Node:Top, Next:Introduction, Previous:(dir), Up:(dir)

- Introduction:

- Functional Categories: All public symbols listed by category

- Alphabetical List: All public symbols in alphabetical order

- Unimplemented: Compatibility functions that either always fail or do nothing

- Master Index:

Node:Introduction, Next:Functional Categories, Previous:Top, Up:Top

# Introduction

The standard C library, `libc.a`, is automatically linked into your programs by the `gcc` control program. It provides many of the functions that are normally associated with C programs. This document gives the proper usage information about each of the functions and variables found in `libc.a`.

For each function or variable that the library provides, the definition of that symbol will include information on which header files to include in your source to obtain prototypes and type definitions relevant to the use of that symbol.

Note that many of the functions in `libm.a` (the math library) are defined in `math.h` but are not present in libc.a. Some are, which may get confusing, but the rule of thumb is this--the C library contains those functions that ANSI dictates must exist, so that you don't need the `-lm` if you only use ANSI functions. In contrast, `libm.a` contains more functions and supports additional functionality such as the `matherr` call-back and compliance to several alternative standards of behavior in case of FP errors. See libm, for more details.

Debugging support functions are in the library `libdbg.a`; link your program with `-ldbg` to use them.

Node:Functional Categories, Next:Alphabetical List, Previous:Introduction, Up:Top

# Functional Categories

- bios functions:
- conio functions:
- cpu functions:
- ctype functions:
- debugging functions:
- dos functions:
- dpmi functions:
- environment functions:
- file system functions:
- go32 functions:
- io functions:
- locale functions:
- math functions:
- memory functions:
- misc functions:
- mono functions:
- posix functions:
- process functions:
- random number functions:
- shell functions:
- signal functions:
- sound functions:
- startup functions:
- stdio functions:
- string functions:
- termios functions:
- time functions:
- unix functions:

Node:bios functions, Next:conio functions, Up:Functional Categories

## bios functions

- _bios_disk:
- _bios_equiplist:
- _bios_keybrd:
- _bios_memsize:
- _bios_printer:
- _bios_serialcom:
- _bios_timeofday:
- bioscom:
- biosdisk:
- biosequip:
- bioskey:
- biosmemory:
- biosprint:
- biostime:
- getkey:
- getxkey:
- kbhit:

Node:conio functions, Next:cpu functions, Previous:bios functions, Up:Functional Categories

## conio functions

- blinkvideo:
- cgets:
- clreol:
- clrscr:
- _conio_kbhit:
- cprintf:
- cputs:
- cscanf:
- delline:
- getch:
- getche:
- gettext:
- gettextinfo:
- gotoxy:
- gppconio_init:
- highvideo:
- insline:
- intensevideo:
- lowvideo:
- movetext:
- normvideo:
- putch:
- puttext:
- Screen Variables:
- ScreenClear:
- ScreenCols:
- ScreenGetChar:
- ScreenGetCursor:
- ScreenMode:
- ScreenPutChar:
- ScreenPutString:
- ScreenRetrieve:
- ScreenRows:
- ScreenSetCursor:
- ScreenUpdate:
- ScreenUpdateLine:
- ScreenVisualBell:
- _set_screen_lines:
- _setcursortype:
- textattr:
- textbackground:
- textcolor:
- textmode:
- ungetch:
- wherex:
- wherey:
- window:

Node:cpu functions, Next:ctype functions, Previous:conio functions, Up:Functional Categories

## cpu functions

- _8087:
- _clear87:
- _control87:
- _detect_80387:
- disable:
- enable:
- _fpreset:
- htonl:
- htons:
- inb:
- inp:
- inportb:
- inportl:
- inportsb:
- inportsl:
- inportsw:
- inportw:
- inpw:
- _my_cs:
- _my_ds:
- _my_ss:
- ntohl:
- ntohs:
- outb:
- outp:
- outportb:
- outportl:
- outportsb:
- outportsl:
- outportsw:
- outportw:
- outpw:
- _status87:

Node:ctype functions, Next:debugging functions, Previous:cpu functions, Up:Functional Categories

## ctype functions

- isalnum:
- isalpha:
- isascii:
- iscntrl:
- isdigit:
- isgraph:
- islower:
- isprint:
- ispunct:
- isspace:
- isupper:
- isxdigit:
- toascii:
- tolower:
- toupper:

Node:debugging functions, Next:dos functions, Previous:ctype functions, Up:Functional Categories

## debugging functions

- cleanup_client:
- edi_init:
- load_npx:
- read_child:
- read_sel_addr:
- redir_cmdline_delete:
- redir_cmdline_parse:
- redir_debug_init:
- redir_to_child:
- redir_to_debugger:
- run_child:
- save_npx:
- syms_init:
- syms_line2val:
- syms_listwild:
- syms_module:
- syms_name2val:
- syms_val2line:
- syms_val2name:
- v2loadimage:
- wild:
- write_child:
- write_sel_addr:

Node:dos functions, Next:dpmi functions, Previous:debugging functions, Up:Functional Categories

## dos functions

- bdos:
- bdosptr:
- delay:
- _dos_close:
- _dos_commit:
- _dos_creat:
- _dos_creatnew:
- _dos_findfirst:
- _dos_findnext:
- _dos_getdate:
- _dos_getdiskfree:
- _dos_getdrive:
- _dos_getfileattr:
- _dos_getftime:
- _dos_gettime:
- _dos_lock:
- _dos_open:
- _dos_read:
- _dos_setdate:
- _dos_setdrive:
- _dos_setfileattr:
- _dos_setftime:
- _dos_settime:
- _dos_unlock:
- _dos_write:
- _doserrno:
- dosexterr:
- _flush_disk_cache:
- getcbrk:
- getdisk:
- int386:
- int386x:
- int86:
- int86x:
- intdos:
- intdosx:
- setcbrk:
- setdisk:

Node:dpmi functions, Next:environment functions, Previous:dos functions, Up:Functional Categories

## dpmi functions

- DPMI Overview:
- DPMI Specification:
- __dpmi_allocate_dos_memory:
- __dpmi_allocate_ldt_descriptors:
- __dpmi_allocate_linear_memory:
- __dpmi_allocate_memory:
- __dpmi_allocate_real_mode_callback:
- __dpmi_allocate_shared_memory:
- __dpmi_allocate_specific_ldt_descriptor:
- __dpmi_clear_debug_watchpoint:
- __dpmi_create_alias_descriptor:
- __dpmi_discard_page_contents:
- __dpmi_free_dos_memory:
- __dpmi_free_ldt_descriptor:
- __dpmi_free_memory:
- __dpmi_free_physical_address_mapping:
- __dpmi_free_real_mode_callback:
- __dpmi_free_serialization_on_shared_memory:
- __dpmi_free_shared_memory:
- __dpmi_get_and_disable_virtual_interrupt_state:
- __dpmi_get_and_enable_virtual_interrupt_state:
- __dpmi_get_and_set_virtual_interrupt_state:
- __dpmi_get_capabilities:
- __dpmi_get_coprocessor_status:
- __dpmi_get_descriptor:
- __dpmi_get_descriptor_access_rights:
- __dpmi_get_extended_exception_handler_vector_pm:
- __dpmi_get_extended_exception_handler_vector_rm:
- __dpmi_get_free_memory_information:
- __dpmi_get_memory_block_size_and_base:
- __dpmi_get_memory_information:
- __dpmi_get_multiple_descriptors:
- __dpmi_get_page_attributes:
- __dpmi_get_page_size:
- __dpmi_get_processor_exception_handler_vector:
- __dpmi_get_protected_mode_interrupt_vector:
- __dpmi_get_raw_mode_switch_addr:
- __dpmi_get_real_mode_interrupt_vector:
- __dpmi_get_segment_base_address:
- __dpmi_get_segment_limit:
- __dpmi_get_selector_increment_value:
- __dpmi_get_state_of_debug_watchpoint:
- __dpmi_get_state_save_restore_addr:
- __dpmi_get_vendor_specific_api_entry_point:
- __dpmi_get_version:
- __dpmi_get_virtual_interrupt_state:
- __dpmi_install_resident_service_provider_callback:
- __dpmi_int:
- __dpmi_lock_linear_region:
- __dpmi_map_conventional_memory_in_memory_block:
- __dpmi_map_device_in_memory_block:
- __dpmi_mark_page_as_demand_paging_candidate:
- __dpmi_mark_real_mode_region_as_pageable:
- __dpmi_physical_address_mapping:
- __dpmi_relock_real_mode_region:
- __dpmi_reset_debug_watchpoint:
- __dpmi_resize_dos_memory:
- __dpmi_resize_linear_memory:
- __dpmi_resize_memory:
- __dpmi_segment_to_descriptor:
- __dpmi_serialize_on_shared_memory:
- __dpmi_set_coprocessor_emulation:
- __dpmi_set_debug_watchpoint:
- __dpmi_set_descriptor:
- __dpmi_set_descriptor_access_rights:
- __dpmi_set_extended_exception_handler_vector_pm:
- __dpmi_set_extended_exception_handler_vector_rm:
- __dpmi_set_multiple_descriptors:
- __dpmi_set_page_attributes:
- __dpmi_set_processor_exception_handler_vector:
- __dpmi_set_protected_mode_interrupt_vector:
- __dpmi_set_real_mode_interrupt_vector:
- __dpmi_set_segment_base_address:
- __dpmi_set_segment_limit:
- __dpmi_simulate_real_mode_interrupt:
- __dpmi_simulate_real_mode_procedure_iret:
- __dpmi_simulate_real_mode_procedure_retf:
- __dpmi_simulate_real_mode_procedure_retf_stack:
- __dpmi_terminate_and_stay_resident:
- __dpmi_unlock_linear_region:
- __dpmi_yield:
- _go32_dpmi_allocate_dos_memory:
- _go32_dpmi_allocate_iret_wrapper:
- _go32_dpmi_allocate_real_mode_callback_iret:
- _go32_dpmi_allocate_real_mode_callback_retf:
- _go32_dpmi_chain_protected_mode_interrupt_vector:
- _go32_dpmi_free_dos_memory:
- _go32_dpmi_free_iret_wrapper:
- _go32_dpmi_free_real_mode_callback:
- _go32_dpmi_get_free_memory_information:
- _go32_dpmi_get_protected_mode_interrupt_vector:
- _go32_dpmi_get_real_mode_interrupt_vector:
- _go32_dpmi_remaining_physical_memory:
- _go32_dpmi_remaining_virtual_memory:
- _go32_dpmi_resize_dos_memory:
- _go32_dpmi_set_protected_mode_interrupt_vector:
- _go32_dpmi_set_real_mode_interrupt_vector:
- _go32_dpmi_simulate_fcall:
- _go32_dpmi_simulate_fcall_iret:
- _go32_dpmi_simulate_int:
- _go32_info_block:

Node:environment functions, Next:file system functions, Previous:dpmi functions, Up:Functional Categories

## environment functions

- getenv:
- putenv:
- setenv:

Node:file system functions, Next:go32 functions, Previous:environment functions, Up:Functional Categories

## file system functions

- access:
- basename:
- chdir:
- chmod:
- _chmod:
- _close:
- closedir:
- _creat:
- _creatnew:
- dirname:
- File System Extensions:
- __file_tree_walk:
- findfirst:
- findnext:
- _fixpath:
- fnmatch:
- fnmerge:
- fnsplit:
- fpathconf:
- __FSEXT_add_open_handler:
- __FSEXT_alloc_fd:
- __FSEXT_call_open_handlers:
- __FSEXT_get_data:
- __FSEXT_get_function:
- __FSEXT_set_data:
- __FSEXT_set_function:
- ftw:
- _get_volume_info:
- getcwd:
- getdfree:
- getftime:
- getwd:
- _invent_inode:
- _lfn_gen_short_fname:
- _lfn_get_ftime:
- mkdir:
- mkstemp:
- mktemp:
- _open:
- opendir:
- _preserve_fncase:
- _read:
- readdir:
- remove:
- _rename:
- rename:
- rewinddir:
- rmdir:
- searchpath:
- seekdir:
- setftime:
- statfs:
- telldir:
- tempnam:
- umask:
- unlink:
- _use_lfn:
- utime:
- _write:

Node:go32 functions, Next:io functions, Previous:file system functions, Up:Functional Categories

## go32 functions

- _go32_conventional_mem_selector:
- _go32_dpmi_lock_code:
- _go32_dpmi_lock_data:
- _go32_interrupt_stack_size:
- _go32_my_cs:
- _go32_my_ds:
- _go32_my_ss:
- _go32_rmcb_stack_size:
- _go32_want_ctrl_break:
- _go32_was_ctrl_break_hit:

Node:io functions, Next:locale functions, Previous:go32 functions, Up:Functional Categories

## io functions

- chsize:
- close:
- creat:
- crlf2nl:
- __djgpp_share_flags:
- dup:
- dup2:
- fcntl:
- __file_exists:
- filelength:
- _get_dev_info:
- ioctl (DOS):
- ioctl (General description):
- ioctl (UNIX):
- _is_executable:
- _is_remote_drive:
- _is_remote_handle:
- link:
- lock:
- lseek:
- open:
- _put_path:
- read:
- setmode:
- stat:
- symlink:
- tell:
- truncate:
- unlock:
- write:

Node:locale functions, Next:math functions, Previous:io functions, Up:Functional Categories

## locale functions

- localeconv:
- mblen:
- mbstowcs:
- mbtowc:
- setlocale:
- strcoll:
- strxfrm:
- wcstombs:
- wctomb:

Node:math functions, Next:memory functions, Previous:locale functions, Up:Functional Categories

## math functions

- abs:
- acos:
- acosh:
- asin:
- asinh:
- atan:
- atan2:
- atanh:
- cbrt:
- ceil:
- cos:
- cosh:
- div:
- exp:
- exp10:
- exp2:
- expm1:
- fabs:
- floor:
- fmod:
- frexp:
- hypot:
- ldexp:
- ldiv:
- libm:
- lldiv:
- log:
- log10:
- log1p:
- log2:
- matherr:
- modf:
- modfl:
- pow:
- pow10:
- pow2:
- powi:
- sin:
- sincos:
- sinh:
- sqrt:
- tan:
- tanh:

Node:memory functions, Next:misc functions, Previous:math functions, Up:Functional Categories

## memory functions

- alloca:
- bcmp:
- bcopy:
- brk:
- bzero:
- calloc:
- cfree:
- __djgpp_map_physical_memory:
- __djgpp_memory_handle:
- __djgpp_memory_handle_list:
- __djgpp_nearptr_disable:
- __djgpp_nearptr_enable:
- __djgpp_set_page_attributes:
- dosmemget:
- dosmemgetb:
- dosmemgetl:
- dosmemgetw:
- dosmemput:
- dosmemputb:
- dosmemputl:
- dosmemputw:
- _far*:
- free:
- malloc:
- memccpy:
- memchr:
- memcmp:
- memcpy:
- memicmp:
- memmove:
- memset:
- movedata:
- movedatab:
- movedatal:
- movedataw:
- mprotect:
- realloc:
- sbrk:
- stackavail:
- swab:
- xfree:
- xmalloc:
- xrealloc:

Node:misc functions, Next:mono functions, Previous:memory functions, Up:Functional Categories

## misc functions

- assert:
- bsearch:
- _dxe_load:
- _get_dos_version:
- gethostname:
- getlongpass:
- getopt:
- getpagesize:
- getpass:
- insque:
- labs:
- llabs:
- longjmp:
- qsort:
- remque:
- setjmp:
- siglongjmp:
- sigsetjmp:
- varargs:

Node:mono functions, Next:posix functions, Previous:misc functions, Up:Functional Categories

## mono functions

- _mono_clear:
- _mono_printf:
- _mono_putc:

Node:posix functions, Next:process functions, Previous:mono functions, Up:Functional Categories

## posix functions

- ctermid:
- getdtablesize:
- pathconf:
- sysconf:

Node:process functions, Next:random number functions, Previous:posix functions, Up:Functional Categories

## process functions

- abort:
- alarm:
- atexit:
- _check_v2_prog:
- exec*:
- __exit:
- _exit:
- exit:
- getitimer:
- kill:
- nice:
- pause:
- setitimer:
- sleep:
- spawn*:
- system:
- usleep:
- wait:
- waitpid:

Node:random number functions, Next:shell functions, Previous:process functions, Up:Functional Categories

## random number functions

- initstate:
- rand:
- rand48:
- random:
- setstate:
- srand:
- srandom:

Node:shell functions, Next:signal functions, Previous:random number functions, Up:Functional Categories

## shell functions

- glob:
- globfree:

Node:signal functions, Next:sound functions, Previous:shell functions, Up:Functional Categories

## signal functions

- __djgpp_exception_toggle:
- __djgpp_set_ctrl_c:
- __djgpp_set_sigint_key:
- __djgpp_set_sigquit_key:
- __djgpp_traceback_exit:
- psignal:
- raise:
- sigaction:
- sigaddset:
- sigdelset:
- sigemptyset:
- sigfillset:
- sigismember:
- signal:
- sigpending:
- sigprocmask:

Node:sound functions, Next:startup functions, Previous:signal functions, Up:Functional Categories

## sound functions

- nosound:
- sound:

Node:startup functions, Next:stdio functions, Previous:sound functions, Up:Functional Categories

## startup functions

- __crt0_glob_function:
- __crt0_load_environment_file:
- __crt0_setup_arguments:
- _crt0_startup_flags:
- _stklen:

