of the program unit into GBEL, ultimating in the generation of assembly code for it.

Some lookahead is performed during this second pass, so the FFE could be viewed as a “two-plus-pass” design.

Next: Why Two Passes, Up: Two-pass Design

#### 21.4.1 Two-pass Code

Most of the code that turns the first pass (parsing) into a second pass for code generation is in gcc/gcc/f/std.c.

It has external functions, called mainly by siblings in gcc/gcc/f/stc.c, that record the information on statements and expressions in the order they are seen in the source code. These functions save that information.

It also has an external function that revisits that information, calling the siblings in gcc/gcc/f/ste.c, which handles the actual code generation (by generating GBEL code, that is, by calling GBE routines to represent and specify expressions, statements, and so on).

Previous: Two-pass Code, Up: Two-pass Design

#### 21.4.2 Why Two Passes

The need for two passes was not immediately evident during the design and implementation of the code in the FFE that was to produce GBEL. Only after a few kludges, to handle things like incorrectly-guessed `ASSIGN` label nature, had been implemented, did enough evidence pile up to make it clear that std.c had to be introduced to intercept, save, then revisit as part of a second pass, the digested contents of a program unit.

Other such missteps have occurred during the evolution of the FFE, because of the different goals of the FFE and the GBE.

Because the GBE's original, and still primary, goal was to directly support the GNU C language, the GBEL, and the GBE itself, requires more complexity on the part of most front ends than it requires of `gcc`'s.

For example, the GBEL offers an interface that permits the `gcc` front end to implement most, or all, of the language features it supports, without the front end having to make use of non-user-defined variables. (It's almost certainly the case that all of K&R C, and probably ANSI C as well, is handled by the `gcc` front end without declaring such variables.)

The FFE, on the other hand, must resort to a variety of “tricks” to achieve its goals.

Consider the following C code:

         int
         foo (int a, int b)
         {
           int c = 0;

           if ((c = bar (c)) == 0)
             goto done;

           quux (c << 1);

         done:
           return c;
         }

Note what kinds of objects are declared, or defined, before their use, and before any actual code generation involving them would normally take place:

- Return type of function
- Entry point(s) of function
- Dummy arguments
- Variables
- Initial values for variables

Whereas, the following items can, and do, suddenly appear “out of the blue” in C:

- Label references
- Function references

Not surprisingly, the GBE faithfully permits the latter set of items to be “discovered” partway through GBEL “programs”, just as they are permitted to in C.

Yet, the GBE has tended, at least in the past, to be reticent to fully support similar “late” discovery of items in the former set.

This makes Fortran a poor fit for the “safe” subset of GBEL. Consider:

               FUNCTION X (A, ARRAY, ID1)
               CHARACTER*(*) A
               DOUBLE PRECISION X, Y, Z, TMP, EE, PI
               REAL ARRAY(ID1*ID2)
               COMMON ID2
               EXTERNAL FRED

               ASSIGN 100 TO J
               CALL FOO (I)
               IF (I .EQ. 0) PRINT *, A(0)
               GOTO 200

               ENTRY Y (Z)
               ASSIGN 101 TO J
         200   PRINT *, A(1)
               READ *, TMP
               GOTO J
         100   X = TMP * EE
               RETURN
         101   Y = TMP * PI
               CALL FRED
               DATA EE, PI /2.71D0, 3.14D0/
               END

Here are some observations about the above code, which, while somewhat contrived, conforms to the FORTRAN 77 and Fortran 90 standards:

- The return type of function X is not known until the DOUBLE PRECISION line has been parsed.
- Whether A is a function or a variable is not known until the PRINT *, A(0) statement has been parsed.
- The bounds of the array of argument ARRAY depend on a computation involving the subsequent argument ID1 and the blank-common member ID2.
- Whether Y and Z are local variables, additional function entry points, or dummy arguments to additional entry points is not known until the `ENTRY` statement is parsed.
- Similarly, whether TMP is a local variable is not known until the READ *, TMP statement is parsed.
- The initial values for EE and PI are not known until after the `DATA` statement is parsed.
- Whether FRED is a function returning type `REAL` or a subroutine (which can be thought of as returning type `void` or, to support alternate returns in a simple way, type `int`) is not known until the CALL FRED statement is parsed.
- Whether 100 is a `FORMAT` label or the label of an executable statement is not known until the X = statement is parsed. (These two types of labels get very different treatment, especially when `ASSIGN`'ed.)
- That J is a local variable is not known until the first `ASSIGN` statement is parsed. (This happens after executable code has been seen.)

Very few of these “discoveries” can be accommodated by the GBE as it has evolved over the years. The GBEL doesn't support several of them, and those it might appear to support don't always work properly, especially in combination with other GBEL and GBE features, as implemented in the GBE.

(Had the GBE and its GBEL originally evolved to support `g77`, the shoe would be on the other foot, so to speak—most, if not all, of the above would be directly supported by the GBEL, and a few C constructs would probably not, as they are in reality, be supported. Both this mythical, and today's real, GBE caters to its GBEL by, sometimes, scrambling around, cleaning up after itself—after discovering that assumptions it made earlier during code generation are incorrect. That's not a great design, since it indicates significant code paths that might be rarely tested but used in some key production environments.)

So, the FFE handles these discrepancies—between the order in which it discovers facts about the code it is compiling, and the order in which the GBEL and GBE support such discoveries—by performing what amounts to two passes over each program unit.

(A few ambiguities can remain at that point, such as whether, given EXTERNAL BAZ and no other reference to BAZ in the program unit, it is a subroutine, a function, or a block-data—which, in C-speak, governs its declared return type. Fortunately, these distinctions are easily finessed for the procedure, library, and object-file interfaces supported by `g77`.)

Next: Transforming Statements, Previous: Two-pass Design, Up: Front End

### 21.5 Challenges Posed

Consider the following Fortran code, which uses various extensions (including some to Fortran 90):

         SUBROUTINE X(A)
         CHARACTER*(*) A
         COMPLEX CFUNC
         INTEGER*2 CLOCKS(200)
         INTEGER IFUNC

         CALL SYSTEM_CLOCK (CLOCKS (IFUNC (CFUNC ('('//A//')'))))

The above poses the following challenges to any Fortran compiler that uses run-time interfaces, and a run-time library, roughly similar to those used by `g77`:

- Assuming the library routine that supports `SYSTEM_CLOCK` expects to set an `INTEGER*4` variable via its `COUNT` argument, the compiler must make available to it a temporary variable of that type.
- Further, after the `SYSTEM_CLOCK` library routine returns, the compiler must ensure that the temporary variable it wrote is copied into the appropriate element of the CLOCKS array. (This assumes the compiler doesn't just reject the code, which it should if it is compiling under some kind of a “strict” option.)
- To determine the correct index into the CLOCKS array, (putting aside the fact that the index, in this particular case, need not be computed until after the `SYSTEM_CLOCK` library routine returns), the compiler must ensure that the `IFUNC` function is called.

  That requires evaluating its argument, which requires, for `g77` (assuming `-ff2c` is in force), reserving a temporary variable of type `COMPLEX` for use as a repository for the return value being computed by CFUNC.

- Before invoking CFUNC, is argument must be evaluated, which requires allocating, at run time, a temporary large enough to hold the result of the concatenation, as well as actually performing the concatenation.
- The large temporary needed during invocation of `CFUNC` should, ideally, be deallocated (or, at least, left to the GBE to dispose of, as it sees fit) as soon as `CFUNC` returns, which means before `IFUNC` is called (as it might need a lot of dynamically allocated memory).

`g77` currently doesn't support all of the above, but, so that it might someday, it has evolved to handle at least some of the above requirements.

Meeting the above requirements is made more challenging by conforming to the requirements of the GBEL/GBE combination.

Next: Transforming Expressions, Previous: Challenges Posed, Up: Front End

### 21.6 Transforming Statements

Most Fortran statements are given their own block, and, for temporary variables they might need, their own scope. (A block is what distinguishes { foo (); } from just foo (); in C. A scope is included with every such block, providing a distinct name space for local variables.)

Label definitions for the statement precede this block, so 10 PRINT *, I is handled more like fl10: { ... } than { fl10: ... } (where fl10 is just a notation meaning “Fortran Label 10” for the purposes of this document).

Next: Transforming DO WHILE, Up: Transforming Statements

#### 21.6.1 Statements Needing Temporaries

Any temporaries needed during, but not beyond, execution of a Fortran statement, are made local to the scope of that statement's block.

This allows the GBE to share storage for these temporaries among the various statements without the FFE having to manage that itself.

(The GBE could, of course, decide to optimize management of these temporaries. For example, it could, theoretically, schedule some of the computations involving these temporaries to occur in parallel. More practically, it might leave the storage for some temporaries “live” beyond their scopes, to reduce the number of manipulations of the stack pointer at run time.)

Temporaries needed across distinct statement boundaries usually are associated with Fortran blocks (such as `DO`/`END DO`). (Also, there might be temporaries not associated with blocks at all—these would be in the scope of the entire program unit.)

Each Fortran block should get its own block/scope in the GBE. This is best, because it allows temporaries to be more naturally handled. However, it might pose problems when handling labels (in particular, when they're the targets of `GOTO`s outside the Fortran block), and generally just hassling with replicating parts of the `gcc` front end (because the FFE needs to support an arbitrary number of nested back-end blocks if each Fortran block gets one).

So, there might still be a need for top-level temporaries, whose “owning” scope is that of the containing procedure.

Also, there seems to be problems declaring new variables after generating code (within a block) in the back end, leading to, e.g., label not defined before binding contour or similar messages, when compiling with -fstack-check or when compiling for certain targets.

Because of that, and because sometimes these temporaries are not discovered until in the middle of of generating code for an expression statement (as in the case of the optimization for X**I), it seems best to always pre-scan all the expressions that'll be expanded for a block before generating any of the code for that block.

This pre-scan then handles discovering and declaring, to the back end, the temporaries needed for that block.

It's also important to treat distinct items in an I/O list as distinct statements deserving their own blocks. That's because there's a requirement that each I/O item be fully processed before the next one, which matters in cases like READ (*,*), I, A(I)—the element of A read in the second item must be determined from the value of I read in the first item.

Next: Transforming Iterative DO, Previous: Statements Needing Temporaries, Up: Transforming Statements

#### 21.6.2 Transforming DO WHILE

DO WHILE(expr) must be implemented so that temporaries needed to evaluate expr are generated just for the test, each time.

Consider how DO WHILE (A//B .NE. 'END'); ...; END DO is transformed:

         for (;;)
           {
             int temp0;

             {
               char temp1[large];

               libg77_catenate (temp1, a, b);
               temp0 = libg77_ne (temp1, 'END');
             }

             if (! temp0)
               break;

             ...
           }

In this case, it seems like a time/space tradeoff between allocating and deallocating temp1 for each iteration and allocating it just once for the entire loop.

However, if temp1 is allocated just once for the entire loop, it could be the wrong size for subsequent iterations of that loop in cases like DO WHILE (A(I:J)//B .NE. 'END'), because the body of the loop might modify I or J.

So, the above implementation is used, though a more optimal one can be used in specific circumstances.

Next: Transforming Block IF, Previous: Transforming DO WHILE, Up: Transforming Statements

#### 21.6.3 Transforming Iterative DO

An iterative `DO` loop (one that specifies an iteration variable) is required by the Fortran standards to be implemented as though an iteration count is computed before entering the loop body, and that iteration count used to determine the number of times the loop body is to be performed (assuming the loop isn't cut short via `GOTO` or `EXIT`).

The FFE handles this by allocating a temporary variable to contain the computed number of iterations. Since this variable must be in a scope that includes the entire loop, a GBEL block is created for that loop, and the variable declared as belonging to the scope of that block.

Next: Transforming SELECT CASE, Previous: Transforming Iterative DO, Up: Transforming Statements

#### 21.6.4 Transforming Block IF

Consider:

         SUBROUTINE X(A,B,C)
         CHARACTER*(*) A, B, C
         LOGICAL LFUNC

         IF (LFUNC (A//B)) THEN
           CALL SUBR1
         ELSE IF (LFUNC (A//C)) THEN
           CALL SUBR2
         ELSE
           CALL SUBR3
         END

The arguments to the two calls to LFUNC require dynamic allocation (at run time), but are not required during execution of the `CALL` statements.

So, the scopes of those temporaries must be within blocks inside the block corresponding to the Fortran `IF` block.

This cannot be represented “naturally” in vanilla C, nor in GBEL. The `if`, `elseif`, `else`, and `endif` constructs provided by both languages must, for a given `if` block, share the same C/GBE block.

Therefore, any temporaries needed during evaluation of expr while executing ELSE IF(expr) must either have been predeclared at the top of the corresponding `IF` block, or declared within a new block for that `ELSE IF`—a block that, since it cannot contain the `else` or `else if` itself (due to the above requirement), actually implements the rest of the `IF` block's `ELSE IF` and `ELSE` statements within an inner block.

The FFE takes the latter approach.

Previous: Transforming Block IF, Up: Transforming Statements

#### 21.6.5 Transforming SELECT CASE

`SELECT CASE` poses a few interesting problems for code generation, if efficiency and frugal stack management are important.

Consider SELECT CASE (I('PREFIX'//A)), where A is `CHARACTER*(*)`. In a case like this—basically, in any case where largish temporaries are needed to evaluate the expression—those temporaries should not be “live” during execution of any of the `CASE` blocks.

So, evaluation of the expression is best done within its own block, which in turn is within the `SELECT CASE` block itself (which contains the code for the CASE blocks as well, though each within their own block).

Otherwise, we'd have the rough equivalent of this pseudo-code:

         {
           char temp[large];

           libg77_catenate (temp, 'prefix', a);

           switch (i (temp))
             {
             case 0:
               ...
             }
         }

And that would leave temp[large] in scope during the CASE blocks (although a clever back end *could* see that it isn't referenced in them, and thus free that temp before executing the blocks).

So this approach is used instead:

         {
           int temp0;

           {
             char temp1[large];

             libg77_catenate (temp1, 'prefix', a);
             temp0 = i (temp1);
           }

           switch (temp0)
             {
             case 0:
               ...
             }
         }

Note how temp1 goes out of scope before starting the switch, thus making it easy for a back end to free it.

The problem that solution has, however, is with SELECT CASE('prefix'//A) (which is currently not supported).

Unless the GBEL is extended to support arbitrarily long character strings in its `case` facility, the FFE has to implement `SELECT CASE` on `CHARACTER` (probably excepting `CHARACTER*1`) using a cascade of `if`, `elseif`, `else`, and `endif` constructs in GBEL.

To prevent the (potentially large) temporary, needed to hold the selected expression itself ('prefix'//A), from being in scope during execution of the `CASE` blocks, two approaches are available:

- Pre-evaluate all the `CASE` tests, producing an integer ordinal that is used, a la temp0 in the earlier example, as if SELECT CASE(temp0) had been written.

  Each corresponding `CASE` is replaced with CASE(i), where i is the ordinal for that case, determined while, or before, generating the cascade of `if`-related constructs to cope with `CHARACTER` selection.

- Make temp0 above just large enough to hold the longest `CASE` string that'll actually be compared against the expression (in this case, 'prefix'//A).

  Since that length must be constant (because `CASE` expressions are all constant), it won't be so large, and, further, temp1 need not be dynamically allocated, since normal `CHARACTER` assignment can be used into the fixed-length temp0.

Both of these solutions require `SELECT CASE` implementation to be changed so all the corresponding `CASE` statements are seen during the actual code generation for `SELECT CASE`.

Next: Internal Naming Conventions, Previous: Transforming Statements, Up: Front End

### 21.7 Transforming Expressions

The interactions between statements, expressions, and subexpressions at program run time can be viewed as:

         action(expr)

Here, action is the series of steps performed to effect the statement, and expr is the expression whose value is used by action.

Expanding the above shows a typical order of events at run time:

         Evaluate expr
         Perform action, using result of evaluation of expr
         Clean up after evaluating expr

So, if evaluating expr requires allocating memory, that memory can be freed before performing action only if it is not needed to hold the result of evaluating expr. Otherwise, it must be freed no sooner than after action has been performed.

The above are recursive definitions, in the sense that they apply to subexpressions of expr.

That is, evaluating expr involves evaluating all of its subexpressions, performing the action that computes the result value of expr, then cleaning up after evaluating those subexpressions.

The recursive nature of this evaluation is implemented via recursive-descent transformation of the top-level statements, their expressions, their subexpressions, and so on.

However, that recursive-descent transformation is, due to the nature of the GBEL, focused primarily on generating a single stream of code to be executed at run time.

Yet, from the above, it's clear that multiple streams of code must effectively be simultaneously generated during the recursive-descent analysis of statements.

The primary stream implements the primary action items, while at least two other streams implement the evaluation and clean-up items.

Requirements imposed by expressions include:

- Whether the caller needs to have a temporary ready to hold the value of the expression.
- Other stuff???

Previous: Transforming Expressions, Up: Front End

### 21.8 Internal Naming Conventions

Names exported by FFE modules have the following (regular-expression) forms. Note that all names beginning `ffe` mod or `FFE` mod, where mod is lowercase or uppercase alphanumerics, respectively, are exported by the module `ffe` mod, with the source code doing the exporting in mod.h. (Usually, the source code for the implementation is in mod.c.)

Identifiers that don't fit the following forms are not considered exported, even if they are according to the C language. (For example, they might be made available to other modules solely for use within expansions of exported macros, not for use within any source code in those other modules.)

`ffe` mod
  The single typedef exported by the module.
`FFE` umod`_[A-Z][A-Z0-9_]*`
  (Where umod is the uppercase for of mod.)

  A `#define` or `enum` constant of the type `ffe` mod.

`ffe` mod`[A-Z][A-Z][a-z0-9]*`
  A typedef exported by the module.

  The portion of the identifier after `ffe` mod is referred to as `ctype`, a capitalized (mixed-case) form of `type`.

`FFE` umod`_`type`[A-Z][A-Z0-9_]*[A-Z0-9]?`
  (Where umod is the uppercase for of mod.)

