# The GNU Fortran Compiler

## Short Contents

- Introduction
- 1 Introduction
- 2 GNU Fortran Command Options
- 3 Runtime: Influencing runtime behavior with environment variables
- 4 Fortran 2003 and 2008 Status
- 5 Compiler Characteristics
- 6 Extensions
- 7 Mixed-Language Programming
- 8 Intrinsic Procedures
- 9 Intrinsic Modules
- Contributing
- GNU General Public License
- GNU Free Documentation License
- Funding Free Software
- Option Index
- Keyword Index

## Table of Contents

- Introduction
- 1 Introduction
  - 1.1 About GNU Fortran
  - 1.2 GNU Fortran and GCC
  - 1.3 Preprocessing and conditional compilation
  - 1.4 GNU Fortran and G77
  - 1.5 Project Status
  - 1.6 Standards
    - 1.6.1 Varying Length Character Strings
- 2 GNU Fortran Command Options
  - 2.1 Option summary
  - 2.2 Options controlling Fortran dialect
  - 2.3 Enable and customize preprocessing
  - 2.4 Options to request or suppress errors and warnings
  - 2.5 Options for debugging your program or GNU Fortran
  - 2.6 Options for directory search
  - 2.7 Influencing the linking step
  - 2.8 Influencing runtime behavior
  - 2.9 Options for code generation conventions
  - 2.10 Environment variables affecting `gfortran`
- 3 Runtime: Influencing runtime behavior with environment variables
  - 3.1 `TMPDIR`—Directory for scratch files
  - 3.2 `GFORTRAN_STDIN_UNIT`—Unit number for standard input
  - 3.3 `GFORTRAN_STDOUT_UNIT`—Unit number for standard output
  - 3.4 `GFORTRAN_STDERR_UNIT`—Unit number for standard error
  - 3.5 `GFORTRAN_UNBUFFERED_ALL`—Do not buffer I/O on all units
  - 3.6 `GFORTRAN_UNBUFFERED_PRECONNECTED`—Do not buffer I/O on preconnected units
  - 3.7 `GFORTRAN_SHOW_LOCUS`—Show location for runtime errors
  - 3.8 `GFORTRAN_OPTIONAL_PLUS`—Print leading + where permitted
  - 3.9 `GFORTRAN_DEFAULT_RECL`—Default record length for new files
  - 3.10 `GFORTRAN_LIST_SEPARATOR`—Separator for list output
  - 3.11 `GFORTRAN_CONVERT_UNIT`—Set endianness for unformatted I/O
  - 3.12 `GFORTRAN_ERROR_BACKTRACE`—Show backtrace on run-time errors
- 4 Fortran 2003 and 2008 Status
  - 4.1 Fortran 2003 status
  - 4.2 Fortran 2008 status
  - 4.3 Technical Specification 29113 Status
- 5 Compiler Characteristics
  - 5.1 KIND Type Parameters
  - 5.2 Internal representation of LOGICAL variables
  - 5.3 Thread-safety of the runtime library
  - 5.4 Data consistency and durability
- 6 Extensions
  - 6.1 Extensions implemented in GNU Fortran
    - 6.1.1 Old-style kind specifications
    - 6.1.2 Old-style variable initialization
    - 6.1.3 Extensions to namelist
    - 6.1.4 `X` format descriptor without count field
    - 6.1.5 Commas in `FORMAT` specifications
    - 6.1.6 Missing period in `FORMAT` specifications
    - 6.1.7 I/O item lists
    - 6.1.8 `Q` exponent-letter
    - 6.1.9 BOZ literal constants
    - 6.1.10 Real array indices
    - 6.1.11 Unary operators
    - 6.1.12 Implicitly convert `LOGICAL` and `INTEGER` values
    - 6.1.13 Hollerith constants support
    - 6.1.14 Cray pointers
    - 6.1.15 `CONVERT` specifier
    - 6.1.16 OpenMP
    - 6.1.17 Argument list functions `%VAL`, `%REF` and `%LOC`
  - 6.2 Extensions not implemented in GNU Fortran
    - 6.2.1 `STRUCTURE` and `RECORD`
    - 6.2.2 `ENCODE` and `DECODE` statements
    - 6.2.3 Variable `FORMAT` expressions
    - 6.2.4 Alternate complex function syntax
    - 6.2.5 Volatile `COMMON` blocks
- 7 Mixed-Language Programming
  - 7.1 Interoperability with C
    - 7.1.1 Intrinsic Types
    - 7.1.2 Derived Types and struct
    - 7.1.3 Interoperable Global Variables
    - 7.1.4 Interoperable Subroutines and Functions
    - 7.1.5 Working with Pointers
    - 7.1.6 Further Interoperability of Fortran with C
  - 7.2 GNU Fortran Compiler Directives
  - 7.3 Non-Fortran Main Program
    - 7.3.1 `_gfortran_set_args` — Save command-line arguments
    - 7.3.2 `_gfortran_set_options` — Set library option flags
    - 7.3.3 `_gfortran_set_convert` — Set endian conversion
    - 7.3.4 `_gfortran_set_record_marker` — Set length of record markers
    - 7.3.5 `_gfortran_set_fpe` — Enable floating point exception traps
    - 7.3.6 `_gfortran_set_max_subrecord_length` — Set subrecord length
  - 7.4 Naming and argument-passing conventions
    - 7.4.1 Naming conventions
    - 7.4.2 Argument passing conventions
- 8 Intrinsic Procedures
  - 8.1 Introduction to intrinsic procedures
  - 8.2 `ABORT` — Abort the program
  - 8.3 `ABS` — Absolute value
  - 8.4 `ACCESS` — Checks file access modes
  - 8.5 `ACHAR` — Character in ASCII collating sequence
  - 8.6 `ACOS` — Arccosine function
  - 8.7 `ACOSH` — Inverse hyperbolic cosine function
  - 8.8 `ADJUSTL` — Left adjust a string
  - 8.9 `ADJUSTR` — Right adjust a string
  - 8.10 `AIMAG` — Imaginary part of complex number
  - 8.11 `AINT` — Truncate to a whole number
  - 8.12 `ALARM` — Execute a routine after a given delay
  - 8.13 `ALL` — All values in MASK along DIM are true
  - 8.14 `ALLOCATED` — Status of an allocatable entity
  - 8.15 `AND` — Bitwise logical AND
  - 8.16 `ANINT` — Nearest whole number
  - 8.17 `ANY` — Any value in MASK along DIM is true
  - 8.18 `ASIN` — Arcsine function
  - 8.19 `ASINH` — Inverse hyperbolic sine function
  - 8.20 `ASSOCIATED` — Status of a pointer or pointer/target pair
  - 8.21 `ATAN` — Arctangent function
  - 8.22 `ATAN2` — Arctangent function
  - 8.23 `ATANH` — Inverse hyperbolic tangent function
  - 8.24 `ATOMIC_DEFINE` — Setting a variable atomically
  - 8.25 `ATOMIC_REF` — Obtaining the value of a variable atomically
  - 8.26 `BACKTRACE` — Show a backtrace
  - 8.27 `BESSEL_J0` — Bessel function of the first kind of order 0
  - 8.28 `BESSEL_J1` — Bessel function of the first kind of order 1
  - 8.29 `BESSEL_JN` — Bessel function of the first kind
  - 8.30 `BESSEL_Y0` — Bessel function of the second kind of order 0
  - 8.31 `BESSEL_Y1` — Bessel function of the second kind of order 1
  - 8.32 `BESSEL_YN` — Bessel function of the second kind
  - 8.33 `BGE` — Bitwise greater than or equal to
  - 8.34 `BGT` — Bitwise greater than
  - 8.35 `BIT_SIZE` — Bit size inquiry function
  - 8.36 `BLE` — Bitwise less than or equal to
  - 8.37 `BLT` — Bitwise less than
  - 8.38 `BTEST` — Bit test function
  - 8.39 `C_ASSOCIATED` — Status of a C pointer
  - 8.40 `C_F_POINTER` — Convert C into Fortran pointer
  - 8.41 `C_F_PROCPOINTER` — Convert C into Fortran procedure pointer
  - 8.42 `C_FUNLOC` — Obtain the C address of a procedure
  - 8.43 `C_LOC` — Obtain the C address of an object
  - 8.44 `C_SIZEOF` — Size in bytes of an expression
  - 8.45 `CEILING` — Integer ceiling function
  - 8.46 `CHAR` — Character conversion function
  - 8.47 `CHDIR` — Change working directory
  - 8.48 `CHMOD` — Change access permissions of files
  - 8.49 `CMPLX` — Complex conversion function
  - 8.50 `COMMAND_ARGUMENT_COUNT` — Get number of command line arguments
  - 8.51 `COMPILER_OPTIONS` — Options passed to the compiler
  - 8.52 `COMPILER_VERSION` — Compiler version string
  - 8.53 `COMPLEX` — Complex conversion function
  - 8.54 `CONJG` — Complex conjugate function
  - 8.55 `COS` — Cosine function
  - 8.56 `COSH` — Hyperbolic cosine function
  - 8.57 `COUNT` — Count function
  - 8.58 `CPU_TIME` — CPU elapsed time in seconds
  - 8.59 `CSHIFT` — Circular shift elements of an array
  - 8.60 `CTIME` — Convert a time into a string
  - 8.61 `DATE_AND_TIME` — Date and time subroutine
  - 8.62 `DBLE` — Double conversion function
  - 8.63 `DCMPLX` — Double complex conversion function
  - 8.64 `DIGITS` — Significant binary digits function
  - 8.65 `DIM` — Positive difference
  - 8.66 `DOT_PRODUCT` — Dot product function
  - 8.67 `DPROD` — Double product function
  - 8.68 `DREAL` — Double real part function
  - 8.69 `DSHIFTL` — Combined left shift
  - 8.70 `DSHIFTR` — Combined right shift
  - 8.71 `DTIME` — Execution time subroutine (or function)
  - 8.72 `EOSHIFT` — End-off shift elements of an array
  - 8.73 `EPSILON` — Epsilon function
  - 8.74 `ERF` — Error function
  - 8.75 `ERFC` — Error function
  - 8.76 `ERFC_SCALED` — Error function
  - 8.77 `ETIME` — Execution time subroutine (or function)
  - 8.78 `EXECUTE_COMMAND_LINE` — Execute a shell command
  - 8.79 `EXIT` — Exit the program with status.
  - 8.80 `EXP` — Exponential function
  - 8.81 `EXPONENT` — Exponent function
  - 8.82 `EXTENDS_TYPE_OF` — Query dynamic type for extension
  - 8.83 `FDATE` — Get the current time as a string
  - 8.84 `FGET` — Read a single character in stream mode from stdin
  - 8.85 `FGETC` — Read a single character in stream mode
  - 8.86 `FLOOR` — Integer floor function
  - 8.87 `FLUSH` — Flush I/O unit(s)
  - 8.88 `FNUM` — File number function
  - 8.89 `FPUT` — Write a single character in stream mode to stdout
  - 8.90 `FPUTC` — Write a single character in stream mode
  - 8.91 `FRACTION` — Fractional part of the model representation
  - 8.92 `FREE` — Frees memory
  - 8.93 `FSEEK` — Low level file positioning subroutine
  - 8.94 `FSTAT` — Get file status
  - 8.95 `FTELL` — Current stream position
  - 8.96 `GAMMA` — Gamma function
  - 8.97 `GERROR` — Get last system error message
  - 8.98 `GETARG` — Get command line arguments
  - 8.99 `GET_COMMAND` — Get the entire command line
  - 8.100 `GET_COMMAND_ARGUMENT` — Get command line arguments
  - 8.101 `GETCWD` — Get current working directory
  - 8.102 `GETENV` — Get an environmental variable
  - 8.103 `GET_ENVIRONMENT_VARIABLE` — Get an environmental variable
  - 8.104 `GETGID` — Group ID function
  - 8.105 `GETLOG` — Get login name
  - 8.106 `GETPID` — Process ID function
  - 8.107 `GETUID` — User ID function
  - 8.108 `GMTIME` — Convert time to GMT info
  - 8.109 `HOSTNM` — Get system host name
  - 8.110 `HUGE` — Largest number of a kind
  - 8.111 `HYPOT` — Euclidean distance function
  - 8.112 `IACHAR` — Code in ASCII collating sequence
  - 8.113 `IALL` — Bitwise AND of array elements
  - 8.114 `IAND` — Bitwise logical and
  - 8.115 `IANY` — Bitwise OR of array elements
  - 8.116 `IARGC` — Get the number of command line arguments
  - 8.117 `IBCLR` — Clear bit
  - 8.118 `IBITS` — Bit extraction
  - 8.119 `IBSET` — Set bit
  - 8.120 `ICHAR` — Character-to-integer conversion function
  - 8.121 `IDATE` — Get current local time subroutine (day/month/year)
  - 8.122 `IEOR` — Bitwise logical exclusive or
  - 8.123 `IERRNO` — Get the last system error number
  - 8.124 `IMAGE_INDEX` — Function that converts a cosubscript to an image index
  - 8.125 `INDEX` — Position of a substring within a string
  - 8.126 `INT` — Convert to integer type
  - 8.127 `INT2` — Convert to 16-bit integer type
  - 8.128 `INT8` — Convert to 64-bit integer type
  - 8.129 `IOR` — Bitwise logical or
  - 8.130 `IPARITY` — Bitwise XOR of array elements
  - 8.131 `IRAND` — Integer pseudo-random number
  - 8.132 `IS_IOSTAT_END` — Test for end-of-file value
  - 8.133 `IS_IOSTAT_EOR` — Test for end-of-record value
  - 8.134 `ISATTY` — Whether a unit is a terminal device.
  - 8.135 `ISHFT` — Shift bits
  - 8.136 `ISHFTC` — Shift bits circularly
  - 8.137 `ISNAN` — Test for a NaN
  - 8.138 `ITIME` — Get current local time subroutine (hour/minutes/seconds)
  - 8.139 `KILL` — Send a signal to a process
  - 8.140 `KIND` — Kind of an entity
  - 8.141 `LBOUND` — Lower dimension bounds of an array
  - 8.142 `LCOBOUND` — Lower codimension bounds of an array
  - 8.143 `LEADZ` — Number of leading zero bits of an integer
  - 8.144 `LEN` — Length of a character entity
  - 8.145 `LEN_TRIM` — Length of a character entity without trailing blank characters
  - 8.146 `LGE` — Lexical greater than or equal
  - 8.147 `LGT` — Lexical greater than
  - 8.148 `LINK` — Create a hard link
  - 8.149 `LLE` — Lexical less than or equal
  - 8.150 `LLT` — Lexical less than
  - 8.151 `LNBLNK` — Index of the last non-blank character in a string
  - 8.152 `LOC` — Returns the address of a variable
  - 8.153 `LOG` — Natural logarithm function
  - 8.154 `LOG10` — Base 10 logarithm function
  - 8.155 `LOG_GAMMA` — Logarithm of the Gamma function
  - 8.156 `LOGICAL` — Convert to logical type
  - 8.157 `LONG` — Convert to integer type
  - 8.158 `LSHIFT` — Left shift bits
  - 8.159 `LSTAT` — Get file status
  - 8.160 `LTIME` — Convert time to local time info
  - 8.161 `MALLOC` — Allocate dynamic memory
  - 8.162 `MASKL` — Left justified mask
  - 8.163 `MASKR` — Right justified mask
  - 8.164 `MATMUL` — matrix multiplication
  - 8.165 `MAX` — Maximum value of an argument list
  - 8.166 `MAXEXPONENT` — Maximum exponent of a real kind
  - 8.167 `MAXLOC` — Location of the maximum value within an array
  - 8.168 `MAXVAL` — Maximum value of an array
  - 8.169 `MCLOCK` — Time function
  - 8.170 `MCLOCK8` — Time function (64-bit)
  - 8.171 `MERGE` — Merge variables
  - 8.172 `MERGE_BITS` — Merge of bits under mask
  - 8.173 `MIN` — Minimum value of an argument list
  - 8.174 `MINEXPONENT` — Minimum exponent of a real kind
  - 8.175 `MINLOC` — Location of the minimum value within an array
  - 8.176 `MINVAL` — Minimum value of an array
  - 8.177 `MOD` — Remainder function
  - 8.178 `MODULO` — Modulo function
  - 8.179 `MOVE_ALLOC` — Move allocation from one object to another
  - 8.180 `MVBITS` — Move bits from one integer to another
  - 8.181 `NEAREST` — Nearest representable number
  - 8.182 `NEW_LINE` — New line character
  - 8.183 `NINT` — Nearest whole number
  - 8.184 `NORM2` — Euclidean vector norms
  - 8.185 `NOT` — Logical negation
  - 8.186 `NULL` — Function that returns an disassociated pointer
  - 8.187 `NUM_IMAGES` — Function that returns the number of images
  - 8.188 `OR` — Bitwise logical OR
  - 8.189 `PACK` — Pack an array into an array of rank one
  - 8.190 `PARITY` — Reduction with exclusive OR
  - 8.191 `PERROR` — Print system error message
  - 8.192 `POPCNT` — Number of bits set
  - 8.193 `POPPAR` — Parity of the number of bits set
  - 8.194 `PRECISION` — Decimal precision of a real kind
  - 8.195 `PRESENT` — Determine whether an optional dummy argument is specified
  - 8.196 `PRODUCT` — Product of array elements
  - 8.197 `RADIX` — Base of a model number
  - 8.198 `RAN` — Real pseudo-random number
  - 8.199 `RAND` — Real pseudo-random number
  - 8.200 `RANDOM_NUMBER` — Pseudo-random number
  - 8.201 `RANDOM_SEED` — Initialize a pseudo-random number sequence
  - 8.202 `RANGE` — Decimal exponent range
  - 8.203 `RANK` — Rank of a data object
  - 8.204 `REAL` — Convert to real type
  - 8.205 `RENAME` — Rename a file
  - 8.206 `REPEAT` — Repeated string concatenation
  - 8.207 `RESHAPE` — Function to reshape an array
  - 8.208 `RRSPACING` — Reciprocal of the relative spacing
  - 8.209 `RSHIFT` — Right shift bits
  - 8.210 `SAME_TYPE_AS` — Query dynamic types for equality
  - 8.211 `SCALE` — Scale a real value
  - 8.212 `SCAN` — Scan a string for the presence of a set of characters
  - 8.213 `SECNDS` — Time function
  - 8.214 `SECOND` — CPU time function
  - 8.215 `SELECTED_CHAR_KIND` — Choose character kind
  - 8.216 `SELECTED_INT_KIND` — Choose integer kind
  - 8.217 `SELECTED_REAL_KIND` — Choose real kind
  - 8.218 `SET_EXPONENT` — Set the exponent of the model
  - 8.219 `SHAPE` — Determine the shape of an array
  - 8.220 `SHIFTA` — Right shift with fill
  - 8.221 `SHIFTL` — Left shift
  - 8.222 `SHIFTR` — Right shift
  - 8.223 `SIGN` — Sign copying function
  - 8.224 `SIGNAL` — Signal handling subroutine (or function)
  - 8.225 `SIN` — Sine function
  - 8.226 `SINH` — Hyperbolic sine function
  - 8.227 `SIZE` — Determine the size of an array
  - 8.228 `SIZEOF` — Size in bytes of an expression
  - 8.229 `SLEEP` — Sleep for the specified number of seconds
  - 8.230 `SPACING` — Smallest distance between two numbers of a given type
  - 8.231 `SPREAD` — Add a dimension to an array
  - 8.232 `SQRT` — Square-root function
  - 8.233 `SRAND` — Reinitialize the random number generator
  - 8.234 `STAT` — Get file status
  - 8.235 `STORAGE_SIZE` — Storage size in bits
  - 8.236 `SUM` — Sum of array elements
  - 8.237 `SYMLNK` — Create a symbolic link
  - 8.238 `SYSTEM` — Execute a shell command
  - 8.239 `SYSTEM_CLOCK` — Time function
  - 8.240 `TAN` — Tangent function
  - 8.241 `TANH` — Hyperbolic tangent function
  - 8.242 `THIS_IMAGE` — Function that returns the cosubscript index of this image
  - 8.243 `TIME` — Time function
  - 8.244 `TIME8` — Time function (64-bit)
  - 8.245 `TINY` — Smallest positive number of a real kind
  - 8.246 `TRAILZ` — Number of trailing zero bits of an integer
  - 8.247 `TRANSFER` — Transfer bit patterns
  - 8.248 `TRANSPOSE` — Transpose an array of rank two
  - 8.249 `TRIM` — Remove trailing blank characters of a string
  - 8.250 `TTYNAM` — Get the name of a terminal device.
  - 8.251 `UBOUND` — Upper dimension bounds of an array
  - 8.252 `UCOBOUND` — Upper codimension bounds of an array
  - 8.253 `UMASK` — Set the file creation mask
  - 8.254 `UNLINK` — Remove a file from the file system
  - 8.255 `UNPACK` — Unpack an array of rank one into an array
  - 8.256 `VERIFY` — Scan a string for characters not a given set
  - 8.257 `XOR` — Bitwise logical exclusive OR
- 9 Intrinsic Modules
  - 9.1 `ISO_FORTRAN_ENV`
  - 9.2 `ISO_C_BINDING`
  - 9.3 OpenMP Modules `OMP_LIB` and `OMP_LIB_KINDS`
- Contributing
  - Contributors to GNU Fortran
  - Projects
  - Proposed Extensions
    - Compiler extensions:
    - Environment Options
- GNU General Public License
- GNU Free Documentation License
  - ADDENDUM: How to use this License for your documents
- Funding Free Software
- Option Index
- Keyword Index

Next: Introduction, Up: (dir)

## Introduction

This manual documents the use of `gfortran`, the GNU Fortran compiler. You can find in this manual how to invoke `gfortran`, as well as its features and incompatibilities.

Part I: Invoking GNU Fortran

Part II: Language Reference

Next: Invoking GNU Fortran, Previous: Top, Up: Top

## 1 Introduction

The GNU Fortran compiler front end was designed initially as a free replacement for, or alternative to, the Unix `f95` command; `gfortran` is the command you will use to invoke the compiler.

Next: GNU Fortran and GCC, Up: Introduction

### 1.1 About GNU Fortran

The GNU Fortran compiler supports the Fortran 77, 90 and 95 standards completely, parts of the Fortran 2003 and Fortran 2008 standards, and several vendor extensions. The development goal is to provide the following features:

- Read a user's program, stored in a file and containing instructions written in Fortran 77, Fortran 90, Fortran 95, Fortran 2003 or Fortran 2008. This file contains source code.
- 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. The result after compilation of a program is machine code, code designed to be efficiently translated and processed by a machine such as your computer. Humans usually are not as good writing machine code as they are at writing Fortran (or C++, Ada, or Java), because it is easy to make tiny mistakes writing machine code.
- Provide the user with information about the reasons why the compiler is unable to create a binary from the source code. Usually this will be the case if the source code is flawed. The Fortran 90 standard requires that the compiler can point out mistakes to the user. An incorrect usage of the language causes an error message.

  The compiler will also attempt to diagnose cases where the user's program contains a correct usage of the language, but instructs the computer to do something questionable. This kind of diagnostics message is called a warning message.

- Provide optional information about the translation passes from the source code to machine code. This can help a user of the compiler to find the cause of certain bugs which may not be obvious in the source code, but may be more easily found at a lower level compiler output. It also helps developers to find bugs in the compiler itself.
- 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 the GNU Debugger `gdb`).
- Locate and gather machine code already generated to perform actions requested by statements in the user's program. This machine code is organized into modules and is located and linked to the user program.

The GNU Fortran compiler consists of several components:

- A version of the `gcc` command (which also might be installed as the system's `cc` command) that also understands and accepts Fortran source code. The `gcc` command is the driver program for all the languages in the GNU Compiler Collection (GCC); With `gcc`, you can compile the source code of any language for which a front end is available in GCC.
- The `gfortran` command itself, which also might be installed as the system's `f95` command. `gfortran` is just another driver program, but specifically for the Fortran compiler only. The difference with `gcc` is that `gfortran` will automatically link the correct libraries to your program.
- A collection of run-time libraries. These libraries contain the machine code needed to support capabilities of the Fortran language that are not directly provided by the machine code generated by the `gfortran` compilation phase, such as intrinsic functions and subroutines, and routines for interaction with files and the operating system.
- The Fortran compiler itself, (`f951`). This is the GNU Fortran parser and code generator, linked to and interfaced with the GCC backend library. `f951` “translates” the source code to assembler code. You would typically not use this program directly; instead, the `gcc` or `gfortran` driver programs will call it for you.

Next: Preprocessing and conditional compilation, Previous: About GNU Fortran, Up: Introduction

### 1.2 GNU Fortran and GCC

GNU Fortran is a part of GCC, the GNU Compiler Collection. GCC consists of a collection of front ends for various languages, which translate the source code into a language-independent form called GENERIC. This is then processed by a common middle end which provides optimization, and then passed to one of a collection of back ends which generate code for different computer architectures and operating systems.

Functionally, this is implemented with a driver program (`gcc`) which provides the command-line interface for the compiler. It calls the relevant compiler front-end program (e.g., `f951` for Fortran) for each file in the source code, and then calls the assembler and linker as appropriate to produce the compiled output. In a copy of GCC which has been compiled with Fortran language support enabled, `gcc` will recognize files with `.f`, `.for`, `.ftn`, `.f90`, `.f95`, `.f03` and `.f08` extensions as Fortran source code, and compile it accordingly. A `gfortran` driver program is also provided, which is identical to `gcc` except that it automatically links the Fortran runtime libraries into the compiled program.

Source files with `.f`, `.for`, `.fpp`, `.ftn`, `.F`, `.FOR`, `.FPP`, and `.FTN` extensions are treated as fixed form. Source files with `.f90`, `.f95`, `.f03`, `.f08`, `.F90`, `.F95`, `.F03` and `.F08` extensions are treated as free form. The capitalized versions of either form are run through preprocessing. Source files with the lower case `.fpp` extension are also run through preprocessing.

This manual specifically documents the Fortran front end, which handles the programming language's syntax and semantics. The aspects of GCC which relate to the optimization passes and the back-end code generation are documented in the GCC manual; see Introduction. The two manuals together provide a complete reference for the GNU Fortran compiler.

Next: GNU Fortran and G77, Previous: GNU Fortran and GCC, Up: Introduction

### 1.3 Preprocessing and conditional compilation

Many Fortran compilers including GNU Fortran allow passing the source code through a C preprocessor (CPP; sometimes also called the Fortran preprocessor, FPP) to allow for conditional compilation. In the case of GNU Fortran, this is the GNU C Preprocessor in the traditional mode. On systems with case-preserving file names, the preprocessor is automatically invoked if the filename extension is `.F`, `.FOR`, `.FTN`, `.fpp`, `.FPP`, `.F90`, `.F95`, `.F03` or `.F08`. To manually invoke the preprocessor on any file, use `-cpp`, to disable preprocessing on files where the preprocessor is run automatically, use `-nocpp`.

If a preprocessed file includes another file with the Fortran `INCLUDE` statement, the included file is not preprocessed. To preprocess included files, use the equivalent preprocessor statement `#include`.

If GNU Fortran invokes the preprocessor, `__GFORTRAN__` is defined and `__GNUC__`, `__GNUC_MINOR__` and `__GNUC_PATCHLEVEL__` can be used to determine the version of the compiler. See Overview for details.

While CPP is the de-facto standard for preprocessing Fortran code, Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines Conditional Compilation, which is not widely used and not directly supported by the GNU Fortran compiler. You can use the program coco to preprocess such files (http://www.daniellnagle.com/coco.html).

Next: Project Status, Previous: Preprocessing and conditional compilation, Up: Introduction

### 1.4 GNU Fortran and G77

The GNU Fortran compiler is the successor to `g77`, the Fortran 77 front end included in GCC prior to version 4. It is an entirely new program that has been designed to provide Fortran 95 support and extensibility for future Fortran language standards, as well as providing backwards compatibility for Fortran 77 and nearly all of the GNU language extensions supported by `g77`.

Next: Standards, Previous: GNU Fortran and G77, Up: Introduction

### 1.5 Project Status

> As soon as `gfortran` can parse all of the statements correctly, it will be in the “larva” state. When we generate code, the “puppa” state. When `gfortran` is done, we'll see if it will be a beautiful butterfly, or just a big bug....

> –Andy Vaught, April 2000

The start of the GNU Fortran 95 project was announced on the GCC homepage in March 18, 2000 (even though Andy had already been working on it for a while, of course).

The GNU Fortran compiler is able to compile nearly all standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs, including a number of standard and non-standard extensions, and can be used on real-world programs. In particular, the supported extensions include OpenMP, Cray-style pointers, and several Fortran 2003 and Fortran 2008 features, including TR 15581. However, it is still under development and has a few remaining rough edges.

At present, the GNU Fortran compiler passes the NIST Fortran 77 Test Suite, and produces acceptable results on the LAPACK Test Suite. It also provides respectable performance on the Polyhedron Fortran compiler benchmarks and the Livermore Fortran Kernels test. It has been used to compile a number of large real-world programs, including the HIRLAM weather-forecasting code and the Tonto quantum chemistry package; see http://gcc.gnu.org/wiki/GfortranApps for an extended list.

Among other things, the GNU Fortran compiler is intended as a replacement for G77. At this point, nearly all programs that could be compiled with G77 can be compiled with GNU Fortran, although there are a few minor known regressions.

The primary work remaining to be done on GNU Fortran falls into three categories: bug fixing (primarily regarding the treatment of invalid code and providing useful error messages), improving the compiler optimizations and the performance of compiled code, and extending the compiler to support future standards—in particular, Fortran 2003 and Fortran 2008.

Previous: Project Status, Up: Introduction

### 1.6 Standards

The GNU Fortran compiler implements ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all standard-compliant Fortran 90 and Fortran 77 programs. It also supports the ISO/IEC TR-15581 enhancements to allocatable arrays.

GNU Fortran also have a partial support for ISO/IEC 1539-1:2004 (Fortran 2003), ISO/IEC 1539-1:2010 (Fortran 2008), the Technical Specification `Further Interoperability of Fortran with C` (ISO/IEC TS 29113:2012). Full support of those standards and future Fortran standards is planned. The current status of the support is can be found in the Fortran 2003 status, Fortran 2008 status and TS 29113 status sections of the documentation.

Additionally, the GNU Fortran compilers supports the OpenMP specification (version 4.0, http://openmp.org/wp/openmp-specifications/).

Up: Standards

#### 1.6.1 Varying Length Character Strings

The Fortran 95 standard specifies in Part 2 (ISO/IEC 1539-2:2000) varying length character strings. While GNU Fortran currently does not support such strings directly, there exist two Fortran implementations for them, which work with GNU Fortran. They can be found at http://www.fortran.com/iso_varying_string.f95 and at ftp://ftp.nag.co.uk/sc22wg5/ISO_VARYING_STRING/.

Deferred-length character strings of Fortran 2003 supports part of the features of `ISO_VARYING_STRING` and should be considered as replacement. (Namely, allocatable or pointers of the type `character(len=:)`.)

Next: Runtime, Previous: Introduction, Up: Top

## 2 GNU Fortran Command Options

The `gfortran` command supports all the options supported by the `gcc` command. Only options specific to GNU Fortran are documented here.

See GCC Command Options, for information on the non-Fortran-specific aspects of the `gcc` command (and, therefore, the `gfortran` command).

All GCC and GNU Fortran options are accepted both by `gfortran` and by `gcc` (as well as any other drivers built at the same time, such as `g++`), since adding GNU Fortran to the GCC distribution enables acceptance of GNU Fortran 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: Fortran Dialect Options, Up: Invoking GNU Fortran

### 2.1 Option summary

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

Fortran Language Options
  See Options controlling Fortran dialect.

                -fall-intrinsics -fbackslash -fcray-pointer -fd-lines-as-code
                -fd-lines-as-comments -fdefault-double-8 -fdefault-integer-8
                -fdefault-real-8 -fdollar-ok -ffixed-line-length-n
                -ffixed-line-length-none -ffree-form -ffree-line-length-n
                -ffree-line-length-none -fimplicit-none -finteger-4-integer-8
                -fmax-identifier-length -fmodule-private -fno-fixed-form -fno-range-check
                -fopenmp -freal-4-real-10 -freal-4-real-16 -freal-4-real-8
                -freal-8-real-10 -freal-8-real-16 -freal-8-real-4 -std=std

Preprocessing Options
  See Enable and customize preprocessing.

                -A-question[=answer]
                -Aquestion=answer -C -CC -Dmacro[=defn]
                -H -P
                -Umacro -cpp -dD -dI -dM -dN -dU -fworking-directory
                -imultilib dir
                -iprefix file -iquote -isysroot dir -isystem dir -nocpp
                -nostdinc
                -undef

Error and Warning Options
  See Options to request or suppress errors and warnings.

                -Waliasing -Wall -Wampersand -Warray-bounds
                -Wc-binding-type -Wcharacter-truncation
                -Wconversion -Wfunction-elimination -Wimplicit-interface
                -Wimplicit-procedure -Wintrinsic-shadow -Wintrinsics-std
                -Wline-truncation -Wno-align-commons -Wno-tabs -Wreal-q-constant
                -Wsurprising -Wunderflow -Wunused-parameter -Wrealloc-lhs -Wrealloc-lhs-all
                -Wtarget-lifetime -fmax-errors=n -fsyntax-only -pedantic -pedantic-errors

Debugging Options
  See Options for debugging your program or GNU Fortran.

                -fbacktrace -fdump-fortran-optimized -fdump-fortran-original
                -fdump-parse-tree -ffpe-trap=list -ffpe-summary=list

Directory Options
  See Options for directory search.

                -Idir  -Jdir -fintrinsic-modules-path dir

Link Options
  See Options for influencing the linking step.

                -static-libgfortran

Runtime Options
  See Options for influencing runtime behavior.

                -fconvert=conversion -fmax-subrecord-length=length
                -frecord-marker=length -fsign-zero

Code Generation Options
  See Options for code generation conventions.

                -faggressive-function-elimination -fblas-matmul-limit=n
                -fbounds-check -fcheck-array-temporaries
                -fcheck=<all|array-temps|bounds|do|mem|pointer|recursion>
                -fcoarray=<none|single|lib> -fexternal-blas -ff2c
                -ffrontend-optimize
                -finit-character=n -finit-integer=n -finit-local-zero
                -finit-logical=<true|false>
                -finit-real=<zero|inf|-inf|nan|snan>
                -fmax-array-constructor=n -fmax-stack-var-size=n
                -fno-align-commons
                -fno-automatic -fno-protect-parens -fno-underscoring
                -fsecond-underscore -fpack-derived -frealloc-lhs -frecursive
                -frepack-arrays -fshort-enums -fstack-arrays

Next: Preprocessing Options, Previous: Option Summary, Up: Invoking GNU Fortran

### 2.2 Options controlling Fortran dialect

The following options control the details of the Fortran dialect accepted by the compiler:

`-ffree-form`
`-ffixed-form`
  Specify the layout used by the source file. The free form layout was introduced in Fortran 90. Fixed form was traditionally used in older Fortran programs. When neither option is specified, the source form is determined by the file extension.
`-fall-intrinsics`
  This option causes all intrinsic procedures (including the GNU-specific extensions) to be accepted. This can be useful with `-std=f95` to force standard-compliance but get access to the full range of intrinsics available with `gfortran`. As a consequence, `-Wintrinsics-std` will be ignored and no user-defined procedure with the same name as any intrinsic will be called except when it is explicitly declared `EXTERNAL`.
`-fd-lines-as-code`
`-fd-lines-as-comments`
  Enable special treatment for lines beginning with `d` or `D` in fixed form sources. If the `-fd-lines-as-code` option is given they are treated as if the first column contained a blank. If the `-fd-lines-as-comments` option is given, they are treated as comment lines.
`-fdollar-ok`
  Allow ``$`' as a valid non-first character in a symbol name. Symbols that start with ``$`' are rejected since it is unclear which rules to apply to implicit typing as different vendors implement different rules. Using ``$`' in `IMPLICIT` statements is also rejected.
`-fbackslash`
  Change the interpretation of backslashes in string literals from a single backslash character to “C-style” escape characters. The following combinations are expanded `\a`, `\b`, `\f`, `\n`, `\r`, `\t`, `\v`, `\\`, and `\0` to the ASCII characters alert, backspace, form feed, newline, carriage return, horizontal tab, vertical tab, backslash, and NUL, respectively. Additionally, `\x` nn, `\u` nnnn and `\U` nnnnnnnn (where each n is a hexadecimal digit) are translated into the Unicode characters corresponding to the specified code points. All other combinations of a character preceded by \ are unexpanded.
`-fmodule-private`
  Set the default accessibility of module entities to `PRIVATE`. Use-associated entities will not be accessible unless they are explicitly declared as `PUBLIC`.
`-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 (corresponding to “extended-source” options in some popular compilers). n may also 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`.

`-ffree-line-length-`n
  Set column after which characters are ignored in typical free-form lines in the source file. The default value is 132. n may be ``none`', meaning that the entire line is meaningful. `-ffree-line-length-0` means the same thing as `-ffree-line-length-none`.
`-fmax-identifier-length=`n
  Specify the maximum allowed identifier length. Typical values are 31 (Fortran 95) and 63 (Fortran 2003 and Fortran 2008).
`-fimplicit-none`
  Specify that no implicit typing is allowed, unless overridden by explicit `IMPLICIT` statements. This is the equivalent of adding `implicit none` to the start of every procedure.
`-fcray-pointer`
  Enable the Cray pointer extension, which provides C-like pointer functionality.
`-fopenmp`
  Enable the OpenMP extensions. This includes OpenMP `!$omp` directives in free form and `c$omp`, `*$omp` and `!$omp` directives in fixed form, `!$` conditional compilation sentinels in free form and `c$`, `*$` and `!$` sentinels in fixed form, and when linking arranges for the OpenMP runtime library to be linked in. The option `-fopenmp` implies `-frecursive`.
`-fno-range-check`
  Disable range checking on results of simplification of constant expressions during compilation. For example, GNU Fortran will give an error at compile time when simplifying `a = 1. / 0`. With this option, no error will be given and `a` will be assigned the value `+Infinity`. If an expression evaluates to a value outside of the relevant range of [`-HUGE()`:`HUGE()`], then the expression will be replaced by `-Inf` or `+Inf` as appropriate. Similarly, `DATA i/Z'FFFFFFFF'/` will result in an integer overflow on most systems, but with `-fno-range-check` the value will “wrap around” and `i` will be initialized to -1 instead.
`-fdefault-integer-8`
  Set the default integer and logical types to an 8 byte wide type. This option also affects the kind of integer constants like `42`. Unlike `-finteger-4-integer-8`, it does not promote variables with explicit kind declaration.
`-fdefault-real-8`
  Set the default real type to an 8 byte wide type. This option also affects the kind of non-double real constants like `1.0`, and does promote the default width of `DOUBLE PRECISION` to 16 bytes if possible, unless `-fdefault-double-8` is given, too. Unlike `-freal-4-real-8`, it does not promote variables with explicit kind declaration.
`-fdefault-double-8`
  Set the `DOUBLE PRECISION` type to an 8 byte wide type. Do nothing if this is already the default. If `-fdefault-real-8` is given, `DOUBLE PRECISION` would instead be promoted to 16 bytes if possible, and `-fdefault-double-8` can be used to prevent this. The kind of real constants like `1.d0` will not be changed by `-fdefault-real-8` though, so also `-fdefault-double-8` does not affect it.
`-finteger-4-integer-8`
  Promote all `INTEGER(KIND=4)` entities to an `INTEGER(KIND=8)` entities. If `KIND=8` is unavailable, then an error will be issued. This option should be used with care and may not be suitable for your codes. Areas of possible concern include calls to external procedures, alignment in `EQUIVALENCE` and/or `COMMON`, generic interfaces, BOZ literal constant conversion, and I/O. Inspection of the intermediate representation of the translated Fortran code, produced by `-fdump-tree-original`, is suggested.
`-freal-4-real-8`
`-freal-4-real-10`
`-freal-4-real-16`
`-freal-8-real-4`
`-freal-8-real-10`
`-freal-8-real-16`
  Promote all `REAL(KIND=M)` entities to `REAL(KIND=N)` entities. If `REAL(KIND=N)` is unavailable, then an error will be issued. All other real kind types are unaffected by this option. These options should be used with care and may not be suitable for your codes. Areas of possible concern include calls to external procedures, alignment in `EQUIVALENCE` and/or `COMMON`, generic interfaces, BOZ literal constant conversion, and I/O. Inspection of the intermediate representation of the translated Fortran code, produced by `-fdump-tree-original`, is suggested.
`-std=`std
  Specify the standard to which the program is expected to conform, which may be one of ``f95`', ``f2003`', ``f2008`', ``gnu`', or ``legacy`'. The default value for std is ``gnu`', which specifies a superset of the Fortran 95 standard that includes all of the extensions supported by GNU Fortran, although warnings will be given for obsolete extensions not recommended for use in new code. The ``legacy`' value is equivalent but without the warnings for obsolete extensions, and may be useful for old non-standard programs. The ``f95`', ``f2003`' and ``f2008`' values specify strict conformance to the Fortran 95, Fortran 2003 and Fortran 2008 standards, respectively; errors are given for all extensions beyond the relevant language standard, and warnings are given for the Fortran 77 features that are permitted but obsolescent in later standards. ``-std=f2008ts`' allows the Fortran 2008 standard including the additions of the Technical Specification (TS) 29113 on Further Interoperability of Fortran with C.

Next: Error and Warning Options, Previous: Fortran Dialect Options, Up: Invoking GNU Fortran

### 2.3 Enable and customize preprocessing

Preprocessor related options. See section Preprocessing and conditional compilation for more detailed information on preprocessing in `gfortran`.

`-cpp`
`-nocpp`
  Enable preprocessing. The preprocessor is automatically invoked if the file extension is `.fpp`, `.FPP`, `.F`, `.FOR`, `.FTN`, `.F90`, `.F95`, `.F03` or `.F08`. Use this option to manually enable preprocessing of any kind of Fortran file.

  To disable preprocessing of files with any of the above listed extensions, use the negative form: `-nocpp`.

  The preprocessor is run in traditional mode. Any restrictions of the file-format, especially the limits on line length, apply for preprocessed output as well, so it might be advisable to use the `-ffree-line-length-none` or `-ffixed-line-length-none` options.

`-dM`
  Instead of the normal output, generate a list of `'#define'` directives for all the macros defined during the execution of the preprocessor, including predefined macros. This gives you a way of finding out what is predefined in your version of the preprocessor. Assuming you have no file `foo.f90`, the command

                  touch foo.f90; gfortran -cpp -E -dM foo.f90

  will show all the predefined macros.

`-dD`
  Like `-dM` except in two respects: it does not include the predefined macros, and it outputs both the `#define` directives and the result of preprocessing. Both kinds of output go to the standard output file.
`-dN`
  Like `-dD`, but emit only the macro names, not their expansions.
`-dU`
  Like `dD` except that only macros that are expanded, or whose definedness is tested in preprocessor directives, are output; the output is delayed until the use or test of the macro; and `'#undef'` directives are also output for macros tested but undefined at the time.
`-dI`
  Output `'#include'` directives in addition to the result of preprocessing.
`-fworking-directory`
  Enable generation of linemarkers in the preprocessor output that will let the compiler know the current working directory at the time of preprocessing. When this option is enabled, the preprocessor will emit, after the initial linemarker, a second linemarker with the current working directory followed by two slashes. GCC will use this directory, when it is present in the preprocessed input, as the directory emitted as the current working directory in some debugging information formats. This option is implicitly enabled if debugging information is enabled, but this can be inhibited with the negated form `-fno-working-directory`. If the `-P` flag is present in the command line, this option has no effect, since no `#line` directives are emitted whatsoever.
`-idirafter` dir
  Search dir for include files, but do it after all directories specified with `-I` and the standard system directories have been exhausted. dir is treated as a system include directory. If dir begins with `=`, then the `=` will be replaced by the sysroot prefix; see `--sysroot` and `-isysroot`.
`-imultilib` dir
  Use dir as a subdirectory of the directory containing target-specific C++ headers.
`-iprefix` prefix
  Specify prefix as the prefix for subsequent `-iwithprefix` options. If the prefix represents a directory, you should include the final `'/'`.
`-isysroot` dir
  This option is like the `--sysroot` option, but applies only to header files. See the `--sysroot` option for more information.
`-iquote` dir
  Search dir only for header files requested with `#include "file"`; they are not searched for `#include <file>`, before all directories specified by `-I` and before the standard system directories. If dir begins with `=`, then the `=` will be replaced by the sysroot prefix; see `--sysroot` and `-isysroot`.
`-isystem` dir
  Search dir for header files, after all directories specified by `-I` but before the standard system directories. Mark it as a system directory, so that it gets the same special treatment as is applied to the standard system directories. If dir begins with `=`, then the `=` will be replaced by the sysroot prefix; see `--sysroot` and `-isysroot`.
`-nostdinc`
  Do not search the standard system directories for header files. Only the directories you have specified with `-I` options (and the directory of the current file, if appropriate) are searched.
`-undef`
  Do not predefine any system-specific or GCC-specific macros. The standard predefined macros remain defined.
`-A` predicate`=`answer
  Make an assertion with the predicate predicate and answer answer. This form is preferred to the older form -A predicate(answer), which is still supported, because it does not use shell special characters.
`-A-`predicate`=`answer
  Cancel an assertion with the predicate predicate and answer answer.
`-C`
  Do not discard comments. All comments are passed through to the output file, except for comments in processed directives, which are deleted along with the directive.

  You should be prepared for side effects when using `-C`; it causes the preprocessor to treat comments as tokens in their own right. For example, comments appearing at the start of what would be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no longer a `'#'`.

  Warning: this currently handles C-Style comments only. The preprocessor does not yet recognize Fortran-style comments.

`-CC`
  Do not discard comments, including during macro expansion. This is like `-C`, except that comments contained within macros are also passed through to the output file where the macro is expanded.

  In addition to the side-effects of the `-C` option, the `-CC` option causes all C++-style comments inside a macro to be converted to C-style comments. This is to prevent later use of that macro from inadvertently commenting out the remainder of the source line. The `-CC` option is generally used to support lint comments.

  Warning: this currently handles C- and C++-Style comments only. The preprocessor does not yet recognize Fortran-style comments.

`-D` name
  Predefine name as a macro, with definition `1`.
`-D` name`=`definition
  The contents of definition are tokenized and processed as if they appeared during translation phase three in a `'#define'` directive. In particular, the definition will be truncated by embedded newline characters.

  If you are invoking the preprocessor from a shell or shell-like program you may need to use the shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax.

  If you wish to define a function-like macro on the command line, write its argument list with surrounding parentheses before the equals sign (if any). Parentheses are meaningful to most shells, so you will need to quote the option. With sh and csh, `-D'name(args...)=definition'` works.

  `-D` and `-U` options are processed in the order they are given on the command line. All -imacros file and -include file options are processed after all -D and -U options.

`-H`
  Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the `'#include'` stack it is.
`-P`
  Inhibit generation of linemarkers in the output from the preprocessor. This might be useful when running the preprocessor on something that is not C code, and will be sent to a program which might be confused by the linemarkers.
`-U` name
  Cancel any previous definition of name, either built in or provided with a `-D` option.

Next: Debugging Options, Previous: Preprocessing Options, Up: Invoking GNU Fortran

### 2.4 Options to request or suppress errors and warnings

Errors are diagnostic messages that report that the GNU Fortran compiler cannot compile the relevant piece of source code. The compiler will continue to process the program in an attempt to report further errors to aid in debugging, but will not produce any compiled output.

Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there is likely to be a bug in the program. Unless `-Werror` is specified, they do not prevent compilation of the program.

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 errors and warnings produced by GNU Fortran:

`-fmax-errors=`n
  Limits the maximum number of error messages to n, at which point GNU Fortran bails out rather than attempting to continue processing the source code. If n is 0, there is no limit on the number of error messages produced.
`-fsyntax-only`
  Check the code for syntax errors, but do not actually compile it. This will generate module files for each module present in the code, but no other output file.
`-pedantic`
  Issue warnings for uses of extensions to Fortran 95. `-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 Fortran 95 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 conformance. They soon find that it does not do quite what they want—it finds some nonstandard practices, but not all. However, improvements to GNU Fortran in this area are welcome.

  This should be used in conjunction with `-std=f95`, `-std=f2003` or `-std=f2008`.

`-pedantic-errors`
  Like `-pedantic`, except that errors are produced rather than warnings.
`-Wall`
  Enables commonly used warning options pertaining to usage that we recommend avoiding and that we believe are easy to avoid. This currently includes `-Waliasing`, `-Wampersand`, `-Wconversion`, `-Wsurprising`, `-Wc-binding-type`, `-Wintrinsics-std`, `-Wno-tabs`, `-Wintrinsic-shadow`, `-Wline-truncation`, `-Wtarget-lifetime`, `-Wreal-q-constant` and `-Wunused`.
`-Waliasing`
  Warn about possible aliasing of dummy arguments. Specifically, it warns if the same actual argument is associated with a dummy argument with `INTENT(IN)` and a dummy argument with `INTENT(OUT)` in a call with an explicit interface.

  The following example will trigger the warning.

                  interface
                    subroutine bar(a,b)
                      integer, intent(in) :: a
                      integer, intent(out) :: b
                    end subroutine
                  end interface
                  integer :: a

                  call bar(a,a)

`-Wampersand`
  Warn about missing ampersand in continued character constants. The warning is given with `-Wampersand`, `-pedantic`, `-std=f95`, `-std=f2003` and `-std=f2008`. Note: With no ampersand given in a continued character constant, GNU Fortran assumes continuation at the first non-comment, non-whitespace character after the ampersand that initiated the continuation.
`-Warray-temporaries`
  Warn about array temporaries generated by the compiler. The information generated by this warning is sometimes useful in optimization, in order to avoid such temporaries.
`-Wc-binding-type`
  Warn if the a variable might not be C interoperable. In particular, warn if the variable has been declared using an intrinsic type with default kind instead of using a kind parameter defined for C interoperability in the intrinsic `ISO_C_Binding` module. This option is implied by `-Wall`.
`-Wcharacter-truncation`
  Warn when a character assignment will truncate the assigned string.
`-Wline-truncation`
  Warn when a source code line will be truncated. This option is implied by `-Wall`.
`-Wconversion`
  Warn about implicit conversions that are likely to change the value of the expression after conversion. Implied by `-Wall`.
`-Wconversion-extra`
  Warn about implicit conversions between different types and kinds.
`-Wextra`
  Enables some warning options for usages of language features which may be problematic. This currently includes `-Wcompare-reals` and `-Wunused-parameter`.
`-Wimplicit-interface`
  Warn if a procedure is called without an explicit interface. Note this only checks that an explicit interface is present. It does not check that the declared interfaces are consistent across program units.
`-Wimplicit-procedure`
  Warn if a procedure is called that has neither an explicit interface nor has been declared as `EXTERNAL`.
`-Wintrinsics-std`
  Warn if `gfortran` finds a procedure named like an intrinsic not available in the currently selected standard (with `-std`) and treats it as `EXTERNAL` procedure because of this. `-fall-intrinsics` can be used to never trigger this behavior and always link to the intrinsic regardless of the selected standard.
`-Wreal-q-constant`
  Produce a warning if a real-literal-constant contains a `q` exponent-letter.
`-Wsurprising`
  Produce a warning when “suspicious” code constructs are encountered. While technically legal these usually indicate that an error has been made.

  This currently produces a warning under the following circumstances:

  - An INTEGER SELECT construct has a CASE that can never be matched as its lower value is greater than its upper value.
  - A LOGICAL SELECT construct has three CASE statements.
  - A TRANSFER specifies a source that is shorter than the destination.
  - The type of a function result is declared more than once with the same type. If `-pedantic` or standard-conforming mode is enabled, this is an error.
  - A `CHARACTER` variable is declared with negative length.
`-Wtabs`
  By default, tabs are accepted as whitespace, but tabs are not members of the Fortran Character Set. For continuation lines, a tab followed by a digit between 1 and 9 is supported. `-Wno-tabs` will cause a warning to be issued if a tab is encountered. Note, `-Wno-tabs` is active for `-pedantic`, `-std=f95`, `-std=f2003`, `-std=f2008` and `-Wall`.
`-Wunderflow`
  Produce a warning when numerical constant expressions are encountered, which yield an UNDERFLOW during compilation.
`-Wintrinsic-shadow`
  Warn if a user-defined procedure or module procedure has the same name as an intrinsic; in this case, an explicit interface or `EXTERNAL` or `INTRINSIC` declaration might be needed to get calls later resolved to the desired intrinsic/procedure. This option is implied by `-Wall`.
`-Wunused-dummy-argument`
  Warn about unused dummy arguments. This option is implied by `-Wall`.
`-Wunused-parameter`
  Contrary to `gcc`'s meaning of `-Wunused-parameter`, `gfortran`'s implementation of this option does not warn about unused dummy arguments (see `-Wunused-dummy-argument`), but about unused `PARAMETER` values. `-Wunused-parameter` is not included in `-Wall` but is implied by `-Wall -Wextra`.
`-Walign-commons`
  By default, `gfortran` warns about any occasion of variables being padded for proper alignment inside a `COMMON` block. This warning can be turned off via `-Wno-align-commons`. See also `-falign-commons`.
`-Wfunction-elimination`
  Warn if any calls to functions are eliminated by the optimizations enabled by the `-ffrontend-optimize` option.
`-Wrealloc-lhs`
  Warn when the compiler might insert code to for allocation or reallocation of an allocatable array variable of intrinsic type in intrinsic assignments. In hot loops, the Fortran 2003 reallocation feature may reduce the performance. If the array is already allocated with the correct shape, consider using a whole-array array-spec (e.g. `(:,:,:)`) for the variable on the left-hand side to prevent the reallocation check. Note that in some cases the warning is shown, even if the compiler will optimize reallocation checks away. For instance, when the right-hand side contains the same variable multiplied by a scalar. See also `-frealloc-lhs`.
`-Wrealloc-lhs-all`
  Warn when the compiler inserts code to for allocation or reallocation of an allocatable variable; this includes scalars and derived types.
`-Wcompare-reals`
  Warn when comparing real or complex types for equality or inequality. This option is implied by `-Wextra`.
`-Wtarget-lifetime`
  Warn if the pointer in a pointer assignment might be longer than the its target. This option is implied by `-Wall`.
`-Wzerotrip`
  Warn if a `DO` loop is known to execute zero times at compile time. This option is implied by `-Wall`.
`-Werror`
  Turns all warnings into errors.

See Options to Request or Suppress Errors and Warnings, for information on more options offered by the GBE shared by `gfortran`, `gcc` and other GNU compilers.

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

Next: Directory Options, Previous: Error and Warning Options, Up: Invoking GNU Fortran

### 2.5 Options for debugging your program or GNU Fortran

GNU Fortran has various special options that are used for debugging either your program or the GNU Fortran compiler.

`-fdump-fortran-original`
  Output the internal parse tree after translating the source program into internal representation. Only really useful for debugging the GNU Fortran compiler itself.
`-fdump-fortran-optimized`
  Output the parse tree after front-end optimization. Only really useful for debugging the GNU Fortran compiler itself.
`-fdump-parse-tree`
  Output the internal parse tree after translating the source program into internal representation. Only really useful for debugging the GNU Fortran compiler itself. This option is deprecated; use `-fdump-fortran-original` instead.
`-ffpe-trap=`list
  Specify a list of floating point exception traps to enable. On most systems, if a floating point exception occurs and the trap for that exception is enabled, a SIGFPE signal will be sent and the program being aborted, producing a core file useful for debugging. list is a (possibly empty) comma-separated list of the following exceptions: ``invalid`' (invalid floating point operation, such as `SQRT(-1.0)`), ``zero`' (division by zero), ``overflow`' (overflow in a floating point operation), ``underflow`' (underflow in a floating point operation), ``inexact`' (loss of precision during operation), and ``denormal`' (operation performed on a denormal value). The first five exceptions correspond to the five IEEE 754 exceptions, whereas the last one (``denormal`') is not part of the IEEE 754 standard but is available on some common architectures such as x86.

  The first three exceptions (``invalid`', ``zero`', and ``overflow`') often indicate serious errors, and unless the program has provisions for dealing with these exceptions, enabling traps for these three exceptions is probably a good idea.

  Many, if not most, floating point operations incur loss of precision due to rounding, and hence the `ffpe-trap=inexact` is likely to be uninteresting in practice.

  By default no exception traps are enabled.