Node:stdio functions, Next:string functions, Previous:startup functions, Up:Functional Categories

## stdio functions

- clearerr:
- _djstat_describe_lossage:
- _djstat_fail_bits:
- _djstat_flags:
- _doprnt:
- _doscan:
- errno:
- fclose:
- fdopen:
- feof:
- ferror:
- fflush:
- fgetc:
- fgetpos:
- fgets:
- fileno:
- _fmode:
- fopen:
- fprintf:
- fpurge:
- fputc:
- fputs:
- fread:
- freopen:
- fscanf:
- fseek:
- fsetpos:
- fstat:
- fsync:
- ftell:
- ftruncate:
- _fwalk:
- fwrite:
- getc:
- getchar:
- gets:
- getw:
- perror:
- printf:
- putc:
- putchar:
- puts:
- putw:
- rewind:
- scanf:
- setbuf:
- setbuffer:
- setlinebuf:
- setvbuf:
- sprintf:
- sscanf:
- strerror:
- sys_errlist:
- sys_nerr:
- tmpfile:
- tmpnam:
- _truename:
- ungetc:
- vfprintf:
- vfscanf:
- vprintf:
- vscanf:
- vsprintf:
- vsscanf:

Node:string functions, Next:termios functions, Previous:stdio functions, Up:Functional Categories

## string functions

- atof:
- atoi:
- atol:
- _atold:
- ecvt:
- ecvtbuf:
- fcvt:
- fcvtbuf:
- ffs:
- gcvt:
- index:
- itoa:
- regcomp:
- regerror:
- regexec:
- regfree:
- rindex:
- stpcpy:
- strcasecmp:
- strcat:
- strchr:
- strcmp:
- strcpy:
- strcspn:
- strdup:
- stricmp:
- strlen:
- strlwr:
- strncasecmp:
- strncat:
- strncmp:
- strncpy:
- strnicmp:
- strpbrk:
- strrchr:
- strsep:
- strspn:
- strstr:
- strtod:
- strtok:
- strtol:
- _strtold:
- strtoll:
- strtoul:
- strtoull:
- strupr:

Node:termios functions, Next:time functions, Previous:string functions, Up:Functional Categories

## termios functions

- cfgetispeed:
- cfgetospeed:
- cfmakeraw:
- cfsetispeed:
- cfsetospeed:
- cfsetspeed:
- __libc_termios_init:
- tcdrain:
- tcflow:
- tcflush:
- tcgetattr:
- tcgetpgrp:
- tcsendbreak:
- tcsetattr:
- tcsetpgrp:
- Termios functions:

Node:time functions, Next:unix functions, Previous:termios functions, Up:Functional Categories

## time functions

- asctime:
- clock:
- ctime:
- difftime:
- ftime:
- getdate:
- gettime:
- gettimeofday:
- gmtime:
- localtime:
- mktime:
- rawclock:
- setdate:
- settime:
- settimeofday:
- strftime:
- time:
- times:
- tzset:
- tzsetwall:
- uclock:
- utimes:

Node:unix functions, Previous:time functions, Up:Functional Categories

## unix functions

- addmntent:
- chown:
- endgrent:
- endmntent:
- endpwent:
- fgetgrent:
- fork:
- getegid:
- geteuid:
- getgid:
- getgrent:
- getgrgid:
- getgrnam:
- getgroups:
- getlogin:
- getmntent:
- getpgrp:
- getpid:
- getpwent:
- getpwnam:
- getpwuid:
- getrlimit:
- getrusage:
- getuid:
- hasmntopt:
- isatty:
- mkfifo:
- mknod:
- pclose:
- pipe:
- popen:
- select:
- setgid:
- setgrent:
- setmntent:
- setpgid:
- setpwent:
- setrlimit:
- setsid:
- setuid:
- sync:
- ttyname:
- uname:
- vfork:

Node:Alphabetical List, Next:Unimplemented, Previous:Functional Categories, Up:Top

# Alphabetical List

- _8087:
- abort:
- abs:
- access:
- acos:
- acosh:
- addmntent:
- alarm:
- alloca:
- asctime:
- asin:
- asinh:
- assert:
- atan:
- atan2:
- atanh:
- atexit:
- atof:
- atoi:
- atol:
- _atold:
- basename:
- bcmp:
- bcopy:
- bdos:
- bdosptr:
- _bios_disk:
- _bios_equiplist:
- _bios_keybrd:
- _bios_memsize:
- _bios_printer:
- _bios_serialcom:
- _bios_timeofday:
- bioscom:
- biosdisk:
- biosequip:
- bioskey:
- biosmemory:
- biosprint:
- biostime:
- blinkvideo:
- brk:
- bsearch:
- bzero:
- calloc:
- cbrt:
- ceil:
- cfgetispeed:
- cfgetospeed:
- cfmakeraw:
- cfree:
- cfsetispeed:
- cfsetospeed:
- cfsetspeed:
- cgets:
- chdir:
- _check_v2_prog:
- chmod:
- _chmod:
- chown:
- chsize:
- cleanup_client:
- _clear87:
- clearerr:
- clock:
- close:
- _close:
- closedir:
- clreol:
- clrscr:
- _conio_kbhit:
- _control87:
- cos:
- cosh:
- cprintf:
- cputs:
- creat:
- _creat:
- _creatnew:
- crlf2nl:
- __crt0_glob_function:
- __crt0_load_environment_file:
- __crt0_setup_arguments:
- _crt0_startup_flags:
- cscanf:
- ctermid:
- ctime:
- delay:
- delline:
- _detect_80387:
- difftime:
- dirname:
- disable:
- div:
- __djgpp_exception_toggle:
- __djgpp_map_physical_memory:
- __djgpp_memory_handle:
- __djgpp_memory_handle_list:
- __djgpp_nearptr_disable:
- __djgpp_nearptr_enable:
- __djgpp_set_ctrl_c:
- __djgpp_set_page_attributes:
- __djgpp_set_sigint_key:
- __djgpp_set_sigquit_key:
- __djgpp_share_flags:
- __djgpp_traceback_exit:
- _djstat_describe_lossage:
- _djstat_fail_bits:
- _djstat_flags:
- _doprnt:
- _dos_close:
- _dos_commit:
- _dos_creat:
- _dos_creatnew:
- _dos_findfirst:
- _dos_findnext:
- _dos_getdate:
- _dos_getdiskfree:
- _dos_getdrive:
- _dos_getfileattr:
- _dos_getftime:
- _dos_gettime:
- _dos_lock:
- _dos_open:
- _dos_read:
- _dos_setdate:
- _dos_setdrive:
- _dos_setfileattr:
- _dos_setftime:
- _dos_settime:
- _dos_unlock:
- _dos_write:
- _doscan:
- _doserrno:
- dosexterr:
- dosmemget:
- dosmemgetb:
- dosmemgetl:
- dosmemgetw:
- dosmemput:
- dosmemputb:
- dosmemputl:
- dosmemputw:
- DPMI Overview:
- DPMI Specification:
- __dpmi_allocate_dos_memory:
- __dpmi_allocate_ldt_descriptors:
- __dpmi_allocate_linear_memory:
- __dpmi_allocate_memory:
- __dpmi_allocate_real_mode_callback:
- __dpmi_allocate_shared_memory:
- __dpmi_allocate_specific_ldt_descriptor:
- __dpmi_clear_debug_watchpoint:
- __dpmi_create_alias_descriptor:
- __dpmi_discard_page_contents:
- __dpmi_free_dos_memory:
- __dpmi_free_ldt_descriptor:
- __dpmi_free_memory:
- __dpmi_free_physical_address_mapping:
- __dpmi_free_real_mode_callback:
- __dpmi_free_serialization_on_shared_memory:
- __dpmi_free_shared_memory:
- __dpmi_get_and_disable_virtual_interrupt_state:
- __dpmi_get_and_enable_virtual_interrupt_state:
- __dpmi_get_and_set_virtual_interrupt_state:
- __dpmi_get_capabilities:
- __dpmi_get_coprocessor_status:
- __dpmi_get_descriptor:
- __dpmi_get_descriptor_access_rights:
- __dpmi_get_extended_exception_handler_vector_pm:
- __dpmi_get_extended_exception_handler_vector_rm:
- __dpmi_get_free_memory_information:
- __dpmi_get_memory_block_size_and_base:
- __dpmi_get_memory_information:
- __dpmi_get_multiple_descriptors:
- __dpmi_get_page_attributes:
- __dpmi_get_page_size:
- __dpmi_get_processor_exception_handler_vector:
- __dpmi_get_protected_mode_interrupt_vector:
- __dpmi_get_raw_mode_switch_addr:
- __dpmi_get_real_mode_interrupt_vector:
- __dpmi_get_segment_base_address:
- __dpmi_get_segment_limit:
- __dpmi_get_selector_increment_value:
- __dpmi_get_state_of_debug_watchpoint:
- __dpmi_get_state_save_restore_addr:
- __dpmi_get_vendor_specific_api_entry_point:
- __dpmi_get_version:
- __dpmi_get_virtual_interrupt_state:
- __dpmi_install_resident_service_provider_callback:
- __dpmi_int:
- __dpmi_lock_linear_region:
- __dpmi_map_conventional_memory_in_memory_block:
- __dpmi_map_device_in_memory_block:
- __dpmi_mark_page_as_demand_paging_candidate:
- __dpmi_mark_real_mode_region_as_pageable:
- __dpmi_physical_address_mapping:
- __dpmi_relock_real_mode_region:
- __dpmi_reset_debug_watchpoint:
- __dpmi_resize_dos_memory:
- __dpmi_resize_linear_memory:
- __dpmi_resize_memory:
- __dpmi_segment_to_descriptor:
- __dpmi_serialize_on_shared_memory:
- __dpmi_set_coprocessor_emulation:
- __dpmi_set_debug_watchpoint:
- __dpmi_set_descriptor:
- __dpmi_set_descriptor_access_rights:
- __dpmi_set_extended_exception_handler_vector_pm:
- __dpmi_set_extended_exception_handler_vector_rm:
- __dpmi_set_multiple_descriptors:
- __dpmi_set_page_attributes:
- __dpmi_set_processor_exception_handler_vector:
- __dpmi_set_protected_mode_interrupt_vector:
- __dpmi_set_real_mode_interrupt_vector:
- __dpmi_set_segment_base_address:
- __dpmi_set_segment_limit:
- __dpmi_simulate_real_mode_interrupt:
- __dpmi_simulate_real_mode_procedure_iret:
- __dpmi_simulate_real_mode_procedure_retf:
- __dpmi_simulate_real_mode_procedure_retf_stack:
- __dpmi_terminate_and_stay_resident:
- __dpmi_unlock_linear_region:
- __dpmi_yield:
- dup:
- dup2:
- _dxe_load:
- ecvt:
- ecvtbuf:
- edi_init:
- enable:
- endgrent:
- endmntent:
- endpwent:
- errno:
- exec*:
- __exit:
- _exit:
- exit:
- exp:
- exp10:
- exp2:
- expm1:
- fabs:
- _far*:
- fclose:
- fcntl:
- fcvt:
- fcvtbuf:
- fdopen:
- feof:
- ferror:
- fflush:
- ffs:
- fgetc:
- fgetgrent:
- fgetpos:
- fgets:
- File System Extensions:
- __file_exists:
- __file_tree_walk:
- filelength:
- fileno:
- findfirst:
- findnext:
- _fixpath:
- floor:
- _flush_disk_cache:
- fmod:
- _fmode:
- fnmatch:
- fnmerge:
- fnsplit:
- fopen:
- fork:
- fpathconf:
- _fpreset:
- fprintf:
- fpurge:
- fputc:
- fputs:
- fread:
- free:
- freopen:
- frexp:
- fscanf:
- fseek:
- fsetpos:
- __FSEXT_add_open_handler:
- __FSEXT_alloc_fd:
- __FSEXT_call_open_handlers:
- __FSEXT_get_data:
- __FSEXT_get_function:
- __FSEXT_set_data:
- __FSEXT_set_function:
- fstat:
- fsync:
- ftell:
- ftime:
- ftruncate:
- ftw:
- _fwalk:
- fwrite:
- gcvt:
- _get_dev_info:
- _get_dos_version:
- _get_volume_info:
- getc:
- getcbrk:
- getch:
- getchar:
- getche:
- getcwd:
- getdate:
- getdfree:
- getdisk:
- getdtablesize:
- getegid:
- getenv:
- geteuid:
- getftime:
- getgid:
- getgrent:
- getgrgid:
- getgrnam:
- getgroups:
- gethostname:
- getitimer:
- getkey:
- getlogin:
- getlongpass:
- getmntent:
- getopt:
- getpagesize:
- getpass:
- getpgrp:
- getpid:
- getpwent:
- getpwnam:
- getpwuid:
- getrlimit:
- getrusage:
- gets:
- gettext:
- gettextinfo:
- gettime:
- gettimeofday:
- getuid:
- getw:
- getwd:
- getxkey:
- glob:
- globfree:
- gmtime:
- _go32_conventional_mem_selector:
- _go32_dpmi_allocate_dos_memory:
- _go32_dpmi_allocate_iret_wrapper:
- _go32_dpmi_allocate_real_mode_callback_iret:
- _go32_dpmi_allocate_real_mode_callback_retf:
- _go32_dpmi_chain_protected_mode_interrupt_vector:
- _go32_dpmi_free_dos_memory:
- _go32_dpmi_free_iret_wrapper:
- _go32_dpmi_free_real_mode_callback:
- _go32_dpmi_get_free_memory_information:
- _go32_dpmi_get_protected_mode_interrupt_vector:
- _go32_dpmi_get_real_mode_interrupt_vector:
- _go32_dpmi_lock_code:
- _go32_dpmi_lock_data:
- _go32_dpmi_remaining_physical_memory:
- _go32_dpmi_remaining_virtual_memory:
- _go32_dpmi_resize_dos_memory:
- _go32_dpmi_set_protected_mode_interrupt_vector:
- _go32_dpmi_set_real_mode_interrupt_vector:
- _go32_dpmi_simulate_fcall:
- _go32_dpmi_simulate_fcall_iret:
- _go32_dpmi_simulate_int:
- _go32_info_block:
- _go32_interrupt_stack_size:
- _go32_my_cs:
- _go32_my_ds:
- _go32_my_ss:
- _go32_rmcb_stack_size:
- _go32_want_ctrl_break:
- _go32_was_ctrl_break_hit:
- gotoxy:
- gppconio_init:
- hasmntopt:
- highvideo:
- htonl:
- htons:
- hypot:
- inb:
- index:
- initstate:
- inp:
- inportb:
- inportl:
- inportsb:
- inportsl:
- inportsw:
- inportw:
- inpw:
- insline:
- insque:
- int386:
- int386x:
- int86:
- int86x:
- intdos:
- intdosx:
- intensevideo:
- _invent_inode:
- ioctl (DOS):
- ioctl (General description):
- ioctl (UNIX):
- _is_executable:
- _is_remote_drive:
- _is_remote_handle:
- isalnum:
- isalpha:
- isascii:
- isatty:
- iscntrl:
- isdigit:
- isgraph:
- islower:
- isprint:
- ispunct:
- isspace:
- isupper:
- isxdigit:
- itoa:
- kbhit:
- kill:
- labs:
- ldexp:
- ldiv:
- _lfn_gen_short_fname:
- _lfn_get_ftime:
- __libc_termios_init:
- libm:
- link:
- llabs:
- lldiv:
- load_npx:
- localeconv:
- localtime:
- lock:
- log:
- log10:
- log1p:
- log2:
- longjmp:
- lowvideo:
- lseek:
- malloc:
- matherr:
- mblen:
- mbstowcs:
- mbtowc:
- memccpy:
- memchr:
- memcmp:
- memcpy:
- memicmp:
- memmove:
- memset:
- mkdir:
- mkfifo:
- mknod:
- mkstemp:
- mktemp:
- mktime:
- modf:
- modfl:
- _mono_clear:
- _mono_printf:
- _mono_putc:
- movedata:
- movedatab:
- movedatal:
- movedataw:
- movetext:
- mprotect:
- _my_cs:
- _my_ds:
- _my_ss:
- nice:
- normvideo:
- nosound:
- ntohl:
- ntohs:
- open:
- _open:
- opendir:
- outb:
- outp:
- outportb:
- outportl:
- outportsb:
- outportsl:
- outportsw:
- outportw:
- outpw:
- pathconf:
- pause:
- pclose:
- perror:
- pipe:
- popen:
- pow:
- pow10:
- pow2:
- powi:
- _preserve_fncase:
- printf:
- psignal:
- _put_path:
- putc:
- putch:
- putchar:
- putenv:
- puts:
- puttext:
- putw:
- qsort:
- raise:
- rand:
- rand48:
- random:
- rawclock:
- read:
- _read:
- read_child:
- read_sel_addr:
- readdir:
- realloc:
- redir_cmdline_delete:
- redir_cmdline_parse:
- redir_debug_init:
- redir_to_child:
- redir_to_debugger:
- regcomp:
- regerror:
- regexec:
- regfree:
- remove:
- remque:
- _rename:
- rename:
- rewind:
- rewinddir:
- rindex:
- rmdir:
- run_child:
- save_npx:
- sbrk:
- scanf:
- Screen Variables:
- ScreenClear:
- ScreenCols:
- ScreenGetChar:
- ScreenGetCursor:
- ScreenMode:
- ScreenPutChar:
- ScreenPutString:
- ScreenRetrieve:
- ScreenRows:
- ScreenSetCursor:
- ScreenUpdate:
- ScreenUpdateLine:
- ScreenVisualBell:
- searchpath:
- seekdir:
- select:
- _set_screen_lines:
- setbuf:
- setbuffer:
- setcbrk:
- _setcursortype:
- setdate:
- setdisk:
- setenv:
- setftime:
- setgid:
- setgrent:
- setitimer:
- setjmp:
- setlinebuf:
- setlocale:
- setmntent:
- setmode:
- setpgid:
- setpwent:
- setrlimit:
- setsid:
- setstate:
- settime:
- settimeofday:
- setuid:
- setvbuf:
- sigaction:
- sigaddset:
- sigdelset:
- sigemptyset:
- sigfillset:
- sigismember:
- siglongjmp:
- signal:
- sigpending:
- sigprocmask:
- sigsetjmp:
- sin:
- sincos:
- sinh:
- sleep:
- sound:
- spawn*:
- sprintf:
- sqrt:
- srand:
- srandom:
- sscanf:
- stackavail:
- stat:
- statfs:
- _status87:
- _stklen:
- stpcpy:
- strcasecmp:
- strcat:
- strchr:
- strcmp:
- strcoll:
- strcpy:
- strcspn:
- strdup:
- strerror:
- strftime:
- stricmp:
- strlen:
- strlwr:
- strncasecmp:
- strncat:
- strncmp:
- strncpy:
- strnicmp:
- strpbrk:
- strrchr:
- strsep:
- strspn:
- strstr:
- strtod:
- strtok:
- strtol:
- _strtold:
- strtoll:
- strtoul:
- strtoull:
- strupr:
- strxfrm:
- swab:
- symlink:
- syms_init:
- syms_line2val:
- syms_listwild:
- syms_module:
- syms_name2val:
- syms_val2line:
- syms_val2name:
- sync:
- sys_errlist:
- sys_nerr:
- sysconf:
- system:
- tan:
- tanh:
- tcdrain:
- tcflow:
- tcflush:
- tcgetattr:
- tcgetpgrp:
- tcsendbreak:
- tcsetattr:
- tcsetpgrp:
- tell:
- telldir:
- tempnam:
- Termios functions:
- textattr:
- textbackground:
- textcolor:
- textmode:
- time:
- times:
- tmpfile:
- tmpnam:
- toascii:
- tolower:
- toupper:
- _truename:
- truncate:
- ttyname:
- tzset:
- tzsetwall:
- uclock:
- umask:
- uname:
- ungetc:
- ungetch:
- unlink:
- unlock:
- _use_lfn:
- usleep:
- utime:
- utimes:
- v2loadimage:
- varargs:
- vfork:
- vfprintf:
- vfscanf:
- vprintf:
- vscanf:
- vsprintf:
- vsscanf:
- wait:
- waitpid:
- wcstombs:
- wctomb:
- wherex:
- wherey:
- wild:
- window:
- write:
- _write:
- write_child:
- write_sel_addr:
- xfree:
- xmalloc:
- xrealloc:

Node:_8087, Next:abort, Up:Alphabetical List

## _8087

### Syntax

    #include <dos.h>

    extern int _8087;

### Description

This variable is provided for compatibility with other DOS compilers. It contains `3` if a numeric coprocessor is installed, otherwise `0`. If the environment variable `387` is set to either `y` or `n`, the value of `_8087` reflects the override (i.e., `_8087` is unconditionally assigned the value 3 if `387` is set to `y`, 0 if it is set to `n`).

### Portability

not ANSI, not POSIX

Node:abort, Next:abs, Previous:_8087, Up:Alphabetical List

## abort

### Syntax

    #include <stdlib.h>

    void abort(void);

### Description

When you call `abort`, the message "Abort!" is printed on stdout and the program is aborted by calling `raise (SIGABRT)` (see SIGABRT). By default, this causes the CPU registers and the call frame stack dump to be printed, and the program then exits with an exit code of -1 (255). If the `SIGABRT` signal is caught by a handler that returns, the program exits with an exit code of 1.

### Return Value

This function does not return.

### Portability

ANSI, POSIX

### Example

    if ((q = malloc(100)) == NULL)
      abort();

Node:abs, Next:access, Previous:abort, Up:Alphabetical List

## abs

### Syntax

    #include <stdlib.h>

    int abs(int value);

### Return Value

The absolute value of `value` is returned.

### Portability

ANSI, POSIX

### Example

    int sq = 7;
    sq = sq * abs(sq) + 1;

Node:access, Next:acos, Previous:abs, Up:Alphabetical List

## access

### Syntax

    #include <unistd.h>

    int access(const char *filename, int flags);

### Description

This function determines what kind of access modes a given file allows. The parameter flags is the logical `or` of one or more of the following flags:

`R_OK`
  Request if the file is readable. Since all files are readable under MS-DOS, this access mode always exists.
`W_OK`
  Request if the file is writable.
`X_OK`
  Request if the file is executable.
`F_OK`
  Request if the file exists.
`D_OK`
  Request if the file is really a directory.

### Return Value

Zero if the requested access mode is allowed, nonzero if not.

### Portability

not ANSI, POSIX

### Example

    if (access("file.ext", W_OK))
      return ERROR_CANNOT_WRITE;
    open("file.ext", O_RDWR);

Node:acos, Next:acosh, Previous:access, Up:Alphabetical List

## acos

### Syntax

    #include <math.h>

    double acos(double x);

### Description

This function returns the angle in the range `[0..Pi]` radians whose cosine is x. If the absolute value of x is greater than 1, a domain error occurs, and `errno` is set to `EDOM`.

### Return Value

The arc cosine, in radians, of x. If the absolute value of x is greater than 1, the function returns a `NaN`.

### Portability

ANSI, POSIX

Node:acosh, Next:addmntent, Previous:acos, Up:Alphabetical List

## acosh

### Syntax

    #include <math.h>

    double acosh(double x);

### Description

This function returns the inverse hyperbolic cosine of x.

### Return Value

The inverse hyperbolic cosine of x. If the value of x is less than 1, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:addmntent, Next:alarm, Previous:acosh, Up:Alphabetical List

## addmntent

### Syntax

    #include <mntent.h>

    int addmntent(FILE *filep, const struct mntent *mnt);

### Description

This function is a no-op for MS-DOS, but is provided to assist in Unix ports. See getmntent.

### Return Value

This function always returns nonzero to signify an error.

### Portability

not ANSI, not POSIX

Node:alarm, Next:alloca, Previous:addmntent, Up:Alphabetical List

## alarm

### Syntax

    #include <unistd.h>

    unsigned alarm(unsigned seconds);

### Description

This function causes the signal `SIGALRM` to be raised in seconds seconds. A value of zero for seconds cancels any pending alarm. If an alarm has previously been set, the new alarm delay will supercede the prior call.

Note that signals in DJGPP are deferred when the program is inside a real-mode (e.g., DOS) call or isn't touching its data; see signal, for more details.

A misfeature of Windows 9X prevents the timer tick interrupt from being delivered to programs that are in the background (i.e. don't have the focus), even though the program itself might continue to run, if you uncheck the Background: Always suspend property in the Property Sheets. Therefore, `alarm` will not work in background programs on Windows 9X.

### Return Value

The number of seconds remaining on the timer (i.e. always seconds).

### Portability

not ANSI, POSIX

### Example

    signal(SIGALRM,my_alarm_routine);
    alarm(5);

Node:alloca, Next:asctime, Previous:alarm, Up:Alphabetical List

## alloca

### Syntax

    #include <stdlib.h>

    void *alloca(size_t _size)

### Description

Allocate memory that will be automatically released when the current procedure exits. Note that, when compiling with gcc, alloca is a built-in function and not a library call.

### Return Value

A pointer to the memory, else NULL.

### Portability

not ANSI, not POSIX

### Example

    q = alloca(strlen(x)+1);
    strcpy(q, x);

Node:asctime, Next:asin, Previous:alloca, Up:Alphabetical List

## asctime

### Syntax

    #include <time.h>

    char *asctime(const struct tm *tptr);

### Description

This function returns an ASCII representation of the time represented by tptr. The string returned is always 26 characters and has this format:

    Sun Jan 01 12:34:56 1993\n\0

The string pointed to is in a static buffer and will be overwritten with each call to asctime. The data should be copied if it needs to be preserved.

The layout of the `struct tm` structure is like this:

    struct tm {
      int    tm_sec;    /* seconds after the minute [0-60] */
      int    tm_min;    /* minutes after the hour [0-59] */
      int    tm_hour;   /* hours since midnight [0-23] */
      int    tm_mday;   /* day of the month [1-31] */
      int    tm_mon;    /* months since January [0-11] */
      int    tm_year;   /* years since 1900 */
      int    tm_wday;   /* days since Sunday [0-6] */
      int    tm_yday;   /* days since January 1 [0-365] */
      int    tm_isdst;  /* Daylight Savings Time flag */
      long   tm_gmtoff; /* offset from GMT in seconds */
      char * tm_zone;   /* timezone abbreviation */
    };

### Return Value

A pointer to the string.

### Portability

ANSI, POSIX

### Example

    time_t now;
    time(&now);
    printf("The current time is %s", asctime(localtime(&now)));

Node:asin, Next:asinh, Previous:asctime, Up:Alphabetical List

## asin

### Syntax

    #include <math.h>

    double asin(double x);

### Description

This function returns the angle in the range `[-Pi/2..Pi/2]` whose sine is x.

### Return Value

The inverse sine, in radians, of x. If the absolute value of x is greater than 1, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:asinh, Next:assert, Previous:asin, Up:Alphabetical List

## asinh

### Syntax

    #include <math.h>

    double asinh(double x);

### Description

This function returns the inverse hyperbolic sine of the argument x.

### Return Value

The inverse hyperbolic sine of x. If the argument x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`. If x is a positive or negative `Inf`, the return value is equal to the value of x, and `errno` is left unchanged.

### Portability

not ANSI, not POSIX

Node:assert, Next:atan, Previous:asinh, Up:Alphabetical List

## assert

### Syntax

    #define NDEBUG
    #include <assert.h>

    assert(expression);
    assertval(expression);

### Description

These macros are used to assist in debugging. The source code includes references to `assert` or `assertval`, passing them expressions that should be `true` (non-zero). When the expression yields `false` (zero), a diagnostic message is printed to the standard error stream, and the program aborts.

If you define the macro `NDEBUG` before including `assert.h`, then these `assert` and `assertval` expand to nothing to reduce code size after debugging is done.

### Return Value

`assert` returns 1 if its argument is non-zero, else it aborts.

`assertval` returns the value of its expression argument, if non-zero, else it aborts.

### Portability

ANSI (see note 1), POSIX (see note 2)

Notes:

1. `assert` is ANSI, `assertval` is not.
2. `assert` is Posix, `assertval` is not.

### Example

    /* Like `strdup', but doesn't crash if the argument is NULL.  */
    char * safe_strdup(const char *s)
    {
      assert(s != 0);
      return strdup(s);
    }

Node:atan, Next:atan2, Previous:assert, Up:Alphabetical List

## atan

### Syntax

    #include <math.h>

    double atan(double x);

### Description

This function computes the angle, in the range `[-Pi/2..Pi/2]` radians, whose tangent is x.

### Return Value

The arc tangent, in radians, of x. If x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`. If x is a positive or negative `Inf`, the return value is equal to positive or negative `Pi/2`, respectively, and `errno` is left unchanged.

### Portability

ANSI, POSIX

Node:atan2, Next:atanh, Previous:atan, Up:Alphabetical List

## atan2

### Syntax

    #include <math.h>

    double atan2(double y, double x);

### Description

This function computes the angle, in the range `[-Pi..Pi]` radians, whose tangent is `y/x`. In other words, it computes the angle, in radians, of the vector (x,y) with respect to the `+x` axis, reckoning the counterclockwise direction as positive, and returning the value in the range `[-Pi, Pi]`.

### Return Value

The arc tangent, in radians, of `y/x`. `Pi` is returned if x is negative and y is a negative zero, `-0.0`. `-Pi` is returned, if x is negative, and y is a positive zero, `+0.0`.

If either x or y is infinite, `atan2` returns, respectively, `Pi` with the sign of y or zero, and `errno` is left unchanged. However, if both arguments are infinite, the return value is `NaN` and `errno` is set to `EDOM`.

A `NaN` is returned, and `errno` is set to `EDOM`, if either x and y are both zero, or if either one of the arguments is a `NaN`.

### Portability

ANSI, POSIX

Node:atanh, Next:atexit, Previous:atan2, Up:Alphabetical List

## atanh

### Syntax

    #include <math.h>

    double atanh(double x);

### Description

This function computes the inverse hyperbolic tangent of x.

### Return Value

The inverse hyperbolic tangent of x. If the the value of x is plus or minus 1, the return value is an `Inf` with the same sign as the argument x, and `errno` is set to `ERANGE`. If the absolute value of x is greater than 1, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:atexit, Next:atof, Previous:atanh, Up:Alphabetical List

## atexit

### Syntax

    #include <stdlib.h>

    int atexit(void (*func)(void));

### Description

This function places the specified function func on a list of functions to be called when `exit` is called. These functions are called as if a last-in-first-out queue is used, that is, the last function registered with `atexit` will be the first function called by `exit`.

At least 32 functions can be registered this way.

### Return Value

Zero on success, non-zero on error.

### Portability

ANSI, POSIX

### Example

    void exit_func()
    {
      remove("file.tmp");
    }

    ...
    atexit(exit_func);
    ...

Node:atof, Next:atoi, Previous:atexit, Up:Alphabetical List

## atof

### Syntax

    #include <stdlib.h>

    double atof(const char *string);

### Description

Convert as much of the string as possible to an equivalent double precision real number.

This function is almost like `strtod(string, NULL)` (see strtod).

### Return Value

The equivalent value, or zero if the string does not represent a number.

### Portability

ANSI, POSIX

### Example

    main(int argc, char **argv)
    {
      double d = atof(argv[1]);
      ...

Node:atoi, Next:atol, Previous:atof, Up:Alphabetical List

## atoi

### Syntax

    #include <stdlib.h>

    int atoi(const char *string);

### Description

Convert as much of the string as possible to an equivalent integer value.

This function is almost like `(int)strtol(string, NULL, 10)` (see strtol).

### Return Value

The equivalent value, or zero if the string does not represent a number.

### Portability

ANSI, POSIX

### Example

    main(int argc, char **argv)
    {
      int i = atoi(argv[1]);
      ...

Node:atol, Next:_atold, Previous:atoi, Up:Alphabetical List

## atol

### Syntax

    #include <stdlib.h>

    long atol(const char *string);

### Description

Convert as much of the string as possible to an equivalent long integer value.

This function is almost like `strtol(string, NULL, 10)` (see strtol).

### Return Value

The equivalent value, or zero if the string does not represent a number.

### Portability

ANSI, POSIX

### Example

    main(int argc, char **argv)
    {
      long l = atol(argv[1]);
      ...

Node:_atold, Next:basename, Previous:atol, Up:Alphabetical List

## _atold

### Syntax

    #include <stdlib.h>

    long double _atold(const char *string);

### Description

Convert as much of the string as possible to an equivalent long double precision real number.

This function is almost like `_strtold(string, NULL)` (see _strtold).

### Return Value

The equivalent value, or zero if the string does not represent a number.

### Portability

not ANSI, not POSIX

### Example

    main(int argc, char **argv)
    {
      long double d = _atold(argv[1]);
      ...

Node:basename, Next:bcmp, Previous:_atold, Up:Alphabetical List

## basename

### Syntax

    #include <unistd.h>

    char * basename (const char *fname);

### Description

This function returns the basename of the file, which is the last part of its full name given by fname, with the drive letter and leading directories stripped off. For example, the basename of `c:/foo/bar/file.ext` is `file.ext`, and the basename of `a:foo` is `foo`. Trailing slashes and backslashes are significant: the basename of `c:/foo/bar/` is an empty string after the rightmost slash.

This function treats both forward- and backslashes like directory separators, so it can handle file names with mixed styles of slashes.

### Return Value

A pointer into the original file name where the basename starts. Note that this is not a new buffer allocated with `malloc`. If fname is a NULL pointer, the function will return a NULL pointer.

### Portability

not ANSI, not POSIX

### Example

      if (strcmp (basename (file_name), "gcc.exe") == 0)
        printf ("The file %s is the GNU C/C++ compiler\n", file_name);

Node:bcmp, Next:bcopy, Previous:basename, Up:Alphabetical List

## bcmp

### Syntax

    #include <string.h>

    int bcmp(const void *ptr1, const void *ptr2, int length);

### Description

Compare memory pointed to by ptr1 and ptr2 for at most length bytes.

### Return Value

The number of bytes remaining when the first mismatch occurred, or zero if all bytes were equal.

### Portability

not ANSI, not POSIX

### Example

    void f(char *s1, char *s2)
    {
      int l = bcmp(s1, s2, strlen(s1));
      printf("Difference: %s, %s\n", s1+strlen(s1)-l, s2+strlen(s1)-l);
    }

Node:bcopy, Next:bdos, Previous:bcmp, Up:Alphabetical List

## bcopy

### Syntax

    #include <string.h>

    void bcopy(const void *source, void *dest, int length);

### Description

Copy length bytes from source to dest. Overlapping regions are handled properly, although this behavior is not portable.