  A `#define` or `enum` constant of the type `ffe` mod type, where type is the lowercase form of ctype in an exported typedef.

`ffe` mod`_`value
  A function that does or returns something, as described by value (see below).
`ffe` mod`_`value`_`input
  A function that does or returns something based primarily on the thing described by input (see below).

Below are names used for value and input, along with their definitions.

`col`
  A column number within a line (first column is number 1).
`file`
  An encapsulation of a file's name.
`find`
  Looks up an instance of some type that matches specified criteria, and returns that, even if it has to create a new instance or crash trying to find it (as appropriate).
`initialize`
  Initializes, usually a module. No type.
`int`
  A generic integer of type `int`.
`is`
  A generic integer that contains a true (nonzero) or false (zero) value.
`len`
  A generic integer that contains the length of something.
`line`
  A line number within a source file, or a global line number.
`lookup`
  Looks up an instance of some type that matches specified criteria, and returns that, or returns nil.
`name`
  A `text` that points to a name of something.
`new`
  Makes a new instance of the indicated type. Might return an existing one if appropriate—if so, similar to `find` without crashing.
`pt`
  Pointer to a particular character (line, column pairs) in the input file (source code being compiled).
`run`
  Performs some herculean task. No type.
`terminate`
  Terminates, usually a module. No type.
`text`
  A `char *` that points to generic text.

Next: Keyword Index, Previous: Front End, Up: Top

## 22 Diagnostics

Some diagnostics produced by g77 require sufficient explanation that the explanations are given below, and the diagnostics themselves identify the appropriate explanation.

Identification uses the GNU Info format—specifically, the info command that displays the explanation is given within square brackets in the diagnostic. For example:

         foo.f:5: Invalid statement [info -f g77 M FOOEY]

More details about the above diagnostic is found in the g77 Info documentation, menu item M, submenu item FOOEY, which is displayed by typing the UNIX command info -f g77 M FOOEY.

Other Info readers, such as EMACS, may be just as easily used to display the pertinent node. In the above example, g77 is the Info document name, M is the top-level menu item to select, and, in that node (named Diagnostics, the name of this chapter, which is the very text you're reading now), FOOEY is the menu item to select.

Next: EXPIMP, Up: Diagnostics

### 22.1 `CMPAMBIG`

         Ambiguous use of intrinsic intrinsic ...

The type of the argument to the invocation of the intrinsic intrinsic is a `COMPLEX` type other than `COMPLEX(KIND=1)`. Typically, it is `COMPLEX(KIND=2)`, also known as `DOUBLE COMPLEX`.

The interpretation of this invocation depends on the particular dialect of Fortran for which the code was written. Some dialects convert the real part of the argument to `REAL(KIND=1)`, thus losing precision; other dialects, and Fortran 90, do no such conversion.

So, GNU Fortran rejects such invocations except under certain circumstances, to avoid making an incorrect assumption that results in generating the wrong code.

To determine the dialect of the program unit, perhaps even whether that particular invocation is properly coded, determine how the result of the intrinsic is used.

The result of intrinsic is expected (by the original programmer) to be `REAL(KIND=1)` (the non-Fortran-90 interpretation) if:

- It is passed as an argument to a procedure that explicitly or implicitly declares that argument `REAL(KIND=1)`.

  For example, a procedure with no `DOUBLE PRECISION` or `IMPLICIT DOUBLE PRECISION` statement specifying the dummy argument corresponding to an actual argument of REAL(Z), where Z is declared `DOUBLE COMPLEX`, strongly suggests that the programmer expected REAL(Z) to return `REAL(KIND=1)` instead of `REAL(KIND=2)`.

- It is used in a context that would otherwise not include any `REAL(KIND=2)` but where treating the intrinsic invocation as `REAL(KIND=2)` would result in unnecessary promotions and (typically) more expensive operations on the wider type.

  For example:

                DOUBLE COMPLEX Z
                ...
                R(1) = T * REAL(Z)

  The above example suggests the programmer expected the real part of Z to be converted to `REAL(KIND=1)` before being multiplied by T (presumed, along with R above, to be type `REAL(KIND=1)`).

  Otherwise, the conversion would have to be delayed until after the multiplication, requiring not only an extra conversion (of T to `REAL(KIND=2)`), but a (typically) more expensive multiplication (a double-precision multiplication instead of a single-precision one).

The result of intrinsic is expected (by the original programmer) to be `REAL(KIND=2)` (the Fortran 90 interpretation) if:

- It is passed as an argument to a procedure that explicitly or implicitly declares that argument `REAL(KIND=2)`.

  For example, a procedure specifying a `DOUBLE PRECISION` dummy argument corresponding to an actual argument of REAL(Z), where Z is declared `DOUBLE COMPLEX`, strongly suggests that the programmer expected REAL(Z) to return `REAL(KIND=2)` instead of `REAL(KIND=1)`.

- It is used in an expression context that includes other `REAL(KIND=2)` operands, or is assigned to a `REAL(KIND=2)` variable or array element.

  For example:

                DOUBLE COMPLEX Z
                DOUBLE PRECISION R, T
                ...
                R(1) = T * REAL(Z)

  The above example suggests the programmer expected the real part of Z to not be converted to `REAL(KIND=1)` by the `REAL()` intrinsic.

  Otherwise, the conversion would have to be immediately followed by a conversion back to `REAL(KIND=2)`, losing the original, full precision of the real part of `Z`, before being multiplied by T.

Once you have determined whether a particular invocation of intrinsic expects the Fortran 90 interpretation, you can:

- Change it to DBLE(expr) (if intrinsic is `REAL`) or DIMAG(expr) (if intrinsic is `AIMAG`) if it expected the Fortran 90 interpretation.

  This assumes expr is `COMPLEX(KIND=2)`—if it is some other type, such as `COMPLEX*32`, you should use the appropriate intrinsic, such as the one to convert to `REAL*16` (perhaps `DBLEQ()` in place of `DBLE()`, and `QIMAG()` in place of `DIMAG()`).

- Change it to REAL(intrinsic(expr)), otherwise. This converts to `REAL(KIND=1)` in all working Fortran compilers.

If you don't want to change the code, and you are certain that all ambiguous invocations of intrinsic in the source file have the same expectation regarding interpretation, you can:

- Compile with the g77 option -ff90, to enable the Fortran 90 interpretation.
- Compile with the g77 options -fno-f90 -fugly-complex, to enable the non-Fortran-90 interpretations.

See REAL() and AIMAG() of Complex, for more information on this issue.

Note: If the above suggestions don't produce enough evidence as to whether a particular program expects the Fortran 90 interpretation of this ambiguous invocation of intrinsic, there is one more thing you can try.

If you have access to most or all the compilers used on the program to create successfully tested and deployed executables, read the documentation for, and also test out, each compiler to determine how it treats the intrinsic intrinsic in this case. (If all the compilers don't agree on an interpretation, there might be lurking bugs in the deployed versions of the program.)

The following sample program might help:

               PROGRAM JCB003
         C
         C Written by James Craig Burley 1997-02-23.
         C
         C Determine how compilers handle non-standard REAL
         C and AIMAG on DOUBLE COMPLEX operands.
         C
               DOUBLE COMPLEX Z
               REAL R
               Z = (3.3D0, 4.4D0)
               R = Z
               CALL DUMDUM(Z, R)
               R = REAL(Z) - R
               IF (R .NE. 0.) PRINT *, 'REAL() is Fortran 90'
               IF (R .EQ. 0.) PRINT *, 'REAL() is not Fortran 90'
               R = 4.4D0
               CALL DUMDUM(Z, R)
               R = AIMAG(Z) - R
               IF (R .NE. 0.) PRINT *, 'AIMAG() is Fortran 90'
               IF (R .EQ. 0.) PRINT *, 'AIMAG() is not Fortran 90'
               END
         C
         C Just to make sure compiler doesn't use naive flow
         C analysis to optimize away careful work above,
         C which might invalidate results....
         C
               SUBROUTINE DUMDUM(Z, R)
               DOUBLE COMPLEX Z
               REAL R
               END

If the above program prints contradictory results on a particular compiler, run away!

Next: INTGLOB, Previous: CMPAMBIG, Up: Diagnostics

### 22.2 `EXPIMP`

         Intrinsic intrinsic referenced ...

The intrinsic is explicitly declared in one program unit in the source file and implicitly used as an intrinsic in another program unit in the same source file.

This diagnostic is designed to catch cases where a program might depend on using the name intrinsic as an intrinsic in one program unit and as a global name (such as the name of a subroutine or function) in another, but g77 recognizes the name as an intrinsic in both cases.

After verifying that the program unit making implicit use of the intrinsic is indeed written expecting the intrinsic, add an INTRINSIC intrinsic statement to that program unit to prevent this warning.

This and related warnings are disabled by using the -Wno-globals option when compiling.

Note that this warning is not issued for standard intrinsics. Standard intrinsics include those described in the FORTRAN 77 standard and, if -ff90 is specified, those described in the Fortran 90 standard. Such intrinsics are not as likely to be confused with user procedures as intrinsics provided as extensions to the standard by g77.

Next: LEX, Previous: EXPIMP, Up: Diagnostics

### 22.3 `INTGLOB`

         Same name `intrinsic' given ...

The name intrinsic is used for a global entity (a common block or a program unit) in one program unit and implicitly used as an intrinsic in another program unit.

This diagnostic is designed to catch cases where a program intends to use a name entirely as a global name, but g77 recognizes the name as an intrinsic in the program unit that references the name, a situation that would likely produce incorrect code.

For example:

         INTEGER FUNCTION TIME()
         ...
         END
         ...
         PROGRAM SAMP
         INTEGER TIME
         PRINT *, 'Time is ', TIME()
         END

The above example defines a program unit named TIME, but the reference to TIME in the main program unit SAMP is normally treated by g77 as a reference to the intrinsic `TIME()` (unless a command-line option that prevents such treatment has been specified).

As a result, the program SAMP will not invoke the TIME function in the same source file.

Since g77 recognizes `libU77` procedures as intrinsics, and since some existing code uses the same names for its own procedures as used by some `libU77` procedures, this situation is expected to arise often enough to make this sort of warning worth issuing.

After verifying that the program unit making implicit use of the intrinsic is indeed written expecting the intrinsic, add an INTRINSIC intrinsic statement to that program unit to prevent this warning.

Or, if you believe the program unit is designed to invoke the program-defined procedure instead of the intrinsic (as recognized by g77), add an EXTERNAL intrinsic statement to the program unit that references the name to prevent this warning.

This and related warnings are disabled by using the -Wno-globals option when compiling.

Note that this warning is not issued for standard intrinsics. Standard intrinsics include those described in the FORTRAN 77 standard and, if -ff90 is specified, those described in the Fortran 90 standard. Such intrinsics are not as likely to be confused with user procedures as intrinsics provided as extensions to the standard by g77.

Next: GLOBALS, Previous: INTGLOB, Up: Diagnostics

### 22.4 `LEX`

         Unrecognized character ...
         Invalid first character ...
         Line too long ...
         Non-numeric character ...
         Continuation indicator ...
         Label at ... invalid with continuation line indicator ...
         Character constant ...
         Continuation line ...
         Statement at ... begins with invalid token

Although the diagnostics identify specific problems, they can be produced when general problems such as the following occur:

- The source file contains something other than Fortran code.

  If the code in the file does not look like many of the examples elsewhere in this document, it might not be Fortran code. (Note that Fortran code often is written in lower case letters, while the examples in this document use upper case letters, for stylistic reasons.)

  For example, if the file contains lots of strange-looking characters, it might be APL source code; if it contains lots of parentheses, it might be Lisp source code; if it contains lots of bugs, it might be C++ source code.

- The source file contains free-form Fortran code, but -ffree-form was not specified on the command line to compile it.

  Free form is a newer form for Fortran code. The older, classic form is called fixed form.

  Fixed-form code is visually fairly distinctive, because numerical labels and comments are all that appear in the first five columns of a line, the sixth column is reserved to denote continuation lines, and actual statements start at or beyond column 7. Spaces generally are not significant, so if you see statements such as REALX,Y and DO10I=1,100, you are looking at fixed-form code. Comment lines are indicated by the letter C or the symbol * in column 1. (Some code uses ! or /* to begin in-line comments, which many compilers support.)

  Free-form code is distinguished from fixed-form source primarily by the fact that statements may start anywhere. (If lots of statements start in columns 1 through 6, that's a strong indicator of free-form source.) Consecutive keywords must be separated by spaces, so REALX,Y is not valid, while REAL X,Y is. There are no comment lines per se, but ! starts a comment anywhere in a line (other than within a character or Hollerith constant).

  See Source Form, for more information.

- The source file is in fixed form and has been edited without sensitivity to the column requirements.

  Statements in fixed-form code must be entirely contained within columns 7 through 72 on a given line. Starting them “early” is more likely to result in diagnostics than finishing them “late”, though both kinds of errors are often caught at compile time.

  For example, if the following code fragment is edited by following the commented instructions literally, the result, shown afterward, would produce a diagnostic when compiled:

                C On XYZZY systems, remove "C" on next line:
                C     CALL XYZZY_RESET

  The result of editing the above line might be:

                C On XYZZY systems, remove "C" on next line:
                     CALL XYZZY_RESET

  However, that leaves the first C in the `CALL` statement in column 6, making it a comment line, which is not really what the author intended, and which is likely to result in one of the above-listed diagnostics.

  Replacing the C in column 1 with a space is the proper change to make, to ensure the `CALL` keyword starts in or after column 7.

  Another common mistake like this is to forget that fixed-form source lines are significant through only column 72, and that, normally, any text beyond column 72 is ignored or is diagnosed at compile time.

  See Source Form, for more information.

- The source file requires preprocessing, and the preprocessing is not being specified at compile time.

  A source file containing lines beginning with `#define`, `#include`, `#if`, and so on is likely one that requires preprocessing.

  If the file's suffix is .f, .for, or .FOR, the file normally will be compiled without preprocessing by g77.

  Change the file's suffix from .f to .F (or, on systems with case-insensitive file names, to .fpp or .FPP), from .for to .fpp, or from .FOR to .FPP. g77 compiles files with such names with preprocessing.

  Or, learn how to use gcc's -x option to specify the language f77-cpp-input for Fortran files that require preprocessing. See Options Controlling the Kind of Output (Using the GNU Compiler Collection (GCC)).

- The source file is preprocessed, and the results of preprocessing result in syntactic errors that are not necessarily obvious to someone examining the source file itself.

  Examples of errors resulting from preprocessor macro expansion include exceeding the line-length limit, improperly starting, terminating, or incorporating the apostrophe or double-quote in a character constant, improperly forming a Hollerith constant, and so on.

  See Options Controlling the Kind of Output, for suggestions about how to use, and not use, preprocessing for Fortran code.

Next: LINKFAIL, Previous: LEX, Up: Diagnostics

### 22.5 `GLOBALS`

         Global name name defined at ... already defined...
         Global name name at ... has different type...
         Too many arguments passed to name at ...
         Too few arguments passed to name at ...
         Argument #n of name is ...

These messages all identify disagreements about the global procedure named name among different program units (usually including name itself).

Whether a particular disagreement is reported as a warning or an error can depend on the relative order of the disagreeing portions of the source file.

Disagreements between a procedure invocation and the subsequent procedure itself are, usually, diagnosed as errors when the procedure itself precedes the invocation. Other disagreements are diagnosed via warnings.

This distinction, between warnings and errors, is due primarily to the present tendency of the gcc back end to inline only those procedure invocations that are preceded by the corresponding procedure definitions. If the gcc back end is changed to inline “forward references”, in which invocations precede definitions, the g77 front end will be changed to treat both orderings as errors, accordingly.

The sorts of disagreements that are diagnosed by g77 include whether a procedure is a subroutine or function; if it is a function, the type of the return value of the procedure; the number of arguments the procedure accepts; and the type of each argument.

Disagreements regarding global names among program units in a Fortran program should be fixed in the code itself. However, if that is not immediately practical, and the code has been working for some time, it is possible it will work when compiled with the -fno-globals option.

The -fno-globals option causes these diagnostics to all be warnings and disables all inlining of references to global procedures (to avoid subsequent compiler crashes and bad-code generation). Use of the -Wno-globals option as well as -fno-globals suppresses all of these diagnostics. (-Wno-globals by itself disables only the warnings, not the errors.)

After using -fno-globals to work around these problems, it is wise to stop using that option and address them by fixing the Fortran code, because such problems, while they might not actually result in bugs on some systems, indicate that the code is not as portable as it could be. In particular, the code might appear to work on a particular system, but have bugs that affect the reliability of the data without exhibiting any other outward manifestations of the bugs.

Next: Y2KBAD, Previous: GLOBALS, Up: Diagnostics

### 22.6 `LINKFAIL`

On AIX 4.1, g77 might not build with the native (non-GNU) tools due to a linker bug in coping with the -bbigtoc option which leads to a Relocation overflow error. The GNU linker is not recommended on current AIX versions, though; it was developed under a now-unsupported version. This bug is said to be fixed by `update PTF U455193 for APAR IX75823'.

Compiling with -mminimal-toc might solve this problem, e.g. by adding

         BOOT_CFLAGS='-mminimal-toc -O2 -g'

to the `make bootstrap` command line.

Previous: LINKFAIL, Up: Diagnostics

### 22.7 `Y2KBAD`

         Intrinsic `name', invoked at (^), known to be non-Y2K-compliant...

This diagnostic indicates that the specific intrinsic invoked by the name name is known to have an interface that is not Year-2000 (Y2K) compliant.

See Year 2000 (Y2K) Problems.