`-ffpe-summary=`list
  Specify a list of floating-point exceptions, whose flag status is printed to `ERROR_UNIT` when invoking `STOP` and `ERROR STOP`. list can be either ``none`', ``all`' or a comma-separated list of the following exceptions: ``invalid`', ``zero`', ``overflow`', ``underflow`', ``inexact`' and ``denormal`'. (See `-ffpe-trap` for a description of the exceptions.)

  By default, a summary for all exceptions but ``inexact`' is shown.

`-fno-backtrace`
  When a serious runtime error is encountered or a deadly signal is emitted (segmentation fault, illegal instruction, bus error, floating-point exception, and the other POSIX signals that have the action ``core`'), the Fortran runtime library tries to output a backtrace of the error. `-fno-backtrace` disables the backtrace generation. This option only has influence for compilation of the Fortran main program.

See Options for Debugging Your Program or GCC, for more information on debugging options.

Next: Link Options, Previous: Debugging Options, Up: Invoking GNU Fortran

### 2.6 Options for directory search

These options affect how GNU Fortran searches for files specified by the `INCLUDE` directive and where it searches for previously compiled modules.

It also affects the search paths used by `cpp` when used to preprocess Fortran source.

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

  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.

  This path is also used to search for `.mod` files when previously compiled modules are required by a `USE` statement.

  See Options for Directory Search, for information on the `-I` option.

`-J` dir
  This option specifies where to put `.mod` files for compiled modules. It is also added to the list of directories to searched by an `USE` statement.

  The default is the current directory.

`-fintrinsic-modules-path` dir
  This option specifies the location of pre-compiled intrinsic modules, if they are not in the default location expected by the compiler.

Next: Runtime Options, Previous: Directory Options, Up: Invoking GNU Fortran

### 2.7 Influencing the linking step

These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step.

`-static-libgfortran`
  On systems that provide `libgfortran` as a shared and a static library, this option forces the use of the static version. If no shared version of `libgfortran` was built when the compiler was configured, this option has no effect.

Next: Code Gen Options, Previous: Link Options, Up: Invoking GNU Fortran

### 2.8 Influencing runtime behavior

These options affect the runtime behavior of programs compiled with GNU Fortran.

`-fconvert=`conversion
  Specify the representation of data for unformatted files. Valid values for conversion are: ``native`', the default; ``swap`', swap between big- and little-endian; ``big-endian`', use big-endian representation for unformatted files; ``little-endian`', use little-endian representation for unformatted files.

  This option has an effect only when used in the main program. The `CONVERT` specifier and the GFORTRAN_CONVERT_UNIT environment variable override the default specified by ``-fconvert.

`-frecord-marker=`length
  Specify the length of record markers for unformatted files. Valid values for length are 4 and 8. Default is 4. This is different from previous versions of ``gfortran, which specified a default record marker length of 8 on most systems. If you want to read or write files compatible with earlier versions of `gfortran`, use `-frecord-marker=8`.
`-fmax-subrecord-length=`length
  Specify the maximum length for a subrecord. The maximum permitted value for length is 2147483639, which is also the default. Only really useful for use by the gfortran testsuite.
`-fsign-zero`
  When enabled, floating point numbers of value zero with the sign bit set are written as negative number in formatted output and treated as negative in the `SIGN` intrinsic. `-fno-sign-zero` does not print the negative sign of zero values (or values rounded to zero for I/O) and regards zero as positive number in the `SIGN` intrinsic for compatibility with Fortran 77. The default is `-fsign-zero`.

Next: Environment Variables, Previous: Runtime Options, Up: Invoking GNU Fortran

### 2.9 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 (except those marked as RECURSIVE) as if the `SAVE` statement were 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` or `-save`.) The default, which is `-fautomatic`, uses the stack for local variables smaller than the value given by `-fmax-stack-var-size`. Use the option `-frecursive` to use no static memory.
`-ff2c`
  Generate code designed to be compatible with code generated by `g77` and `f2c`.

  The calling conventions used by `g77` (originally implemented in `f2c`) require functions that return type default `REAL` 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 default GNU calling conventions, such functions simply return their results as they would in GNU C—default `REAL` functions return the C type `float`, and `COMPLEX` functions return the GNU C type `complex`. Additionally, this option implies the `-fsecond-underscore` option, unless `-fno-second-underscore` is explicitly requested.

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

  Caution: It is not a good idea to mix Fortran code compiled with `-ff2c` with code compiled with the default `-fno-f2c` calling conventions as, calling `COMPLEX` or default `REAL` functions between program parts which were compiled with different calling conventions will break at execution time.

  Caution: This will break code which passes intrinsic functions of type default `REAL` or `COMPLEX` as actual arguments, as the library implementations use the `-fno-f2c` calling conventions.

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

  With `-funderscoring` in effect, GNU Fortran appends one underscore to external names with no underscores. This is done to ensure compatibility with code produced by many UNIX Fortran compilers.

  Caution: The default behavior of GNU Fortran is incompatible with `f2c` and `g77`, please use the `-ff2c` option if you want object files compiled with GNU Fortran to be compatible with object code created with these tools.

  Use of `-fno-underscoring` is not recommended unless you are experimenting with issues such as integration of GNU Fortran into existing system environments (vis-à-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 GNU Fortran code with other languages.

  Note that just because the names match does not mean that the interface implemented by GNU Fortran for an external name matches the interface implemented by some other language for that same name. That is, getting code produced by GNU Fortran 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 GNU Fortran 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.

`-fsecond-underscore`
  By default, GNU Fortran appends an underscore to external names. If this option is used GNU Fortran appends two underscores to names with underscores and one underscore to external names with no underscores. GNU Fortran also appends two underscores to internal names with underscores to avoid naming collisions with external names.

  This option has no effect if `-fno-underscoring` is in effect. It is implied by the `-ff2c` option.

  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_`. This is required for compatibility with `g77` and `f2c`, and is implied by use of the `-ff2c` option.

`-fcoarray=`<keyword>
  ``none`'
    Disable coarray support; using coarray declarations and image-control statements will produce a compile-time error. (Default)
  ``single`'
    Single-image mode, i.e. `num_images()` is always one.
  ``lib`'
    Library-based coarray parallelization; a suitable GNU Fortran coarray library needs to be linked.
`-fcheck=`<keyword>
  Enable the generation of run-time checks; the argument shall be a comma-delimited list of the following keywords.
  ``all`'
    Enable all run-time test of `-fcheck`.
  ``array-temps`'
    Warns at run time when for passing an actual argument a temporary array had to be generated. The information generated by this warning is sometimes useful in optimization, in order to avoid such temporaries.

    Note: The warning is only printed once per location.

  ``bounds`'
    Enable generation of run-time checks for array subscripts and against the declared minimum and maximum values. It also checks array indices for assumed and deferred shape arrays against the actual allocated bounds and ensures that all string lengths are equal for character array constructors without an explicit typespec.

    Some checks require that `-fcheck=bounds` is set for the compilation of the main program.

    Note: In the future this may also include other forms of checking, e.g., checking substring references.

  ``do`'
    Enable generation of run-time checks for invalid modification of loop iteration variables.
  ``mem`'
    Enable generation of run-time checks for memory allocation. Note: This option does not affect explicit allocations using the `ALLOCATE` statement, which will be always checked.
  ``pointer`'
    Enable generation of run-time checks for pointers and allocatables.
  ``recursion`'
    Enable generation of run-time checks for recursively called subroutines and functions which are not marked as recursive. See also `-frecursive`. Note: This check does not work for OpenMP programs and is disabled if used together with `-frecursive` and `-fopenmp`.
`-fbounds-check`
  Deprecated alias for `-fcheck=bounds`.
`-fcheck-array-temporaries`
  Deprecated alias for `-fcheck=array-temps`.
`-fmax-array-constructor=`n
  This option can be used to increase the upper limit permitted in array constructors. The code below requires this option to expand the array at compile time.

                program test
                implicit none
                integer j
                integer, parameter :: n = 100000
                integer, parameter :: i(n) = (/ (2*j, j = 1, n) /)
                print '(10(I0,1X))', i
                end program test

  Caution: This option can lead to long compile times and excessively large object files.

  The default value for n is 65535.

`-fmax-stack-var-size=`n
  This option specifies the size in bytes of the largest array that will be put on the stack; if the size is exceeded static memory is used (except in procedures marked as RECURSIVE). Use the option `-frecursive` to allow for recursive procedures which do not have a RECURSIVE attribute or for parallel programs. Use `-fno-automatic` to never use the stack.

  This option currently only affects local arrays declared with constant bounds, and may not apply to all character variables. Future versions of GNU Fortran may improve this behavior.

  The default value for n is 32768.

`-fstack-arrays`
  Adding this option will make the Fortran compiler put all local arrays, even those of unknown size onto stack memory. If your program uses very large local arrays it is possible that you will have to extend your runtime limits for stack memory on some operating systems. This flag is enabled by default at optimization level `-Ofast`.
`-fpack-derived`
  This option tells GNU Fortran to pack derived type members as closely as possible. Code compiled with this option is likely to be incompatible with code compiled without this option, and may execute slower.
`-frepack-arrays`
  In some circumstances GNU Fortran may pass assumed shape array sections via a descriptor describing a noncontiguous area of memory. This option adds code to the function prologue to repack the data into a contiguous block at runtime.

  This should result in faster accesses to the array. However it can introduce significant overhead to the function call, especially when the passed data is noncontiguous.

`-fshort-enums`
  This option is provided for interoperability with C code that was compiled with the `-fshort-enums` option. It will make GNU Fortran choose the smallest `INTEGER` kind a given enumerator set will fit in, and give all its enumerators this kind.
`-fexternal-blas`
  This option will make `gfortran` generate calls to BLAS functions for some matrix operations like `MATMUL`, instead of using our own algorithms, if the size of the matrices involved is larger than a given limit (see `-fblas-matmul-limit`). This may be profitable if an optimized vendor BLAS library is available. The BLAS library will have to be specified at link time.
`-fblas-matmul-limit=`n
  Only significant when `-fexternal-blas` is in effect. Matrix multiplication of matrices with size larger than (or equal to) n will be performed by calls to BLAS functions, while others will be handled by `gfortran` internal algorithms. If the matrices involved are not square, the size comparison is performed using the geometric mean of the dimensions of the argument and result matrices.

  The default value for n is 30.

`-frecursive`
  Allow indirect recursion by forcing all local arrays to be allocated on the stack. This flag cannot be used together with `-fmax-stack-var-size=` or `-fno-automatic`.
`-finit-local-zero`
`-finit-integer=`n
`-finit-real=`<zero|inf|-inf|nan|snan>
`-finit-logical=`<true|false>
`-finit-character=`n
  The `-finit-local-zero` option instructs the compiler to initialize local `INTEGER`, `REAL`, and `COMPLEX` variables to zero, `LOGICAL` variables to false, and `CHARACTER` variables to a string of null bytes. Finer-grained initialization options are provided by the `-finit-integer=n`, `-finit-real=<zero|inf|-inf|nan|snan>` (which also initializes the real and imaginary parts of local `COMPLEX` variables), `-finit-logical=<true|false>`, and `-finit-character=n` (where n is an ASCII character value) options. These options do not initialize
  - allocatable arrays
  - components of derived type variables
  - variables that appear in an `EQUIVALENCE` statement.
  (These limitations may be removed in future releases).

  Note that the `-finit-real=nan` option initializes `REAL` and `COMPLEX` variables with a quiet NaN. For a signalling NaN use `-finit-real=snan`; note, however, that compile-time optimizations may convert them into quiet NaN and that trapping needs to be enabled (e.g. via `-ffpe-trap`).

  Finally, note that enabling any of the `-finit-*` options will silence warnings that would have been emitted by `-Wuninitialized` for the affected local variables.

`-falign-commons`
  By default, `gfortran` enforces proper alignment of all variables in a `COMMON` block by padding them as needed. On certain platforms this is mandatory, on others it increases performance. If a `COMMON` block is not declared with consistent data types everywhere, this padding can cause trouble, and `-fno-align-commons` can be used to disable automatic alignment. The same form of this option should be used for all files that share a `COMMON` block. To avoid potential alignment issues in `COMMON` blocks, it is recommended to order objects from largest to smallest.
`-fno-protect-parens`
  By default the parentheses in expression are honored for all optimization levels such that the compiler does not do any re-association. Using `-fno-protect-parens` allows the compiler to reorder `REAL` and `COMPLEX` expressions to produce faster code. Note that for the re-association optimization `-fno-signed-zeros` and `-fno-trapping-math` need to be in effect. The parentheses protection is enabled by default, unless `-Ofast` is given.
`-frealloc-lhs`
  An allocatable left-hand side of an intrinsic assignment is automatically (re)allocated if it is either unallocated or has a different shape. The option is enabled by default except when `-std=f95` is given. See also `-Wrealloc-lhs`.
`-faggressive-function-elimination`
  Functions with identical argument lists are eliminated within statements, regardless of whether these functions are marked `PURE` or not. For example, in

                  a = f(b,c) + f(b,c)

  there will only be a single call to `f`. This option only works if `-ffrontend-optimize` is in effect.

`-ffrontend-optimize`
  This option performs front-end optimization, based on manipulating parts the Fortran parse tree. Enabled by default by any `-O` option. Optimizations enabled by this option include elimination of identical function calls within expressions, removing unnecessary calls to `TRIM` in comparisons and assignments and replacing `TRIM(a)` with `a(1:LEN_TRIM(a))`. It can be deselected by specifying `-fno-frontend-optimize`.

See Options for Code Generation Conventions, for information on more options offered by the GBE shared by `gfortran`, `gcc`, and other GNU compilers.

Previous: Code Gen Options, Up: Invoking GNU Fortran

### 2.10 Environment variables affecting `gfortran`

The `gfortran` compiler 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, for information on environment variables.

See Runtime, for environment variables that affect the run-time behavior of programs compiled with GNU Fortran.

Next: Fortran 2003 and 2008 status, Previous: Invoking GNU Fortran, Up: Top

## 3 Runtime: Influencing runtime behavior with environment variables

The behavior of the `gfortran` can be influenced by environment variables.

Malformed environment variables are silently ignored.

Next: GFORTRAN_STDIN_UNIT, Up: Runtime

### 3.1 `TMPDIR`—Directory for scratch files

When opening a file with `STATUS='SCRATCH'`, GNU Fortran tries to create the file in one of the potential directories by testing each directory in the order below.

1. The environment variable `TMPDIR`, if it exists.
2. On the MinGW target, the directory returned by the `GetTempPath` function. Alternatively, on the Cygwin target, the `TMP` and `TEMP` environment variables, if they exist, in that order.
3. The `P_tmpdir` macro if it is defined, otherwise the directory `/tmp`.

Next: GFORTRAN_STDOUT_UNIT, Previous: TMPDIR, Up: Runtime

### 3.2 `GFORTRAN_STDIN_UNIT`—Unit number for standard input

This environment variable can be used to select the unit number preconnected to standard input. This must be a positive integer. The default value is 5.

Next: GFORTRAN_STDERR_UNIT, Previous: GFORTRAN_STDIN_UNIT, Up: Runtime

### 3.3 `GFORTRAN_STDOUT_UNIT`—Unit number for standard output

This environment variable can be used to select the unit number preconnected to standard output. This must be a positive integer. The default value is 6.

Next: GFORTRAN_UNBUFFERED_ALL, Previous: GFORTRAN_STDOUT_UNIT, Up: Runtime

### 3.4 `GFORTRAN_STDERR_UNIT`—Unit number for standard error

This environment variable can be used to select the unit number preconnected to standard error. This must be a positive integer. The default value is 0.

Next: GFORTRAN_UNBUFFERED_PRECONNECTED, Previous: GFORTRAN_STDERR_UNIT, Up: Runtime

### 3.5 `GFORTRAN_UNBUFFERED_ALL`—Do not buffer I/O on all units

This environment variable controls whether all I/O is unbuffered. If the first letter is ``y`', ``Y`' or ``1`', all I/O is unbuffered. This will slow down small sequential reads and writes. If the first letter is ``n`', ``N`' or ``0`', I/O is buffered. This is the default.

Next: GFORTRAN_SHOW_LOCUS, Previous: GFORTRAN_UNBUFFERED_ALL, Up: Runtime

### 3.6 `GFORTRAN_UNBUFFERED_PRECONNECTED`—Do not buffer I/O on preconnected units

The environment variable named `GFORTRAN_UNBUFFERED_PRECONNECTED` controls whether I/O on a preconnected unit (i.e. STDOUT or STDERR) is unbuffered. If the first letter is ``y`', ``Y`' or ``1`', I/O is unbuffered. This will slow down small sequential reads and writes. If the first letter is ``n`', ``N`' or ``0`', I/O is buffered. This is the default.

Next: GFORTRAN_OPTIONAL_PLUS, Previous: GFORTRAN_UNBUFFERED_PRECONNECTED, Up: Runtime

### 3.7 `GFORTRAN_SHOW_LOCUS`—Show location for runtime errors

If the first letter is ``y`', ``Y`' or ``1`', filename and line numbers for runtime errors are printed. If the first letter is ``n`', ``N`' or ``0`', do not print filename and line numbers for runtime errors. The default is to print the location.

Next: GFORTRAN_DEFAULT_RECL, Previous: GFORTRAN_SHOW_LOCUS, Up: Runtime

### 3.8 `GFORTRAN_OPTIONAL_PLUS`—Print leading + where permitted

If the first letter is ``y`', ``Y`' or ``1`', a plus sign is printed where permitted by the Fortran standard. If the first letter is ``n`', ``N`' or ``0`', a plus sign is not printed in most cases. Default is not to print plus signs.

Next: GFORTRAN_LIST_SEPARATOR, Previous: GFORTRAN_OPTIONAL_PLUS, Up: Runtime

### 3.9 `GFORTRAN_DEFAULT_RECL`—Default record length for new files

This environment variable specifies the default record length, in bytes, for files which are opened without a `RECL` tag in the `OPEN` statement. This must be a positive integer. The default value is 1073741824 bytes (1 GB).

Next: GFORTRAN_CONVERT_UNIT, Previous: GFORTRAN_DEFAULT_RECL, Up: Runtime

### 3.10 `GFORTRAN_LIST_SEPARATOR`—Separator for list output

This environment variable specifies the separator when writing list-directed output. It may contain any number of spaces and at most one comma. If you specify this on the command line, be sure to quote spaces, as in

         $ GFORTRAN_LIST_SEPARATOR='  ,  ' ./a.out

when `a.out` is the compiled Fortran program that you want to run. Default is a single space.

Next: GFORTRAN_ERROR_BACKTRACE, Previous: GFORTRAN_LIST_SEPARATOR, Up: Runtime

### 3.11 `GFORTRAN_CONVERT_UNIT`—Set endianness for unformatted I/O

By setting the `GFORTRAN_CONVERT_UNIT` variable, it is possible to change the representation of data for unformatted files. The syntax for the `GFORTRAN_CONVERT_UNIT` variable is:

         GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ;
         mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ;
         exception: mode ':' unit_list | unit_list ;
         unit_list: unit_spec | unit_list unit_spec ;
         unit_spec: INTEGER | INTEGER '-' INTEGER ;

The variable consists of an optional default mode, followed by a list of optional exceptions, which are separated by semicolons from the preceding default and each other. Each exception consists of a format and a comma-separated list of units. Valid values for the modes are the same as for the `CONVERT` specifier:

- `NATIVE` Use the native format. This is the default.
- `SWAP` Swap between little- and big-endian.
- `LITTLE_ENDIAN` Use the little-endian format for unformatted files.
- `BIG_ENDIAN` Use the big-endian format for unformatted files.

A missing mode for an exception is taken to mean `BIG_ENDIAN`. Examples of values for `GFORTRAN_CONVERT_UNIT` are:

- `'big_endian'` Do all unformatted I/O in big_endian mode.
- `'little_endian;native:10-20,25'` Do all unformatted I/O in little_endian mode, except for units 10 to 20 and 25, which are in native format.
- `'10-20'` Units 10 to 20 are big-endian, the rest is native.

Setting the environment variables should be done on the command line or via the `export` command for `sh`-compatible shells and via `setenv` for `csh`-compatible shells.

Example for `sh`:

         $ gfortran foo.f90
         $ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out

Example code for `csh`:

         % gfortran foo.f90
         % setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20'
         % ./a.out

Using anything but the native representation for unformatted data carries a significant speed overhead. If speed in this area matters to you, it is best if you use this only for data that needs to be portable.

See CONVERT specifier, for an alternative way to specify the data representation for unformatted files. See Runtime Options, for setting a default data representation for the whole program. The `CONVERT` specifier overrides the `-fconvert` compile options.

Note that the values specified via the GFORTRAN_CONVERT_UNIT environment variable will override the CONVERT specifier in the open statement. This is to give control over data formats to users who do not have the source code of their program available.

Previous: GFORTRAN_CONVERT_UNIT, Up: Runtime

### 3.12 `GFORTRAN_ERROR_BACKTRACE`—Show backtrace on run-time errors

If the `GFORTRAN_ERROR_BACKTRACE` variable is set to ``y`', ``Y`' or ``1`' (only the first letter is relevant) then a backtrace is printed when a serious run-time error occurs. To disable the backtracing, set the variable to ``n`', ``N`', ``0`'. Default is to print a backtrace unless the `-fno-backtrace` compile option was used.

Next: Compiler Characteristics, Previous: Runtime, Up: Top

## 4 Fortran 2003 and 2008 Status

Next: Fortran 2008 status, Up: Fortran 2003 and 2008 status

### 4.1 Fortran 2003 status

GNU Fortran supports several Fortran 2003 features; an incomplete list can be found below. See also the wiki page about Fortran 2003.

- Procedure pointers including procedure-pointer components with `PASS` attribute.
- Procedures which are bound to a derived type (type-bound procedures) including `PASS`, `PROCEDURE` and `GENERIC`, and operators bound to a type.
- Abstract interfaces and type extension with the possibility to override type-bound procedures or to have deferred binding.
- Polymorphic entities (“`CLASS`”) for derived types and unlimited polymorphism (“`CLASS(*)`”) – including `SAME_TYPE_AS`, `EXTENDS_TYPE_OF` and `SELECT TYPE` for scalars and arrays and finalization.
- Generic interface names, which have the same name as derived types, are now supported. This allows one to write constructor functions. Note that Fortran does not support static constructor functions. For static variables, only default initialization or structure-constructor initialization are available.
- The `ASSOCIATE` construct.
- Interoperability with C including enumerations,
- In structure constructors the components with default values may be omitted.
- Extensions to the `ALLOCATE` statement, allowing for a type-specification with type parameter and for allocation and initialization from a `SOURCE=` expression; `ALLOCATE` and `DEALLOCATE` optionally return an error message string via `ERRMSG=`.
- Reallocation on assignment: If an intrinsic assignment is used, an allocatable variable on the left-hand side is automatically allocated (if unallocated) or reallocated (if the shape is different). Currently, scalar deferred character length left-hand sides are correctly handled but arrays are not yet fully implemented.
- Deferred-length character variables and scalar deferred-length character components of derived types are supported. (Note that array-valued compoents are not yet implemented.)
- Transferring of allocations via `MOVE_ALLOC`.
- The `PRIVATE` and `PUBLIC` attributes may be given individually to derived-type components.
- In pointer assignments, the lower bound may be specified and the remapping of elements is supported.
- For pointers an `INTENT` may be specified which affect the association status not the value of the pointer target.
- Intrinsics `command_argument_count`, `get_command`, `get_command_argument`, and `get_environment_variable`.
- Support for Unicode characters (ISO 10646) and UTF-8, including the `SELECTED_CHAR_KIND` and `NEW_LINE` intrinsic functions.
- Support for binary, octal and hexadecimal (BOZ) constants in the intrinsic functions `INT`, `REAL`, `CMPLX` and `DBLE`.
- Support for namelist variables with allocatable and pointer attribute and nonconstant length type parameter.
- Array constructors using square brackets. That is, `[...]` rather than `(/.../)`. Type-specification for array constructors like `(/ some-type :: ... /)`.
- Extensions to the specification and initialization expressions, including the support for intrinsics with real and complex arguments.
- Support for the asynchronous input/output syntax; however, the data transfer is currently always synchronously performed.
- `FLUSH` statement.
- `IOMSG=` specifier for I/O statements.
- Support for the declaration of enumeration constants via the `ENUM` and `ENUMERATOR` statements. Interoperability with `gcc` is guaranteed also for the case where the `-fshort-enums` command line option is given.
- TR 15581:
  - `ALLOCATABLE` dummy arguments.
  - `ALLOCATABLE` function results
  - `ALLOCATABLE` components of derived types
- The `OPEN` statement supports the `ACCESS='STREAM'` specifier, allowing I/O without any record structure.
- Namelist input/output for internal files.
- Minor I/O features: Rounding during formatted output, using of a decimal comma instead of a decimal point, setting whether a plus sign should appear for positive numbers. On system where `strtod` honours the rounding mode, the rounding mode is also supported for input.
- The `PROTECTED` statement and attribute.
- The `VALUE` statement and attribute.
- The `VOLATILE` statement and attribute.
- The `IMPORT` statement, allowing to import host-associated derived types.
- The intrinsic modules `ISO_FORTRAN_ENVIRONMENT` is supported, which contains parameters of the I/O units, storage sizes. Additionally, procedures for C interoperability are available in the `ISO_C_BINDING` module.
- `USE` statement with `INTRINSIC` and `NON_INTRINSIC` attribute; supported intrinsic modules: `ISO_FORTRAN_ENV`, `ISO_C_BINDING`, `OMP_LIB` and `OMP_LIB_KINDS`.
- Renaming of operators in the `USE` statement.

Next: TS 29113 status, Previous: Fortran 2003 status, Up: Fortran 2003 and 2008 status

### 4.2 Fortran 2008 status

The latest version of the Fortran standard is ISO/IEC 1539-1:2010, informally known as Fortran 2008. The official version is available from International Organization for Standardization (ISO) or its national member organizations. The the final draft (FDIS) can be downloaded free of charge from http://www.nag.co.uk/sc22wg5/links.html. Fortran is developed by the Working Group 5 of Sub-Committee 22 of the Joint Technical Committee 1 of the International Organization for Standardization and the International Electrotechnical Commission (IEC). This group is known as WG5.

The GNU Fortran compiler supports several of the new features of Fortran 2008; the wiki has some information about the current Fortran 2008 implementation status. In particular, the following is implemented.

- The `-std=f2008` option and support for the file extensions `.f08` and `.F08`.
- The `OPEN` statement now supports the `NEWUNIT=` option, which returns a unique file unit, thus preventing inadvertent use of the same unit in different parts of the program.
- The `g0` format descriptor and unlimited format items.
- The mathematical intrinsics `ASINH`, `ACOSH`, `ATANH`, `ERF`, `ERFC`, `GAMMA`, `LOG_GAMMA`, `BESSEL_J0`, `BESSEL_J1`, `BESSEL_JN`, `BESSEL_Y0`, `BESSEL_Y1`, `BESSEL_YN`, `HYPOT`, `NORM2`, and `ERFC_SCALED`.
- Using complex arguments with `TAN`, `SINH`, `COSH`, `TANH`, `ASIN`, `ACOS`, and `ATAN` is now possible; `ATAN`(Y,X) is now an alias for `ATAN2`(Y,X).
- Support of the `PARITY` intrinsic functions.
- The following bit intrinsics: `LEADZ` and `TRAILZ` for counting the number of leading and trailing zero bits, `POPCNT` and `POPPAR` for counting the number of one bits and returning the parity; `BGE`, `BGT`, `BLE`, and `BLT` for bitwise comparisons; `DSHIFTL` and `DSHIFTR` for combined left and right shifts, `MASKL` and `MASKR` for simple left and right justified masks, `MERGE_BITS` for a bitwise merge using a mask, `SHIFTA`, `SHIFTL` and `SHIFTR` for shift operations, and the transformational bit intrinsics `IALL`, `IANY` and `IPARITY`.
- Support of the `EXECUTE_COMMAND_LINE` intrinsic subroutine.
- Support for the `STORAGE_SIZE` intrinsic inquiry function.
- The `INT{8,16,32}` and `REAL{32,64,128}` kind type parameters and the array-valued named constants `INTEGER_KINDS`, `LOGICAL_KINDS`, `REAL_KINDS` and `CHARACTER_KINDS` of the intrinsic module `ISO_FORTRAN_ENV`.
- The module procedures `C_SIZEOF` of the intrinsic module `ISO_C_BINDINGS` and `COMPILER_VERSION` and `COMPILER_OPTIONS` of `ISO_FORTRAN_ENV`.
- Coarray support for serial programs with `-fcoarray=single` flag and experimental support for multiple images with the `-fcoarray=lib` flag.
- The `DO CONCURRENT` construct is supported.
- The `BLOCK` construct is supported.
- The `STOP` and the new `ERROR STOP` statements now support all constant expressions. Both show the signals which were signaling at termination.
- Support for the `CONTIGUOUS` attribute.
- Support for `ALLOCATE` with `MOLD`.
- Support for the `IMPURE` attribute for procedures, which allows for `ELEMENTAL` procedures without the restrictions of `PURE`.
- Null pointers (including `NULL()`) and not-allocated variables can be used as actual argument to optional non-pointer, non-allocatable dummy arguments, denoting an absent argument.
- Non-pointer variables with `TARGET` attribute can be used as actual argument to `POINTER` dummies with `INTENT(IN)`.
- Pointers including procedure pointers and those in a derived type (pointer components) can now be initialized by a target instead of only by `NULL`.
- The `EXIT` statement (with construct-name) can be now be used to leave not only the `DO` but also the `ASSOCIATE`, `BLOCK`, `IF`, `SELECT CASE` and `SELECT TYPE` constructs.
- Internal procedures can now be used as actual argument.
- Minor features: obsolesce diagnostics for `ENTRY` with `-std=f2008`; a line may start with a semicolon; for internal and module procedures `END` can be used instead of `END SUBROUTINE` and `END FUNCTION`; `SELECTED_REAL_KIND` now also takes a `RADIX` argument; intrinsic types are supported for `TYPE`(intrinsic-type-spec); multiple type-bound procedures can be declared in a single `PROCEDURE` statement; implied-shape arrays are supported for named constants (`PARAMETER`).

Previous: Fortran 2008 status, Up: Fortran 2003 and 2008 status

### 4.3 Technical Specification 29113 Status

GNU Fortran supports some of the new features of the Technical Specification (TS) 29113 on Further Interoperability of Fortran with C. The wiki has some information about the current TS 29113 implementation status. In particular, the following is implemented.

See also Further Interoperability of Fortran with C.

- The `-std=f2008ts` option.
- The `OPTIONAL` attribute is allowed for dummy arguments of `BIND(C) procedures.`
- The `RANK` intrinsic is supported.
- GNU Fortran's implementation for variables with `ASYNCHRONOUS` attribute is compatible with TS 29113.
- Assumed types (`TYPE(*)`.
- Assumed-rank (`DIMENSION(..)`). However, the array descriptor of the TS is not yet supported.

Next: Extensions, Previous: Fortran 2003 and 2008 status, Up: Top

## 5 Compiler Characteristics

This chapter describes certain characteristics of the GNU Fortran compiler, that are not specified by the Fortran standard, but which might in some way or another become visible to the programmer.

Next: Internal representation of LOGICAL variables, Up: Compiler Characteristics

### 5.1 KIND Type Parameters

The `KIND` type parameters supported by GNU Fortran for the primitive data types are:

`INTEGER`
  1, 2, 4, 8*, 16*, default: 4**
`LOGICAL`
  1, 2, 4, 8*, 16*, default: 4**
`REAL`
  4, 8, 10*, 16*, default: 4***
`COMPLEX`
  4, 8, 10*, 16*, default: 4***
`DOUBLE PRECISION`
  4, 8, 10*, 16*, default: 8***
`CHARACTER`
  1, 4, default: 1

* not available on all systems
** unless `-fdefault-integer-8` is used
*** unless `-fdefault-real-8` is used (see Fortran Dialect Options)

The `KIND` value matches the storage size in bytes, except for `COMPLEX` where the storage size is twice as much (or both real and imaginary part are a real value of the given size). It is recommended to use the SELECTED_CHAR_KIND, SELECTED_INT_KIND and SELECTED_REAL_KIND intrinsics or the `INT8`, `INT16`, `INT32`, `INT64`, `REAL32`, `REAL64`, and `REAL128` parameters of the `ISO_FORTRAN_ENV` module instead of the concrete values. The available kind parameters can be found in the constant arrays `CHARACTER_KINDS`, `INTEGER_KINDS`, `LOGICAL_KINDS` and `REAL_KINDS` in the ISO_FORTRAN_ENV module. For C interoperability, the kind parameters of the ISO_C_BINDING module should be used.

Next: Thread-safety of the runtime library, Previous: KIND Type Parameters, Up: Compiler Characteristics

### 5.2 Internal representation of LOGICAL variables

The Fortran standard does not specify how variables of `LOGICAL` type are represented, beyond requiring that `LOGICAL` variables of default kind have the same storage size as default `INTEGER` and `REAL` variables. The GNU Fortran internal representation is as follows.

A `LOGICAL(KIND=N)` variable is represented as an `INTEGER(KIND=N)` variable, however, with only two permissible values: `1` for `.TRUE.` and `0` for `.FALSE.`. Any other integer value results in undefined behavior.

See also Argument passing conventions and Interoperability with C.

Next: Data consistency and durability, Previous: Internal representation of LOGICAL variables, Up: Compiler Characteristics

### 5.3 Thread-safety of the runtime library

GNU Fortran can be used in programs with multiple threads, e.g. by using OpenMP, by calling OS thread handling functions via the `ISO_C_BINDING` facility, or by GNU Fortran compiled library code being called from a multi-threaded program.

The GNU Fortran runtime library, (`libgfortran`), supports being called concurrently from multiple threads with the following exceptions.

During library initialization, the C `getenv` function is used, which need not be thread-safe. Similarly, the `getenv` function is used to implement the `GET_ENVIRONMENT_VARIABLE` and `GETENV` intrinsics. It is the responsibility of the user to ensure that the environment is not being updated concurrently when any of these actions are taking place.

The `EXECUTE_COMMAND_LINE` and `SYSTEM` intrinsics are implemented with the `system` function, which need not be thread-safe. It is the responsibility of the user to ensure that `system` is not called concurrently.

Finally, for platforms not supporting thread-safe POSIX functions, further functionality might not be thread-safe. For details, please consult the documentation for your operating system.

Previous: Thread-safety of the runtime library, Up: Compiler Characteristics

### 5.4 Data consistency and durability

This section contains a brief overview of data and metadata consistency and durability issues when doing I/O.

With respect to durability, GNU Fortran makes no effort to ensure that data is committed to stable storage. If this is required, the GNU Fortran programmer can use the intrinsic `FNUM` to retrieve the low level file descriptor corresponding to an open Fortran unit. Then, using e.g. the `ISO_C_BINDING` feature, one can call the underlying system call to flush dirty data to stable storage, such as `fsync` on POSIX, `_commit` on MingW, or `fcntl(fd, F_FULLSYNC, 0)` on Mac OS X. The following example shows how to call fsync:

           ! Declare the interface for POSIX fsync function
           interface
             function fsync (fd) bind(c,name="fsync")
             use iso_c_binding, only: c_int
               integer(c_int), value :: fd
               integer(c_int) :: fsync
             end function fsync
           end interface

           ! Variable declaration
           integer :: ret

           ! Opening unit 10
           open (10,file="foo")

           ! ...
           ! Perform I/O on unit 10
           ! ...

           ! Flush and sync
           flush(10)
           ret = fsync(fnum(10))

           ! Handle possible error
           if (ret /= 0) stop "Error calling FSYNC"

With respect to consistency, for regular files GNU Fortran uses buffered I/O in order to improve performance. This buffer is flushed automatically when full and in some other situations, e.g. when closing a unit. It can also be explicitly flushed with the `FLUSH` statement. Also, the buffering can be turned off with the `GFORTRAN_UNBUFFERED_ALL` and `GFORTRAN_UNBUFFERED_PRECONNECTED` environment variables. Special files, such as terminals and pipes, are always unbuffered. Sometimes, however, further things may need to be done in order to allow other processes to see data that GNU Fortran has written, as follows.

The Windows platform supports a relaxed metadata consistency model, where file metadata is written to the directory lazily. This means that, for instance, the `dir` command can show a stale size for a file. One can force a directory metadata update by closing the unit, or by calling `_commit` on the file descriptor. Note, though, that `_commit` will force all dirty data to stable storage, which is often a very slow operation.

The Network File System (NFS) implements a relaxed consistency model called open-to-close consistency. Closing a file forces dirty data and metadata to be flushed to the server, and opening a file forces the client to contact the server in order to revalidate cached data. `fsync` will also force a flush of dirty data and metadata to the server. Similar to `open` and `close`, acquiring and releasing `fcntl` file locks, if the server supports them, will also force cache validation and flushing dirty data and metadata.

Next: Mixed-Language Programming, Previous: Compiler Characteristics, Up: Top

## 6 Extensions

The two sections below detail the extensions to standard Fortran that are implemented in GNU Fortran, as well as some of the popular or historically important extensions that are not (or not yet) implemented. For the latter case, we explain the alternatives available to GNU Fortran users, including replacement by standard-conforming code or GNU extensions.

Next: Extensions not implemented in GNU Fortran, Up: Extensions

### 6.1 Extensions implemented in GNU Fortran

GNU Fortran implements a number of extensions over standard Fortran. This chapter contains information on their syntax and meaning. There are currently two categories of GNU Fortran extensions, those that provide functionality beyond that provided by any standard, and those that are supported by GNU Fortran purely for backward compatibility with legacy compilers. By default, `-std=gnu` allows the compiler to accept both types of extensions, but to warn about the use of the latter. Specifying either `-std=f95`, `-std=f2003` or `-std=f2008` disables both types of extensions, and `-std=legacy` allows both without warning.

Next: Old-style variable initialization, Up: Extensions implemented in GNU Fortran

#### 6.1.1 Old-style kind specifications

GNU Fortran allows old-style kind specifications in declarations. These look like:

               TYPESPEC*size x,y,z

where `TYPESPEC` is a basic type (`INTEGER`, `REAL`, etc.), and where `size` is a byte count corresponding to the storage size of a valid kind for that type. (For `COMPLEX` variables, `size` is the total size of the real and imaginary parts.) The statement then declares `x`, `y` and `z` to be of type `TYPESPEC` with the appropriate kind. This is equivalent to the standard-conforming declaration

               TYPESPEC(k) x,y,z

where `k` is the kind parameter suitable for the intended precision. As kind parameters are implementation-dependent, use the `KIND`, `SELECTED_INT_KIND` and `SELECTED_REAL_KIND` intrinsics to retrieve the correct value, for instance `REAL*8 x` can be replaced by:

         INTEGER, PARAMETER :: dbl = KIND(1.0d0)
         REAL(KIND=dbl) :: x

Next: Extensions to namelist, Previous: Old-style kind specifications, Up: Extensions implemented in GNU Fortran

#### 6.1.2 Old-style variable initialization

GNU Fortran allows old-style initialization of variables of the form:

               INTEGER i/1/,j/2/
               REAL x(2,2) /3*0.,1./

The syntax for the initializers is as for the `DATA` statement, but unlike in a `DATA` statement, an initializer only applies to the variable immediately preceding the initialization. In other words, something like `INTEGER I,J/2,3/` is not valid. This style of initialization is only allowed in declarations without double colons (`::`); the double colons were introduced in Fortran 90, which also introduced a standard syntax for initializing variables in type declarations.

Examples of standard-conforming code equivalent to the above example are:

         ! Fortran 90
               INTEGER :: i = 1, j = 2
               REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x))
         ! Fortran 77
               INTEGER i, j
               REAL x(2,2)
               DATA i/1/, j/2/, x/3*0.,1./

Note that variables which are explicitly initialized in declarations or in `DATA` statements automatically acquire the `SAVE` attribute.

Next: X format descriptor without count field, Previous: Old-style variable initialization, Up: Extensions implemented in GNU Fortran

#### 6.1.3 Extensions to namelist

GNU Fortran fully supports the Fortran 95 standard for namelist I/O including array qualifiers, substrings and fully qualified derived types. The output from a namelist write is compatible with namelist read. The output has all names in upper case and indentation to column 1 after the namelist name. Two extensions are permitted:

Old-style use of ``$`' instead of ``&`'

         $MYNML
          X(:)%Y(2) = 1.0 2.0 3.0
          CH(1:4) = "abcd"
         $END

It should be noted that the default terminator is ``/`' rather than ``&END`'.

Querying of the namelist when inputting from stdin. After at least one space, entering ``?`' sends to stdout the namelist name and the names of the variables in the namelist:

          ?

         &mynml
          x
          x%y
          ch
         &end

Entering ``=?`' outputs the namelist to stdout, as if `WRITE(*,NML = mynml)` had been called:

         =?

         &MYNML
          X(1)%Y=  0.000000    ,  1.000000    ,  0.000000    ,
          X(2)%Y=  0.000000    ,  2.000000    ,  0.000000    ,
          X(3)%Y=  0.000000    ,  3.000000    ,  0.000000    ,
          CH=abcd,  /

To aid this dialog, when input is from stdin, errors send their messages to stderr and execution continues, even if `IOSTAT` is set.

`PRINT` namelist is permitted. This causes an error if `-std=f95` is used.

         PROGRAM test_print
           REAL, dimension (4)  ::  x = (/1.0, 2.0, 3.0, 4.0/)
           NAMELIST /mynml/ x
           PRINT mynml
         END PROGRAM test_print

Expanded namelist reads are permitted. This causes an error if `-std=f95` is used. In the following example, the first element of the array will be given the value 0.00 and the two succeeding elements will be given the values 1.00 and 2.00.

         &MYNML
           X(1,1) = 0.00 , 1.00 , 2.00
         /

When writing a namelist, if no `DELIM=` is specified, by default a double quote is used to delimit character strings. If -std=F95, F2003, or F2008, etc, the delim status is set to 'none'. Defaulting to quotes ensures that namelists with character strings can be subsequently read back in accurately.

Next: Commas in FORMAT specifications, Previous: Extensions to namelist, Up: Extensions implemented in GNU Fortran

#### 6.1.4 `X` format descriptor without count field

To support legacy codes, GNU Fortran permits the count field of the `X` edit descriptor in `FORMAT` statements to be omitted. When omitted, the count is implicitly assumed to be one.

                PRINT 10, 2, 3
         10     FORMAT (I1, X, I1)

Next: Missing period in FORMAT specifications, Previous: X format descriptor without count field, Up: Extensions implemented in GNU Fortran

#### 6.1.5 Commas in `FORMAT` specifications

To support legacy codes, GNU Fortran allows the comma separator to be omitted immediately before and after character string edit descriptors in `FORMAT` statements.

                PRINT 10, 2, 3
         10     FORMAT ('FOO='I1' BAR='I2)

Next: I/O item lists, Previous: Commas in FORMAT specifications, Up: Extensions implemented in GNU Fortran

#### 6.1.6 Missing period in `FORMAT` specifications

To support legacy codes, GNU Fortran allows missing periods in format specifications if and only if `-std=legacy` is given on the command line. This is considered non-conforming code and is discouraged.

                REAL :: value
                READ(*,10) value
         10     FORMAT ('F4')

Next: <code>Q</code> exponent-letter, Previous: Missing period in FORMAT specifications, Up: Extensions implemented in GNU Fortran

#### 6.1.7 I/O item lists

To support legacy codes, GNU Fortran allows the input item list of the `READ` statement, and the output item lists of the `WRITE` and `PRINT` statements, to start with a comma.

Next: BOZ literal constants, Previous: I/O item lists, Up: Extensions implemented in GNU Fortran

#### 6.1.8 `Q` exponent-letter

GNU Fortran accepts real literal constants with an exponent-letter of `Q`, for example, `1.23Q45`. The constant is interpreted as a `REAL(16)` entity on targets that support this type. If the target does not support `REAL(16)` but has a `REAL(10)` type, then the real-literal-constant will be interpreted as a `REAL(10)` entity. In the absence of `REAL(16)` and `REAL(10)`, an error will occur.

Next: Real array indices, Previous: <code>Q</code> exponent-letter, Up: Extensions implemented in GNU Fortran

#### 6.1.9 BOZ literal constants

Besides decimal constants, Fortran also supports binary (`b`), octal (`o`) and hexadecimal (`z`) integer constants. The syntax is: ``prefix quote digits quote`', were the prefix is either `b`, `o` or `z`, quote is either `'` or `"` and the digits are for binary `0` or `1`, for octal between `0` and `7`, and for hexadecimal between `0` and `F`. (Example: `b'01011101'`.)

Up to Fortran 95, BOZ literals were only allowed to initialize integer variables in DATA statements. Since Fortran 2003 BOZ literals are also allowed as argument of `REAL`, `DBLE`, `INT` and `CMPLX`; the result is the same as if the integer BOZ literal had been converted by `TRANSFER` to, respectively, `real`, `double precision`, `integer` or `complex`. As GNU Fortran extension the intrinsic procedures `FLOAT`, `DFLOAT`, `COMPLEX` and `DCMPLX` are treated alike.

As an extension, GNU Fortran allows hexadecimal BOZ literal constants to be specified using the `X` prefix, in addition to the standard `Z` prefix. The BOZ literal can also be specified by adding a suffix to the string, for example, `Z'ABC'` and `'ABC'Z` are equivalent.

Furthermore, GNU Fortran allows using BOZ literal constants outside DATA statements and the four intrinsic functions allowed by Fortran 2003. In DATA statements, in direct assignments, where the right-hand side only contains a BOZ literal constant, and for old-style initializers of the form `integer i /o'0173'/`, the constant is transferred as if `TRANSFER` had been used; for `COMPLEX` numbers, only the real part is initialized unless `CMPLX` is used. In all other cases, the BOZ literal constant is converted to an `INTEGER` value with the largest decimal representation. This value is then converted numerically to the type and kind of the variable in question. (For instance, `real :: r = b'0000001' + 1` initializes `r` with `2.0`.) As different compilers implement the extension differently, one should be careful when doing bitwise initialization of non-integer variables.

Note that initializing an `INTEGER` variable with a statement such as `DATA i/Z'FFFFFFFF'/` will give an integer overflow error rather than the desired result of -1 when `i` is a 32-bit integer on a system that supports 64-bit integers. The ``-fno-range-check`' option can be used as a workaround for legacy code that initializes integers in this manner.

Next: Unary operators, Previous: BOZ literal constants, Up: Extensions implemented in GNU Fortran

#### 6.1.10 Real array indices

As an extension, GNU Fortran allows the use of `REAL` expressions or variables as array indices.

Next: Implicitly convert LOGICAL and INTEGER values, Previous: Real array indices, Up: Extensions implemented in GNU Fortran

#### 6.1.11 Unary operators

As an extension, GNU Fortran allows unary plus and unary minus operators to appear as the second operand of binary arithmetic operators without the need for parenthesis.

                X = Y * -Z

Next: Hollerith constants support, Previous: Unary operators, Up: Extensions implemented in GNU Fortran

#### 6.1.12 Implicitly convert `LOGICAL` and `INTEGER` values

As an extension for backwards compatibility with other compilers, GNU Fortran allows the implicit conversion of `LOGICAL` values to `INTEGER` values and vice versa. When converting from a `LOGICAL` to an `INTEGER`, `.FALSE.` is interpreted as zero, and `.TRUE.` is interpreted as one. When converting from `INTEGER` to `LOGICAL`, the value zero is interpreted as `.FALSE.` and any nonzero value is interpreted as `.TRUE.`.

                 LOGICAL :: l
                 l = 1

                 INTEGER :: i
                 i = .TRUE.

However, there is no implicit conversion of `INTEGER` values in `if`-statements, nor of `LOGICAL` or `INTEGER` values in I/O operations.

Next: Cray pointers, Previous: Implicitly convert LOGICAL and INTEGER values, Up: Extensions implemented in GNU Fortran

#### 6.1.13 Hollerith constants support

GNU Fortran supports Hollerith constants in assignments, function arguments, and `DATA` and `ASSIGN` statements. A Hollerith constant is written as a string of characters preceded by an integer constant indicating the character count, and the letter `H` or `h`, and stored in bytewise fashion in a numeric (`INTEGER`, `REAL`, or `complex`) or `LOGICAL` variable. The constant will be padded or truncated to fit the size of the variable in which it is stored.

Examples of valid uses of Hollerith constants:

               complex*16 x(2)
               data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/
               x(1) = 16HABCDEFGHIJKLMNOP
               call foo (4h abc)

Invalid Hollerith constants examples:

               integer*4 a
               a = 8H12345678 ! Valid, but the Hollerith constant will be truncated.
               a = 0H         ! At least one character is needed.

In general, Hollerith constants were used to provide a rudimentary facility for handling character strings in early Fortran compilers, prior to the introduction of `CHARACTER` variables in Fortran 77; in those cases, the standard-compliant equivalent is to convert the program to use proper character strings. On occasion, there may be a case where the intent is specifically to initialize a numeric variable with a given byte sequence. In these cases, the same result can be obtained by using the `TRANSFER` statement, as in this example.

               INTEGER(KIND=4) :: a
               a = TRANSFER ("abcd", a)     ! equivalent to: a = 4Habcd

Next: CONVERT specifier, Previous: Hollerith constants support, Up: Extensions implemented in GNU Fortran

#### 6.1.14 Cray pointers

Cray pointers are part of a non-standard extension that provides a C-like pointer in Fortran. This is accomplished through a pair of variables: an integer "pointer" that holds a memory address, and a "pointee" that is used to dereference the pointer.

Pointer/pointee pairs are declared in statements of the form:

                 pointer ( <pointer> , <pointee> )

or,

                 pointer ( <pointer1> , <pointee1> ), ( <pointer2> , <pointee2> ), ...

The pointer is an integer that is intended to hold a memory address. The pointee may be an array or scalar. A pointee can be an assumed size array—that is, the last dimension may be left unspecified by using a `*` in place of a value—but a pointee cannot be an assumed shape array. No space is allocated for the pointee.

The pointee may have its type declared before or after the pointer statement, and its array specification (if any) may be declared before, during, or after the pointer statement. The pointer may be declared as an integer prior to the pointer statement. However, some machines have default integer sizes that are different than the size of a pointer, and so the following code is not portable:

                 integer ipt
                 pointer (ipt, iarr)

If a pointer is declared with a kind that is too small, the compiler will issue a warning; the resulting binary will probably not work correctly, because the memory addresses stored in the pointers may be truncated. It is safer to omit the first line of the above example; if explicit declaration of ipt's type is omitted, then the compiler will ensure that ipt is an integer variable large enough to hold a pointer.

Pointer arithmetic is valid with Cray pointers, but it is not the same as C pointer arithmetic. Cray pointers are just ordinary integers, so the user is responsible for determining how many bytes to add to a pointer in order to increment it. Consider the following example:

                 real target(10)
                 real pointee(10)
                 pointer (ipt, pointee)
                 ipt = loc (target)
                 ipt = ipt + 1

The last statement does not set `ipt` to the address of `target(1)`, as it would in C pointer arithmetic. Adding `1` to `ipt` just adds one byte to the address stored in `ipt`.

Any expression involving the pointee will be translated to use the value stored in the pointer as the base address.

To get the address of elements, this extension provides an intrinsic function `LOC()`. The `LOC()` function is equivalent to the `&` operator in C, except the address is cast to an integer type:

                 real ar(10)
                 pointer(ipt, arpte(10))
                 real arpte
                 ipt = loc(ar)  ! Makes arpte is an alias for ar
                 arpte(1) = 1.0 ! Sets ar(1) to 1.0

The pointer can also be set by a call to the `MALLOC` intrinsic (see MALLOC).

Cray pointees often are used to alias an existing variable. For example:

                 integer target(10)
                 integer iarr(10)
                 pointer (ipt, iarr)
                 ipt = loc(target)

As long as `ipt` remains unchanged, `iarr` is now an alias for `target`. The optimizer, however, will not detect this aliasing, so it is unsafe to use `iarr` and `target` simultaneously. Using a pointee in any way that violates the Fortran aliasing rules or assumptions is illegal. It is the user's responsibility to avoid doing this; the compiler works under the assumption that no such aliasing occurs.

Cray pointers will work correctly when there is no aliasing (i.e., when they are used to access a dynamically allocated block of memory), and also in any routine where a pointee is used, but any variable with which it shares storage is not used. Code that violates these rules may not run as the user intends. This is not a bug in the optimizer; any code that violates the aliasing rules is illegal. (Note that this is not unique to GNU Fortran; any Fortran compiler that supports Cray pointers will “incorrectly” optimize code with illegal aliasing.)

There are a number of restrictions on the attributes that can be applied to Cray pointers and pointees. Pointees may not have the `ALLOCATABLE`, `INTENT`, `OPTIONAL`, `DUMMY`, `TARGET`, `INTRINSIC`, or `POINTER` attributes. Pointers may not have the `DIMENSION`, `POINTER`, `TARGET`, `ALLOCATABLE`, `EXTERNAL`, or `INTRINSIC` attributes, nor may they be function results. Pointees may not occur in more than one pointer statement. A pointee cannot be a pointer. Pointees cannot occur in equivalence, common, or data statements.

A Cray pointer may also point to a function or a subroutine. For example, the following excerpt is valid:

           implicit none
           external sub
           pointer (subptr,subpte)
           external subpte
           subptr = loc(sub)
           call subpte()
           [...]
           subroutine sub
           [...]
           end subroutine sub

A pointer may be modified during the course of a program, and this will change the location to which the pointee refers. However, when pointees are passed as arguments, they are treated as ordinary variables in the invoked function. Subsequent changes to the pointer will not change the base address of the array that was passed.

Next: OpenMP, Previous: Cray pointers, Up: Extensions implemented in GNU Fortran

#### 6.1.15 `CONVERT` specifier

GNU Fortran allows the conversion of unformatted data between little- and big-endian representation to facilitate moving of data between different systems. The conversion can be indicated with the `CONVERT` specifier on the `OPEN` statement. See GFORTRAN_CONVERT_UNIT, for an alternative way of specifying the data format via an environment variable.

Valid values for `CONVERT` are:

- `CONVERT='NATIVE'` Use the native format. This is the default.
- `CONVERT='SWAP'` Swap between little- and big-endian.
- `CONVERT='LITTLE_ENDIAN'` Use the little-endian representation for unformatted files.
- `CONVERT='BIG_ENDIAN'` Use the big-endian representation for unformatted files.

Using the option could look like this:

           open(file='big.dat',form='unformatted',access='sequential', &
                convert='big_endian')

The value of the conversion can be queried by using `INQUIRE(CONVERT=ch)`. The values returned are `'BIG_ENDIAN'` and `'LITTLE_ENDIAN'`.

`CONVERT` works between big- and little-endian for `INTEGER` values of all supported kinds and for `REAL` on IEEE systems of kinds 4 and 8. Conversion between different “extended double” types on different architectures such as m68k and x86_64, which GNU Fortran supports as `REAL(KIND=10)` and `REAL(KIND=16)`, will probably not work.

Note that the values specified via the GFORTRAN_CONVERT_UNIT environment variable will override the CONVERT specifier in the open statement. This is to give control over data formats to users who do not have the source code of their program available.

Using anything but the native representation for unformatted data carries a significant speed overhead. If speed in this area matters to you, it is best if you use this only for data that needs to be portable.

Next: Argument list functions, Previous: CONVERT specifier, Up: Extensions implemented in GNU Fortran

#### 6.1.16 OpenMP

OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C/C++ and Fortran on many architectures, including Unix and Microsoft Windows platforms. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior.

GNU Fortran strives to be compatible to the OpenMP Application Program Interface v4.0.

To enable the processing of the OpenMP directive `!$omp` in free-form source code; the `c$omp`, `*$omp` and `!$omp` directives in fixed form; the `!$` conditional compilation sentinels in free form; and the `c$`, `*$` and `!$` sentinels in fixed form, `gfortran` needs to be invoked with the `-fopenmp`. This also arranges for automatic linking of the GNU OpenMP runtime library libgomp.

The OpenMP Fortran runtime library routines are provided both in a form of a Fortran 90 module named `omp_lib` and in a form of a Fortran `include` file named `omp_lib.h`.