### Return Value

No value is returned.

### Portability

not ANSI, not POSIX

### Example

    struct s a, b;
    bcopy(a, b, sizeof(struct s));

Node:bdos, Next:bdosptr, Previous:bcopy, Up:Alphabetical List

## bdos

### Syntax

    #include <dos.h>

    int bdos(int func, unsigned dx, unsigned al);

### Description

Calls function func of the software interrupt 0x21, passing it al as the subfunction and (the lower 16 bit of) dx in the `DX` register. This function will only work for a subset of DOS functions which require no arguments at all, or take non-pointer arguments in the `AL` and `DX` registers only. For functions which require a pointer in the `DX` register, use `bdosptr` (see bdosptr).

### Return Value

Whatever the called function returns in the AX register.

### Portability

not ANSI, not POSIX

### Example

    /* read a character */
    int ch = bdos(1, 0, 0) & 0xff;

Node:bdosptr, Next:_bios_disk, Previous:bdos, Up:Alphabetical List

## bdosptr

### Syntax

    #include <dos.h>

    int bdosptr(int func, void *ptr, unsigned al);

### Description

Calls function func of the software interrupt 0x21, passing it al as the subfunction and a pointer to a copy of the buffer contents whose address is in ptr through the `DX` register. This function will only work for a subset of DOS which require an argument in the `AL` register and a pointer in `DX` register. For functions which require non-pointer arguments in the `DX` register, use `bdos` (see bdos). To make the contents of ptr available to DOS, `bdosptr` copies it to the transfer buffer located in the low (below 1 Meg mark) memory.

Currently, some of the functions which take a pointer to a buffer in `DX` are NOT supported (notably, most of the FCB-based functions). See int86, for the list of supported functions.

### Return Value

Whatever the called function returns in the AX register.

### Portability

not ANSI, not POSIX

### Example

    /* print a string */
    bdosptr(9, "Hello, there$", 0);

Node:_bios_disk, Next:_bios_equiplist, Previous:bdosptr, Up:Alphabetical List

## _bios_disk

### Syntax

    #include <bios.h>

    unsigned _bios_disk(unsigned cmd, struct diskinfo_t *di)

### Description

This function interfaces with the BIOS disk sevice (interrupt 0x13). The parameter cmd select the corresponding disk service and the structure di holds the disk parameters.

    struct diskinfo_t {
      unsigned drive;       /* Drive number. */
      unsigned head;        /* Head number. */
      unsigned track;       /* Track number. */
      unsigned sector;      /* Sector number. */
      unsigned nsectors;    /* Number of sectors to read/write/verify. */
      void    *buffer;      /* Buffer for reading/writing/verifying. */
    }

The following services are available based on value of cmd:

`_DISK_RESET`
  Forces the disk controller to do a hard reset, preparing for floppy-disk I/O. This is useful after an error occurs in another operation, such as a read. If this service is specified, the di argument is ignored. Status is returned in the 8 high-order bits (AH) of the return value. If there is an error, the high-order byte will contain a set of status flags, as defined below under Return Value.
`_DISK_STATUS`
  Obtains the status of the last disk operation. If this service is specified, the <diskinfo> argument is ignored. Status is returned in the 8 low-order bits (AL) of the return value. If there is an error, the low-order byte (AL) will contain a set of status flags, as defined below under Return Value.
`_DISK_READ`
  Reads one or more disk sectors into memory. This service uses all fields of the structure pointed to by diskinfo. If no error occurs, the function returns 0 in the high-order byte and the number of sectors read in the low-order byte. If there is an error, the high-order byte (AH) will contain a set of status flags, as defined below under Return Value.
`_DISK_WRITE`
  Writes data from memory to one or more disk sectors. This service uses all fields of the structure pointed to by <diskinfo>. If no error occurs, the function returns 0 in the high-order byte (AH) and the number of sectors written in the low-order byte (AL). If there is an error, the high-order byte will contain a set of status flags, as defined below under Return Value.
`_DISK_FORMAT`
  Formats the track specified by diskinfo. The head and track fields indicate the track to format. Only one track can be formatted in a single call. The buffer field points to a set of sector markers. The format of the markers depends on the type of disk drive (see a technical reference to the PC BIOS to determine the marker format). The high-order byte (AH) of the return value contains the status of the call; 0 equals success. If there is an error, the high-order byte will contain a set of status flags, as defined below under Return Value.
`_DISK_VERIFY`
  Checks the disk to be sure the specified sectors exist and can be read. It also runs a CRC (cyclic redundancy check) test. This service uses all fields (except buffer) of the structure pointed to by diskinfo. If no error occurs, the function returns 0 in the high-order byte (AH) and the number of sectors compared in the low-order byte (AL), as defined below under Return Value.

### Return Value

Return value of AX register. The meaning of high-order byte (AH):

    0x00  No error
    0x01  Invalid request or a bad command
    0x02  Address mark not found
    0x03  Disk write protected
    0x04  Sector not found
    0x05  Reset failed
    0x06  Floppy disk removed
    0x07  Drive parameter activity failed
    0x08  Direct Memory Access (DMA) overrun
    0x09  DMA crossed 64K boundary
    0x0A  Bad sector flag detected
    0x0B  Bad track flag detected
    0x0C  Media type not found
    0x0D  Invalid number of sectors on format
    0x0E  Control data access mark detected
    0x0F  DMA arbitration level out of range
    0x10  Data read (CRC or ECC) error
    0x11  Corrected data read (ECC) error
    0x20  Controller failure
    0x40  Seek error
    0x80  Disk timed out or failed to respond
    0xAA  Drive not ready
    0xBB  Undefined error
    0xCC  Write fault on drive
    0xE0  Status error
    0xFF  Sense operation failed

### Portability

not ANSI, not POSIX

### Example

    char record_buffer[512];
    struct diskinfo_t di;

    di.drive    = 0x80;
    di.head     = 0;
    di.track    = 0;
    di.sector   = 0;
    di.nsectors = 1;
    di.buffer   = &record_buffer;
    if ( _bios_disk(_DISK_READ, &di) )
      puts("Disk error.");

Node:_bios_equiplist, Next:_bios_keybrd, Previous:_bios_disk, Up:Alphabetical List

## _bios_equiplist

### Syntax

    #include <bios.h>

    unsigned _bios_equiplist(void)

### Description

This function returns the equipment word from BIOS request 0x11. The bits correspond to the following values:

    Bits  Meaning
    0     True (1) if disk drive(s) installed
    1     True (1) if math coprocessor installed
    2-3   System RAM in 16K blocks (16-64K)
    4-5   Initial video mode:
               00 = Reserved
               01 = 40 x 25 color
               10 = 80 x 25 color
               11 = 80 x 25 monochrome
    6-7   Number of floppy-disk drives installed
          (00 = 1, 01 = 2, etc.)
    8     False (0) if and only if a Direct Memory Access (DMA)
          chip is installed
    9-11  Number of RS232 serial ports installed
    12    True (1) if and only if a game adapter is installed
    13    True (1) if and only if an internal modem is installed
    14-15 Number of printers installed

### Return Value

The equipment word.

### Portability

not ANSI, not POSIX

### Example

    if ( _bios_equiplist() & 0xc000 )
      do_printing();

Node:_bios_keybrd, Next:_bios_memsize, Previous:_bios_equiplist, Up:Alphabetical List

## _bios_keybrd

### Syntax

    #include <bios.h>

    unsigned _bios_keybrd(unsigned cmd);

### Description

The `_bios_keybrd` function uses INT 0x16 to access the keyboard services. The cmd argument can be any of the following manifest constants:

`_KEYBRD_READ`
  read the next key pressed.
`_NKEYBRD_READ`
  read the next extended key pressed. Unlike `_KEYBRD_READ`, this command knows about keys introduced with the AT-style 101-key keyboards, such as <F11> and <F12>, and can distinguish between the editing keys on the numeric pad and the grey keys of the edit pad. On the other hand, some of the extended keys return two-byte sequences which typically begin with the `E0h` (224 decimal) prefix, so code that uses `_NKEYBRD_READ` should deal with this complexity.
`_KEYBRD_READY`
  check if a key is waiting in the keyboard buffer.
`_NKEYBRD_READY`
  check if an extended key is waiting in the keyboard buffer. Like `_KEYBRD_READY`, but recognizes extended keys such as <F12>, which `_KEYBRD_READY` ignores.
`_KEYBRD_SHIFTSTATUS`
  read keyboard shift state (the byte at the address `40h:17h` in the BIOS data area):

      7654 3210  Meaning
      ---- ---X  Right SHIFT is pressed
      ---- --X-  Left SHIFT is pressed
      ---- -X--  CTRL is pressed
      ---- X---  ALT is pressed
      ---X ----  Scroll Lock locked
      --X- ----  Num Lock locked
      -X-- ----  Caps Lock locked
      X--- ----  Insert locked

`_NKEYBRD_SHIFTSTATUS`
  read keyboard shift and extended shift state (the byte at the address `40h:17h` in the BIOS data area combined with the extended shift flags from the bytes at addresses `40h:18h` and `40h:96h`):

      FEDC BA98  7654 3210  Meaning
      ---- ----  ---- ---X  Right SHIFT is pressed
      ---- ----  ---- --X-  Left SHIFT is pressed
      ---- ----  ---- -X--  CTRL is pressed
      ---- ----  ---- X---  ALT is pressed
      ---- ----  ---X ----  Scroll Lock locked
      ---- ----  --X- ----  Num Lock locked
      ---- ----  -X-- ----  Caps Lock locked
      ---- ----  X--- ----  Insert locked

      ---- ---X  ---- ----  Left CTRL is pressed
      ---- --X-  ---- ----  Left ALT is pressed
      ---- -X--  ---- ----  Right CTRL is pressed
      ---- X---  ---- ----  Right ALT is pressed
      ---X ----  ---- ----  Scroll Lock is pressed
      --X- ----  ---- ----  Num Lock is pressed
      -X-- ----  ---- ----  Caps Lock is pressed
      X--- ----  ---- ----  SysReq is pressed

Return Value

With the `*_READ` and `*_SHIFTSTATUS` arguments, the `_bios_keybrd` function returns the contents of the AX register after the BIOS call. For the `*_READ` arguments, this is the combination of scan code and ASCII code for alphanumeric keys, or a scan code and either zero or the `E0h` prefix for special keys.

With the `*_READY` arguments, `_bios_keybrd` returns 0 if no key is waiting in the BIOS keyboard buffer. If there is a key, `_bios_keybrd` returns the key waiting to be read (that is, the same value as the corresponding `*_READ` would return).

With the `*_READ` and `*_READY` arguments, the `_bios_keybrd` function returns -1 if `Ctrl+<BREAK>` has been pressed and is the next keystroke to be read.

### Portability

not ANSI, not POSIX

### Example

    while( !_bios_keybrd(_KEYBRD_READY) )
      try_to_do_something();

Node:_bios_memsize, Next:_bios_printer, Previous:_bios_keybrd, Up:Alphabetical List

## _bios_memsize

### Syntax

    #include <bios.h>

    unsigned _bios_memsize(void);

### Description

This function returns the amount of system memory in 1K blocks (up to 640K).

### Return Value

Size of memory (in K).

### Portability

not ANSI, not POSIX

### Example

    printf("This system has %d bytes of memory\n", _bios_memsize() * 1024);

Node:_bios_printer, Next:_bios_serialcom, Previous:_bios_memsize, Up:Alphabetical List

## _bios_printer

### Syntax

    #include <bios.h>

    unsigned _bios_printer(unsigned cmd, unsigned printer, unsigned data);

### Description

The _bios_printer routine uses INT 0x17 to perform printer output services for parallel printers. The printer argument specifies the affected printer, where 0 is LPT1, 1 is LPT2, and so on. The cmd argument can be any of the following manifest constants:

`_PRINTER_INIT`
`Reset and initialize the specified printer port`
`_PRINTER_STATUS`
  Return the status of the specified printer port
`_PRINTER_WRITE`
  Print the data argument to the specified printer port

### Return Value

The _bios_printer function returns the value in the AX register after the BIOS interrupt. The high-order byte (AH) of the return value indicates the printer status after the operation, as defined below:

    Bit     Meaning if True

    0       Printer timed out
    1       Not used
    2       Not used
    3       I/O error
    4       Printer selected
    5       Out of paper
    6       Acknowledge
    7       Printer not busy

### Portability

not ANSI, not POSIX

### Example

    while (*c)
      _bios_printer(_PRINTER_WRITE, *c++, 0);

Node:_bios_serialcom, Next:_bios_timeofday, Previous:_bios_printer, Up:Alphabetical List

## _bios_serialcom

### Syntax

    #include <bios.h>

    unsigned _bios_serialcom(unsigned cmd, unsingned serialport, unsigned data);

### Description

The _bios_serialcom routine uses INT 0x14 to provide serial communications services. The serialport argument is set to 0 for COM1, to 1 for COM2, and so on. The cmd argument can be set to one of the following manifest constants:

`_COM_INIT`
  Initialize com port (data is the settings)
`_COM_RECEIVE`
  Read a byte from port
`_COM_SEND`
  Write a byte to port
`_COM_STATUS`
  Get the port status

The data argument is ignored if cmd is set to _COM_RECEIVE or _COM_STATUS. The data argument for _COM_INIT is created by combining one or more of the following constants (with the OR operator):

    _COM_CHR7         7 bits/character
    _COM_CHR8         8 bits/character
    _COM_STOP1        1 stop bit
    _COM_STOP2        2 stop bits
    _COM_NOPARITY     no parity
    _COM_EVENPARITY   even parity
    _COM_ODDPARITY    odd parity
    _COM_110          110 baud
    _COM_150          150 baud
    _COM_300          300 baud
    _COM_600          600 baud
    _COM_1200         1200 baud
    _COM_2400         2400 baud
    _COM_4800         4800 baud
    _COM_9600         9600 baud

The default value of data is 1 stop bit, no parity, and 110 baud.

### Return Value

The function returns a 16-bit integer whose high-order byte contains status bits. The meaning of the low-order byte varies, depending on the cmd value. The high-order bits are as follows:

    Bit     Meaning if Set

    15      Timed out
    14      Transmission-shift register empty
    13      Transmission-hold register empty
    12      Break detected
    11      Framing error
    10      Parity error
     9      Overrun error
     8      Data ready

When service is _COM_SEND, bit 15 is set if data cannot be sent.

When service is _COM_RECEIVE, the byte read is returned in the low-order bits if the call is successful. If an error occurs, any of the bits 9, 10, 11, or 15 is set.

When service is _COM_INIT or _COM_STATUS, the low-order bits are defined as follows:

    Bit     Meaning if Set

    7       Receive-line signal detected
    6       Ring indicator
    5       Data-set-ready
    4       Clear-to-send
    3       Change in receive-line signal detected
    2       Trailing-edge ring indicator
    1       Change in data-set-ready status
    0       Change in clear-to-send status

### Portability

not ANSI, not POSIX

### Example

    /* 9600 baud, no parity, one stop, 8 bits */
    _bios_serialcom(_COM_INIT, 0, _COM_9600|_COM_NOPARITY|_COM_STOP1|_COM_CHR8);
    for(i=0; buf[i]; i++)
      _bios_serialcom(_COM_SEND, 0, buf[i]);

Node:_bios_timeofday, Next:bioscom, Previous:_bios_serialcom, Up:Alphabetical List

## _bios_timeofday

### Syntax

    #include <bios.h>

    unsigned _bios_timeofday(unsigned cmd, unsigned long *timeval);

### Description

The _bios_timeofday routine uses INT 0x1A to get or set the clock count (which is the number of 18.2 Hz ticks since midnight). The cmd argument can be either the _TIME_GETCLOCK or _TIME_SETCLOCK manifest constant.

### Return Value

If the argument is _TIME_GETCLOCK, the routine returns a nonzero value if midnight was passed since last read, or zero if midnight was not passed. If the argument is _TIME_SETCLOCK, the return value is undefined.

### Portability

not ANSI, not POSIX

### Example

    unsigned hour, min, sec, hsec;
    unsigned long ticks;
    ...
    ticks = (unsigned long)(hour * 65543.33) + (min * 1092.38) +
            (sec * 18.21) + (hsec * 0.182);
    _bios_timeofday(_TIME_SETCLOCK, &ticks);

Node:bioscom, Next:biosdisk, Previous:_bios_timeofday, Up:Alphabetical List

## bioscom

### Syntax

    #include <bios.h>

    int bioscom(int cmd, char data, int port);

### Description

This function accesses the BIOS interrupt 0x14 function, serial communication services. `port` should be the COM port (0=COM1, 1=COM2, etc).

The valid values of cmd are:

0 - initialize com port (data is the settings)
1 - write byte to port
2 - read byte from port (data is ignored)
3 - get port status

For initialization, the byte is made up of the following bits:

    0000 0000
    7654 3210  Meaning

    ---- --10  7 bits/character
    ---- --11  8 bits/character
    ---- -0--  1 stop bit
    ---- -1--  2 stop bits
    ---X 0---  no parity
    ---0 1---  odd parity
    ---1 1---  even parity
    000- ----  110 baud
    001- ----  150 baud
    010- ----  300 baud
    011- ----  600 baud
    100- ----  1200 baud
    101- ----  2400 baud
    110- ----  4800 baud
    111- ----  9600 baud

For writing a character out to the port, the return value's lower 8 bits contain the same byte as passed as the data argument.