Previous: Diagnostics, Up: Top

## Keyword Index

- !: LEX
- !: Exclamation Point
- !: Trailing Comment
- !: Character Set
- !: Statements Comments Lines
- ": Character Set
- #: Cpp-style directives
- #: Character Set
- #define: Overall Options
- #if: Overall Options
- #include: Overall Options
- $: Dollar Signs
- %: Character Set
- %DESCR() construct: %DESCR()
- %LOC() construct: %LOC()
- %REF() construct: %REF()
- %VAL() construct: %VAL()
- &: Character Set
- *: LEX
- *n notation: Compiler Types
- *n notation: Star Notation
- --driver option: Changes
- --driver option: News
- -falias-check option: Aliasing Assumed To Work
- -falias-check option: Code Gen Options
- -fargument-alias option: Aliasing Assumed To Work
- -fargument-alias option: Code Gen Options
- -fargument-noalias option: Aliasing Assumed To Work
- -fargument-noalias option: Code Gen Options
- -fbadu77-intrinsics-delete option: Fortran Dialect Options
- -fbadu77-intrinsics-disable option: Fortran Dialect Options
- -fbadu77-intrinsics-enable option: Fortran Dialect Options
- -fbadu77-intrinsics-hide option: Fortran Dialect Options
- -fbounds-check option: Code Gen Options
- -fcaller-saves option: Optimize Options
- -fcase-initcap option: Fortran Dialect Options
- -fcase-lower option: Fortran Dialect Options
- -fcase-preserve option: Fortran Dialect Options
- -fcase-strict-lower option: Fortran Dialect Options
- -fcase-strict-upper option: Fortran Dialect Options
- -fcase-upper option: Fortran Dialect Options
- -fdelayed-branch option: Optimize Options
- -fdollar-ok option: Fortran Dialect Options
- -femulate-complex option: Code Gen Options
- -fexpensive-optimizations option: Optimize Options
- -ff2c-intrinsics-delete option: Fortran Dialect Options
- -ff2c-intrinsics-disable option: Fortran Dialect Options
- -ff2c-intrinsics-enable option: Fortran Dialect Options
- -ff2c-intrinsics-hide option: Fortran Dialect Options
- -ff2c-library option: Code Gen Options
- -ff66 option: Shorthand Options
- -ff77 option: Shorthand Options
- -ff90: Fortran 90 Features
- -ff90 option: Fortran Dialect Options
- -ff90-intrinsics-delete option: Fortran Dialect Options
- -ff90-intrinsics-disable option: Fortran Dialect Options
- -ff90-intrinsics-enable option: Fortran Dialect Options
- -ff90-intrinsics-hide option: Fortran Dialect Options
- -ffast-math option: Optimize Options
- -ffinite-math-only option: Optimize Options
- -ffixed-line-length-n option: Fortran Dialect Options
- -fflatten-arrays option: Code Gen Options
- -ffloat-store option: Optimize Options
- -fforce-addr option: Optimize Options
- -fforce-mem option: Optimize Options
- -ffortran-bounds-check option: Code Gen Options
- -ffree-form: Fortran 90 Features
- -ffree-form option: Fortran Dialect Options
- -fgnu-intrinsics-delete option: Fortran Dialect Options
- -fgnu-intrinsics-disable option: Fortran Dialect Options
- -fgnu-intrinsics-enable option: Fortran Dialect Options
- -fgnu-intrinsics-hide option: Fortran Dialect Options
- -fgroup-intrinsics-hide option: Overly Convenient Options
- -finit-local-zero option: Overly Convenient Options
- -finit-local-zero option: Code Gen Options
- -fintrin-case-any option: Fortran Dialect Options
- -fintrin-case-initcap option: Fortran Dialect Options
- -fintrin-case-lower option: Fortran Dialect Options
- -fintrin-case-upper option: Fortran Dialect Options
- -fmatch-case-any option: Fortran Dialect Options
- -fmatch-case-initcap option: Fortran Dialect Options
- -fmatch-case-lower option: Fortran Dialect Options
- -fmatch-case-upper option: Fortran Dialect Options
- -fmil-intrinsics-delete option: Fortran Dialect Options
- -fmil-intrinsics-disable option: Fortran Dialect Options
- -fmil-intrinsics-enable option: Fortran Dialect Options
- -fmil-intrinsics-hide option: Fortran Dialect Options
- -fno-argument-noalias-global option: Aliasing Assumed To Work
- -fno-argument-noalias-global option: Code Gen Options
- -fno-automatic option: Overly Convenient Options
- -fno-automatic option: Code Gen Options
- -fno-backslash option: Fortran Dialect Options
- -fno-common option: Code Gen Options
- -fno-f2c option: Avoid f2c Compatibility
- -fno-f2c option: Code Gen Options
- -fno-f77 option: Shorthand Options
- -fno-fixed-form option: Fortran Dialect Options
- -fno-globals option: Code Gen Options
- -fno-ident option: Code Gen Options
- -fno-inline option: Optimize Options
- -fno-move-all-movables option: Optimize Options
- -fno-reduce-all-givs option: Optimize Options
- -fno-rerun-loop-opt option: Optimize Options
- -fno-second-underscore: f2c Skeletons and Prototypes
- -fno-second-underscore option: Names
- -fno-second-underscore option: Code Gen Options
- -fno-silent option: Overall Options
- -fno-trapping-math option: Optimize Options
- -fno-ugly option: Shorthand Options
- -fno-ugly-args option: Fortran Dialect Options
- -fno-ugly-init option: Fortran Dialect Options
- -fno-underscoring option: Names
- -fno-underscoring option: Code Gen Options
- -fonetrip option: Fortran Dialect Options
- -fpack-struct option: Code Gen Options
- -fpcc-struct-return option: Code Gen Options
- -fpedantic option: Warning Options
- -fPIC option: News
- -freg-struct-return option: Code Gen Options
- -frerun-cse-after-loop option: Optimize Options
- -fschedule-insns option: Optimize Options
- -fschedule-insns2 option: Optimize Options
- -fset-g77-defaults option: Overall Options
- -fshort-double option: Code Gen Options
- -fsource-case-lower option: Fortran Dialect Options
- -fsource-case-preserve option: Fortran Dialect Options
- -fsource-case-upper option: Fortran Dialect Options
- -fstrength-reduce option: Optimize Options
- -fsymbol-case-any option: Fortran Dialect Options
- -fsymbol-case-initcap option: Fortran Dialect Options
- -fsymbol-case-lower option: Fortran Dialect Options
- -fsymbol-case-upper option: Fortran Dialect Options
- -fsyntax-only option: Warning Options
- -ftypeless-boz option: Fortran Dialect Options
- -fugly option: Shorthand Options
- -fugly-assign option: Fortran Dialect Options
- -fugly-assumed option: Fortran Dialect Options
- -fugly-comma option: Fortran Dialect Options
- -fugly-complex option: Fortran Dialect Options
- -fugly-logint option: Fortran Dialect Options
- -funix-intrinsics-delete option: Fortran Dialect Options
- -funix-intrinsics-disable option: Fortran Dialect Options
- -funix-intrinsics-enable option: Fortran Dialect Options
- -funix-intrinsics-hide option: Fortran Dialect Options
- -funroll-all-loops option: Optimize Options
- -funroll-loops option: Optimize Options
- -funsafe-math-optimizations option: Optimize Options
- -fversion option: Overall Options
- -fvxt option: Fortran Dialect Options
- -fvxt-intrinsics-delete option: Fortran Dialect Options
- -fvxt-intrinsics-disable option: Fortran Dialect Options
- -fvxt-intrinsics-enable option: Fortran Dialect Options
- -fvxt-intrinsics-hide option: Fortran Dialect Options
- -fzeros option: Code Gen Options
- -g option: Debugging Options
- -I- option: Directory Options
- -i8: Increasing Precision/Range
- -Idir option: Directory Options
- -malign-double: Changes
- -malign-double: News
- -malign-double option: Aligned Data
- -malign-double option: Optimize Options
- -Nl option: Compiler Limits
- -Nx option: Compiler Limits
- -O2: News
- -pedantic option: Warning Options
- -pedantic-errors option: Warning Options
- -qrealsize=8: Increasing Precision/Range
- -r8: Increasing Precision/Range
- -u option: Warning Options
- -v option: G77 and GCC
- -W option: Warning Options
- -w option: Warning Options
- -Waggregate-return option: Warning Options
- -Wall option: Warning Options
- -Wcomment option: Warning Options
- -Wconversion option: Warning Options
- -Werror option: Warning Options
- -Wformat option: Warning Options
- -Wid-clash-len option: Warning Options
- -Wimplicit option: Warning Options
- -Wlarger-than-len option: Warning Options
- -Wno-globals option: Warning Options
- -Wparentheses option: Warning Options
- -Wredundant-decls option: Warning Options
- -Wshadow option: Warning Options
- -Wsurprising option: Warning Options
- -Wswitch option: Warning Options
- -Wswitch-default option: Warning Options
- -Wswitch-enum option: Warning Options
- -Wtraditional option: Warning Options
- -Wuninitialized option: Warning Options
- -Wunused option: Warning Options
- -x f77-cpp-input option: LEX
- .EQV., with integer operands: Equivalence Versus Equality
- .F filename suffix: Overall Options
- .f filename suffix: Overall Options
- .FOR filename suffix: Overall Options
- .for filename suffix: Overall Options
- .FPP filename suffix: Overall Options
- .fpp filename suffix: Overall Options
- .gdbinit: Main Program Unit
- .r filename suffix: Overall Options
- /*: Trailing Comment
- /*: Overall Options
- /WARNINGS=DECLARATIONS switch: Warning Options
- 80-bit spills: Floating-point Errors
- ;: Character Set
- ;: Statements Comments Lines
- <: Character Set
- <> edit descriptor: I/O
- >: Character Set
- ?: Character Set
- \: Character Set
- _: Character Set
- Abort intrinsic: Abort Intrinsic
- Abs intrinsic: Abs Intrinsic
- ACCEPT statement: TYPE and ACCEPT I/O Statements
- Access intrinsic: Access Intrinsic
- AChar intrinsic: AChar Intrinsic
- ACos intrinsic: ACos Intrinsic
- ACosD intrinsic: ACosD Intrinsic
- adding options: Adding Options
- adjustable arrays: Adjustable Arrays
- AdjustL intrinsic: AdjustL Intrinsic
- AdjustR intrinsic: AdjustR Intrinsic
- AImag intrinsic: AImag Intrinsic
- `AImag` intrinsic: REAL() and AIMAG() of Complex
- AIMax0 intrinsic: AIMax0 Intrinsic
- AIMin0 intrinsic: AIMin0 Intrinsic
- AInt intrinsic: AInt Intrinsic
- AJMax0 intrinsic: AJMax0 Intrinsic
- AJMin0 intrinsic: AJMin0 Intrinsic
- Alarm intrinsic: Alarm Intrinsic
- aliasing: Known Bugs
- aliasing: Aliasing Assumed To Work
- aligned data: Aligned Data
- aligned stack: Aligned Data
- alignment: Aligned Data
- alignment: Changes
- alignment: News
- All intrinsic: All Intrinsic
- all warnings: Warning Options
- Allocated intrinsic: Allocated Intrinsic
- ALog intrinsic: ALog Intrinsic
- ALog10 intrinsic: ALog10 Intrinsic
- Alpha, support: Known Bugs
- alternate entry points: Alternate Entry Points
- alternate returns: Alternate Returns
- ALWAYS_FLUSH: Output Assumed To Flush
- AMax0 intrinsic: AMax0 Intrinsic
- AMax1 intrinsic: AMax1 Intrinsic
- AMin0 intrinsic: AMin0 Intrinsic
- AMin1 intrinsic: AMin1 Intrinsic
- AMod intrinsic: AMod Intrinsic
- ampersand: Character Set
- ampersand continuation line: Ampersands
- `And` intrinsic: Bit Operations on Floating-point Data
- And intrinsic: And Intrinsic
- ANInt intrinsic: ANInt Intrinsic
- ANS carriage control: OPEN CLOSE and INQUIRE Keywords
- ANSI FORTRAN 77 standard: Language
- ANSI FORTRAN 77 support: Standard Support
- anti-aliasing: Aliasing Assumed To Work
- Any intrinsic: Any Intrinsic
- arguments, null: Ugly Null Arguments
- arguments, omitting: Ugly Null Arguments
- arguments, unused: Unused Arguments
- arguments, unused: Warning Options
- array bounds checking: Code Gen Options
- array bounds, adjustable: Array Bounds Expressions
- array elements, in adjustable array bounds: Array Bounds Expressions
- array ordering: Arrays
- array performance: Code Gen Options
- array size: Array Size
- arrays: Arrays
- arrays, adjustable: Adjustable Arrays
- arrays, assumed-size: Ugly Assumed-Size Arrays
- arrays, automatic: Large Automatic Arrays
- arrays, automatic: Stack Overflow
- arrays, automatic: Overly Convenient Options
- arrays, automatic: Adjustable Arrays
- arrays, dimensioning: Adjustable Arrays
- arrays, dimensioning: Array Size
- arrays, flattening: Code Gen Options
- as command: What is GNU Fortran?
- ASin intrinsic: ASin Intrinsic
- ASinD intrinsic: ASinD Intrinsic
- assembler: What is GNU Fortran?
- assembly code: What is GNU Fortran?
- assembly code, invalid: Bug Criteria
- ASSIGN statement: Assigned Statement Labels
- ASSIGN statement: Ugly Assigned Labels
- assigned labels: Ugly Assigned Labels
- assigned statement labels: Assigned Statement Labels
- Associated intrinsic: Associated Intrinsic
- association, storage: Aliasing Assumed To Work
- assumed-size arrays: Ugly Assumed-Size Arrays
- asterisk: LEX
- ATan intrinsic: ATan Intrinsic
- ATan2 intrinsic: ATan2 Intrinsic
- ATan2D intrinsic: ATan2D Intrinsic
- ATanD intrinsic: ATanD Intrinsic
- automatic arrays: Large Automatic Arrays
- automatic arrays: Stack Overflow
- automatic arrays: Overly Convenient Options
- automatic arrays: Adjustable Arrays
- `AUTOMATIC` statement: AUTOMATIC Statement
- automatic variables: AUTOMATIC Statement
- back end, gcc: Philosophy of Code Generation
- back end, gcc: What is GNU Fortran?
- backslash: Backslash in Constants
- backslash: Character Set
- backslash: Fortran Dialect Options
- `badu77` intrinsics: Fortran Dialect Options
- `badu77` intrinsics group: Intrinsic Groups
- basic concepts: What is GNU Fortran?
- Bear-poking: Philosophy of Code Generation
- beginners: Getting Started
- BesJ0 intrinsic: BesJ0 Intrinsic
- BesJ1 intrinsic: BesJ1 Intrinsic
- BesJN intrinsic: BesJN Intrinsic
- BesY0 intrinsic: BesY0 Intrinsic
- BesY1 intrinsic: BesY1 Intrinsic
- BesYN intrinsic: BesYN Intrinsic
- binary data: Portable Unformatted Files
- Bit_Size intrinsic: Bit_Size Intrinsic
- BITest intrinsic: BITest Intrinsic
- BJTest intrinsic: BJTest Intrinsic
- blank: Lines
- blank: Character Set
- block data: Multiple Definitions of External Names
- block data and libraries: Block Data and Libraries
- BLOCK DATA statement: Multiple Definitions of External Names
- BLOCK DATA statement: Block Data and Libraries
- bounds checking: Code Gen Options
- BTest intrinsic: BTest Intrinsic
- bug criteria: Bug Criteria
- bugs: Bugs
- bugs, finding: What is GNU Fortran?
- bugs, known: Trouble
- bus error: Strange Behavior at Run Time
- bus error: NeXTStep Problems
- but-bugs: But-bugs
- byte ordering: Portable Unformatted Files
- C library: Strange Behavior at Run Time
- C preprocessor: Overall Options
- C routines calling Fortran: Debugging and Interfacing
- C++: C++ Considerations
- C++, linking with: Interoperating with C and C++
- C, linking with: Interoperating with C and C++
- CAbs intrinsic: CAbs Intrinsic
- calling C routines: Debugging and Interfacing
- card image: Fortran Dialect Options
- carriage control: OPEN CLOSE and INQUIRE Keywords
- carriage returns: Carriage Returns
- case sensitivity: Case Sensitivity
- cc1 program: What is GNU Fortran?
- cc1plus program: What is GNU Fortran?
- CCos intrinsic: CCos Intrinsic
- CDAbs intrinsic: CDAbs Intrinsic
- CDCos intrinsic: CDCos Intrinsic
- CDExp intrinsic: CDExp Intrinsic
- CDLog intrinsic: CDLog Intrinsic
- CDSin intrinsic: CDSin Intrinsic
- CDSqRt intrinsic: CDSqRt Intrinsic
- Ceiling intrinsic: Ceiling Intrinsic
- CExp intrinsic: CExp Intrinsic
- cfortran.h: C Interfacing Tools
- changes, user-visible: Changes
- Char intrinsic: Char Intrinsic
- character assignments: Fortran 90 Features
- character constants: Character and Hollerith Constants
- character constants: Ugly Conversion of Initializers