An example of a parallelized loop taken from Appendix A.1 of the OpenMP Application Program Interface v2.5:

         SUBROUTINE A1(N, A, B)
           INTEGER I, N
           REAL B(N), A(N)
         !$OMP PARALLEL DO !I is private by default
           DO I=2,N
             B(I) = (A(I) + A(I-1)) / 2.0
           ENDDO
         !$OMP END PARALLEL DO
         END SUBROUTINE A1

Please note:

- `-fopenmp` implies `-frecursive`, i.e., all local arrays will be allocated on the stack. When porting existing code to OpenMP, this may lead to surprising results, especially to segmentation faults if the stacksize is limited.
- On glibc-based systems, OpenMP enabled applications cannot be statically linked due to limitations of the underlying pthreads-implementation. It might be possible to get a working solution if `-Wl,--whole-archive -lpthread -Wl,--no-whole-archive` is added to the command line. However, this is not supported by `gcc` and thus not recommended.

Previous: OpenMP, Up: Extensions implemented in GNU Fortran

#### 6.1.17 Argument list functions `%VAL`, `%REF` and `%LOC`

GNU Fortran supports argument list functions `%VAL`, `%REF` and `%LOC` statements, for backward compatibility with g77. It is recommended that these should be used 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.

`%VAL` passes a scalar argument by value, `%REF` passes it by reference and `%LOC` passes its memory location. Since gfortran already passes scalar arguments by reference, `%REF` is in effect a do-nothing. `%LOC` has the same effect as a Fortran pointer.

An example of passing an argument by value to a C subroutine foo.:

         C
         C prototype      void foo_ (float x);
         C
               external foo
               real*4 x
               x = 3.14159
               call foo (%VAL (x))
               end

For details refer to the g77 manual http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top.

Also, `c_by_val.f` and its partner `c_by_val.c` of the GNU Fortran testsuite are worth a look.

Previous: Extensions implemented in GNU Fortran, Up: Extensions

### 6.2 Extensions not implemented in GNU Fortran

The long history of the Fortran language, its wide use and broad userbase, the large number of different compiler vendors and the lack of some features crucial to users in the first standards have lead to the existence of a number of important extensions to the language. While some of the most useful or popular extensions are supported by the GNU Fortran compiler, not all existing extensions are supported. This section aims at listing these extensions and offering advice on how best make code that uses them running with the GNU Fortran compiler.

Next: ENCODE and DECODE statements, Up: Extensions not implemented in GNU Fortran

#### 6.2.1 `STRUCTURE` and `RECORD`

Record structures are a pre-Fortran-90 vendor extension to create user-defined aggregate data types. GNU Fortran does not support record structures, only Fortran 90's “derived types”, which have a different syntax.

In many cases, record structures can easily be converted to derived types. To convert, replace `STRUCTURE /`structure-name`/` by `TYPE` type-name. Additionally, replace `RECORD /`structure-name`/` by `TYPE(`type-name`)`. Finally, in the component access, replace the period (`.`) by the percent sign (`%`).

Here is an example of code using the non portable record structure syntax:

         ! Declaring a structure named ``item'' and containing three fields:
         ! an integer ID, an description string and a floating-point price.
         STRUCTURE /item/
           INTEGER id
           CHARACTER(LEN=200) description
           REAL price
         END STRUCTURE

         ! Define two variables, an single record of type ``item''
         ! named ``pear'', and an array of items named ``store_catalog''
         RECORD /item/ pear, store_catalog(100)

         ! We can directly access the fields of both variables
         pear.id = 92316
         pear.description = "juicy D'Anjou pear"
         pear.price = 0.15
         store_catalog(7).id = 7831
         store_catalog(7).description = "milk bottle"
         store_catalog(7).price = 1.2

         ! We can also manipulate the whole structure
         store_catalog(12) = pear
         print *, store_catalog(12)

This code can easily be rewritten in the Fortran 90 syntax as following:

         ! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
         ! ``TYPE name ... END TYPE''
         TYPE item
           INTEGER id
           CHARACTER(LEN=200) description
           REAL price
         END TYPE

         ! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
         TYPE(item) pear, store_catalog(100)

         ! Instead of using a dot (.) to access fields of a record, the
         ! standard syntax uses a percent sign (%)
         pear%id = 92316
         pear%description = "juicy D'Anjou pear"
         pear%price = 0.15
         store_catalog(7)%id = 7831
         store_catalog(7)%description = "milk bottle"
         store_catalog(7)%price = 1.2

         ! Assignments of a whole variable do not change
         store_catalog(12) = pear
         print *, store_catalog(12)

Next: Variable FORMAT expressions, Previous: STRUCTURE and RECORD, Up: Extensions not implemented in GNU Fortran

#### 6.2.2 `ENCODE` and `DECODE` statements

GNU Fortran does not support the `ENCODE` and `DECODE` statements. These statements are best replaced by `READ` and `WRITE` statements involving internal files (`CHARACTER` variables and arrays), which have been part of the Fortran standard since Fortran 77. For example, replace a code fragment like

               INTEGER*1 LINE(80)
               REAL A, B, C
         c     ... Code that sets LINE
               DECODE (80, 9000, LINE) A, B, C
          9000 FORMAT (1X, 3(F10.5))

with the following:

               CHARACTER(LEN=80) LINE
               REAL A, B, C
         c     ... Code that sets 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)
               REAL A, B, C
         c     ... Code that sets A, B and C
               ENCODE (80, 9000, LINE) A, B, C
          9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))

with the following:

               CHARACTER(LEN=80) LINE
               REAL A, B, C
         c     ... Code that sets A, B and C
               WRITE (UNIT=LINE, FMT=9000) A, B, C
          9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5))

Next: Alternate complex function syntax, Previous: ENCODE and DECODE statements, Up: Extensions not implemented in GNU Fortran

#### 6.2.3 Variable `FORMAT` expressions

A variable `FORMAT` expression is format statement which includes angle brackets enclosing a Fortran expression: `FORMAT(I<N>)`. GNU Fortran does not support this legacy extension. The effect of variable format expressions can be reproduced by using the more powerful (and standard) combination of internal output and string formats. For example, replace a code fragment like this:

               WRITE(6,20) INT1
          20   FORMAT(I<N+1>)

with the following:

         c     Variable declaration
               CHARACTER(LEN=20) FMT
         c
         c     Other code here...
         c
               WRITE(FMT,'("(I", I0, ")")') N+1
               WRITE(6,FMT) INT1

or with:

         c     Variable declaration
               CHARACTER(LEN=20) FMT
         c
         c     Other code here...
         c
               WRITE(FMT,*) N+1
               WRITE(6,"(I" // ADJUSTL(FMT) // ")") INT1

Next: Volatile COMMON blocks, Previous: Variable FORMAT expressions, Up: Extensions not implemented in GNU Fortran

#### 6.2.4 Alternate complex function syntax

Some Fortran compilers, including `g77`, let the user declare complex functions with the syntax `COMPLEX FUNCTION name*16()`, as well as `COMPLEX*16 FUNCTION name()`. Both are non-standard, legacy extensions. `gfortran` accepts the latter form, which is more common, but not the former.

Previous: Alternate complex function syntax, Up: Extensions not implemented in GNU Fortran

#### 6.2.5 Volatile `COMMON` blocks

Some Fortran compilers, including `g77`, let the user declare `COMMON` with the `VOLATILE` attribute. This is invalid standard Fortran syntax and is not supported by `gfortran`. Note that `gfortran` accepts `VOLATILE` variables in `COMMON` blocks since revision 4.3.

Next: Intrinsic Procedures, Previous: Extensions, Up: Top

## 7 Mixed-Language Programming

This chapter is about mixed-language interoperability, but also applies if one links Fortran code compiled by different compilers. In most cases, use of the C Binding features of the Fortran 2003 standard is sufficient, and their use is highly recommended.

Next: GNU Fortran Compiler Directives, Up: Mixed-Language Programming

### 7.1 Interoperability with C

Since Fortran 2003 (ISO/IEC 1539-1:2004(E)) there is a standardized way to generate procedure and derived-type declarations and global variables which are interoperable with C (ISO/IEC 9899:1999). The `bind(C)` attribute has been added to inform the compiler that a symbol shall be interoperable with C; also, some constraints are added. Note, however, that not all C features have a Fortran equivalent or vice versa. For instance, neither C's unsigned integers nor C's functions with variable number of arguments have an equivalent in Fortran.

Note that array dimensions are reversely ordered in C and that arrays in C always start with index 0 while in Fortran they start by default with 1. Thus, an array declaration `A(n,m)` in Fortran matches `A[m][n]` in C and accessing the element `A(i,j)` matches `A[j-1][i-1]`. The element following `A(i,j)` (C: `A[j-1][i-1]`; assuming i < n) in memory is `A(i+1,j)` (C: `A[j-1][i]`).

Next: Derived Types and struct, Up: Interoperability with C

#### 7.1.1 Intrinsic Types

In order to ensure that exactly the same variable type and kind is used in C and Fortran, the named constants shall be used which are defined in the `ISO_C_BINDING` intrinsic module. That module contains named constants for kind parameters and character named constants for the escape sequences in C. For a list of the constants, see ISO_C_BINDING.

For logical types, please note that the Fortran standard only guarantees interoperability between C99's `_Bool` and Fortran's `C_Bool`-kind logicals and C99 defines that `true` has the value 1 and `false` the value 0. Using any other integer value with GNU Fortran's `LOGICAL` (with any kind parameter) gives an undefined result. (Passing other integer values than 0 and 1 to GCC's `_Bool` is also undefined, unless the integer is explicitly or implicitly casted to `_Bool`.)

Next: Interoperable Global Variables, Previous: Intrinsic Types, Up: Interoperability with C

#### 7.1.2 Derived Types and struct

For compatibility of derived types with `struct`, one needs to use the `BIND(C)` attribute in the type declaration. For instance, the following type declaration

          USE ISO_C_BINDING
          TYPE, BIND(C) :: myType
            INTEGER(C_INT) :: i1, i2
            INTEGER(C_SIGNED_CHAR) :: i3
            REAL(C_DOUBLE) :: d1
            COMPLEX(C_FLOAT_COMPLEX) :: c1
            CHARACTER(KIND=C_CHAR) :: str(5)
          END TYPE

matches the following `struct` declaration in C

          struct {
            int i1, i2;
            /* Note: "char" might be signed or unsigned.  */
            signed char i3;
            double d1;
            float _Complex c1;
            char str[5];
          } myType;

Derived types with the C binding attribute shall not have the `sequence` attribute, type parameters, the `extends` attribute, nor type-bound procedures. Every component must be of interoperable type and kind and may not have the `pointer` or `allocatable` attribute. The names of the components are irrelevant for interoperability.

As there exist no direct Fortran equivalents, neither unions nor structs with bit field or variable-length array members are interoperable.

Next: Interoperable Subroutines and Functions, Previous: Derived Types and struct, Up: Interoperability with C

#### 7.1.3 Interoperable Global Variables

Variables can be made accessible from C using the C binding attribute, optionally together with specifying a binding name. Those variables have to be declared in the declaration part of a `MODULE`, be of interoperable type, and have neither the `pointer` nor the `allocatable` attribute.

           MODULE m
             USE myType_module
             USE ISO_C_BINDING
             integer(C_INT), bind(C, name="_MyProject_flags") :: global_flag
             type(myType), bind(C) :: tp
           END MODULE

Here, `_MyProject_flags` is the case-sensitive name of the variable as seen from C programs while `global_flag` is the case-insensitive name as seen from Fortran. If no binding name is specified, as for tp, the C binding name is the (lowercase) Fortran binding name. If a binding name is specified, only a single variable may be after the double colon. Note of warning: You cannot use a global variable to access errno of the C library as the C standard allows it to be a macro. Use the `IERRNO` intrinsic (GNU extension) instead.

Next: Working with Pointers, Previous: Interoperable Global Variables, Up: Interoperability with C

#### 7.1.4 Interoperable Subroutines and Functions

Subroutines and functions have to have the `BIND(C)` attribute to be compatible with C. The dummy argument declaration is relatively straightforward. However, one needs to be careful because C uses call-by-value by default while Fortran behaves usually similar to call-by-reference. Furthermore, strings and pointers are handled differently. Note that in Fortran 2003 and 2008 only explicit size and assumed-size arrays are supported but not assumed-shape or deferred-shape (i.e. allocatable or pointer) arrays. However, those are allowed since the Technical Specification 29113, see Further Interoperability of Fortran with C

To pass a variable by value, use the `VALUE` attribute. Thus, the following C prototype

         int func(int i, int *j)

matches the Fortran declaration

           integer(c_int) function func(i,j)
             use iso_c_binding, only: c_int
             integer(c_int), VALUE :: i
             integer(c_int) :: j

Note that pointer arguments also frequently need the `VALUE` attribute, see Working with Pointers.

Strings are handled quite differently in C and Fortran. In C a string is a `NUL`-terminated array of characters while in Fortran each string has a length associated with it and is thus not terminated (by e.g. `NUL`). For example, if one wants to use the following C function,

           #include <stdio.h>
           void print_C(char *string) /* equivalent: char string[]  */
           {
              printf("%s\n", string);
           }

to print “Hello World” from Fortran, one can call it using

           use iso_c_binding, only: C_CHAR, C_NULL_CHAR
           interface
             subroutine print_c(string) bind(C, name="print_C")
               use iso_c_binding, only: c_char
               character(kind=c_char) :: string(*)
             end subroutine print_c
           end interface
           call print_c(C_CHAR_"Hello World"//C_NULL_CHAR)

As the example shows, one needs to ensure that the string is `NUL` terminated. Additionally, the dummy argument string of `print_C` is a length-one assumed-size array; using `character(len=*)` is not allowed. The example above uses `c_char_"Hello World"` to ensure the string literal has the right type; typically the default character kind and `c_char` are the same and thus `"Hello World"` is equivalent. However, the standard does not guarantee this.

The use of strings is now further illustrated using the C library function `strncpy`, whose prototype is

           char *strncpy(char *restrict s1, const char *restrict s2, size_t n);

The function `strncpy` copies at most n characters from string s2 to s1 and returns s1. In the following example, we ignore the return value:

           use iso_c_binding
           implicit none
           character(len=30) :: str,str2
           interface
             ! Ignore the return value of strncpy -> subroutine
             ! "restrict" is always assumed if we do not pass a pointer
             subroutine strncpy(dest, src, n) bind(C)
               import
               character(kind=c_char),  intent(out) :: dest(*)
               character(kind=c_char),  intent(in)  :: src(*)
               integer(c_size_t), value, intent(in) :: n
             end subroutine strncpy
           end interface
           str = repeat('X',30) ! Initialize whole string with 'X'
           call strncpy(str, c_char_"Hello World"//C_NULL_CHAR, &
                        len(c_char_"Hello World",kind=c_size_t))
           print '(a)', str ! prints: "Hello WorldXXXXXXXXXXXXXXXXXXX"
           end

The intrinsic procedures are described in Intrinsic Procedures.

Next: Further Interoperability of Fortran with C, Previous: Interoperable Subroutines and Functions, Up: Interoperability with C

#### 7.1.5 Working with Pointers

C pointers are represented in Fortran via the special opaque derived type `type(c_ptr)` (with private components). Thus one needs to use intrinsic conversion procedures to convert from or to C pointers.

For some applications, using an assumed type (`TYPE(*)`) can be an alternative to a C pointer; see Further Interoperability of Fortran with C.

For example,

           use iso_c_binding
           type(c_ptr) :: cptr1, cptr2
           integer, target :: array(7), scalar
           integer, pointer :: pa(:), ps
           cptr1 = c_loc(array(1)) ! The programmer needs to ensure that the
                                   ! array is contiguous if required by the C
                                   ! procedure
           cptr2 = c_loc(scalar)
           call c_f_pointer(cptr2, ps)
           call c_f_pointer(cptr2, pa, shape=[7])

When converting C to Fortran arrays, the one-dimensional `SHAPE` argument has to be passed.

If a pointer is a dummy-argument of an interoperable procedure, it usually has to be declared using the `VALUE` attribute. `void*` matches `TYPE(C_PTR), VALUE`, while `TYPE(C_PTR)` alone matches `void**`.

Procedure pointers are handled analogously to pointers; the C type is `TYPE(C_FUNPTR)` and the intrinsic conversion procedures are `C_F_PROCPOINTER` and `C_FUNLOC`.

Let us consider two examples of actually passing a procedure pointer from C to Fortran and vice versa. Note that these examples are also very similar to passing ordinary pointers between both languages. First, consider this code in C:

         /* Procedure implemented in Fortran.  */
         void get_values (void (*)(double));

         /* Call-back routine we want called from Fortran.  */
         void
         print_it (double x)
         {
           printf ("Number is %f.\n", x);
         }

         /* Call Fortran routine and pass call-back to it.  */
         void
         foobar ()
         {
           get_values (&print_it);
         }

A matching implementation for `get_values` in Fortran, that correctly receives the procedure pointer from C and is able to call it, is given in the following `MODULE`:

         MODULE m
           IMPLICIT NONE

           ! Define interface of call-back routine.
           ABSTRACT INTERFACE
             SUBROUTINE callback (x)
               USE, INTRINSIC :: ISO_C_BINDING
               REAL(KIND=C_DOUBLE), INTENT(IN), VALUE :: x
             END SUBROUTINE callback
           END INTERFACE

         CONTAINS

           ! Define C-bound procedure.
           SUBROUTINE get_values (cproc) BIND(C)
             USE, INTRINSIC :: ISO_C_BINDING
             TYPE(C_FUNPTR), INTENT(IN), VALUE :: cproc

             PROCEDURE(callback), POINTER :: proc

             ! Convert C to Fortran procedure pointer.
             CALL C_F_PROCPOINTER (cproc, proc)

             ! Call it.
             CALL proc (1.0_C_DOUBLE)
             CALL proc (-42.0_C_DOUBLE)
             CALL proc (18.12_C_DOUBLE)
           END SUBROUTINE get_values

         END MODULE m

Next, we want to call a C routine that expects a procedure pointer argument and pass it a Fortran procedure (which clearly must be interoperable!). Again, the C function may be:

         int
         call_it (int (*func)(int), int arg)
         {
           return func (arg);
         }

It can be used as in the following Fortran code:

         MODULE m
           USE, INTRINSIC :: ISO_C_BINDING
           IMPLICIT NONE

           ! Define interface of C function.
           INTERFACE
             INTEGER(KIND=C_INT) FUNCTION call_it (func, arg) BIND(C)
               USE, INTRINSIC :: ISO_C_BINDING
               TYPE(C_FUNPTR), INTENT(IN), VALUE :: func
               INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
             END FUNCTION call_it
           END INTERFACE

         CONTAINS

           ! Define procedure passed to C function.
           ! It must be interoperable!
           INTEGER(KIND=C_INT) FUNCTION double_it (arg) BIND(C)
             INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg
             double_it = arg + arg
           END FUNCTION double_it

           ! Call C function.
           SUBROUTINE foobar ()
             TYPE(C_FUNPTR) :: cproc
             INTEGER(KIND=C_INT) :: i

             ! Get C procedure pointer.
             cproc = C_FUNLOC (double_it)

             ! Use it.
             DO i = 1_C_INT, 10_C_INT
               PRINT *, call_it (cproc, i)
             END DO
           END SUBROUTINE foobar

         END MODULE m

Previous: Working with Pointers, Up: Interoperability with C

#### 7.1.6 Further Interoperability of Fortran with C

The Technical Specification ISO/IEC TS 29113:2012 on further interoperability of Fortran with C extends the interoperability support of Fortran 2003 and Fortran 2008. Besides removing some restrictions and constraints, it adds assumed-type (`TYPE(*)`) and assumed-rank (`dimension`) variables and allows for interoperability of assumed-shape, assumed-rank and deferred-shape arrays, including allocatables and pointers.

Note: Currently, GNU Fortran does not support the array descriptor (dope vector) as specified in the Technical Specification, but uses an array descriptor with different fields. The Chasm Language Interoperability Tools, http://chasm-interop.sourceforge.net/, provide an interface to GNU Fortran's array descriptor.

The Technical Specification adds the following new features, which are supported by GNU Fortran:

- The `ASYNCHRONOUS` attribute has been clarified and extended to allow its use with asynchronous communication in user-provided libraries such as in implementations of the Message Passing Interface specification.
- Many constraints have been relaxed, in particular for the `C_LOC` and `C_F_POINTER` intrinsics.
- The `OPTIONAL` attribute is now allowed for dummy arguments; an absent argument matches a `NULL` pointer.
- Assumed types (`TYPE(*)`) have been added, which may only be used for dummy arguments. They are unlimited polymorphic but contrary to `CLASS(*)` they do not contain any type information, similar to C's `void *` pointers. Expressions of any type and kind can be passed; thus, it can be used as replacement for `TYPE(C_PTR)`, avoiding the use of `C_LOC` in the caller.

  Note, however, that `TYPE(*)` only accepts scalar arguments, unless the `DIMENSION` is explicitly specified. As `DIMENSION(*)` only supports array (including array elements) but no scalars, it is not a full replacement for `C_LOC`. On the other hand, assumed-type assumed-rank dummy arguments (`TYPE(*), DIMENSION(..)`) allow for both scalars and arrays, but require special code on the callee side to handle the array descriptor.

- Assumed-rank arrays (`DIMENSION(..)`) as dummy argument allow that scalars and arrays of any rank can be passed as actual argument. As the Technical Specification does not provide for direct means to operate with them, they have to be used either from the C side or be converted using `C_LOC` and `C_F_POINTER` to scalars or arrays of a specific rank. The rank can be determined using the `RANK` intrinisic.

Currently unimplemented:

- GNU Fortran always uses an array descriptor, which does not match the one of the Technical Specification. The `ISO_Fortran_binding.h` header file and the C functions it specifies are not available.
- Using assumed-shape, assumed-rank and deferred-shape arrays in `BIND(C)` procedures is not fully supported. In particular, C interoperable strings of other length than one are not supported as this requires the new array descriptor.

Next: Non-Fortran Main Program, Previous: Interoperability with C, Up: Mixed-Language Programming

### 7.2 GNU Fortran Compiler Directives

The Fortran standard describes how a conforming program shall behave; however, the exact implementation is not standardized. In order to allow the user to choose specific implementation details, compiler directives can be used to set attributes of variables and procedures which are not part of the standard. Whether a given attribute is supported and its exact effects depend on both the operating system and on the processor; see C Extensions for details.

For procedures and procedure pointers, the following attributes can be used to change the calling convention:

- `CDECL` – standard C calling convention
- `STDCALL` – convention where the called procedure pops the stack
- `FASTCALL` – part of the arguments are passed via registers instead using the stack

Besides changing the calling convention, the attributes also influence the decoration of the symbol name, e.g., by a leading underscore or by a trailing at-sign followed by the number of bytes on the stack. When assigning a procedure to a procedure pointer, both should use the same calling convention.

On some systems, procedures and global variables (module variables and `COMMON` blocks) need special handling to be accessible when they are in a shared library. The following attributes are available:

- `DLLEXPORT` – provide a global pointer to a pointer in the DLL
- `DLLIMPORT` – reference the function or variable using a global pointer

For dummy arguments, the `NO_ARG_CHECK` attribute can be used; in other compilers, it is also known as `IGNORE_TKR`. For dummy arguments with this attribute actual arguments of any type and kind (similar to `TYPE(*)`), scalars and arrays of any rank (no equivalent in Fortran standard) are accepted. As with `TYPE(*)`, the argument is unlimited polymorphic and no type information is available. Additionally, the argument may only be passed to dummy arguments with the `NO_ARG_CHECK` attribute and as argument to the `PRESENT` intrinsic function and to `C_LOC` of the `ISO_C_BINDING` module.

Variables with `NO_ARG_CHECK` attribute shall be of assumed-type (`TYPE(*)`; recommended) or of type `INTEGER`, `LOGICAL`, `REAL` or `COMPLEX`. They shall not have the `ALLOCATE`, `CODIMENSION`, `INTENT(OUT)`, `POINTER` or `VALUE` attribute; furthermore, they shall be either scalar or of assumed-size (`dimension(*)`). As `TYPE(*)`, the `NO_ARG_CHECK` attribute requires an explicit interface.

- `NO_ARG_CHECK` – disable the type, kind and rank checking

The attributes are specified using the syntax

`!GCC$ ATTRIBUTES` attribute-list `::` variable-list

where in free-form source code only whitespace is allowed before `!GCC$` and in fixed-form source code `!GCC$`, `cGCC$` or `*GCC$` shall start in the first column.

For procedures, the compiler directives shall be placed into the body of the procedure; for variables and procedure pointers, they shall be in the same declaration part as the variable or procedure pointer.

Next: Naming and argument-passing conventions, Previous: GNU Fortran Compiler Directives, Up: Mixed-Language Programming

### 7.3 Non-Fortran Main Program

Even if you are doing mixed-language programming, it is very likely that you do not need to know or use the information in this section. Since it is about the internal structure of GNU Fortran, it may also change in GCC minor releases.

When you compile a `PROGRAM` with GNU Fortran, a function with the name `main` (in the symbol table of the object file) is generated, which initializes the libgfortran library and then calls the actual program which uses the name `MAIN__`, for historic reasons. If you link GNU Fortran compiled procedures to, e.g., a C or C++ program or to a Fortran program compiled by a different compiler, the libgfortran library is not initialized and thus a few intrinsic procedures do not work properly, e.g. those for obtaining the command-line arguments.

Therefore, if your `PROGRAM` is not compiled with GNU Fortran and the GNU Fortran compiled procedures require intrinsics relying on the library initialization, you need to initialize the library yourself. Using the default options, gfortran calls `_gfortran_set_args` and `_gfortran_set_options`. The initialization of the former is needed if the called procedures access the command line (and for backtracing); the latter sets some flags based on the standard chosen or to enable backtracing. In typical programs, it is not necessary to call any initialization function.

If your `PROGRAM` is compiled with GNU Fortran, you shall not call any of the following functions. The libgfortran initialization functions are shown in C syntax but using C bindings they are also accessible from Fortran.

Next: _gfortran_set_options, Up: Non-Fortran Main Program

#### 7.3.1 `_gfortran_set_args` — Save command-line arguments

Description:
  `_gfortran_set_args` saves the command-line arguments; this initialization is required if any of the command-line intrinsics is called. Additionally, it shall be called if backtracing is enabled (see `_gfortran_set_options`).
Syntax:
  `void _gfortran_set_args (int argc, char *argv[])`
Arguments:

  argc | number of command line argument strings
  argv | the command-line argument strings; argv[0] is the pathname of the executable itself.

Example:

                int main (int argc, char *argv[])
                {
                  /* Initialize libgfortran.  */
                  _gfortran_set_args (argc, argv);
                  return 0;
                }

Next: _gfortran_set_convert, Previous: _gfortran_set_args, Up: Non-Fortran Main Program

#### 7.3.2 `_gfortran_set_options` — Set library option flags

Description:
  `_gfortran_set_options` sets several flags related to the Fortran standard to be used, whether backtracing should be enabled and whether range checks should be performed. The syntax allows for upward compatibility since the number of passed flags is specified; for non-passed flags, the default value is used. See also see Code Gen Options. Please note that not all flags are actually used.
Syntax:
  `void _gfortran_set_options (int num, int options[])`
Arguments:

  num | number of options passed
  argv | The list of flag values

option flag list:

  option[0] | Allowed standard; can give run-time errors if e.g. an input-output edit descriptor is invalid in a given standard. Possible values are (bitwise or-ed) `GFC_STD_F77` (1), `GFC_STD_F95_OBS` (2), `GFC_STD_F95_DEL` (4), `GFC_STD_F95` (8), `GFC_STD_F2003` (16), `GFC_STD_GNU` (32), `GFC_STD_LEGACY` (64), `GFC_STD_F2008` (128), `GFC_STD_F2008_OBS` (256) and GFC_STD_F2008_TS (512). Default: `GFC_STD_F95_OBS | GFC_STD_F95_DEL | GFC_STD_F95 | GFC_STD_F2003 | GFC_STD_F2008 | GFC_STD_F2008_TS | GFC_STD_F2008_OBS | GFC_STD_F77 | GFC_STD_GNU | GFC_STD_LEGACY`.
  option[1] | Standard-warning flag; prints a warning to standard error. Default: `GFC_STD_F95_DEL | GFC_STD_LEGACY`.
  option[2] | If non zero, enable pedantic checking. Default: off.
  option[3] | Unused.
  option[4] | If non zero, enable backtracing on run-time errors. Default: off. (Default in the compiler: on.) Note: Installs a signal handler and requires command-line initialization using `_gfortran_set_args`.
  option[5] | If non zero, supports signed zeros. Default: enabled.
  option[6] | Enables run-time checking. Possible values are (bitwise or-ed): GFC_RTCHECK_BOUNDS (1), GFC_RTCHECK_ARRAY_TEMPS (2), GFC_RTCHECK_RECURSION (4), GFC_RTCHECK_DO (16), GFC_RTCHECK_POINTER (32). Default: disabled.
  option[7] | Unused.
  option[8] | Show a warning when invoking `STOP` and `ERROR STOP` if a floating-point exception occurred. Possible values are (bitwise or-ed) `GFC_FPE_INVALID` (1), `GFC_FPE_DENORMAL` (2), `GFC_FPE_ZERO` (4), `GFC_FPE_OVERFLOW` (8), `GFC_FPE_UNDERFLOW` (16), `GFC_FPE_INEXACT` (32). Default: None (0). (Default in the compiler: `GFC_FPE_INVALID | GFC_FPE_DENORMAL | GFC_FPE_ZERO | GFC_FPE_OVERFLOW | GFC_FPE_UNDERFLOW`.)

Example:

                  /* Use gfortran 4.9 default options.  */
                  static int options[] = {68, 511, 0, 0, 1, 1, 0, 0, 31};
                  _gfortran_set_options (9, &options);

Next: _gfortran_set_record_marker, Previous: _gfortran_set_options, Up: Non-Fortran Main Program

#### 7.3.3 `_gfortran_set_convert` — Set endian conversion

Description:
  `_gfortran_set_convert` set the representation of data for unformatted files.
Syntax:
  `void _gfortran_set_convert (int conv)`
Arguments:

  conv | Endian conversion, possible values: GFC_CONVERT_NATIVE (0, default), GFC_CONVERT_SWAP (1), GFC_CONVERT_BIG (2), GFC_CONVERT_LITTLE (3).

Example:

                int main (int argc, char *argv[])
                {
                  /* Initialize libgfortran.  */
                  _gfortran_set_args (argc, argv);
                  _gfortran_set_convert (1);
                  return 0;
                }

Next: _gfortran_set_fpe, Previous: _gfortran_set_convert, Up: Non-Fortran Main Program

#### 7.3.4 `_gfortran_set_record_marker` — Set length of record markers

Description:
  `_gfortran_set_record_marker` sets the length of record markers for unformatted files.
Syntax:
  `void _gfortran_set_record_marker (int val)`
Arguments:

  val | Length of the record marker; valid values are 4 and 8. Default is 4.

Example:

                int main (int argc, char *argv[])
                {
                  /* Initialize libgfortran.  */
                  _gfortran_set_args (argc, argv);
                  _gfortran_set_record_marker (8);
                  return 0;
                }

Next: _gfortran_set_max_subrecord_length, Previous: _gfortran_set_record_marker, Up: Non-Fortran Main Program

#### 7.3.5 `_gfortran_set_fpe` — Enable floating point exception traps

Description:
  `_gfortran_set_fpe` enables floating point exception traps for the specified exceptions. On most systems, this will result in a SIGFPE signal being sent and the program being aborted.
Syntax:
  `void _gfortran_set_fpe (int val)`
Arguments:

  option[0] | IEEE exceptions. Possible values are (bitwise or-ed) zero (0, default) no trapping, `GFC_FPE_INVALID` (1), `GFC_FPE_DENORMAL` (2), `GFC_FPE_ZERO` (4), `GFC_FPE_OVERFLOW` (8), `GFC_FPE_UNDERFLOW` (16), and `GFC_FPE_INEXACT` (32).

Example:

                int main (int argc, char *argv[])
                {
                  /* Initialize libgfortran.  */
                  _gfortran_set_args (argc, argv);
                  /* FPE for invalid operations such as SQRT(-1.0).  */
                  _gfortran_set_fpe (1);
                  return 0;
                }

Previous: _gfortran_set_fpe, Up: Non-Fortran Main Program

#### 7.3.6 `_gfortran_set_max_subrecord_length` — Set subrecord length

Description:
  `_gfortran_set_max_subrecord_length` set the maximum length for a subrecord. This option only makes sense for testing and debugging of unformatted I/O.
Syntax:
  `void _gfortran_set_max_subrecord_length (int val)`
Arguments:

  val | the maximum length for a subrecord; the maximum permitted value is 2147483639, which is also the default.

Example:

                int main (int argc, char *argv[])
                {
                  /* Initialize libgfortran.  */
                  _gfortran_set_args (argc, argv);
                  _gfortran_set_max_subrecord_length (8);
                  return 0;
                }

Previous: Non-Fortran Main Program, Up: Mixed-Language Programming

### 7.4 Naming and argument-passing conventions

This section gives an overview about the naming convention of procedures and global variables and about the argument passing conventions used by GNU Fortran. If a C binding has been specified, the naming convention and some of the argument-passing conventions change. If possible, mixed-language and mixed-compiler projects should use the better defined C binding for interoperability. See see Interoperability with C.

Next: Argument passing conventions, Up: Naming and argument-passing conventions

#### 7.4.1 Naming conventions

According the Fortran standard, valid Fortran names consist of a letter between `A` to `Z`, `a` to `z`, digits `0`, `1` to `9` and underscores (`_`) with the restriction that names may only start with a letter. As vendor extension, the dollar sign (`$`) is additionally permitted with the option `-fdollar-ok`, but not as first character and only if the target system supports it.

By default, the procedure name is the lower-cased Fortran name with an appended underscore (`_`); using `-fno-underscoring` no underscore is appended while `-fsecond-underscore` appends two underscores. Depending on the target system and the calling convention, the procedure might be additionally dressed; for instance, on 32bit Windows with `stdcall`, an at-sign `@` followed by an integer number is appended. For the changing the calling convention, see see GNU Fortran Compiler Directives.

For common blocks, the same convention is used, i.e. by default an underscore is appended to the lower-cased Fortran name. Blank commons have the name `__BLNK__`.

For procedures and variables declared in the specification space of a module, the name is formed by `__`, followed by the lower-cased module name, `_MOD_`, and the lower-cased Fortran name. Note that no underscore is appended.

Previous: Naming conventions, Up: Naming and argument-passing conventions

#### 7.4.2 Argument passing conventions

Subroutines do not return a value (matching C99's `void`) while functions either return a value as specified in the platform ABI or the result variable is passed as hidden argument to the function and no result is returned. A hidden result variable is used when the result variable is an array or of type `CHARACTER`.

Arguments are passed according to the platform ABI. In particular, complex arguments might not be compatible to a struct with two real components for the real and imaginary part. The argument passing matches the one of C99's `_Complex`. Functions with scalar complex result variables return their value and do not use a by-reference argument. Note that with the `-ff2c` option, the argument passing is modified and no longer completely matches the platform ABI. Some other Fortran compilers use `f2c` semantic by default; this might cause problems with interoperablility.

GNU Fortran passes most arguments by reference, i.e. by passing a pointer to the data. Note that the compiler might use a temporary variable into which the actual argument has been copied, if required semantically (copy-in/copy-out).

For arguments with `ALLOCATABLE` and `POINTER` attribute (including procedure pointers), a pointer to the pointer is passed such that the pointer address can be modified in the procedure.

For dummy arguments with the `VALUE` attribute: Scalar arguments of the type `INTEGER`, `LOGICAL`, `REAL` and `COMPLEX` are passed by value according to the platform ABI. (As vendor extension and not recommended, using `%VAL()` in the call to a procedure has the same effect.) For `TYPE(C_PTR)` and procedure pointers, the pointer itself is passed such that it can be modified without affecting the caller.

For Boolean (`LOGICAL`) arguments, please note that GCC expects only the integer value 0 and 1. If a GNU Fortran `LOGICAL` variable contains another integer value, the result is undefined. As some other Fortran compilers use -1 for `.TRUE.`, extra care has to be taken – such as passing the value as `INTEGER`. (The same value restriction also applies to other front ends of GCC, e.g. to GCC's C99 compiler for `_Bool` or GCC's Ada compiler for `Boolean`.)

For arguments of `CHARACTER` type, the character length is passed as hidden argument. For deferred-length strings, the value is passed by reference, otherwise by value. The character length has the type `INTEGER(kind=4)`. Note with C binding, `CHARACTER(len=1)` result variables are returned according to the platform ABI and no hidden length argument is used for dummy arguments; with `VALUE`, those variables are passed by value.

For `OPTIONAL` dummy arguments, an absent argument is denoted by a NULL pointer, except for scalar dummy arguments of type `INTEGER`, `LOGICAL`, `REAL` and `COMPLEX` which have the `VALUE` attribute. For those, a hidden Boolean argument (`logical(kind=C_bool),value`) is used to indicate whether the argument is present.

Arguments which are assumed-shape, assumed-rank or deferred-rank arrays or, with `-fcoarray=lib`, allocatable scalar coarrays use an array descriptor. All other arrays pass the address of the first element of the array. With `-fcoarray=lib`, the token and the offset belonging to nonallocatable coarrays dummy arguments are passed as hidden argument along the character length hidden arguments. The token is an oparque pointer identifying the coarray and the offset is a passed-by-value integer of kind `C_PTRDIFF_T`, denoting the byte offset between the base address of the coarray and the passed scalar or first element of the passed array.

The arguments are passed in the following order

- Result variable, when the function result is passed by reference
- Character length of the function result, if it is a of type `CHARACTER` and no C binding is used
- The arguments in the order in which they appear in the Fortran declaration
- The the present status for optional arguments with value attribute, which are internally passed by value
- The character length and/or coarray token and offset for the first argument which is a `CHARACTER` or a nonallocatable coarray dummy argument, followed by the hidden arguments of the next dummy argument of such a type

Next: Intrinsic Modules, Previous: Mixed-Language Programming, Up: Top

## 8 Intrinsic Procedures

Next: ABORT, Up: Intrinsic Procedures

### 8.1 Introduction to intrinsic procedures

The intrinsic procedures provided by GNU Fortran include all of the intrinsic procedures required by the Fortran 95 standard, a set of intrinsic procedures for backwards compatibility with G77, and a selection of intrinsic procedures from the Fortran 2003 and Fortran 2008 standards. Any conflict between a description here and a description in either the Fortran 95 standard, the Fortran 2003 standard or the Fortran 2008 standard is unintentional, and the standard(s) should be considered authoritative.

The enumeration of the `KIND` type parameter is processor defined in the Fortran 95 standard. GNU Fortran defines the default integer type and default real type by `INTEGER(KIND=4)` and `REAL(KIND=4)`, respectively. The standard mandates that both data types shall have another kind, which have more precision. On typical target architectures supported by `gfortran`, this kind type parameter is `KIND=8`. Hence, `REAL(KIND=8)` and `DOUBLE PRECISION` are equivalent. In the description of generic intrinsic procedures, the kind type parameter will be specified by `KIND=*`, and in the description of specific names for an intrinsic procedure the kind type parameter will be explicitly given (e.g., `REAL(KIND=4)` or `REAL(KIND=8)`). Finally, for brevity the optional `KIND=` syntax will be omitted.

Many of the intrinsic procedures take one or more optional arguments. This document follows the convention used in the Fortran 95 standard, and denotes such arguments by square brackets.

GNU Fortran offers the `-std=f95` and `-std=gnu` options, which can be used to restrict the set of intrinsic procedures to a given standard. By default, `gfortran` sets the `-std=gnu` option, and so all intrinsic procedures described here are accepted. There is one caveat. For a select group of intrinsic procedures, `g77` implemented both a function and a subroutine. Both classes have been implemented in `gfortran` for backwards compatibility with `g77`. It is noted here that these functions and subroutines cannot be intermixed in a given subprogram. In the descriptions that follow, the applicable standard for each intrinsic procedure is noted.

Next: ABS, Previous: Introduction to Intrinsics, Up: Intrinsic Procedures

### 8.2 `ABORT` — Abort the program

Description:
  `ABORT` causes immediate termination of the program. On operating systems that support a core dump, `ABORT` will produce a core dump. It will also print a backtrace, unless `-fno-backtrace` is given.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL ABORT`
Return value:
  Does not return.
Example:

                program test_abort
                  integer :: i = 1, j = 2
                  if (i /= j) call abort
                end program test_abort

See also:
  EXIT, KILL, BACKTRACE

Next: ACCESS, Previous: ABORT, Up: Intrinsic Procedures

### 8.3 `ABS` — Absolute value

Description:
  `ABS(A)` computes the absolute value of `A`.
Standard:
  Fortran 77 and later, has overloads that are GNU extensions
Class:
  Elemental function
Syntax:
  `RESULT = ABS(A)`
Arguments:

  A | The type of the argument shall be an `INTEGER`, `REAL`, or `COMPLEX`.

Return value:
  The return value is of the same type and kind as the argument except the return value is `REAL` for a `COMPLEX` argument.
Example:

                program test_abs
                  integer :: i = -1
                  real :: x = -1.e0
                  complex :: z = (-1.e0,0.e0)
                  i = abs(i)
                  x = abs(x)
                  x = abs(z)
                end program test_abs

Specific names:

  Name | Argument | Return type | Standard
  `ABS(A)` | `REAL(4) A` | `REAL(4)` | Fortran 77 and later
  `CABS(A)` | `COMPLEX(4) A` | `REAL(4)` | Fortran 77 and later
  `DABS(A)` | `REAL(8) A` | `REAL(8)` | Fortran 77 and later
  `IABS(A)` | `INTEGER(4) A` | `INTEGER(4)` | Fortran 77 and later
  `ZABS(A)` | `COMPLEX(8) A` | `COMPLEX(8)` | GNU extension
  `CDABS(A)` | `COMPLEX(8) A` | `COMPLEX(8)` | GNU extension

Next: ACHAR, Previous: ABS, Up: Intrinsic Procedures

### 8.4 `ACCESS` — Checks file access modes

Description:
  `ACCESS(NAME, MODE)` checks whether the file NAME exists, is readable, writable or executable. Except for the executable check, `ACCESS` can be replaced by Fortran 95's `INQUIRE`.
Standard:
  GNU extension
Class:
  Inquiry function
Syntax:
  `RESULT = ACCESS(NAME, MODE)`
Arguments:

  NAME | Scalar `CHARACTER` of default kind with the file name. Tailing blank are ignored unless the character `achar(0)` is present, then all characters up to and excluding `achar(0)` are used as file name.
  MODE | Scalar `CHARACTER` of default kind with the file access mode, may be any concatenation of `"r"` (readable), `"w"` (writable) and `"x"` (executable), or `" "` to check for existence.

Return value:
  Returns a scalar `INTEGER`, which is `0` if the file is accessible in the given mode; otherwise or if an invalid argument has been given for `MODE` the value `1` is returned.
Example:

                program access_test
                  implicit none
                  character(len=*), parameter :: file  = 'test.dat'
                  character(len=*), parameter :: file2 = 'test.dat  '//achar(0)
                  if(access(file,' ') == 0) print *, trim(file),' is exists'
                  if(access(file,'r') == 0) print *, trim(file),' is readable'
                  if(access(file,'w') == 0) print *, trim(file),' is writable'
                  if(access(file,'x') == 0) print *, trim(file),' is executable'
                  if(access(file2,'rwx') == 0) &
                    print *, trim(file2),' is readable, writable and executable'
                end program access_test

Specific names:
See also:

Next: ACOS, Previous: ACCESS, Up: Intrinsic Procedures

### 8.5 `ACHAR` — Character in ASCII collating sequence

Description:
  `ACHAR(I)` returns the character located at position `I` in the ASCII collating sequence.
Standard:
  Fortran 77 and later, with KIND argument Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = ACHAR(I [, KIND])`
Arguments:

  I | The type shall be `INTEGER`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `CHARACTER` with a length of one. If the KIND argument is present, the return value is of the specified kind and of the default kind otherwise.
Example:

                program test_achar
                  character c
                  c = achar(32)
                end program test_achar

Note:
  See ICHAR for a discussion of converting between numerical values and formatted string representations.
See also:
  CHAR, IACHAR, ICHAR

Next: ACOSH, Previous: ACHAR, Up: Intrinsic Procedures

### 8.6 `ACOS` — Arccosine function

Description:
  `ACOS(X)` computes the arccosine of X (inverse of `COS(X)`).
Standard:
  Fortran 77 and later, for a complex argument Fortran 2008 or later
Class:
  Elemental function
Syntax:
  `RESULT = ACOS(X)`
Arguments:

  X | The type shall either be `REAL` with a magnitude that is less than or equal to one - or the type shall be `COMPLEX`.

Return value:
  The return value is of the same type and kind as X. The real part of the result is in radians and lies in the range 0 \leq \Re \acos(x) \leq \pi.
Example:

                program test_acos
                  real(8) :: x = 0.866_8
                  x = acos(x)
                end program test_acos

Specific names:

  Name | Argument | Return type | Standard
  `ACOS(X)` | `REAL(4) X` | `REAL(4)` | Fortran 77 and later
  `DACOS(X)` | `REAL(8) X` | `REAL(8)` | Fortran 77 and later

See also:
  Inverse function: COS

Next: ADJUSTL, Previous: ACOS, Up: Intrinsic Procedures

### 8.7 `ACOSH` — Inverse hyperbolic cosine function

Description:
  `ACOSH(X)` computes the inverse hyperbolic cosine of X.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = ACOSH(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has the same type and kind as X. If X is complex, the imaginary part of the result is in radians and lies between 0 \leq \Im \acosh(x) \leq \pi.
Example:

                PROGRAM test_acosh
                  REAL(8), DIMENSION(3) :: x = (/ 1.0, 2.0, 3.0 /)
                  WRITE (*,*) ACOSH(x)
                END PROGRAM

Specific names:

  Name | Argument | Return type | Standard
  `DACOSH(X)` | `REAL(8) X` | `REAL(8)` | GNU extension

See also:
  Inverse function: COSH

Next: ADJUSTR, Previous: ACOSH, Up: Intrinsic Procedures

### 8.8 `ADJUSTL` — Left adjust a string

Description:
  `ADJUSTL(STRING)` will left adjust a string by removing leading spaces. Spaces are inserted at the end of the string as needed.
Standard:
  Fortran 90 and later
Class:
  Elemental function
Syntax:
  `RESULT = ADJUSTL(STRING)`
Arguments:

  STRING | The type shall be `CHARACTER`.

Return value:
  The return value is of type `CHARACTER` and of the same kind as STRING where leading spaces are removed and the same number of spaces are inserted on the end of STRING.
Example:

                program test_adjustl
                  character(len=20) :: str = '   gfortran'
                  str = adjustl(str)
                  print *, str
                end program test_adjustl

See also:
  ADJUSTR, TRIM

Next: AIMAG, Previous: ADJUSTL, Up: Intrinsic Procedures

### 8.9 `ADJUSTR` — Right adjust a string

Description:
  `ADJUSTR(STRING)` will right adjust a string by removing trailing spaces. Spaces are inserted at the start of the string as needed.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = ADJUSTR(STRING)`
Arguments:

  STR | The type shall be `CHARACTER`.

Return value:
  The return value is of type `CHARACTER` and of the same kind as STRING where trailing spaces are removed and the same number of spaces are inserted at the start of STRING.
Example:

                program test_adjustr
                  character(len=20) :: str = 'gfortran'
                  str = adjustr(str)
                  print *, str
                end program test_adjustr

See also:
  ADJUSTL, TRIM

Next: AINT, Previous: ADJUSTR, Up: Intrinsic Procedures

### 8.10 `AIMAG` — Imaginary part of complex number

Description:
  `AIMAG(Z)` yields the imaginary part of complex argument `Z`. The `IMAG(Z)` and `IMAGPART(Z)` intrinsic functions are provided for compatibility with `g77`, and their use in new code is strongly discouraged.
Standard:
  Fortran 77 and later, has overloads that are GNU extensions
Class:
  Elemental function
Syntax:
  `RESULT = AIMAG(Z)`
Arguments:

  Z | The type of the argument shall be `COMPLEX`.

Return value:
  The return value is of type `REAL` with the kind type parameter of the argument.
Example:

                program test_aimag
                  complex(4) z4
                  complex(8) z8
                  z4 = cmplx(1.e0_4, 0.e0_4)
                  z8 = cmplx(0.e0_8, 1.e0_8)
                  print *, aimag(z4), dimag(z8)
                end program test_aimag

Specific names:

  Name | Argument | Return type | Standard
  `AIMAG(Z)` | `COMPLEX Z` | `REAL` | GNU extension
  `DIMAG(Z)` | `COMPLEX(8) Z` | `REAL(8)` | GNU extension
  `IMAG(Z)` | `COMPLEX Z` | `REAL` | GNU extension
  `IMAGPART(Z)` | `COMPLEX Z` | `REAL` | GNU extension

Next: ALARM, Previous: AIMAG, Up: Intrinsic Procedures

### 8.11 `AINT` — Truncate to a whole number

Description:
  `AINT(A [, KIND])` truncates its argument to a whole number.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = AINT(A [, KIND])`
Arguments:

  A | The type of the argument shall be `REAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `REAL` with the kind type parameter of the argument if the optional KIND is absent; otherwise, the kind type parameter will be given by KIND. If the magnitude of X is less than one, `AINT(X)` returns zero. If the magnitude is equal to or greater than one then it returns the largest whole number that does not exceed its magnitude. The sign is the same as the sign of X.
Example:

                program test_aint
                  real(4) x4
                  real(8) x8
                  x4 = 1.234E0_4
                  x8 = 4.321_8
                  print *, aint(x4), dint(x8)
                  x8 = aint(x4,8)
                end program test_aint

Specific names:

  Name | Argument | Return type | Standard
  `AINT(A)` | `REAL(4) A` | `REAL(4)` | Fortran 77 and later
  `DINT(A)` | `REAL(8) A` | `REAL(8)` | Fortran 77 and later

Next: ALL, Previous: AINT, Up: Intrinsic Procedures

### 8.12 `ALARM` — Execute a routine after a given delay

Description:
  `ALARM(SECONDS, HANDLER [, STATUS])` causes external subroutine HANDLER to be executed after a delay of SECONDS by using `alarm(2)` 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.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL ALARM(SECONDS, HANDLER [, STATUS])`
Arguments:

  SECONDS | The type of the argument shall be a scalar `INTEGER`. It is `INTENT(IN)`.
  HANDLER | Signal handler (`INTEGER FUNCTION` or `SUBROUTINE`) or dummy/global `INTEGER` scalar. The scalar values may be either `SIG_IGN=1` to ignore the alarm generated or `SIG_DFL=0` to set the default action. It is `INTENT(IN)`.
  STATUS | (Optional) STATUS shall be a scalar variable of the default `INTEGER` kind. It is `INTENT(OUT)`.

Example:

                program test_alarm
                  external handler_print
                  integer i
                  call alarm (3, handler_print, i)
                  print *, i
                  call sleep(10)
                end program test_alarm

  This will cause the external routine handler_print to be called after 3 seconds.

Next: ALLOCATED, Previous: ALARM, Up: Intrinsic Procedures

### 8.13 `ALL` — All values in MASK along DIM are true

Description:
  `ALL(MASK [, DIM])` determines if all the values are true in MASK in the array along dimension DIM.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = ALL(MASK [, DIM])`
Arguments:

  MASK | The type of the argument shall be `LOGICAL` and it shall not be scalar.
  DIM | (Optional) DIM shall be a scalar integer with a value that lies between one and the rank of MASK.

Return value:
  `ALL(MASK)` returns a scalar value of type `LOGICAL` where the kind type parameter is the same as the kind type parameter of MASK. If DIM is present, then `ALL(MASK, DIM)` returns an array with the rank of MASK minus 1. The shape is determined from the shape of MASK where the DIM dimension is elided.
  (A)
    `ALL(MASK)` is true if all elements of MASK are true. It also is true if MASK has zero size; otherwise, it is false.
  (B)
    If the rank of MASK is one, then `ALL(MASK,DIM)` is equivalent to `ALL(MASK)`. If the rank is greater than one, then `ALL(MASK,DIM)` is determined by applying `ALL` to the array sections.
Example:

                program test_all
                  logical l
                  l = all((/.true., .true., .true./))
                  print *, l
                  call section
                  contains
                    subroutine section
                      integer a(2,3), b(2,3)
                      a = 1
                      b = 1
                      b(2,2) = 2
                      print *, all(a .eq. b, 1)
                      print *, all(a .eq. b, 2)
                    end subroutine section
                end program test_all

Next: AND, Previous: ALL, Up: Intrinsic Procedures

### 8.14 `ALLOCATED` — Status of an allocatable entity

Description:
  `ALLOCATED(ARRAY)` and `ALLOCATED(SCALAR)` check the allocation status of ARRAY and SCALAR, respectively.
Standard:
  Fortran 95 and later. Note, the `SCALAR=` keyword and allocatable scalar entities are available in Fortran 2003 and later.
Class:
  Inquiry function
Syntax:

  `RESULT = ALLOCATED(ARRAY)`
  `RESULT = ALLOCATED(SCALAR)`

Arguments:

  ARRAY | The argument shall be an `ALLOCATABLE` array.
  SCALAR | The argument shall be an `ALLOCATABLE` scalar.

Return value:
  The return value is a scalar `LOGICAL` with the default logical kind type parameter. If the argument is allocated, then the result is `.TRUE.`; otherwise, it returns `.FALSE.`
Example:

                program test_allocated
                  integer :: i = 4
                  real(4), allocatable :: x(:)
                  if (.not. allocated(x)) allocate(x(i))
                end program test_allocated

Next: ANINT, Previous: ALLOCATED, Up: Intrinsic Procedures

### 8.15 `AND` — Bitwise logical AND

Description:
  Bitwise logical `AND`.

  This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. For integer arguments, programmers should consider the use of the IAND intrinsic defined by the Fortran standard.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = AND(I, J)`
Arguments:

  I | The type shall be either a scalar `INTEGER` type or a scalar `LOGICAL` type.
  J | The type shall be the same as the type of I.

Return value:
  The return type is either a scalar `INTEGER` or a scalar `LOGICAL`. If the kind type parameters differ, then the smaller kind type is implicitly converted to larger kind, and the return has the larger kind.
Example:

                PROGRAM test_and
                  LOGICAL :: T = .TRUE., F = .FALSE.
                  INTEGER :: a, b
                  DATA a / Z'F' /, b / Z'3' /

                  WRITE (*,*) AND(T, T), AND(T, F), AND(F, T), AND(F, F)
                  WRITE (*,*) AND(a, b)
                END PROGRAM

See also:
  Fortran 95 elemental function: IAND

Next: ANY, Previous: AND, Up: Intrinsic Procedures

### 8.16 `ANINT` — Nearest whole number

Description:
  `ANINT(A [, KIND])` rounds its argument to the nearest whole number.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = ANINT(A [, KIND])`
Arguments:

  A | The type of the argument shall be `REAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type real with the kind type parameter of the argument if the optional KIND is absent; otherwise, the kind type parameter will be given by KIND. If A is greater than zero, `ANINT(A)` returns `AINT(X+0.5)`. If A is less than or equal to zero then it returns `AINT(X-0.5)`.
Example:

                program test_anint
                  real(4) x4
                  real(8) x8
                  x4 = 1.234E0_4
                  x8 = 4.321_8
                  print *, anint(x4), dnint(x8)
                  x8 = anint(x4,8)
                end program test_anint

Specific names:

  Name | Argument | Return type | Standard
  `AINT(A)` | `REAL(4) A` | `REAL(4)` | Fortran 77 and later
  `DNINT(A)` | `REAL(8) A` | `REAL(8)` | Fortran 77 and later

Next: ASIN, Previous: ANINT, Up: Intrinsic Procedures

### 8.17 `ANY` — Any value in MASK along DIM is true

Description:
  `ANY(MASK [, DIM])` determines if any of the values in the logical array MASK along dimension DIM are `.TRUE.`.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = ANY(MASK [, DIM])`
Arguments:

  MASK | The type of the argument shall be `LOGICAL` and it shall not be scalar.
  DIM | (Optional) DIM shall be a scalar integer with a value that lies between one and the rank of MASK.