For reading a character from the port, the value of data is ignored, and the lower 8 bits of the return value contain the byte read. Also, the "timeout" bit in the upper 8 bits is used as an error indicator in this case (0=success, 1=error). If it indicates an error, you should call the "get port status" variant to get the detailed error bits.

### Return Value

The return value is a sequence of bits that indicate the port status and, for cmd=0 and 3, the modem status. For read/write operations, the lower eight bits are the character read.

    1111 1100 0000 0000
    5432 1098 7654 3210  Meaning

    ---- ---- ---- ---1  CTS change
    ---- ---- ---- --1-  DSR change
    ---- ---- ---- -1--  ring change
    ---- ---- ---- 1---  carrier detect change
    ---- ---- ---1 ----  CTS present
    ---- ---- --1- ----  DSR present
    ---- ---- -1-- ----  ring present
    ---- ---- 1--- ----  carrier detect
    ---- ---1 ---- ----  data ready
    ---- --1- ---- ----  overrun error
    ---- -1-- ---- ----  parity error
    ---- 1--- ---- ----  framing error
    ---1 ---- ---- ----  break detected
    --1- ---- ---- ----  transmit holding register empty
    -1-- ---- ---- ----  transmit shift register empty
    1--- ---- ---- ----  time out (=1 if error present for cmd=1,2)

### Portability

not ANSI, not POSIX

### Example

    bioscom(0, 0xe3, 0); /* 9600 baud, no parity, one stop, 8 bits */
    for (i=0; buf[i]; i++)
      bioscom(1, buf[i], 0);

Node:biosdisk, Next:biosequip, Previous:bioscom, Up:Alphabetical List

## biosdisk

### Syntax

    #include <bios.h>

    int biosdisk(int cmd, int drive, int head, int track,
    	     int sector, int nsects, void *buffer);

### Description

This function interfaces with the BIOS disk sevice (interrupt 0x13). Please refer to a BIOS reference manual for detailed information about the parameters of this call. The function assumes a sector size of 512 bytes.

The following functions of Int 13h are currently supported:

0 - reset disk subsystem
1 - get status of last operation
2 - read one or more sectors
3 - write one or more sectors
5 - format a track
6 - format a cylinder and set bad sector flag
7 - format drive from specified cylinder
8 - get drive parameters
9 - initialize drive parameters
10 - read long sectors
11 - write long sectors
12 - seek to cylinder
13 - alternate fixed disk reset
14 - read sector buffer
15 - write sector buffer
16 - test for drive ready
17 - recalibrate drive
18 - controller RAM diagnostic
19 - controller drive diagnostic
20 - controller internal diagnostic
21 - get DASD type
22 - read disk change line status
23 - set DASD type (pass DASD code in nsects)
24 - set media type for format

The first request with more sectors than will fit in the transfer buffer will cause a DOS buffer to be allocated. This buffer is automatically freed when your application exits. Requests for more sectors than 18 sectors (9K) will fail.

Function 8 returns values in buffer as follows:

byte 0 = sectors per track (bits 0..5) and top two bits of cylinder (in bits 6..7)
byte 1 = cyliders (bits 0..7)
byte 2 = number of drives
byte 3 = number of heads

### Return Value

The value of AH returned by the BIOS. See _bios_disk, for a detailed list of possible status and error codes.

### Portability

not ANSI, not POSIX

### Example

    char buffer[512];
    if (biosdisk(2, 0x80, 0, 0, 0, 1, buffer))
      error("disk");

Node:biosequip, Next:bioskey, Previous:biosdisk, Up:Alphabetical List

## biosequip

### Syntax

    #include <bios.h>

    int biosequip(void);

### Description

This function returns the equipment word from BIOS request 0x11. The bits correspond to the following values:

    1111 1100 0000 0000
    5432 1098 7654 3210  Meaning

    ---- ---- ---- ---X  1 = disk drive(s) installed
    ---- ---- ---- --X-  1 = math coprocessor installed
    ---- ---- ---- XX--  System memory 00=16k 01=32k 10=48k 11=64k (non PS/2)
    ---- ---- ---- -X--  1 = pointing device installed (PS/2)
    ---- ---- ---- X---  not used on PS/2
    ---- ---- --XX ----  initial video mode: 01=CO40 10=CO80 11=MONO
    ---- ---- XX-- ----  disk drives 00=1 01=2 10=3 11=4 (zero if bit 1=0)
    ---- ---X ---- ----  1 = no DMA available
    ---- XXX- ---- ----  number of serial ports installed (000=0 001=1 etc)
    ---X ---- ---- ----  1 = game port adapter installed
    --X- ---- ---- ----  1 = internal modem installed (PS/2)
    --X- ---- ---- ----  1 = serial printer attached (non PS/2)
    XX-- ---- ---- ----  number of printers installed (00=0 01=1 10=2 11=3)

### Return Value

The equipment word.

### Portability

not ANSI, not POSIX

### Example

    if (biosequip() & 0xc000)
      do_printing();

Node:bioskey, Next:biosmemory, Previous:biosequip, Up:Alphabetical List

## bioskey

### Syntax

    #include <bios.h>

    int bioskey(int command)

### Description

This function issues the BIOS keyboard interrupt 16h with command in the AH register, and returns the results of that call. The argument command can accept the following values:

command = 0
  Returns the next key pressed. The value returned is a combination of the key's scan code in the high 8 bits and its ASCII code in the low 8 bits. For non-alphanumeric keys, such as the arrow keys, the low 8 bits are zeroed.
command = 1
  Checks the keyboard, returns zero if no key pressed, else the key. Does not dequeue the key from the keyboard buffer. The value returned when a key was pressed is a combination of the key's scan code in the high 8 bits and either its ASCII code or zero in the low 8 bits.

  If the `Ctrl-<BREAK>` key was pressed, returns -1.

command = 2
  Returns the keyboard shift state:

      7654 3210  Meaning

      ---- ---X  Right shift key down
      ---- --X-  Left shift key down
      ---- -X--  Ctrl key down
      ---- X---  Alt key down
      ---X ----  Scroll lock on
      --X- ----  Num lock on
      -X-- ----  Caps lock on
      X--- ----  Insert on

command = 10
  Returns the next extended key pressed. This works like the case of command = 0, but it recognizes additional keys from the AT-style extended 101-key keyboard, like the second <Alt> key and <F12>. If a key was pressed, returns the scan code and ASCII code packed in same way as for command = 0, except that the extended keys have the `E0h` prefix in the low 8 bits.

  Almost every PC nowadays has an extended 101-key keyboard.

command = 11
  Like the case of command = 1, but recognizes the additional keys of the extended keyboard.
command = 12
  Returns the two status bytes of the enhanced keyboard, packed in the low 16 bits of the return value. The individual bits of the return value are defined in the following table:

      FEDC BA98  7654 3210  Meaning
      ---- ----  ---- ---X  Right SHIFT is pressed
      ---- ----  ---- --X-  Left SHIFT is pressed
      ---- ----  ---- -X--  CTRL is pressed
      ---- ----  ---- X---  ALT is pressed
      ---- ----  ---X ----  Scroll Lock locked
      ---- ----  --X- ----  Num Lock locked
      ---- ----  -X-- ----  Caps Lock locked
      ---- ----  X--- ----  Insert locked

      ---- ---X  ---- ----  Left CTRL is pressed
      ---- --X-  ---- ----  Left ALT is pressed
      ---- -X--  ---- ----  Right CTRL is pressed
      ---- X---  ---- ----  Right ALT is pressed
      ---X ----  ---- ----  Scroll Lock is pressed
      --X- ----  ---- ----  Num Lock is pressed
      -X-- ----  ---- ----  Caps Lock is pressed
      X--- ----  ---- ----  SysReq is pressed

### Return Value

Depends on command.

### Portability

not ANSI, not POSIX

### Example

    while (!bioskey(1))
      do_stuff();

Node:biosmemory, Next:biosprint, Previous:bioskey, Up:Alphabetical List

## biosmemory

### Syntax

    #include <bios.h>

    unsigned biosmemory(void);

### Description

This function returns the amount of system memory in 1k blocks.

Note that this function doesn't know about extended memory above the 640K mark, so it will report 640K at most. This is a limitation of the BIOS.

### Return Value

Bytes of memory / 1024.

### Portability

not ANSI, not POSIX

### Example

    printf("This system has %d bytes of memory\n", biosmemory()*1024);

Node:biosprint, Next:biostime, Previous:biosmemory, Up:Alphabetical List

## biosprint

### Syntax

    #include <bios.h>

    int biosprint(int cmd, int byte, int port)

### Description

command = 0
  `byte` is sent to parallel port port.
command = 1
  Parallel port port is reset and initialized.
command = 2
  The status of parallel port port is returned.

      7654 3210  Meaning

      ---- ---X  Timeout
      ---- -XX-  Unused
      ---- X---  I/O Error
      ---X ----  Selected
      --X- ----  Out of paper
      -X-- ----  Acknowledged
      X--- ----  Idle

### Return Value

The printer status.

### Portability

not ANSI, not POSIX

### Example

    while (*c)
      biosprint(0, *c++, 0);

Node:biostime, Next:blinkvideo, Previous:biosprint, Up:Alphabetical List

## biostime

### Syntax

    #include <bios.h>

    long biostime(int cmd, long newtime);

### Description

This function reads (cmd=0) or sets (cmd=1) the internal tick counter, which is the number of 18.2 Hz ticks since midnight.

### Return Value

When reading, the number of ticks since midnight.

### Portability

not ANSI, not POSIX

### Example

    long ticks = biostime(0, 0);

Node:blinkvideo, Next:brk, Previous:biostime, Up:Alphabetical List

## blinkvideo

### Syntax

    #include <conio.h>

    void blinkvideo(void);

### Description

Bit 7 (`MSB`) of the character attribute byte has two possible effects on EGA and VGA displays: it can either make the character blink or change the background color to bright (thus allowing for 16 background colors as opposed to the usual 8). This function sets that bit to display blinking characters. After a call to this function, every character written to the screen with bit 7 of the attribute byte set, will blink. The companion function `intensevideo` (see intensevideo) has the opposite effect.

Note that there is no BIOS function to get the current status of this bit, but bit 5 of the byte at `0040h:0065h` in the BIOS area indicates the current state: if it's 1 (the default), blinking characters will be displayed.

### Portability

not ANSI, not POSIX

Node:brk, Next:bsearch, Previous:blinkvideo, Up:Alphabetical List

## brk

### Syntax

    #include <unistd.h>

    int brk(void *ptr);

### Description

This function changes the break for the program. This is the first address that, if referenced, will cause a fault to occur. The program asks for more memory by specifying larger values for ptr. Normally, this is done transparently through the `malloc` function.

### Return Value

Zero if the break was changed, -1 if not. errno is set to the error.

### Portability

not ANSI, not POSIX

### Example

    if (brk(old_brk+1000))
      printf("no memory\n");

Node:bsearch, Next:bzero, Previous:brk, Up:Alphabetical List

## bsearch

### Syntax

    #include <stdlib.h>

    void *bsearch (const void *key, const void *base, size_t num,
      size_t size, int (*ptf)(const void *ckey, const void *celem));

### Description

Given an array of values, perform a binary search on the values looking for value that "matches" the given key. A match is determined by calling the provided function ptf and passing it the key as ckey and a pointer to one of the elements of the array as celem. This function must return a negative number if the key is closer than the element to the beginning of the array, positive if it is closer to the end, and zero if the element matches the key.

The array begins at address base and contains num elements, each of size size.

### Return Value

Returns a pointer to the element that matches the key, else NULL.

### Portability

ANSI, POSIX

### Example

    typedef struct {
      int a, b;
    } q;

    int compare(void *key, void *elem)
    {
      return *(int *)key - ((q *)elem)->a;
    }

    q qlist[100];

    ...
    q *match = bsearch(4, qlist, 100, sizeof(q), compare);
    printf("4->%d=n", match->b);
    ...

Node:bzero, Next:calloc, Previous:bsearch, Up:Alphabetical List

## bzero

### Syntax

    #include <string.h>

    void bzero(void *pointer, int length);

### Description

The data at pointer is filled with length zeros.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    char foo[100];
    bzero(foo,100);

Node:calloc, Next:cbrt, Previous:bzero, Up:Alphabetical List

## calloc

### Syntax

    #include <stdlib.h>

    void *calloc(size_t num_elements, size_t size);

### Description

This function allocates enough memory for num_elements objects of size size. The memory returned is initialized to all zeros. The pointer returned should later be passed to free (see free) so that the memory can be returned to the heap.

You may use cfree (see xfree) to free the pointer also; it just calls free.

### Return Value

A pointer to the memory, or `NULL` if no more memory is available.

### Portability

ANSI, POSIX

### Example

    Complex *x = calloc(12, sizeof(Complex));
    cfree(x);

Node:cbrt, Next:ceil, Previous:calloc, Up:Alphabetical List

## cbrt

### Syntax

    #include <math.h>

    double cbrt(double x);

### Description

This function computes the cube root of x. It is faster and more accurate to call `cbrt(x)` than to call `pow(x, 1./3.)`.

### Return Value

The cube root of x. If the value of x is `NaN`, the return value is `NaN` and `errno` is set to `EDOM`. Infinite arguments are returned unchanged, without setting `errno`.

### Portability

not ANSI, not POSIX

Node:ceil, Next:cfgetispeed, Previous:cbrt, Up:Alphabetical List

## ceil

### Syntax

    #include <math.h>

    double ceil(double x);

### Description

This function computes the smallest integer greater than or equal to x.

### Return Value

The smallest integer value greater than or equal to x.

### Portability

ANSI, POSIX

Node:cfgetispeed, Next:cfgetospeed, Previous:ceil, Up:Alphabetical List

## cfgetispeed

### Syntax

    #include <termios.h>

    speed_t cfgetispeed (const struct termios *termiosp);

### Description

This function gets the input line speed stored in the structure termiosp. See Termios functions, for more details about this structure and the baudrate values it supports.

Note that the termios emulation handles console only, and that the input baudrate value is ignored by this implementation.

### Return Value

The input line speed on success, (speed_t) -1 for error.

### Portability

not ANSI, POSIX

Node:cfgetospeed, Next:cfmakeraw, Previous:cfgetispeed, Up:Alphabetical List

## cfgetospeed

### Syntax

    #include <termios.h>

    speed_t cfgetospeed (const struct termios *termiosp);

### Description

This function gets the output line speed stored in the structure termiosp. See Termios functions, for more details about this structure and the baudrate values it supports.

Note that the termios emulation handles console only, and that the baudrate value has no effect in this implementation.

### Return Value

The output line speed on success, (speed_t) -1 for error.

### Portability

not ANSI, POSIX

Node:cfmakeraw, Next:cfree, Previous:cfgetospeed, Up:Alphabetical List

## cfmakeraw

### Syntax

    #include <termios.h>

    void cfmakeraw (struct termios *termiosp);

### Description

This function sets the structure specified by termiosp for raw mode. It is provided for compatibility only. Note that the termios emulation handles console only.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

Node:cfree, Next:cfsetispeed, Previous:cfmakeraw, Up:Alphabetical List

## cfree

### Syntax

    #include <stdlib.h>

    void cfree(void *pointer);

### Description

This function returns the memory allocated by calloc (see calloc) to the heap.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    Complex *x = calloc(12, sizeof(Complex));
    cfree(x);

Node:cfsetispeed, Next:cfsetospeed, Previous:cfree, Up:Alphabetical List

## cfsetispeed

### Syntax

    #include <termios.h>

    int cfsetispeed (struct termios *termiosp, speed_t speed);

### Description

This function sets the input line speed stored in the structure termiosp to speed. See Termios functions, for more details about this structure and the baudrate values it supports.

Note that the termios emulation handles console only, and that the baudrate values have no effect in this implementation.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

Node:cfsetospeed, Next:cfsetspeed, Previous:cfsetispeed, Up:Alphabetical List

## cfsetospeed

### Syntax

    #include <termios.h>

    int cfsetospeed (struct termios *termiosp, speed_t speed);

### Description

This function sets the output line speed stored in the structure termiosp to speed. See Termios functions, for more details about this structure and the baudrate values it supports.

Note that the termios emulation handles console only, and that the baudrate values have no effect in this implementation.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

Node:cfsetspeed, Next:cgets, Previous:cfsetospeed, Up:Alphabetical List

## cfsetspeed

### Syntax

    #include <termios.h>

    int cfsetspeed (struct termios *termiosp, speed_t speed);

### Description

This function sets the input and output line speed stored in the structure termiosp to speed. It is provided for compatibility only. Note that the termios emulation handles console only.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

Node:cgets, Next:chdir, Previous:cfsetspeed, Up:Alphabetical List

## cgets

### Syntax

    #include <conio.h>

    char *cgets(char *_str);

### Description

Get a string from the console. This will take advantage of any command-line editing TSRs. To use, you must pre-fill the first character of the buffer. The first character is the size of the buffer. On return, the second character is the number of characters read. The third character is the first character read.

### Return Value

A pointer to the first character read.

### Portability

not ANSI, not POSIX

Node:chdir, Next:_check_v2_prog, Previous:cgets, Up:Alphabetical List

## chdir

### Syntax

    #include <unistd.h>

    int chdir(const char *new_directory);

### Description

This function changes the current directory to new_directory. If a drive letter is specified, the current directory for that drive is changed and the current disk is set to that drive, else the current directory for the current drive is changed.