- character constants: Double Quote Meaning
- character constants: Fortran Dialect Options
- character set: Fortran Dialect Options
- CHARACTER*(*): Arbitrary Concatenation
- CHARACTER, null: Character Type
- character-variable length: Character-variable Length
- characters: Character Set
- characters, comma: Ugly Null Arguments
- characters, comment: LEX
- characters, comment: Exclamation Point
- characters, comment: Trailing Comment
- characters, comment: Statements Comments Lines
- characters, continuation: LEX
- characters, continuation: Exclamation Point
- characters, continuation: Statements Comments Lines
- ChDir intrinsic: ChDir Intrinsic (function)
- ChDir intrinsic: ChDir Intrinsic (subroutine)
- checking subscripts: Code Gen Options
- checking substrings: Code Gen Options
- checks, of internal consistency: Overall Options
- ChMod intrinsic: ChMod Intrinsic (function)
- ChMod intrinsic: ChMod Intrinsic (subroutine)
- CLog intrinsic: CLog Intrinsic
- close angle: Character Set
- close bracket: Character Set
- CLOSE statement: OPEN CLOSE and INQUIRE Keywords
- Cmplx intrinsic: Cmplx Intrinsic
- `Cmplx` intrinsic: CMPLX() of DOUBLE PRECISION
- code generation, conventions: Code Gen Options
- code generation, improving: Better Optimization
- code generator: Philosophy of Code Generation
- code generator: What is GNU Fortran?
- code, assembly: What is GNU Fortran?
- code, displaying main source: Known Bugs
- code, in-line: What is GNU Fortran?
- code, legacy: Collected Fortran Wisdom
- code, machine: What is GNU Fortran?
- code, source: Case Sensitivity
- code, source: Source Form
- code, source: Lines
- code, source: What is GNU Fortran?
- code, user: Cannot Link Fortran Programs
- code, writing: Collected Fortran Wisdom
- column-major ordering: Arrays
- columns 73 through 80: Better Source Model
- comma, trailing: Ugly Null Arguments
- command options: Invoking G77
- commands, as: What is GNU Fortran?
- commands, g77: G77 and GCC
- commands, g77: What is GNU Fortran?
- commands, gcc: G77 and GCC
- commands, gcc: What is GNU Fortran?
- commands, gdb: What is GNU Fortran?
- commands, ld: What is GNU Fortran?
- comment: LEX
- comment: Trailing Comment
- comment: Statements Comments Lines
- comment character: Exclamation Point
- comment line, debug: Enabling Debug Lines
- comment line, debug: Debug Line
- common blocks: Mangling of Names
- common blocks: Known Bugs
- common blocks: Common Blocks
- common blocks, large: Large Common Blocks
- `COMMON` layout: Aligned Data
- `COMMON` statement: Multiple Definitions of External Names
- `COMMON` statement: Common Blocks
- comparing logical expressions: Equivalence Versus Equality
- compatibility, f2c: Avoid f2c Compatibility
- compatibility, f2c: Block Data and Libraries
- compatibility, f2c: Code Gen Options
- compatibility, f2c: Shorthand Options
- compatibility, f2c: Overall Options
- compatibility, f77: Shorthand Options
- compatibility, FORTRAN 66: Fortran Dialect Options
- compatibility, FORTRAN 66: Shorthand Options
- compatibility, FORTRAN 77: Standard Support
- compatibility, Fortran 90: Fortran 90
- compilation, in-line: GLOBALS
- compilation, in-line: Code Gen Options
- compilation, in-line: Optimize Options
- compilation, pedantic: Pedantic Compilation
- compilation, status: Overall Options
- compiler bugs, reporting: Bug Reporting
- compiler limits: Compiler Limits
- compiler memory usage: Known Bugs
- compiler speed: Known Bugs
- compilers: What is GNU Fortran?
- compiling programs: G77 and GCC
- Complex intrinsic: Complex Intrinsic
- `COMPLEX` intrinsics: Fortran Dialect Options
- complex performance: Known Bugs
- COMPLEX statement: Complex Variables
- complex values: Ugly Complex Part Extraction
- complex variables: Complex Variables
- COMPLEX(KIND=1) type: Compiler Types
- COMPLEX(KIND=2) type: Compiler Types
- components of g77: What is GNU Fortran?
- concatenation: Arbitrary Concatenation
- concepts, basic: What is GNU Fortran?
- conformance, IEEE 754: Floating-point precision
- conformance, IEEE 754: Optimize Options
- Conjg intrinsic: Conjg Intrinsic
- consistency checks: Overall Options
- constants: Compiler Constants
- constants: Constants
- constants, character: Character and Hollerith Constants
- constants, character: Ugly Conversion of Initializers
- constants, character: Double Quote Meaning
- constants, context-sensitive: Context-Sensitive Constants
- constants, Hollerith: Character and Hollerith Constants
- constants, Hollerith: Ugly Conversion of Initializers
- constants, Hollerith: Ugly Implicit Argument Conversion
- constants, integer: Known Bugs
- constants, octal: Double Quote Meaning
- constants, prefix-radix: Fortran Dialect Options
- constants, types: Fortran Dialect Options
- construct names: Construct Names
- context-sensitive constants: Context-Sensitive Constants
- context-sensitive intrinsics: Context-Sensitive Intrinsicness
- continuation character: LEX
- continuation character: Exclamation Point
- continuation character: Statements Comments Lines
- continuation line, ampersand: Ampersands
- continuation line, number of: Continuation Line
- contributors: Contributors
- conversions, nonportable: Nonportable Conversions
- core dump: Bug Criteria
- Cos intrinsic: Cos Intrinsic
- CosD intrinsic: CosD Intrinsic
- CosH intrinsic: CosH Intrinsic
- Count intrinsic: Count Intrinsic
- cpp preprocessor: Overall Options
- cpp program: LEX
- cpp program: Preprocessor Options
- cpp program: Overall Options
- cpp program: What is GNU Fortran?
- CPU_Time intrinsic: CPU_Time Intrinsic
- Cray pointers: POINTER Statements
- credits: Contributors
- CShift intrinsic: CShift Intrinsic
- CSin intrinsic: CSin Intrinsic
- CSqRt intrinsic: CSqRt Intrinsic
- CTime intrinsic: CTime Intrinsic (function)
- CTime intrinsic: CTime Intrinsic (subroutine)
- CYCLE statement: CYCLE and EXIT
- DAbs intrinsic: DAbs Intrinsic
- DACos intrinsic: DACos Intrinsic
- DACosD intrinsic: DACosD Intrinsic
- DASin intrinsic: DASin Intrinsic
- DASinD intrinsic: DASinD Intrinsic
- DATA statement: Known Bugs
- DATA statement: Code Gen Options
- data types: Compiler Types
- data, aligned: Aligned Data
- data, overwritten: Strange Behavior at Run Time
- DATan intrinsic: DATan Intrinsic
- DATan2 intrinsic: DATan2 Intrinsic
- DATan2D intrinsic: DATan2D Intrinsic
- DATanD intrinsic: DATanD Intrinsic
- Date intrinsic: Date Intrinsic
- Date_and_Time intrinsic: Date_and_Time Intrinsic
- date_y2kbuggy_0: Year 2000 (Y2K) Problems
- DbesJ0 intrinsic: DbesJ0 Intrinsic
- DbesJ1 intrinsic: DbesJ1 Intrinsic
- DbesJN intrinsic: DbesJN Intrinsic
- DbesY0 intrinsic: DbesY0 Intrinsic
- DbesY1 intrinsic: DbesY1 Intrinsic
- DbesYN intrinsic: DbesYN Intrinsic
- Dble intrinsic: Dble Intrinsic
- DbleQ intrinsic: DbleQ Intrinsic
- DCmplx intrinsic: DCmplx Intrinsic
- DConjg intrinsic: DConjg Intrinsic
- DCos intrinsic: DCos Intrinsic
- DCosD intrinsic: DCosD Intrinsic
- DCosH intrinsic: DCosH Intrinsic
- DDiM intrinsic: DDiM Intrinsic
- debug line: Enabling Debug Lines
- debug line: Debug Line
- debugger: Known Bugs
- debugger: What is GNU Fortran?
- debugging: Names
- debugging: Main Program Unit
- debugging: Debugging and Interfacing
- debugging information options: Debugging Options
- debugging main source code: Known Bugs
- DECODE statement: ENCODE and DECODE
- deleted intrinsics: Intrinsic Groups
- DErF intrinsic: DErF Intrinsic
- DErFC intrinsic: DErFC Intrinsic
- DExp intrinsic: DExp Intrinsic
- DFloat intrinsic: DFloat Intrinsic
- DFlotI intrinsic: DFlotI Intrinsic
- DFlotJ intrinsic: DFlotJ Intrinsic
- diagnostics: Diagnostics
- diagnostics, incorrect: What is GNU Fortran?
- dialect options: Fortran Dialect Options
- Digital Fortran features: Fortran Dialect Options
- Digits intrinsic: Digits Intrinsic
- DiM intrinsic: DiM Intrinsic
- DImag intrinsic: DImag Intrinsic
- `DIMENSION` statement: Array Bounds Expressions
- DIMENSION statement: Adjustable Arrays
- DIMENSION statement: Arrays
- DIMENSION X(1): Ugly Assumed-Size Arrays
- dimensioning arrays: Adjustable Arrays
- DInt intrinsic: DInt Intrinsic
- direction of language development: Direction of Language Development
- directive, INCLUDE: Directory Options
- directive, INCLUDE: Preprocessor Options
- directory, options: Directory Options
- directory, search paths for inclusion: Directory Options
- disabled intrinsics: Intrinsic Groups
- disk full: Output Assumed To Flush
- displaying main source code: Known Bugs
- disposition of files: OPEN CLOSE and INQUIRE Keywords
- distensions: Distensions
- DLog intrinsic: DLog Intrinsic
- DLog10 intrinsic: DLog10 Intrinsic
- DMax1 intrinsic: DMax1 Intrinsic
- DMin1 intrinsic: DMin1 Intrinsic
- DMod intrinsic: DMod Intrinsic
- DNInt intrinsic: DNInt Intrinsic
- DNRM2: News
- DO: DO WHILE
- `DO` loops, one-trip: Fortran Dialect Options
- `DO` loops, zero-trip: Fortran Dialect Options
- DO statement: Loops
- DO statement: Warning Options
- DO WHILE: DO WHILE
- DO WHILE: Optimize Options
- dollar sign: Dollar Signs
- dollar sign: I/O
- dollar sign: Fortran Dialect Options
- Dot_Product intrinsic: Dot_Product Intrinsic
- DOUBLE COMPLEX: DOUBLE COMPLEX
- DOUBLE COMPLEX type: Compiler Types
- DOUBLE PRECISION type: Compiler Types
- double quote: Character Set
- double quoted character constants: Fortran 90 Features
- double quoted character constants: Character Type
- double quotes: Double Quote Meaning
- double-precision performance: Changes
- double-precision performance: News
- DProd intrinsic: DProd Intrinsic
- DReal intrinsic: DReal Intrinsic
- driver, gcc command as: What is GNU Fortran?
- DSign intrinsic: DSign Intrinsic
- DSin intrinsic: DSin Intrinsic
- DSinD intrinsic: DSinD Intrinsic
- DSinH intrinsic: DSinH Intrinsic
- DSqRt intrinsic: DSqRt Intrinsic
- DTan intrinsic: DTan Intrinsic
- DTanD intrinsic: DTanD Intrinsic
- DTanH intrinsic: DTanH Intrinsic
- DTime intrinsic: DTime Intrinsic (function)
- DTime intrinsic: DTime Intrinsic (subroutine)
- dummies, unused: Warning Options
- edit descriptor, <>: I/O
- edit descriptor, O: I/O
- edit descriptor, Q: Q Edit Descriptor
- edit descriptor, Z: Fortran 90 Features
- edit descriptor, Z: I/O
- effecting IMPLICIT NONE: Warning Options
- efficiency: Efficiency
- ELF support: News
- empty CHARACTER strings: Character Type
- enabled intrinsics: Intrinsic Groups
- ENCODE statement: ENCODE and DECODE
- END DO: END DO
- entry points: Alternate Entry Points
- ENTRY statement: Alternate Entry Points
- environment variables: Environment Variables
- EOShift intrinsic: EOShift Intrinsic
- Epsilon intrinsic: Epsilon Intrinsic
- equivalence areas: Known Bugs
- equivalence areas: Local Equivalence Areas
- EQUIVALENCE statement: Local Equivalence Areas
- ErF intrinsic: ErF Intrinsic
- ErFC intrinsic: ErFC Intrinsic
- error messages: Warnings and Errors
- error messages: Run-time Library Errors
- error messages, incorrect: What is GNU Fortran?
- error values: Run-time Library Errors
- errors, linker: Large Common Blocks
- ETime intrinsic: ETime Intrinsic (function)
- ETime intrinsic: ETime Intrinsic (subroutine)
- exceptions, floating-point: Floating-point Exception Handling
- exclamation point: LEX
- exclamation point: Exclamation Point
- exclamation point: Trailing Comment
- exclamation point: Character Set
- exclamation point: Statements Comments Lines
- executable file: What is GNU Fortran?
- Exit intrinsic: Exit Intrinsic
- EXIT statement: CYCLE and EXIT
- Exp intrinsic: Exp Intrinsic
- Exponent intrinsic: Exponent Intrinsic
- extended-source option: Fortran Dialect Options
- extensions, file name: Overall Options
- extensions, from Fortran 90: Fortran 90 Features
- extensions, more: More Extensions
- extensions, VXT: VXT Fortran
- external names: Mangling of Names
- extra warnings: Warning Options
- f2c: Increasing Precision/Range
- f2c compatibility: Avoid f2c Compatibility
- f2c compatibility: Block Data and Libraries
- f2c compatibility: Debugging and Interfacing
- f2c compatibility: Code Gen Options
- f2c compatibility: Shorthand Options
- f2c compatibility: Overall Options
- f2c intrinsics: Fortran Dialect Options
- f2c intrinsics group: Intrinsic Groups
- f77 compatibility: Shorthand Options
- f77 support: Backslash in Constants
- `f771`, program: What is GNU Fortran?
- `f90` intrinsics group: Intrinsic Groups
- fatal signal: Bug Criteria
- FDate intrinsic: FDate Intrinsic (function)
- FDate intrinsic: FDate Intrinsic (subroutine)
- FDL, GNU Free Documentation License: GNU Free Documentation License
- features, language: Direction of Language Development
- features, ugly: Distensions
- features, ugly: Shorthand Options
- FFE: Front End
- FFE: What is GNU Fortran?
- fflush(): Output Assumed To Flush
- FGet intrinsic: FGet Intrinsic (function)
- FGet intrinsic: FGet Intrinsic (subroutine)
- FGetC intrinsic: FGetC Intrinsic (function)
- FGetC intrinsic: FGetC Intrinsic (subroutine)
- file format not recognized: What is GNU Fortran?
- file formats: Portable Unformatted Files
- file name extension: Overall Options
- file name suffix: Overall Options
- file type: Overall Options
- file, source: Source Form
- file, source: Lines
- file, source: What is GNU Fortran?
- files, executable: What is GNU Fortran?
- fixed form: Source Form
- fixed form: Lines
- fixed form: Fortran Dialect Options
- Float intrinsic: Float Intrinsic
- FloatI intrinsic: FloatI Intrinsic
- floating-point errors: Floating-point Errors
- floating-point, errors: Inconsistent Calling Sequences
- floating-point, exceptions: Floating-point Exception Handling
- floating-point, precision: Floating-point precision
- floating-point, precision: Optimize Options
- FloatJ intrinsic: FloatJ Intrinsic
- Floor intrinsic: Floor Intrinsic
- Flush intrinsic: Flush Intrinsic
- flushing output: Output Assumed To Flush
- FNum intrinsic: FNum Intrinsic
- FORM='PRINT': OPEN CLOSE and INQUIRE Keywords
- FORMAT descriptors: Fortran 90 Features
- FORMAT descriptors: I/O
- FORMAT statement: Q Edit Descriptor
- FORMAT statement: Expressions in FORMAT Statements
- FORTRAN 66: Fortran Dialect Options
- FORTRAN 66: Shorthand Options
- FORTRAN 77 compatibility: Standard Support
- Fortran 90: Fortran 90 Features
- Fortran 90, compatibility: Fortran 90
- Fortran 90, features: Fortran Dialect Options
- Fortran 90, intrinsics: Fortran Dialect Options
- Fortran 90, support: Fortran 90 Support
- Fortran preprocessor: Overall Options
- forward references: GLOBALS
- FPE handling: Floating-point Exception Handling
- FPut intrinsic: FPut Intrinsic (function)
- FPut intrinsic: FPut Intrinsic (subroutine)
- FPutC intrinsic: FPutC Intrinsic (function)
- FPutC intrinsic: FPutC Intrinsic (subroutine)
- Fraction intrinsic: Fraction Intrinsic
- free form: Source Form
- free form: Lines
- free form: Fortran Dialect Options
- front end, `g77`: Front End
- front end, g77: What is GNU Fortran?
- FSeek intrinsic: FSeek Intrinsic
- FSF, funding the: Funding GNU Fortran
- FStat intrinsic: FStat Intrinsic (function)
- FStat intrinsic: FStat Intrinsic (subroutine)
- FTell intrinsic: FTell Intrinsic (function)