Return value:
  `ANY(MASK)` returns a scalar value of type `LOGICAL` where the kind type parameter is the same as the kind type parameter of MASK. If DIM is present, then `ANY(MASK, DIM)` returns an array with the rank of MASK minus 1. The shape is determined from the shape of MASK where the DIM dimension is elided.
  (A)
    `ANY(MASK)` is true if any element of MASK is true; otherwise, it is false. It also is false if MASK has zero size.
  (B)
    If the rank of MASK is one, then `ANY(MASK,DIM)` is equivalent to `ANY(MASK)`. If the rank is greater than one, then `ANY(MASK,DIM)` is determined by applying `ANY` to the array sections.
Example:

                program test_any
                  logical l
                  l = any((/.true., .true., .true./))
                  print *, l
                  call section
                  contains
                    subroutine section
                      integer a(2,3), b(2,3)
                      a = 1
                      b = 1
                      b(2,2) = 2
                      print *, any(a .eq. b, 1)
                      print *, any(a .eq. b, 2)
                    end subroutine section
                end program test_any

Next: ASINH, Previous: ANY, Up: Intrinsic Procedures

### 8.18 `ASIN` — Arcsine function

Description:
  `ASIN(X)` computes the arcsine of its X (inverse of `SIN(X)`).
Standard:
  Fortran 77 and later, for a complex argument Fortran 2008 or later
Class:
  Elemental function
Syntax:
  `RESULT = ASIN(X)`
Arguments:

  X | The type shall be either `REAL` and a magnitude that is less than or equal to one - or be `COMPLEX`.

Return value:
  The return value is of the same type and kind as X. The real part of the result is in radians and lies in the range -\pi/2 \leq \Re \asin(x) \leq \pi/2.
Example:

                program test_asin
                  real(8) :: x = 0.866_8
                  x = asin(x)
                end program test_asin

Specific names:

  Name | Argument | Return type | Standard
  `ASIN(X)` | `REAL(4) X` | `REAL(4)` | Fortran 77 and later
  `DASIN(X)` | `REAL(8) X` | `REAL(8)` | Fortran 77 and later

See also:
  Inverse function: SIN

Next: ASSOCIATED, Previous: ASIN, Up: Intrinsic Procedures

### 8.19 `ASINH` — Inverse hyperbolic sine function

Description:
  `ASINH(X)` computes the inverse hyperbolic sine of X.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = ASINH(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value is of the same type and kind as X. If X is complex, the imaginary part of the result is in radians and lies between -\pi/2 \leq \Im \asinh(x) \leq \pi/2.
Example:

                PROGRAM test_asinh
                  REAL(8), DIMENSION(3) :: x = (/ -1.0, 0.0, 1.0 /)
                  WRITE (*,*) ASINH(x)
                END PROGRAM

Specific names:

  Name | Argument | Return type | Standard
  `DASINH(X)` | `REAL(8) X` | `REAL(8)` | GNU extension.

See also:
  Inverse function: SINH

Next: ATAN, Previous: ASINH, Up: Intrinsic Procedures

### 8.20 `ASSOCIATED` — Status of a pointer or pointer/target pair

Description:
  `ASSOCIATED(POINTER [, TARGET])` determines the status of the pointer POINTER or if POINTER is associated with the target TARGET.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = ASSOCIATED(POINTER [, TARGET])`
Arguments:

  POINTER | POINTER shall have the `POINTER` attribute and it can be of any type.
  TARGET | (Optional) TARGET shall be a pointer or a target. It must have the same type, kind type parameter, and array rank as POINTER.

  The association status of neither POINTER nor TARGET shall be undefined.
Return value:
  `ASSOCIATED(POINTER)` returns a scalar value of type `LOGICAL(4)`. There are several cases:
  (A) When the optional TARGET is not present then
    `ASSOCIATED(POINTER)` is true if POINTER is associated with a target; otherwise, it returns false.
  (B) If TARGET is present and a scalar target, the result is true if
    TARGET is not a zero-sized storage sequence and the target associated with POINTER occupies the same storage units. If POINTER is disassociated, the result is false.
  (C) If TARGET is present and an array target, the result is true if
    TARGET and POINTER have the same shape, are not zero-sized arrays, are arrays whose elements are not zero-sized storage sequences, and TARGET and POINTER occupy the same storage units in array element order. As in case(B), the result is false, if POINTER is disassociated.
  (D) If TARGET is present and an scalar pointer, the result is true
    if TARGET is associated with POINTER, the target associated with TARGET are not zero-sized storage sequences and occupy the same storage units. The result is false, if either TARGET or POINTER is disassociated.
  (E) If TARGET is present and an array pointer, the result is true if
    target associated with POINTER and the target associated with TARGET have the same shape, are not zero-sized arrays, are arrays whose elements are not zero-sized storage sequences, and TARGET and POINTER occupy the same storage units in array element order. The result is false, if either TARGET or POINTER is disassociated.
Example:

                program test_associated
                   implicit none
                   real, target  :: tgt(2) = (/1., 2./)
                   real, pointer :: ptr(:)
                   ptr => tgt
                   if (associated(ptr)     .eqv. .false.) call abort
                   if (associated(ptr,tgt) .eqv. .false.) call abort
                end program test_associated

See also:
  NULL

Next: ATAN2, Previous: ASSOCIATED, Up: Intrinsic Procedures

### 8.21 `ATAN` — Arctangent function

Description:
  `ATAN(X)` computes the arctangent of X.
Standard:
  Fortran 77 and later, for a complex argument and for two arguments Fortran 2008 or later
Class:
  Elemental function
Syntax:

  `RESULT = ATAN(X)`
  `RESULT = ATAN(Y, X)`

Arguments:

  X | The type shall be `REAL` or `COMPLEX`; if Y is present, X shall be REAL.
  Y shall be of the same type and kind as X.

Return value:
  The return value is of the same type and kind as X. If Y is present, the result is identical to `ATAN2(Y,X)`. Otherwise, it the arcus tangent of X, where the real part of the result is in radians and lies in the range -\pi/2 \leq \Re \atan(x) \leq \pi/2.
Example:

                program test_atan
                  real(8) :: x = 2.866_8
                  x = atan(x)
                end program test_atan

Specific names:

  Name | Argument | Return type | Standard
  `ATAN(X)` | `REAL(4) X` | `REAL(4)` | Fortran 77 and later
  `DATAN(X)` | `REAL(8) X` | `REAL(8)` | Fortran 77 and later

See also:
  Inverse function: TAN

Next: ATANH, Previous: ATAN, Up: Intrinsic Procedures

### 8.22 `ATAN2` — Arctangent function

Description:
  `ATAN2(Y, X)` computes the principal value of the argument function of the complex number X + i Y. This function can be used to transform from Cartesian into polar coordinates and allows to determine the angle in the correct quadrant.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = ATAN2(Y, X)`
Arguments:

  Y | The type shall be `REAL`.
  X | The type and kind type parameter shall be the same as Y. If Y is zero, then X must be nonzero.

Return value:
  The return value has the same type and kind type parameter as Y. It is the principal value of the complex number X + i Y. If X is nonzero, then it lies in the range -\pi \le \atan (x) \leq \pi. The sign is positive if Y is positive. If Y is zero, then the return value is zero if X is strictly positive, \pi if X is negative and Y is positive zero (or the processor does not handle signed zeros), and -\pi if X is negative and Y is negative zero. Finally, if X is zero, then the magnitude of the result is \pi/2.
Example:

                program test_atan2
                  real(4) :: x = 1.e0_4, y = 0.5e0_4
                  x = atan2(y,x)
                end program test_atan2

Specific names:

  Name | Argument | Return type | Standard
  `ATAN2(X, Y)` | `REAL(4) X, Y` | `REAL(4)` | Fortran 77 and later
  `DATAN2(X, Y)` | `REAL(8) X, Y` | `REAL(8)` | Fortran 77 and later

Next: ATOMIC_DEFINE, Previous: ATAN2, Up: Intrinsic Procedures

### 8.23 `ATANH` — Inverse hyperbolic tangent function

Description:
  `ATANH(X)` computes the inverse hyperbolic tangent of X.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = ATANH(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has same type and kind as X. If X is complex, the imaginary part of the result is in radians and lies between -\pi/2 \leq \Im \atanh(x) \leq \pi/2.
Example:

                PROGRAM test_atanh
                  REAL, DIMENSION(3) :: x = (/ -1.0, 0.0, 1.0 /)
                  WRITE (*,*) ATANH(x)
                END PROGRAM

Specific names:

  Name | Argument | Return type | Standard
  `DATANH(X)` | `REAL(8) X` | `REAL(8)` | GNU extension

See also:
  Inverse function: TANH

Next: ATOMIC_REF, Previous: ATANH, Up: Intrinsic Procedures

### 8.24 `ATOMIC_DEFINE` — Setting a variable atomically

Description:
  `ATOMIC_DEFINE(ATOM, VALUE)` defines the variable ATOM with the value VALUE atomically.
Standard:
  Fortran 2008 and later
Class:
  Atomic subroutine
Syntax:
  `CALL ATOMIC_DEFINE(ATOM, VALUE)`
Arguments:

  ATOM | Scalar coarray or coindexed variable of either integer type with `ATOMIC_INT_KIND` kind or logical type with `ATOMIC_LOGICAL_KIND` kind.
  VALURE | Scalar and of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.

Example:

                program atomic
                  use iso_fortran_env
                  integer(atomic_int_kind) :: atom[*]
                  call atomic_define (atom[1], this_image())
                end program atomic

See also:
  ATOMIC_REF, ISO_FORTRAN_ENV

Next: BACKTRACE, Previous: ATOMIC_DEFINE, Up: Intrinsic Procedures

### 8.25 `ATOMIC_REF` — Obtaining the value of a variable atomically

Description:
  `ATOMIC_DEFINE(ATOM, VALUE)` atomically assigns the value of the variable ATOM to VALUE.
Standard:
  Fortran 2008 and later
Class:
  Atomic subroutine
Syntax:
  `CALL ATOMIC_REF(VALUE, ATOM)`
Arguments:

  VALURE | Scalar and of the same type as ATOM. If the kind is different, the value is converted to the kind of ATOM.
  ATOM | Scalar coarray or coindexed variable of either integer type with `ATOMIC_INT_KIND` kind or logical type with `ATOMIC_LOGICAL_KIND` kind.

Example:

                program atomic
                  use iso_fortran_env
                  logical(atomic_logical_kind) :: atom[*]
                  logical :: val
                  call atomic_ref (atom, .false.)
                  ! ...
                  call atomic_ref (atom, val)
                  if (val) then
                    print *, "Obtained"
                  end if
                end program atomic

See also:
  ATOMIC_DEFINE, ISO_FORTRAN_ENV

Next: BESSEL_J0, Previous: ATOMIC_REF, Up: Intrinsic Procedures

### 8.26 `BACKTRACE` — Show a backtrace

Description:
  `BACKTRACE` shows a backtrace at an arbitrary place in user code. Program execution continues normally afterwards. The backtrace information is printed to the unit corresponding to `ERROR_UNIT` in `ISO_FORTRAN_ENV`.
Standard:
  GNU Extension
Class:
  Subroutine
Syntax:
  `CALL BACKTRACE`
Arguments:
  None
See also:
  ABORT

Next: BESSEL_J1, Previous: BACKTRACE, Up: Intrinsic Procedures

### 8.27 `BESSEL_J0` — Bessel function of the first kind of order 0

Description:
  `BESSEL_J0(X)` computes the Bessel function of the first kind of order 0 of X. This function is available under the name `BESJ0` as a GNU extension.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = BESSEL_J0(X)`
Arguments:

  X | The type shall be `REAL`, and it shall be scalar.

Return value:
  The return value is of type `REAL` and lies in the range - 0.4027... \leq Bessel (0,x) \leq 1. It has the same kind as X.
Example:

                program test_besj0
                  real(8) :: x = 0.0_8
                  x = bessel_j0(x)
                end program test_besj0

Specific names:

  Name | Argument | Return type | Standard
  `DBESJ0(X)` | `REAL(8) X` | `REAL(8)` | GNU extension

Next: BESSEL_JN, Previous: BESSEL_J0, Up: Intrinsic Procedures

### 8.28 `BESSEL_J1` — Bessel function of the first kind of order 1

Description:
  `BESSEL_J1(X)` computes the Bessel function of the first kind of order 1 of X. This function is available under the name `BESJ1` as a GNU extension.
Standard:
  Fortran 2008
Class:
  Elemental function
Syntax:
  `RESULT = BESSEL_J1(X)`
Arguments:

  X | The type shall be `REAL`, and it shall be scalar.

Return value:
  The return value is of type `REAL` and it lies in the range - 0.5818... \leq Bessel (0,x) \leq 0.5818 . It has the same kind as X.
Example:

                program test_besj1
                  real(8) :: x = 1.0_8
                  x = bessel_j1(x)
                end program test_besj1

Specific names:

  Name | Argument | Return type | Standard
  `DBESJ1(X)` | `REAL(8) X` | `REAL(8)` | GNU extension

Next: BESSEL_Y0, Previous: BESSEL_J1, Up: Intrinsic Procedures

### 8.29 `BESSEL_JN` — Bessel function of the first kind

Description:
  `BESSEL_JN(N, X)` computes the Bessel function of the first kind of order N of X. This function is available under the name `BESJN` as a GNU extension. If N and X are arrays, their ranks and shapes shall conform.

  `BESSEL_JN(N1, N2, X)` returns an array with the Bessel functions of the first kind of the orders N1 to N2.

Standard:
  Fortran 2008 and later, negative N is allowed as GNU extension
Class:
  Elemental function, except for the transformational function `BESSEL_JN(N1, N2, X)`
Syntax:

  `RESULT = BESSEL_JN(N, X)`
  `RESULT = BESSEL_JN(N1, N2, X)`

Arguments:

  N | Shall be a scalar or an array of type `INTEGER`.
  N1 | Shall be a non-negative scalar of type `INTEGER`.
  N2 | Shall be a non-negative scalar of type `INTEGER`.
  X | Shall be a scalar or an array of type `REAL`; for `BESSEL_JN(N1, N2, X)` it shall be scalar.

Return value:
  The return value is a scalar of type `REAL`. It has the same kind as X.
Note:
  The transformational function uses a recurrence algorithm which might, for some values of X, lead to different results than calls to the elemental function.
Example:

                program test_besjn
                  real(8) :: x = 1.0_8
                  x = bessel_jn(5,x)
                end program test_besjn

Specific names:

  Name | Argument | Return type | Standard
  `DBESJN(N, X)` | `INTEGER N` | `REAL(8)` | GNU extension
  | `REAL(8) X` |  |

Next: BESSEL_Y1, Previous: BESSEL_JN, Up: Intrinsic Procedures

### 8.30 `BESSEL_Y0` — Bessel function of the second kind of order 0

Description:
  `BESSEL_Y0(X)` computes the Bessel function of the second kind of order 0 of X. This function is available under the name `BESY0` as a GNU extension.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = BESSEL_Y0(X)`
Arguments:

  X | The type shall be `REAL`, and it shall be scalar.

Return value:
  The return value is a scalar of type `REAL`. It has the same kind as X.
Example:

                program test_besy0
                  real(8) :: x = 0.0_8
                  x = bessel_y0(x)
                end program test_besy0

Specific names:

  Name | Argument | Return type | Standard
  `DBESY0(X)` | `REAL(8) X` | `REAL(8)` | GNU extension

Next: BESSEL_YN, Previous: BESSEL_Y0, Up: Intrinsic Procedures

### 8.31 `BESSEL_Y1` — Bessel function of the second kind of order 1

Description:
  `BESSEL_Y1(X)` computes the Bessel function of the second kind of order 1 of X. This function is available under the name `BESY1` as a GNU extension.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = BESSEL_Y1(X)`
Arguments:

  X | The type shall be `REAL`, and it shall be scalar.

Return value:
  The return value is a scalar of type `REAL`. It has the same kind as X.
Example:

                program test_besy1
                  real(8) :: x = 1.0_8
                  x = bessel_y1(x)
                end program test_besy1

Specific names:

  Name | Argument | Return type | Standard
  `DBESY1(X)` | `REAL(8) X` | `REAL(8)` | GNU extension

Next: BGE, Previous: BESSEL_Y1, Up: Intrinsic Procedures

### 8.32 `BESSEL_YN` — Bessel function of the second kind

Description:
  `BESSEL_YN(N, X)` computes the Bessel function of the second kind of order N of X. This function is available under the name `BESYN` as a GNU extension. If N and X are arrays, their ranks and shapes shall conform.

  `BESSEL_YN(N1, N2, X)` returns an array with the Bessel functions of the first kind of the orders N1 to N2.

Standard:
  Fortran 2008 and later, negative N is allowed as GNU extension
Class:
  Elemental function, except for the transformational function `BESSEL_YN(N1, N2, X)`
Syntax:

  `RESULT = BESSEL_YN(N, X)`
  `RESULT = BESSEL_YN(N1, N2, X)`

Arguments:

  N | Shall be a scalar or an array of type `INTEGER` .
  N1 | Shall be a non-negative scalar of type `INTEGER`.
  N2 | Shall be a non-negative scalar of type `INTEGER`.
  X | Shall be a scalar or an array of type `REAL`; for `BESSEL_YN(N1, N2, X)` it shall be scalar.

Return value:
  The return value is a scalar of type `REAL`. It has the same kind as X.
Note:
  The transformational function uses a recurrence algorithm which might, for some values of X, lead to different results than calls to the elemental function.
Example:

                program test_besyn
                  real(8) :: x = 1.0_8
                  x = bessel_yn(5,x)
                end program test_besyn

Specific names:

  Name | Argument | Return type | Standard
  `DBESYN(N,X)` | `INTEGER N` | `REAL(8)` | GNU extension
  | `REAL(8) X` |  |

Next: BGT, Previous: BESSEL_YN, Up: Intrinsic Procedures

### 8.33 `BGE` — Bitwise greater than or equal to

Description:
  Determines whether an integral is a bitwise greater than or equal to another.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = BGE(I, J)`
Arguments:

  I | Shall be of `INTEGER` type.
  J | Shall be of `INTEGER` type, and of the same kind as I.

Return value:
  The return value is of type `LOGICAL` and of the default kind.
See also:
  BGT, BLE, BLT

Next: BIT_SIZE, Previous: BGE, Up: Intrinsic Procedures

### 8.34 `BGT` — Bitwise greater than

Description:
  Determines whether an integral is a bitwise greater than another.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = BGT(I, J)`
Arguments:

  I | Shall be of `INTEGER` type.
  J | Shall be of `INTEGER` type, and of the same kind as I.

Return value:
  The return value is of type `LOGICAL` and of the default kind.
See also:
  BGE, BLE, BLT

Next: BLE, Previous: BGT, Up: Intrinsic Procedures

### 8.35 `BIT_SIZE` — Bit size inquiry function

Description:
  `BIT_SIZE(I)` returns the number of bits (integer precision plus sign bit) represented by the type of I. The result of `BIT_SIZE(I)` is independent of the actual value of I.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = BIT_SIZE(I)`
Arguments:

  I | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER`
Example:

                program test_bit_size
                    integer :: i = 123
                    integer :: size
                    size = bit_size(i)
                    print *, size
                end program test_bit_size

Next: BLT, Previous: BIT_SIZE, Up: Intrinsic Procedures

### 8.36 `BLE` — Bitwise less than or equal to

Description:
  Determines whether an integral is a bitwise less than or equal to another.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = BLE(I, J)`
Arguments:

  I | Shall be of `INTEGER` type.
  J | Shall be of `INTEGER` type, and of the same kind as I.

Return value:
  The return value is of type `LOGICAL` and of the default kind.
See also:
  BGT, BGE, BLT

Next: BTEST, Previous: BLE, Up: Intrinsic Procedures

### 8.37 `BLT` — Bitwise less than

Description:
  Determines whether an integral is a bitwise less than another.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = BLT(I, J)`
Arguments:

  I | Shall be of `INTEGER` type.
  J | Shall be of `INTEGER` type, and of the same kind as I.

Return value:
  The return value is of type `LOGICAL` and of the default kind.
See also:
  BGE, BGT, BLE

Next: C_ASSOCIATED, Previous: BLT, Up: Intrinsic Procedures

### 8.38 `BTEST` — Bit test function

Description:
  `BTEST(I,POS)` returns logical `.TRUE.` if the bit at POS in I is set. The counting of the bits starts at 0.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = BTEST(I, POS)`
Arguments:

  I | The type shall be `INTEGER`.
  POS | The type shall be `INTEGER`.

Return value:
  The return value is of type `LOGICAL`
Example:

                program test_btest
                    integer :: i = 32768 + 1024 + 64
                    integer :: pos
                    logical :: bool
                    do pos=0,16
                        bool = btest(i, pos)
                        print *, pos, bool
                    end do
                end program test_btest

Next: C_F_POINTER, Previous: BTEST, Up: Intrinsic Procedures

### 8.39 `C_ASSOCIATED` — Status of a C pointer

Description:
  `C_ASSOCIATED(c_prt_1[, c_ptr_2])` determines the status of the C pointer c_ptr_1 or if c_ptr_1 is associated with the target c_ptr_2.
Standard:
  Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = C_ASSOCIATED(c_prt_1[, c_ptr_2])`
Arguments:

  c_ptr_1 | Scalar of the type `C_PTR` or `C_FUNPTR`.
  c_ptr_2 | (Optional) Scalar of the same type as c_ptr_1.

Return value:
  The return value is of type `LOGICAL`; it is `.false.` if either c_ptr_1 is a C NULL pointer or if c_ptr1 and c_ptr_2 point to different addresses.
Example:

                subroutine association_test(a,b)
                  use iso_c_binding, only: c_associated, c_loc, c_ptr
                  implicit none
                  real, pointer :: a
                  type(c_ptr) :: b
                  if(c_associated(b, c_loc(a))) &
                     stop 'b and a do not point to same target'
                end subroutine association_test

See also:
  C_LOC, C_FUNLOC

Next: C_F_PROCPOINTER, Previous: C_ASSOCIATED, Up: Intrinsic Procedures

### 8.40 `C_F_POINTER` — Convert C into Fortran pointer

Description:
  `C_F_POINTER(CPTR, FPTR[, SHAPE])` assigns the target of the C pointer CPTR to the Fortran pointer FPTR and specifies its shape.
Standard:
  Fortran 2003 and later
Class:
  Subroutine
Syntax:
  `CALL C_F_POINTER(CPTR, FPTR[, SHAPE])`
Arguments:

  CPTR | scalar of the type `C_PTR`. It is `INTENT(IN)`.
  FPTR | pointer interoperable with cptr. It is `INTENT(OUT)`.
  SHAPE | (Optional) Rank-one array of type `INTEGER` with `INTENT(IN)`. It shall be present if and only if fptr is an array. The size must be equal to the rank of fptr.

Example:

                program main
                  use iso_c_binding
                  implicit none
                  interface
                    subroutine my_routine(p) bind(c,name='myC_func')
                      import :: c_ptr
                      type(c_ptr), intent(out) :: p
                    end subroutine
                  end interface
                  type(c_ptr) :: cptr
                  real,pointer :: a(:)
                  call my_routine(cptr)
                  call c_f_pointer(cptr, a, [12])
                end program main

See also:
  C_LOC, C_F_PROCPOINTER

Next: C_FUNLOC, Previous: C_F_POINTER, Up: Intrinsic Procedures

### 8.41 `C_F_PROCPOINTER` — Convert C into Fortran procedure pointer

Description:
  `C_F_PROCPOINTER(CPTR, FPTR)` Assign the target of the C function pointer CPTR to the Fortran procedure pointer FPTR.
Standard:
  Fortran 2003 and later
Class:
  Subroutine
Syntax:
  `CALL C_F_PROCPOINTER(cptr, fptr)`
Arguments:

  CPTR | scalar of the type `C_FUNPTR`. It is `INTENT(IN)`.
  FPTR | procedure pointer interoperable with cptr. It is `INTENT(OUT)`.

Example:

                program main
                  use iso_c_binding
                  implicit none
                  abstract interface
                    function func(a)
                      import :: c_float
                      real(c_float), intent(in) :: a
                      real(c_float) :: func
                    end function
                  end interface
                  interface
                     function getIterFunc() bind(c,name="getIterFunc")
                       import :: c_funptr
                       type(c_funptr) :: getIterFunc
                     end function
                  end interface
                  type(c_funptr) :: cfunptr
                  procedure(func), pointer :: myFunc
                  cfunptr = getIterFunc()
                  call c_f_procpointer(cfunptr, myFunc)
                end program main

See also:
  C_LOC, C_F_POINTER

Next: C_LOC, Previous: C_F_PROCPOINTER, Up: Intrinsic Procedures

### 8.42 `C_FUNLOC` — Obtain the C address of a procedure

Description:
  `C_FUNLOC(x)` determines the C address of the argument.
Standard:
  Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = C_FUNLOC(x)`
Arguments:

  x | Interoperable function or pointer to such function.

Return value:
  The return value is of type `C_FUNPTR` and contains the C address of the argument.
Example:

                module x
                  use iso_c_binding
                  implicit none
                contains
                  subroutine sub(a) bind(c)
                    real(c_float) :: a
                    a = sqrt(a)+5.0
                  end subroutine sub
                end module x
                program main
                  use iso_c_binding
                  use x
                  implicit none
                  interface
                    subroutine my_routine(p) bind(c,name='myC_func')
                      import :: c_funptr
                      type(c_funptr), intent(in) :: p
                    end subroutine
                  end interface
                  call my_routine(c_funloc(sub))
                end program main

See also:
  C_ASSOCIATED, C_LOC, C_F_POINTER, C_F_PROCPOINTER

Next: C_SIZEOF, Previous: C_FUNLOC, Up: Intrinsic Procedures

### 8.43 `C_LOC` — Obtain the C address of an object

Description:
  `C_LOC(X)` determines the C address of the argument.
Standard:
  Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = C_LOC(X)`
Arguments:

  X | Shall have either the POINTER or TARGET attribute. It shall not be a coindexed object. It shall either be a variable with interoperable type and kind type parameters, or be a scalar, nonpolymorphic variable with no length type parameters.

Return value:
  The return value is of type `C_PTR` and contains the C address of the argument.
Example:

                subroutine association_test(a,b)
                  use iso_c_binding, only: c_associated, c_loc, c_ptr
                  implicit none
                  real, pointer :: a
                  type(c_ptr) :: b
                  if(c_associated(b, c_loc(a))) &
                     stop 'b and a do not point to same target'
                end subroutine association_test

See also:
  C_ASSOCIATED, C_FUNLOC, C_F_POINTER, C_F_PROCPOINTER

Next: CEILING, Previous: C_LOC, Up: Intrinsic Procedures

### 8.44 `C_SIZEOF` — Size in bytes of an expression

Description:
  `C_SIZEOF(X)` calculates the number of bytes of storage the expression `X` occupies.
Standard:
  Fortran 2008
Class:
  Inquiry function of the module `ISO_C_BINDING`
Syntax:
  `N = C_SIZEOF(X)`
Arguments:

  X | The argument shall be an interoperable data entity.

Return value:
  The return value is of type integer and of the system-dependent kind `C_SIZE_T` (from the `ISO_C_BINDING` module). Its value is the number of bytes occupied by the argument. If the argument has the `POINTER` attribute, the number of bytes of the storage area pointed to is returned. If the argument is of a derived type with `POINTER` or `ALLOCATABLE` components, the return value does not account for the sizes of the data pointed to by these components.
Example:

                   use iso_c_binding
                   integer(c_int) :: i
                   real(c_float) :: r, s(5)
                   print *, (c_sizeof(s)/c_sizeof(r) == 5)
                   end

  The example will print `.TRUE.` unless you are using a platform where default `REAL` variables are unusually padded.

See also:
  SIZEOF, STORAGE_SIZE

Next: CHAR, Previous: C_SIZEOF, Up: Intrinsic Procedures

### 8.45 `CEILING` — Integer ceiling function

Description:
  `CEILING(A)` returns the least integer greater than or equal to A.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = CEILING(A [, KIND])`
Arguments:

  A | The type shall be `REAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER(KIND)` if KIND is present and a default-kind `INTEGER` otherwise.
Example:

                program test_ceiling
                    real :: x = 63.29
                    real :: y = -63.59
                    print *, ceiling(x) ! returns 64
                    print *, ceiling(y) ! returns -63
                end program test_ceiling

See also:
  FLOOR, NINT

Next: CHDIR, Previous: CEILING, Up: Intrinsic Procedures

### 8.46 `CHAR` — Character conversion function

Description:
  `CHAR(I [, KIND])` returns the character represented by the integer I.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = CHAR(I [, KIND])`
Arguments:

  I | The type shall be `INTEGER`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `CHARACTER(1)`
Example:

                program test_char
                    integer :: i = 74
                    character(1) :: c
                    c = char(i)
                    print *, i, c ! returns 'J'
                end program test_char

Specific names:

  Name | Argument | Return type | Standard
  `CHAR(I)` | `INTEGER I` | `CHARACTER(LEN=1)` | F77 and later

Note:
  See ICHAR for a discussion of converting between numerical values and formatted string representations.
See also:
  ACHAR, IACHAR, ICHAR

Next: CHMOD, Previous: CHAR, Up: Intrinsic Procedures

### 8.47 `CHDIR` — Change working directory

Description:
  Change current working directory to a specified path.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL CHDIR(NAME [, STATUS])`
  `STATUS = CHDIR(NAME)`

Arguments:

  NAME | The type shall be `CHARACTER` of default kind and shall specify a valid path within the file system.
  STATUS | (Optional) `INTEGER` status flag of the default kind. Returns 0 on success, and a system specific and nonzero error code otherwise.

Example:

                PROGRAM test_chdir
                  CHARACTER(len=255) :: path
                  CALL getcwd(path)
                  WRITE(*,*) TRIM(path)
                  CALL chdir("/tmp")
                  CALL getcwd(path)
                  WRITE(*,*) TRIM(path)
                END PROGRAM

See also:
  GETCWD

Next: CMPLX, Previous: CHDIR, Up: Intrinsic Procedures

### 8.48 `CHMOD` — Change access permissions of files

Description:
  `CHMOD` changes the permissions of a file.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL CHMOD(NAME, MODE[, STATUS])`
  `STATUS = CHMOD(NAME, MODE)`

Arguments:

  NAME | Scalar `CHARACTER` of default kind with the file name. Trailing blanks are ignored unless the character `achar(0)` is present, then all characters up to and excluding `achar(0)` are used as the file name.
  MODE | Scalar `CHARACTER` of default kind giving the file permission. MODE uses the same syntax as the `chmod` utility as defined by the POSIX standard. The argument shall either be a string of a nonnegative octal number or a symbolic mode.
  STATUS | (optional) scalar `INTEGER`, which is `0` on success and nonzero otherwise.

Return value:
  In either syntax, STATUS is set to `0` on success and nonzero otherwise.
Example:
  `CHMOD` as subroutine

                program chmod_test
                  implicit none
                  integer :: status
                  call chmod('test.dat','u+x',status)
                  print *, 'Status: ', status
                end program chmod_test

  `CHMOD` as function:

                program chmod_test
                  implicit none
                  integer :: status
                  status = chmod('test.dat','u+x')
                  print *, 'Status: ', status
                end program chmod_test

Next: COMMAND_ARGUMENT_COUNT, Previous: CHMOD, Up: Intrinsic Procedures

### 8.49 `CMPLX` — Complex conversion function

Description:
  `CMPLX(X [, Y [, KIND]])` returns a complex number where X is converted to the real component. If Y is present it is converted to the imaginary component. If Y is not present then the imaginary component is set to 0.0. If X is complex then Y must not be present.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = CMPLX(X [, Y [, KIND]])`
Arguments:

  X | The type may be `INTEGER`, `REAL`, or `COMPLEX`.
  Y | (Optional; only allowed if X is not `COMPLEX`.) May be `INTEGER` or `REAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of `COMPLEX` type, with a kind equal to KIND if it is specified. If KIND is not specified, the result is of the default `COMPLEX` kind, regardless of the kinds of X and Y.
Example:

                program test_cmplx
                    integer :: i = 42
                    real :: x = 3.14
                    complex :: z
                    z = cmplx(i, x)
                    print *, z, cmplx(x)
                end program test_cmplx

See also:
  COMPLEX

Next: COMPILER_OPTIONS, Previous: CMPLX, Up: Intrinsic Procedures

### 8.50 `COMMAND_ARGUMENT_COUNT` — Get number of command line arguments

Description:
  `COMMAND_ARGUMENT_COUNT` returns the number of arguments passed on the command line when the containing program was invoked.
Standard:
  Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = COMMAND_ARGUMENT_COUNT()`
Arguments:

  None

Return value:
  The return value is an `INTEGER` of default kind.
Example:

                program test_command_argument_count
                    integer :: count
                    count = command_argument_count()
                    print *, count
                end program test_command_argument_count

See also:
  GET_COMMAND, GET_COMMAND_ARGUMENT

Next: COMPILER_VERSION, Previous: COMMAND_ARGUMENT_COUNT, Up: Intrinsic Procedures

### 8.51 `COMPILER_OPTIONS` — Options passed to the compiler

Description:
  `COMPILER_OPTIONS` returns a string with the options used for compiling.
Standard:
  Fortran 2008
Class:
  Inquiry function of the module `ISO_FORTRAN_ENV`
Syntax:
  `STR = COMPILER_OPTIONS()`
Arguments:
  None.
Return value:
  The return value is a default-kind string with system-dependent length. It contains the compiler flags used to compile the file, which called the `COMPILER_OPTIONS` intrinsic.
Example:

                   use iso_fortran_env
                   print '(4a)', 'This file was compiled by ', &
                                 compiler_version(), ' using the options ', &
                                 compiler_options()
                   end

See also:
  COMPILER_VERSION, ISO_FORTRAN_ENV

Next: COMPLEX, Previous: COMPILER_OPTIONS, Up: Intrinsic Procedures

### 8.52 `COMPILER_VERSION` — Compiler version string

Description:
  `COMPILER_VERSION` returns a string with the name and the version of the compiler.
Standard:
  Fortran 2008
Class:
  Inquiry function of the module `ISO_FORTRAN_ENV`
Syntax:
  `STR = COMPILER_VERSION()`
Arguments:
  None.
Return value:
  The return value is a default-kind string with system-dependent length. It contains the name of the compiler and its version number.
Example:

                   use iso_fortran_env
                   print '(4a)', 'This file was compiled by ', &
                                 compiler_version(), ' using the options ', &
                                 compiler_options()
                   end

See also:
  COMPILER_OPTIONS, ISO_FORTRAN_ENV

Next: CONJG, Previous: COMPILER_VERSION, Up: Intrinsic Procedures

### 8.53 `COMPLEX` — Complex conversion function

Description:
  `COMPLEX(X, Y)` returns a complex number where X is converted to the real component and Y is converted to the imaginary component.
Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = COMPLEX(X, Y)`
Arguments:

  X | The type may be `INTEGER` or `REAL`.
  Y | The type may be `INTEGER` or `REAL`.

Return value:
  If X and Y are both of `INTEGER` type, then the return value is of default `COMPLEX` type.

  If X and Y are of `REAL` type, or one is of `REAL` type and one is of `INTEGER` type, then the return value is of `COMPLEX` type with a kind equal to that of the `REAL` argument with the highest precision.

Example:

                program test_complex
                    integer :: i = 42
                    real :: x = 3.14
                    print *, complex(i, x)
                end program test_complex

See also:
  CMPLX

Next: COS, Previous: COMPLEX, Up: Intrinsic Procedures

### 8.54 `CONJG` — Complex conjugate function

Description:
  `CONJG(Z)` returns the conjugate of Z. If Z is `(x, y)` then the result is `(x, -y)`
Standard:
  Fortran 77 and later, has overloads that are GNU extensions
Class:
  Elemental function
Syntax:
  `Z = CONJG(Z)`
Arguments:

  Z | The type shall be `COMPLEX`.

Return value:
  The return value is of type `COMPLEX`.
Example:

                program test_conjg
                    complex :: z = (2.0, 3.0)
                    complex(8) :: dz = (2.71_8, -3.14_8)
                    z= conjg(z)
                    print *, z
                    dz = dconjg(dz)
                    print *, dz
                end program test_conjg

Specific names:

  Name | Argument | Return type | Standard
  `CONJG(Z)` | `COMPLEX Z` | `COMPLEX` | GNU extension
  `DCONJG(Z)` | `COMPLEX(8) Z` | `COMPLEX(8)` | GNU extension

Next: COSH, Previous: CONJG, Up: Intrinsic Procedures

### 8.55 `COS` — Cosine function

Description:
  `COS(X)` computes the cosine of X.
Standard:
  Fortran 77 and later, has overloads that are GNU extensions
Class:
  Elemental function
Syntax:
  `RESULT = COS(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value is of the same type and kind as X. The real part of the result is in radians. If X is of the type `REAL`, the return value lies in the range -1 \leq \cos (x) \leq 1.
Example:

                program test_cos
                  real :: x = 0.0
                  x = cos(x)
                end program test_cos

Specific names:

  Name | Argument | Return type | Standard
  `COS(X)` | `REAL(4) X` | `REAL(4)` | Fortran 77 and later
  `DCOS(X)` | `REAL(8) X` | `REAL(8)` | Fortran 77 and later
  `CCOS(X)` | `COMPLEX(4) X` | `COMPLEX(4)` | Fortran 77 and later
  `ZCOS(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | GNU extension
  `CDCOS(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | GNU extension

See also:
  Inverse function: ACOS

Next: COUNT, Previous: COS, Up: Intrinsic Procedures

### 8.56 `COSH` — Hyperbolic cosine function

Description:
  `COSH(X)` computes the hyperbolic cosine of X.
Standard:
  Fortran 77 and later, for a complex argument Fortran 2008 or later
Class:
  Elemental function
Syntax:
  `X = COSH(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has same type and kind as X. If X is complex, the imaginary part of the result is in radians. If X is `REAL`, the return value has a lower bound of one, \cosh (x) \geq 1.
Example:

                program test_cosh
                  real(8) :: x = 1.0_8
                  x = cosh(x)
                end program test_cosh

Specific names:

  Name | Argument | Return type | Standard
  `COSH(X)` | `REAL(4) X` | `REAL(4)` | Fortran 77 and later
  `DCOSH(X)` | `REAL(8) X` | `REAL(8)` | Fortran 77 and later

See also:
  Inverse function: ACOSH

Next: CPU_TIME, Previous: COSH, Up: Intrinsic Procedures

### 8.57 `COUNT` — Count function

Description:
  Counts the number of `.TRUE.` elements in a logical MASK, or, if the DIM argument is supplied, counts the number of elements along each row of the array in the DIM direction. If the array has zero size, or all of the elements of MASK are `.FALSE.`, then the result is `0`.
Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Transformational function
Syntax:
  `RESULT = COUNT(MASK [, DIM, KIND])`
Arguments:

  MASK | The type shall be `LOGICAL`.
  DIM | (Optional) The type shall be `INTEGER`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind. If DIM is present, the result is an array with a rank one less than the rank of ARRAY, and a size corresponding to the shape of ARRAY with the DIM dimension removed.
Example:

                program test_count
                    integer, dimension(2,3) :: a, b
                    logical, dimension(2,3) :: mask
                    a = reshape( (/ 1, 2, 3, 4, 5, 6 /), (/ 2, 3 /))
                    b = reshape( (/ 0, 7, 3, 4, 5, 8 /), (/ 2, 3 /))
                    print '(3i3)', a(1,:)
                    print '(3i3)', a(2,:)
                    print *
                    print '(3i3)', b(1,:)
                    print '(3i3)', b(2,:)
                    print *
                    mask = a.ne.b
                    print '(3l3)', mask(1,:)
                    print '(3l3)', mask(2,:)
                    print *
                    print '(3i3)', count(mask)
                    print *
                    print '(3i3)', count(mask, 1)
                    print *
                    print '(3i3)', count(mask, 2)
                end program test_count

Next: CSHIFT, Previous: COUNT, Up: Intrinsic Procedures

### 8.58 `CPU_TIME` — CPU elapsed time in seconds

Description:
  Returns a `REAL` value representing the elapsed CPU time in seconds. This is useful for testing segments of code to determine execution time.

  If a time source is available, time will be reported with microsecond resolution. If no time source is available, TIME is set to `-1.0`.

  Note that TIME may contain a, system dependent, arbitrary offset and may not start with `0.0`. For `CPU_TIME`, the absolute value is meaningless, only differences between subsequent calls to this subroutine, as shown in the example below, should be used.

Standard:
  Fortran 95 and later
Class:
  Subroutine
Syntax:
  `CALL CPU_TIME(TIME)`
Arguments:

  TIME | The type shall be `REAL` with `INTENT(OUT)`.

Return value:
  None
Example:

                program test_cpu_time
                    real :: start, finish
                    call cpu_time(start)
                        ! put code to test here
                    call cpu_time(finish)
                    print '("Time = ",f6.3," seconds.")',finish-start
                end program test_cpu_time

See also:
  SYSTEM_CLOCK, DATE_AND_TIME

Next: CTIME, Previous: CPU_TIME, Up: Intrinsic Procedures

### 8.59 `CSHIFT` — Circular shift elements of an array

Description:
  `CSHIFT(ARRAY, SHIFT [, DIM])` performs a circular shift on elements of ARRAY along the dimension of DIM. If DIM is omitted it is taken to be `1`. DIM is a scalar of type `INTEGER` in the range of 1 \leq DIM \leq n) where n is the rank of ARRAY. If the rank of ARRAY is one, then all elements of ARRAY are shifted by SHIFT places. If rank is greater than one, then all complete rank one sections of ARRAY along the given dimension are shifted. Elements shifted out one end of each rank one section are shifted back in the other end.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = CSHIFT(ARRAY, SHIFT [, DIM])`
Arguments:

  ARRAY | Shall be an array of any type.
  SHIFT | The type shall be `INTEGER`.
  DIM | The type shall be `INTEGER`.

Return value:
  Returns an array of same type and rank as the ARRAY argument.
Example:

                program test_cshift
                    integer, dimension(3,3) :: a
                    a = reshape( (/ 1, 2, 3, 4, 5, 6, 7, 8, 9 /), (/ 3, 3 /))
                    print '(3i3)', a(1,:)
                    print '(3i3)', a(2,:)
                    print '(3i3)', a(3,:)
                    a = cshift(a, SHIFT=(/1, 2, -1/), DIM=2)
                    print *
                    print '(3i3)', a(1,:)
                    print '(3i3)', a(2,:)
                    print '(3i3)', a(3,:)
                end program test_cshift

Next: DATE_AND_TIME, Previous: CSHIFT, Up: Intrinsic Procedures

### 8.60 `CTIME` — Convert a time into a string

Description:
  `CTIME` converts a system time value, such as returned by `TIME8`, to a string. The output will be of the form ``Sat Aug 19 18:13:14 1995`'.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL CTIME(TIME, RESULT)`.
  `RESULT = CTIME(TIME)`.

Arguments:

  TIME | The type shall be of type `INTEGER`.
  RESULT | The type shall be of type `CHARACTER` and of default kind. It is an `INTENT(OUT)` argument. If the length of this variable is too short for the time and date string to fit completely, it will be blank on procedure return.

Return value:
  The converted date and time as a string.
Example:

                program test_ctime
                    integer(8) :: i
                    character(len=30) :: date
                    i = time8()

                    ! Do something, main part of the program

                    call ctime(i,date)
                    print *, 'Program was started on ', date
                end program test_ctime

See Also:
  DATE_AND_TIME, GMTIME, LTIME, TIME, TIME8

Next: DBLE, Previous: CTIME, Up: Intrinsic Procedures

### 8.61 `DATE_AND_TIME` — Date and time subroutine

Description:
  `DATE_AND_TIME(DATE, TIME, ZONE, VALUES)` gets the corresponding date and time information from the real-time system clock. DATE is `INTENT(OUT)` and has form ccyymmdd. TIME is `INTENT(OUT)` and has form hhmmss.sss. ZONE is `INTENT(OUT)` and has form (+-)hhmm, representing the difference with respect to Coordinated Universal Time (UTC). Unavailable time and date parameters return blanks.

  VALUES is `INTENT(OUT)` and provides the following:

  | `VALUE(1)`: | The year
  | `VALUE(2)`: | The month
  | `VALUE(3)`: | The day of the month
  | `VALUE(4)`: | Time difference with UTC in minutes
  | `VALUE(5)`: | The hour of the day
  | `VALUE(6)`: | The minutes of the hour
  | `VALUE(7)`: | The seconds of the minute
  | `VALUE(8)`: | The milliseconds of the second

Standard:
  Fortran 95 and later
Class:
  Subroutine
Syntax:
  `CALL DATE_AND_TIME([DATE, TIME, ZONE, VALUES])`
Arguments:

  DATE | (Optional) The type shall be `CHARACTER(LEN=8)` or larger, and of default kind.
  TIME | (Optional) The type shall be `CHARACTER(LEN=10)` or larger, and of default kind.
  ZONE | (Optional) The type shall be `CHARACTER(LEN=5)` or larger, and of default kind.
  VALUES | (Optional) The type shall be `INTEGER(8)`.

Return value:
  None
Example:

                program test_time_and_date
                    character(8)  :: date
                    character(10) :: time
                    character(5)  :: zone
                    integer,dimension(8) :: values
                    ! using keyword arguments
                    call date_and_time(date,time,zone,values)
                    call date_and_time(DATE=date,ZONE=zone)
                    call date_and_time(TIME=time)
                    call date_and_time(VALUES=values)
                    print '(a,2x,a,2x,a)', date, time, zone
                    print '(8i5)', values
                end program test_time_and_date

See also:
  CPU_TIME, SYSTEM_CLOCK

Next: DCMPLX, Previous: DATE_AND_TIME, Up: Intrinsic Procedures

### 8.62 `DBLE` — Double conversion function

Description:
  `DBLE(A)` Converts A to double precision real type.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = DBLE(A)`
Arguments:

  A | The type shall be `INTEGER`, `REAL`, or `COMPLEX`.

Return value:
  The return value is of type double precision real.
Example:

                program test_dble
                    real    :: x = 2.18
                    integer :: i = 5
                    complex :: z = (2.3,1.14)
                    print *, dble(x), dble(i), dble(z)
                end program test_dble

See also:
  REAL

Next: DIGITS, Previous: DBLE, Up: Intrinsic Procedures

### 8.63 `DCMPLX` — Double complex conversion function

Description:
  `DCMPLX(X [,Y])` returns a double complex number where X is converted to the real component. If Y is present it is converted to the imaginary component. If Y is not present then the imaginary component is set to 0.0. If X is complex then Y must not be present.
Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = DCMPLX(X [, Y])`
Arguments:

  X | The type may be `INTEGER`, `REAL`, or `COMPLEX`.
  Y | (Optional if X is not `COMPLEX`.) May be `INTEGER` or `REAL`.

Return value:
  The return value is of type `COMPLEX(8)`
Example:

                program test_dcmplx
                    integer :: i = 42
                    real :: x = 3.14
                    complex :: z
                    z = cmplx(i, x)
                    print *, dcmplx(i)
                    print *, dcmplx(x)
                    print *, dcmplx(z)
                    print *, dcmplx(x,i)
                end program test_dcmplx

Next: DIM, Previous: DCMPLX, Up: Intrinsic Procedures

### 8.64 `DIGITS` — Significant binary digits function

Description:
  `DIGITS(X)` returns the number of significant binary digits of the internal model representation of X. For example, on a system using a 32-bit floating point representation, a default real number would likely return 24.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = DIGITS(X)`
Arguments:

  X | The type may be `INTEGER` or `REAL`.

Return value:
  The return value is of type `INTEGER`.
Example:

                program test_digits
                    integer :: i = 12345
                    real :: x = 3.143
                    real(8) :: y = 2.33
                    print *, digits(i)
                    print *, digits(x)
                    print *, digits(y)
                end program test_digits

Next: DOT_PRODUCT, Previous: DIGITS, Up: Intrinsic Procedures

### 8.65 `DIM` — Positive difference

Description:
  `DIM(X,Y)` returns the difference `X-Y` if the result is positive; otherwise returns zero.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = DIM(X, Y)`
Arguments:

  X | The type shall be `INTEGER` or `REAL`
  Y | The type shall be the same type and kind as X.

Return value:
  The return value is of type `INTEGER` or `REAL`.
Example:

                program test_dim
                    integer :: i
                    real(8) :: x
                    i = dim(4, 15)
                    x = dim(4.345_8, 2.111_8)
                    print *, i
                    print *, x
                end program test_dim

Specific names:

  Name | Argument | Return type | Standard
  `DIM(X,Y)` | `REAL(4) X, Y` | `REAL(4)` | Fortran 77 and later
  `IDIM(X,Y)` | `INTEGER(4) X, Y` | `INTEGER(4)` | Fortran 77 and later
  `DDIM(X,Y)` | `REAL(8) X, Y` | `REAL(8)` | Fortran 77 and later

Next: DPROD, Previous: DIM, Up: Intrinsic Procedures

### 8.66 `DOT_PRODUCT` — Dot product function

Description:
  `DOT_PRODUCT(VECTOR_A, VECTOR_B)` computes the dot product multiplication of two vectors VECTOR_A and VECTOR_B. The two vectors may be either numeric or logical and must be arrays of rank one and of equal size. If the vectors are `INTEGER` or `REAL`, the result is `SUM(VECTOR_A*VECTOR_B)`. If the vectors are `COMPLEX`, the result is `SUM(CONJG(VECTOR_A)*VECTOR_B)`. If the vectors are `LOGICAL`, the result is `ANY(VECTOR_A .AND. VECTOR_B)`.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = DOT_PRODUCT(VECTOR_A, VECTOR_B)`
Arguments:

  VECTOR_A | The type shall be numeric or `LOGICAL`, rank 1.
  VECTOR_B | The type shall be numeric if VECTOR_A is of numeric type or `LOGICAL` if VECTOR_A is of type `LOGICAL`. VECTOR_B shall be a rank-one array.

Return value:
  If the arguments are numeric, the return value is a scalar of numeric type, `INTEGER`, `REAL`, or `COMPLEX`. If the arguments are `LOGICAL`, the return value is `.TRUE.` or `.FALSE.`.
Example:

                program test_dot_prod
                    integer, dimension(3) :: a, b
                    a = (/ 1, 2, 3 /)
                    b = (/ 4, 5, 6 /)
                    print '(3i3)', a
                    print *
                    print '(3i3)', b
                    print *
                    print *, dot_product(a,b)
                end program test_dot_prod

Next: DREAL, Previous: DOT_PRODUCT, Up: Intrinsic Procedures

### 8.67 `DPROD` — Double product function

Description:
  `DPROD(X,Y)` returns the product `X*Y`.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = DPROD(X, Y)`
Arguments:

  X | The type shall be `REAL`.
  Y | The type shall be `REAL`.

Return value:
  The return value is of type `REAL(8)`.
Example:

                program test_dprod
                    real :: x = 5.2
                    real :: y = 2.3
                    real(8) :: d
                    d = dprod(x,y)
                    print *, d
                end program test_dprod

Specific names:

  Name | Argument | Return type | Standard
  `DPROD(X,Y)` | `REAL(4) X, Y` | `REAL(4)` | Fortran 77 and later

Next: DSHIFTL, Previous: DPROD, Up: Intrinsic Procedures

### 8.68 `DREAL` — Double real part function

Description:
  `DREAL(Z)` returns the real part of complex variable Z.
Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = DREAL(A)`
Arguments:

  A | The type shall be `COMPLEX(8)`.

Return value:
  The return value is of type `REAL(8)`.
Example:

                program test_dreal
                    complex(8) :: z = (1.3_8,7.2_8)
                    print *, dreal(z)
                end program test_dreal

See also:
  AIMAG

Next: DSHIFTR, Previous: DREAL, Up: Intrinsic Procedures

### 8.69 `DSHIFTL` — Combined left shift

Description:
  `DSHIFTL(I, J, SHIFT)` combines bits of I and J. The rightmost SHIFT bits of the result are the leftmost SHIFT bits of J, and the remaining bits are the rightmost bits of I.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = DSHIFTL(I, J, SHIFT)`
Arguments:

  I | Shall be of type `INTEGER` or a BOZ constant.
  J | Shall be of type `INTEGER` or a BOZ constant. If both I and J have integer type, then they shall have the same kind type parameter. I and J shall not both be BOZ constants.
  SHIFT | Shall be of type `INTEGER`. It shall be nonnegative. If I is not a BOZ constant, then SHIFT shall be less than or equal to `BIT_SIZE(I)`; otherwise, SHIFT shall be less than or equal to `BIT_SIZE(J)`.

Return value:
  If either I or J is a BOZ constant, it is first converted as if by the intrinsic function `INT` to an integer type with the kind type parameter of the other.
See also:
  DSHIFTR

Next: DTIME, Previous: DSHIFTL, Up: Intrinsic Procedures

### 8.70 `DSHIFTR` — Combined right shift

Description:
  `DSHIFTR(I, J, SHIFT)` combines bits of I and J. The leftmost SHIFT bits of the result are the rightmost SHIFT bits of I, and the remaining bits are the leftmost bits of J.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = DSHIFTR(I, J, SHIFT)`
Arguments:

  I | Shall be of type `INTEGER` or a BOZ constant.
  J | Shall be of type `INTEGER` or a BOZ constant. If both I and J have integer type, then they shall have the same kind type parameter. I and J shall not both be BOZ constants.
  SHIFT | Shall be of type `INTEGER`. It shall be nonnegative. If I is not a BOZ constant, then SHIFT shall be less than or equal to `BIT_SIZE(I)`; otherwise, SHIFT shall be less than or equal to `BIT_SIZE(J)`.

Return value:
  If either I or J is a BOZ constant, it is first converted as if by the intrinsic function `INT` to an integer type with the kind type parameter of the other.
See also:
  DSHIFTL

Next: EOSHIFT, Previous: DSHIFTR, Up: Intrinsic Procedures

### 8.71 `DTIME` — Execution time subroutine (or function)

Description:
  `DTIME(VALUES, TIME)` initially returns the number of seconds of runtime since the start of the process's execution in TIME. VALUES returns the user and system components of this time in `VALUES(1)` and `VALUES(2)` respectively. TIME is equal to `VALUES(1) + VALUES(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 (wrap around) 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.

  Please note, that this implementation is thread safe if used within OpenMP directives, i.e., its state will be consistent while called from multiple threads. However, if `DTIME` is called from multiple threads, the result is still the time since the last invocation. This may not give the intended results. If possible, use `CPU_TIME` instead.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

  VALUES and TIME are `INTENT(OUT)` and provide the following:

  | `VALUES(1)`: | User time in seconds.
  | `VALUES(2)`: | System time in seconds.
  | `TIME`: | Run time since start in seconds.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL DTIME(VALUES, TIME)`.
  `TIME = DTIME(VALUES)`, (not recommended).

Arguments:

  VALUES | The type shall be `REAL(4), DIMENSION(2)`.
  TIME | The type shall be `REAL(4)`.

Return value:
  Elapsed time in seconds since the last invocation or since the start of program execution if not called before.
Example:

                program test_dtime
                    integer(8) :: i, j
                    real, dimension(2) :: tarray
                    real :: result
                    call dtime(tarray, result)
                    print *, result
                    print *, tarray(1)
                    print *, tarray(2)
                    do i=1,100000000    ! Just a delay
                        j = i * i - i
                    end do
                    call dtime(tarray, result)
                    print *, result
                    print *, tarray(1)
                    print *, tarray(2)
                end program test_dtime

See also:
  CPU_TIME

Next: EPSILON, Previous: DTIME, Up: Intrinsic Procedures

### 8.72 `EOSHIFT` — End-off shift elements of an array

Description:
  `EOSHIFT(ARRAY, SHIFT[, BOUNDARY, DIM])` performs an end-off shift on elements of ARRAY along the dimension of DIM. If DIM is omitted it is taken to be `1`. DIM is a scalar of type `INTEGER` in the range of 1 \leq DIM \leq n) where n is the rank of ARRAY. If the rank of ARRAY is one, then all elements of ARRAY are shifted by SHIFT places. If rank is greater than one, then all complete rank one sections of ARRAY along the given dimension are shifted. Elements shifted out one end of each rank one section are dropped. If BOUNDARY is present then the corresponding value of from BOUNDARY is copied back in the other end. If BOUNDARY is not present then the following are copied in depending on the type of ARRAY.

  Array Type | Boundary Value
  Numeric | 0 of the type and kind of ARRAY.
  Logical | `.FALSE.`.
  Character(len) | len blanks.

Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = EOSHIFT(ARRAY, SHIFT [, BOUNDARY, DIM])`
Arguments:

  ARRAY | May be any type, not scalar.
  SHIFT | The type shall be `INTEGER`.
  BOUNDARY | Same type as ARRAY.
  DIM | The type shall be `INTEGER`.