### Return Value

Zero if the new directory exists, else nonzero and errno set if error.

### Portability

not ANSI, POSIX

### Example

    if (chdir("/tmp"))
      perror("/tmp");

Node:_check_v2_prog, Next:chmod, Previous:chdir, Up:Alphabetical List

## _check_v2_prog

### Syntax

    #include <sys/system.h>

    const _v2_prog_type *_check_v2_prog(const char *program, int fd);

### Description

This function checks a given program for various known types of executables and/or other things. This function povides two differnt entry points. One is to call the function with a not `NULL` pointer as `program` (in this case `fd` is ignored), then the file named by `program` is opened and closed by `_check_v2_prog`.

When you pass `NULL` as `program`, then you have to pass a valid file handle in `fd` and `_check_v2_prog` uses that handle and does also not close the file on return.

### Return Value

`_v2_prog_type` is defined in `sys/system.h` like the following:

    typedef struct {
      char magic[16];
      int struct_length;
      char go32[16];
      unsigned char buffer[0];
    } _v1_stubinfo;

    typedef struct {
      union {
        unsigned version:8; /* The version of DJGPP created that COFF exe */
        struct {
          unsigned minor:4; /* The minor version of DJGPP */
          unsigned major:4; /* The major version of DJGPP */
        } v;
      } version;

      unsigned object_format:4; /* What an object format */
    # define _V2_OBJECT_FORMAT_UNKNOWN 0x00
    # define _V2_OBJECT_FORMAT_COFF    0x01
    # define _V2_OBJECT_FORMAT_PE_COFF 0x02

      unsigned exec_format:4; /* What an executable format */
    # define _V2_EXEC_FORMAT_UNKNOWN    0x00
    # define _V2_EXEC_FORMAT_COFF       0x01
    # define _V2_EXEC_FORMAT_STUBCOFF   0x02
    # define _V2_EXEC_FORMAT_EXE        0x03
    # define _V2_EXEC_FORMAT_UNIXSCRIPT 0x04

      unsigned valid:1; /* Only when nonzero all the information is valid */

      unsigned has_stubinfo:1; /* When nonzero the stubinfo info is valid */

      unsigned unused:14;

      _v1_stubinfo *stubinfo;
    } _v2_prog_type;

The macros shown above can be used to test the different members of that structure for known values.

Warning: Do not modify any of the data in this structure.

After calling `_check_v2_prog` you should check at first the member `valid`. Only if this is nonzero you can be sure that all the other information in the struct is valid.

The same is for the `stubinfo` member of the above struct, it is valid only, when `has_stubinfo` is nonzero.

### Portability

not ANSI, not POSIX

### Example

To use the information returned in the struct you can use code like the following:

    #include <stdio.h>
    #include <sys/system.h>

    int main()
    {
      const _v2_prog_type *type;
      /* Since we pass a valid name, we can use -1 as the second argument */
      type = _check_v2_prog ("foo", -1);

      /* There was something wrong */
      if (!type->valid)
      {
        fprintf(stderr, "Could not check the file 'foo'. Giving up.\\n");
        return 1;
      }

      /* Currently only the COFF format is valid to be a V2 executable */
      if (type->object_format != _V2_OBJECT_FORMAT_COFF)
      {
        fprintf(stderr, "File 'foo' is not in COFF format\\n");
        return 2;
      }

      /* The major version is not 2 */
      if (type->version.v.major != 2)
      {
        fprintf(stderr, "File 'foo' is not from DJGPP 2.xx\\n");
        return 3;
      }

      fprintf(stdout, "File 'foo' is a valid DJGPP 2.xx executable\\n");

      if (type->exec_format == _V2_EXEC_FORMAT_STUBCOFF)
      {
        fprintf(stdout, "File 'foo' has a stub loader prepended\\n");
      }

      return 0;
    }

Node:chmod, Next:_chmod, Previous:_check_v2_prog, Up:Alphabetical List

## chmod

### Syntax

    #include <sys/stat.h>

    int chmod(const char *path, mode_t mode);

### Description

This function changes the mode (writable or write-only) of the specified file. The value of mode can be a combination of one or more of the following:

`S_IRUSR`
  Make the file readable
`S_IWUSR`
  Make the file writable

Other `S_I*` values could be included, but they will be ignored.

### Return Value

Zero if the file exists and the mode was changed, else nonzero.

### Portability

not ANSI, POSIX

### Example

    chmod("/tmp/dj.dat", S_IWUSR|S_IRUSR);

Node:_chmod, Next:chown, Previous:chmod, Up:Alphabetical List

## _chmod

### Syntax

    #include <io.h>

    int _chmod(const char *filename, int func, mode_t mode);

### Description

This is a direct connection to the MS-DOS chmod function call, int 0x21, %ax = 0x4300/0x4301. If func is 0, then DOS is called with AX = 0x4300, which returns an attribute byte of a file. If func is 1, then the attributes of a file are set as specified in mode. Note that the directory and volume attribute bits must always be 0 when `_chmod()` is called with func = 1, or else the call will fail. The third argument is optional when getting attributes. The attribute bits are defined as follows:

      Bit       Meaning
    76543210
    .......1    Read-only
    ......1.    Hidden
    .....1..    System
    ....1...    Volume Label
    ...1....    Directory
    ..1.....    Archive
    xx......    Reserved (used by some network redirectors)

On platforms where the LFN API (see LFN) is available, `_chmod` calls function 0x7143 of Interrupt 21h, to support long file names.

### Return Value

If the file exists, `_chmod()` returns its attribute byte in case it succeded, or -1 in case of failure.

### Portability

not ANSI, not POSIX

Node:chown, Next:chsize, Previous:_chmod, Up:Alphabetical List

## chown

### Syntax

    #include <unistd.h>

    int chown(const char *file, int owner, int group);

### Description

This function does nothing under MS-DOS

### Return Value

This function always returns zero if the file exists, else it returns -1 and sets errno to `ENOENT`.

### Portability

not ANSI, POSIX

Node:chsize, Next:cleanup_client, Previous:chown, Up:Alphabetical List

## chsize

### Syntax

    #include <io.h>

    int chsize(int handle, long size);

### Description

Just calls ftruncate (see ftruncate).

### Return Value

Zero on success, -1 on failure.

### Portability

not ANSI, not POSIX

Node:cleanup_client, Next:_clear87, Previous:chsize, Up:Alphabetical List

## cleanup_client

### Syntax

    #include <debug/dbgcom.h>

    void cleanup_client (void);

### Description

This functions is typically called when the debugged process exits or is aborted. It restores segment descriptors, closes file handles that were left open by the debuggee, frees protected-mode and conventional memory and any segment descriptors allocated by the debuggee, and restores the debugger's original signal handlers.

Node:_clear87, Next:clearerr, Previous:cleanup_client, Up:Alphabetical List

## _clear87

### Syntax

    #include <float.h>

    unsigned int _clear87(void);

### Description

Clears the floating point processor's exception flags.

### Return Value

The previous status word.

### Portability

not ANSI, not POSIX

Node:clearerr, Next:clock, Previous:_clear87, Up:Alphabetical List

## clearerr

### Syntax

    #include <stdio.h>

    void clearerr(FILE *stream);

### Description

This function clears the EOF and error indicators for the file stream.

### Return Value

None.

### Portability

ANSI, POSIX

### Example

    clearerr(stdout);

Node:clock, Next:close, Previous:clearerr, Up:Alphabetical List

## clock

### Syntax

    #include <time.h>

    clock_t clock(void);

### Description

This function returns the number of clock ticks since an arbitrary time, actually, since the first call to `clock`, which itself returns zero. The number of tics per second is CLOCKS_PER_SEC.

### Return Value

The number of tics.

### Portability

ANSI, POSIX

### Example

    printf("%d seconds have elapsed\n", clock()/CLOCKS_PER_SEC);

Node:close, Next:_close, Previous:clock, Up:Alphabetical List

## close

### Syntax

    #include <unistd.h>

    int close(int fd);

### Description

The open file associated with fd is closed.

### Return Value

Zero if the file was closed, nonzero if fd was invalid or already closed.

### Portability

not ANSI, POSIX

### Example

    int fd = open("data", O_RDONLY);
    close(fd);

Node:_close, Next:closedir, Previous:close, Up:Alphabetical List

## _close

### Syntax

    #include <io.h>

    int _close(int fd);

### Description

This is a direct connection to the MS-DOS close function call, int 0x21, %ah = 0x3e. This function can be hooked by the See File System Extensions. If you don't want this, you should use See _dos_close.

### Return Value

Zero if the file was closed, else nonzero.

### Portability

not ANSI, not POSIX

Node:closedir, Next:clreol, Previous:_close, Up:Alphabetical List

## closedir

### Syntax

    #include <dirent.h>

    int closedir(DIR *dir);

### Description

This function closes a directory opened by opendir (see opendir).

### Return Value

Zero on success, nonzero if dir is invalid.

### Portability

not ANSI, POSIX

Node:clreol, Next:clrscr, Previous:closedir, Up:Alphabetical List

## clreol

### Syntax

    #include <conio.h>

    void clreol(void);

### Description

Clear to end of line.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:clrscr, Next:_conio_kbhit, Previous:clreol, Up:Alphabetical List

## clrscr

### Syntax

    #include <conio.h>

    void clrscr(void);

### Description

Clear the entire screen.

### Portability

not ANSI, not POSIX

Node:_conio_kbhit, Next:_control87, Previous:clrscr, Up:Alphabetical List

## _conio_kbhit

### Syntax

    #include <conio.h>

    int _conio_kbhit(void);

### Description

Determines whether or not a character is waiting at the keyboard. If there is an ungetch'd character, this function returns true. Note that if you include `conio.h`, the kbhit function is redefined to be this function instead.

### Return Value

Nonzero if a key is waiting, else zero.

### Portability

not ANSI, not POSIX

Node:_control87, Next:cos, Previous:_conio_kbhit, Up:Alphabetical List

## _control87

### Syntax

    #include <float.h>

    unsigned int _control87(unsigned int newcw, unsigned int mask);

### Description

This function sets and retrieves the FPU's control word.

The control word is a special 16-bit register maintained by the math coprocessor. By setting and clearing bit fields in the control word, you can exercise control of certain aspects of coprocessor operation. The individual bits of the x87 control word are defined by macros in float.h, and shown in this table:

    ---- ---- --XX XXXX = MCW_EM - exception masks (1=handle exception internally, 0=fault)
    ---- ---- ---- ---X = EM_INVALID - invalid operation
    ---- ---- ---- --X- = EM_DENORMAL - denormal operand
    ---- ---- ---- -X-- = EM_ZERODIVIDE - divide by zero
    ---- ---- ---- X--- = EM_OVERFLOW - overflow
    ---- ---- ---X ---- = EM_UNDERFLOW - underflow
    ---- ---- --X- ---- = EM_INEXACT - rounding was required
    ---- --XX ---- ---- = MCW_PC - precision control
    ---- --00 ---- ---- = PC_24 - single precision
    ---- --10 ---- ---- = PC_53 - double precision
    ---- --11 ---- ---- = PC_64 - extended precision
    ---- XX-- ---- ---- = MCW_RC - rounding control
    ---- 00-- ---- ---- = RC_NEAR - round to nearest
    ---- 01-- ---- ---- = RC_DOWN - round towards -Inf
    ---- 10-- ---- ---- = RC_UP - round towards +Inf
    ---- 11-- ---- ---- = RC_CHOP - round towards zero
    ---X ---- ---- ---- = MCW_IC - infinity control (obsolete, always affine)
    ---0 ---- ---- ---- = IC_AFFINE - -Inf < +Inf
    ---1 ---- ---- ---- = IC_PROJECTIVE - -Inf == +Inf

`_control87` uses the value of newcw and mask variables together to determine which bits of the FPU's control word should be set, and to what values. For each bit in mask that is set (equals to 1), the corresponding bit in newcw specifies the new value of the same bit in the FPU's control word, which `_control87` should set. Bits which correspond to reset (zero) bits in mask are not changed in the FPU's control word. Thus, using a zero value for mask retrieves the current value of the control word without changing it.

The exception bits `MCW_EM` (the low-order 6 bits) of the control word define the exception mask. That is, if a certain bit is set, the corresponding exception will be masked, i.e., it will not generate an FP exception (which normally causes signal `SIGFPE` to be delivered). A masked exception will be handled internally by the coprocessor. In general, that means that it will generate special results, such as NaN, Not-a-Number (e.g., when you attempt to compute a square root of a negative number), denormalized result (in case of underflow), or infinity (e.g., in the case of division by zero, or when the result overflows).

By default, DJGPP startup code masks all FP exceptions.

The precision-control field `MCW_PC` (bits 8 and 9) controls the internal precision of the coprocessor by selecting the number of precision bits in the mantissa of the FP numbers. The values `PC_24`, `PC_53`, and `PC_64` set the precision to 24, 53, and 64-bit mantissa, respectively. This feature of the coprocessor is for compatibility with the IEEE 745 standard and only affect the `FADD`, `FSUB` `FSUBR`, `FMUL`, `FDIV`, `FDIVR`, and `FSQRT` instructions. Lowering the precision will not decrease the execution time of FP instructions.

The `MCW_PC` field is set to use the full-precision 64-bit mantissa by the DJGPP startup code.

The rounding-control field `MCW_RC` (bits 10 and 11) controls the type (round or chop) and direction (-Inf or +Inf) of the rounding. It only affects arithmetic instructions. Set to round-to-nearest state by the DJGPP startup code.

The infinity-control bit `MCW_IC` has no effect on 80387 and later coprocessors.

### Return Value

The previous control word.

(Note that this is different from what `_control87` from the Borland C library which returns the new control word.)

### Portability

not ANSI, not POSIX

### Example

      /* mask all exceptions, except invalid operation */
      _control87 (0x033e, 0xffff);

Node:cos, Next:cosh, Previous:_control87, Up:Alphabetical List

## cos

### Syntax

    #include <math.h>

    double cos(double x);

### Description

This function computes the cosine of x (which should be given in radians).

### Return Value

The cosine of x. If the absolute value of x is finite but greater than or equal to 2^63, the value is 1 (since for arguments that large each bit of the mantissa is more than `Pi`). If the value of x is infinite or `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

### Accuracy

In general, this function's relative accuracy is about 1.7*10^(-16), which is close to the machine precision for a `double`. However, for arguments very close to `Pi/2` and its odd multiples, the relative accuracy can be many times worse, due to loss of precision in the internal FPU computations. Since cos(Pi/2) is zero, the absolute accuracy is still very good; but if your program needs to preserve high relative accuracy for such arguments, link with `-lm` and use the version of `cos` from `libm.a` which does elaborate argument reduction, but is about three times slower.

Node:cosh, Next:cprintf, Previous:cos, Up:Alphabetical List

## cosh

### Syntax

    #include <math.h>

    double cosh(double x);

### Description

This function computes the hyperbolic sine of x.

### Return Value

The hyperbolic cosine of x. If the value of x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`. If the value of x is so large that the result would overflow a `double`, the return value is `Inf` and `errno` is set to `ERANGE`. If x is either a positive or a negative infinity, the result is `+Inf`, and `errno` is not changed.

### Portability

ANSI, POSIX

Node:cprintf, Next:cputs, Previous:cosh, Up:Alphabetical List

## cprintf

### Syntax

    #include <conio.h>

    int cprintf(const char *_format, ...);

### Description

Like `printf` (see printf), but prints through the console, taking into consideration window borders and text attributes. There is currently a 2048-byte limit on the size of each individual cprintf call.

### Return Value

The number of characters written.

### Portability

not ANSI, not POSIX

Node:cputs, Next:creat, Previous:cprintf, Up:Alphabetical List

## cputs

### Syntax

    #include <conio.h>

    int cputs(const char *_str);

### Description

Puts the string onto the console. The cursor position is updated.

### Return Value

Zero on success.

### Portability

not ANSI, not POSIX

Node:creat, Next:_creat, Previous:cputs, Up:Alphabetical List

## creat

### Syntax

    #include <fcntl.h>
    #include <sys/stat.h> /* for mode definitions */

    int creat(const char *filename, mode_t mode);

### Description

This function creates the given file and opens it for writing. If the file exists, it is truncated to zero size, unless it is read-only, in which case the function fails. If the file does not exist, it will be created read-only if mode does not have `S_IWUSR` set.

### Return Value

A file descriptor >= 0, or a negative number on error.

### Portability

not ANSI, POSIX

### Example

    int fd = creat("data", S_IRUSR|S_IWUSR);
    write(fd, buf, 1024);
    close(fd);

Node:_creat, Next:_creatnew, Previous:creat, Up:Alphabetical List

## _creat

### Syntax

    #include <io.h>

    int _creat(const char *path, int attrib);

### Description

This is a direct connection to the MS-DOS creat function call, int 0x21, %ah = 0x3c. The file is set to binary mode. This function can be hooked by the File System Extensions, see File System Extensions. If you don't want this, you should use `_dos_creat` (see _dos_creat) or `_dos_creatnew` (see _dos_creatnew).

On platforms where the LFN API (see LFN) is available, `_creat` calls function 0x716C of Interrupt 21h, to support long file names.

### Return Value

The new file descriptor, else -1 on error.