- FTell intrinsic: FTell Intrinsic (subroutine)
- function references, in adjustable array bounds: Array Bounds Expressions
- FUNCTION statement: Functions
- FUNCTION statement: Procedures
- functions: Functions
- functions, mistyped: Not My Type
- funding improvements: Funding GNU Fortran
- funding the FSF: Funding GNU Fortran
- g77 options, --driver: Changes
- g77 options, --driver: News
- g77 options, -v: G77 and GCC
- g77, command: G77 and GCC
- g77, command: What is GNU Fortran?
- g77, components of: What is GNU Fortran?
- `g77`, front end: Front End
- g77, front end: What is GNU Fortran?
- g77, modifying: Overall Options
- G77_date_y2kbuggy_0: Year 2000 (Y2K) Problems
- G77_vxtidate_y2kbuggy_0: Year 2000 (Y2K) Problems
- GBE: Philosophy of Code Generation
- GBE: What is GNU Fortran?
- GBEL: Philosophy of Code Generation
- `gcc`, back end: Philosophy of Code Generation
- gcc, back end: What is GNU Fortran?
- gcc, command: G77 and GCC
- gcc, command: What is GNU Fortran?
- gcc, command as driver: What is GNU Fortran?
- gcc, not recognizing Fortran source: What is GNU Fortran?
- gdb, command: What is GNU Fortran?
- gdb, support: Debugger Problems
- generic intrinsics: Generics and Specifics
- GError intrinsic: GError Intrinsic
- `GetArg` intrinsic: Main Program Unit
- GetArg intrinsic: GetArg Intrinsic
- GetCWD intrinsic: GetCWD Intrinsic (function)
- GetCWD intrinsic: GetCWD Intrinsic (subroutine)
- GetEnv intrinsic: GetEnv Intrinsic
- GetGId intrinsic: GetGId Intrinsic
- GetLog intrinsic: GetLog Intrinsic
- GetPId intrinsic: GetPId Intrinsic
- getting started: Getting Started
- GetUId intrinsic: GetUId Intrinsic
- global names, warning: Code Gen Options
- global names, warning: Warning Options
- GMTime intrinsic: GMTime Intrinsic
- GNU Back End (GBE): Philosophy of Code Generation
- GNU Back End (GBE): What is GNU Fortran?
- GNU Back End Language (GBEL): Philosophy of Code Generation
- GNU Fortran command options: Invoking G77
- GNU Fortran Front End (FFE): Front End
- GNU Fortran Front End (FFE): What is GNU Fortran?
- `gnu` intrinsics group: Intrinsic Groups
- GOTO statement: Assigned Statement Labels
- groups of intrinsics: Intrinsic Groups
- hardware errors: Signal 11 and Friends
- hash mark: Character Set
- HDF: Portable Unformatted Files
- hidden intrinsics: Intrinsic Groups
- Hollerith constants: Character and Hollerith Constants
- Hollerith constants: Ugly Conversion of Initializers
- Hollerith constants: Ugly Implicit Argument Conversion
- Hollerith constants: Fortran Dialect Options
- horizontal tab: Tabs
- HostNm intrinsic: HostNm Intrinsic (function)
- HostNm intrinsic: HostNm Intrinsic (subroutine)
- Huge intrinsic: Huge Intrinsic
- I/O, errors: Run-time Library Errors
- I/O, flushing: Output Assumed To Flush
- IAbs intrinsic: IAbs Intrinsic
- IAChar intrinsic: IAChar Intrinsic
- IAnd intrinsic: IAnd Intrinsic
- `IArgC` intrinsic: Main Program Unit
- IArgC intrinsic: IArgC Intrinsic
- IBClr intrinsic: IBClr Intrinsic
- IBits intrinsic: IBits Intrinsic
- IBSet intrinsic: IBSet Intrinsic
- IChar intrinsic: IChar Intrinsic
- IDate intrinsic: IDate Intrinsic (VXT)
- IDate intrinsic: IDate Intrinsic (UNIX)
- IDiM intrinsic: IDiM Intrinsic
- IDInt intrinsic: IDInt Intrinsic
- IDNInt intrinsic: IDNInt Intrinsic
- IEEE 754 conformance: Floating-point precision
- IEEE 754 conformance: Optimize Options
- IEOr intrinsic: IEOr Intrinsic
- IErrNo intrinsic: IErrNo Intrinsic
- IFix intrinsic: IFix Intrinsic
- IIAbs intrinsic: IIAbs Intrinsic
- IIAnd intrinsic: IIAnd Intrinsic
- IIBClr intrinsic: IIBClr Intrinsic
- IIBits intrinsic: IIBits Intrinsic
- IIBSet intrinsic: IIBSet Intrinsic
- IIDiM intrinsic: IIDiM Intrinsic
- IIDInt intrinsic: IIDInt Intrinsic
- IIDNnt intrinsic: IIDNnt Intrinsic
- IIEOr intrinsic: IIEOr Intrinsic
- IIFix intrinsic: IIFix Intrinsic
- IInt intrinsic: IInt Intrinsic
- IIOr intrinsic: IIOr Intrinsic
- IIQint intrinsic: IIQint Intrinsic
- IIQNnt intrinsic: IIQNnt Intrinsic
- IIShftC intrinsic: IIShftC Intrinsic
- IISign intrinsic: IISign Intrinsic
- illegal unit number: Large File Unit Numbers
- Imag intrinsic: Imag Intrinsic
- imaginary part: Complex Variables
- imaginary part: Ugly Complex Part Extraction
- ImagPart intrinsic: ImagPart Intrinsic
- IMax0 intrinsic: IMax0 Intrinsic
- IMax1 intrinsic: IMax1 Intrinsic
- IMin0 intrinsic: IMin0 Intrinsic
- IMin1 intrinsic: IMin1 Intrinsic
- IMod intrinsic: IMod Intrinsic
- IMPLICIT CHARACTER*(*) statement: Limitation on Implicit Declarations
- implicit declaration, warning: Warning Options
- IMPLICIT NONE, similar effect: Warning Options
- implicit typing: Not My Type
- improvements, funding: Funding GNU Fortran
- in-line code: GLOBALS
- in-line code: Code Gen Options
- in-line code: Optimize Options
- in-line code: What is GNU Fortran?
- INCLUDE directive: INCLUDE
- INCLUDE directive: Directory Options
- INCLUDE directive: Preprocessor Options
- inclusion, directory search paths for: Directory Options
- inconsistent floating-point results: Floating-point Errors
- incorrect diagnostics: What is GNU Fortran?
- incorrect error messages: What is GNU Fortran?
- incorrect use of language: What is GNU Fortran?
- increasing maximum unit number: Large File Unit Numbers
- increasing precision: Increasing Precision/Range
- increasing range: Increasing Precision/Range
- Index intrinsic: Index Intrinsic
- indexed (iterative) `DO`: Optimize Options
- infinite spaces printed: Strange Behavior at Run Time
- INInt intrinsic: INInt Intrinsic
- initialization, bug: Known Bugs
- initialization, of local variables: Code Gen Options
- initialization, run-time: Startup Code
- initialization, statement placement: Initializing Before Specifying
- INot intrinsic: INot Intrinsic
- INQUIRE statement: OPEN CLOSE and INQUIRE Keywords
- installation trouble: Trouble
- Int intrinsic: Int Intrinsic
- Int2 intrinsic: Int2 Intrinsic
- Int8 intrinsic: Int8 Intrinsic
- integer constants: Known Bugs
- INTEGER(KIND=1) type: Compiler Types
- INTEGER(KIND=2) type: Compiler Types
- INTEGER(KIND=3) type: Compiler Types
- INTEGER(KIND=6) type: Compiler Types
- `INTEGER*2` support: Popular Non-standard Types
- `INTEGER*8` support: Full Support for Compiler Types
- Intel x86: News
- interfacing: Debugging and Interfacing
- internal consistency checks: Overall Options
- intrinsics, Abort: Abort Intrinsic
- intrinsics, Abs: Abs Intrinsic
- intrinsics, Access: Access Intrinsic
- intrinsics, AChar: AChar Intrinsic
- intrinsics, ACos: ACos Intrinsic
- intrinsics, ACosD: ACosD Intrinsic
- intrinsics, AdjustL: AdjustL Intrinsic
- intrinsics, AdjustR: AdjustR Intrinsic
- intrinsics, AImag: AImag Intrinsic
- intrinsics, `AImag`: REAL() and AIMAG() of Complex
- intrinsics, AIMax0: AIMax0 Intrinsic
- intrinsics, AIMin0: AIMin0 Intrinsic
- intrinsics, AInt: AInt Intrinsic
- intrinsics, AJMax0: AJMax0 Intrinsic
- intrinsics, AJMin0: AJMin0 Intrinsic
- intrinsics, Alarm: Alarm Intrinsic
- intrinsics, All: All Intrinsic
- intrinsics, Allocated: Allocated Intrinsic
- intrinsics, ALog: ALog Intrinsic
- intrinsics, ALog10: ALog10 Intrinsic
- intrinsics, AMax0: AMax0 Intrinsic
- intrinsics, AMax1: AMax1 Intrinsic
- intrinsics, AMin0: AMin0 Intrinsic
- intrinsics, AMin1: AMin1 Intrinsic
- intrinsics, AMod: AMod Intrinsic
- intrinsics, `And`: Bit Operations on Floating-point Data
- intrinsics, And: And Intrinsic
- intrinsics, ANInt: ANInt Intrinsic
- intrinsics, Any: Any Intrinsic
- intrinsics, ASin: ASin Intrinsic
- intrinsics, ASinD: ASinD Intrinsic
- intrinsics, Associated: Associated Intrinsic
- intrinsics, ATan: ATan Intrinsic
- intrinsics, ATan2: ATan2 Intrinsic
- intrinsics, ATan2D: ATan2D Intrinsic
- intrinsics, ATanD: ATanD Intrinsic
- intrinsics, `badu77`: Fortran Dialect Options
- intrinsics, BesJ0: BesJ0 Intrinsic
- intrinsics, BesJ1: BesJ1 Intrinsic
- intrinsics, BesJN: BesJN Intrinsic
- intrinsics, BesY0: BesY0 Intrinsic
- intrinsics, BesY1: BesY1 Intrinsic
- intrinsics, BesYN: BesYN Intrinsic
- intrinsics, Bit_Size: Bit_Size Intrinsic
- intrinsics, BITest: BITest Intrinsic
- intrinsics, BJTest: BJTest Intrinsic
- intrinsics, BTest: BTest Intrinsic
- intrinsics, CAbs: CAbs Intrinsic
- intrinsics, CCos: CCos Intrinsic
- intrinsics, CDAbs: CDAbs Intrinsic
- intrinsics, CDCos: CDCos Intrinsic
- intrinsics, CDExp: CDExp Intrinsic
- intrinsics, CDLog: CDLog Intrinsic
- intrinsics, CDSin: CDSin Intrinsic
- intrinsics, CDSqRt: CDSqRt Intrinsic
- intrinsics, Ceiling: Ceiling Intrinsic
- intrinsics, CExp: CExp Intrinsic
- intrinsics, Char: Char Intrinsic
- intrinsics, ChDir: ChDir Intrinsic (function)
- intrinsics, ChDir: ChDir Intrinsic (subroutine)
- intrinsics, ChMod: ChMod Intrinsic (function)
- intrinsics, ChMod: ChMod Intrinsic (subroutine)
- intrinsics, CLog: CLog Intrinsic
- intrinsics, Cmplx: Cmplx Intrinsic
- intrinsics, `Cmplx`: CMPLX() of DOUBLE PRECISION
- intrinsics, Complex: Complex Intrinsic
- intrinsics, `COMPLEX`: Fortran Dialect Options
- intrinsics, Conjg: Conjg Intrinsic
- intrinsics, context-sensitive: Context-Sensitive Intrinsicness
- intrinsics, Cos: Cos Intrinsic
- intrinsics, CosD: CosD Intrinsic
- intrinsics, CosH: CosH Intrinsic
- intrinsics, Count: Count Intrinsic
- intrinsics, CPU_Time: CPU_Time Intrinsic
- intrinsics, CShift: CShift Intrinsic
- intrinsics, CSin: CSin Intrinsic
- intrinsics, CSqRt: CSqRt Intrinsic
- intrinsics, CTime: CTime Intrinsic (function)
- intrinsics, CTime: CTime Intrinsic (subroutine)
- intrinsics, DAbs: DAbs Intrinsic
- intrinsics, DACos: DACos Intrinsic
- intrinsics, DACosD: DACosD Intrinsic
- intrinsics, DASin: DASin Intrinsic
- intrinsics, DASinD: DASinD Intrinsic
- intrinsics, DATan: DATan Intrinsic
- intrinsics, DATan2: DATan2 Intrinsic
- intrinsics, DATan2D: DATan2D Intrinsic
- intrinsics, DATanD: DATanD Intrinsic
- intrinsics, Date: Date Intrinsic
- intrinsics, Date_and_Time: Date_and_Time Intrinsic
- intrinsics, DbesJ0: DbesJ0 Intrinsic
- intrinsics, DbesJ1: DbesJ1 Intrinsic
- intrinsics, DbesJN: DbesJN Intrinsic
- intrinsics, DbesY0: DbesY0 Intrinsic
- intrinsics, DbesY1: DbesY1 Intrinsic
- intrinsics, DbesYN: DbesYN Intrinsic
- intrinsics, Dble: Dble Intrinsic
- intrinsics, DbleQ: DbleQ Intrinsic
- intrinsics, DCmplx: DCmplx Intrinsic
- intrinsics, DConjg: DConjg Intrinsic
- intrinsics, DCos: DCos Intrinsic
- intrinsics, DCosD: DCosD Intrinsic
- intrinsics, DCosH: DCosH Intrinsic
- intrinsics, DDiM: DDiM Intrinsic
- intrinsics, deleted: Intrinsic Groups
- intrinsics, DErF: DErF Intrinsic
- intrinsics, DErFC: DErFC Intrinsic
- intrinsics, DExp: DExp Intrinsic
- intrinsics, DFloat: DFloat Intrinsic
- intrinsics, DFlotI: DFlotI Intrinsic
- intrinsics, DFlotJ: DFlotJ Intrinsic
- intrinsics, Digits: Digits Intrinsic
- intrinsics, DiM: DiM Intrinsic
- intrinsics, DImag: DImag Intrinsic
- intrinsics, DInt: DInt Intrinsic
- intrinsics, disabled: Intrinsic Groups
- intrinsics, DLog: DLog Intrinsic
- intrinsics, DLog10: DLog10 Intrinsic
- intrinsics, DMax1: DMax1 Intrinsic
- intrinsics, DMin1: DMin1 Intrinsic
- intrinsics, DMod: DMod Intrinsic
- intrinsics, DNInt: DNInt Intrinsic
- intrinsics, Dot_Product: Dot_Product Intrinsic
- intrinsics, DProd: DProd Intrinsic
- intrinsics, DReal: DReal Intrinsic
- intrinsics, DSign: DSign Intrinsic
- intrinsics, DSin: DSin Intrinsic
- intrinsics, DSinD: DSinD Intrinsic
- intrinsics, DSinH: DSinH Intrinsic
- intrinsics, DSqRt: DSqRt Intrinsic
- intrinsics, DTan: DTan Intrinsic
- intrinsics, DTanD: DTanD Intrinsic
- intrinsics, DTanH: DTanH Intrinsic
- intrinsics, DTime: DTime Intrinsic (function)
- intrinsics, DTime: DTime Intrinsic (subroutine)
- intrinsics, enabled: Intrinsic Groups
- intrinsics, EOShift: EOShift Intrinsic
- intrinsics, Epsilon: Epsilon Intrinsic
- intrinsics, ErF: ErF Intrinsic
- intrinsics, ErFC: ErFC Intrinsic
- intrinsics, ETime: ETime Intrinsic (function)
- intrinsics, ETime: ETime Intrinsic (subroutine)
- intrinsics, Exit: Exit Intrinsic
- intrinsics, Exp: Exp Intrinsic
- intrinsics, Exponent: Exponent Intrinsic
- intrinsics, f2c: Fortran Dialect Options
- intrinsics, FDate: FDate Intrinsic (function)
- intrinsics, FDate: FDate Intrinsic (subroutine)
- intrinsics, FGet: FGet Intrinsic (function)
- intrinsics, FGet: FGet Intrinsic (subroutine)
- intrinsics, FGetC: FGetC Intrinsic (function)
- intrinsics, FGetC: FGetC Intrinsic (subroutine)
- intrinsics, Float: Float Intrinsic
- intrinsics, FloatI: FloatI Intrinsic
- intrinsics, FloatJ: FloatJ Intrinsic
- intrinsics, Floor: Floor Intrinsic
- intrinsics, Flush: Flush Intrinsic
- intrinsics, FNum: FNum Intrinsic
- intrinsics, Fortran 90: Fortran Dialect Options
- intrinsics, FPut: FPut Intrinsic (function)
- intrinsics, FPut: FPut Intrinsic (subroutine)
- intrinsics, FPutC: FPutC Intrinsic (function)
- intrinsics, FPutC: FPutC Intrinsic (subroutine)
- intrinsics, Fraction: Fraction Intrinsic
- intrinsics, FSeek: FSeek Intrinsic
- intrinsics, FStat: FStat Intrinsic (function)
- intrinsics, FStat: FStat Intrinsic (subroutine)
- intrinsics, FTell: FTell Intrinsic (function)
- intrinsics, FTell: FTell Intrinsic (subroutine)
- intrinsics, generic: Generics and Specifics
- intrinsics, GError: GError Intrinsic
- intrinsics, `GetArg`: Main Program Unit
- intrinsics, GetArg: GetArg Intrinsic
- intrinsics, GetCWD: GetCWD Intrinsic (function)
- intrinsics, GetCWD: GetCWD Intrinsic (subroutine)
- intrinsics, GetEnv: GetEnv Intrinsic
- intrinsics, GetGId: GetGId Intrinsic
- intrinsics, GetLog: GetLog Intrinsic
- intrinsics, GetPId: GetPId Intrinsic
- intrinsics, GetUId: GetUId Intrinsic
- intrinsics, GMTime: GMTime Intrinsic
- intrinsics, groups: Intrinsic Groups
- intrinsics, groups of: Intrinsic Groups
- intrinsics, hidden: Intrinsic Groups
- intrinsics, HostNm: HostNm Intrinsic (function)
- intrinsics, HostNm: HostNm Intrinsic (subroutine)
- intrinsics, Huge: Huge Intrinsic
- intrinsics, IAbs: IAbs Intrinsic
- intrinsics, IAChar: IAChar Intrinsic
- intrinsics, IAnd: IAnd Intrinsic
- intrinsics, `IArgC`: Main Program Unit
- intrinsics, IArgC: IArgC Intrinsic
- intrinsics, IBClr: IBClr Intrinsic
- intrinsics, IBits: IBits Intrinsic
- intrinsics, IBSet: IBSet Intrinsic
- intrinsics, IChar: IChar Intrinsic
- intrinsics, IDate: IDate Intrinsic (VXT)
- intrinsics, IDate: IDate Intrinsic (UNIX)
- intrinsics, IDiM: IDiM Intrinsic
- intrinsics, IDInt: IDInt Intrinsic
- intrinsics, IDNInt: IDNInt Intrinsic
- intrinsics, IEOr: IEOr Intrinsic
- intrinsics, IErrNo: IErrNo Intrinsic
- intrinsics, IFix: IFix Intrinsic
- intrinsics, IIAbs: IIAbs Intrinsic
- intrinsics, IIAnd: IIAnd Intrinsic
- intrinsics, IIBClr: IIBClr Intrinsic
- intrinsics, IIBits: IIBits Intrinsic
- intrinsics, IIBSet: IIBSet Intrinsic
- intrinsics, IIDiM: IIDiM Intrinsic
- intrinsics, IIDInt: IIDInt Intrinsic
- intrinsics, IIDNnt: IIDNnt Intrinsic
- intrinsics, IIEOr: IIEOr Intrinsic
- intrinsics, IIFix: IIFix Intrinsic
- intrinsics, IInt: IInt Intrinsic
- intrinsics, IIOr: IIOr Intrinsic
- intrinsics, IIQint: IIQint Intrinsic
- intrinsics, IIQNnt: IIQNnt Intrinsic
- intrinsics, IIShftC: IIShftC Intrinsic
- intrinsics, IISign: IISign Intrinsic