Return value:
  Returns an array of same type and rank as the ARRAY argument.
Example:

                program test_eoshift
                    integer, dimension(3,3) :: a
                    a = reshape( (/ 1, 2, 3, 4, 5, 6, 7, 8, 9 /), (/ 3, 3 /))
                    print '(3i3)', a(1,:)
                    print '(3i3)', a(2,:)
                    print '(3i3)', a(3,:)
                    a = EOSHIFT(a, SHIFT=(/1, 2, 1/), BOUNDARY=-5, DIM=2)
                    print *
                    print '(3i3)', a(1,:)
                    print '(3i3)', a(2,:)
                    print '(3i3)', a(3,:)
                end program test_eoshift

Next: ERF, Previous: EOSHIFT, Up: Intrinsic Procedures

### 8.73 `EPSILON` — Epsilon function

Description:
  `EPSILON(X)` returns the smallest number E of the same kind as X such that 1 + E > 1.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = EPSILON(X)`
Arguments:

  X | The type shall be `REAL`.

Return value:
  The return value is of same type as the argument.
Example:

                program test_epsilon
                    real :: x = 3.143
                    real(8) :: y = 2.33
                    print *, EPSILON(x)
                    print *, EPSILON(y)
                end program test_epsilon

Next: ERFC, Previous: EPSILON, Up: Intrinsic Procedures

### 8.74 `ERF` — Error function

Description:
  `ERF(X)` computes the error function of X.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = ERF(X)`
Arguments:

  X | The type shall be `REAL`.

Return value:
  The return value is of type `REAL`, of the same kind as X and lies in the range -1 \leq erf (x) \leq 1 .
Example:

                program test_erf
                  real(8) :: x = 0.17_8
                  x = erf(x)
                end program test_erf

Specific names:

  Name | Argument | Return type | Standard
  `DERF(X)` | `REAL(8) X` | `REAL(8)` | GNU extension

Next: ERFC_SCALED, Previous: ERF, Up: Intrinsic Procedures

### 8.75 `ERFC` — Error function

Description:
  `ERFC(X)` computes the complementary error function of X.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = ERFC(X)`
Arguments:

  X | The type shall be `REAL`.

Return value:
  The return value is of type `REAL` and of the same kind as X. It lies in the range 0 \leq erfc (x) \leq 2 .
Example:

                program test_erfc
                  real(8) :: x = 0.17_8
                  x = erfc(x)
                end program test_erfc

Specific names:

  Name | Argument | Return type | Standard
  `DERFC(X)` | `REAL(8) X` | `REAL(8)` | GNU extension

Next: ETIME, Previous: ERFC, Up: Intrinsic Procedures

### 8.76 `ERFC_SCALED` — Error function

Description:
  `ERFC_SCALED(X)` computes the exponentially-scaled complementary error function of X.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = ERFC_SCALED(X)`
Arguments:

  X | The type shall be `REAL`.

Return value:
  The return value is of type `REAL` and of the same kind as X.
Example:

                program test_erfc_scaled
                  real(8) :: x = 0.17_8
                  x = erfc_scaled(x)
                end program test_erfc_scaled

Next: EXECUTE_COMMAND_LINE, Previous: ERFC_SCALED, Up: Intrinsic Procedures

### 8.77 `ETIME` — Execution time subroutine (or function)

Description:
  `ETIME(VALUES, TIME)` returns the number of seconds of runtime since the start of the process's execution in TIME. VALUES returns the user and system components of this time in `VALUES(1)` and `VALUES(2)` respectively. TIME is equal to `VALUES(1) + VALUES(2)`.

  On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wrap around) 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 intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

  VALUES and TIME are `INTENT(OUT)` and provide the following:

  | `VALUES(1)`: | User time in seconds.
  | `VALUES(2)`: | System time in seconds.
  | `TIME`: | Run time since start in seconds.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL ETIME(VALUES, TIME)`.
  `TIME = ETIME(VALUES)`, (not recommended).

Arguments:

  VALUES | The type shall be `REAL(4), DIMENSION(2)`.
  TIME | The type shall be `REAL(4)`.

Return value:
  Elapsed time in seconds since the start of program execution.
Example:

                program test_etime
                    integer(8) :: i, j
                    real, dimension(2) :: tarray
                    real :: result
                    call ETIME(tarray, result)
                    print *, result
                    print *, tarray(1)
                    print *, tarray(2)
                    do i=1,100000000    ! Just a delay
                        j = i * i - i
                    end do
                    call ETIME(tarray, result)
                    print *, result
                    print *, tarray(1)
                    print *, tarray(2)
                end program test_etime

See also:
  CPU_TIME

Next: EXIT, Previous: ETIME, Up: Intrinsic Procedures

### 8.78 `EXECUTE_COMMAND_LINE` — Execute a shell command

Description:
  `EXECUTE_COMMAND_LINE` runs a shell command, synchronously or asynchronously.

  The `COMMAND` argument is passed to the shell and executed, using the C library's `system` call. (The shell is `sh` on Unix systems, and `cmd.exe` on Windows.) If `WAIT` is present and has the value false, the execution of the command is asynchronous if the system supports it; otherwise, the command is executed synchronously.

  The three last arguments allow the user to get status information. After synchronous execution, `EXITSTAT` contains the integer exit code of the command, as returned by `system`. `CMDSTAT` is set to zero if the command line was executed (whatever its exit status was). `CMDMSG` is assigned an error message if an error has occurred.

  Note that the `system` function need not be thread-safe. It is the responsibility of the user to ensure that `system` is not called concurrently.

Standard:
  Fortran 2008 and later
Class:
  Subroutine
Syntax:
  `CALL EXECUTE_COMMAND_LINE(COMMAND [, WAIT, EXITSTAT, CMDSTAT, CMDMSG ])`
Arguments:

  COMMAND | Shall be a default `CHARACTER` scalar.
  WAIT | (Optional) Shall be a default `LOGICAL` scalar.
  EXITSTAT | (Optional) Shall be an `INTEGER` of the default kind.
  CMDSTAT | (Optional) Shall be an `INTEGER` of the default kind.
  CMDMSG | (Optional) Shall be an `CHARACTER` scalar of the default kind.

Example:

                program test_exec
                  integer :: i

                  call execute_command_line ("external_prog.exe", exitstat=i)
                  print *, "Exit status of external_prog.exe was ", i

                  call execute_command_line ("reindex_files.exe", wait=.false.)
                  print *, "Now reindexing files in the background"

                end program test_exec

Note:
  Because this intrinsic is implemented in terms of the `system` function call, its behavior with respect to signaling is processor dependent. In particular, on POSIX-compliant systems, the SIGINT and SIGQUIT signals will be ignored, and the SIGCHLD will be blocked. As such, if the parent process is terminated, the child process might not be terminated alongside.
See also:
  SYSTEM

Next: EXP, Previous: EXECUTE_COMMAND_LINE, Up: Intrinsic Procedures

### 8.79 `EXIT` — Exit the program with status.

Description:
  `EXIT` causes immediate termination of the program with status. If status is omitted it returns the canonical success for the system. All Fortran I/O units are closed.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL EXIT([STATUS])`
Arguments:

  STATUS | Shall be an `INTEGER` of the default kind.

Return value:
  `STATUS` is passed to the parent process on exit.
Example:

                program test_exit
                  integer :: STATUS = 0
                  print *, 'This program is going to exit.'
                  call EXIT(STATUS)
                end program test_exit

See also:
  ABORT, KILL

Next: EXPONENT, Previous: EXIT, Up: Intrinsic Procedures

### 8.80 `EXP` — Exponential function

Description:
  `EXP(X)` computes the base e exponential of X.
Standard:
  Fortran 77 and later, has overloads that are GNU extensions
Class:
  Elemental function
Syntax:
  `RESULT = EXP(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has same type and kind as X.
Example:

                program test_exp
                  real :: x = 1.0
                  x = exp(x)
                end program test_exp

Specific names:

  Name | Argument | Return type | Standard
  `EXP(X)` | `REAL(4) X` | `REAL(4)` | Fortran 77 and later
  `DEXP(X)` | `REAL(8) X` | `REAL(8)` | Fortran 77 and later
  `CEXP(X)` | `COMPLEX(4) X` | `COMPLEX(4)` | Fortran 77 and later
  `ZEXP(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | GNU extension
  `CDEXP(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | GNU extension

Next: EXTENDS_TYPE_OF, Previous: EXP, Up: Intrinsic Procedures

### 8.81 `EXPONENT` — Exponent function

Description:
  `EXPONENT(X)` returns the value of the exponent part of X. If X is zero the value returned is zero.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = EXPONENT(X)`
Arguments:

  X | The type shall be `REAL`.

Return value:
  The return value is of type default `INTEGER`.
Example:

                program test_exponent
                  real :: x = 1.0
                  integer :: i
                  i = exponent(x)
                  print *, i
                  print *, exponent(0.0)
                end program test_exponent

Next: FDATE, Previous: EXPONENT, Up: Intrinsic Procedures

### 8.82 `EXTENDS_TYPE_OF` — Query dynamic type for extension

Description:
  Query dynamic type for extension.
Standard:
  Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = EXTENDS_TYPE_OF(A, MOLD)`
Arguments:

  A | Shall be an object of extensible declared type or unlimited polymorphic.
  MOLD | Shall be an object of extensible declared type or unlimited polymorphic.

Return value:
  The return value is a scalar of type default logical. It is true if and only if the dynamic type of A is an extension type of the dynamic type of MOLD.
See also:
  SAME_TYPE_AS

Next: FGET, Previous: EXTENDS_TYPE_OF, Up: Intrinsic Procedures

### 8.83 `FDATE` — Get the current time as a string

Description:
  `FDATE(DATE)` returns the current date (using the same format as `CTIME`) in DATE. It is equivalent to `CALL CTIME(DATE, TIME())`.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL FDATE(DATE)`.
  `DATE = FDATE()`.

Arguments:

  DATE | The type shall be of type `CHARACTER` of the default kind. It is an `INTENT(OUT)` argument. If the length of this variable is too short for the date and time string to fit completely, it will be blank on procedure return.

Return value:
  The current date and time as a string.
Example:

                program test_fdate
                    integer(8) :: i, j
                    character(len=30) :: date
                    call fdate(date)
                    print *, 'Program started on ', date
                    do i = 1, 100000000 ! Just a delay
                        j = i * i - i
                    end do
                    call fdate(date)
                    print *, 'Program ended on ', date
                end program test_fdate

See also:
  DATE_AND_TIME, CTIME

Next: FGETC, Previous: FDATE, Up: Intrinsic Procedures

### 8.84 `FGET` — Read a single character in stream mode from stdin

Description:
  Read a single character in stream mode from stdin by bypassing normal formatted output. Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

  Note that the `FGET` intrinsic is provided for backwards compatibility with `g77`. GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL FGET(C [, STATUS])`
  `STATUS = FGET(C)`

Arguments:

  C | The type shall be `CHARACTER` and of default kind.
  STATUS | (Optional) status flag of type `INTEGER`. Returns 0 on success, -1 on end-of-file, and a system specific positive error code otherwise.

Example:

                PROGRAM test_fget
                  INTEGER, PARAMETER :: strlen = 100
                  INTEGER :: status, i = 1
                  CHARACTER(len=strlen) :: str = ""

                  WRITE (*,*) 'Enter text:'
                  DO
                    CALL fget(str(i:i), status)
                    if (status /= 0 .OR. i > strlen) exit
                    i = i + 1
                  END DO
                  WRITE (*,*) TRIM(str)
                END PROGRAM

See also:
  FGETC, FPUT, FPUTC

Next: FLOOR, Previous: FGET, Up: Intrinsic Procedures

### 8.85 `FGETC` — Read a single character in stream mode

Description:
  Read a single character in stream mode by bypassing normal formatted output. Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

  Note that the `FGET` intrinsic is provided for backwards compatibility with `g77`. GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL FGETC(UNIT, C [, STATUS])`
  `STATUS = FGETC(UNIT, C)`

Arguments:

  UNIT | The type shall be `INTEGER`.
  C | The type shall be `CHARACTER` and of default kind.
  STATUS | (Optional) status flag of type `INTEGER`. Returns 0 on success, -1 on end-of-file and a system specific positive error code otherwise.

Example:

                PROGRAM test_fgetc
                  INTEGER :: fd = 42, status
                  CHARACTER :: c

                  OPEN(UNIT=fd, FILE="/etc/passwd", ACTION="READ", STATUS = "OLD")
                  DO
                    CALL fgetc(fd, c, status)
                    IF (status /= 0) EXIT
                    call fput(c)
                  END DO
                  CLOSE(UNIT=fd)
                END PROGRAM

See also:
  FGET, FPUT, FPUTC

Next: FLUSH, Previous: FGETC, Up: Intrinsic Procedures

### 8.86 `FLOOR` — Integer floor function

Description:
  `FLOOR(A)` returns the greatest integer less than or equal to X.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = FLOOR(A [, KIND])`
Arguments:

  A | The type shall be `REAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER(KIND)` if KIND is present and of default-kind `INTEGER` otherwise.
Example:

                program test_floor
                    real :: x = 63.29
                    real :: y = -63.59
                    print *, floor(x) ! returns 63
                    print *, floor(y) ! returns -64
                end program test_floor

See also:
  CEILING, NINT

Next: FNUM, Previous: FLOOR, Up: Intrinsic Procedures

### 8.87 `FLUSH` — Flush I/O unit(s)

Description:
  Flushes Fortran unit(s) currently open for output. Without the optional argument, all units are flushed, otherwise just the unit specified.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL FLUSH(UNIT)`
Arguments:

  UNIT | (Optional) The type shall be `INTEGER`.

Note:
  Beginning with the Fortran 2003 standard, there is a `FLUSH` statement that should be preferred over the `FLUSH` intrinsic.

  The `FLUSH` intrinsic and the Fortran 2003 `FLUSH` statement have identical effect: they flush the runtime library's I/O buffer so that the data becomes visible to other processes. This does not guarantee that the data is committed to disk.

  On POSIX systems, you can request that all data is transferred to the storage device by calling the `fsync` function, with the POSIX file descriptor of the I/O unit as argument (retrieved with GNU intrinsic `FNUM`). The following example shows how:

                  ! Declare the interface for POSIX fsync function
                  interface
                    function fsync (fd) bind(c,name="fsync")
                    use iso_c_binding, only: c_int
                      integer(c_int), value :: fd
                      integer(c_int) :: fsync
                    end function fsync
                  end interface

                  ! Variable declaration
                  integer :: ret

                  ! Opening unit 10
                  open (10,file="foo")

                  ! ...
                  ! Perform I/O on unit 10
                  ! ...

                  ! Flush and sync
                  flush(10)
                  ret = fsync(fnum(10))

                  ! Handle possible error
                  if (ret /= 0) stop "Error calling FSYNC"

Next: FPUT, Previous: FLUSH, Up: Intrinsic Procedures

### 8.88 `FNUM` — File number function

Description:
  `FNUM(UNIT)` returns the POSIX file descriptor number corresponding to the open Fortran I/O unit `UNIT`.
Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = FNUM(UNIT)`
Arguments:

  UNIT | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER`
Example:

                program test_fnum
                  integer :: i
                  open (unit=10, status = "scratch")
                  i = fnum(10)
                  print *, i
                  close (10)
                end program test_fnum

Next: FPUTC, Previous: FNUM, Up: Intrinsic Procedures

### 8.89 `FPUT` — Write a single character in stream mode to stdout

Description:
  Write a single character in stream mode to stdout by bypassing normal formatted output. Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

  Note that the `FGET` intrinsic is provided for backwards compatibility with `g77`. GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL FPUT(C [, STATUS])`
  `STATUS = FPUT(C)`

Arguments:

  C | The type shall be `CHARACTER` and of default kind.
  STATUS | (Optional) status flag of type `INTEGER`. Returns 0 on success, -1 on end-of-file and a system specific positive error code otherwise.

Example:

                PROGRAM test_fput
                  CHARACTER(len=10) :: str = "gfortran"
                  INTEGER :: i
                  DO i = 1, len_trim(str)
                    CALL fput(str(i:i))
                  END DO
                END PROGRAM

See also:
  FPUTC, FGET, FGETC

Next: FRACTION, Previous: FPUT, Up: Intrinsic Procedures

### 8.90 `FPUTC` — Write a single character in stream mode

Description:
  Write a single character in stream mode by bypassing normal formatted output. Stream I/O should not be mixed with normal record-oriented (formatted or unformatted) I/O on the same unit; the results are unpredictable.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

  Note that the `FGET` intrinsic is provided for backwards compatibility with `g77`. GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL FPUTC(UNIT, C [, STATUS])`
  `STATUS = FPUTC(UNIT, C)`

Arguments:

  UNIT | The type shall be `INTEGER`.
  C | The type shall be `CHARACTER` and of default kind.
  STATUS | (Optional) status flag of type `INTEGER`. Returns 0 on success, -1 on end-of-file and a system specific positive error code otherwise.

Example:

                PROGRAM test_fputc
                  CHARACTER(len=10) :: str = "gfortran"
                  INTEGER :: fd = 42, i

                  OPEN(UNIT = fd, FILE = "out", ACTION = "WRITE", STATUS="NEW")
                  DO i = 1, len_trim(str)
                    CALL fputc(fd, str(i:i))
                  END DO
                  CLOSE(fd)
                END PROGRAM

See also:
  FPUT, FGET, FGETC

Next: FREE, Previous: FPUTC, Up: Intrinsic Procedures

### 8.91 `FRACTION` — Fractional part of the model representation

Description:
  `FRACTION(X)` returns the fractional part of the model representation of `X`.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `Y = FRACTION(X)`
Arguments:

  X | The type of the argument shall be a `REAL`.

Return value:
  The return value is of the same type and kind as the argument. The fractional part of the model representation of `X` is returned; it is `X * RADIX(X)**(-EXPONENT(X))`.
Example:

                program test_fraction
                  real :: x
                  x = 178.1387e-4
                  print *, fraction(x), x * radix(x)**(-exponent(x))
                end program test_fraction

Next: FSEEK, Previous: FRACTION, Up: Intrinsic Procedures

### 8.92 `FREE` — Frees memory

Description:
  Frees memory previously allocated by `MALLOC`. The `FREE` intrinsic is an extension intended to be used with Cray pointers, and is provided in GNU Fortran to allow user to compile legacy code. For new code using Fortran 95 pointers, the memory de-allocation intrinsic is `DEALLOCATE`.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL FREE(PTR)`
Arguments:

  PTR | The type shall be `INTEGER`. It represents the location of the memory that should be de-allocated.

Return value:
  None
Example:
  See `MALLOC` for an example.
See also:
  MALLOC

Next: FSTAT, Previous: FREE, Up: Intrinsic Procedures

### 8.93 `FSEEK` — Low level file positioning subroutine

Description:
  Moves UNIT to the specified OFFSET. If WHENCE is set to 0, the OFFSET is taken as an absolute value `SEEK_SET`, if set to 1, OFFSET is taken to be relative to the current position `SEEK_CUR`, and if set to 2 relative to the end of the file `SEEK_END`. On error, STATUS is set to a nonzero value. If STATUS the seek fails silently.

  This intrinsic routine is not fully backwards compatible with `g77`. In `g77`, the `FSEEK` takes a statement label instead of a STATUS variable. If FSEEK is used in old code, change

                  CALL FSEEK(UNIT, OFFSET, WHENCE, *label)

  to

                  INTEGER :: status
                  CALL FSEEK(UNIT, OFFSET, WHENCE, status)
                  IF (status /= 0) GOTO label

  Please note that GNU Fortran provides the Fortran 2003 Stream facility. Programmers should consider the use of new stream IO feature in new code for future portability. See also Fortran 2003 status.

Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL FSEEK(UNIT, OFFSET, WHENCE[, STATUS])`
Arguments:

  UNIT | Shall be a scalar of type `INTEGER`.
  OFFSET | Shall be a scalar of type `INTEGER`.
  WHENCE | Shall be a scalar of type `INTEGER`. Its value shall be either 0, 1 or 2.
  STATUS | (Optional) shall be a scalar of type `INTEGER(4)`.

Example:

                PROGRAM test_fseek
                  INTEGER, PARAMETER :: SEEK_SET = 0, SEEK_CUR = 1, SEEK_END = 2
                  INTEGER :: fd, offset, ierr

                  ierr   = 0
                  offset = 5
                  fd     = 10

                  OPEN(UNIT=fd, FILE="fseek.test")
                  CALL FSEEK(fd, offset, SEEK_SET, ierr)  ! move to OFFSET
                  print *, FTELL(fd), ierr

                  CALL FSEEK(fd, 0, SEEK_END, ierr)       ! move to end
                  print *, FTELL(fd), ierr

                  CALL FSEEK(fd, 0, SEEK_SET, ierr)       ! move to beginning
                  print *, FTELL(fd), ierr

                  CLOSE(UNIT=fd)
                END PROGRAM

See also:
  FTELL

Next: FTELL, Previous: FSEEK, Up: Intrinsic Procedures

### 8.94 `FSTAT` — Get file status

Description:
  `FSTAT` is identical to STAT, except that information about an already opened file is obtained.

  The elements in `VALUES` are the same as described by STAT.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL FSTAT(UNIT, VALUES [, STATUS])`
  `STATUS = FSTAT(UNIT, VALUES)`

Arguments:

  UNIT | An open I/O unit number of type `INTEGER`.
  VALUES | The type shall be `INTEGER(4), DIMENSION(13)`.
  STATUS | (Optional) status flag of type `INTEGER(4)`. Returns 0 on success and a system specific error code otherwise.

Example:
  See STAT for an example.
See also:
  To stat a link: LSTAT, to stat a file: STAT

Next: GAMMA, Previous: FSTAT, Up: Intrinsic Procedures

### 8.95 `FTELL` — Current stream position

Description:
  Retrieves the current position within an open file.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL FTELL(UNIT, OFFSET)`
  `OFFSET = FTELL(UNIT)`

Arguments:

  OFFSET | Shall of type `INTEGER`.
  UNIT | Shall of type `INTEGER`.

Return value:
  In either syntax, OFFSET is set to the current offset of unit number UNIT, or to -1 if the unit is not currently open.
Example:

                PROGRAM test_ftell
                  INTEGER :: i
                  OPEN(10, FILE="temp.dat")
                  CALL ftell(10,i)
                  WRITE(*,*) i
                END PROGRAM

See also:
  FSEEK

Next: GERROR, Previous: FTELL, Up: Intrinsic Procedures

### 8.96 `GAMMA` — Gamma function

Description:
  `GAMMA(X)` computes Gamma (\Gamma) of X. For positive, integer values of X the Gamma function simplifies to the factorial function \Gamma(x)=(x-1)!.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `X = GAMMA(X)`
Arguments:

  X | Shall be of type `REAL` and neither zero nor a negative integer.

Return value:
  The return value is of type `REAL` of the same kind as X.
Example:

                program test_gamma
                  real :: x = 1.0
                  x = gamma(x) ! returns 1.0
                end program test_gamma

Specific names:

  Name | Argument | Return type | Standard
  `GAMMA(X)` | `REAL(4) X` | `REAL(4)` | GNU Extension
  `DGAMMA(X)` | `REAL(8) X` | `REAL(8)` | GNU Extension

See also:
  Logarithm of the Gamma function: LOG_GAMMA

Next: GETARG, Previous: GAMMA, Up: Intrinsic Procedures

### 8.97 `GERROR` — Get last system error message

Description:
  Returns the system error message corresponding to the last system error. This resembles the functionality of `strerror(3)` in C.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL GERROR(RESULT)`
Arguments:

  RESULT | Shall of type `CHARACTER` and of default

Example:

                PROGRAM test_gerror
                  CHARACTER(len=100) :: msg
                  CALL gerror(msg)
                  WRITE(*,*) msg
                END PROGRAM

See also:
  IERRNO, PERROR

Next: GET_COMMAND, Previous: GERROR, Up: Intrinsic Procedures

### 8.98 `GETARG` — Get command line arguments

Description:
  Retrieve the POS-th argument that was passed on the command line when the containing program was invoked.

  This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the GET_COMMAND_ARGUMENT intrinsic defined by the Fortran 2003 standard.

Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL GETARG(POS, VALUE)`
Arguments:

  POS | Shall be of type `INTEGER` and not wider than the default integer kind; POS \geq 0
  VALUE | Shall be of type `CHARACTER` and of default kind.
  VALUE | Shall be of type `CHARACTER`.

Return value:
  After `GETARG` returns, the VALUE argument holds the POSth command line argument. If VALUE can not hold the argument, it is truncated to fit the length of VALUE. If there are less than POS arguments specified at the command line, VALUE will be filled with blanks. If POS = 0, VALUE is set to the name of the program (on systems that support this feature).
Example:

                PROGRAM test_getarg
                  INTEGER :: i
                  CHARACTER(len=32) :: arg

                  DO i = 1, iargc()
                    CALL getarg(i, arg)
                    WRITE (*,*) arg
                  END DO
                END PROGRAM

See also:
  GNU Fortran 77 compatibility function: IARGC

  Fortran 2003 functions and subroutines: GET_COMMAND, GET_COMMAND_ARGUMENT, COMMAND_ARGUMENT_COUNT

Next: GET_COMMAND_ARGUMENT, Previous: GETARG, Up: Intrinsic Procedures

### 8.99 `GET_COMMAND` — Get the entire command line

Description:
  Retrieve the entire command line that was used to invoke the program.
Standard:
  Fortran 2003 and later
Class:
  Subroutine
Syntax:
  `CALL GET_COMMAND([COMMAND, LENGTH, STATUS])`
Arguments:

  COMMAND | (Optional) shall be of type `CHARACTER` and of default kind.
  LENGTH | (Optional) Shall be of type `INTEGER` and of default kind.
  STATUS | (Optional) Shall be of type `INTEGER` and of default kind.

Return value:
  If COMMAND is present, stores the entire command line that was used to invoke the program in COMMAND. If LENGTH is present, it is assigned the length of the command line. If STATUS is present, it is assigned 0 upon success of the command, -1 if COMMAND is too short to store the command line, or a positive value in case of an error.
Example:

                PROGRAM test_get_command
                  CHARACTER(len=255) :: cmd
                  CALL get_command(cmd)
                  WRITE (*,*) TRIM(cmd)
                END PROGRAM

See also:
  GET_COMMAND_ARGUMENT, COMMAND_ARGUMENT_COUNT

Next: GETCWD, Previous: GET_COMMAND, Up: Intrinsic Procedures

### 8.100 `GET_COMMAND_ARGUMENT` — Get command line arguments

Description:
  Retrieve the NUMBER-th argument that was passed on the command line when the containing program was invoked.
Standard:
  Fortran 2003 and later
Class:
  Subroutine
Syntax:
  `CALL GET_COMMAND_ARGUMENT(NUMBER [, VALUE, LENGTH, STATUS])`
Arguments:

  NUMBER | Shall be a scalar of type `INTEGER` and of default kind, NUMBER \geq 0
  VALUE | (Optional) Shall be a scalar of type `CHARACTER` and of default kind.
  LENGTH | (Optional) Shall be a scalar of type `INTEGER` and of default kind.
  STATUS | (Optional) Shall be a scalar of type `INTEGER` and of default kind.

Return value:
  After `GET_COMMAND_ARGUMENT` returns, the VALUE argument holds the NUMBER-th command line argument. If VALUE can not hold the argument, it is truncated to fit the length of VALUE. If there are less than NUMBER arguments specified at the command line, VALUE will be filled with blanks. If NUMBER = 0, VALUE is set to the name of the program (on systems that support this feature). The LENGTH argument contains the length of the NUMBER-th command line argument. If the argument retrieval fails, STATUS is a positive number; if VALUE contains a truncated command line argument, STATUS is -1; and otherwise the STATUS is zero.
Example:

                PROGRAM test_get_command_argument
                  INTEGER :: i
                  CHARACTER(len=32) :: arg

                  i = 0
                  DO
                    CALL get_command_argument(i, arg)
                    IF (LEN_TRIM(arg) == 0) EXIT

                    WRITE (*,*) TRIM(arg)
                    i = i+1
                  END DO
                END PROGRAM

See also:
  GET_COMMAND, COMMAND_ARGUMENT_COUNT

Next: GETENV, Previous: GET_COMMAND_ARGUMENT, Up: Intrinsic Procedures

### 8.101 `GETCWD` — Get current working directory

Description:
  Get current working directory.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL GETCWD(C [, STATUS])`
  `STATUS = GETCWD(C)`

Arguments:

  C | The type shall be `CHARACTER` and of default kind.
  STATUS | (Optional) status flag. Returns 0 on success, a system specific and nonzero error code otherwise.

Example:

                PROGRAM test_getcwd
                  CHARACTER(len=255) :: cwd
                  CALL getcwd(cwd)
                  WRITE(*,*) TRIM(cwd)
                END PROGRAM

See also:
  CHDIR

Next: GET_ENVIRONMENT_VARIABLE, Previous: GETCWD, Up: Intrinsic Procedures

### 8.102 `GETENV` — Get an environmental variable

Description:
  Get the VALUE of the environmental variable NAME.

  This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the GET_ENVIRONMENT_VARIABLE intrinsic defined by the Fortran 2003 standard.

  Note that `GETENV` need not be thread-safe. It is the responsibility of the user to ensure that the environment is not being updated concurrently with a call to the `GETENV` intrinsic.

Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL GETENV(NAME, VALUE)`
Arguments:

  NAME | Shall be of type `CHARACTER` and of default kind.
  VALUE | Shall be of type `CHARACTER` and of default kind.

Return value:
  Stores the value of NAME in VALUE. If VALUE is not large enough to hold the data, it is truncated. If NAME is not set, VALUE will be filled with blanks.
Example:

                PROGRAM test_getenv
                  CHARACTER(len=255) :: homedir
                  CALL getenv("HOME", homedir)
                  WRITE (*,*) TRIM(homedir)
                END PROGRAM

See also:
  GET_ENVIRONMENT_VARIABLE

Next: GETGID, Previous: GETENV, Up: Intrinsic Procedures

### 8.103 `GET_ENVIRONMENT_VARIABLE` — Get an environmental variable

Description:
  Get the VALUE of the environmental variable NAME.

  Note that `GET_ENVIRONMENT_VARIABLE` need not be thread-safe. It is the responsibility of the user to ensure that the environment is not being updated concurrently with a call to the `GET_ENVIRONMENT_VARIABLE` intrinsic.

Standard:
  Fortran 2003 and later
Class:
  Subroutine
Syntax:
  `CALL GET_ENVIRONMENT_VARIABLE(NAME[, VALUE, LENGTH, STATUS, TRIM_NAME)`
Arguments:

  NAME | Shall be a scalar of type `CHARACTER` and of default kind.
  VALUE | (Optional) Shall be a scalar of type `CHARACTER` and of default kind.
  LENGTH | (Optional) Shall be a scalar of type `INTEGER` and of default kind.
  STATUS | (Optional) Shall be a scalar of type `INTEGER` and of default kind.
  TRIM_NAME | (Optional) Shall be a scalar of type `LOGICAL` and of default kind.

Return value:
  Stores the value of NAME in VALUE. If VALUE is not large enough to hold the data, it is truncated. If NAME is not set, VALUE will be filled with blanks. Argument LENGTH contains the length needed for storing the environment variable NAME or zero if it is not present. STATUS is -1 if VALUE is present but too short for the environment variable; it is 1 if the environment variable does not exist and 2 if the processor does not support environment variables; in all other cases STATUS is zero. If TRIM_NAME is present with the value `.FALSE.`, the trailing blanks in NAME are significant; otherwise they are not part of the environment variable name.
Example:

                PROGRAM test_getenv
                  CHARACTER(len=255) :: homedir
                  CALL get_environment_variable("HOME", homedir)
                  WRITE (*,*) TRIM(homedir)
                END PROGRAM

Next: GETLOG, Previous: GET_ENVIRONMENT_VARIABLE, Up: Intrinsic Procedures

### 8.104 `GETGID` — Group ID function

Description:
  Returns the numerical group ID of the current process.
Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = GETGID()`
Return value:
  The return value of `GETGID` is an `INTEGER` of the default kind.
Example:
  See `GETPID` for an example.
See also:
  GETPID, GETUID

Next: GETPID, Previous: GETGID, Up: Intrinsic Procedures

### 8.105 `GETLOG` — Get login name

Description:
  Gets the username under which the program is running.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL GETLOG(C)`
Arguments:

  C | Shall be of type `CHARACTER` and of default kind.

Return value:
  Stores the current user name in LOGIN. (On systems where POSIX functions `geteuid` and `getpwuid` are not available, and the `getlogin` function is not implemented either, this will return a blank string.)
Example:

                PROGRAM TEST_GETLOG
                  CHARACTER(32) :: login
                  CALL GETLOG(login)
                  WRITE(*,*) login
                END PROGRAM

See also:
  GETUID

Next: GETUID, Previous: GETLOG, Up: Intrinsic Procedures

### 8.106 `GETPID` — Process ID function

Description:
  Returns the numerical process identifier of the current process.
Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = GETPID()`
Return value:
  The return value of `GETPID` is an `INTEGER` of the default kind.
Example:

                program info
                  print *, "The current process ID is ", getpid()
                  print *, "Your numerical user ID is ", getuid()
                  print *, "Your numerical group ID is ", getgid()
                end program info

See also:
  GETGID, GETUID

Next: GMTIME, Previous: GETPID, Up: Intrinsic Procedures

### 8.107 `GETUID` — User ID function

Description:
  Returns the numerical user ID of the current process.
Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = GETUID()`
Return value:
  The return value of `GETUID` is an `INTEGER` of the default kind.
Example:
  See `GETPID` for an example.
See also:
  GETPID, GETLOG

Next: HOSTNM, Previous: GETUID, Up: Intrinsic Procedures

### 8.108 `GMTIME` — Convert time to GMT info

Description:
  Given a system time value TIME (as provided by the `TIME8` intrinsic), fills VALUES with values extracted from it appropriate to the UTC time zone (Universal Coordinated Time, also known in some countries as GMT, Greenwich Mean Time), using `gmtime(3)`.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL GMTIME(TIME, VALUES)`
Arguments:

  TIME | An `INTEGER` scalar expression corresponding to a system time, with `INTENT(IN)`.
  VALUES | A default `INTEGER` array with 9 elements, with `INTENT(OUT)`.

Return value:
  The elements of VALUES are assigned 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 is not available.
See also:
  CTIME, LTIME, TIME, TIME8

Next: HUGE, Previous: GMTIME, Up: Intrinsic Procedures

### 8.109 `HOSTNM` — Get system host name

Description:
  Retrieves the host name of the system on which the program is running.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL HOSTNM(C [, STATUS])`
  `STATUS = HOSTNM(NAME)`

Arguments:

  C | Shall of type `CHARACTER` and of default kind.
  STATUS | (Optional) status flag of type `INTEGER`. Returns 0 on success, or a system specific error code otherwise.

Return value:
  In either syntax, NAME is set to the current hostname if it can be obtained, or to a blank string otherwise.

Next: HYPOT, Previous: HOSTNM, Up: Intrinsic Procedures

### 8.110 `HUGE` — Largest number of a kind

Description:
  `HUGE(X)` returns the largest number that is not an infinity in the model of the type of `X`.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = HUGE(X)`
Arguments:

  X | Shall be of type `REAL` or `INTEGER`.

Return value:
  The return value is of the same type and kind as X
Example:

                program test_huge_tiny
                  print *, huge(0), huge(0.0), huge(0.0d0)
                  print *, tiny(0.0), tiny(0.0d0)
                end program test_huge_tiny

Next: IACHAR, Previous: HUGE, Up: Intrinsic Procedures

### 8.111 `HYPOT` — Euclidean distance function

Description:
  `HYPOT(X,Y)` is the Euclidean distance function. It is equal to \sqrtX^2 + Y^2, without undue underflow or overflow.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = HYPOT(X, Y)`
Arguments:

  X | The type shall be `REAL`.
  Y | The type and kind type parameter shall be the same as X.

Return value:
  The return value has the same type and kind type parameter as X.
Example:

                program test_hypot
                  real(4) :: x = 1.e0_4, y = 0.5e0_4
                  x = hypot(x,y)
                end program test_hypot

Next: IALL, Previous: HYPOT, Up: Intrinsic Procedures

### 8.112 `IACHAR` — Code in ASCII collating sequence

Description:
  `IACHAR(C)` returns the code for the ASCII character in the first character position of `C`.
Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = IACHAR(C [, KIND])`
Arguments:

  C | Shall be a scalar `CHARACTER`, with `INTENT(IN)`
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind.
Example:

                program test_iachar
                  integer i
                  i = iachar(' ')
                end program test_iachar

Note:
  See ICHAR for a discussion of converting between numerical values and formatted string representations.
See also:
  ACHAR, CHAR, ICHAR

Next: IAND, Previous: IACHAR, Up: Intrinsic Procedures

### 8.113 `IALL` — Bitwise AND of array elements

Description:
  Reduces with bitwise AND the elements of ARRAY along dimension DIM if the corresponding element in MASK is `TRUE`.
Standard:
  Fortran 2008 and later
Class:
  Transformational function
Syntax:

  `RESULT = IALL(ARRAY[, MASK])`
  `RESULT = IALL(ARRAY, DIM[, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER`
  DIM | (Optional) shall be a scalar of type `INTEGER` with a value in the range from 1 to n, where n equals the rank of ARRAY.
  MASK | (Optional) shall be of type `LOGICAL` and either be a scalar or an array of the same shape as ARRAY.

Return value:
  The result is of the same type as ARRAY.

  If DIM is absent, a scalar with the bitwise ALL of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:

                PROGRAM test_iall
                  INTEGER(1) :: a(2)

                  a(1) = b'00100100'
                  a(2) = b'01101010'

                  ! prints 00100000
                  PRINT '(b8.8)', IALL(a)
                END PROGRAM

See also:
  IANY, IPARITY, IAND

Next: IANY, Previous: IALL, Up: Intrinsic Procedures

### 8.114 `IAND` — Bitwise logical and

Description:
  Bitwise logical `AND`.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = IAND(I, J)`
Arguments:

  I | The type shall be `INTEGER`.
  J | The type shall be `INTEGER`, of the same kind as I. (As a GNU extension, different kinds are also permitted.)

Return value:
  The return type is `INTEGER`, of the same kind as the arguments. (If the argument kinds differ, it is of the same kind as the larger argument.)
Example:

                PROGRAM test_iand
                  INTEGER :: a, b
                  DATA a / Z'F' /, b / Z'3' /
                  WRITE (*,*) IAND(a, b)
                END PROGRAM

See also:
  IOR, IEOR, IBITS, IBSET, IBCLR, NOT

Next: IARGC, Previous: IAND, Up: Intrinsic Procedures

### 8.115 `IANY` — Bitwise OR of array elements

Description:
  Reduces with bitwise OR (inclusive or) the elements of ARRAY along dimension DIM if the corresponding element in MASK is `TRUE`.
Standard:
  Fortran 2008 and later
Class:
  Transformational function
Syntax:

  `RESULT = IANY(ARRAY[, MASK])`
  `RESULT = IANY(ARRAY, DIM[, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER`
  DIM | (Optional) shall be a scalar of type `INTEGER` with a value in the range from 1 to n, where n equals the rank of ARRAY.
  MASK | (Optional) shall be of type `LOGICAL` and either be a scalar or an array of the same shape as ARRAY.

Return value:
  The result is of the same type as ARRAY.

  If DIM is absent, a scalar with the bitwise OR of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:

                PROGRAM test_iany
                  INTEGER(1) :: a(2)

                  a(1) = b'00100100'
                  a(2) = b'01101010'

                  ! prints 01101110
                  PRINT '(b8.8)', IANY(a)
                END PROGRAM

See also:
  IPARITY, IALL, IOR

Next: IBCLR, Previous: IANY, Up: Intrinsic Procedures

### 8.116 `IARGC` — Get the number of command line arguments

Description:
  `IARGC` returns the number of arguments passed on the command line when the containing program was invoked.

  This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. In new code, programmers should consider the use of the COMMAND_ARGUMENT_COUNT intrinsic defined by the Fortran 2003 standard.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = IARGC()`
Arguments:
  None.
Return value:
  The number of command line arguments, type `INTEGER(4)`.
Example:
  See GETARG
See also:
  GNU Fortran 77 compatibility subroutine: GETARG

  Fortran 2003 functions and subroutines: GET_COMMAND, GET_COMMAND_ARGUMENT, COMMAND_ARGUMENT_COUNT

Next: IBITS, Previous: IARGC, Up: Intrinsic Procedures

### 8.117 `IBCLR` — Clear bit

Description:
  `IBCLR` returns the value of I with the bit at position POS set to zero.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = IBCLR(I, POS)`
Arguments:

  I | The type shall be `INTEGER`.
  POS | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  IBITS, IBSET, IAND, IOR, IEOR, MVBITS

Next: IBSET, Previous: IBCLR, Up: Intrinsic Procedures

### 8.118 `IBITS` — Bit extraction

Description:
  `IBITS` extracts a field 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)`.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = IBITS(I, POS, LEN)`
Arguments:

  I | The type shall be `INTEGER`.
  POS | The type shall be `INTEGER`.
  LEN | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  BIT_SIZE, IBCLR, IBSET, IAND, IOR, IEOR

Next: ICHAR, Previous: IBITS, Up: Intrinsic Procedures

### 8.119 `IBSET` — Set bit

Description:
  `IBSET` returns the value of I with the bit at position POS set to one.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = IBSET(I, POS)`
Arguments:

  I | The type shall be `INTEGER`.
  POS | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  IBCLR, IBITS, IAND, IOR, IEOR, MVBITS

Next: IDATE, Previous: IBSET, Up: Intrinsic Procedures

### 8.120 `ICHAR` — Character-to-integer conversion function

Description:
  `ICHAR(C)` returns the code for the character in the first character position of `C` in the system's native character set. The correspondence between characters and their codes is not necessarily the same across different GNU Fortran implementations.
Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = ICHAR(C [, KIND])`
Arguments:

  C | Shall be a scalar `CHARACTER`, with `INTENT(IN)`
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind.
Example:

                program test_ichar
                  integer i
                  i = ichar(' ')
                end program test_ichar

Specific names:

  Name | Argument | Return type | Standard
  `ICHAR(C)` | `CHARACTER C` | `INTEGER(4)` | Fortran 77 and later

Note:
  No intrinsic exists to convert between a numeric value and a formatted character string representation – for instance, given the `CHARACTER` value `'154'`, obtaining an `INTEGER` or `REAL` value with the value 154, or vice versa. Instead, this functionality is provided by internal-file I/O, as in the following example:

                program read_val
                  integer value
                  character(len=10) string, string2
                  string = '154'

                  ! Convert a string to a numeric value
                  read (string,'(I10)') value
                  print *, value

                  ! Convert a value to a formatted string
                  write (string2,'(I10)') value
                  print *, string2
                end program read_val

See also:
  ACHAR, CHAR, IACHAR

Next: IEOR, Previous: ICHAR, Up: Intrinsic Procedures

### 8.121 `IDATE` — Get current local time subroutine (day/month/year)

Description:
  `IDATE(VALUES)` Fills VALUES 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 VALUES, respectively. The year has four significant digits.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL IDATE(VALUES)`
Arguments:

  VALUES | The type shall be `INTEGER, DIMENSION(3)` and the kind shall be the default integer kind.

Return value:
  Does not return anything.
Example:

                program test_idate
                  integer, dimension(3) :: tarray
                  call idate(tarray)
                  print *, tarray(1)
                  print *, tarray(2)
                  print *, tarray(3)
                end program test_idate

Next: IERRNO, Previous: IDATE, Up: Intrinsic Procedures

### 8.122 `IEOR` — Bitwise logical exclusive or

Description:
  `IEOR` returns the bitwise Boolean exclusive-OR of I and J.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = IEOR(I, J)`
Arguments:

  I | The type shall be `INTEGER`.
  J | The type shall be `INTEGER`, of the same kind as I. (As a GNU extension, different kinds are also permitted.)

Return value:
  The return type is `INTEGER`, of the same kind as the arguments. (If the argument kinds differ, it is of the same kind as the larger argument.)
See also:
  IOR, IAND, IBITS, IBSET, IBCLR, NOT

Next: IMAGE_INDEX, Previous: IEOR, Up: Intrinsic Procedures

### 8.123 `IERRNO` — Get the last system error number

Description:
  Returns the last system error number, as given by the C `errno` variable.
Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = IERRNO()`
Arguments:
  None.
Return value:
  The return value is of type `INTEGER` and of the default integer kind.
See also:
  PERROR

Next: INDEX intrinsic, Previous: IERRNO, Up: Intrinsic Procedures

### 8.124 `IMAGE_INDEX` — Function that converts a cosubscript to an image index

Description:
  Returns the image index belonging to a cosubscript.
Standard:
  Fortran 2008 and later
Class:
  Inquiry function.
Syntax:
  `RESULT = IMAGE_INDEX(COARRAY, SUB)`
Arguments: None.

  COARRAY | Coarray of any type.
  SUB | default integer rank-1 array of a size equal to the corank of COARRAY.

Return value:
  Scalar default integer with the value of the image index which corresponds to the cosubscripts. For invalid cosubscripts the result is zero.
Example:

                INTEGER :: array[2,-1:4,8,*]
                ! Writes  28 (or 0 if there are fewer than 28 images)
                WRITE (*,*) IMAGE_INDEX (array, [2,0,3,1])

See also:
  THIS_IMAGE, NUM_IMAGES

Next: INT, Previous: IMAGE_INDEX, Up: Intrinsic Procedures

### 8.125 `INDEX` — Position of a substring within a string

Description:
  Returns the position of the start of the first occurrence of string SUBSTRING as a substring in STRING, counting from one. If SUBSTRING is not present in STRING, zero is returned. If the BACK argument is present and true, the return value is the start of the last occurrence rather than the first.
Standard:
  Fortran 77 and later, with KIND argument Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = INDEX(STRING, SUBSTRING [, BACK [, KIND]])`
Arguments:

  STRING | Shall be a scalar `CHARACTER`, with `INTENT(IN)`
  SUBSTRING | Shall be a scalar `CHARACTER`, with `INTENT(IN)`
  BACK | (Optional) Shall be a scalar `LOGICAL`, with `INTENT(IN)`
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind.
Specific names:

  Name | Argument | Return type | Standard
  `INDEX(STRING, SUBSTRING)` | `CHARACTER` | `INTEGER(4)` | Fortran 77 and later

See also:
  SCAN, VERIFY

Next: INT2, Previous: INDEX intrinsic, Up: Intrinsic Procedures

### 8.126 `INT` — Convert to integer type

Description:
  Convert to integer type
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = INT(A [, KIND))`
Arguments:

  A | Shall be of type `INTEGER`, `REAL`, or `COMPLEX`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  These functions return a `INTEGER` variable or array under the following rules:
  (A)
    If A is of type `INTEGER`, `INT(A) = A`
  (B)
    If A is of type `REAL` and |A| < 1, `INT(A)` equals `0`. If |A| \geq 1, then `INT(A)` equals the largest integer that does not exceed the range of A and whose sign is the same as the sign of A.
  (C)
    If A is of type `COMPLEX`, rule B is applied to the real part of A.
Example:

                program test_int
                  integer :: i = 42
                  complex :: z = (-3.7, 1.0)
                  print *, int(i)
                  print *, int(z), int(z,8)
                end program

Specific names:

  Name | Argument | Return type | Standard
  `INT(A)` | `REAL(4) A` | `INTEGER` | Fortran 77 and later
  `IFIX(A)` | `REAL(4) A` | `INTEGER` | Fortran 77 and later
  `IDINT(A)` | `REAL(8) A` | `INTEGER` | Fortran 77 and later

Next: INT8, Previous: INT, Up: Intrinsic Procedures

### 8.127 `INT2` — Convert to 16-bit integer type

Description:
  Convert to a `KIND=2` integer type. This is equivalent to the standard `INT` intrinsic with an optional argument of `KIND=2`, and is only included for backwards compatibility.

  The `SHORT` intrinsic is equivalent to `INT2`.

Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = INT2(A)`
Arguments:

  A | Shall be of type `INTEGER`, `REAL`, or `COMPLEX`.

Return value:
  The return value is a `INTEGER(2)` variable.
See also:
  INT, INT8, LONG

Next: IOR, Previous: INT2, Up: Intrinsic Procedures

### 8.128 `INT8` — Convert to 64-bit integer type

Description:
  Convert to a `KIND=8` integer type. This is equivalent to the standard `INT` intrinsic with an optional argument of `KIND=8`, and is only included for backwards compatibility.
Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = INT8(A)`
Arguments:

  A | Shall be of type `INTEGER`, `REAL`, or `COMPLEX`.

Return value:
  The return value is a `INTEGER(8)` variable.
See also:
  INT, INT2, LONG

Next: IPARITY, Previous: INT8, Up: Intrinsic Procedures

### 8.129 `IOR` — Bitwise logical or

Description:
  `IOR` returns the bitwise Boolean inclusive-OR of I and J.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = IOR(I, J)`
Arguments:

  I | The type shall be `INTEGER`.
  J | The type shall be `INTEGER`, of the same kind as I. (As a GNU extension, different kinds are also permitted.)

Return value:
  The return type is `INTEGER`, of the same kind as the arguments. (If the argument kinds differ, it is of the same kind as the larger argument.)
See also:
  IEOR, IAND, IBITS, IBSET, IBCLR, NOT

Next: IRAND, Previous: IOR, Up: Intrinsic Procedures

### 8.130 `IPARITY` — Bitwise XOR of array elements

Description:
  Reduces with bitwise XOR (exclusive or) the elements of ARRAY along dimension DIM if the corresponding element in MASK is `TRUE`.
Standard:
  Fortran 2008 and later
Class:
  Transformational function
Syntax:

  `RESULT = IPARITY(ARRAY[, MASK])`
  `RESULT = IPARITY(ARRAY, DIM[, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER`
  DIM | (Optional) shall be a scalar of type `INTEGER` with a value in the range from 1 to n, where n equals the rank of ARRAY.
  MASK | (Optional) shall be of type `LOGICAL` and either be a scalar or an array of the same shape as ARRAY.

Return value:
  The result is of the same type as ARRAY.

  If DIM is absent, a scalar with the bitwise XOR of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:

                PROGRAM test_iparity
                  INTEGER(1) :: a(2)

                  a(1) = b'00100100'
                  a(2) = b'01101010'

                  ! prints 01001110
                  PRINT '(b8.8)', IPARITY(a)
                END PROGRAM

See also:
  IANY, IALL, IEOR, PARITY

Next: IS_IOSTAT_END, Previous: IPARITY, Up: Intrinsic Procedures

### 8.131 `IRAND` — Integer pseudo-random number

Description:
  `IRAND(FLAG)` returns a pseudo-random number from a uniform distribution between 0 and a system-dependent limit (which is in most cases 2147483647). If FLAG is 0, the next number in the current sequence is returned; if FLAG is 1, the generator is restarted by `CALL SRAND(0)`; if FLAG has any other value, it is used as a new seed with `SRAND`.

  This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. It implements a simple modulo generator as provided by `g77`. For new code, one should consider the use of RANDOM_NUMBER as it implements a superior algorithm.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = IRAND(I)`
Arguments:

  I | Shall be a scalar `INTEGER` of kind 4.

Return value:
  The return value is of `INTEGER(kind=4)` type.
Example:

                program test_irand
                  integer,parameter :: seed = 86456

                  call srand(seed)
                  print *, irand(), irand(), irand(), irand()
                  print *, irand(seed), irand(), irand(), irand()
                end program test_irand

Next: IS_IOSTAT_EOR, Previous: IRAND, Up: Intrinsic Procedures

### 8.132 `IS_IOSTAT_END` — Test for end-of-file value

Description:
  `IS_IOSTAT_END` tests whether an variable has the value of the I/O status “end of file”. The function is equivalent to comparing the variable with the `IOSTAT_END` parameter of the intrinsic module `ISO_FORTRAN_ENV`.
Standard:
  Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = IS_IOSTAT_END(I)`
Arguments:

  I | Shall be of the type `INTEGER`.

Return value:
  Returns a `LOGICAL` of the default kind, which `.TRUE.` if I has the value which indicates an end of file condition for `IOSTAT=` specifiers, and is `.FALSE.` otherwise.
Example:

                PROGRAM iostat
                  IMPLICIT NONE
                  INTEGER :: stat, i
                  OPEN(88, FILE='test.dat')
                  READ(88, *, IOSTAT=stat) i
                  IF(IS_IOSTAT_END(stat)) STOP 'END OF FILE'
                END PROGRAM

Next: ISATTY, Previous: IS_IOSTAT_END, Up: Intrinsic Procedures

### 8.133 `IS_IOSTAT_EOR` — Test for end-of-record value

Description:
  `IS_IOSTAT_EOR` tests whether an variable has the value of the I/O status “end of record”. The function is equivalent to comparing the variable with the `IOSTAT_EOR` parameter of the intrinsic module `ISO_FORTRAN_ENV`.
Standard:
  Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = IS_IOSTAT_EOR(I)`
Arguments:

  I | Shall be of the type `INTEGER`.

Return value:
  Returns a `LOGICAL` of the default kind, which `.TRUE.` if I has the value which indicates an end of file condition for `IOSTAT=` specifiers, and is `.FALSE.` otherwise.
Example:

                PROGRAM iostat
                  IMPLICIT NONE
                  INTEGER :: stat, i(50)
                  OPEN(88, FILE='test.dat', FORM='UNFORMATTED')
                  READ(88, IOSTAT=stat) i
                  IF(IS_IOSTAT_EOR(stat)) STOP 'END OF RECORD'
                END PROGRAM

Next: ISHFT, Previous: IS_IOSTAT_EOR, Up: Intrinsic Procedures

### 8.134 `ISATTY` — Whether a unit is a terminal device.

Description:
  Determine whether a unit is connected to a terminal device.
Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = ISATTY(UNIT)`
Arguments:

  UNIT | Shall be a scalar `INTEGER`.

Return value:
  Returns `.TRUE.` if the UNIT is connected to a terminal device, `.FALSE.` otherwise.
Example:

                PROGRAM test_isatty
                  INTEGER(kind=1) :: unit
                  DO unit = 1, 10
                    write(*,*) isatty(unit=unit)
                  END DO
                END PROGRAM

See also:
  TTYNAM

Next: ISHFTC, Previous: ISATTY, Up: Intrinsic Procedures

### 8.135 `ISHFT` — Shift bits

Description:
  `ISHFT` returns a value corresponding to I with all of the bits shifted SHIFT places. A value of SHIFT greater than zero corresponds to a left shift, a value of zero corresponds to no shift, and a value less than zero corresponds to a right shift. If the absolute value of SHIFT is greater than `BIT_SIZE(I)`, the value is undefined. Bits shifted out from the left end or right end are lost; zeros are shifted in from the opposite end.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = ISHFT(I, SHIFT)`
Arguments:

  I | The type shall be `INTEGER`.
  SHIFT | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  ISHFTC

Next: ISNAN, Previous: ISHFT, Up: Intrinsic Procedures

### 8.136 `ISHFTC` — Shift bits circularly

Description:
  `ISHFTC` returns a value corresponding to I with the rightmost SIZE bits shifted circularly SHIFT places; that is, bits shifted out one end are shifted into the opposite end. A value of SHIFT greater than zero corresponds to a left shift, a value of zero corresponds to no shift, and a value less than zero corresponds to a right shift. The absolute value of SHIFT must be less than SIZE. If the SIZE argument is omitted, it is taken to be equivalent to `BIT_SIZE(I)`.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = ISHFTC(I, SHIFT [, SIZE])`
Arguments:

  I | The type shall be `INTEGER`.
  SHIFT | The type shall be `INTEGER`.
  SIZE | (Optional) The type shall be `INTEGER`; the value must be greater than zero and less than or equal to `BIT_SIZE(I)`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  ISHFT

Next: ITIME, Previous: ISHFTC, Up: Intrinsic Procedures

### 8.137 `ISNAN` — Test for a NaN

Description:
  `ISNAN` tests whether a floating-point value is an IEEE Not-a-Number (NaN).
Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `ISNAN(X)`
Arguments:

  X | Variable of the type `REAL`.

Return value:
  Returns a default-kind `LOGICAL`. The returned value is `TRUE` if X is a NaN and `FALSE` otherwise.
Example:

                program test_nan
                  implicit none
                  real :: x
                  x = -1.0
                  x = sqrt(x)
                  if (isnan(x)) stop '"x" is a NaN'
                end program test_nan

Next: KILL, Previous: ISNAN, Up: Intrinsic Procedures

### 8.138 `ITIME` — Get current local time subroutine (hour/minutes/seconds)

Description:
  `IDATE(VALUES)` Fills VALUES with the numerical values at the current local time. The hour (in the range 1-24), minute (in the range 1-60), and seconds (in the range 1-60) appear in elements 1, 2, and 3 of VALUES, respectively.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL ITIME(VALUES)`
Arguments:

  VALUES | The type shall be `INTEGER, DIMENSION(3)` and the kind shall be the default integer kind.