### Portability

not ANSI, not POSIX

Node:_creatnew, Next:crlf2nl, Previous:_creat, Up:Alphabetical List

## _creatnew

### Syntax

    #include <fcntl.h>
    #include <dir.h>
    #include <io.h>

    int _creatnew(const char *path, int attrib, int flags);

### Description

This function creates a file given by path and opens it, like `_creat` does, but only if it didn't already exist. If the named file exists, `_creatnew` fails. (In contrast, `_creat` opens existing files and overwrites their contents, see _creat.)

The attributes of the created file are determined by attrib. The file is usually given the normal attribute (00H). If attrib is non-zero, additional attributes will be set. The following macros, defined on `<dir.h>`, can be used to control the attributes of the created file (the associated numeric values appear in parentheses):

`FA_RDONLY (1)`
  The file is created with the read-only bit set.
`FA_HIDDEN (2)`
  The file is created with the hidden bit set. Such files will not appear in directory listings unless you use special options to the commands which list files.
`FA_SYSTEM (4)`
  The file is created with the system bit set. Such files will not appear in directory listings unless you use special options to the commands which list files.

Other bits (`FA_LABEL` and `FA_DIREC`) are ignored by DOS.

The argument flags controls the sharing mode and the fine details of how the file is handled by the operating system. The following macros, defined on `<fcntl.h>`, can be used for this (associated numeric values are given in parentheses):

`SH_COMPAT (00h)`
  Opens the file in compatibility mode, which allows any other process to open the file and read from the file any number of times.
`SH_DENYRW (10h)`
  Denies both read and write access by other processes.
`SH_DENYWR (20h)`
  Denies write access by other processes.
`SH_DENYRD (30h)`
  Denies read access by other processes.
`SH_DENYNO (40h)`
  Allows read and write access by other processes, but prevents other processes from opening the file in compatibility mode.

Note that the file is always open for both reading and writing; `_creatnew` ignores any bits in the lower nibble of flags (`O_RDONLY`, `O_WRONLY`, etc.).

`_creatnew` calls DOS function 716Ch when long file names are supported, 6C00h otherwise. (On DOS version 3.x, function 5B00h is called which ignores the value of flags, since function 6C00h is only supported by DOS 4.0 and later.)

The file handle returned by `_creatnew` is set to binary mode.

This function can be hooked by the Filesystem Extensions handlers, as described in File System Extensions. If you don't want this, you should use `_dos_creatnew` (see _dos_creatnew) instead.

### Return Value

The new file descriptor, else -1 on error.

### Portability

not ANSI, not POSIX

Node:crlf2nl, Next:__crt0_glob_function, Previous:_creatnew, Up:Alphabetical List

## crlf2nl

### Syntax

    #include <io.h>

    size_t crlf2nl(char *buf, ssize_t len);

### Description

This function removes Ctrl-M characters from the given buf.

### Return Value

The number of characters remaining in the buffer are returned.

### Portability

not ANSI, not POSIX

Node:__crt0_glob_function, Next:__crt0_load_environment_file, Previous:crlf2nl, Up:Alphabetical List

## __crt0_glob_function

### Syntax

    #include <crt0.h>

    char **__crt0_glob_function(char *_argument);

### Description

If the application wishes to provide a wildcard expansion function, it should define a `__crt0_glob_function` function. It should return a list of the expanded values, or 0 if no expansion will occur. The startup code will free the returned pointer if it is nonzero.

If no expander function is provided, wildcards will be expanded in the POSIX.1 style by the default `__crt0_glob_function` from the C library. To disable expansion, provide a `__crt0_glob_function` that always returns 0.

### Portability

not ANSI, not POSIX

Node:__crt0_load_environment_file, Next:__crt0_setup_arguments, Previous:__crt0_glob_function, Up:Alphabetical List

## __crt0_load_environment_file

### Syntax

    #include <crt0.h>

    void   __crt0_load_environment_file(char *_app_name);

### Description

This function, provided by libc.a, does all the work required to load additional environment variables from the file `djgpp.env` whose full pathname is given by the `DJGPP` environment variable. If the application does not use environment variables, the programmer can reduce the size of the program image by providing a version of this function that does nothing.

See __crt0_setup_arguments.

### Portability

not ANSI, not POSIX

Node:__crt0_setup_arguments, Next:_crt0_startup_flags, Previous:__crt0_load_environment_file, Up:Alphabetical List

## __crt0_setup_arguments

### Syntax

    #include <crt0.h>

    void   __crt0_setup_arguments(void);

### Description

This function, provided by libc.a, does all the work required to provide the two arguments passed to main() (usually `argc` and `argv`). If main() does not use these arguments, the programmer can reduce the size of the program image by providing a version of this function that does nothing.

Note that since the default `__crt0_setup_arguments_function` will not expand wildcards inside quotes (`"` or `'`), you can quote a part of the argument that doesn't include wildcards and still have them expanded. This is so you could use wildcard expansion with filenames which have embedded whitespace (on LFN filesystems).

See __crt0_load_environment_file.

### Portability

not ANSI, not POSIX

Node:_crt0_startup_flags, Next:cscanf, Previous:__crt0_setup_arguments, Up:Alphabetical List

## _crt0_startup_flags

### Syntax

    #include <crt0.h>

    int _crt0_startup_flags = ...;

### Description

This variable can be used to determine what the startup code will (or will not) do when the program begins. This can be used to tailor the startup environment to a particular program.

`_CRT0_FLAG_PRESERVE_UPPER_CASE`
  If set, `argv[0]` is left in whatever case it was. If not set, all characters are mapped to lower case. Note that if the `argv0` field in the stubinfo structure is present, the case of that part of `argv[0]` is not affected.
`_CRT0_FLAG_USE_DOS_SLASHES`
  If set, reverse slashes (dos-style) are preserved in `argv[0]`. If not set, all reverse slashes are replaced with unix-style slashes.
`_CRT0_FLAG_DROP_EXE_SUFFIX`
  If set, the `.exe` suffix is removed from the file name component of `argv[0]`. If not set, the suffix remains.
`_CRT0_FLAG_DROP_DRIVE_SPECIFIER`
  If set, the drive specifier (e.g. `C:`) is removed from the beginning of `argv[0]` (if present). If not set, the drive specifier remains.
`_CRT0_FLAG_DISALLOW_RESPONSE_FILES`
  If set, response files (e.g. `@gcc.rf`) are not expanded. If not set, the contents of the response files are used to create arguments. Note that if the file does not exist, that argument remains unexpanded.
`_CRT0_FLAG_KEEP_QUOTES`
  If set, the quote characters `'`, `"`, and `\` will be retained in `argv[]` elements when processing command lines passed by DOS and via `system`. This is used by the `redir` program, and should only be needed if you want to get the original command line exactly as it was passed by the caller.
`_CRT0_FLAG_FILL_SBRK_MEMORY`
  If set, fill `sbrk`'d memory with a constant value. If not, memory gets whatever happens to have been in there, which breaks some applications.
`_CRT0_FLAG_FILL_DEADBEEF`
  If set, fill memory (above) with `0xdeadbeef`, else fill with zero. This is especially useful for debugging uninitialized memory problems.
`_CRT0_FLAG_NEARPTR`
  If set, set DS limit to 4GB which allows use of near pointers to DOS (and other) memory. WARNING, disables memory protection and bad pointers may crash the machine or wipe out your data. This flag is silently ignored on NT and DOSEmu, which disallow such huge selector limits.
`_CRT0_FLAG_NULLOK`
  If set, disable NULL pointer protection (if it can be controlled at all).
`_CRT0_FLAG_NMI_SIGNAL`
  If set, enabled capture of NMI in exception code. This may cause problems with laptops and "green" boxes which use it to wake up. Default is to leave NMIs alone and pass through to real mode code. You decide.
`_CRT0_FLAG_NO_LFN`
  If set, disable usage of long file name functions even on systems (such as Windows 9X) which support them. This might be needed to work around program assumptions on file name format on programs written specifically for DOS. Note that this flag overrides the value of the environment variable `LFN`.
`_CRT0_FLAG_NONMOVE_SBRK`
  If set, the `sbrk` algorithm uses multiple DPMI memory blocks which makes sure the base of CS/DS/SS does not change. This may cause problems with `sbrk(0)` values and programs with other assumptions about `sbrk` behavior. This flag is useful with near pointers, since a constant pointer to DOS/Video memory can be computed without needing to reload it after any routine which might call `sbrk`.
`_CRT0_FLAG_UNIX_SBRK`
  If set, the `sbrk` algorithm resizes memory blocks so that the layout of memory is set up to be the most compatible with Unix `sbrk` expectations. This mode should not be used with hardware interrupts, near pointers, and may cause problems with QDPMI virtual memory. On NT, this is the recommended algorithm.

  If your program requires a specific `sbrk` behavior, you should set either this or the previous flag, since the default may change in different libc releases.

`_CRT0_FLAG_LOCK_MEMORY`
  If set, locks all memory as it is allocated. This effectively disables virtual memory, and may be useful if using extensive hardware interrupt codes in a relatively small image size. The memory is locked after it is `sbrk`'ed, so the locking may fail. This bit may be set or cleared during execution. When `sbrk` uses multiple memory zones, it can be difficult to lock all memory since the memory block size and location is impossible to determine.
`_CRT0_FLAG_PRESERVE_FILENAME_CASE`
  If set, disables all filename letter-case conversions in functions that traverse directories (except findfirst/findnext which always return the filenames exactly as found in the directory entry). When reset, all filenames on 8+3 MSDOS filesystems and DOS-style 8+3 filenames on LFN systems are converted to lower-case by functions such as `readdir', `getcwd`, `_fixpath` and others. Note that when this flag is set, ALL filenames on MSDOS systems will appear in upper-case, which is both ugly and will break many Unix-born programs. Use only if you know exactly what you are doing!

  This flag overrides the value of the environment variable `FNCASE`, See _preserve_fncase.

### Portability

not ANSI, not POSIX

Node:cscanf, Next:ctermid, Previous:_crt0_startup_flags, Up:Alphabetical List

## cscanf

### Syntax

    #include <conio.h>

    int cscanf(const char *_format, ...);

### Description

Like `scanf` (see scanf), but it reads from the standard input device directly, avoiding buffering both by DOS and by the library. Each character is read by `getche` (see getche).

### Return Value

The number of fields stored.

### Portability

not ANSI, not POSIX

Node:ctermid, Next:ctime, Previous:cscanf, Up:Alphabetical List

## ctermid

### Syntax

    #include <unistd.h>

    char *ctermid(char *s);

### Description

This function returns the name of the current terminal device. Under MS-DOS, this is always "con".

### Return Value

If s is null, returns pointer to internal static string "con". Otherwise, copies "con" to buffer pointed by s.

### Portability

not ANSI, POSIX

Node:ctime, Next:delay, Previous:ctermid, Up:Alphabetical List

## ctime

### Syntax

    #include <time.h>

    char *ctime(const time_t *cal);

### Description

This function returns an ASCII representation of the time in cal. This is equivalent to `asctime(localtime(cal))`. See asctime. See localtime.

### Return Value

The ascii representation of the time.

### Portability

ANSI, POSIX

Node:delay, Next:delline, Previous:ctime, Up:Alphabetical List

## delay

### Syntax

    #include <dos.h>

    void delay(unsigned msec);

### Description

This function causes the program to pause for msec milliseconds. It uses the `int 15h` delay function to relinquish the CPU to other programs that might need it.

Some operating systems that emulate DOS, such as OS/2 and Windows/NT, hang the DOS session when the <Pause> key is pressed during the call to `delay`. Plain DOS and Windows 3.X and 9X are known to not have this bug.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    delay(200); /* delay for 1/5 second */

Node:delline, Next:_detect_80387, Previous:delay, Up:Alphabetical List

## delline

### Syntax

    #include <conio.h>

    void    delline(void);

### Description

The line the cursor is on is deleted; lines below it scroll up.

### Portability

not ANSI, not POSIX

Node:_detect_80387, Next:difftime, Previous:delline, Up:Alphabetical List

## _detect_80387

### Syntax

    #include <dos.h>

    int _detect_80387(void);

### Description

Detects whether a numeric coprocessor is present. Note that floating-point code will work even without a coprocessor, due to the existence of emulation.

### Return Value

1 if a coprocessor is present, 0 if not.

### Portability

not ANSI, not POSIX

### Example

    if (_detect_80387())
      printf("You have a coprocessor\n");

Node:difftime, Next:dirname, Previous:_detect_80387, Up:Alphabetical List

## difftime

### Syntax

    #include <time.h>

    double difftime(time_t t1, time_t t0);

### Description

This function returns the difference in time, in seconds, from t0 to t1.

### Return Value

The number of seconds.

### Portability

ANSI, POSIX

### Example

    time_t t1, t0;
    double elapsed;
    time(&t0);
    do_something();
    time(&t1);
    elapsed = difftime(t1, t0);

Node:dirname, Next:disable, Previous:difftime, Up:Alphabetical List

## dirname

### Syntax

    #include <unistd.h>

    char * dirname (const char *fname);

### Description

This function returns the directory part of the argument fname copied to a buffer allocated by calling `malloc`. The directory part is everything up to but not including the rightmost slash (either forward- or backslash) in fname. If fname includes a drive letter but no slashes, the function will return `x:.` where x is the drive letter. If fname includes neither the drive letter nor any slashes, `"."` will be returned. Trailing slashes are removed from the result, unless it is a root directory, with or without a drive letter.

### Return value

The directory part in malloc'ed storage, or a NULL pointer of either there's not enough free memory, or fname is a NULL pointer.

### Portability

not ANSI, not POSIX

### Example

     printf ("The parent of current directory is %s\n",
             dirname (getcwd (0, PATH_MAX)));

Node:disable, Next:div, Previous:dirname, Up:Alphabetical List

## disable

### Syntax

    #include <dos.h>

    int disable(void);

### Description

This function disables interrupts.

See enable.

### Return Value

Returns nonzero if the interrupts had been enabled before this call, zero if they were already disabled.

### Portability

not ANSI, not POSIX

### Example

    int ints_were_enabled;

    ints_were_enabled = disable();
    . . . do some stuff . . .
    if (ints_were_enabled)
      enable();

Node:div, Next:__djgpp_exception_toggle, Previous:disable, Up:Alphabetical List

## div

### Syntax

    #include <stdlib.h>

    div_t div(int numerator, int denominator);

### Description

Returns the quotient and remainder of the division numerator divided by denominator. The return type is as follows:

    typedef struct {
      int quot;
      int rem;
    } div_t;

### Return Value

The results of the division are returned.

### Portability

ANSI, POSIX

### Example

    div_t d = div(42, 3);
    printf("42 = %d x 3 + %d\n", d.quot, d.rem);

    div(+40, +3) = { +13, +1 }
    div(+40, -3) = { -13, -1 }
    div(-40, +3) = { -13, -1 }
    div(-40, -3) = { +13, -1 }

Node:__djgpp_exception_toggle, Next:__djgpp_map_physical_memory, Previous:div, Up:Alphabetical List

## __djgpp_exception_toggle

### Syntax

    #include <sys/exceptn.h>

    void __djgpp_exception_toggle(void);

### Description

This function is automatically called when the program exits, to restore handling of all the exceptions to their normal state. You may also call it from your program, around the code fragments where you need to temporarily restore all the exceptions to their default handling. One example of such case might be a call to a library functions that spawn child programs, when you don't want to handle signals generated while the child runs (by default, those signals are also passed to the parent).

### Portability

not ANSI, not POSIX

### Example

      __djgpp_exception_toggle();
      system("myprog");
      __djgpp_exception_toggle();

Node:__djgpp_map_physical_memory, Next:__djgpp_memory_handle, Previous:__djgpp_exception_toggle, Up:Alphabetical List

## __djgpp_map_physical_memory

### Syntax

    #include <dpmi.h>

    int __djgpp_map_physical_memory(void *our_addr, unsigned long num_bytes,
    			        unsigned long phys_addr);

### Description

This function attempts to map a range of physical memory over the specified addresses. One common use of this routine is to map device memory, such as a linear frame buffer, into the address space of the calling program. our_addr, num_bytes, and phys_addr must be page-aligned. If they are not page-aligned, errno will be set to `EINVAL` and the routine will fail.

This routine properly handles memory ranges that span multiple DPMI handles, while `__dpmi_map_device_in_memory_block` does not.

Consult DPMI documentation on function 0508H for details on how this function works. Note: since 0508H is a DPMI service new with DPMI 1.0, this call will fail on most DPMI 0.9 servers. For your program to work on a wide range of systems, you should not assume this call will succeed.

Even on failure, this routine may affect a subset of the pages specified.

### Return Value

0 on success, -1 on failure. On failure, errno will be set to `EINVAL` for illegal input parameters, or `EACCES` if the DPMI server rejected the mapping request.

### Portability

not ANSI, not POSIX

### Example

    if (__djgpp_map_physical_memory (my_page_aligned_memory, 16384, 0x40000000))
      printf ("Failed to map physical addresses!\n");

Node:__djgpp_memory_handle, Next:__djgpp_memory_handle_list, Previous:__djgpp_map_physical_memory, Up:Alphabetical List

## __djgpp_memory_handle

### Syntax

    #include <crt0.h>

    __djgpp_sbrk_handle *__djgpp_memory_handle(unsigned address);

### Description

This function returns a pointer to a structure containing the memory handle and program relative offset associated with the address passed. It is just a convenient way to process the __djgpp_memory_handle_list.

### Return Value

A pointer to the __djgpp_sbrk_handle associated with a particular address.