- intrinsics, Imag: Imag Intrinsic
- intrinsics, ImagPart: ImagPart Intrinsic
- intrinsics, IMax0: IMax0 Intrinsic
- intrinsics, IMax1: IMax1 Intrinsic
- intrinsics, IMin0: IMin0 Intrinsic
- intrinsics, IMin1: IMin1 Intrinsic
- intrinsics, IMod: IMod Intrinsic
- intrinsics, Index: Index Intrinsic
- intrinsics, INInt: INInt Intrinsic
- intrinsics, INot: INot Intrinsic
- intrinsics, Int: Int Intrinsic
- intrinsics, Int2: Int2 Intrinsic
- intrinsics, Int8: Int8 Intrinsic
- intrinsics, IOr: IOr Intrinsic
- intrinsics, IRand: IRand Intrinsic
- intrinsics, IsaTty: IsaTty Intrinsic
- intrinsics, IShft: IShft Intrinsic
- intrinsics, IShftC: IShftC Intrinsic
- intrinsics, ISign: ISign Intrinsic
- intrinsics, ITime: ITime Intrinsic
- intrinsics, IZExt: IZExt Intrinsic
- intrinsics, JIAbs: JIAbs Intrinsic
- intrinsics, JIAnd: JIAnd Intrinsic
- intrinsics, JIBClr: JIBClr Intrinsic
- intrinsics, JIBits: JIBits Intrinsic
- intrinsics, JIBSet: JIBSet Intrinsic
- intrinsics, JIDiM: JIDiM Intrinsic
- intrinsics, JIDInt: JIDInt Intrinsic
- intrinsics, JIDNnt: JIDNnt Intrinsic
- intrinsics, JIEOr: JIEOr Intrinsic
- intrinsics, JIFix: JIFix Intrinsic
- intrinsics, JInt: JInt Intrinsic
- intrinsics, JIOr: JIOr Intrinsic
- intrinsics, JIQint: JIQint Intrinsic
- intrinsics, JIQNnt: JIQNnt Intrinsic
- intrinsics, JIShft: JIShft Intrinsic
- intrinsics, JIShftC: JIShftC Intrinsic
- intrinsics, JISign: JISign Intrinsic
- intrinsics, JMax0: JMax0 Intrinsic
- intrinsics, JMax1: JMax1 Intrinsic
- intrinsics, JMin0: JMin0 Intrinsic
- intrinsics, JMin1: JMin1 Intrinsic
- intrinsics, JMod: JMod Intrinsic
- intrinsics, JNInt: JNInt Intrinsic
- intrinsics, JNot: JNot Intrinsic
- intrinsics, JZExt: JZExt Intrinsic
- intrinsics, Kill: Kill Intrinsic (function)
- intrinsics, Kill: Kill Intrinsic (subroutine)
- intrinsics, Kind: Kind Intrinsic
- intrinsics, LBound: LBound Intrinsic
- intrinsics, Len: Len Intrinsic
- intrinsics, Len_Trim: Len_Trim Intrinsic
- intrinsics, LGe: LGe Intrinsic
- intrinsics, LGt: LGt Intrinsic
- intrinsics, Link: Link Intrinsic (function)
- intrinsics, Link: Link Intrinsic (subroutine)
- intrinsics, LLe: LLe Intrinsic
- intrinsics, LLt: LLt Intrinsic
- intrinsics, LnBlnk: LnBlnk Intrinsic
- intrinsics, Loc: Loc Intrinsic
- intrinsics, Log: Log Intrinsic
- intrinsics, Log10: Log10 Intrinsic
- intrinsics, Logical: Logical Intrinsic
- intrinsics, Long: Long Intrinsic
- intrinsics, LShift: LShift Intrinsic
- intrinsics, LStat: LStat Intrinsic (function)
- intrinsics, LStat: LStat Intrinsic (subroutine)
- intrinsics, LTime: LTime Intrinsic
- intrinsics, MatMul: MatMul Intrinsic
- intrinsics, Max: Max Intrinsic
- intrinsics, Max0: Max0 Intrinsic
- intrinsics, Max1: Max1 Intrinsic
- intrinsics, MaxExponent: MaxExponent Intrinsic
- intrinsics, MaxLoc: MaxLoc Intrinsic
- intrinsics, MaxVal: MaxVal Intrinsic
- intrinsics, MClock: MClock Intrinsic
- intrinsics, MClock8: MClock8 Intrinsic
- intrinsics, Merge: Merge Intrinsic
- intrinsics, MIL-STD 1753: Fortran Dialect Options
- intrinsics, Min: Min Intrinsic
- intrinsics, Min0: Min0 Intrinsic
- intrinsics, Min1: Min1 Intrinsic
- intrinsics, MinExponent: MinExponent Intrinsic
- intrinsics, MinLoc: MinLoc Intrinsic
- intrinsics, MinVal: MinVal Intrinsic
- intrinsics, Mod: Mod Intrinsic
- intrinsics, Modulo: Modulo Intrinsic
- intrinsics, MvBits: MvBits Intrinsic
- intrinsics, Nearest: Nearest Intrinsic
- intrinsics, NInt: NInt Intrinsic
- intrinsics, Not: Not Intrinsic
- intrinsics, `Or`: Bit Operations on Floating-point Data
- intrinsics, Or: Or Intrinsic
- intrinsics, others: Other Intrinsics
- intrinsics, Pack: Pack Intrinsic
- intrinsics, PError: PError Intrinsic
- intrinsics, Precision: Precision Intrinsic
- intrinsics, Present: Present Intrinsic
- intrinsics, Product: Product Intrinsic
- intrinsics, QAbs: QAbs Intrinsic
- intrinsics, QACos: QACos Intrinsic
- intrinsics, QACosD: QACosD Intrinsic
- intrinsics, QASin: QASin Intrinsic
- intrinsics, QASinD: QASinD Intrinsic
- intrinsics, QATan: QATan Intrinsic
- intrinsics, QATan2: QATan2 Intrinsic
- intrinsics, QATan2D: QATan2D Intrinsic
- intrinsics, QATanD: QATanD Intrinsic
- intrinsics, QCos: QCos Intrinsic
- intrinsics, QCosD: QCosD Intrinsic
- intrinsics, QCosH: QCosH Intrinsic
- intrinsics, QDiM: QDiM Intrinsic
- intrinsics, QExp: QExp Intrinsic
- intrinsics, QExt: QExt Intrinsic
- intrinsics, QExtD: QExtD Intrinsic
- intrinsics, QFloat: QFloat Intrinsic
- intrinsics, QInt: QInt Intrinsic
- intrinsics, QLog: QLog Intrinsic
- intrinsics, QLog10: QLog10 Intrinsic
- intrinsics, QMax1: QMax1 Intrinsic
- intrinsics, QMin1: QMin1 Intrinsic
- intrinsics, QMod: QMod Intrinsic
- intrinsics, QNInt: QNInt Intrinsic
- intrinsics, QSin: QSin Intrinsic
- intrinsics, QSinD: QSinD Intrinsic
- intrinsics, QSinH: QSinH Intrinsic
- intrinsics, QSqRt: QSqRt Intrinsic
- intrinsics, QTan: QTan Intrinsic
- intrinsics, QTanD: QTanD Intrinsic
- intrinsics, QTanH: QTanH Intrinsic
- intrinsics, Radix: Radix Intrinsic
- intrinsics, Rand: Rand Intrinsic
- intrinsics, Random_Number: Random_Number Intrinsic
- intrinsics, Random_Seed: Random_Seed Intrinsic
- intrinsics, Range: Range Intrinsic
- intrinsics, Real: Real Intrinsic
- intrinsics, `Real`: REAL() and AIMAG() of Complex
- intrinsics, RealPart: RealPart Intrinsic
- intrinsics, Rename: Rename Intrinsic (function)
- intrinsics, Rename: Rename Intrinsic (subroutine)
- intrinsics, Repeat: Repeat Intrinsic
- intrinsics, Reshape: Reshape Intrinsic
- intrinsics, RRSpacing: RRSpacing Intrinsic
- intrinsics, RShift: RShift Intrinsic
- intrinsics, Scale: Scale Intrinsic
- intrinsics, Scan: Scan Intrinsic
- intrinsics, Secnds: Secnds Intrinsic
- intrinsics, Second: Second Intrinsic (subroutine)
- intrinsics, Second: Second Intrinsic (function)
- intrinsics, Selected_Int_Kind: Selected_Int_Kind Intrinsic
- intrinsics, Selected_Real_Kind: Selected_Real_Kind Intrinsic
- intrinsics, Set_Exponent: Set_Exponent Intrinsic
- intrinsics, Shape: Shape Intrinsic
- intrinsics, `Shift`: Bit Operations on Floating-point Data
- intrinsics, Short: Short Intrinsic
- intrinsics, Sign: Sign Intrinsic
- intrinsics, Signal: Signal Intrinsic (function)
- intrinsics, Signal: Signal Intrinsic (subroutine)
- intrinsics, Sin: Sin Intrinsic
- intrinsics, SinD: SinD Intrinsic
- intrinsics, SinH: SinH Intrinsic
- intrinsics, Sleep: Sleep Intrinsic
- intrinsics, Sngl: Sngl Intrinsic
- intrinsics, SnglQ: SnglQ Intrinsic
- intrinsics, Spacing: Spacing Intrinsic
- intrinsics, Spread: Spread Intrinsic
- intrinsics, SqRt: SqRt Intrinsic
- intrinsics, SRand: SRand Intrinsic
- intrinsics, Stat: Stat Intrinsic (function)
- intrinsics, Stat: Stat Intrinsic (subroutine)
- intrinsics, Sum: Sum Intrinsic
- intrinsics, SymLnk: SymLnk Intrinsic (function)
- intrinsics, SymLnk: SymLnk Intrinsic (subroutine)
- intrinsics, System: System Intrinsic (function)
- intrinsics, System: System Intrinsic (subroutine)
- intrinsics, System_Clock: System_Clock Intrinsic
- intrinsics, table of: Table of Intrinsic Functions
- intrinsics, Tan: Tan Intrinsic
- intrinsics, TanD: TanD Intrinsic
- intrinsics, TanH: TanH Intrinsic
- intrinsics, Time: Time Intrinsic (VXT)
- intrinsics, Time: Time Intrinsic (UNIX)
- intrinsics, Time8: Time8 Intrinsic
- intrinsics, Tiny: Tiny Intrinsic
- intrinsics, Transfer: Transfer Intrinsic
- intrinsics, Transpose: Transpose Intrinsic
- intrinsics, Trim: Trim Intrinsic
- intrinsics, TtyNam: TtyNam Intrinsic (function)
- intrinsics, TtyNam: TtyNam Intrinsic (subroutine)
- intrinsics, UBound: UBound Intrinsic
- intrinsics, UMask: UMask Intrinsic (function)
- intrinsics, UMask: UMask Intrinsic (subroutine)
- intrinsics, UNIX: Fortran Dialect Options
- intrinsics, Unlink: Unlink Intrinsic (function)
- intrinsics, Unlink: Unlink Intrinsic (subroutine)
- intrinsics, Unpack: Unpack Intrinsic
- intrinsics, Verify: Verify Intrinsic
- intrinsics, VXT: Fortran Dialect Options
- intrinsics, XOr: XOr Intrinsic
- intrinsics, ZAbs: ZAbs Intrinsic
- intrinsics, ZCos: ZCos Intrinsic
- intrinsics, ZExp: ZExp Intrinsic
- intrinsics, ZExt: ZExt Intrinsic
- intrinsics, ZLog: ZLog Intrinsic
- intrinsics, ZSin: ZSin Intrinsic
- intrinsics, ZSqRt: ZSqRt Intrinsic
- Introduction: Top
- invalid assembly code: Bug Criteria
- invalid input: Bug Criteria
- IOr intrinsic: IOr Intrinsic
- IOSTAT=: Run-time Library Errors
- IRand intrinsic: IRand Intrinsic
- IsaTty intrinsic: IsaTty Intrinsic
- IShft intrinsic: IShft Intrinsic
- IShftC intrinsic: IShftC Intrinsic
- ISign intrinsic: ISign Intrinsic
- iterative `DO`: Optimize Options
- ITime intrinsic: ITime Intrinsic
- ix86 floating-point: Floating-point precision
- ix86 FPU stack: Inconsistent Calling Sequences
- IZExt intrinsic: IZExt Intrinsic
- JCB002 program: Generics and Specifics
- JCB003 program: CMPAMBIG
- JIAbs intrinsic: JIAbs Intrinsic
- JIAnd intrinsic: JIAnd Intrinsic
- JIBClr intrinsic: JIBClr Intrinsic
- JIBits intrinsic: JIBits Intrinsic
- JIBSet intrinsic: JIBSet Intrinsic
- JIDiM intrinsic: JIDiM Intrinsic
- JIDInt intrinsic: JIDInt Intrinsic
- JIDNnt intrinsic: JIDNnt Intrinsic
- JIEOr intrinsic: JIEOr Intrinsic
- JIFix intrinsic: JIFix Intrinsic
- JInt intrinsic: JInt Intrinsic
- JIOr intrinsic: JIOr Intrinsic
- JIQint intrinsic: JIQint Intrinsic
- JIQNnt intrinsic: JIQNnt Intrinsic
- JIShft intrinsic: JIShft Intrinsic
- JIShftC intrinsic: JIShftC Intrinsic
- JISign intrinsic: JISign Intrinsic
- JMax0 intrinsic: JMax0 Intrinsic
- JMax1 intrinsic: JMax1 Intrinsic
- JMin0 intrinsic: JMin0 Intrinsic
- JMin1 intrinsic: JMin1 Intrinsic
- JMod intrinsic: JMod Intrinsic
- JNInt intrinsic: JNInt Intrinsic
- JNot intrinsic: JNot Intrinsic
- JZExt intrinsic: JZExt Intrinsic
- keywords, RECURSIVE: RECURSIVE Keyword
- Kill intrinsic: Kill Intrinsic (function)
- Kill intrinsic: Kill Intrinsic (subroutine)
- Kind intrinsic: Kind Intrinsic
- KIND= notation: Kind Notation
- known causes of trouble: Trouble
- lack of recursion: RECURSIVE Keyword
- language, dialect options: Fortran Dialect Options
- language, features: Direction of Language Development
- language, incorrect use of: What is GNU Fortran?
- large aggregate areas: Known Bugs
- large common blocks: Large Common Blocks
- layout of `COMMON` blocks: Aligned Data
- LBound intrinsic: LBound Intrinsic
- ld command: What is GNU Fortran?
- ld, can't find _main: Cannot Link Fortran Programs
- ld, can't find strange names: Cannot Link Fortran Programs
- ld, error linking user code: Cannot Link Fortran Programs
- ld, errors: Large Common Blocks
- left angle: Character Set
- left bracket: Character Set
- legacy code: Collected Fortran Wisdom
- Len intrinsic: Len Intrinsic
- Len_Trim intrinsic: Len_Trim Intrinsic
- length of source lines: Fortran Dialect Options
- letters, lowercase: Case Sensitivity
- letters, uppercase: Case Sensitivity
- LGe intrinsic: LGe Intrinsic
- LGt intrinsic: LGt Intrinsic
- libc, non-ANSI or non-default: Strange Behavior at Run Time
- libf2c library: What is GNU Fortran?
- libg2c library: What is GNU Fortran?
- libraries: What is GNU Fortran?
- libraries, containing BLOCK DATA: Block Data and Libraries
- libraries, libf2c: What is GNU Fortran?
- libraries, libg2c: What is GNU Fortran?
- limits, array dimensions: Compiler Limits
- limits, array size: Array Size
- limits, compiler: Compiler Limits
- limits, continuation lines: Compiler Limits
- limits, continuation lines: Continuation Line
- limits, lengths of names: Compiler Limits
- limits, lengths of names: Syntactic Items
- limits, lengths of source lines: Fortran Dialect Options
- limits, multi-dimension arrays: Array Size
- limits, on character-variable length: Character-variable Length
- limits, rank: Compiler Limits
- limits, run-time library: Run-time Environment Limits
- limits, timings: Secnds Intrinsic
- limits, timings: DTime Intrinsic (function)
- limits, timings: Time8 Intrinsic
- limits, timings: Time Intrinsic (UNIX)
- limits, timings: System_Clock Intrinsic
- limits, timings: Second Intrinsic (subroutine)
- limits, timings: Second Intrinsic (function)
- limits, timings: MClock8 Intrinsic
- limits, timings: MClock Intrinsic
- limits, timings: ETime Intrinsic (function)
- limits, timings: ETime Intrinsic (subroutine)
- limits, timings: DTime Intrinsic (subroutine)
- limits, timings: CPU_Time Intrinsic
- limits, Y10K: Time Intrinsic (VXT)
- limits, Y10K: IDate Intrinsic (UNIX)
- limits, Y10K: FDate Intrinsic (function)
- limits, Y10K: FDate Intrinsic (subroutine)
- limits, Y10K: Date_and_Time Intrinsic
- limits, Y2K: IDate Intrinsic (VXT)
- lines: Lines
- lines, continuation: Continuation Line
- lines, length: Fortran Dialect Options
- lines, long: Long Lines
- lines, short: Short Lines
- Link intrinsic: Link Intrinsic (function)
- Link intrinsic: Link Intrinsic (subroutine)
- linking: What is GNU Fortran?
- linking against non-standard library: Strange Behavior at Run Time
- linking error for user code: Cannot Link Fortran Programs
- linking error, user code: Cannot Link Fortran Programs
- linking with C: Interoperating with C and C++
- linking, errors: Large Common Blocks
- LLe intrinsic: LLe Intrinsic
- LLt intrinsic: LLt Intrinsic
- LnBlnk intrinsic: LnBlnk Intrinsic
- Loc intrinsic: Loc Intrinsic
- local equivalence areas: Local Equivalence Areas
- Log intrinsic: Log Intrinsic
- Log10 intrinsic: Log10 Intrinsic
- logical expressions, comparing: Equivalence Versus Equality
- Logical intrinsic: Logical Intrinsic
- LOGICAL(KIND=1) type: Compiler Types
- LOGICAL(KIND=2) type: Compiler Types
- LOGICAL(KIND=3) type: Compiler Types
- LOGICAL(KIND=6) type: Compiler Types
- `LOGICAL*1` support: Popular Non-standard Types
- Long intrinsic: Long Intrinsic
- long source lines: Long Lines
- long time: Timer Wraparounds
- loops, optimizing: Optimize Options
- loops, speeding up: Optimize Options
- loops, unrolling: Optimize Options
- lowercase letters: Case Sensitivity
- LShift intrinsic: LShift Intrinsic
- LStat intrinsic: LStat Intrinsic (function)
- LStat intrinsic: LStat Intrinsic (subroutine)
- LTime intrinsic: LTime Intrinsic
- machine code: What is GNU Fortran?
- macro options: Shorthand Options
- main program unit, debugging: Main Program Unit
- main(): Main Program Unit
- MAIN__(): Main Program Unit
- Makefile example: Bug Criteria
- MAP statement: STRUCTURE UNION RECORD MAP
- MatMul intrinsic: MatMul Intrinsic
- Max intrinsic: Max Intrinsic
- Max0 intrinsic: Max0 Intrinsic
- Max1 intrinsic: Max1 Intrinsic
- MaxExponent intrinsic: MaxExponent Intrinsic
- maximum number of dimensions: Compiler Limits
- maximum rank: Compiler Limits
- maximum unit number: Large File Unit Numbers
- MaxLoc intrinsic: MaxLoc Intrinsic
- MaxVal intrinsic: MaxVal Intrinsic
- MClock intrinsic: MClock Intrinsic
- MClock8 intrinsic: MClock8 Intrinsic
- memory usage, of compiler: Known Bugs
- Merge intrinsic: Merge Intrinsic
- messages, run-time: Run-time Library Errors
- messages, warning: Warning Options
- messages, warning and error: Warnings and Errors
- `mil` intrinsics group: Intrinsic Groups
- MIL-STD 1753: MIL-STD 1753
- MIL-STD 1753: END DO