Return value:
  Does not return anything.
Example:

                program test_itime
                  integer, dimension(3) :: tarray
                  call itime(tarray)
                  print *, tarray(1)
                  print *, tarray(2)
                  print *, tarray(3)
                end program test_itime

Next: KIND, Previous: ITIME, Up: Intrinsic Procedures

### 8.139 `KILL` — Send a signal to a process

Description:
Standard:
  Sends the signal specified by SIGNAL to the process PID. See `kill(2)`.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Class:
  Subroutine, function
Syntax:

  `CALL KILL(C, VALUE [, STATUS])`
  `STATUS = KILL(C, VALUE)`

Arguments:

  C | Shall be a scalar `INTEGER`, with `INTENT(IN)`
  VALUE | Shall be a scalar `INTEGER`, with `INTENT(IN)`
  STATUS | (Optional) status flag of type `INTEGER(4)` or `INTEGER(8)`. Returns 0 on success, or a system-specific error code otherwise.

See also:
  ABORT, EXIT

Next: LBOUND, Previous: KILL, Up: Intrinsic Procedures

### 8.140 `KIND` — Kind of an entity

Description:
  `KIND(X)` returns the kind value of the entity X.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `K = KIND(X)`
Arguments:

  X | Shall be of type `LOGICAL`, `INTEGER`, `REAL`, `COMPLEX` or `CHARACTER`.

Return value:
  The return value is a scalar of type `INTEGER` and of the default integer kind.
Example:

                program test_kind
                  integer,parameter :: kc = kind(' ')
                  integer,parameter :: kl = kind(.true.)

                  print *, "The default character kind is ", kc
                  print *, "The default logical kind is ", kl
                end program test_kind

Next: LCOBOUND, Previous: KIND, Up: Intrinsic Procedures

### 8.141 `LBOUND` — Lower dimension bounds of an array

Description:
  Returns the lower bounds of an array, or a single lower bound along the DIM dimension.
Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = LBOUND(ARRAY [, DIM [, KIND]])`
Arguments:

  ARRAY | Shall be an array, of any type.
  DIM | (Optional) Shall be a scalar `INTEGER`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind. If DIM is absent, the result is an array of the lower bounds of ARRAY. If DIM is present, the result is a scalar corresponding to the lower bound of the array along that dimension. If ARRAY is an expression rather than a whole array or array structure component, or if it has a zero extent along the relevant dimension, the lower bound is taken to be 1.
See also:
  UBOUND, LCOBOUND

Next: LEADZ, Previous: LBOUND, Up: Intrinsic Procedures

### 8.142 `LCOBOUND` — Lower codimension bounds of an array

Description:
  Returns the lower bounds of a coarray, or a single lower cobound along the DIM codimension.
Standard:
  Fortran 2008 and later
Class:
  Inquiry function
Syntax:
  `RESULT = LCOBOUND(COARRAY [, DIM [, KIND]])`
Arguments:

  ARRAY | Shall be an coarray, of any type.
  DIM | (Optional) Shall be a scalar `INTEGER`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind. If DIM is absent, the result is an array of the lower cobounds of COARRAY. If DIM is present, the result is a scalar corresponding to the lower cobound of the array along that codimension.
See also:
  UCOBOUND, LBOUND

Next: LEN, Previous: LCOBOUND, Up: Intrinsic Procedures

### 8.143 `LEADZ` — Number of leading zero bits of an integer

Description:
  `LEADZ` returns the number of leading zero bits of an integer.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = LEADZ(I)`
Arguments:

  I | Shall be of type `INTEGER`.

Return value:
  The type of the return value is the default `INTEGER`. If all the bits of `I` are zero, the result value is `BIT_SIZE(I)`.
Example:

                PROGRAM test_leadz
                  WRITE (*,*) BIT_SIZE(1)  ! prints 32
                  WRITE (*,*) LEADZ(1)     ! prints 31
                END PROGRAM

See also:
  BIT_SIZE, TRAILZ, POPCNT, POPPAR

Next: LEN_TRIM, Previous: LEADZ, Up: Intrinsic Procedures

### 8.144 `LEN` — Length of a character entity

Description:
  Returns the length of a character 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.
Standard:
  Fortran 77 and later, with KIND argument Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `L = LEN(STRING [, KIND])`
Arguments:

  STRING | Shall be a scalar or array of type `CHARACTER`, with `INTENT(IN)`
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind.
Specific names:

  Name | Argument | Return type | Standard
  `LEN(STRING)` | `CHARACTER` | `INTEGER` | Fortran 77 and later

See also:
  LEN_TRIM, ADJUSTL, ADJUSTR

Next: LGE, Previous: LEN, Up: Intrinsic Procedures

### 8.145 `LEN_TRIM` — Length of a character entity without trailing blank characters

Description:
  Returns the length of a character string, ignoring any trailing blanks.
Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = LEN_TRIM(STRING [, KIND])`
Arguments:

  STRING | Shall be a scalar of type `CHARACTER`, with `INTENT(IN)`
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind.
See also:
  LEN, ADJUSTL, ADJUSTR

Next: LGT, Previous: LEN_TRIM, Up: Intrinsic Procedures

### 8.146 `LGE` — Lexical greater than or equal

Description:
  Determines whether one string is lexically greater than or equal to another string, where the two strings are interpreted as containing ASCII character codes. 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.

  In general, the lexical comparison intrinsics `LGE`, `LGT`, `LLE`, and `LLT` differ from the corresponding intrinsic operators `.GE.`, `.GT.`, `.LE.`, and `.LT.`, in that the latter use the processor's character ordering (which is not ASCII on some targets), whereas the former always use the ASCII ordering.

Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = LGE(STRING_A, STRING_B)`
Arguments:

  STRING_A | Shall be of default `CHARACTER` type.
  STRING_B | Shall be of default `CHARACTER` type.

Return value:
  Returns `.TRUE.` if `STRING_A >= STRING_B`, and `.FALSE.` otherwise, based on the ASCII ordering.
Specific names:

  Name | Argument | Return type | Standard
  `LGE(STRING_A, STRING_B)` | `CHARACTER` | `LOGICAL` | Fortran 77 and later

See also:
  LGT, LLE, LLT

Next: LINK, Previous: LGE, Up: Intrinsic Procedures

### 8.147 `LGT` — Lexical greater than

Description:
  Determines whether one string is lexically greater than another string, where the two strings are interpreted as containing ASCII character codes. 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.

  In general, the lexical comparison intrinsics `LGE`, `LGT`, `LLE`, and `LLT` differ from the corresponding intrinsic operators `.GE.`, `.GT.`, `.LE.`, and `.LT.`, in that the latter use the processor's character ordering (which is not ASCII on some targets), whereas the former always use the ASCII ordering.

Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = LGT(STRING_A, STRING_B)`
Arguments:

  STRING_A | Shall be of default `CHARACTER` type.
  STRING_B | Shall be of default `CHARACTER` type.

Return value:
  Returns `.TRUE.` if `STRING_A > STRING_B`, and `.FALSE.` otherwise, based on the ASCII ordering.
Specific names:

  Name | Argument | Return type | Standard
  `LGT(STRING_A, STRING_B)` | `CHARACTER` | `LOGICAL` | Fortran 77 and later

See also:
  LGE, LLE, LLT

Next: LLE, Previous: LGT, Up: Intrinsic Procedures

### 8.148 `LINK` — Create a hard link

Description:
  Makes a (hard) link from file PATH1 to PATH2. A null character (`CHAR(0)`) can be used to mark the end of the names in PATH1 and PATH2; otherwise, trailing blanks in the file names are ignored. If the STATUS argument is supplied, it contains 0 on success or a nonzero error code upon return; see `link(2)`.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL LINK(PATH1, PATH2 [, STATUS])`
  `STATUS = LINK(PATH1, PATH2)`

Arguments:

  PATH1 | Shall be of default `CHARACTER` type.
  PATH2 | Shall be of default `CHARACTER` type.
  STATUS | (Optional) Shall be of default `INTEGER` type.

See also:
  SYMLNK, UNLINK

Next: LLT, Previous: LINK, Up: Intrinsic Procedures

### 8.149 `LLE` — Lexical less than or equal

Description:
  Determines whether one string is lexically less than or equal to another string, where the two strings are interpreted as containing ASCII character codes. 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.

  In general, the lexical comparison intrinsics `LGE`, `LGT`, `LLE`, and `LLT` differ from the corresponding intrinsic operators `.GE.`, `.GT.`, `.LE.`, and `.LT.`, in that the latter use the processor's character ordering (which is not ASCII on some targets), whereas the former always use the ASCII ordering.

Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = LLE(STRING_A, STRING_B)`
Arguments:

  STRING_A | Shall be of default `CHARACTER` type.
  STRING_B | Shall be of default `CHARACTER` type.

Return value:
  Returns `.TRUE.` if `STRING_A <= STRING_B`, and `.FALSE.` otherwise, based on the ASCII ordering.
Specific names:

  Name | Argument | Return type | Standard
  `LLE(STRING_A, STRING_B)` | `CHARACTER` | `LOGICAL` | Fortran 77 and later

See also:
  LGE, LGT, LLT

Next: LNBLNK, Previous: LLE, Up: Intrinsic Procedures

### 8.150 `LLT` — Lexical less than

Description:
  Determines whether one string is lexically less than another string, where the two strings are interpreted as containing ASCII character codes. 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.

  In general, the lexical comparison intrinsics `LGE`, `LGT`, `LLE`, and `LLT` differ from the corresponding intrinsic operators `.GE.`, `.GT.`, `.LE.`, and `.LT.`, in that the latter use the processor's character ordering (which is not ASCII on some targets), whereas the former always use the ASCII ordering.

Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = LLT(STRING_A, STRING_B)`
Arguments:

  STRING_A | Shall be of default `CHARACTER` type.
  STRING_B | Shall be of default `CHARACTER` type.

Return value:
  Returns `.TRUE.` if `STRING_A < STRING_B`, and `.FALSE.` otherwise, based on the ASCII ordering.
Specific names:

  Name | Argument | Return type | Standard
  `LLT(STRING_A, STRING_B)` | `CHARACTER` | `LOGICAL` | Fortran 77 and later

See also:
  LGE, LGT, LLE

Next: LOC, Previous: LLT, Up: Intrinsic Procedures

### 8.151 `LNBLNK` — Index of the last non-blank character in a string

Description:
  Returns the length of a character string, ignoring any trailing blanks. This is identical to the standard `LEN_TRIM` intrinsic, and is only included for backwards compatibility.
Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = LNBLNK(STRING)`
Arguments:

  STRING | Shall be a scalar of type `CHARACTER`, with `INTENT(IN)`

Return value:
  The return value is of `INTEGER(kind=4)` type.
See also:
  INDEX intrinsic, LEN_TRIM

Next: LOG, Previous: LNBLNK, Up: Intrinsic Procedures

### 8.152 `LOC` — Returns the address of a variable

Description:
  `LOC(X)` returns the address of X as an integer.
Standard:
  GNU extension
Class:
  Inquiry function
Syntax:
  `RESULT = LOC(X)`
Arguments:

  X | Variable of any type.

Return value:
  The return value is of type `INTEGER`, with a `KIND` corresponding to the size (in bytes) of a memory address on the target machine.
Example:

                program test_loc
                  integer :: i
                  real :: r
                  i = loc(r)
                  print *, i
                end program test_loc

Next: LOG10, Previous: LOC, Up: Intrinsic Procedures

### 8.153 `LOG` — Natural logarithm function

Description:
  `LOG(X)` computes the natural logarithm of X, i.e. the logarithm to the base e.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = LOG(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value is of type `REAL` or `COMPLEX`. The kind type parameter is the same as X. If X is `COMPLEX`, the imaginary part \omega is in the range -\pi \leq \omega \leq \pi.
Example:

                program test_log
                  real(8) :: x = 2.7182818284590451_8
                  complex :: z = (1.0, 2.0)
                  x = log(x)    ! will yield (approximately) 1
                  z = log(z)
                end program test_log

Specific names:

  Name | Argument | Return type | Standard
  `ALOG(X)` | `REAL(4) X` | `REAL(4)` | f95, gnu
  `DLOG(X)` | `REAL(8) X` | `REAL(8)` | f95, gnu
  `CLOG(X)` | `COMPLEX(4) X` | `COMPLEX(4)` | f95, gnu
  `ZLOG(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | f95, gnu
  `CDLOG(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | f95, gnu

Next: LOG_GAMMA, Previous: LOG, Up: Intrinsic Procedures

### 8.154 `LOG10` — Base 10 logarithm function

Description:
  `LOG10(X)` computes the base 10 logarithm of X.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = LOG10(X)`
Arguments:

  X | The type shall be `REAL`.

Return value:
  The return value is of type `REAL` or `COMPLEX`. The kind type parameter is the same as X.
Example:

                program test_log10
                  real(8) :: x = 10.0_8
                  x = log10(x)
                end program test_log10

Specific names:

  Name | Argument | Return type | Standard
  `ALOG10(X)` | `REAL(4) X` | `REAL(4)` | Fortran 95 and later
  `DLOG10(X)` | `REAL(8) X` | `REAL(8)` | Fortran 95 and later

Next: LOGICAL, Previous: LOG10, Up: Intrinsic Procedures

### 8.155 `LOG_GAMMA` — Logarithm of the Gamma function

Description:
  `LOG_GAMMA(X)` computes the natural logarithm of the absolute value of the Gamma (\Gamma) function.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `X = LOG_GAMMA(X)`
Arguments:

  X | Shall be of type `REAL` and neither zero nor a negative integer.

Return value:
  The return value is of type `REAL` of the same kind as X.
Example:

                program test_log_gamma
                  real :: x = 1.0
                  x = lgamma(x) ! returns 0.0
                end program test_log_gamma

Specific names:

  Name | Argument | Return type | Standard
  `LGAMMA(X)` | `REAL(4) X` | `REAL(4)` | GNU Extension
  `ALGAMA(X)` | `REAL(4) X` | `REAL(4)` | GNU Extension
  `DLGAMA(X)` | `REAL(8) X` | `REAL(8)` | GNU Extension

See also:
  Gamma function: GAMMA

Next: LONG, Previous: LOG_GAMMA, Up: Intrinsic Procedures

### 8.156 `LOGICAL` — Convert to logical type

Description:
  Converts one kind of `LOGICAL` variable to another.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = LOGICAL(L [, KIND])`
Arguments:

  L | The type shall be `LOGICAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is a `LOGICAL` value equal to L, with a kind corresponding to KIND, or of the default logical kind if KIND is not given.
See also:
  INT, REAL, CMPLX

Next: LSHIFT, Previous: LOGICAL, Up: Intrinsic Procedures

### 8.157 `LONG` — Convert to integer type

Description:
  Convert to a `KIND=4` integer type, which is the same size as a C `long` integer. This is equivalent to the standard `INT` intrinsic with an optional argument of `KIND=4`, and is only included for backwards compatibility.
Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = LONG(A)`
Arguments:

  A | Shall be of type `INTEGER`, `REAL`, or `COMPLEX`.

Return value:
  The return value is a `INTEGER(4)` variable.
See also:
  INT, INT2, INT8

Next: LSTAT, Previous: LONG, Up: Intrinsic Procedures

### 8.158 `LSHIFT` — Left shift bits

Description:
  `LSHIFT` returns a value corresponding to I with all of the bits shifted left by SHIFT places. If the absolute value of SHIFT is greater than `BIT_SIZE(I)`, the value is undefined. Bits shifted out from the left end are lost; zeros are shifted in from the opposite end.

  This function has been superseded by the `ISHFT` intrinsic, which is standard in Fortran 95 and later, and the `SHIFTL` intrinsic, which is standard in Fortran 2008 and later.

Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = LSHIFT(I, SHIFT)`
Arguments:

  I | The type shall be `INTEGER`.
  SHIFT | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  ISHFT, ISHFTC, RSHIFT, SHIFTA, SHIFTL, SHIFTR

Next: LTIME, Previous: LSHIFT, Up: Intrinsic Procedures

### 8.159 `LSTAT` — Get file status

Description:
  `LSTAT` is identical to STAT, except that if path is a symbolic link, then the link itself is statted, not the file that it refers to.

  The elements in `VALUES` are the same as described by STAT.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL LSTAT(NAME, VALUES [, STATUS])`
  `STATUS = LSTAT(NAME, VALUES)`

Arguments:

  NAME | The type shall be `CHARACTER` of the default kind, a valid path within the file system.
  VALUES | The type shall be `INTEGER(4), DIMENSION(13)`.
  STATUS | (Optional) status flag of type `INTEGER(4)`. Returns 0 on success and a system specific error code otherwise.

Example:
  See STAT for an example.
See also:
  To stat an open file: FSTAT, to stat a file: STAT

Next: MALLOC, Previous: LSTAT, Up: Intrinsic Procedures

### 8.160 `LTIME` — Convert time to local time info

Description:
  Given a system time value TIME (as provided by the `TIME8` intrinsic), fills VALUES with values extracted from it appropriate to the local time zone using `localtime(3)`.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL LTIME(TIME, VALUES)`
Arguments:

  TIME | An `INTEGER` scalar expression corresponding to a system time, with `INTENT(IN)`.
  VALUES | A default `INTEGER` array with 9 elements, with `INTENT(OUT)`.

Return value:
  The elements of VALUES are assigned 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 is not available.
See also:
  CTIME, GMTIME, TIME, TIME8

Next: MASKL, Previous: LTIME, Up: Intrinsic Procedures

### 8.161 `MALLOC` — Allocate dynamic memory

Description:
  `MALLOC(SIZE)` allocates SIZE bytes of dynamic memory and returns the address of the allocated memory. The `MALLOC` intrinsic is an extension intended to be used with Cray pointers, and is provided in GNU Fortran to allow the user to compile legacy code. For new code using Fortran 95 pointers, the memory allocation intrinsic is `ALLOCATE`.
Standard:
  GNU extension
Class:
  Function
Syntax:
  `PTR = MALLOC(SIZE)`
Arguments:

  SIZE | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER(K)`, with K such that variables of type `INTEGER(K)` have the same size as C pointers (`sizeof(void *)`).
Example:
  The following example demonstrates the use of `MALLOC` and `FREE` with Cray pointers.

                program test_malloc
                  implicit none
                  integer i
                  real*8 x(*), z
                  pointer(ptr_x,x)

                  ptr_x = malloc(20*8)
                  do i = 1, 20
                    x(i) = sqrt(1.0d0 / i)
                  end do
                  z = 0
                  do i = 1, 20
                    z = z + x(i)
                    print *, z
                  end do
                  call free(ptr_x)
                end program test_malloc

See also:
  FREE

Next: MASKR, Previous: MALLOC, Up: Intrinsic Procedures

### 8.162 `MASKL` — Left justified mask

Description:
  `MASKL(I[, KIND])` has its leftmost I bits set to 1, and the remaining bits set to 0.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = MASKL(I[, KIND])`
Arguments:

  I | Shall be of type `INTEGER`.
  KIND | Shall be a scalar constant expression of type `INTEGER`.

Return value:
  The return value is of type `INTEGER`. If KIND is present, it specifies the kind value of the return type; otherwise, it is of the default integer kind.
See also:
  MASKR

Next: MATMUL, Previous: MASKL, Up: Intrinsic Procedures

### 8.163 `MASKR` — Right justified mask

Description:
  `MASKL(I[, KIND])` has its rightmost I bits set to 1, and the remaining bits set to 0.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = MASKR(I[, KIND])`
Arguments:

  I | Shall be of type `INTEGER`.
  KIND | Shall be a scalar constant expression of type `INTEGER`.

Return value:
  The return value is of type `INTEGER`. If KIND is present, it specifies the kind value of the return type; otherwise, it is of the default integer kind.
See also:
  MASKL

Next: MAX, Previous: MASKR, Up: Intrinsic Procedures

### 8.164 `MATMUL` — matrix multiplication

Description:
  Performs a matrix multiplication on numeric or logical arguments.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = MATMUL(MATRIX_A, MATRIX_B)`
Arguments:

  MATRIX_A | An array of `INTEGER`, `REAL`, `COMPLEX`, or `LOGICAL` type, with a rank of one or two.
  MATRIX_B | An array of `INTEGER`, `REAL`, or `COMPLEX` type if MATRIX_A is of a numeric type; otherwise, an array of `LOGICAL` type. The rank shall be one or two, and the first (or only) dimension of MATRIX_B shall be equal to the last (or only) dimension of MATRIX_A.

Return value:
  The matrix product of MATRIX_A and MATRIX_B. The type and kind of the result follow the usual type and kind promotion rules, as for the `*` or `.AND.` operators.
See also:

Next: MAXEXPONENT, Previous: MATMUL, Up: Intrinsic Procedures

### 8.165 `MAX` — Maximum value of an argument list

Description:
  Returns the argument with the largest (most positive) value.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = MAX(A1, A2 [, A3 [, ...]])`
Arguments:

  A1 | The type shall be `INTEGER` or `REAL`.
  A2, A3, ... | An expression of the same type and kind as A1. (As a GNU extension, arguments of different kinds are permitted.)

Return value:
  The return value corresponds to the maximum value among the arguments, and has the same type and kind as the first argument.
Specific names:

  Name | Argument | Return type | Standard
  `MAX0(A1)` | `INTEGER(4) A1` | `INTEGER(4)` | Fortran 77 and later
  `AMAX0(A1)` | `INTEGER(4) A1` | `REAL(MAX(X))` | Fortran 77 and later
  `MAX1(A1)` | `REAL A1` | `INT(MAX(X))` | Fortran 77 and later
  `AMAX1(A1)` | `REAL(4) A1` | `REAL(4)` | Fortran 77 and later
  `DMAX1(A1)` | `REAL(8) A1` | `REAL(8)` | Fortran 77 and later

See also:
  MAXLOC MAXVAL, MIN

Next: MAXLOC, Previous: MAX, Up: Intrinsic Procedures

### 8.166 `MAXEXPONENT` — Maximum exponent of a real kind

Description:
  `MAXEXPONENT(X)` returns the maximum exponent in the model of the type of `X`.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = MAXEXPONENT(X)`
Arguments:

  X | Shall be of type `REAL`.

Return value:
  The return value is of type `INTEGER` and of the default integer kind.
Example:

                program exponents
                  real(kind=4) :: x
                  real(kind=8) :: y

                  print *, minexponent(x), maxexponent(x)
                  print *, minexponent(y), maxexponent(y)
                end program exponents

Next: MAXVAL, Previous: MAXEXPONENT, Up: Intrinsic Procedures

### 8.167 `MAXLOC` — Location of the maximum value within an array

Description:
  Determines the location of the element in the array with the maximum value, or, if the DIM argument is supplied, determines the locations of the maximum element along each row of the array in the DIM direction. If MASK is present, only the elements for which MASK is `.TRUE.` are considered. If more than one element in the array has the maximum value, the location returned is that of the first such element in array element order. If the array has zero size, or all of the elements of MASK are `.FALSE.`, then the result is an array of zeroes. Similarly, if DIM is supplied and all of the elements of MASK along a given row are zero, the result value for that row is zero.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:

  `RESULT = MAXLOC(ARRAY, DIM [, MASK])`
  `RESULT = MAXLOC(ARRAY [, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER` or `REAL`.
  DIM | (Optional) Shall be a scalar of type `INTEGER`, with a value between one and the rank of ARRAY, inclusive. It may not be an optional dummy argument.
  MASK | Shall be an array of type `LOGICAL`, and conformable with ARRAY.

Return value:
  If DIM is absent, the result is a rank-one array with a length equal to the rank of ARRAY. If DIM is present, the result is an array with a rank one less than the rank of ARRAY, and a size corresponding to the size of ARRAY with the DIM dimension removed. If DIM is present and ARRAY has a rank of one, the result is a scalar. In all cases, the result is of default `INTEGER` type.
See also:
  MAX, MAXVAL

Next: MCLOCK, Previous: MAXLOC, Up: Intrinsic Procedures

### 8.168 `MAXVAL` — Maximum value of an array

Description:
  Determines the maximum value of the elements in an array value, or, if the DIM argument is supplied, determines the maximum value along each row of the array in the DIM direction. If MASK is present, only the elements for which MASK is `.TRUE.` are considered. If the array has zero size, or all of the elements of MASK are `.FALSE.`, then the result is `-HUGE(ARRAY)` if ARRAY is numeric, or a string of nulls if ARRAY is of character type.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:

  `RESULT = MAXVAL(ARRAY, DIM [, MASK])`
  `RESULT = MAXVAL(ARRAY [, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER` or `REAL`.
  DIM | (Optional) Shall be a scalar of type `INTEGER`, with a value between one and the rank of ARRAY, inclusive. It may not be an optional dummy argument.
  MASK | Shall be an array of type `LOGICAL`, and conformable with ARRAY.

Return value:
  If DIM is absent, or if ARRAY has a rank of one, the result is a scalar. If DIM is present, the result is an array with a rank one less than the rank of ARRAY, and a size corresponding to the size of ARRAY with the DIM dimension removed. In all cases, the result is of the same type and kind as ARRAY.
See also:
  MAX, MAXLOC

Next: MCLOCK8, Previous: MAXVAL, Up: Intrinsic Procedures

### 8.169 `MCLOCK` — Time function

Description:
  Returns the number of clock ticks since the start of the process, based on the function `clock(3)` in the C standard library.

  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.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = MCLOCK()`
Return value:
  The return value is a scalar of type `INTEGER(4)`, equal to the number of clock ticks since the start of the process, or `-1` if the system does not support `clock(3)`.
See also:
  CTIME, GMTIME, LTIME, MCLOCK, TIME

Next: MERGE, Previous: MCLOCK, Up: Intrinsic Procedures

### 8.170 `MCLOCK8` — Time function (64-bit)

Description:
  Returns the number of clock ticks since the start of the process, based on the function `clock(3)` in the C standard library.

  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 it is converted to a 64-bit `INTEGER(8)` 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.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = MCLOCK8()`
Return value:
  The return value is a scalar of type `INTEGER(8)`, equal to the number of clock ticks since the start of the process, or `-1` if the system does not support `clock(3)`.
See also:
  CTIME, GMTIME, LTIME, MCLOCK, TIME8

Next: MERGE_BITS, Previous: MCLOCK8, Up: Intrinsic Procedures

### 8.171 `MERGE` — Merge variables

Description:
  Select values from two arrays according to a logical mask. The result is equal to TSOURCE if MASK is `.TRUE.`, or equal to FSOURCE if it is `.FALSE.`.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = MERGE(TSOURCE, FSOURCE, MASK)`
Arguments:

  TSOURCE | May be of any type.
  FSOURCE | Shall be of the same type and type parameters as TSOURCE.
  MASK | Shall be of type `LOGICAL`.

Return value:
  The result is of the same type and type parameters as TSOURCE.

Next: MIN, Previous: MERGE, Up: Intrinsic Procedures

### 8.172 `MERGE_BITS` — Merge of bits under mask

Description:
  `MERGE_BITS(I, J, MASK)` merges the bits of I and J as determined by the mask. The i-th bit of the result is equal to the i-th bit of I if the i-th bit of MASK is 1; it is equal to the i-th bit of J otherwise.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = MERGE_BITS(I, J, MASK)`
Arguments:

  I | Shall be of type `INTEGER`.
  J | Shall be of type `INTEGER` and of the same kind as I.
  MASK | Shall be of type `INTEGER` and of the same kind as I.

Return value:
  The result is of the same type and kind as I.

Next: MINEXPONENT, Previous: MERGE_BITS, Up: Intrinsic Procedures

### 8.173 `MIN` — Minimum value of an argument list

Description:
  Returns the argument with the smallest (most negative) value.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = MIN(A1, A2 [, A3, ...])`
Arguments:

  A1 | The type shall be `INTEGER` or `REAL`.
  A2, A3, ... | An expression of the same type and kind as A1. (As a GNU extension, arguments of different kinds are permitted.)

Return value:
  The return value corresponds to the maximum value among the arguments, and has the same type and kind as the first argument.
Specific names:

  Name | Argument | Return type | Standard
  `MIN0(A1)` | `INTEGER(4) A1` | `INTEGER(4)` | Fortran 77 and later
  `AMIN0(A1)` | `INTEGER(4) A1` | `REAL(4)` | Fortran 77 and later
  `MIN1(A1)` | `REAL A1` | `INTEGER(4)` | Fortran 77 and later
  `AMIN1(A1)` | `REAL(4) A1` | `REAL(4)` | Fortran 77 and later
  `DMIN1(A1)` | `REAL(8) A1` | `REAL(8)` | Fortran 77 and later

See also:
  MAX, MINLOC, MINVAL

Next: MINLOC, Previous: MIN, Up: Intrinsic Procedures

### 8.174 `MINEXPONENT` — Minimum exponent of a real kind

Description:
  `MINEXPONENT(X)` returns the minimum exponent in the model of the type of `X`.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = MINEXPONENT(X)`
Arguments:

  X | Shall be of type `REAL`.

Return value:
  The return value is of type `INTEGER` and of the default integer kind.
Example:
  See `MAXEXPONENT` for an example.

Next: MINVAL, Previous: MINEXPONENT, Up: Intrinsic Procedures

### 8.175 `MINLOC` — Location of the minimum value within an array

Description:
  Determines the location of the element in the array with the minimum value, or, if the DIM argument is supplied, determines the locations of the minimum element along each row of the array in the DIM direction. If MASK is present, only the elements for which MASK is `.TRUE.` are considered. If more than one element in the array has the minimum value, the location returned is that of the first such element in array element order. If the array has zero size, or all of the elements of MASK are `.FALSE.`, then the result is an array of zeroes. Similarly, if DIM is supplied and all of the elements of MASK along a given row are zero, the result value for that row is zero.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:

  `RESULT = MINLOC(ARRAY, DIM [, MASK])`
  `RESULT = MINLOC(ARRAY [, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER` or `REAL`.
  DIM | (Optional) Shall be a scalar of type `INTEGER`, with a value between one and the rank of ARRAY, inclusive. It may not be an optional dummy argument.
  MASK | Shall be an array of type `LOGICAL`, and conformable with ARRAY.

Return value:
  If DIM is absent, the result is a rank-one array with a length equal to the rank of ARRAY. If DIM is present, the result is an array with a rank one less than the rank of ARRAY, and a size corresponding to the size of ARRAY with the DIM dimension removed. If DIM is present and ARRAY has a rank of one, the result is a scalar. In all cases, the result is of default `INTEGER` type.
See also:
  MIN, MINVAL

Next: MOD, Previous: MINLOC, Up: Intrinsic Procedures

### 8.176 `MINVAL` — Minimum value of an array

Description:
  Determines the minimum value of the elements in an array value, or, if the DIM argument is supplied, determines the minimum value along each row of the array in the DIM direction. If MASK is present, only the elements for which MASK is `.TRUE.` are considered. If the array has zero size, or all of the elements of MASK are `.FALSE.`, then the result is `HUGE(ARRAY)` if ARRAY is numeric, or a string of `CHAR(255)` characters if ARRAY is of character type.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:

  `RESULT = MINVAL(ARRAY, DIM [, MASK])`
  `RESULT = MINVAL(ARRAY [, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER` or `REAL`.
  DIM | (Optional) Shall be a scalar of type `INTEGER`, with a value between one and the rank of ARRAY, inclusive. It may not be an optional dummy argument.
  MASK | Shall be an array of type `LOGICAL`, and conformable with ARRAY.

Return value:
  If DIM is absent, or if ARRAY has a rank of one, the result is a scalar. If DIM is present, the result is an array with a rank one less than the rank of ARRAY, and a size corresponding to the size of ARRAY with the DIM dimension removed. In all cases, the result is of the same type and kind as ARRAY.
See also:
  MIN, MINLOC

Next: MODULO, Previous: MINVAL, Up: Intrinsic Procedures

### 8.177 `MOD` — Remainder function

Description:
  `MOD(A,P)` computes the remainder of the division of A by P.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = MOD(A, P)`
Arguments:

  A | Shall be a scalar of type `INTEGER` or `REAL`.
  P | Shall be a scalar of the same type and kind as A and not equal to zero.

Return value:
  The return value is the result of `A - (INT(A/P) * P)`. The type and kind of the return value is the same as that of the arguments. The returned value has the same sign as A and a magnitude less than the magnitude of P.
Example:

                program test_mod
                  print *, mod(17,3)
                  print *, mod(17.5,5.5)
                  print *, mod(17.5d0,5.5)
                  print *, mod(17.5,5.5d0)

                  print *, mod(-17,3)
                  print *, mod(-17.5,5.5)
                  print *, mod(-17.5d0,5.5)
                  print *, mod(-17.5,5.5d0)

                  print *, mod(17,-3)
                  print *, mod(17.5,-5.5)
                  print *, mod(17.5d0,-5.5)
                  print *, mod(17.5,-5.5d0)
                end program test_mod

Specific names:

  Name | Arguments | Return type | Standard
  `MOD(A,P)` | `INTEGER A,P` | `INTEGER` | Fortran 95 and later
  `AMOD(A,P)` | `REAL(4) A,P` | `REAL(4)` | Fortran 95 and later
  `DMOD(A,P)` | `REAL(8) A,P` | `REAL(8)` | Fortran 95 and later

See also:
  MODULO

Next: MOVE_ALLOC, Previous: MOD, Up: Intrinsic Procedures

### 8.178 `MODULO` — Modulo function

Description:
  `MODULO(A,P)` computes the A modulo P.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = MODULO(A, P)`
Arguments:

  A | Shall be a scalar of type `INTEGER` or `REAL`.
  P | Shall be a scalar of the same type and kind as A. It shall not be zero.

Return value:
  The type and kind of the result are those of the arguments.
  If A and P are of type `INTEGER`:
    `MODULO(A,P)` has the value R such that `A=Q*P+R`, where Q is an integer and R is between 0 (inclusive) and P (exclusive).
  If A and P are of type `REAL`:
    `MODULO(A,P)` has the value of `A - FLOOR (A / P) * P`.
  The returned value has the same sign as P and a magnitude less than the magnitude of P.
Example:

                program test_modulo
                  print *, modulo(17,3)
                  print *, modulo(17.5,5.5)

                  print *, modulo(-17,3)
                  print *, modulo(-17.5,5.5)

                  print *, modulo(17,-3)
                  print *, modulo(17.5,-5.5)
                end program

See also:
  MOD

Next: MVBITS, Previous: MODULO, Up: Intrinsic Procedures

### 8.179 `MOVE_ALLOC` — Move allocation from one object to another

Description:
  `MOVE_ALLOC(FROM, TO)` moves the allocation from FROM to TO. FROM will become deallocated in the process.
Standard:
  Fortran 2003 and later
Class:
  Pure subroutine
Syntax:
  `CALL MOVE_ALLOC(FROM, TO)`
Arguments:

  FROM | `ALLOCATABLE`, `INTENT(INOUT)`, may be of any type and kind.
  TO | `ALLOCATABLE`, `INTENT(OUT)`, shall be of the same type, kind and rank as FROM.

Return value:
  None
Example:

                program test_move_alloc
                    integer, allocatable :: a(:), b(:)

                    allocate(a(3))
                    a = [ 1, 2, 3 ]
                    call move_alloc(a, b)
                    print *, allocated(a), allocated(b)
                    print *, b
                end program test_move_alloc

Next: NEAREST, Previous: MOVE_ALLOC, Up: Intrinsic Procedures

### 8.180 `MVBITS` — Move bits from one integer to another

Description:
  Moves LEN bits from positions FROMPOS through `FROMPOS+LEN-1` of FROM to positions TOPOS through `TOPOS+LEN-1` of TO. The portion of argument TO not affected by the movement of bits is unchanged. The values of `FROMPOS+LEN-1` and `TOPOS+LEN-1` must be less than `BIT_SIZE(FROM)`.
Standard:
  Fortran 95 and later
Class:
  Elemental subroutine
Syntax:
  `CALL MVBITS(FROM, FROMPOS, LEN, TO, TOPOS)`
Arguments:

  FROM | The type shall be `INTEGER`.
  FROMPOS | The type shall be `INTEGER`.
  LEN | The type shall be `INTEGER`.
  TO | The type shall be `INTEGER`, of the same kind as FROM.
  TOPOS | The type shall be `INTEGER`.

See also:
  IBCLR, IBSET, IBITS, IAND, IOR, IEOR

Next: NEW_LINE, Previous: MVBITS, Up: Intrinsic Procedures

### 8.181 `NEAREST` — Nearest representable number

Description:
  `NEAREST(X, S)` returns the processor-representable number nearest to `X` in the direction indicated by the sign of `S`.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = NEAREST(X, S)`
Arguments:

  X | Shall be of type `REAL`.
  S | Shall be of type `REAL` and not equal to zero.

Return value:
  The return value is of the same type as `X`. If `S` is positive, `NEAREST` returns the processor-representable number greater than `X` and nearest to it. If `S` is negative, `NEAREST` returns the processor-representable number smaller than `X` and nearest to it.
Example:

                program test_nearest
                  real :: x, y
                  x = nearest(42.0, 1.0)
                  y = nearest(42.0, -1.0)
                  write (*,"(3(G20.15))") x, y, x - y
                end program test_nearest

Next: NINT, Previous: NEAREST, Up: Intrinsic Procedures

### 8.182 `NEW_LINE` — New line character

Description:
  `NEW_LINE(C)` returns the new-line character.
Standard:
  Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = NEW_LINE(C)`
Arguments:

  C | The argument shall be a scalar or array of the type `CHARACTER`.

Return value:
  Returns a CHARACTER scalar of length one with the new-line character of the same kind as parameter C.
Example:

                program newline
                  implicit none
                  write(*,'(A)') 'This is record 1.'//NEW_LINE('A')//'This is record 2.'
                end program newline

Next: NORM2, Previous: NEW_LINE, Up: Intrinsic Procedures

### 8.183 `NINT` — Nearest whole number

Description:
  `NINT(A)` rounds its argument to the nearest whole number.
Standard:
  Fortran 77 and later, with KIND argument Fortran 90 and later
Class:
  Elemental function
Syntax:
  `RESULT = NINT(A [, KIND])`
Arguments:

  A | The type of the argument shall be `REAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  Returns A with the fractional portion of its magnitude eliminated by rounding to the nearest whole number and with its sign preserved, converted to an `INTEGER` of the default kind.
Example:

                program test_nint
                  real(4) x4
                  real(8) x8
                  x4 = 1.234E0_4
                  x8 = 4.321_8
                  print *, nint(x4), idnint(x8)
                end program test_nint

Specific names:

  Name | Argument | Return Type | Standard
  `NINT(A)` | `REAL(4) A` | `INTEGER` | Fortran 95 and later
  `IDNINT(A)` | `REAL(8) A` | `INTEGER` | Fortran 95 and later

See also:
  CEILING, FLOOR

Next: NOT, Previous: NINT, Up: Intrinsic Procedures

### 8.184 `NORM2` — Euclidean vector norms

Description:
  Calculates the Euclidean vector norm (L_2 norm) of of ARRAY along dimension DIM.
Standard:
  Fortran 2008 and later
Class:
  Transformational function
Syntax:

  `RESULT = NORM2(ARRAY[, DIM])`

Arguments:

  ARRAY | Shall be an array of type `REAL`
  DIM | (Optional) shall be a scalar of type `INTEGER` with a value in the range from 1 to n, where n equals the rank of ARRAY.

Return value:
  The result is of the same type as ARRAY.

  If DIM is absent, a scalar with the square root of the sum of all elements in ARRAY squared is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:

                PROGRAM test_sum
                  REAL :: x(5) = [ real :: 1, 2, 3, 4, 5 ]
                  print *, NORM2(x)  ! = sqrt(55.) ~ 7.416
                END PROGRAM

Next: NULL, Previous: NORM2, Up: Intrinsic Procedures

### 8.185 `NOT` — Logical negation

Description:
  `NOT` returns the bitwise Boolean inverse of I.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = NOT(I)`
Arguments:

  I | The type shall be `INTEGER`.

Return value:
  The return type is `INTEGER`, of the same kind as the argument.
See also:
  IAND, IEOR, IOR, IBITS, IBSET, IBCLR

Next: NUM_IMAGES, Previous: NOT, Up: Intrinsic Procedures

### 8.186 `NULL` — Function that returns an disassociated pointer

Description:
  Returns a disassociated pointer.

  If MOLD is present, a disassociated pointer of the same type is returned, otherwise the type is determined by context.

  In Fortran 95, MOLD is optional. Please note that Fortran 2003 includes cases where it is required.

Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `PTR => NULL([MOLD])`
Arguments:

  MOLD | (Optional) shall be a pointer of any association status and of any type.

Return value:
  A disassociated pointer.
Example:

                REAL, POINTER, DIMENSION(:) :: VEC => NULL ()

See also:
  ASSOCIATED

Next: OR, Previous: NULL, Up: Intrinsic Procedures

### 8.187 `NUM_IMAGES` — Function that returns the number of images

Description:
  Returns the number of images.
Standard:
  Fortran 2008 and later
Class:
  Transformational function
Syntax:
  `RESULT = NUM_IMAGES()`
Arguments: None.
Return value:
  Scalar default-kind integer.
Example:

                INTEGER :: value[*]
                INTEGER :: i
                value = THIS_IMAGE()
                SYNC ALL
                IF (THIS_IMAGE() == 1) THEN
                  DO i = 1, NUM_IMAGES()
                    WRITE(*,'(2(a,i0))') 'value[', i, '] is ', value[i]
                  END DO
                END IF

See also:
  THIS_IMAGE, IMAGE_INDEX

Next: PACK, Previous: NUM_IMAGES, Up: Intrinsic Procedures

### 8.188 `OR` — Bitwise logical OR

Description:
  Bitwise logical `OR`.

  This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. For integer arguments, programmers should consider the use of the IOR intrinsic defined by the Fortran standard.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = OR(I, J)`
Arguments:

  I | The type shall be either a scalar `INTEGER` type or a scalar `LOGICAL` type.
  J | The type shall be the same as the type of J.

Return value:
  The return type is either a scalar `INTEGER` or a scalar `LOGICAL`. If the kind type parameters differ, then the smaller kind type is implicitly converted to larger kind, and the return has the larger kind.
Example:

                PROGRAM test_or
                  LOGICAL :: T = .TRUE., F = .FALSE.
                  INTEGER :: a, b
                  DATA a / Z'F' /, b / Z'3' /

                  WRITE (*,*) OR(T, T), OR(T, F), OR(F, T), OR(F, F)
                  WRITE (*,*) OR(a, b)
                END PROGRAM

See also:
  Fortran 95 elemental function: IOR

Next: PARITY, Previous: OR, Up: Intrinsic Procedures

### 8.189 `PACK` — Pack an array into an array of rank one

Description:
  Stores the elements of ARRAY in an array of rank one.

  The beginning of the resulting array is made up of elements whose MASK equals `TRUE`. Afterwards, positions are filled with elements taken from VECTOR.

Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = PACK(ARRAY, MASK[,VECTOR])`
Arguments:

  ARRAY | Shall be an array of any type.
  MASK | Shall be an array of type `LOGICAL` and of the same size as ARRAY. Alternatively, it may be a `LOGICAL` scalar.
  VECTOR | (Optional) shall be an array of the same type as ARRAY and of rank one. If present, the number of elements in VECTOR shall be equal to or greater than the number of true elements in MASK. If MASK is scalar, the number of elements in VECTOR shall be equal to or greater than the number of elements in ARRAY.

Return value:
  The result is an array of rank one and the same type as that of ARRAY. If VECTOR is present, the result size is that of VECTOR, the number of `TRUE` values in MASK otherwise.
Example:
  Gathering nonzero elements from an array:

                PROGRAM test_pack_1
                  INTEGER :: m(6)
                  m = (/ 1, 0, 0, 0, 5, 0 /)
                  WRITE(*, FMT="(6(I0, ' '))") pack(m, m /= 0)  ! "1 5"
                END PROGRAM

  Gathering nonzero elements from an array and appending elements from VECTOR:

                PROGRAM test_pack_2
                  INTEGER :: m(4)
                  m = (/ 1, 0, 0, 2 /)
                  WRITE(*, FMT="(4(I0, ' '))") pack(m, m /= 0, (/ 0, 0, 3, 4 /))  ! "1 2 3 4"
                END PROGRAM

See also:
  UNPACK

Next: PERROR, Previous: PACK, Up: Intrinsic Procedures

### 8.190 `PARITY` — Reduction with exclusive OR

Description:
  Calculates the parity, i.e. the reduction using `.XOR.`, of MASK along dimension DIM.
Standard:
  Fortran 2008 and later
Class:
  Transformational function
Syntax:

  `RESULT = PARITY(MASK[, DIM])`

Arguments:

  LOGICAL | Shall be an array of type `LOGICAL`
  DIM | (Optional) shall be a scalar of type `INTEGER` with a value in the range from 1 to n, where n equals the rank of MASK.

Return value:
  The result is of the same type as MASK.

  If DIM is absent, a scalar with the parity of all elements in MASK is returned, i.e. true if an odd number of elements is `.true.` and false otherwise. If DIM is present, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of MASK with dimension DIM dropped is returned.

Example:

                PROGRAM test_sum
                  LOGICAL :: x(2) = [ .true., .false. ]
                  print *, PARITY(x) ! prints "T" (true).
                END PROGRAM

Next: POPCNT, Previous: PARITY, Up: Intrinsic Procedures

### 8.191 `PERROR` — Print system error message

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)`.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL PERROR(STRING)`
Arguments:

  STRING | A scalar of type `CHARACTER` and of the default kind.

See also:
  IERRNO

Next: POPPAR, Previous: PERROR, Up: Intrinsic Procedures

### 8.192 `POPCNT` — Number of bits set

Description:
  `POPCNT(I)` returns the number of bits set ('1' bits) in the binary representation of `I`.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = POPCNT(I)`
Arguments:

  I | Shall be of type `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the default integer kind.
See also:
  POPPAR, LEADZ, TRAILZ
Example:

                program test_population
                  print *, popcnt(127),       poppar(127)
                  print *, popcnt(huge(0_4)), poppar(huge(0_4))
                  print *, popcnt(huge(0_8)), poppar(huge(0_8))
                end program test_population

Next: PRECISION, Previous: POPCNT, Up: Intrinsic Procedures

### 8.193 `POPPAR` — Parity of the number of bits set

Description:
  `POPPAR(I)` returns parity of the integer `I`, i.e. the parity of the number of bits set ('1' bits) in the binary representation of `I`. It is equal to 0 if `I` has an even number of bits set, and 1 for an odd number of '1' bits.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = POPPAR(I)`
Arguments:

  I | Shall be of type `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the default integer kind.
See also:
  POPCNT, LEADZ, TRAILZ
Example:

                program test_population
                  print *, popcnt(127),       poppar(127)
                  print *, popcnt(huge(0_4)), poppar(huge(0_4))
                  print *, popcnt(huge(0_8)), poppar(huge(0_8))
                end program test_population

Next: PRESENT, Previous: POPPAR, Up: Intrinsic Procedures

### 8.194 `PRECISION` — Decimal precision of a real kind

Description:
  `PRECISION(X)` returns the decimal precision in the model of the type of `X`.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = PRECISION(X)`
Arguments:

  X | Shall be of type `REAL` or `COMPLEX`.

Return value:
  The return value is of type `INTEGER` and of the default integer kind.
See also:
  SELECTED_REAL_KIND, RANGE
Example:

                program prec_and_range
                  real(kind=4) :: x(2)
                  complex(kind=8) :: y

                  print *, precision(x), range(x)
                  print *, precision(y), range(y)
                end program prec_and_range

Next: PRODUCT, Previous: PRECISION, Up: Intrinsic Procedures

### 8.195 `PRESENT` — Determine whether an optional dummy argument is specified

Description:
  Determines whether an optional dummy argument is present.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = PRESENT(A)`
Arguments:

  A | May be of any type and may be a pointer, scalar or array value, or a dummy procedure. It shall be the name of an optional dummy argument accessible within the current subroutine or function.

Return value:
  Returns either `TRUE` if the optional argument A is present, or `FALSE` otherwise.
Example:

                PROGRAM test_present
                  WRITE(*,*) f(), f(42)      ! "F T"
                CONTAINS
                  LOGICAL FUNCTION f(x)
                    INTEGER, INTENT(IN), OPTIONAL :: x
                    f = PRESENT(x)
                  END FUNCTION
                END PROGRAM

Next: RADIX, Previous: PRESENT, Up: Intrinsic Procedures

### 8.196 `PRODUCT` — Product of array elements

Description:
  Multiplies the elements of ARRAY along dimension DIM if the corresponding element in MASK is `TRUE`.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:

  `RESULT = PRODUCT(ARRAY[, MASK])`
  `RESULT = PRODUCT(ARRAY, DIM[, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER`, `REAL` or `COMPLEX`.
  DIM | (Optional) shall be a scalar of type `INTEGER` with a value in the range from 1 to n, where n equals the rank of ARRAY.
  MASK | (Optional) shall be of type `LOGICAL` and either be a scalar or an array of the same shape as ARRAY.

Return value:
  The result is of the same type as ARRAY.

  If DIM is absent, a scalar with the product of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:

                PROGRAM test_product
                  INTEGER :: x(5) = (/ 1, 2, 3, 4 ,5 /)
                  print *, PRODUCT(x)                    ! all elements, product = 120
                  print *, PRODUCT(x, MASK=MOD(x, 2)==1) ! odd elements, product = 15
                END PROGRAM

See also:
  SUM

Next: RAN, Previous: PRODUCT, Up: Intrinsic Procedures

### 8.197 `RADIX` — Base of a model number

Description:
  `RADIX(X)` returns the base of the model representing the entity X.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = RADIX(X)`
Arguments:

  X | Shall be of type `INTEGER` or `REAL`

Return value:
  The return value is a scalar of type `INTEGER` and of the default integer kind.
See also:
  SELECTED_REAL_KIND
Example:

                program test_radix
                  print *, "The radix for the default integer kind is", radix(0)
                  print *, "The radix for the default real kind is", radix(0.0)
                end program test_radix

Next: RAND, Previous: RADIX, Up: Intrinsic Procedures

### 8.198 `RAN` — Real pseudo-random number

Description:
  For compatibility with HP FORTRAN 77/iX, the `RAN` intrinsic is provided as an alias for `RAND`. See RAND for complete documentation.
Standard:
  GNU extension
Class:
  Function
See also:
  RAND, RANDOM_NUMBER

Next: RANDOM_NUMBER, Previous: RAN, Up: Intrinsic Procedures

### 8.199 `RAND` — Real pseudo-random number

Description:
  `RAND(FLAG)` returns a pseudo-random number from a uniform distribution between 0 and 1. If FLAG is 0, the next number in the current sequence is returned; if FLAG is 1, the generator is restarted by `CALL SRAND(0)`; if FLAG has any other value, it is used as a new seed with `SRAND`.

  This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. It implements a simple modulo generator as provided by `g77`. For new code, one should consider the use of RANDOM_NUMBER as it implements a superior algorithm.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = RAND(I)`
Arguments:

  I | Shall be a scalar `INTEGER` of kind 4.

Return value:
  The return value is of `REAL` type and the default kind.
Example:

                program test_rand
                  integer,parameter :: seed = 86456

                  call srand(seed)
                  print *, rand(), rand(), rand(), rand()
                  print *, rand(seed), rand(), rand(), rand()
                end program test_rand

See also:
  SRAND, RANDOM_NUMBER

Next: RANDOM_SEED, Previous: RAND, Up: Intrinsic Procedures

### 8.200 `RANDOM_NUMBER` — Pseudo-random number

Description:
  Returns a single pseudorandom number or an array of pseudorandom numbers from the uniform distribution over the range 0 \leq x < 1.

  The runtime-library implements George Marsaglia's KISS (Keep It Simple Stupid) random number generator (RNG). This RNG combines:

  1. The congruential generator x(n) = 69069 \cdot x(n-1) + 1327217885 with a period of 2^32,
  2. A 3-shift shift-register generator with a period of 2^32 - 1,
  3. Two 16-bit multiply-with-carry generators with a period of 597273182964842497 > 2^59.
  The overall period exceeds 2^123.

  Please note, this RNG is thread safe if used within OpenMP directives, i.e., its state will be consistent while called from multiple threads. However, the KISS generator does not create random numbers in parallel from multiple sources, but in sequence from a single source. If an OpenMP-enabled application heavily relies on random numbers, one should consider employing a dedicated parallel random number generator instead.

Standard:
  Fortran 95 and later
Class:
  Subroutine
Syntax:
  `RANDOM_NUMBER(HARVEST)`
Arguments:

  HARVEST | Shall be a scalar or an array of type `REAL`.

Example:

                program test_random_number
                  REAL :: r(5,5)
                  CALL init_random_seed()         ! see example of RANDOM_SEED
                  CALL RANDOM_NUMBER(r)
                end program

See also:
  RANDOM_SEED

Next: RANGE, Previous: RANDOM_NUMBER, Up: Intrinsic Procedures

### 8.201 `RANDOM_SEED` — Initialize a pseudo-random number sequence

Description:
  Restarts or queries the state of the pseudorandom number generator used by `RANDOM_NUMBER`.

  If `RANDOM_SEED` is called without arguments, it is initialized to a default state. The example below shows how to initialize the random seed with a varying seed in order to ensure a different random number sequence for each invocation of the program. Note that setting any of the seed values to zero should be avoided as it can result in poor quality random numbers being generated.

Standard:
  Fortran 95 and later
Class:
  Subroutine
Syntax:
  `CALL RANDOM_SEED([SIZE, PUT, GET])`
Arguments:

  SIZE | (Optional) Shall be a scalar and of type default `INTEGER`, with `INTENT(OUT)`. It specifies the minimum size of the arrays used with the PUT and GET arguments.
  PUT | (Optional) Shall be an array of type default `INTEGER` and rank one. It is `INTENT(IN)` and the size of the array must be larger than or equal to the number returned by the SIZE argument.
  GET | (Optional) Shall be an array of type default `INTEGER` and rank one. It is `INTENT(OUT)` and the size of the array must be larger than or equal to the number returned by the SIZE argument.

Example:

                subroutine init_random_seed()
                  use iso_fortran_env, only: int64
                  implicit none
                  integer, allocatable :: seed(:)
                  integer :: i, n, un, istat, dt(8), pid
                  integer(int64) :: t

                  call random_seed(size = n)
                  allocate(seed(n))
                  ! First try if the OS provides a random number generator
                  open(newunit=un, file="/dev/urandom", access="stream", &
                       form="unformatted", action="read", status="old", iostat=istat)
                  if (istat == 0) then
                     read(un) seed
                     close(un)
                  else
                     ! Fallback to XOR:ing the current time and pid. The PID is
                     ! useful in case one launches multiple instances of the same
                     ! program in parallel.
                     call system_clock(t)
                     if (t == 0) then
                        call date_and_time(values=dt)
                        t = (dt(1) - 1970) * 365_int64 * 24 * 60 * 60 * 1000 &
                             + dt(2) * 31_int64 * 24 * 60 * 60 * 1000 &
                             + dt(3) * 24_int64 * 60 * 60 * 1000 &
                             + dt(5) * 60 * 60 * 1000 &
                             + dt(6) * 60 * 1000 + dt(7) * 1000 &
                             + dt(8)
                     end if
                     pid = getpid()
                     t = ieor(t, int(pid, kind(t)))
                     do i = 1, n
                        seed(i) = lcg(t)
                     end do
                  end if
                  call random_seed(put=seed)
                contains
                  ! This simple PRNG might not be good enough for real work, but is
                  ! sufficient for seeding a better PRNG.
                  function lcg(s)
                    integer :: lcg
                    integer(int64) :: s
                    if (s == 0) then
                       s = 104729
                    else
                       s = mod(s, 4294967296_int64)
                    end if
                    s = mod(s * 279470273_int64, 4294967291_int64)
                    lcg = int(mod(s, int(huge(0), int64)), kind(0))
                  end function lcg
                end subroutine init_random_seed

See also:
  RANDOM_NUMBER

Next: RANK, Previous: RANDOM_SEED, Up: Intrinsic Procedures

### 8.202 `RANGE` — Decimal exponent range

Description:
  `RANGE(X)` returns the decimal exponent range in the model of the type of `X`.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = RANGE(X)`
Arguments:

  X | Shall be of type `INTEGER`, `REAL` or `COMPLEX`.