- MIL-STD 1753: DO WHILE
- MIL-STD 1753: Fortran Dialect Options
- Min intrinsic: Min Intrinsic
- Min0 intrinsic: Min0 Intrinsic
- Min1 intrinsic: Min1 Intrinsic
- MinExponent intrinsic: MinExponent Intrinsic
- MinLoc intrinsic: MinLoc Intrinsic
- MinVal intrinsic: MinVal Intrinsic
- mistakes: What is GNU Fortran?
- mistyped functions: Not My Type
- mistyped variables: Not My Type
- Mod intrinsic: Mod Intrinsic
- modifying g77: Overall Options
- Modulo intrinsic: Modulo Intrinsic
- multi-dimension arrays: Array Size
- MvBits intrinsic: MvBits Intrinsic
- MXUNIT: Large File Unit Numbers
- name space: Mangling of Names
- NAMELIST statement: NAMELIST
- naming conflicts: Multiple Definitions of External Names
- naming issues: Mangling of Names
- naming programs: Nothing Happens
- NaN values: Floating-point Exception Handling
- Nearest intrinsic: Nearest Intrinsic
- negative forms of options: Invoking G77
- negative time: Timer Wraparounds
- Netlib: Increasing Precision/Range
- Netlib: C Interfacing Tools
- network file system: Output Assumed To Flush
- new users: Getting Started
- newbies: Getting Started
- NeXTStep problems: NeXTStep Problems
- NFS: Output Assumed To Flush
- NInt intrinsic: NInt Intrinsic
- nonportable conversions: Nonportable Conversions
- Not intrinsic: Not Intrinsic
- nothing happens: Nothing Happens
- null arguments: Ugly Null Arguments
- null byte, trailing: Character and Hollerith Constants
- null CHARACTER strings: Character Type
- number of continuation lines: Continuation Line
- number of dimensions, maximum: Compiler Limits
- number of trips: Loops
- O edit descriptor: I/O
- octal constants: Double Quote Meaning
- omitting arguments: Ugly Null Arguments
- one-trip `DO` loops: Fortran Dialect Options
- open angle: Character Set
- open bracket: Character Set
- OPEN statement: OPEN CLOSE and INQUIRE Keywords
- optimization, better: Better Optimization
- optimization, for Pentium: Aligned Data
- optimize options: Optimize Options
- options, --driver: Changes
- options, --driver: News
- options, -falias-check: Aliasing Assumed To Work
- options, -falias-check: Code Gen Options
- options, -fargument-alias: Aliasing Assumed To Work
- options, -fargument-alias: Code Gen Options
- options, -fargument-noalias: Aliasing Assumed To Work
- options, -fargument-noalias: Code Gen Options
- options, -fbadu77-intrinsics-delete: Fortran Dialect Options
- options, -fbadu77-intrinsics-disable: Fortran Dialect Options
- options, -fbadu77-intrinsics-enable: Fortran Dialect Options
- options, -fbadu77-intrinsics-hide: Fortran Dialect Options
- options, -fcaller-saves: Optimize Options
- options, -fcase-initcap: Fortran Dialect Options
- options, -fcase-lower: Fortran Dialect Options
- options, -fcase-preserve: Fortran Dialect Options
- options, -fcase-strict-lower: Fortran Dialect Options
- options, -fcase-strict-upper: Fortran Dialect Options
- options, -fcase-upper: Fortran Dialect Options
- options, -fdelayed-branch: Optimize Options
- options, -fdollar-ok: Fortran Dialect Options
- options, -femulate-complex: Code Gen Options
- options, -fexpensive-optimizations: Optimize Options
- options, -ff2c-intrinsics-delete: Fortran Dialect Options
- options, -ff2c-intrinsics-disable: Fortran Dialect Options
- options, -ff2c-intrinsics-enable: Fortran Dialect Options
- options, -ff2c-intrinsics-hide: Fortran Dialect Options
- options, -ff2c-library: Code Gen Options
- options, -ff66: Shorthand Options
- options, -ff77: Shorthand Options
- options, -ff90: Fortran Dialect Options
- options, -ff90-intrinsics-delete: Fortran Dialect Options
- options, -ff90-intrinsics-disable: Fortran Dialect Options
- options, -ff90-intrinsics-enable: Fortran Dialect Options
- options, -ff90-intrinsics-hide: Fortran Dialect Options
- options, -ffast-math: Optimize Options
- options, -ffinite-math-only: Optimize Options
- options, -ffixed-line-length-n: Fortran Dialect Options
- options, -ffloat-store: Optimize Options
- options, -fforce-addr: Optimize Options
- options, -fforce-mem: Optimize Options
- options, -ffree-form: Fortran Dialect Options
- options, -fgnu-intrinsics-delete: Fortran Dialect Options
- options, -fgnu-intrinsics-disable: Fortran Dialect Options
- options, -fgnu-intrinsics-enable: Fortran Dialect Options
- options, -fgnu-intrinsics-hide: Fortran Dialect Options
- options, -fgroup-intrinsics-hide: Overly Convenient Options
- options, -finit-local-zero: Overly Convenient Options
- options, -finit-local-zero: Code Gen Options
- options, -fintrin-case-any: Fortran Dialect Options
- options, -fintrin-case-initcap: Fortran Dialect Options
- options, -fintrin-case-lower: Fortran Dialect Options
- options, -fintrin-case-upper: Fortran Dialect Options
- options, -fmatch-case-any: Fortran Dialect Options
- options, -fmatch-case-initcap: Fortran Dialect Options
- options, -fmatch-case-lower: Fortran Dialect Options
- options, -fmatch-case-upper: Fortran Dialect Options
- options, -fmil-intrinsics-delete: Fortran Dialect Options
- options, -fmil-intrinsics-disable: Fortran Dialect Options
- options, -fmil-intrinsics-enable: Fortran Dialect Options
- options, -fmil-intrinsics-hide: Fortran Dialect Options
- options, -fno-argument-noalias-global: Aliasing Assumed To Work
- options, -fno-argument-noalias-global: Code Gen Options
- options, -fno-automatic: Overly Convenient Options
- options, -fno-automatic: Code Gen Options
- options, -fno-backslash: Fortran Dialect Options
- options, -fno-common: Code Gen Options
- options, -fno-f2c: Avoid f2c Compatibility
- options, -fno-f2c: Code Gen Options
- options, -fno-f77: Shorthand Options
- options, -fno-fixed-form: Fortran Dialect Options
- options, -fno-globals: Code Gen Options
- options, -fno-ident: Code Gen Options
- options, -fno-inline: Optimize Options
- options, -fno-move-all-movables: Optimize Options
- options, -fno-reduce-all-givs: Optimize Options
- options, -fno-rerun-loop-opt: Optimize Options
- options, -fno-second-underscore: Code Gen Options
- options, -fno-silent: Overall Options
- options, -fno-trapping-math: Optimize Options
- options, -fno-ugly: Shorthand Options
- options, -fno-ugly-args: Fortran Dialect Options
- options, -fno-ugly-init: Fortran Dialect Options
- options, -fno-underscoring: Names
- options, -fno-underscoring: Code Gen Options
- options, -fonetrip: Fortran Dialect Options
- options, -fpack-struct: Code Gen Options
- options, -fpcc-struct-return: Code Gen Options
- options, -fpedantic: Warning Options
- options, -fPIC: News
- options, -freg-struct-return: Code Gen Options
- options, -frerun-cse-after-loop: Optimize Options
- options, -fschedule-insns: Optimize Options
- options, -fschedule-insns2: Optimize Options
- options, -fset-g77-defaults: Overall Options
- options, -fshort-double: Code Gen Options
- options, -fsource-case-lower: Fortran Dialect Options
- options, -fsource-case-preserve: Fortran Dialect Options
- options, -fsource-case-upper: Fortran Dialect Options
- options, -fstrength-reduce: Optimize Options
- options, -fsymbol-case-any: Fortran Dialect Options
- options, -fsymbol-case-initcap: Fortran Dialect Options
- options, -fsymbol-case-lower: Fortran Dialect Options
- options, -fsymbol-case-upper: Fortran Dialect Options
- options, -fsyntax-only: Warning Options
- options, -ftypeless-boz: Fortran Dialect Options
- options, -fugly: Shorthand Options
- options, -fugly-assign: Fortran Dialect Options
- options, -fugly-assumed: Fortran Dialect Options
- options, -fugly-comma: Fortran Dialect Options
- options, -fugly-complex: Fortran Dialect Options
- options, -fugly-logint: Fortran Dialect Options
- options, -funix-intrinsics-delete: Fortran Dialect Options
- options, -funix-intrinsics-disable: Fortran Dialect Options
- options, -funix-intrinsics-enable: Fortran Dialect Options
- options, -funix-intrinsics-hide: Fortran Dialect Options
- options, -funroll-all-loops: Optimize Options
- options, -funroll-loops: Optimize Options
- options, -funsafe-math-optimizations: Optimize Options
- options, -fversion: Overall Options
- options, -fvxt: Fortran Dialect Options
- options, -fvxt-intrinsics-delete: Fortran Dialect Options
- options, -fvxt-intrinsics-disable: Fortran Dialect Options
- options, -fvxt-intrinsics-enable: Fortran Dialect Options
- options, -fvxt-intrinsics-hide: Fortran Dialect Options
- options, -fzeros: Code Gen Options
- options, -g: Debugging Options
- options, -I-: Directory Options
- options, -Idir: Directory Options
- options, -malign-double: Aligned Data
- options, -malign-double: Optimize Options
- options, -Nl: Compiler Limits
- options, -Nx: Compiler Limits
- options, -pedantic: Warning Options
- options, -pedantic-errors: Warning Options
- options, -v: G77 and GCC
- options, -W: Warning Options
- options, -w: Warning Options
- options, -Waggregate-return: Warning Options
- options, -Wall: Warning Options
- options, -Wcomment: Warning Options
- options, -Wconversion: Warning Options
- options, -Werror: Warning Options
- options, -Wformat: Warning Options
- options, -Wid-clash-len: Warning Options
- options, -Wimplicit: Warning Options
- options, -Wlarger-than-len: Warning Options
- options, -Wno-globals: Warning Options
- options, -Wparentheses: Warning Options
- options, -Wredundant-decls: Warning Options
- options, -Wshadow: Warning Options
- options, -Wsurprising: Warning Options
- options, -Wswitch: Warning Options
- options, -Wswitch-default: Warning Options
- options, -Wswitch-enum: Warning Options
- options, -Wtraditional: Warning Options
- options, -Wuninitialized: Warning Options
- options, -Wunused: Warning Options
- options, -x f77-cpp-input: LEX
- options, adding: Adding Options
- options, code generation: Code Gen Options
- options, debugging: Debugging Options
- options, dialect: Fortran Dialect Options
- options, directory search: Directory Options
- options, GNU Fortran command: Invoking G77
- options, macro: Shorthand Options
- options, negative forms: Invoking G77
- options, optimization: Optimize Options
- options, overall: Overall Options
- options, overly convenient: Overly Convenient Options
- options, preprocessor: Preprocessor Options
- options, shorthand: Shorthand Options
- options, warnings: Warning Options
- `Or` intrinsic: Bit Operations on Floating-point Data
- Or intrinsic: Or Intrinsic
- order of evaluation, side effects: Order of Side Effects
- ordering, array: Arrays
- other intrinsics: Other Intrinsics
- output, flushing: Output Assumed To Flush
- overall options: Overall Options
- overflow: Warning Options
- overlapping arguments: Aliasing Assumed To Work
- overlays: Aliasing Assumed To Work
- overly convenient options: Overly Convenient Options
- overwritten data: Strange Behavior at Run Time
- Pack intrinsic: Pack Intrinsic
- padding: Known Bugs
- parallel processing: Support for Threads
- PARAMETER statement: Old-style PARAMETER Statements
- PARAMETER statement: Intrinsics in PARAMETER Statements
- parameters, unused: Warning Options
- paths, search: Directory Options
- PDB: Portable Unformatted Files
- pedantic compilation: Pedantic Compilation
- Pentium optimizations: Aligned Data
- percent sign: Character Set
- PError intrinsic: PError Intrinsic
- placing initialization statements: Initializing Before Specifying
- POINTER statement: POINTER Statements
- pointers: Ugly Assigned Labels
- pointers: Kind Notation
- Poking the bear: Philosophy of Code Generation
- porting, simplify: Simplify Porting
- pound sign: Character Set
- Precision intrinsic: Precision Intrinsic
- precision, increasing: Increasing Precision/Range
- prefix-radix constants: Fortran Dialect Options
- preprocessor: LEX
- preprocessor: Cpp-style directives
- preprocessor: Overall Options
- preprocessor: What is GNU Fortran?
- preprocessor options: Preprocessor Options
- Present intrinsic: Present Intrinsic
- printing compilation status: Overall Options
- printing main source: Known Bugs
- printing version information: Overall Options
- printing version information: What is GNU Fortran?
- procedures: Procedures
- Product intrinsic: Product Intrinsic
- PROGRAM statement: Main Program Unit
- programs, cc1: What is GNU Fortran?
- programs, cc1plus: What is GNU Fortran?
- programs, compiling: G77 and GCC
- programs, cpp: LEX
- programs, cpp: Preprocessor Options
- programs, cpp: Overall Options
- programs, cpp: What is GNU Fortran?
- programs, `f771`: What is GNU Fortran?
- programs, ratfor: Overall Options
- programs, speeding up: Faster Programs
- programs, test: Nothing Happens
- projects: Projects
- Q edit descriptor: Q Edit Descriptor
- QAbs intrinsic: QAbs Intrinsic
- QACos intrinsic: QACos Intrinsic
- QACosD intrinsic: QACosD Intrinsic
- QASin intrinsic: QASin Intrinsic
- QASinD intrinsic: QASinD Intrinsic
- QATan intrinsic: QATan Intrinsic
- QATan2 intrinsic: QATan2 Intrinsic
- QATan2D intrinsic: QATan2D Intrinsic
- QATanD intrinsic: QATanD Intrinsic
- QCos intrinsic: QCos Intrinsic
- QCosD intrinsic: QCosD Intrinsic
- QCosH intrinsic: QCosH Intrinsic
- QDiM intrinsic: QDiM Intrinsic
- QExp intrinsic: QExp Intrinsic
- QExt intrinsic: QExt Intrinsic
- QExtD intrinsic: QExtD Intrinsic
- QFloat intrinsic: QFloat Intrinsic
- QInt intrinsic: QInt Intrinsic
- QLog intrinsic: QLog Intrinsic
- QLog10 intrinsic: QLog10 Intrinsic
- QMax1 intrinsic: QMax1 Intrinsic
- QMin1 intrinsic: QMin1 Intrinsic
- QMod intrinsic: QMod Intrinsic
- QNInt intrinsic: QNInt Intrinsic
- QSin intrinsic: QSin Intrinsic
- QSinD intrinsic: QSinD Intrinsic
- QSinH intrinsic: QSinH Intrinsic
- QSqRt intrinsic: QSqRt Intrinsic
- QTan intrinsic: QTan Intrinsic
- QTanD intrinsic: QTanD Intrinsic
- QTanH intrinsic: QTanH Intrinsic
- question mark: Character Set
- questionable instructions: What is GNU Fortran?
- Radix intrinsic: Radix Intrinsic
- Rand intrinsic: Rand Intrinsic
- Random_Number intrinsic: Random_Number Intrinsic
- Random_Seed intrinsic: Random_Seed Intrinsic
- range checking: Code Gen Options
- Range intrinsic: Range Intrinsic
- range, increasing: Increasing Precision/Range
- rank, maximum: Compiler Limits
- ratfor: Overall Options
- Ratfor preprocessor: Overall Options
- READONLY: READONLY Keyword
- reads and writes, scheduling: Aliasing Assumed To Work
- Real intrinsic: Real Intrinsic
- `Real` intrinsic: REAL() and AIMAG() of Complex
- real part: Ugly Complex Part Extraction
- REAL(KIND=1) type: Compiler Types
- REAL(KIND=2) type: Compiler Types
- `REAL*16` support: Full Support for Compiler Types
- RealPart intrinsic: RealPart Intrinsic
- recent versions: Changes
- recent versions: News
- RECORD statement: STRUCTURE UNION RECORD MAP
- recursion, lack of: RECURSIVE Keyword
- RECURSIVE keyword: RECURSIVE Keyword
- reference works: Language
- Rename intrinsic: Rename Intrinsic (function)
- Rename intrinsic: Rename Intrinsic (subroutine)
- Repeat intrinsic: Repeat Intrinsic
- reporting bugs: Bugs
- reporting compilation status: Overall Options
- Reshape intrinsic: Reshape Intrinsic
- results, inconsistent: Floating-point Errors
- RETURN statement: Alternate Returns
- RETURN statement: Functions