Return value:
  The return value is of type `INTEGER` and of the default integer kind.
See also:
  SELECTED_REAL_KIND, PRECISION
Example:
  See `PRECISION` for an example.

Next: REAL, Previous: RANGE, Up: Intrinsic Procedures

### 8.203 `RANK` — Rank of a data object

Description:
  `RANK(A)` returns the rank of a scalar or array data object.
Standard:
  Technical Specification (TS) 29113
Class:
  Inquiry function
Syntax:
  `RESULT = RANK(A)`
Arguments:

  A | can be of any type

Return value:
  The return value is of type `INTEGER` and of the default integer kind. For arrays, their rank is returned; for scalars zero is returned.
Example:

                program test_rank
                  integer :: a
                  real, allocatable :: b(:,:)

                  print *, rank(a), rank(b) ! Prints:  0  2
                end program test_rank

Next: RENAME, Previous: RANK, Up: Intrinsic Procedures

### 8.204 `REAL` — Convert to real type

Description:
  `REAL(A [, KIND])` converts its argument A to a real type. The `REALPART` function is provided for compatibility with `g77`, and its use is strongly discouraged.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:

  `RESULT = REAL(A [, KIND])`
  `RESULT = REALPART(Z)`

Arguments:

  A | Shall be `INTEGER`, `REAL`, or `COMPLEX`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  These functions return a `REAL` variable or array under the following rules:
  (A)
    `REAL(A)` is converted to a default real type if A is an integer or real variable.
  (B)
    `REAL(A)` is converted to a real type with the kind type parameter of A if A is a complex variable.
  (C)
    `REAL(A, KIND)` is converted to a real type with kind type parameter KIND if A is a complex, integer, or real variable.
Example:

                program test_real
                  complex :: x = (1.0, 2.0)
                  print *, real(x), real(x,8), realpart(x)
                end program test_real

Specific names:

  Name | Argument | Return type | Standard
  `FLOAT(A)` | `INTEGER(4)` | `REAL(4)` | Fortran 77 and later
  `DFLOAT(A)` | `INTEGER(4)` | `REAL(8)` | GNU extension
  `SNGL(A)` | `INTEGER(8)` | `REAL(4)` | Fortran 77 and later

See also:
  DBLE

Next: REPEAT, Previous: REAL, Up: Intrinsic Procedures

### 8.205 `RENAME` — Rename a file

Description:
  Renames a file from file PATH1 to PATH2. A null character (`CHAR(0)`) can be used to mark the end of the names in PATH1 and PATH2; otherwise, trailing blanks in the file names are ignored. If the STATUS argument is supplied, it contains 0 on success or a nonzero error code upon return; see `rename(2)`.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL RENAME(PATH1, PATH2 [, STATUS])`
  `STATUS = RENAME(PATH1, PATH2)`

Arguments:

  PATH1 | Shall be of default `CHARACTER` type.
  PATH2 | Shall be of default `CHARACTER` type.
  STATUS | (Optional) Shall be of default `INTEGER` type.

See also:
  LINK

Next: RESHAPE, Previous: RENAME, Up: Intrinsic Procedures

### 8.206 `REPEAT` — Repeated string concatenation

Description:
  Concatenates NCOPIES copies of a string.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = REPEAT(STRING, NCOPIES)`
Arguments:

  STRING | Shall be scalar and of type `CHARACTER`.
  NCOPIES | Shall be scalar and of type `INTEGER`.

Return value:
  A new scalar of type `CHARACTER` built up from NCOPIES copies of STRING.
Example:

                program test_repeat
                  write(*,*) repeat("x", 5)   ! "xxxxx"
                end program

Next: RRSPACING, Previous: REPEAT, Up: Intrinsic Procedures

### 8.207 `RESHAPE` — Function to reshape an array

Description:
  Reshapes SOURCE to correspond to SHAPE. If necessary, the new array may be padded with elements from PAD or permuted as defined by ORDER.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = RESHAPE(SOURCE, SHAPE[, PAD, ORDER])`
Arguments:

  SOURCE | Shall be an array of any type.
  SHAPE | Shall be of type `INTEGER` and an array of rank one. Its values must be positive or zero.
  PAD | (Optional) shall be an array of the same type as SOURCE.
  ORDER | (Optional) shall be of type `INTEGER` and an array of the same shape as SHAPE. Its values shall be a permutation of the numbers from 1 to n, where n is the size of SHAPE. If ORDER is absent, the natural ordering shall be assumed.

Return value:
  The result is an array of shape SHAPE with the same type as SOURCE.
Example:

                PROGRAM test_reshape
                  INTEGER, DIMENSION(4) :: x
                  WRITE(*,*) SHAPE(x)                       ! prints "4"
                  WRITE(*,*) SHAPE(RESHAPE(x, (/2, 2/)))    ! prints "2 2"
                END PROGRAM

See also:
  SHAPE

Next: RSHIFT, Previous: RESHAPE, Up: Intrinsic Procedures

### 8.208 `RRSPACING` — Reciprocal of the relative spacing

Description:
  `RRSPACING(X)` returns the reciprocal of the relative spacing of model numbers near X.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = RRSPACING(X)`
Arguments:

  X | Shall be of type `REAL`.

Return value:
  The return value is of the same type and kind as X. The value returned is equal to `ABS(FRACTION(X)) * FLOAT(RADIX(X))**DIGITS(X)`.
See also:
  SPACING

Next: SAME_TYPE_AS, Previous: RRSPACING, Up: Intrinsic Procedures

### 8.209 `RSHIFT` — Right shift bits

Description:
  `RSHIFT` returns a value corresponding to I with all of the bits shifted right by SHIFT places. If the absolute value of SHIFT is greater than `BIT_SIZE(I)`, the value is undefined. Bits shifted out from the right end are lost. The fill is arithmetic: the bits shifted in from the left end are equal to the leftmost bit, which in two's complement representation is the sign bit.

  This function has been superseded by the `SHIFTA` intrinsic, which is standard in Fortran 2008 and later.

Standard:
  GNU extension
Class:
  Elemental function
Syntax:
  `RESULT = RSHIFT(I, SHIFT)`
Arguments:

  I | The type shall be `INTEGER`.
  SHIFT | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  ISHFT, ISHFTC, LSHIFT, SHIFTA, SHIFTR, SHIFTL

Next: SCALE, Previous: RSHIFT, Up: Intrinsic Procedures

### 8.210 `SAME_TYPE_AS` — Query dynamic types for equality

Description:
  Query dynamic types for equality.
Standard:
  Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = SAME_TYPE_AS(A, B)`
Arguments:

  A | Shall be an object of extensible declared type or unlimited polymorphic.
  B | Shall be an object of extensible declared type or unlimited polymorphic.

Return value:
  The return value is a scalar of type default logical. It is true if and only if the dynamic type of A is the same as the dynamic type of B.
See also:
  EXTENDS_TYPE_OF

Next: SCAN, Previous: SAME_TYPE_AS, Up: Intrinsic Procedures

### 8.211 `SCALE` — Scale a real value

Description:
  `SCALE(X,I)` returns `X * RADIX(X)**I`.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = SCALE(X, I)`
Arguments:

  X | The type of the argument shall be a `REAL`.
  I | The type of the argument shall be a `INTEGER`.

Return value:
  The return value is of the same type and kind as X. Its value is `X * RADIX(X)**I`.
Example:

                program test_scale
                  real :: x = 178.1387e-4
                  integer :: i = 5
                  print *, scale(x,i), x*radix(x)**i
                end program test_scale

Next: SECNDS, Previous: SCALE, Up: Intrinsic Procedures

### 8.212 `SCAN` — Scan a string for the presence of a set of characters

Description:
  Scans a STRING for any of the characters in a SET of characters.

  If BACK is either absent or equals `FALSE`, this function returns the position of the leftmost character of STRING that is in SET. If BACK equals `TRUE`, the rightmost position is returned. If no character of SET is found in STRING, the result is zero.

Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = SCAN(STRING, SET[, BACK [, KIND]])`
Arguments:

  STRING | Shall be of type `CHARACTER`.
  SET | Shall be of type `CHARACTER`.
  BACK | (Optional) shall be of type `LOGICAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind.
Example:

                PROGRAM test_scan
                  WRITE(*,*) SCAN("FORTRAN", "AO")          ! 2, found 'O'
                  WRITE(*,*) SCAN("FORTRAN", "AO", .TRUE.)  ! 6, found 'A'
                  WRITE(*,*) SCAN("FORTRAN", "C++")         ! 0, found none
                END PROGRAM

See also:
  INDEX intrinsic, VERIFY

Next: SECOND, Previous: SCAN, Up: Intrinsic Procedures

### 8.213 `SECNDS` — Time function

Description:
  `SECNDS(X)` gets the time in seconds from the real-time system clock. X is a reference time, also in seconds. If this is zero, the time in seconds from midnight is returned. This function is non-standard and its use is discouraged.
Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = SECNDS (X)`
Arguments:

  T | Shall be of type `REAL(4)`.
  X | Shall be of type `REAL(4)`.

Return value:
  None
Example:

                program test_secnds
                    integer :: i
                    real(4) :: t1, t2
                    print *, secnds (0.0)   ! seconds since midnight
                    t1 = secnds (0.0)       ! reference time
                    do i = 1, 10000000      ! do something
                    end do
                    t2 = secnds (t1)        ! elapsed time
                    print *, "Something took ", t2, " seconds."
                end program test_secnds

Next: SELECTED_CHAR_KIND, Previous: SECNDS, Up: Intrinsic Procedures

### 8.214 `SECOND` — CPU time function

Description:
  Returns a `REAL(4)` value representing the elapsed CPU time in seconds. This provides the same functionality as the standard `CPU_TIME` intrinsic, and is only included for backwards compatibility.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL SECOND(TIME)`
  `TIME = SECOND()`

Arguments:

  TIME | Shall be of type `REAL(4)`.

Return value:
  In either syntax, TIME is set to the process's current runtime in seconds.
See also:
  CPU_TIME

Next: SELECTED_INT_KIND, Previous: SECOND, Up: Intrinsic Procedures

### 8.215 `SELECTED_CHAR_KIND` — Choose character kind

Description:
  `SELECTED_CHAR_KIND(NAME)` returns the kind value for the character set named NAME, if a character set with such a name is supported, or -1 otherwise. Currently, supported character sets include “ASCII” and “DEFAULT”, which are equivalent, and “ISO_10646” (Universal Character Set, UCS-4) which is commonly known as Unicode.
Standard:
  Fortran 2003 and later
Class:
  Transformational function
Syntax:
  `RESULT = SELECTED_CHAR_KIND(NAME)`
Arguments:

  NAME | Shall be a scalar and of the default character type.

Example:

                program character_kind
                  use iso_fortran_env
                  implicit none
                  integer, parameter :: ascii = selected_char_kind ("ascii")
                  integer, parameter :: ucs4  = selected_char_kind ('ISO_10646')

                  character(kind=ascii, len=26) :: alphabet
                  character(kind=ucs4,  len=30) :: hello_world

                  alphabet = ascii_"abcdefghijklmnopqrstuvwxyz"
                  hello_world = ucs4_'Hello World and Ni Hao -- ' &
                                // char (int (z'4F60'), ucs4)     &
                                // char (int (z'597D'), ucs4)

                  write (*,*) alphabet

                  open (output_unit, encoding='UTF-8')
                  write (*,*) trim (hello_world)
                end program character_kind

Next: SELECTED_REAL_KIND, Previous: SELECTED_CHAR_KIND, Up: Intrinsic Procedures

### 8.216 `SELECTED_INT_KIND` — Choose integer kind

Description:
  `SELECTED_INT_KIND(R)` return the kind value of the smallest integer type that can represent all values ranging from -10^R (exclusive) to 10^R (exclusive). If there is no integer kind that accommodates this range, `SELECTED_INT_KIND` returns -1.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = SELECTED_INT_KIND(R)`
Arguments:

  R | Shall be a scalar and of type `INTEGER`.

Example:

                program large_integers
                  integer,parameter :: k5 = selected_int_kind(5)
                  integer,parameter :: k15 = selected_int_kind(15)
                  integer(kind=k5) :: i5
                  integer(kind=k15) :: i15

                  print *, huge(i5), huge(i15)

                  ! The following inequalities are always true
                  print *, huge(i5) >= 10_k5**5-1
                  print *, huge(i15) >= 10_k15**15-1
                end program large_integers

Next: SET_EXPONENT, Previous: SELECTED_INT_KIND, Up: Intrinsic Procedures

### 8.217 `SELECTED_REAL_KIND` — Choose real kind

Description:
  `SELECTED_REAL_KIND(P,R)` returns the kind value of a real data type with decimal precision of at least `P` digits, exponent range of at least `R`, and with a radix of `RADIX`.
Standard:
  Fortran 95 and later, with `RADIX` Fortran 2008 or later
Class:
  Transformational function
Syntax:
  `RESULT = SELECTED_REAL_KIND([P, R, RADIX])`
Arguments:

  P | (Optional) shall be a scalar and of type `INTEGER`.
  R | (Optional) shall be a scalar and of type `INTEGER`.
  RADIX | (Optional) shall be a scalar and of type `INTEGER`.

  Before Fortran 2008, at least one of the arguments R or P shall be present; since Fortran 2008, they are assumed to be zero if absent.
Return value:
  `SELECTED_REAL_KIND` returns the value of the kind type parameter of a real data type with decimal precision of at least `P` digits, a decimal exponent range of at least `R`, and with the requested `RADIX`. If the `RADIX` parameter is absent, real kinds with any radix can be returned. If more than one real data type meet the criteria, the kind of the data type with the smallest decimal precision is returned. If no real data type matches the criteria, the result is
  -1 if the processor does not support a real data type with a
    precision greater than or equal to `P`, but the `R` and `RADIX` requirements can be fulfilled
  -2 if the processor does not support a real type with an exponent
    range greater than or equal to `R`, but `P` and `RADIX` are fulfillable
  -3 if `RADIX` but not `P` and `R` requirements
    are fulfillable
  -4 if `RADIX` and either `P` or `R` requirements
    are fulfillable
  -5 if there is no real type with the given `RADIX`
See also:
  PRECISION, RANGE, RADIX
Example:

                program real_kinds
                  integer,parameter :: p6 = selected_real_kind(6)
                  integer,parameter :: p10r100 = selected_real_kind(10,100)
                  integer,parameter :: r400 = selected_real_kind(r=400)
                  real(kind=p6) :: x
                  real(kind=p10r100) :: y
                  real(kind=r400) :: z

                  print *, precision(x), range(x)
                  print *, precision(y), range(y)
                  print *, precision(z), range(z)
                end program real_kinds

Next: SHAPE, Previous: SELECTED_REAL_KIND, Up: Intrinsic Procedures

### 8.218 `SET_EXPONENT` — Set the exponent of the model

Description:
  `SET_EXPONENT(X, I)` returns the real number whose fractional part is that that of X and whose exponent part is I.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = SET_EXPONENT(X, I)`
Arguments:

  X | Shall be of type `REAL`.
  I | Shall be of type `INTEGER`.

Return value:
  The return value is of the same type and kind as X. The real number whose fractional part is that that of X and whose exponent part if I is returned; it is `FRACTION(X) * RADIX(X)**I`.
Example:

                PROGRAM test_setexp
                  REAL :: x = 178.1387e-4
                  INTEGER :: i = 17
                  PRINT *, SET_EXPONENT(x, i), FRACTION(x) * RADIX(x)**i
                END PROGRAM

Next: SHIFTA, Previous: SET_EXPONENT, Up: Intrinsic Procedures

### 8.219 `SHAPE` — Determine the shape of an array

Description:
  Determines the shape of an array.
Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = SHAPE(SOURCE [, KIND])`
Arguments:

  SOURCE | Shall be an array or scalar of any type. If SOURCE is a pointer it must be associated and allocatable arrays must be allocated.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  An `INTEGER` array of rank one with as many elements as SOURCE has dimensions. The elements of the resulting array correspond to the extend of SOURCE along the respective dimensions. If SOURCE is a scalar, the result is the rank one array of size zero. If KIND is absent, the return value has the default integer kind otherwise the specified kind.
Example:

                PROGRAM test_shape
                  INTEGER, DIMENSION(-1:1, -1:2) :: A
                  WRITE(*,*) SHAPE(A)             ! (/ 3, 4 /)
                  WRITE(*,*) SIZE(SHAPE(42))      ! (/ /)
                END PROGRAM

See also:
  RESHAPE, SIZE

Next: SHIFTL, Previous: SHAPE, Up: Intrinsic Procedures

### 8.220 `SHIFTA` — Right shift with fill

Description:
  `SHIFTA` returns a value corresponding to I with all of the bits shifted right by SHIFT places. If the absolute value of SHIFT is greater than `BIT_SIZE(I)`, the value is undefined. Bits shifted out from the right end are lost. The fill is arithmetic: the bits shifted in from the left end are equal to the leftmost bit, which in two's complement representation is the sign bit.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = SHIFTA(I, SHIFT)`
Arguments:

  I | The type shall be `INTEGER`.
  SHIFT | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  SHIFTL, SHIFTR

Next: SHIFTR, Previous: SHIFTA, Up: Intrinsic Procedures

### 8.221 `SHIFTL` — Left shift

Description:
  `SHIFTL` returns a value corresponding to I with all of the bits shifted left by SHIFT places. If the absolute value of SHIFT is greater than `BIT_SIZE(I)`, the value is undefined. Bits shifted out from the left end are lost, and bits shifted in from the right end are set to 0.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = SHIFTL(I, SHIFT)`
Arguments:

  I | The type shall be `INTEGER`.
  SHIFT | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  SHIFTA, SHIFTR

Next: SIGN, Previous: SHIFTL, Up: Intrinsic Procedures

### 8.222 `SHIFTR` — Right shift

Description:
  `SHIFTR` returns a value corresponding to I with all of the bits shifted right by SHIFT places. If the absolute value of SHIFT is greater than `BIT_SIZE(I)`, the value is undefined. Bits shifted out from the right end are lost, and bits shifted in from the left end are set to 0.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = SHIFTR(I, SHIFT)`
Arguments:

  I | The type shall be `INTEGER`.
  SHIFT | The type shall be `INTEGER`.

Return value:
  The return value is of type `INTEGER` and of the same kind as I.
See also:
  SHIFTA, SHIFTL

Next: SIGNAL, Previous: SHIFTR, Up: Intrinsic Procedures

### 8.223 `SIGN` — Sign copying function

Description:
  `SIGN(A,B)` returns the value of A with the sign of B.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = SIGN(A, B)`
Arguments:

  A | Shall be of type `INTEGER` or `REAL`
  B | Shall be of the same type and kind as A

Return value:
  The kind of the return value is that of A and B. If B\ge 0 then the result is `ABS(A)`, else it is `-ABS(A)`.
Example:

                program test_sign
                  print *, sign(-12,1)
                  print *, sign(-12,0)
                  print *, sign(-12,-1)

                  print *, sign(-12.,1.)
                  print *, sign(-12.,0.)
                  print *, sign(-12.,-1.)
                end program test_sign

Specific names:

  Name | Arguments | Return type | Standard
  `SIGN(A,B)` | `REAL(4) A, B` | `REAL(4)` | f77, gnu
  `ISIGN(A,B)` | `INTEGER(4) A, B` | `INTEGER(4)` | f77, gnu
  `DSIGN(A,B)` | `REAL(8) A, B` | `REAL(8)` | f77, gnu

Next: SIN, Previous: SIGN, Up: Intrinsic Procedures

### 8.224 `SIGNAL` — Signal handling subroutine (or function)

Description:
  `SIGNAL(NUMBER, HANDLER [, STATUS])` causes external subroutine HANDLER to be executed with a single integer argument 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)`.

  If `SIGNAL` is called as a subroutine and the STATUS argument is supplied, it is set to the value returned by `signal(2)`.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL SIGNAL(NUMBER, HANDLER [, STATUS])`
  `STATUS = SIGNAL(NUMBER, HANDLER)`

Arguments:

  NUMBER | Shall be a scalar integer, with `INTENT(IN)`
  HANDLER | Signal handler (`INTEGER FUNCTION` or `SUBROUTINE`) or dummy/global `INTEGER` scalar. `INTEGER`. It is `INTENT(IN)`.
  STATUS | (Optional) STATUS shall be a scalar integer. It has `INTENT(OUT)`.

Return value:
  The `SIGNAL` function returns the value returned by `signal(2)`.
Example:

                program test_signal
                  intrinsic signal
                  external handler_print

                  call signal (12, handler_print)
                  call signal (10, 1)

                  call sleep (30)
                end program test_signal

Next: SINH, Previous: SIGNAL, Up: Intrinsic Procedures

### 8.225 `SIN` — Sine function

Description:
  `SIN(X)` computes the sine of X.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = SIN(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has same type and kind as X.
Example:

                program test_sin
                  real :: x = 0.0
                  x = sin(x)
                end program test_sin

Specific names:

  Name | Argument | Return type | Standard
  `SIN(X)` | `REAL(4) X` | `REAL(4)` | f77, gnu
  `DSIN(X)` | `REAL(8) X` | `REAL(8)` | f95, gnu
  `CSIN(X)` | `COMPLEX(4) X` | `COMPLEX(4)` | f95, gnu
  `ZSIN(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | f95, gnu
  `CDSIN(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | f95, gnu

See also:
  ASIN

Next: SIZE, Previous: SIN, Up: Intrinsic Procedures

### 8.226 `SINH` — Hyperbolic sine function

Description:
  `SINH(X)` computes the hyperbolic sine of X.
Standard:
  Fortran 95 and later, for a complex argument Fortran 2008 or later
Class:
  Elemental function
Syntax:
  `RESULT = SINH(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has same type and kind as X.
Example:

                program test_sinh
                  real(8) :: x = - 1.0_8
                  x = sinh(x)
                end program test_sinh

Specific names:

  Name | Argument | Return type | Standard
  `SINH(X)` | `REAL(4) X` | `REAL(4)` | Fortran 95 and later
  `DSINH(X)` | `REAL(8) X` | `REAL(8)` | Fortran 95 and later

See also:
  ASINH

Next: SIZEOF, Previous: SINH, Up: Intrinsic Procedures

### 8.227 `SIZE` — Determine the size of an array

Description:
  Determine the extent of ARRAY along a specified dimension DIM, or the total number of elements in ARRAY if DIM is absent.
Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = SIZE(ARRAY[, DIM [, KIND]])`
Arguments:

  ARRAY | Shall be an array of any type. If ARRAY is a pointer it must be associated and allocatable arrays must be allocated.
  DIM | (Optional) shall be a scalar of type `INTEGER` and its value shall be in the range from 1 to n, where n equals the rank of ARRAY.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind.
Example:

                PROGRAM test_size
                  WRITE(*,*) SIZE((/ 1, 2 /))    ! 2
                END PROGRAM

See also:
  SHAPE, RESHAPE

Next: SLEEP, Previous: SIZE, Up: Intrinsic Procedures

### 8.228 `SIZEOF` — Size in bytes of an expression

Description:
  `SIZEOF(X)` calculates the number of bytes of storage the expression `X` occupies.
Standard:
  GNU extension
Class:
  Inquiry function
Syntax:
  `N = SIZEOF(X)`
Arguments:

  X | The argument shall be of any type, rank or shape.

Return value:
  The return value is of type integer and of the system-dependent kind C_SIZE_T (from the ISO_C_BINDING module). Its value is the number of bytes occupied by the argument. If the argument has the `POINTER` attribute, the number of bytes of the storage area pointed to is returned. If the argument is of a derived type with `POINTER` or `ALLOCATABLE` components, the return value does not account for the sizes of the data pointed to by these components. If the argument is polymorphic, the size according to the declared type is returned. The argument may not be a procedure or procedure pointer.
Example:

                   integer :: i
                   real :: r, s(5)
                   print *, (sizeof(s)/sizeof(r) == 5)
                   end

  The example will print `.TRUE.` unless you are using a platform where default `REAL` variables are unusually padded.

See also:
  C_SIZEOF, STORAGE_SIZE

Next: SPACING, Previous: SIZEOF, Up: Intrinsic Procedures

### 8.229 `SLEEP` — Sleep for the specified number of seconds

Description:
  Calling this subroutine causes the process to pause for SECONDS seconds.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL SLEEP(SECONDS)`
Arguments:

  SECONDS | The type shall be of default `INTEGER`.

Example:

                program test_sleep
                  call sleep(5)
                end

Next: SPREAD, Previous: SLEEP, Up: Intrinsic Procedures

### 8.230 `SPACING` — Smallest distance between two numbers of a given type

Description:
  Determines the distance between the argument X and the nearest adjacent number of the same type.
Standard:
  Fortran 95 and later
Class:
  Elemental function
Syntax:
  `RESULT = SPACING(X)`
Arguments:

  X | Shall be of type `REAL`.

Return value:
  The result is of the same type as the input argument X.
Example:

                PROGRAM test_spacing
                  INTEGER, PARAMETER :: SGL = SELECTED_REAL_KIND(p=6, r=37)
                  INTEGER, PARAMETER :: DBL = SELECTED_REAL_KIND(p=13, r=200)

                  WRITE(*,*) spacing(1.0_SGL)      ! "1.1920929E-07"          on i686
                  WRITE(*,*) spacing(1.0_DBL)      ! "2.220446049250313E-016" on i686
                END PROGRAM

See also:
  RRSPACING

Next: SQRT, Previous: SPACING, Up: Intrinsic Procedures

### 8.231 `SPREAD` — Add a dimension to an array

Description:
  Replicates a SOURCE array NCOPIES times along a specified dimension DIM.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = SPREAD(SOURCE, DIM, NCOPIES)`
Arguments:

  SOURCE | Shall be a scalar or an array of any type and a rank less than seven.
  DIM | Shall be a scalar of type `INTEGER` with a value in the range from 1 to n+1, where n equals the rank of SOURCE.
  NCOPIES | Shall be a scalar of type `INTEGER`.

Return value:
  The result is an array of the same type as SOURCE and has rank n+1 where n equals the rank of SOURCE.
Example:

                PROGRAM test_spread
                  INTEGER :: a = 1, b(2) = (/ 1, 2 /)
                  WRITE(*,*) SPREAD(A, 1, 2)            ! "1 1"
                  WRITE(*,*) SPREAD(B, 1, 2)            ! "1 1 2 2"
                END PROGRAM

See also:
  UNPACK

Next: SRAND, Previous: SPREAD, Up: Intrinsic Procedures

### 8.232 `SQRT` — Square-root function

Description:
  `SQRT(X)` computes the square root of X.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = SQRT(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value is of type `REAL` or `COMPLEX`. The kind type parameter is the same as X.
Example:

                program test_sqrt
                  real(8) :: x = 2.0_8
                  complex :: z = (1.0, 2.0)
                  x = sqrt(x)
                  z = sqrt(z)
                end program test_sqrt

Specific names:

  Name | Argument | Return type | Standard
  `SQRT(X)` | `REAL(4) X` | `REAL(4)` | Fortran 95 and later
  `DSQRT(X)` | `REAL(8) X` | `REAL(8)` | Fortran 95 and later
  `CSQRT(X)` | `COMPLEX(4) X` | `COMPLEX(4)` | Fortran 95 and later
  `ZSQRT(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | GNU extension
  `CDSQRT(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | GNU extension

Next: STAT, Previous: SQRT, Up: Intrinsic Procedures

### 8.233 `SRAND` — Reinitialize the random number generator

Description:
  `SRAND` reinitializes the pseudo-random number generator called by `RAND` and `IRAND`. The new seed used by the generator is specified by the required argument SEED.
Standard:
  GNU extension
Class:
  Subroutine
Syntax:
  `CALL SRAND(SEED)`
Arguments:

  SEED | Shall be a scalar `INTEGER(kind=4)`.

Return value:
  Does not return anything.
Example:
  See `RAND` and `IRAND` for examples.
Notes:
  The Fortran 2003 standard specifies the intrinsic `RANDOM_SEED` to initialize the pseudo-random numbers generator and `RANDOM_NUMBER` to generate pseudo-random numbers. Please note that in GNU Fortran, these two sets of intrinsics (`RAND`, `IRAND` and `SRAND` on the one hand, `RANDOM_NUMBER` and `RANDOM_SEED` on the other hand) access two independent pseudo-random number generators.
See also:
  RAND, RANDOM_SEED, RANDOM_NUMBER

Next: STORAGE_SIZE, Previous: SRAND, Up: Intrinsic Procedures

### 8.234 `STAT` — Get file status

Description:
  This function returns information about a file. No permissions are required on the file itself, but execute (search) permission is required on all of the directories in path that lead to the file.

  The elements that are obtained and stored in the array `VALUES`:

  `VALUES(1)` | Device ID
  `VALUES(2)` | Inode number
  `VALUES(3)` | File mode
  `VALUES(4)` | Number of links
  `VALUES(5)` | Owner's uid
  `VALUES(6)` | Owner's gid
  `VALUES(7)` | ID of device containing directory entry for file (0 if not available)
  `VALUES(8)` | File size (bytes)
  `VALUES(9)` | Last access time
  `VALUES(10)` | Last modification time
  `VALUES(11)` | Last file status change time
  `VALUES(12)` | Preferred I/O block size (-1 if not available)
  `VALUES(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.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL STAT(NAME, VALUES [, STATUS])`
  `STATUS = STAT(NAME, VALUES)`

Arguments:

  NAME | The type shall be `CHARACTER`, of the default kind and a valid path within the file system.
  VALUES | The type shall be `INTEGER(4), DIMENSION(13)`.
  STATUS | (Optional) status flag of type `INTEGER(4)`. Returns 0 on success and a system specific error code otherwise.

Example:

                PROGRAM test_stat
                  INTEGER, DIMENSION(13) :: buff
                  INTEGER :: status

                  CALL STAT("/etc/passwd", buff, status)

                  IF (status == 0) THEN
                    WRITE (*, FMT="('Device ID:',               T30, I19)") buff(1)
                    WRITE (*, FMT="('Inode number:',            T30, I19)") buff(2)
                    WRITE (*, FMT="('File mode (octal):',       T30, O19)") buff(3)
                    WRITE (*, FMT="('Number of links:',         T30, I19)") buff(4)
                    WRITE (*, FMT="('Owner''s uid:',            T30, I19)") buff(5)
                    WRITE (*, FMT="('Owner''s gid:',            T30, I19)") buff(6)
                    WRITE (*, FMT="('Device where located:',    T30, I19)") buff(7)
                    WRITE (*, FMT="('File size:',               T30, I19)") buff(8)
                    WRITE (*, FMT="('Last access time:',        T30, A19)") CTIME(buff(9))
                    WRITE (*, FMT="('Last modification time',   T30, A19)") CTIME(buff(10))
                    WRITE (*, FMT="('Last status change time:', T30, A19)") CTIME(buff(11))
                    WRITE (*, FMT="('Preferred block size:',    T30, I19)") buff(12)
                    WRITE (*, FMT="('No. of blocks allocated:', T30, I19)") buff(13)
                  END IF
                END PROGRAM

See also:
  To stat an open file: FSTAT, to stat a link: LSTAT

Next: SUM, Previous: STAT, Up: Intrinsic Procedures

### 8.235 `STORAGE_SIZE` — Storage size in bits

Description:
  Returns the storage size of argument A in bits.
Standard:
  Fortran 2008 and later
Class:
  Inquiry function
Syntax:
  `RESULT = STORAGE_SIZE(A [, KIND])`
Arguments:

  A | Shall be a scalar or array of any type.
  KIND | (Optional) shall be a scalar integer constant expression.

Return Value:
  The result is a scalar integer with the kind type parameter specified by KIND (or default integer type if KIND is missing). The result value is the size expressed in bits for an element of an array that has the dynamic type and type parameters of A.
See also:
  C_SIZEOF, SIZEOF

Next: SYMLNK, Previous: STORAGE_SIZE, Up: Intrinsic Procedures

### 8.236 `SUM` — Sum of array elements

Description:
  Adds the elements of ARRAY along dimension DIM if the corresponding element in MASK is `TRUE`.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:

  `RESULT = SUM(ARRAY[, MASK])`
  `RESULT = SUM(ARRAY, DIM[, MASK])`

Arguments:

  ARRAY | Shall be an array of type `INTEGER`, `REAL` or `COMPLEX`.
  DIM | (Optional) shall be a scalar of type `INTEGER` with a value in the range from 1 to n, where n equals the rank of ARRAY.
  MASK | (Optional) shall be of type `LOGICAL` and either be a scalar or an array of the same shape as ARRAY.

Return value:
  The result is of the same type as ARRAY.

  If DIM is absent, a scalar with the sum of all elements in ARRAY is returned. Otherwise, an array of rank n-1, where n equals the rank of ARRAY, and a shape similar to that of ARRAY with dimension DIM dropped is returned.

Example:

                PROGRAM test_sum
                  INTEGER :: x(5) = (/ 1, 2, 3, 4 ,5 /)
                  print *, SUM(x)                        ! all elements, sum = 15
                  print *, SUM(x, MASK=MOD(x, 2)==1)     ! odd elements, sum = 9
                END PROGRAM

See also:
  PRODUCT

Next: SYSTEM, Previous: SUM, Up: Intrinsic Procedures

### 8.237 `SYMLNK` — Create a symbolic link

Description:
  Makes a symbolic link from file PATH1 to PATH2. A null character (`CHAR(0)`) can be used to mark the end of the names in PATH1 and PATH2; otherwise, trailing blanks in the file names are ignored. If the STATUS argument is supplied, it contains 0 on success or a nonzero error code upon return; see `symlink(2)`. If the system does not supply `symlink(2)`, `ENOSYS` is returned.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL SYMLNK(PATH1, PATH2 [, STATUS])`
  `STATUS = SYMLNK(PATH1, PATH2)`

Arguments:

  PATH1 | Shall be of default `CHARACTER` type.
  PATH2 | Shall be of default `CHARACTER` type.
  STATUS | (Optional) Shall be of default `INTEGER` type.

See also:
  LINK, UNLINK

Next: SYSTEM_CLOCK, Previous: SYMLNK, Up: Intrinsic Procedures

### 8.238 `SYSTEM` — Execute a shell command

Description:
  Passes the command COMMAND to a shell (see `system(3)`). If argument STATUS is present, it contains the value returned by `system(3)`, which is presumably 0 if the shell command succeeded. Note that which shell is used to invoke the command is system-dependent and environment-dependent.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

  Note that the `system` function need not be thread-safe. It is the responsibility of the user to ensure that `system` is not called concurrently.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL SYSTEM(COMMAND [, STATUS])`
  `STATUS = SYSTEM(COMMAND)`

Arguments:

  COMMAND | Shall be of default `CHARACTER` type.
  STATUS | (Optional) Shall be of default `INTEGER` type.

See also:
  EXECUTE_COMMAND_LINE, which is part of the Fortran 2008 standard and should considered in new code for future portability.

Next: TAN, Previous: SYSTEM, Up: Intrinsic Procedures

### 8.239 `SYSTEM_CLOCK` — Time function

Description:
  Determines the COUNT of a processor clock since an unspecified time in the past modulo COUNT_MAX, COUNT_RATE determines the number of clock ticks per second. If the platform supports a monotonic clock, that clock is used and can, depending on the platform clock implementation, provide up to nanosecond resolution. If a monotonic clock is not available, the implementation falls back to a realtime clock.

  COUNT_RATE is system dependent and can vary depending on the kind of the arguments. For kind=4 arguments, COUNT represents milliseconds, while for kind=8 arguments, COUNT typically represents micro- or nanoseconds depending on resolution of the underlying platform clock. COUNT_MAX usually equals `HUGE(COUNT_MAX)`. Note that the millisecond resolution of the kind=4 version implies that the COUNT will wrap around in roughly 25 days. In order to avoid issues with the wrap around and for more precise timing, please use the kind=8 version.

  If there is no clock, or querying the clock fails, COUNT is set to `-HUGE(COUNT)`, and COUNT_RATE and COUNT_MAX are set to zero.

  When running on a platform using the GNU C library (glibc) version 2.16 or older, or a derivative thereof, the high resolution monotonic clock is available only when linking with the rt library. This can be done explicitly by adding the `-lrt` flag when linking the application, but is also done implicitly when using OpenMP.

  On the Windows platform, the version with kind=4 arguments uses the `GetTickCount` function, whereas the kind=8 version uses `QueryPerformanceCounter` and `QueryPerformanceCounterFrequency`. For more information, and potential caveats, please see the platform documentation.

Standard:
  Fortran 95 and later
Class:
  Subroutine
Syntax:
  `CALL SYSTEM_CLOCK([COUNT, COUNT_RATE, COUNT_MAX])`
Arguments:

  COUNT | (Optional) shall be a scalar of type `INTEGER` with `INTENT(OUT)`.
  COUNT_RATE | (Optional) shall be a scalar of type `INTEGER` with `INTENT(OUT)`.
  COUNT_MAX | (Optional) shall be a scalar of type `INTEGER` with `INTENT(OUT)`.

Example:

                PROGRAM test_system_clock
                  INTEGER :: count, count_rate, count_max
                  CALL SYSTEM_CLOCK(count, count_rate, count_max)
                  WRITE(*,*) count, count_rate, count_max
                END PROGRAM

See also:
  DATE_AND_TIME, CPU_TIME

Next: TANH, Previous: SYSTEM_CLOCK, Up: Intrinsic Procedures

### 8.240 `TAN` — Tangent function

Description:
  `TAN(X)` computes the tangent of X.
Standard:
  Fortran 77 and later, for a complex argument Fortran 2008 or later
Class:
  Elemental function
Syntax:
  `RESULT = TAN(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has same type and kind as X.
Example:

                program test_tan
                  real(8) :: x = 0.165_8
                  x = tan(x)
                end program test_tan

Specific names:

  Name | Argument | Return type | Standard
  `TAN(X)` | `REAL(4) X` | `REAL(4)` | Fortran 95 and later
  `DTAN(X)` | `REAL(8) X` | `REAL(8)` | Fortran 95 and later

See also:
  ATAN

Next: THIS_IMAGE, Previous: TAN, Up: Intrinsic Procedures

### 8.241 `TANH` — Hyperbolic tangent function

Description:
  `TANH(X)` computes the hyperbolic tangent of X.
Standard:
  Fortran 77 and later, for a complex argument Fortran 2008 or later
Class:
  Elemental function
Syntax:
  `X = TANH(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has same type and kind as X. If X is complex, the imaginary part of the result is in radians. If X is `REAL`, the return value lies in the range - 1 \leq tanh(x) \leq 1 .
Example:

                program test_tanh
                  real(8) :: x = 2.1_8
                  x = tanh(x)
                end program test_tanh

Specific names:

  Name | Argument | Return type | Standard
  `TANH(X)` | `REAL(4) X` | `REAL(4)` | Fortran 95 and later
  `DTANH(X)` | `REAL(8) X` | `REAL(8)` | Fortran 95 and later

See also:
  ATANH

Next: TIME, Previous: TANH, Up: Intrinsic Procedures

### 8.242 `THIS_IMAGE` — Function that returns the cosubscript index of this image

Description:
  Returns the cosubscript for this image.
Standard:
  Fortran 2008 and later
Class:
  Transformational function
Syntax:

  `RESULT = THIS_IMAGE()`
  `RESULT = THIS_IMAGE(COARRAY [, DIM])`

Arguments:

  COARRAY | Coarray of any type (optional; if DIM present, required).
  DIM | default integer scalar (optional). If present, DIM shall be between one and the corank of COARRAY.

Return value:
  Default integer. If COARRAY is not present, it is scalar and its value is the index of the invoking image. Otherwise, if DIM is not present, a rank-1 array with corank elements is returned, containing the cosubscripts for COARRAY specifying the invoking image. If DIM is present, a scalar is returned, with the value of the DIM element of `THIS_IMAGE(COARRAY)`.
Example:

                INTEGER :: value[*]
                INTEGER :: i
                value = THIS_IMAGE()
                SYNC ALL
                IF (THIS_IMAGE() == 1) THEN
                  DO i = 1, NUM_IMAGES()
                    WRITE(*,'(2(a,i0))') 'value[', i, '] is ', value[i]
                  END DO
                END IF

See also:
  NUM_IMAGES, IMAGE_INDEX

Next: TIME8, Previous: THIS_IMAGE, Up: Intrinsic Procedures

### 8.243 `TIME` — Time function

Description:
  Returns the current time encoded as an integer (in the manner of the function `time(3)` in the C standard library). 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, for information on a similar intrinsic that might be portable to more GNU Fortran implementations, though to fewer Fortran compilers.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = TIME()`
Return value:
  The return value is a scalar of type `INTEGER(4)`.
See also:
  CTIME, GMTIME, LTIME, MCLOCK, TIME8

Next: TINY, Previous: TIME, Up: Intrinsic Procedures

### 8.244 `TIME8` — Time function (64-bit)

Description:
  Returns the current time encoded as an integer (in the manner of the function `time(3)` in the C standard library). 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 it is converted to a 64-bit `INTEGER(8)` 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.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = TIME8()`
Return value:
  The return value is a scalar of type `INTEGER(8)`.
See also:
  CTIME, GMTIME, LTIME, MCLOCK8, TIME

Next: TRAILZ, Previous: TIME8, Up: Intrinsic Procedures

### 8.245 `TINY` — Smallest positive number of a real kind

Description:
  `TINY(X)` returns the smallest positive (non zero) number in the model of the type of `X`.
Standard:
  Fortran 95 and later
Class:
  Inquiry function
Syntax:
  `RESULT = TINY(X)`
Arguments:

  X | Shall be of type `REAL`.

Return value:
  The return value is of the same type and kind as X
Example:
  See `HUGE` for an example.

Next: TRANSFER, Previous: TINY, Up: Intrinsic Procedures

### 8.246 `TRAILZ` — Number of trailing zero bits of an integer

Description:
  `TRAILZ` returns the number of trailing zero bits of an integer.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `RESULT = TRAILZ(I)`
Arguments:

  I | Shall be of type `INTEGER`.

Return value:
  The type of the return value is the default `INTEGER`. If all the bits of `I` are zero, the result value is `BIT_SIZE(I)`.
Example:

                PROGRAM test_trailz
                  WRITE (*,*) TRAILZ(8)  ! prints 3
                END PROGRAM

See also:
  BIT_SIZE, LEADZ, POPPAR, POPCNT

Next: TRANSPOSE, Previous: TRAILZ, Up: Intrinsic Procedures

### 8.247 `TRANSFER` — Transfer bit patterns

Description:
  Interprets the bitwise representation of SOURCE in memory as if it is the representation of a variable or array of the same type and type parameters as MOLD.

  This is approximately equivalent to the C concept of casting one type to another.

Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = TRANSFER(SOURCE, MOLD[, SIZE])`
Arguments:

  SOURCE | Shall be a scalar or an array of any type.
  MOLD | Shall be a scalar or an array of any type.
  SIZE | (Optional) shall be a scalar of type `INTEGER`.

Return value:
  The result has the same type as MOLD, with the bit level representation of SOURCE. If SIZE is present, the result is a one-dimensional array of length SIZE. If SIZE is absent but MOLD is an array (of any size or shape), the result is a one- dimensional array of the minimum length needed to contain the entirety of the bitwise representation of SOURCE. If SIZE is absent and MOLD is a scalar, the result is a scalar.

  If the bitwise representation of the result is longer than that of SOURCE, then the leading bits of the result correspond to those of SOURCE and any trailing bits are filled arbitrarily.

  When the resulting bit representation does not correspond to a valid representation of a variable of the same type as MOLD, the results are undefined, and subsequent operations on the result cannot be guaranteed to produce sensible behavior. For example, it is possible to create `LOGICAL` variables for which VAR and `.NOT.`VAR both appear to be true.

Example:

                PROGRAM test_transfer
                  integer :: x = 2143289344
                  print *, transfer(x, 1.0)    ! prints "NaN" on i686
                END PROGRAM

Next: TRIM, Previous: TRANSFER, Up: Intrinsic Procedures

### 8.248 `TRANSPOSE` — Transpose an array of rank two

Description:
  Transpose an array of rank two. Element (i, j) of the result has the value `MATRIX(j, i)`, for all i, j.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = TRANSPOSE(MATRIX)`
Arguments:

  MATRIX | Shall be an array of any type and have a rank of two.

Return value:
  The result has the same type as MATRIX, and has shape `(/ m, n /)` if MATRIX has shape `(/ n, m /)`.

Next: TTYNAM, Previous: TRANSPOSE, Up: Intrinsic Procedures

### 8.249 `TRIM` — Remove trailing blank characters of a string

Description:
  Removes trailing blank characters of a string.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = TRIM(STRING)`
Arguments:

  STRING | Shall be a scalar of type `CHARACTER`.

Return value:
  A scalar of type `CHARACTER` which length is that of STRING less the number of trailing blanks.
Example:

                PROGRAM test_trim
                  CHARACTER(len=10), PARAMETER :: s = "GFORTRAN  "
                  WRITE(*,*) LEN(s), LEN(TRIM(s))  ! "10 8", with/without trailing blanks
                END PROGRAM

See also:
  ADJUSTL, ADJUSTR

Next: UBOUND, Previous: TRIM, Up: Intrinsic Procedures

### 8.250 `TTYNAM` — Get the name of a terminal device.

Description:
  Get the name of a terminal device. For more information, see `ttyname(3)`.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL TTYNAM(UNIT, NAME)`
  `NAME = TTYNAM(UNIT)`

Arguments:

  UNIT | Shall be a scalar `INTEGER`.
  NAME | Shall be of type `CHARACTER`.

Example:

                PROGRAM test_ttynam
                  INTEGER :: unit
                  DO unit = 1, 10
                    IF (isatty(unit=unit)) write(*,*) ttynam(unit)
                  END DO
                END PROGRAM

See also:
  ISATTY

Next: UCOBOUND, Previous: TTYNAM, Up: Intrinsic Procedures

### 8.251 `UBOUND` — Upper dimension bounds of an array

Description:
  Returns the upper bounds of an array, or a single upper bound along the DIM dimension.
Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Inquiry function
Syntax:
  `RESULT = UBOUND(ARRAY [, DIM [, KIND]])`
Arguments:

  ARRAY | Shall be an array, of any type.
  DIM | (Optional) Shall be a scalar `INTEGER`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind. If DIM is absent, the result is an array of the upper bounds of ARRAY. If DIM is present, the result is a scalar corresponding to the upper bound of the array along that dimension. If ARRAY is an expression rather than a whole array or array structure component, or if it has a zero extent along the relevant dimension, the upper bound is taken to be the number of elements along the relevant dimension.
See also:
  LBOUND, LCOBOUND

Next: UMASK, Previous: UBOUND, Up: Intrinsic Procedures

### 8.252 `UCOBOUND` — Upper codimension bounds of an array

Description:
  Returns the upper cobounds of a coarray, or a single upper cobound along the DIM codimension.
Standard:
  Fortran 2008 and later
Class:
  Inquiry function
Syntax:
  `RESULT = UCOBOUND(COARRAY [, DIM [, KIND]])`
Arguments:

  ARRAY | Shall be an coarray, of any type.
  DIM | (Optional) Shall be a scalar `INTEGER`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind. If DIM is absent, the result is an array of the lower cobounds of COARRAY. If DIM is present, the result is a scalar corresponding to the lower cobound of the array along that codimension.
See also:
  LCOBOUND, LBOUND

Next: UNLINK, Previous: UCOBOUND, Up: Intrinsic Procedures

### 8.253 `UMASK` — Set the file creation mask

Description:
  Sets the file creation mask to MASK. If called as a function, it returns the old value. If called as a subroutine and argument OLD if it is supplied, it is set to the old value. See `umask(2)`.
Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL UMASK(MASK [, OLD])`
  `OLD = UMASK(MASK)`

Arguments:

  MASK | Shall be a scalar of type `INTEGER`.
  OLD | (Optional) Shall be a scalar of type `INTEGER`.

Next: UNPACK, Previous: UMASK, Up: Intrinsic Procedures

### 8.254 `UNLINK` — Remove a file from the file system

Description:
  Unlinks the file PATH. A null character (`CHAR(0)`) can be used to mark the end of the name in PATH; otherwise, trailing blanks in the file name are ignored. If the STATUS argument is supplied, it contains 0 on success or a nonzero error code upon return; see `unlink(2)`.

  This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

Standard:
  GNU extension
Class:
  Subroutine, function
Syntax:

  `CALL UNLINK(PATH [, STATUS])`
  `STATUS = UNLINK(PATH)`

Arguments:

  PATH | Shall be of default `CHARACTER` type.
  STATUS | (Optional) Shall be of default `INTEGER` type.

See also:
  LINK, SYMLNK

Next: VERIFY, Previous: UNLINK, Up: Intrinsic Procedures

### 8.255 `UNPACK` — Unpack an array of rank one into an array

Description:
  Store the elements of VECTOR in an array of higher rank.
Standard:
  Fortran 95 and later
Class:
  Transformational function
Syntax:
  `RESULT = UNPACK(VECTOR, MASK, FIELD)`
Arguments:

  VECTOR | Shall be an array of any type and rank one. It shall have at least as many elements as MASK has `TRUE` values.
  MASK | Shall be an array of type `LOGICAL`.
  FIELD | Shall be of the same type as VECTOR and have the same shape as MASK.

Return value:
  The resulting array corresponds to FIELD with `TRUE` elements of MASK replaced by values from VECTOR in array element order.
Example:

                PROGRAM test_unpack
                  integer :: vector(2)  = (/1,1/)
                  logical :: mask(4)  = (/ .TRUE., .FALSE., .FALSE., .TRUE. /)
                  integer :: field(2,2) = 0, unity(2,2)

                  ! result: unity matrix
                  unity = unpack(vector, reshape(mask, (/2,2/)), field)
                END PROGRAM

See also:
  PACK, SPREAD

Next: XOR, Previous: UNPACK, Up: Intrinsic Procedures

### 8.256 `VERIFY` — Scan a string for characters not a given set

Description:
  Verifies that all the characters in STRING belong to the set of characters in SET.

  If BACK is either absent or equals `FALSE`, this function returns the position of the leftmost character of STRING that is not in SET. If BACK equals `TRUE`, the rightmost position is returned. If all characters of STRING are found in SET, the result is zero.

Standard:
  Fortran 95 and later, with KIND argument Fortran 2003 and later
Class:
  Elemental function
Syntax:
  `RESULT = VERIFY(STRING, SET[, BACK [, KIND]])`
Arguments:

  STRING | Shall be of type `CHARACTER`.
  SET | Shall be of type `CHARACTER`.
  BACK | (Optional) shall be of type `LOGICAL`.
  KIND | (Optional) An `INTEGER` initialization expression indicating the kind parameter of the result.

Return value:
  The return value is of type `INTEGER` and of kind KIND. If KIND is absent, the return value is of default integer kind.
Example:

                PROGRAM test_verify
                  WRITE(*,*) VERIFY("FORTRAN", "AO")           ! 1, found 'F'
                  WRITE(*,*) VERIFY("FORTRAN", "FOO")          ! 3, found 'R'
                  WRITE(*,*) VERIFY("FORTRAN", "C++")          ! 1, found 'F'
                  WRITE(*,*) VERIFY("FORTRAN", "C++", .TRUE.)  ! 7, found 'N'
                  WRITE(*,*) VERIFY("FORTRAN", "FORTRAN")      ! 0' found none
                END PROGRAM

See also:
  SCAN, INDEX intrinsic

Previous: VERIFY, Up: Intrinsic Procedures

### 8.257 `XOR` — Bitwise logical exclusive OR

Description:
  Bitwise logical exclusive or.

  This intrinsic routine is provided for backwards compatibility with GNU Fortran 77. For integer arguments, programmers should consider the use of the IEOR intrinsic and for logical arguments the `.NEQV.` operator, which are both defined by the Fortran standard.

Standard:
  GNU extension
Class:
  Function
Syntax:
  `RESULT = XOR(I, J)`
Arguments:

  I | The type shall be either a scalar `INTEGER` type or a scalar `LOGICAL` type.
  J | The type shall be the same as the type of I.

Return value:
  The return type is either a scalar `INTEGER` or a scalar `LOGICAL`. If the kind type parameters differ, then the smaller kind type is implicitly converted to larger kind, and the return has the larger kind.
Example:

                PROGRAM test_xor
                  LOGICAL :: T = .TRUE., F = .FALSE.
                  INTEGER :: a, b
                  DATA a / Z'F' /, b / Z'3' /

                  WRITE (*,*) XOR(T, T), XOR(T, F), XOR(F, T), XOR(F, F)
                  WRITE (*,*) XOR(a, b)
                END PROGRAM

See also:
  Fortran 95 elemental function: IEOR

Next: Contributing, Previous: Intrinsic Procedures, Up: Top

## 9 Intrinsic Modules

Next: ISO_C_BINDING, Up: Intrinsic Modules

### 9.1 `ISO_FORTRAN_ENV`

Standard:
  Fortran 2003 and later, except when otherwise noted

The `ISO_FORTRAN_ENV` module provides the following scalar default-integer named constants:

`ATOMIC_INT_KIND`:
  Default-kind integer constant to be used as kind parameter when defining integer variables used in atomic operations. (Fortran 2008 or later.)
`ATOMIC_LOGICAL_KIND`:
  Default-kind integer constant to be used as kind parameter when defining logical variables used in atomic operations. (Fortran 2008 or later.)
`CHARACTER_KINDS`:
  Default-kind integer constant array of rank one containing the supported kind parameters of the `CHARACTER` type. (Fortran 2008 or later.)
`CHARACTER_STORAGE_SIZE`:
  Size in bits of the character storage unit.
`ERROR_UNIT`:
  Identifies the preconnected unit used for error reporting.
`FILE_STORAGE_SIZE`:
  Size in bits of the file-storage unit.
`INPUT_UNIT`:
  Identifies the preconnected unit identified by the asterisk (`*`) in `READ` statement.
`INT8`, `INT16`, `INT32`, `INT64`:
  Kind type parameters to specify an INTEGER type with a storage size of 16, 32, and 64 bits. It is negative if a target platform does not support the particular kind. (Fortran 2008 or later.)
`INTEGER_KINDS`:
  Default-kind integer constant array of rank one containing the supported kind parameters of the `INTEGER` type. (Fortran 2008 or later.)
`IOSTAT_END`:
  The value assigned to the variable passed to the `IOSTAT=` specifier of an input/output statement if an end-of-file condition occurred.
`IOSTAT_EOR`:
  The value assigned to the variable passed to the `IOSTAT=` specifier of an input/output statement if an end-of-record condition occurred.
`IOSTAT_INQUIRE_INTERNAL_UNIT`:
  Scalar default-integer constant, used by `INQUIRE` for the `IOSTAT=` specifier to denote an that a unit number identifies an internal unit. (Fortran 2008 or later.)
`NUMERIC_STORAGE_SIZE`:
  The size in bits of the numeric storage unit.
`LOGICAL_KINDS`:
  Default-kind integer constant array of rank one containing the supported kind parameters of the `LOGICAL` type. (Fortran 2008 or later.)
`OUTPUT_UNIT`:
  Identifies the preconnected unit identified by the asterisk (`*`) in `WRITE` statement.
`REAL32`, `REAL64`, `REAL128`:
  Kind type parameters to specify a REAL type with a storage size of 32, 64, and 128 bits. It is negative if a target platform does not support the particular kind. (Fortran 2008 or later.)
`REAL_KINDS`:
  Default-kind integer constant array of rank one containing the supported kind parameters of the `REAL` type. (Fortran 2008 or later.)
`STAT_LOCKED`:
  Scalar default-integer constant used as STAT= return value by `LOCK` to denote that the lock variable is locked by the executing image. (Fortran 2008 or later.)
`STAT_LOCKED_OTHER_IMAGE`:
  Scalar default-integer constant used as STAT= return value by `UNLOCK` to denote that the lock variable is locked by another image. (Fortran 2008 or later.)
`STAT_STOPPED_IMAGE`:
  Positive, scalar default-integer constant used as STAT= return value if the argument in the statement requires synchronisation with an image, which has initiated the termination of the execution. (Fortran 2008 or later.)
`STAT_UNLOCKED`:
  Scalar default-integer constant used as STAT= return value by `UNLOCK` to denote that the lock variable is unlocked. (Fortran 2008 or later.)

The module provides the following derived type:

`LOCK_TYPE`:
  Derived type with private components to be use with the `LOCK` and `UNLOCK` statement. A variable of its type has to be always declared as coarray and may not appear in a variable-definition context. (Fortran 2008 or later.)

The module also provides the following intrinsic procedures: COMPILER_OPTIONS and COMPILER_VERSION.

Next: OpenMP Modules OMP_LIB and OMP_LIB_KINDS, Previous: ISO_FORTRAN_ENV, Up: Intrinsic Modules

### 9.2 `ISO_C_BINDING`

Standard:
  Fortran 2003 and later, GNU extensions

The following intrinsic procedures are provided by the module; their definition can be found in the section Intrinsic Procedures of this manual.

`C_ASSOCIATED`
`C_F_POINTER`
`C_F_PROCPOINTER`
`C_FUNLOC`
`C_LOC`
`C_SIZEOF`

The `ISO_C_BINDING` module provides the following named constants of type default integer, which can be used as KIND type parameters.

In addition to the integer named constants required by the Fortran 2003 standard and `C_PTRDIFF_T` of TS 29113, GNU Fortran provides as an extension named constants for the 128-bit integer types supported by the C compiler: `C_INT128_T, C_INT_LEAST128_T, C_INT_FAST128_T`. Furthermore, if `__float128` is supported in C, the named constants `C_FLOAT128, C_FLOAT128_COMPLEX` are defined.

Fortran Type | Named constant | C type | Extension
`INTEGER` | `C_INT` | `int`
`INTEGER` | `C_SHORT` | `short int`
`INTEGER` | `C_LONG` | `long int`
`INTEGER` | `C_LONG_LONG` | `long long int`
`INTEGER` | `C_SIGNED_CHAR` | `signed char`/`unsigned char`
`INTEGER` | `C_SIZE_T` | `size_t`
`INTEGER` | `C_INT8_T` | `int8_t`
`INTEGER` | `C_INT16_T` | `int16_t`
`INTEGER` | `C_INT32_T` | `int32_t`
`INTEGER` | `C_INT64_T` | `int64_t`
`INTEGER` | `C_INT128_T` | `int128_t` | Ext.
`INTEGER` | `C_INT_LEAST8_T` | `int_least8_t`
`INTEGER` | `C_INT_LEAST16_T` | `int_least16_t`
`INTEGER` | `C_INT_LEAST32_T` | `int_least32_t`
`INTEGER` | `C_INT_LEAST64_T` | `int_least64_t`
`INTEGER` | `C_INT_LEAST128_T` | `int_least128_t` | Ext.
`INTEGER` | `C_INT_FAST8_T` | `int_fast8_t`
`INTEGER` | `C_INT_FAST16_T` | `int_fast16_t`
`INTEGER` | `C_INT_FAST32_T` | `int_fast32_t`
`INTEGER` | `C_INT_FAST64_T` | `int_fast64_t`
`INTEGER` | `C_INT_FAST128_T` | `int_fast128_t` | Ext.
`INTEGER` | `C_INTMAX_T` | `intmax_t`
`INTEGER` | `C_INTPTR_T` | `intptr_t`
`INTEGER` | `C_PTRDIFF_T` | `intptr_t` | TS 29113
`REAL` | `C_FLOAT` | `float`
`REAL` | `C_DOUBLE` | `double`
`REAL` | `C_LONG_DOUBLE` | `long double`
`REAL` | `C_FLOAT128` | `__float128` | Ext.
`COMPLEX` | `C_FLOAT_COMPLEX` | `float _Complex`
`COMPLEX` | `C_DOUBLE_COMPLEX` | `double _Complex`
`COMPLEX` | `C_LONG_DOUBLE_COMPLEX` | `long double _Complex`
`REAL` | `C_FLOAT128_COMPLEX` | `__float128 _Complex` | Ext.
`LOGICAL` | `C_BOOL` | `_Bool`
`CHARACTER` | `C_CHAR` | `char`

Additionally, the following parameters of type `CHARACTER(KIND=C_CHAR)` are defined.

Name | C definition | Value
`C_NULL_CHAR` | null character | `'\0'`
`C_ALERT` | alert | `'\a'`
`C_BACKSPACE` | backspace | `'\b'`
`C_FORM_FEED` | form feed | `'\f'`
`C_NEW_LINE` | new line | `'\n'`
`C_CARRIAGE_RETURN` | carriage return | `'\r'`
`C_HORIZONTAL_TAB` | horizontal tab | `'\t'`
`C_VERTICAL_TAB` | vertical tab | `'\v'`

Moreover, the following two named constants are defined:

Name | Type
`C_NULL_PTR` | `C_PTR`
`C_NULL_FUNPTR` | `C_FUNPTR`

Both are equivalent to the value `NULL` in C.

Previous: ISO_C_BINDING, Up: Intrinsic Modules

### 9.3 OpenMP Modules `OMP_LIB` and `OMP_LIB_KINDS`

Standard:
  OpenMP Application Program Interface v4.0

The OpenMP Fortran runtime library routines are provided both in a form of two Fortran 90 modules, named `OMP_LIB` and `OMP_LIB_KINDS`, and in a form of a Fortran `include` file named `omp_lib.h`. The procedures provided by `OMP_LIB` can be found in the Introduction manual, the named constants defined in the modules are listed below.

For details refer to the actual OpenMP Application Program Interface v4.0.

`OMP_LIB_KINDS` provides the following scalar default-integer named constants:

`omp_lock_kind`
`omp_nest_lock_kind`
`omp_proc_bind_kind`
`omp_sched_kind`

`OMP_LIB` provides the scalar default-integer named constant `openmp_version` with a value of the form yyyymm, where `yyyy` is the year and mm the month of the OpenMP version; for OpenMP v4.0 the value is `201307`.

The following scalar integer named constants of the kind `omp_sched_kind`:

`omp_sched_static`
`omp_sched_dynamic`
`omp_sched_guided`
`omp_sched_auto`

And the following scalar integer named constants of the kind `omp_proc_bind_kind`:

`omp_proc_bind_false`
`omp_proc_bind_true`
`omp_proc_bind_master`
`omp_proc_bind_close`
`omp_proc_bind_spread`

Next: Copying, Previous: Intrinsic Modules, Up: Top

## Contributing

Free software is only possible if people contribute to efforts to create it. We're always in need of more people helping out with ideas and comments, writing documentation and contributing code.

If you want to contribute to GNU Fortran, have a look at the long lists of projects you can take on. Some of these projects are small, some of them are large; some are completely orthogonal to the rest of what is happening on GNU Fortran, but others are “mainstream” projects in need of enthusiastic hackers. All of these projects are important! We will eventually get around to the things here, but they are also things doable by someone who is willing and able.

Next: Projects, Up: Contributing

### Contributors to GNU Fortran

Most of the parser was hand-crafted by Andy Vaught, who is also the initiator of the whole project. Thanks Andy! Most of the interface with GCC was written by Paul Brook.

The following individuals have contributed code and/or ideas and significant help to the GNU Fortran project (in alphabetical order):

- Janne Blomqvist
- Steven Bosscher
- Paul Brook
- Tobias Burnus
- François-Xavier Coudert
- Bud Davis
- Jerry DeLisle
- Erik Edelmann
- Bernhard Fischer
- Daniel Franke
- Richard Guenther
- Richard Henderson
- Katherine Holcomb
- Jakub Jelinek
- Niels Kristian Bech Jensen
- Steven Johnson
- Steven G. Kargl
- Thomas Koenig
- Asher Langton
- H. J. Lu
- Toon Moene
- Brooks Moses
- Andrew Pinski
- Tim Prince
- Christopher D. Rickett
- Richard Sandiford
- Tobias Schlüter
- Roger Sayle
- Paul Thomas
- Andy Vaught
- Feng Wang
- Janus Weil
- Daniel Kraft

The following people have contributed bug reports, smaller or larger patches, and much needed feedback and encouragement for the GNU Fortran project:

- Bill Clodius
- Dominique d'Humières
- Kate Hedstrom
- Erik Schnetter
- Joost VandeVondele

Many other individuals have helped debug, test and improve the GNU Fortran compiler over the past few years, and we welcome you to do the same! If you already have done so, and you would like to see your name listed in the list above, please contact us.

Next: Proposed Extensions, Previous: Contributors, Up: Contributing

### Projects

Help build the test suite
  Solicit more code for donation to the test suite: the more extensive the testsuite, the smaller the risk of breaking things in the future! We can keep code private on request.
Bug hunting/squishing
  Find bugs and write more test cases! Test cases are especially very welcome, because it allows us to concentrate on fixing bugs instead of isolating them. Going through the bugzilla database at http://gcc.gnu.org/bugzilla/ to reduce testcases posted there and add more information (for example, for which version does the testcase work, for which versions does it fail?) is also very helpful.

Previous: Projects, Up: Contributing

### Proposed Extensions

Here's a list of proposed extensions for the GNU Fortran compiler, in no particular order. Most of these are necessary to be fully compatible with existing Fortran compilers, but they are not part of the official J3 Fortran 95 standard.

#### Compiler extensions:

- User-specified alignment rules for structures.
- Automatically extend single precision constants to double.
- Compile code that conserves memory by dynamically allocating common and module storage either on stack or heap.
- Compile flag to generate code for array conformance checking (suggest -CC).
- User control of symbol names (underscores, etc).
- Compile setting for maximum size of stack frame size before spilling parts to static or heap.
- Flag to force local variables into static space.
- Flag to force local variables onto stack.

#### Environment Options

- Pluggable library modules for random numbers, linear algebra. LA should use BLAS calling conventions.
- Environment variables controlling actions on arithmetic exceptions like overflow, underflow, precision loss—Generate NaN, abort, default. action.
- Set precision for fp units that support it (i387).
- Variable for setting fp rounding mode.
- Variable to fill uninitialized variables with a user-defined bit pattern.
- Environment variable controlling filename that is opened for that unit number.
- Environment variable to clear/trash memory being freed.
- Environment variable to control tracing of allocations and frees.
- Environment variable to display allocated memory at normal program end.
- Environment variable for filename for * IO-unit.
- Environment variable for temporary file directory.
- Environment variable forcing standard output to be line buffered (Unix).

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

## GNU General Public License

Version 3, 29 June 2007

         Copyright © 2007 Free Software Foundation, Inc. http://fsf.org/

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### Preamble

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    You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.

11. Patents.

    A “contributor” is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's “contributor version”.

    A contributor's “essential patent claims” are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, “control” includes the right to grant patent sublicenses in a manner consistent with the requirements of this License.

    Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version.

    In the following three paragraphs, a “patent license” is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission to practice a patent or covenant not to sue for patent infringement). To “grant” such a patent license to a party means to make such an agreement or commitment not to enforce a patent against the party.

    If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. “Knowingly relying” means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid.

    If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it.

    A patent license is “discriminatory” if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.

    Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law.

12. No Surrender of Others' Freedom.

    If 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 convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program.

13. Use with the GNU Affero General Public License.

    Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such.

14. Revised Versions of this License.

    The Free Software Foundation may publish revised and/or new versions of the GNU 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 that a certain numbered version of the GNU General Public License “or any later version” applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.

    If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program.

    Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version.

15. Disclaimer of Warranty.

    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.

16. Limitation of Liability.

    IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 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.

17. Interpretation of Sections 15 and 16.

    If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee.

### 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 state 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 3 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, see http://www.gnu.org/licenses/.

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

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

         program Copyright (C) year name of author
         This program 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, your program's commands might be different; for a GUI interface, you would use an “about box”.

You should also get your employer (if you work as a programmer) or school, if any, to sign a “copyright disclaimer” for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see http://www.gnu.org/licenses/.

The GNU 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 Lesser General Public License instead of this License. But first, please read http://www.gnu.org/philosophy/why-not-lgpl.html.

Next: Funding, Previous: Copying, Up: Top

## GNU Free Documentation License

Version 1.3, 3 November 2008

         Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
         http://fsf.org/

         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.

   The “publisher” means any person or entity that distributes copies of the Document to the public.

   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 in 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 Warranty 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 under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

   However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

   Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

   Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

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. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

11. RELICENSING

    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

### 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 1.3
           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: Option Index, Previous: GNU Free Documentation License, 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: Keyword Index, Previous: Funding, Up: Top

## Option Index

`gfortran`'s command line options are indexed here without any initial ``-`' or ``--`'. Where an option has both positive and negative forms (such as -foption and -fno-option), relevant entries in the manual are indexed under the most appropriate form; it may sometimes be useful to look up both forms.

- `A-`predicate`=`answer: Preprocessing Options
- `A` predicate`=`answer: Preprocessing Options
- `backslash`: Fortran Dialect Options
- `C`: Preprocessing Options
- `CC`: Preprocessing Options
- `cpp`: Preprocessing Options
- `dD`: Preprocessing Options
- `dI`: Preprocessing Options
- `dM`: Preprocessing Options
- `dN`: Preprocessing Options
- `D` name: Preprocessing Options
- `D` name`=`definition: Preprocessing Options
- `dU`: Preprocessing Options
- `faggressive-function-elimination`: Code Gen Options
- `falign-commons`: Code Gen Options
- `fall-intrinsics`: Fortran Dialect Options
- `fblas-matmul-limit`: Code Gen Options
- `fbounds-check`: Code Gen Options
- `fcheck`: Code Gen Options
- `fcheck-array-temporaries`: Code Gen Options
- `fcoarray`: Code Gen Options
- `fconvert=`conversion: Runtime Options
- `fcray-pointer`: Fortran Dialect Options
- `fd-lines-as-code`: Fortran Dialect Options
- `fd-lines-as-comments`: Fortran Dialect Options
- `fdefault-double-8`: Fortran Dialect Options
- `fdefault-integer-8`: Fortran Dialect Options
- `fdefault-real-8`: Fortran Dialect Options
- `fdollar-ok`: Fortran Dialect Options
- `fdump-fortran-optimized`: Debugging Options
- `fdump-fortran-original`: Debugging Options
- `fdump-parse-tree`: Debugging Options
- `fexternal-blas`: Code Gen Options
- `ff2c`: Code Gen Options
- `ffixed-line-length-`n: Fortran Dialect Options
- `ffpe-summary=`list: Debugging Options
- `ffpe-trap=`list: Debugging Options
- `ffree-form`: Fortran Dialect Options
- `ffree-line-length-`n: Fortran Dialect Options
- `fimplicit-none`: Fortran Dialect Options
- `finit-character`: Code Gen Options
- `finit-integer`: Code Gen Options
- `finit-local-zero`: Code Gen Options
- `finit-logical`: Code Gen Options
- `finit-real`: Code Gen Options
- `finteger-4-integer-8`: Fortran Dialect Options
- `fintrinsic-modules-path` dir: Directory Options
- `fmax-array-constructor`: Code Gen Options
- `fmax-errors=`n: Error and Warning Options
- `fmax-identifier-length=`n: Fortran Dialect Options
- `fmax-stack-var-size`: Code Gen Options
- `fmax-subrecord-length=`length: Runtime Options
- `fmodule-private`: Fortran Dialect Options
- `fno-automatic`: Code Gen Options
- `fno-backtrace`: Debugging Options
- `fno-fixed-form`: Fortran Dialect Options
- `fno-protect-parens`: Code Gen Options
- `fno-underscoring`: Code Gen Options
- `fopenmp`: Fortran Dialect Options
- `fpack-derived`: Code Gen Options
- `fpp`: Preprocessing Options
- `frange-check`: Fortran Dialect Options
- `freal-4-real-10`: Fortran Dialect Options
- `freal-4-real-16`: Fortran Dialect Options
- `freal-4-real-8`: Fortran Dialect Options
- `freal-8-real-10`: Fortran Dialect Options
- `freal-8-real-16`: Fortran Dialect Options
- `freal-8-real-4`: Fortran Dialect Options
- `frealloc-lhs`: Code Gen Options
- `frecord-marker=`length: Runtime Options
- `frecursive`: Code Gen Options
- `frepack-arrays`: Code Gen Options
- `frontend-optimize`: Code Gen Options
- `fsecond-underscore`: Code Gen Options
- `fshort-enums`: Fortran 2003 status
- `fshort-enums`: Code Gen Options
- `fsign-zero`: Runtime Options
- `fstack-arrays`: Code Gen Options
- `fsyntax-only`: Error and Warning Options
- `fworking-directory`: Preprocessing Options
- `H`: Preprocessing Options
- `I` dir: Directory Options
- `idirafter` dir: Preprocessing Options
- `imultilib` dir: Preprocessing Options
- `iprefix` prefix: Preprocessing Options
- `iquote` dir: Preprocessing Options
- `isysroot` dir: Preprocessing Options
- `isystem` dir: Preprocessing Options
- `J` dir: Directory Options
- `M` dir: Directory Options
- `nostdinc`: Preprocessing Options
- `P`: Preprocessing Options
- `pedantic`: Error and Warning Options
- `pedantic-errors`: Error and Warning Options
- `static-libgfortran`: Link Options
- `std=`std `option`: Fortran Dialect Options
- `U` name: Preprocessing Options
- `undef`: Preprocessing Options
- `Waliasing`: Error and Warning Options
- `Walign-commons`: Error and Warning Options
- `Wall`: Error and Warning Options
- `Wampersand`: Error and Warning Options
- `Warray-temporaries`: Error and Warning Options
- `Wc-binding-type`: Error and Warning Options
- `Wcharacter-truncation`: Error and Warning Options
- `Wcompare-reals`: Error and Warning Options
- `Wconversion`: Error and Warning Options
- `Wconversion-extra`: Error and Warning Options
- `Werror`: Error and Warning Options
- `Wextra`: Error and Warning Options
- `Wfunction-elimination`: Error and Warning Options
- `Wimplicit-interface`: Error and Warning Options
- `Wimplicit-procedure`: Error and Warning Options
- `Wintrinsic-shadow`: Error and Warning Options
- `Wintrinsics-std`: Error and Warning Options
- `Wline-truncation`: Error and Warning Options
- `Wreal-q-constant`: Error and Warning Options
- `Wrealloc-lhs`: Error and Warning Options
- `Wrealloc-lhs-all`: Error and Warning Options
- `Wsurprising`: Error and Warning Options
- `Wtabs`: Error and Warning Options
- `Wtargt-lifetime`: Error and Warning Options
- `Wunderflow`: Error and Warning Options
- `Wunused-dummy-argument`: Error and Warning Options
- `Wunused-parameter`: Error and Warning Options
- `Wzerotrip`: Error and Warning Options

Previous: Option Index, Up: Top

## Keyword Index

- `$`: Fortran Dialect Options
- `%LOC`: Argument list functions
- `%REF`: Argument list functions
- `%VAL`: Argument list functions
- `&`: Error and Warning Options
- `[...]`: Fortran 2003 status
- `_gfortran_set_args`: _gfortran_set_args
- `_gfortran_set_convert`: _gfortran_set_convert
- `_gfortran_set_fpe`: _gfortran_set_fpe
- `_gfortran_set_max_subrecord_length`: _gfortran_set_max_subrecord_length
- `_gfortran_set_options`: _gfortran_set_options
- `_gfortran_set_record_marker`: _gfortran_set_record_marker
- `ABORT`: ABORT
- `ABS`: ABS
- absolute value: ABS
- `ACCESS`: ACCESS
- `ACCESS='STREAM'` I/O: Fortran 2003 status
- `ACHAR`: ACHAR
- `ACOS`: ACOS
- `ACOSH`: ACOSH
- adjust string: ADJUSTR
- adjust string: ADJUSTL
- `ADJUSTL`: ADJUSTL
- `ADJUSTR`: ADJUSTR
- `AIMAG`: AIMAG
- `AINT`: AINT
- `ALARM`: ALARM
- `ALGAMA`: LOG_GAMMA
- aliasing: Error and Warning Options
- alignment of `COMMON` blocks: Code Gen Options
- alignment of `COMMON` blocks: Error and Warning Options
- `ALL`: ALL
- all warnings: Error and Warning Options
- `ALLOCATABLE` components of derived types: Fortran 2003 status
- `ALLOCATABLE` dummy arguments: Fortran 2003 status
- `ALLOCATABLE` function results: Fortran 2003 status
- `ALLOCATED`: ALLOCATED
- allocation, moving: MOVE_ALLOC
- allocation, status: ALLOCATED
- `ALOG`: LOG
- `ALOG10`: LOG10
- `AMAX0`: MAX
- `AMAX1`: MAX
- `AMIN0`: MIN
- `AMIN1`: MIN
- `AMOD`: MOD
- `AND`: AND
- `ANINT`: ANINT
- `ANY`: ANY
- area hyperbolic cosine: ACOSH
- area hyperbolic sine: ASINH
- area hyperbolic tangent: ATANH
- argument list functions: Argument list functions
- arguments, to program: IARGC
- arguments, to program: GET_COMMAND_ARGUMENT
- arguments, to program: GET_COMMAND
- arguments, to program: GETARG
- arguments, to program: COMMAND_ARGUMENT_COUNT
- array, add elements: SUM
- array, AND: IALL
- array, apply condition: ANY
- array, apply condition: ALL
- array, bounds checking: Code Gen Options
- array, change dimensions: RESHAPE
- array, combine arrays: MERGE
- array, condition testing: ANY
- array, condition testing: ALL
- array, conditionally add elements: SUM
- array, conditionally count elements: COUNT
- array, conditionally multiply elements: PRODUCT
- array, constructors: Fortran 2003 status
- array, count elements: SIZE
- array, duplicate dimensions: SPREAD
- array, duplicate elements: SPREAD
- array, element counting: COUNT
- array, gather elements: PACK
- array, increase dimension: UNPACK
- array, increase dimension: SPREAD
- array, indices of type real: Real array indices
- array, location of maximum element: MAXLOC
- array, location of minimum element: MINLOC
- array, lower bound: LBOUND
- array, maximum value: MAXVAL
- array, merge arrays: MERGE
- array, minimum value: MINVAL
- array, multiply elements: PRODUCT
- array, number of elements: SIZE
- array, number of elements: COUNT
- array, OR: IANY
- array, packing: PACK
- array, parity: IPARITY
- array, permutation: CSHIFT
- array, product: PRODUCT
- array, reduce dimension: PACK
- array, rotate: CSHIFT
- array, scatter elements: UNPACK
- array, shape: SHAPE
- array, shift: EOSHIFT
- array, shift circularly: CSHIFT
- array, size: SIZE
- array, sum: SUM
- array, transmogrify: RESHAPE
- array, transpose: TRANSPOSE
- array, unpacking: UNPACK
- array, upper bound: UBOUND
- array, XOR: IPARITY
- ASCII collating sequence: IACHAR
- ASCII collating sequence: ACHAR
- `ASIN`: ASIN
- `ASINH`: ASINH
- `ASSOCIATED`: ASSOCIATED
- association status: ASSOCIATED
- association status, C pointer: C_ASSOCIATED
- `ATAN`: ATAN
- `ATAN2`: ATAN2
- `ATANH`: ATANH
- Atomic subroutine, define: ATOMIC_DEFINE
- Atomic subroutine, reference: ATOMIC_REF
- `ATOMIC_DEFINE`: ATOMIC_DEFINE
- `ATOMIC_REF`: ATOMIC_REF
- Authors: Contributors
- backslash: Fortran Dialect Options
- backtrace: BACKTRACE
- `BACKTRACE`: BACKTRACE
- backtrace: Debugging Options
- base 10 logarithm function: LOG10
- `BESJ0`: BESSEL_J0
- `BESJ1`: BESSEL_J1
- `BESJN`: BESSEL_JN
- Bessel function, first kind: BESSEL_JN
- Bessel function, first kind: BESSEL_J1
- Bessel function, first kind: BESSEL_J0
- Bessel function, second kind: BESSEL_YN
- Bessel function, second kind: BESSEL_Y1
- Bessel function, second kind: BESSEL_Y0
- `BESSEL_J0`: BESSEL_J0
- `BESSEL_J1`: BESSEL_J1
- `BESSEL_JN`: BESSEL_JN
- `BESSEL_Y0`: BESSEL_Y0
- `BESSEL_Y1`: BESSEL_Y1
- `BESSEL_YN`: BESSEL_YN
- `BESY0`: BESSEL_Y0
- `BESY1`: BESSEL_Y1
- `BESYN`: BESSEL_YN
- `BGE`: BGE
- `BGT`: BGT
- binary representation: POPPAR
- binary representation: POPCNT
- `BIT_SIZE`: BIT_SIZE
- bits set: POPCNT
- bits, AND of array elements: IALL
- bits, clear: IBCLR
- bits, extract: IBITS
- bits, get: IBITS
- bits, merge: MERGE_BITS
- bits, move: TRANSFER
- bits, move: MVBITS
- bits, negate: NOT
- bits, number of: BIT_SIZE
- bits, OR of array elements: IANY
- bits, set: IBSET
- bits, shift: ISHFT
- bits, shift circular: ISHFTC
- bits, shift left: SHIFTL
- bits, shift left: LSHIFT
- bits, shift right: SHIFTR
- bits, shift right: SHIFTA
- bits, shift right: RSHIFT
- bits, testing: BTEST
- bits, unset: IBCLR
- bits, XOR of array elements: IPARITY
- bitwise comparison: BLT
- bitwise comparison: BLE
- bitwise comparison: BGT
- bitwise comparison: BGE
- bitwise logical and: IAND
- bitwise logical and: AND
- bitwise logical exclusive or: XOR
- bitwise logical exclusive or: IEOR
- bitwise logical not: NOT
- bitwise logical or: OR
- bitwise logical or: IOR
- `BLE`: BLE
- `BLT`: BLT
- bounds checking: Code Gen Options
- BOZ literal constants: BOZ literal constants
- `BTEST`: BTEST
- `C_ASSOCIATED`: C_ASSOCIATED
- `C_F_POINTER`: C_F_POINTER
- `C_F_PROCPOINTER`: C_F_PROCPOINTER
- `C_FUNLOC`: C_FUNLOC
- `C_LOC`: C_LOC
- `C_SIZEOF`: C_SIZEOF
- `CABS`: ABS
- calling convention: Code Gen Options
- `CCOS`: COS
- `CDABS`: ABS
- `CDCOS`: COS
- `CDEXP`: EXP
- `CDLOG`: LOG
- `CDSIN`: SIN
- `CDSQRT`: SQRT
- ceiling: CEILING
- `CEILING`: CEILING
- ceiling: ANINT
- `CEXP`: EXP
- `CHAR`: CHAR
- character kind: SELECTED_CHAR_KIND
- character set: Fortran Dialect Options
- `CHDIR`: CHDIR
- checking array temporaries: Code Gen Options
- checking subscripts: Code Gen Options
- `CHMOD`: CHMOD
- clock ticks: SYSTEM_CLOCK
- clock ticks: MCLOCK8
- clock ticks: MCLOCK
- `CLOG`: LOG
- `CMPLX`: CMPLX
- coarray, `IMAGE_INDEX`: IMAGE_INDEX
- coarray, lower bound: LCOBOUND
- coarray, `NUM_IMAGES`: NUM_IMAGES
- coarray, `THIS_IMAGE`: THIS_IMAGE
- coarray, upper bound: UCOBOUND
- coarrays: Code Gen Options
- code generation, conventions: Code Gen Options
- collating sequence, ASCII: IACHAR
- collating sequence, ASCII: ACHAR
- command line: EXECUTE_COMMAND_LINE
- command options: Invoking GNU Fortran
- command-line arguments: IARGC
- command-line arguments: GET_COMMAND_ARGUMENT
- command-line arguments: GET_COMMAND
- command-line arguments: GETARG
- command-line arguments: COMMAND_ARGUMENT_COUNT
- command-line arguments, number of: IARGC
- command-line arguments, number of: COMMAND_ARGUMENT_COUNT
- `COMMAND_ARGUMENT_COUNT`: COMMAND_ARGUMENT_COUNT
- `COMMON`: Volatile COMMON blocks
- compiler flags inquiry function: COMPILER_OPTIONS
- compiler, name and version: COMPILER_VERSION
- `COMPILER_OPTIONS`: COMPILER_OPTIONS
- `COMPILER_VERSION`: COMPILER_VERSION
- `COMPLEX`: COMPLEX
- complex conjugate: CONJG
- Complex function: Alternate complex function syntax
- complex numbers, conversion to: DCMPLX
- complex numbers, conversion to: COMPLEX
- complex numbers, conversion to: CMPLX
- complex numbers, imaginary part: AIMAG
- complex numbers, real part: REAL
- complex numbers, real part: DREAL
- Conditional compilation: Preprocessing and conditional compilation
- `CONJG`: CONJG
- consistency, durability: Data consistency and durability
- Contributing: Contributing
- Contributors: Contributors
- conversion: Error and Warning Options
- conversion, to character: CHAR
- conversion, to complex: DCMPLX
- conversion, to complex: COMPLEX
- conversion, to complex: CMPLX
- conversion, to integer: LONG
- conversion, to integer: INT8
- conversion, to integer: INT2
- conversion, to integer: INT
- conversion, to integer: ICHAR
- conversion, to integer: IACHAR
- conversion, to integer: Implicitly convert LOGICAL and INTEGER values
- conversion, to logical: LOGICAL
- conversion, to logical: Implicitly convert LOGICAL and INTEGER values
- conversion, to real: REAL
- conversion, to real: DBLE
- conversion, to string: CTIME
- `CONVERT` specifier: CONVERT specifier
- core, dump: ABORT
- `COS`: COS
- `COSH`: COSH
- cosine: COS
- cosine, hyperbolic: COSH
- cosine, hyperbolic, inverse: ACOSH
- cosine, inverse: ACOS
- `COUNT`: COUNT
- CPP: Preprocessing Options
- CPP: Preprocessing and conditional compilation
- `CPU_TIME`: CPU_TIME
- Credits: Contributors
- `CSHIFT`: CSHIFT
- `CSIN`: SIN
- `CSQRT`: SQRT
- `CTIME`: CTIME
- current date: IDATE
- current date: FDATE
- current date: DATE_AND_TIME
- current time: TIME8
- current time: TIME
- current time: ITIME
- current time: FDATE
- current time: DATE_AND_TIME
- `DABS`: ABS
- `DACOS`: ACOS
- `DACOSH`: ACOSH
- `DASIN`: ASIN
- `DASINH`: ASINH
- `DATAN`: ATAN
- `DATAN2`: ATAN2
- `DATANH`: ATANH
- date, current: IDATE
- date, current: FDATE
- date, current: DATE_AND_TIME
- `DATE_AND_TIME`: DATE_AND_TIME
- `DBESJ0`: BESSEL_J0
- `DBESJ1`: BESSEL_J1
- `DBESJN`: BESSEL_JN
- `DBESY0`: BESSEL_Y0
- `DBESY1`: BESSEL_Y1
- `DBESYN`: BESSEL_YN
- `DBLE`: DBLE
- `DCMPLX`: DCMPLX
- `DCONJG`: CONJG
- `DCOS`: COS
- `DCOSH`: COSH
- `DDIM`: DIM
- debugging information options: Debugging Options
- debugging, preprocessor: Preprocessing Options
- `DECODE`: ENCODE and DECODE statements
- delayed execution: SLEEP
- delayed execution: ALARM
- `DEXP`: EXP
- `DFLOAT`: REAL
- `DGAMMA`: GAMMA
- dialect options: Fortran Dialect Options
- `DIGITS`: DIGITS
- `DIM`: DIM
- `DIMAG`: AIMAG
- `DINT`: AINT
- directive, `INCLUDE`: Directory Options
- directory, options: Directory Options
- directory, search paths for inclusion: Directory Options
- division, modulo: MODULO
- division, remainder: MOD
- `DLGAMA`: LOG_GAMMA
- `DLOG`: LOG
- `DLOG10`: LOG10
- `DMAX1`: MAX
- `DMIN1`: MIN
- `DMOD`: MOD
- `DNINT`: ANINT
- dot product: DOT_PRODUCT
- `DOT_PRODUCT`: DOT_PRODUCT
- `DPROD`: DPROD
- `DREAL`: DREAL
- `DSHIFTL`: DSHIFTL
- `DSHIFTR`: DSHIFTR
- `DSIGN`: SIGN
- `DSIN`: SIN
- `DSINH`: SINH
- `DSQRT`: SQRT
- `DTAN`: TAN
- `DTANH`: TANH
- `DTIME`: DTIME
- dummy argument, unused: Error and Warning Options
- elapsed time: SECOND
- elapsed time: SECNDS
- elapsed time: DTIME
- Elimination of functions with identical argument lists: Code Gen Options
- `ENCODE`: ENCODE and DECODE statements
- `ENUM` statement: Fortran 2003 status
- `ENUMERATOR` statement: Fortran 2003 status
- environment variable: GET_ENVIRONMENT_VARIABLE
- environment variable: GETENV
- environment variable: Runtime
- environment variable: Environment Variables
- `EOSHIFT`: EOSHIFT
- `EPSILON`: EPSILON
- `ERF`: ERF
- `ERFC`: ERFC
- `ERFC_SCALED`: ERFC_SCALED
- error function: ERF
- error function, complementary: ERFC
- error function, complementary, exponentially-scaled: ERFC_SCALED
- errors, limiting: Error and Warning Options
- escape characters: Fortran Dialect Options
- `ETIME`: ETIME
- Euclidean distance: HYPOT
- Euclidean vector norm: NORM2
- `EXECUTE_COMMAND_LINE`: EXECUTE_COMMAND_LINE
- `EXIT`: EXIT
- `EXP`: EXP
- `EXPONENT`: EXPONENT
- exponential function: EXP
- exponential function, inverse: LOG10
- exponential function, inverse: LOG
- expression size: SIZEOF
- expression size: C_SIZEOF
- `EXTENDS_TYPE_OF`: EXTENDS_TYPE_OF
- extensions: Extensions
- extensions, implemented: Extensions implemented in GNU Fortran
- extensions, not implemented: Extensions not implemented in GNU Fortran
- extra warnings: Error and Warning Options
- `f2c` calling convention: Code Gen Options
- Factorial function: GAMMA
- `FDATE`: FDATE
- FDL, GNU Free Documentation License: GNU Free Documentation License
- `FGET`: FGET
- `FGETC`: FGETC
- file format, fixed: Fortran Dialect Options
- file format, free: Fortran Dialect Options
- file operation, file number: FNUM
- file operation, flush: FLUSH
- file operation, position: FTELL
- file operation, position: FSEEK
- file operation, read character: FGETC
- file operation, read character: FGET
- file operation, seek: FSEEK
- file operation, write character: FPUTC
- file operation, write character: FPUT
- file system, access mode: ACCESS
- file system, change access mode: CHMOD
- file system, create link: SYMLNK
- file system, create link: LINK
- file system, file creation mask: UMASK
- file system, file status: STAT
- file system, file status: LSTAT
- file system, file status: FSTAT
- file system, hard link: LINK
- file system, remove file: UNLINK
- file system, rename file: RENAME
- file system, soft link: SYMLNK
- flags inquiry function: COMPILER_OPTIONS
- `FLOAT`: REAL
- floating point, exponent: EXPONENT
- floating point, fraction: FRACTION
- floating point, nearest different: NEAREST
- floating point, relative spacing: SPACING
- floating point, relative spacing: RRSPACING
- floating point, scale: SCALE
- floating point, set exponent: SET_EXPONENT
- floor: FLOOR
- `FLOOR`: FLOOR
- floor: AINT
- `FLUSH`: FLUSH
- `FLUSH` statement: Fortran 2003 status
- `FNUM`: FNUM
- `FORMAT`: Variable FORMAT expressions
- Fortran 77: GNU Fortran and G77
- FPP: Preprocessing and conditional compilation
- `FPUT`: FPUT
- `FPUTC`: FPUTC
- `FRACTION`: FRACTION
- `FREE`: FREE
- Front-end optimization: Code Gen Options
- `FSEEK`: FSEEK
- `FSTAT`: FSTAT
- `FTELL`: FTELL
- function elimination: Error and Warning Options
- `g77`: GNU Fortran and G77
- `g77` calling convention: Code Gen Options
- `GAMMA`: GAMMA
- Gamma function: GAMMA
- Gamma function, logarithm of: LOG_GAMMA
- GCC: GNU Fortran and GCC
- `GERROR`: GERROR
- `GET_COMMAND`: GET_COMMAND
- `GET_COMMAND_ARGUMENT`: GET_COMMAND_ARGUMENT
- `GET_ENVIRONMENT_VARIABLE`: GET_ENVIRONMENT_VARIABLE
- `GETARG`: GETARG
- `GETCWD`: GETCWD
- `GETENV`: GETENV
- `GETGID`: GETGID
- `GETLOG`: GETLOG
- `GETPID`: GETPID
- `GETUID`: GETUID
- `GMTIME`: GMTIME
- GNU Compiler Collection: GNU Fortran and GCC
- GNU Fortran command options: Invoking GNU Fortran
- Hollerith constants: Hollerith constants support
- `HOSTNM`: HOSTNM
- `HUGE`: HUGE
- hyperbolic cosine: COSH
- hyperbolic function, cosine: COSH
- hyperbolic function, cosine, inverse: ACOSH
- hyperbolic function, sine: SINH
- hyperbolic function, sine, inverse: ASINH
- hyperbolic function, tangent: TANH
- hyperbolic function, tangent, inverse: ATANH
- hyperbolic sine: SINH
- hyperbolic tangent: TANH
- `HYPOT`: HYPOT
- I/O item lists: I/O item lists
- `IABS`: ABS
- `IACHAR`: IACHAR
- `IALL`: IALL
- `IAND`: IAND
- `IANY`: IANY
- `IARGC`: IARGC
- `IBCLR`: IBCLR
- `IBITS`: IBITS
- `IBSET`: IBSET
- `ICHAR`: ICHAR
- `IDATE`: IDATE
- `IDIM`: DIM
- `IDINT`: INT
- `IDNINT`: NINT
- IEEE, ISNAN: ISNAN
- `IEOR`: IEOR
- `IERRNO`: IERRNO
- `IFIX`: INT
- `IMAG`: AIMAG
- `IMAGE_INDEX`: IMAGE_INDEX
- images, cosubscript to image index conversion: IMAGE_INDEX
- images, index of this image: THIS_IMAGE
- images, number of: NUM_IMAGES
- `IMAGPART`: AIMAG
- `IMPORT` statement: Fortran 2003 status
- `INCLUDE` directive: Directory Options
- inclusion, directory search paths for: Directory Options
- `INDEX`: INDEX intrinsic
- `INT`: INT
- `INT2`: INT2
- `INT8`: INT8
- integer kind: SELECTED_INT_KIND
- Interoperability: Mixed-Language Programming
- intrinsic: Error and Warning Options
- intrinsic Modules: Intrinsic Modules
- intrinsic procedures: Intrinsic Procedures
- Introduction: Top
- inverse hyperbolic cosine: ACOSH
- inverse hyperbolic sine: ASINH
- inverse hyperbolic tangent: ATANH
- `IOMSG=` specifier: Fortran 2003 status
- `IOR`: IOR
- `IOSTAT`, end of file: IS_IOSTAT_END
- `IOSTAT`, end of record: IS_IOSTAT_EOR
- `IPARITY`: IPARITY
- `IRAND`: IRAND
- `IS_IOSTAT_END`: IS_IOSTAT_END
- `IS_IOSTAT_EOR`: IS_IOSTAT_EOR
- `ISATTY`: ISATTY
- `ISHFT`: ISHFT
- `ISHFTC`: ISHFTC
- `ISIGN`: SIGN
- `ISNAN`: ISNAN
- `ISO_FORTRAN_ENV` statement: Fortran 2003 status
- `ITIME`: ITIME
- `KILL`: KILL
- kind: KIND
- `KIND`: KIND
- kind: KIND Type Parameters
- kind, character: SELECTED_CHAR_KIND
- kind, integer: SELECTED_INT_KIND
- kind, old-style: Old-style kind specifications
- kind, real: SELECTED_REAL_KIND
- L2 vector norm: NORM2
- language, dialect options: Fortran Dialect Options
- `LBOUND`: LBOUND
- `LCOBOUND`: LCOBOUND
- `LEADZ`: LEADZ
- left shift, combined: DSHIFTL
- `LEN`: LEN
- `LEN_TRIM`: LEN_TRIM
- lexical comparison of strings: LLT
- lexical comparison of strings: LLE
- lexical comparison of strings: LGT
- lexical comparison of strings: LGE
- `LGAMMA`: LOG_GAMMA
- `LGE`: LGE
- `LGT`: LGT
- libf2c calling convention: Code Gen Options
- libgfortran initialization, set_args: _gfortran_set_args
- libgfortran initialization, set_convert: _gfortran_set_convert
- libgfortran initialization, set_fpe: _gfortran_set_fpe
- libgfortran initialization, set_max_subrecord_length: _gfortran_set_max_subrecord_length
- libgfortran initialization, set_options: _gfortran_set_options
- libgfortran initialization, set_record_marker: _gfortran_set_record_marker
- limits, largest number: HUGE
- limits, smallest number: TINY
- `LINK`: LINK
- linking, static: Link Options
- `LLE`: LLE
- `LLT`: LLT
- `LNBLNK`: LNBLNK
- `LOC`: LOC
- location of a variable in memory: LOC
- `LOG`: LOG
- `LOG10`: LOG10
- `LOG_GAMMA`: LOG_GAMMA
- logarithm function: LOG
- logarithm function with base 10: LOG10
- logarithm function, inverse: EXP
- `LOGICAL`: LOGICAL
- logical and, bitwise: IAND
- logical and, bitwise: AND
- logical exclusive or, bitwise: XOR
- logical exclusive or, bitwise: IEOR
- logical not, bitwise: NOT
- logical or, bitwise: OR
- logical or, bitwise: IOR
- logical, variable representation: Internal representation of LOGICAL variables
- login name: GETLOG
- `LONG`: LONG
- `LSHIFT`: LSHIFT
- `LSTAT`: LSTAT
- `LTIME`: LTIME
- `MALLOC`: MALLOC
- mask, left justified: MASKL
- mask, right justified: MASKR
- `MASKL`: MASKL
- `MASKR`: MASKR
- `MATMUL`: MATMUL
- matrix multiplication: MATMUL
- matrix, transpose: TRANSPOSE
- `MAX`: MAX
- `MAX0`: MAX
- `MAX1`: MAX
- `MAXEXPONENT`: MAXEXPONENT
- maximum value: MAXVAL
- maximum value: MAX
- `MAXLOC`: MAXLOC
- `MAXVAL`: MAXVAL
- `MCLOCK`: MCLOCK
- `MCLOCK8`: MCLOCK8
- memory checking: Code Gen Options
- `MERGE`: MERGE
- `MERGE_BITS`: MERGE_BITS
- messages, error: Error and Warning Options
- messages, warning: Error and Warning Options
- `MIN`: MIN
- `MIN0`: MIN
- `MIN1`: MIN
- `MINEXPONENT`: MINEXPONENT
- minimum value: MINVAL
- minimum value: MIN
- `MINLOC`: MINLOC
- `MINVAL`: MINVAL
- Mixed-language programming: Mixed-Language Programming
- `MOD`: MOD
- model representation, base: RADIX
- model representation, epsilon: EPSILON
- model representation, largest number: HUGE
- model representation, maximum exponent: MAXEXPONENT
- model representation, minimum exponent: MINEXPONENT
- model representation, precision: PRECISION
- model representation, radix: RADIX
- model representation, range: RANGE
- model representation, significant digits: DIGITS
- model representation, smallest number: TINY
- module entities: Fortran Dialect Options
- module search path: Directory Options
- modulo: MODULO
- `MODULO`: MODULO
- `MOVE_ALLOC`: MOVE_ALLOC
- moving allocation: MOVE_ALLOC
- multiply array elements: PRODUCT
- `MVBITS`: MVBITS
- Namelist: Extensions to namelist
- natural logarithm function: LOG
- `NEAREST`: NEAREST
- `NEW_LINE`: NEW_LINE
- newline: NEW_LINE
- `NINT`: NINT
- norm, Euclidean: NORM2
- `NORM2`: NORM2
- `NOT`: NOT
- `NULL`: NULL
- `NUM_IMAGES`: NUM_IMAGES
- OpenMP: OpenMP
- OpenMP: Fortran Dialect Options
- operators, unary: Unary operators
- options inquiry function: COMPILER_OPTIONS
- options, code generation: Code Gen Options
- options, debugging: Debugging Options
- options, dialect: Fortran Dialect Options
- options, directory search: Directory Options
- options, errors: Error and Warning Options
- options, Fortran dialect: Fortran Dialect Options
- options, `gfortran` command: Invoking GNU Fortran
- options, linking: Link Options
- options, negative forms: Invoking GNU Fortran
- options, preprocessor: Preprocessing Options
- options, real kind type promotion: Fortran Dialect Options
- options, run-time: Code Gen Options
- options, runtime: Runtime Options
- options, warnings: Error and Warning Options
- `OR`: OR
- output, newline: NEW_LINE
- `PACK`: PACK
- parity: POPPAR
- Parity: PARITY
- `PARITY`: PARITY
- paths, search: Directory Options
- `PERROR`: PERROR
- pointer checking: Code Gen Options
- pointer, C address of pointers: C_F_PROCPOINTER
- pointer, C address of procedures: C_FUNLOC
- pointer, C association status: C_ASSOCIATED
- pointer, convert C to Fortran: C_F_POINTER
- pointer, cray: MALLOC
- pointer, cray: FREE
- pointer, Cray: Cray pointers
- pointer, disassociated: NULL
- pointer, status: NULL
- pointer, status: ASSOCIATED
- `POPCNT`: POPCNT
- `POPPAR`: POPPAR
- positive difference: DIM
- `PRECISION`: PRECISION
- Preprocessing: Preprocessing and conditional compilation
- preprocessing, assertion: Preprocessing Options
- preprocessing, define macros: Preprocessing Options
- preprocessing, include path: Preprocessing Options
- preprocessing, keep comments: Preprocessing Options
- preprocessing, no linemarkers: Preprocessing Options
- preprocessing, undefine macros: Preprocessing Options
- preprocessor: Preprocessing Options
- preprocessor, debugging: Preprocessing Options
- preprocessor, disable: Preprocessing Options
- preprocessor, enable: Preprocessing Options
- preprocessor, include file handling: Preprocessing and conditional compilation
- preprocessor, working directory: Preprocessing Options
- `PRESENT`: PRESENT
- private: Fortran Dialect Options
- procedure pointer, convert C to Fortran: C_LOC
- process ID: GETPID
- `PRODUCT`: PRODUCT
- product, double-precision: DPROD
- product, matrix: MATMUL
- product, vector: DOT_PRODUCT
- program termination: EXIT
- program termination, with core dump: ABORT
- `PROTECTED` statement: Fortran 2003 status
- `Q` exponent-letter: <code>Q</code> exponent-letter
- `RADIX`: RADIX
- radix, real: SELECTED_REAL_KIND
- `RAN`: RAN
- `RAND`: RAND
- random number generation: RANDOM_NUMBER
- random number generation: RAND
- random number generation: RAN
- random number generation: IRAND
- random number generation, seeding: SRAND
- random number generation, seeding: RANDOM_SEED
- `RANDOM_NUMBER`: RANDOM_NUMBER
- `RANDOM_SEED`: RANDOM_SEED
- `RANGE`: RANGE
- range checking: Code Gen Options
- rank: RANK
- `RANK`: RANK
- re-association of parenthesized expressions: Code Gen Options
- read character, stream mode: FGETC
- read character, stream mode: FGET
- `REAL`: REAL
- real kind: SELECTED_REAL_KIND
- real number, exponent: EXPONENT
- real number, fraction: FRACTION
- real number, nearest different: NEAREST
- real number, relative spacing: SPACING
- real number, relative spacing: RRSPACING
- real number, scale: SCALE
- real number, set exponent: SET_EXPONENT
- Reallocate the LHS in assignments: Code Gen Options
- Reallocate the LHS in assignments, notification: Error and Warning Options
- `REALPART`: REAL
- `RECORD`: STRUCTURE and RECORD
- Reduction, XOR: PARITY
- remainder: MOD
- `RENAME`: RENAME
- repacking arrays: Code Gen Options
- `REPEAT`: REPEAT
- `RESHAPE`: RESHAPE
- right shift, combined: DSHIFTR
- root: SQRT
- rounding, ceiling: CEILING
- rounding, ceiling: ANINT
- rounding, floor: FLOOR
- rounding, floor: AINT
- rounding, nearest whole number: NINT
- `RRSPACING`: RRSPACING
- `RSHIFT`: RSHIFT
- run-time checking: Code Gen Options
- `SAME_TYPE_AS`: SAME_TYPE_AS
- `SAVE` statement: Code Gen Options
- `SCALE`: SCALE
- `SCAN`: SCAN
- search path: Directory Options
- search paths, for included files: Directory Options
- `SECNDS`: SECNDS
- `SECOND`: SECOND
- seeding a random number generator: SRAND
- seeding a random number generator: RANDOM_SEED
- `SELECTED_CHAR_KIND`: SELECTED_CHAR_KIND
- `SELECTED_INT_KIND`: SELECTED_INT_KIND
- `SELECTED_REAL_KIND`: SELECTED_REAL_KIND
- `SET_EXPONENT`: SET_EXPONENT
- `SHAPE`: SHAPE
- shift, left: SHIFTL
- shift, left: DSHIFTL
- shift, right: SHIFTR
- shift, right: DSHIFTR
- shift, right with fill: SHIFTA
- `SHIFTA`: SHIFTA
- `SHIFTL`: SHIFTL
- `SHIFTR`: SHIFTR
- `SHORT`: INT2
- `SIGN`: SIGN
- sign copying: SIGN
- `SIGNAL`: SIGNAL
- `SIN`: SIN
- sine: SIN
- sine, hyperbolic: SINH
- sine, hyperbolic, inverse: ASINH
- sine, inverse: ASIN
- `SINH`: SINH
- `SIZE`: SIZE
- size of a variable, in bits: BIT_SIZE
- size of an expression: SIZEOF
- size of an expression: C_SIZEOF
- `SIZEOF`: SIZEOF
- `SLEEP`: SLEEP
- `SNGL`: REAL
- `SPACING`: SPACING
- `SPREAD`: SPREAD
- `SQRT`: SQRT
- square-root: SQRT
- `SRAND`: SRAND
- Standards: Standards
- `STAT`: STAT
- statement, `ENUM`: Fortran 2003 status
- statement, `ENUMERATOR`: Fortran 2003 status
- statement, `FLUSH`: Fortran 2003 status
- statement, `IMPORT`: Fortran 2003 status
- statement, `ISO_FORTRAN_ENV`: Fortran 2003 status
- statement, `PROTECTED`: Fortran 2003 status
- statement, `SAVE`: Code Gen Options
- statement, `USE, INTRINSIC`: Fortran 2003 status
- statement, `VALUE`: Fortran 2003 status
- statement, `VOLATILE`: Fortran 2003 status
- storage size: STORAGE_SIZE
- `STORAGE_SIZE`: STORAGE_SIZE
- `STREAM` I/O: Fortran 2003 status
- stream mode, read character: FGETC
- stream mode, read character: FGET
- stream mode, write character: FPUTC
- stream mode, write character: FPUT
- string, adjust left: ADJUSTL
- string, adjust right: ADJUSTR
- string, comparison: LLT
- string, comparison: LLE
- string, comparison: LGT
- string, comparison: LGE
- string, concatenate: REPEAT
- string, find missing set: VERIFY
- string, find non-blank character: LNBLNK
- string, find subset: SCAN
- string, find substring: INDEX intrinsic
- string, length: LEN
- string, length, without trailing whitespace: LEN_TRIM
- string, remove trailing whitespace: TRIM
- string, repeat: REPEAT
- strings, varying length: Varying Length Character Strings
- `STRUCTURE`: STRUCTURE and RECORD
- structure packing: Code Gen Options
- subscript checking: Code Gen Options
- substring position: INDEX intrinsic
- `SUM`: SUM
- sum array elements: SUM
- suppressing warnings: Error and Warning Options
- symbol names: Fortran Dialect Options
- symbol names, transforming: Code Gen Options
- symbol names, underscores: Code Gen Options
- `SYMLNK`: SYMLNK
- syntax checking: Error and Warning Options
- `SYSTEM`: SYSTEM
- system, error handling: PERROR
- system, error handling: IERRNO
- system, error handling: GERROR
- system, group ID: GETGID
- system, host name: HOSTNM
- system, login name: GETLOG
- system, process ID: GETPID
- system, signal handling: SIGNAL
- system, system call: SYSTEM
- system, system call: EXECUTE_COMMAND_LINE
- system, terminal: TTYNAM
- system, terminal: ISATTY
- system, user ID: GETUID
- system, working directory: GETCWD
- system, working directory: CHDIR
- `SYSTEM_CLOCK`: SYSTEM_CLOCK
- tabulators: Error and Warning Options
- `TAN`: TAN
- tangent: TAN
- tangent, hyperbolic: TANH
- tangent, hyperbolic, inverse: ATANH
- tangent, inverse: ATAN2
- tangent, inverse: ATAN
- `TANH`: TANH
- terminate program: EXIT
- terminate program, with core dump: ABORT
- `THIS_IMAGE`: THIS_IMAGE
- thread-safety, threads: Thread-safety of the runtime library
- `TIME`: TIME
- time, clock ticks: SYSTEM_CLOCK
- time, clock ticks: MCLOCK8
- time, clock ticks: MCLOCK
- time, conversion to GMT info: GMTIME
- time, conversion to local time info: LTIME
- time, conversion to string: CTIME
- time, current: TIME8
- time, current: TIME
- time, current: ITIME
- time, current: FDATE
- time, current: DATE_AND_TIME
- time, elapsed: SECOND
- time, elapsed: SECNDS
- time, elapsed: ETIME
- time, elapsed: DTIME
- time, elapsed: CPU_TIME
- `TIME8`: TIME8
- `TINY`: TINY
- TR 15581: Fortran 2003 status
- trace: Debugging Options
- `TRAILZ`: TRAILZ
- `TRANSFER`: TRANSFER
- transforming symbol names: Code Gen Options
- transpose: TRANSPOSE
- `TRANSPOSE`: TRANSPOSE
- trigonometric function, cosine: COS
- trigonometric function, cosine, inverse: ACOS
- trigonometric function, sine: SIN
- trigonometric function, sine, inverse: ASIN
- trigonometric function, tangent: TAN
- trigonometric function, tangent, inverse: ATAN2
- trigonometric function, tangent, inverse: ATAN
- `TRIM`: TRIM
- `TTYNAM`: TTYNAM
- type cast: TRANSFER
- `UBOUND`: UBOUND
- `UCOBOUND`: UCOBOUND
- `UMASK`: UMASK
- underflow: Error and Warning Options
- underscore: Code Gen Options
- `UNLINK`: UNLINK
- `UNPACK`: UNPACK
- unused dummy argument: Error and Warning Options
- unused parameter: Error and Warning Options
- `USE, INTRINSIC` statement: Fortran 2003 status
- user id: GETUID
- `VALUE` statement: Fortran 2003 status
- Varying length character strings: Varying Length Character Strings
- Varying length strings: Varying Length Character Strings
- vector product: DOT_PRODUCT
- `VERIFY`: VERIFY
- version of the compiler: COMPILER_VERSION
- `VOLATILE`: Volatile COMMON blocks
- `VOLATILE` statement: Fortran 2003 status
- warning, C binding type: Error and Warning Options
- warnings, aliasing: Error and Warning Options
- warnings, alignment of `COMMON` blocks: Error and Warning Options
- warnings, all: Error and Warning Options
- warnings, ampersand: Error and Warning Options
- warnings, array temporaries: Error and Warning Options
- warnings, character truncation: Error and Warning Options
- warnings, conversion: Error and Warning Options
- warnings, extra: Error and Warning Options
- warnings, function elimination: Error and Warning Options
- warnings, implicit interface: Error and Warning Options
- warnings, implicit procedure: Error and Warning Options
- warnings, intrinsic: Error and Warning Options
- warnings, intrinsics of other standards: Error and Warning Options
- warnings, line truncation: Error and Warning Options
- warnings, non-standard intrinsics: Error and Warning Options
- warnings, `q` exponent-letter: Error and Warning Options
- warnings, suppressing: Error and Warning Options
- warnings, suspicious code: Error and Warning Options
- warnings, tabs: Error and Warning Options
- warnings, to errors: Error and Warning Options
- warnings, underflow: Error and Warning Options
- warnings, unused dummy argument: Error and Warning Options
- warnings, unused parameter: Error and Warning Options
- write character, stream mode: FPUTC
- write character, stream mode: FPUT
- `XOR`: XOR
- XOR reduction: PARITY
- `ZABS`: ABS
- `ZCOS`: COS
- zero bits: TRAILZ
- zero bits: LEADZ
- `ZEXP`: EXP
- `ZLOG`: LOG
- `ZSIN`: SIN
- `ZSQRT`: SQRT