- return type of functions: Functions
- right angle: Character Set
- right bracket: Character Set
- rounding errors: Floating-point Errors
- row-major ordering: Arrays
- RRSpacing intrinsic: RRSpacing Intrinsic
- RShift intrinsic: RShift Intrinsic
- run-time, dynamic allocation: Arbitrary Concatenation
- run-time, initialization: Startup Code
- run-time, library: What is GNU Fortran?
- run-time, options: Code Gen Options
- SAVE statement: Code Gen Options
- saved variables: Variables Assumed To Be Saved
- Scale intrinsic: Scale Intrinsic
- Scan intrinsic: Scan Intrinsic
- scheduling of reads and writes: Aliasing Assumed To Work
- scope: Scope and Classes of Names
- scope: Scope of Names and Labels
- search path: Directory Options
- search paths, for included files: Directory Options
- Secnds intrinsic: Secnds Intrinsic
- Second intrinsic: Second Intrinsic (subroutine)
- Second intrinsic: Second Intrinsic (function)
- segmentation violation: Strange Behavior at Run Time
- segmentation violation: Stack Overflow
- segmentation violation: NeXTStep Problems
- Selected_Int_Kind intrinsic: Selected_Int_Kind Intrinsic
- Selected_Real_Kind intrinsic: Selected_Real_Kind Intrinsic
- semicolon: Character Set
- semicolon: Statements Comments Lines
- sequence numbers: Better Source Model
- Set_Exponent intrinsic: Set_Exponent Intrinsic
- Shape intrinsic: Shape Intrinsic
- SHARED: READONLY Keyword
- `Shift` intrinsic: Bit Operations on Floating-point Data
- Short intrinsic: Short Intrinsic
- short source lines: Short Lines
- short time: Timer Wraparounds
- shorthand options: Shorthand Options
- side effects, order of evaluation: Order of Side Effects
- Sign intrinsic: Sign Intrinsic
- signal 11: Signal 11 and Friends
- Signal intrinsic: Signal Intrinsic (function)
- Signal intrinsic: Signal Intrinsic (subroutine)
- signature of procedures: Procedures
- simplify porting: Simplify Porting
- Sin intrinsic: Sin Intrinsic
- SinD intrinsic: SinD Intrinsic
- SinH intrinsic: SinH Intrinsic
- Sleep intrinsic: Sleep Intrinsic
- Sngl intrinsic: Sngl Intrinsic
- SnglQ intrinsic: SnglQ Intrinsic
- Solaris: Strange Behavior at Run Time
- source code: Case Sensitivity
- source code: Source Form
- source code: Lines
- source code: What is GNU Fortran?
- source file: What is GNU Fortran?
- source file format: Case Sensitivity
- source file format: Source Form
- source file format: Lines
- source file format: Fortran Dialect Options
- source format: Source Form
- source format: Lines
- source lines, long: Long Lines
- source lines, short: Short Lines
- space: Lines
- space: Character Set
- space, endless printing of: Strange Behavior at Run Time
- space, padding with: Short Lines
- Spacing intrinsic: Spacing Intrinsic
- SPC: Lines
- SPC: Character Set
- speed, of compiler: Known Bugs
- speed, of loops: Optimize Options
- speed, of programs: Faster Programs
- spills of floating-point results: Floating-point Errors
- Spread intrinsic: Spread Intrinsic
- SqRt intrinsic: SqRt Intrinsic
- SRand intrinsic: SRand Intrinsic
- stack, 387 coprocessor: News
- stack, aligned: Aligned Data
- stack, overflow: Stack Overflow
- standard, ANSI FORTRAN 77: Language
- standard, support for: Standard Support
- startup code: Startup Code
- Stat intrinsic: Stat Intrinsic (function)
- Stat intrinsic: Stat Intrinsic (subroutine)
- statement labels, assigned: Assigned Statement Labels
- statements, ACCEPT: TYPE and ACCEPT I/O Statements
- statements, ASSIGN: Assigned Statement Labels
- statements, ASSIGN: Ugly Assigned Labels
- statements, `AUTOMATIC`: AUTOMATIC Statement
- statements, BLOCK DATA: Multiple Definitions of External Names
- statements, BLOCK DATA: Block Data and Libraries
- statements, CLOSE: OPEN CLOSE and INQUIRE Keywords
- statements, `COMMON`: Multiple Definitions of External Names
- statements, `COMMON`: Common Blocks
- statements, COMPLEX: Complex Variables
- statements, CYCLE: CYCLE and EXIT
- statements, DATA: Known Bugs
- statements, DATA: Code Gen Options
- statements, DECODE: ENCODE and DECODE
- statements, `DIMENSION`: Array Bounds Expressions
- statements, DIMENSION: Adjustable Arrays
- statements, DIMENSION: Arrays
- statements, DO: Loops
- statements, DO: Warning Options
- statements, ENCODE: ENCODE and DECODE
- statements, ENTRY: Alternate Entry Points
- statements, EQUIVALENCE: Local Equivalence Areas
- statements, EXIT: CYCLE and EXIT
- statements, FORMAT: Expressions in FORMAT Statements
- statements, FUNCTION: Functions
- statements, FUNCTION: Procedures
- statements, GOTO: Assigned Statement Labels
- statements, IMPLICIT CHARACTER*(*): Limitation on Implicit Declarations
- statements, INQUIRE: OPEN CLOSE and INQUIRE Keywords
- statements, MAP: STRUCTURE UNION RECORD MAP
- statements, NAMELIST: NAMELIST
- statements, OPEN: OPEN CLOSE and INQUIRE Keywords
- statements, PARAMETER: Old-style PARAMETER Statements
- statements, PARAMETER: Intrinsics in PARAMETER Statements
- statements, POINTER: POINTER Statements
- statements, PROGRAM: Main Program Unit
- statements, RECORD: STRUCTURE UNION RECORD MAP
- statements, RETURN: Alternate Returns
- statements, RETURN: Functions
- statements, SAVE: Code Gen Options
- statements, separated by semicolon: Statements Comments Lines
- statements, STRUCTURE: STRUCTURE UNION RECORD MAP
- statements, SUBROUTINE: Alternate Returns
- statements, SUBROUTINE: Procedures
- statements, TYPE: TYPE and ACCEPT I/O Statements
- statements, UNION: STRUCTURE UNION RECORD MAP
- STATIC: AUTOMATIC Statement
- static variables: Variables Assumed To Be Saved
- status, compilation: Overall Options
- storage association: Aliasing Assumed To Work
- strings, empty: Character Type
- STRUCTURE statement: STRUCTURE UNION RECORD MAP
- structures: Known Bugs
- submodels: Use Submodel Options
- SUBROUTINE statement: Alternate Returns
- SUBROUTINE statement: Procedures
- subroutines: Alternate Returns
- subscript checking: Code Gen Options
- substring checking: Code Gen Options
- suffixes, file name: Overall Options
- Sum intrinsic: Sum Intrinsic
- support, Alpha: Known Bugs
- support, ELF: News
- support, f77: Backslash in Constants
- support, FORTRAN 77: Standard Support
- support, Fortran 90: Fortran 90 Support
- support, gdb: Debugger Problems
- suppressing warnings: Warning Options
- symbol names: Names
- symbol names: Fortran Dialect Options
- symbol names, scope and classes: Scope and Classes of Names
- symbol names, transforming: Code Gen Options
- symbol names, underscores: Code Gen Options
- SymLnk intrinsic: SymLnk Intrinsic (function)
- SymLnk intrinsic: SymLnk Intrinsic (subroutine)
- synchronous write errors: Output Assumed To Flush
- syntax checking: Warning Options
- System intrinsic: System Intrinsic (function)
- System intrinsic: System Intrinsic (subroutine)
- System_Clock intrinsic: System_Clock Intrinsic
- tab character: Tabs
- table of intrinsics: Table of Intrinsic Functions
- Tan intrinsic: Tan Intrinsic
- TanD intrinsic: TanD Intrinsic
- TanH intrinsic: TanH Intrinsic
- test programs: Nothing Happens
- textbooks: Language
- threads: Support for Threads
- Time intrinsic: Time Intrinsic (VXT)
- Time intrinsic: Time Intrinsic (UNIX)
- Time8 intrinsic: Time8 Intrinsic
- Tiny intrinsic: Tiny Intrinsic
- Toolpack: Increasing Precision/Range
- trailing comma: Ugly Null Arguments
- trailing comment: LEX
- trailing comment: Trailing Comment
- trailing comment: Statements Comments Lines
- trailing null byte: Character and Hollerith Constants
- Transfer intrinsic: Transfer Intrinsic
- transforming symbol names: Names
- transforming symbol names: Code Gen Options
- translation of user programs: What is GNU Fortran?
- Transpose intrinsic: Transpose Intrinsic
- Trim intrinsic: Trim Intrinsic
- trips, number of: Loops
- truncation, of floating-point values: Floating-point Errors
- truncation, of long lines: Long Lines
- TtyNam intrinsic: TtyNam Intrinsic (function)
- TtyNam intrinsic: TtyNam Intrinsic (subroutine)
- TYPE statement: TYPE and ACCEPT I/O Statements
- types, COMPLEX(KIND=1): Compiler Types
- types, COMPLEX(KIND=2): Compiler Types
- types, constants: Compiler Constants
- types, constants: Constants
- types, constants: Fortran Dialect Options
- types, DOUBLE COMPLEX: Compiler Types
- types, DOUBLE PRECISION: Compiler Types
- types, file: Overall Options
- types, Fortran/C: C Access to Type Information
- types, INTEGER(KIND=1): Compiler Types
- types, INTEGER(KIND=2): Compiler Types
- types, INTEGER(KIND=3): Compiler Types
- types, INTEGER(KIND=6): Compiler Types
- types, `INTEGER*2`: Popular Non-standard Types
- types, `INTEGER*8`: Full Support for Compiler Types
- types, LOGICAL(KIND=1): Compiler Types
- types, LOGICAL(KIND=2): Compiler Types
- types, LOGICAL(KIND=3): Compiler Types
- types, LOGICAL(KIND=6): Compiler Types
- types, `LOGICAL*1`: Popular Non-standard Types
- types, of data: Compiler Types
- types, REAL(KIND=1): Compiler Types
- types, REAL(KIND=2): Compiler Types
- types, `REAL*16`: Full Support for Compiler Types
- UBound intrinsic: UBound Intrinsic
- ugly features: Distensions
- ugly features: Shorthand Options
- UMask intrinsic: UMask Intrinsic (function)
- UMask intrinsic: UMask Intrinsic (subroutine)
- undefined behavior: Bug Criteria
- undefined function value: Bug Criteria
- undefined reference (_main): Cannot Link Fortran Programs
- underscore: Mangling of Names
- underscore: Underscores in Symbol Names
- underscore: Character Set
- underscore: Code Gen Options
- unformatted files: Portable Unformatted Files
- uninitialized variables: Variables Assumed To Be Zero
- uninitialized variables: Code Gen Options
- uninitialized variables: Warning Options
- UNION statement: STRUCTURE UNION RECORD MAP
- unit numbers: Large File Unit Numbers
- UNIX f77: Shorthand Options
- UNIX intrinsics: Fortran Dialect Options
- Unlink intrinsic: Unlink Intrinsic (function)
- Unlink intrinsic: Unlink Intrinsic (subroutine)
- Unpack intrinsic: Unpack Intrinsic
- unrecognized file format: What is GNU Fortran?
- unresolved reference (various): Cannot Link Fortran Programs
- unrolling loops: Optimize Options
- UNSAVE: AUTOMATIC Statement
- unsupported warnings: Warning Options
- unused arguments: Unused Arguments
- unused arguments: Warning Options
- unused dummies: Warning Options
- unused parameters: Warning Options
- unused variables: Warning Options
- uppercase letters: Case Sensitivity
- user-visible changes: Changes
- variables, assumed to be zero: Variables Assumed To Be Zero
- variables, automatic: AUTOMATIC Statement
- variables, initialization of: Code Gen Options
- variables, mistyped: Not My Type
- variables, retaining values across calls: Variables Assumed To Be Saved
- variables, uninitialized: Code Gen Options
- variables, uninitialized: Warning Options
- variables, unused: Warning Options
- Verify intrinsic: Verify Intrinsic
- version information, printing: Overall Options
- version information, printing: What is GNU Fortran?
- versions, recent: Changes
- versions, recent: News
- VXT extensions: VXT Fortran
- VXT extensions: Fortran Dialect Options
- VXT intrinsics: Fortran Dialect Options
- vxtidate_y2kbuggy_0: Year 2000 (Y2K) Problems
- warnings: What is GNU Fortran?
- warnings vs errors: Warnings and Errors
- warnings, all: Warning Options
- warnings, extra: Warning Options
- warnings, global names: Code Gen Options
- warnings, global names: Warning Options
- warnings, implicit declaration: Warning Options
- warnings, suppressing: Warning Options
- warnings, unsupported: Warning Options
- wisdom: Collected Fortran Wisdom
- wraparound: Run-time Environment Limits
- wraparound, timings: Secnds Intrinsic
- wraparound, timings: DTime Intrinsic (function)
- wraparound, timings: Time8 Intrinsic
- wraparound, timings: Time Intrinsic (UNIX)
- wraparound, timings: System_Clock Intrinsic
- wraparound, timings: Second Intrinsic (subroutine)
- wraparound, timings: Second Intrinsic (function)
- wraparound, timings: MClock8 Intrinsic
- wraparound, timings: MClock Intrinsic
- wraparound, timings: ETime Intrinsic (function)
- wraparound, timings: ETime Intrinsic (subroutine)
- wraparound, timings: DTime Intrinsic (subroutine)
- wraparound, timings: CPU_Time Intrinsic
- wraparound, Y10K: Time Intrinsic (VXT)
- wraparound, Y10K: IDate Intrinsic (UNIX)
- wraparound, Y10K: FDate Intrinsic (function)
- wraparound, Y10K: FDate Intrinsic (subroutine)
- wraparound, Y10K: Date_and_Time Intrinsic
- wraparound, Y2K: IDate Intrinsic (VXT)
- writes, flushing: Output Assumed To Flush
- writing code: Collected Fortran Wisdom
- x86 floating-point: Floating-point precision
- x86 FPU stack: Inconsistent Calling Sequences
- XOr intrinsic: XOr Intrinsic
- Y10K compliance: Time Intrinsic (VXT)
- Y10K compliance: Year 10000 (Y10K) Problems
- Y10K compliance: IDate Intrinsic (UNIX)
- Y10K compliance: FDate Intrinsic (function)
- Y10K compliance: FDate Intrinsic (subroutine)
- Y10K compliance: Date_and_Time Intrinsic
- Y2K compliance: Y2KBAD
- Y2K compliance: IDate Intrinsic (VXT)
- Y2K compliance: Date Intrinsic
- Y2K compliance: Year 2000 (Y2K) Problems
- y2kbuggy: Year 2000 (Y2K) Problems
- Year 10000 compliance: Time Intrinsic (VXT)
- Year 10000 compliance: Year 10000 (Y10K) Problems
- Year 10000 compliance: IDate Intrinsic (UNIX)
- Year 10000 compliance: FDate Intrinsic (function)
- Year 10000 compliance: FDate Intrinsic (subroutine)
- Year 10000 compliance: Date_and_Time Intrinsic
- Year 2000 compliance: Y2KBAD
- Year 2000 compliance: IDate Intrinsic (VXT)
- Year 2000 compliance: Date Intrinsic
- Year 2000 compliance: Year 2000 (Y2K) Problems
- Z edit descriptor: Fortran 90 Features
- Z edit descriptor: I/O
- ZAbs intrinsic: ZAbs Intrinsic
- ZCos intrinsic: ZCos Intrinsic
- zero byte, trailing: Character and Hollerith Constants
- zero-initialized variables: Variables Assumed To Be Zero
- zero-length CHARACTER: Character Type
- zero-trip `DO` loops: Fortran Dialect Options
- ZExp intrinsic: ZExp Intrinsic
- ZExt intrinsic: ZExt Intrinsic
- ZLog intrinsic: ZLog Intrinsic
- ZSin intrinsic: ZSin Intrinsic
- ZSqRt intrinsic: ZSqRt Intrinsic

#### Footnotes

[1] loop discovery refers to the process by which a compiler, or indeed any reader of a program, determines which portions of the program are more likely to be executed repeatedly as it is being run. Such discovery typically is done early when compiling using optimization techniques, so the “discovered” loops get more attention—and more run-time resources, such as registers—from the compiler. It is easy to “discover” loops that are constructed out of looping constructs in the language (such as Fortran's `DO`). For some programs, “discovering” loops constructed out of lower-level constructs (such as `IF` and `GOTO`) can lead to generation of more optimal code than otherwise.

[2] The files generated like this can also be used for inter-unit consistency checking of dummy and actual arguments, although the ftnchek tool from ftp://ftp.netlib.org/fortran or ftp://ftp.dsm.fordham.edu is probably better for this purpose.

[3] No, not that one.