### Portability

not ANSI, not POSIX

Node:__djgpp_memory_handle_list, Next:__djgpp_nearptr_disable, Previous:__djgpp_memory_handle, Up:Alphabetical List

## __djgpp_memory_handle_list

### Syntax

    #include <crt0.h>

    extern __djgpp_sbrk_handle __djgpp_memory_handle_list[256];

### Description

This array contains a list of memory handles and program relative offsets allocated by sbrk() in addition to the handle allocated by the stub. These values are normally not needed unless you are doing low-level DPMI page protection or memory mapping.

### Portability

not ANSI, not POSIX

Node:__djgpp_nearptr_disable, Next:__djgpp_nearptr_enable, Previous:__djgpp_memory_handle_list, Up:Alphabetical List

## __djgpp_nearptr_disable

### Syntax

    #include <sys/nearptr.h>

    void __djgpp_nearptr_disable(void);

### Description

This function disables near pointers, and re-enables protection. See __djgpp_nearptr_enable.

### Portability

not ANSI, not POSIX

Node:__djgpp_nearptr_enable, Next:__djgpp_set_ctrl_c, Previous:__djgpp_nearptr_disable, Up:Alphabetical List

## __djgpp_nearptr_enable

### Syntax

    #include <sys/nearptr.h>

    int __djgpp_nearptr_enable(void);

### Description

This function enables "near pointers" to be used to access the DOS memory arena. Sort of. When you call this function, it will return nonzero if it has successfully enabled near pointers. If so, you must add the value `__djgpp_conventional_base` to the linear address of the physical memory. For example:

    if (__djgpp_nearptr_enable())
    {
      short *screen = (short *)(__djgpp_conventional_base + 0xb8000);
      for (i=0; i<80*24*2; i++)
        screen[i] = 0x0720;
      __djgpp_nearptr_disable();
    }

The variable `__djgpp_base_address` contains the linear base address of the application's data segment. You can subtract this value from other linear addresses that DPMI functions might return in order to obtain a near pointer to those linear regions as well.

If using the Unix-like sbrk algorithm, near pointers are only valid until the next `malloc`, `system`, `spawn*`, or `exec*` function call, since the linear base address of the application may be changed by these calls.

WARNING: When you enable near pointers, you disable all the protection that the system is providing. If you are not careful, your application may destroy the data in your computer. USE AT YOUR OWN RISK!

### Return Value

Returns 0 if near pointers are not available, or nonzero if they are.

### Portability

not ANSI, not POSIX

Node:__djgpp_set_ctrl_c, Next:__djgpp_set_page_attributes, Previous:__djgpp_nearptr_enable, Up:Alphabetical List

## __djgpp_set_ctrl_c

### Syntax

    #include <sys/exceptn.h>

    int __djgpp_set_ctrl_c(int enable);

### Description

This function sets and resets the bit which controls whether signals `SIGINT` and `SIGQUIT` (see signal) will be raised when you press the INTR or QUIT keys. By default these generate signals which, if uncaught by a signal handler, will abort your program. However, when you call the `setmode` library function to switch the console reads to binary mode, or open the console in binary mode for reading, this generation of signals is turned off, because some programs want to get the `^C` and `^\` characters as any other character and handle them by themselves.

`__djgpp_set_ctrl_c` lets you explicitly determine the effect of INTR and QUIT keys. When called with a non-zero, positive value of enable, it arranges for `SIGINT` and `SIGQUIT` signals to be generated when the appropriate key is pressed; if you call it with a zero in enable, these keys are treated as normal characters. If enable is negative, `__djgpp_set_ctrl_c` returns the current state of the signal generation, but doesn't change it.

For getting similar effects via the POSIX `termios` functions, see tcsetattr.

Note that the effect of `Ctrl-<BREAK>` key is unaffected by this function; use the `_go32_want_ctrl_break` library function to control it.

Also note that in DJGPP, the effect of the interrupt signal will only be seen when the program is in protected mode (See Signal Mechanism, for more details). Thus, if you press `Ctrl-C` while your program calls DOS (e.g., when reading from the console), the `SIGINT` signal handler will only be called after that call returns.

### Return Value

The state of `SIGINT` and `SIGQUIT` generation before the call: 0 if it was disabled, 1 if it was enabled. If the argument enable is negative, the state is not altered.

### Portability

not ANSI, not POSIX

### Example

      setmode(fileno(stdin), O_BINARY);
      if (isatty(fileno(stdin)));
        __djgpp_set_ctrl_c(1);

Node:__djgpp_set_page_attributes, Next:__djgpp_set_sigint_key, Previous:__djgpp_set_ctrl_c, Up:Alphabetical List

## __djgpp_set_page_attributes

### Syntax

    #include <dpmi.h>

    int __djgpp_set_page_attributes(void *our_addr, unsigned long num_bytes,
    			        unsigned short attributes);

### Description

This function sets the DPMI page attributes for the pages in a range of memory. our_addr and num_bytes must be page-aligned. If they are not page-aligned, errno will be set to `EINVAL` and the routine will fail.

Consult DPMI documentation on function 0507H for the meaning of the attributes argument. Note: since 0507H is a DPMI service new with DPMI 1.0, this call will fail on most DPMI 0.9 servers. For your program to work on a wide range of systems, you should not assume this call will succeed.

Even on failure, this routine may affect a subset of the pages specified.

### Return Value

0 on success, -1 on failure. On failure, errno will be set to `EINVAL` for illegal input parameters, or `EACCES` if the DPMI server rejected the attribute setting.

### Portability

not ANSI, not POSIX

### Example

    if (__djgpp_set_page_attributes (my_page_aligned_memory, 16384, 0))
      printf ("Failed to make pages uncommitted!\n");

Node:__djgpp_set_sigint_key, Next:__djgpp_set_sigquit_key, Previous:__djgpp_set_page_attributes, Up:Alphabetical List

## __djgpp_set_sigint_key

### Syntax

    #include <sys/exceptn.h>

    void __djgpp_set_sigint_key(int new_key);

### Description

This function changes the INTR key that generates the signal `SIGINT`. By default, `Ctrl-C` is set as the INTR key. To replace it with another key, put the scan code of the new INTR key into the bits 0-7 and the required keyboard status byte into bits 8-15 of new_key, and call this function. Here's how the keyboard status bits are defined:

       Bit
     76543210    Meaning

     .......X    Right Shift key
     ......X.    Left Shift key
     .....X..    Ctrl key
     ....X...    Alt key
     ...X....    Scroll Lock key
     ..X.....    Num Lock key
     .X......    Caps Lock key
     X.......    Insert

A 1 in any of the above bits means that the corresponding key should be pressed; a zero means it should be released. Currently, all but the lower 4 bits are always ignored by the DJGPP keyboard handler when you set the INTR key using this function.

For example, the default `Ctrl-C` key should be passed as `0x042e`, since the scan code of the <C> key is 2Eh, and when the <Ctrl> key is pressed, the keyboard status byte is 04h.

To disable `SIGINT` generation, pass zero as the argument (since no key has a zero scan code).

This function will set things up so that the left <Shift> key doesn't affect Ctrl- and Alt-modified keys; the right <Shift> key won't affect them either, unless its bit is explicitly set in new_key. This means that `Ctrl-C` and `Ctrl-c` will both trigger `SIGINT` if `0x042e` is passed to this function.

The DJGPP built-in keyboard handler pretends that when the right <Shift> key is pressed, so is the left <Shift> key (but not vice versa).

For getting similar effects via the POSIX `termios` functions, see tcsetattr.

### Return Value

The previous INTR key (scan code in bits 0-7, keyboad status in bits 8-15).

### Portability

not ANSI, not POSIX

### Example

      __djgpp_set_sigint_key(0x0422);  /* make Ctrl-g generate SIGINT's */

Node:__djgpp_set_sigquit_key, Next:__djgpp_share_flags, Previous:__djgpp_set_sigint_key, Up:Alphabetical List

## __djgpp_set_sigquit_key

### Syntax

    #include <sys/exceptn.h>

    void __djgpp_set_sigquit_key(int new_key);

### Description

This function changes the QUIT key that generates the signal `SIGQUIT`. By default, `Ctrl-\` is set as the QUIT key. To replace it with another key, put the scan code of the new QUIT key into the bits 0-7 and the required keyboard status byte into bits 8-15 of new_key, and call this function. Here's how the keyboard status bits are defined:

       Bit
     76543210    Meaning

     .......X    Right Shift key
     ......X.    Left Shift key
     .....X..    Ctrl key
     ....X...    Alt key
     ...X....    Scroll Lock key
     ..X.....    Num Lock key
     .X......    Caps Lock key
     X.......    Insert

A 1 in any of the above bits means that the corresponding key should be pressed; a zero means it should be released. Currently, all but the lower 4 bits are always ignored by the DJGPP keyboard handler when you set the QUIT key with this function.

For example, the default `Ctrl-\` key should be passed as `0x042b`, since the scan code of `\` is 2Bh and when the <Ctrl> key is pressed, the keyboard status byte is 04h.

To disable `SIGQUIT` generation, pass zero as the argument (since no key has a zero scan code).

This function will set things up so that the left <Shift> key doesn't affect Ctrl- and Alt-modified keys; the right <Shift> key won't affect them either, unless its bit is explicitly set in new_key. This means that `Ctrl-\` and `Ctrl-|` will both trigger `SIGQUIT` if `0x042b` is passed to this function.

The DJGPP built-in keyboard handler pretends that when the right <Shift> key is pressed, so is the left <Shift> key (but not vice versa).

For getting similar effects via the POSIX `termios` functions, see tcsetattr.

### Return Value

The previous QUIT key (scan code in bits 0-7, keyboad status in bits 8-15).

### Portability

not ANSI, not POSIX

### Example

      __djgpp_set_sigint_key(0);  /* disable SIGQUIT's */

Node:__djgpp_share_flags, Next:__djgpp_traceback_exit, Previous:__djgpp_set_sigquit_key, Up:Alphabetical List

## __djgpp_share_flags

### Syntax

    #include <fcntl.h>

    int __djgpp_share_flags = ...;

### Description

This variable controls the share flags used by `open` (and hence `fopen`) when opening a file.

If you assign any value other than 0 to this variable libc will use that value for the sharing bits when if calls DOS to open the file. But if you specify any share flag in the `open` call then these flags will remain untouched. In this way `__djgpp_share_flags` acts just like a default and by default is 0 ensuring maximum compatibility with older versions of djgpp.

If you don't know how the share flags act consult any DOS reference. They allow to share or protect a file when it's opened more than once by the same task or by two or more tasks. The exact behavior depends on the exact case. One interesting thing is that when the file is opened by two tasks under Windows the results are different if you use Windows 3.1 or Windows 95. To add even more complexity Windows 3.1 is affected by `SHARE.EXE`.

The available flags are:

`SH_COMPAT 0x0000`
  That's the compatible mode.
`SH_DENYRW 0x0010`
  Deny read and deny write.
`SH_DENYWR 0x0020`
  Deny write.
`SH_DENYRD 0x0030`
  Deny read.
`SH_DENYNO 0x0040`
  No deny.

Of course these flags are DOS specific and doesn't exist under other OSs; and as you can imagine `__djgpp_share_flags` is djgpp specific.

See open. See fopen.

### Portability

not ANSI, not POSIX

Node:__djgpp_traceback_exit, Next:_djstat_describe_lossage, Previous:__djgpp_share_flags, Up:Alphabetical List

## __djgpp_traceback_exit

### Syntax

    #include <signal.h>

    void __djgpp_traceback_exit(int signo);

### Description

This function is a signal handler which will print a traceback and abort the program. It is called by default by the DJGPP signal-handling code when any signal except `SIGQUIT` is raised (`SIGQUIT` is by default discarded).

You can use this function to get the Unix behavior of aborting the program on `SIGQUIT` (see the example below).

When this function is called directly, pass the signal number as its signo argument.

### Portability

not ANSI, not POSIX

### Example

      signal(SIGQUIT, __djgpp_traceback_exit);

Node:_djstat_describe_lossage, Next:_djstat_fail_bits, Previous:__djgpp_traceback_exit, Up:Alphabetical List

## _djstat_describe_lossage

### Syntax

    #include <stdio.h>

    void _djstat_describe_lossage(FILE *fp);

### Description

Accesses the global variable _djstat_fail_bits and prints to the stream given by fp a human-readable description of the undocumented DOS features which the last call to `stat()` or `fstat()` failed to use. (If fp is zero, the function prints to stderr.) If the last call to `f?stat()` didn't set any failure bits, an "all's well" message is printed. This function is designed to help in debugging these functions in hostile environments (like DOS clones) and in adapting them to the future DOS versions. If you ever have any strange results returned by `f?stat()`, please call this function and post the diagnostics it printed to the DJGPP mailing list.

The diagnostic messages this function prints are almost self-explanatory. Some explanations of terminology and abbreviations used by the printed messages will further clarify them.

SDA (Swappable DOS Area) - this is an internal DOS structure. `stat()` uses it to get the full directory entry (including the starting cluster number) of a file. The pointer to SDA found by `stat()` is trusted only if we find the pathname of our file at a specific offset in that SDA.

SFT (System File Table) - another internal DOS structure, used in file operations. `fstat()` uses it to get full information on a file given its handle. An SFT entry which is found by `fstat()` is only trusted if it contains files size and time stamp like those returned by DOS functions 57h and 42h. Novell NetWare 3.x traps DOS file operations in such a way they never get to SFT, so some failure messages refer specifically to Novell.

Hashing - the fall-back method of returning a unique inode number for each file. It is used whenever the starting cluster of a file couldn't be reliably determined.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

      if (stat(path, &stat_buf))
        _djstat_describe_lossage((FILE *)0);

Node:_djstat_fail_bits, Next:_djstat_flags, Previous:_djstat_describe_lossage, Up:Alphabetical List

## _djstat_fail_bits

### Syntax

    #include <sys/stat.h>

    extern unsigned short   _djstat_fail_bits;

As proper operation of `stat` (see stat) and `fstat` (see fstat) depend on undocumented DOS features, they could fail in some incompatible environment or a future DOS version. If they do, the `_djstat_fail_bits` variable will have some of its bits set. Each bit describes a single feature which was used and failed. The function _djstat_describe_lossage may be called to print a human-readable description of the bits which were set by the last call to `f?stat`. This should make debugging `f?stat` failures in an unanticipated environment a lot easier.

The following bits are currently defined:

`_STFAIL_SDA`
  Indicates that Get SDA call failed.
`_STFAIL_OSVER`
  Indicates an unsupported DOS version (less than 3.10 for `stat` or less than 2.0 for `fstat`).
`_STFAIL_BADSDA`
  The pointer to SDA was found to be bogus.
`_STFAIL_TRUENAME`
  Indicates that `_truename` (see _truename) function call failed.
`_STFAIL_HASH`
  Indicates that the starting cluster of the file is unavailable, and inode number was computed by hashing its name.
`_STFAIL_LABEL`
  The application requested the time stamp of a root dir, but no volume label was found.
`_STFAIL_DCOUNT`
  The number of SDA reported is ridiculously large (probably an unsupported DOS clone).
`_STFAIL_WRITEBIT`
  `fstat` was asked to get write access bit of a file, but couldn't.
`_STFAIL_DEVNO`
  `fstat` failed to get device number.
`_STFAIL_BADSFT`
  An SFT entry for this file was found by `fstat`, but its contents can't be trusted because it didn't match file size and time stamp as reported by DOS.
`_STFAIL_SFTIDX`
  The SFT index in Job File Table in program's PSP is negative.
`_STFAIL_SFTNF`
  The file entry was not found in the SFT array.

Below are some explanations of terminology and abbreviations used by the printed messages, which will further clarify the meaning of the above bits and their descriptions printed by `_djstat_describe_lossage` (see _djstat_describe_lossage).

SDA (Swappable Data Area) - this is an internal DOS structure. `stat` uses it to get the full directory entry (including the starting cluster number) of a file. The pointer to SDA found by `stat` is trusted only if we find the pathname of our file at a specific offset in that SDA.

SFT (System File Table) - another internal DOS structure, used in file operations. `fstat` uses it to get full information on a file given its handle. An SFT entry which is found by `fstat` is only trusted if it contains files size and time stamp like those returned by DOS functions 57h and 42h. Novell NetWare 3.x traps DOS file operations in such a way they never get to SFT, so some failure messages refer specifically to Novell.

Hashing - the fall-back method of returning a unique inode number for each file. It is used whenever the starting cluster of a file couldn't be reliably determined. The full pathname of the file is looked up in a table of files seen earlier (hashing is used to speed the lookup process). If found, the inode from the table is returned; this ensures that a given file will get the same inode number. Otherwise a new inode number is invented, recorded in the table and returned to caller.

### Portability

not ANSI, not POSIX

Node:_djstat_flags, Next:_doprnt, Previous:_djstat_fail_bits, Up:Alphabetical List

## _djstat_flags

### Syntax

    #include <sys/stat.h>

    extern unsigned short   _djstat_flags;

This variable contains bits for some fields of `struct stat` which are expensive to compute under DOS. Any such computation is only done by `stat` (see stat) or `fstat` (see fstat) if the corresponding bit in `_djstat_flags` is cleared. By default, all the bits are cleared, so applications which don't care, automagically get a full version, possibly at a price of performance. To get the fastest possible version for your application, clear only the bits which you need and set all the others.

The following bits are currently defined:

`_STAT_INODE`
  Causes `stat` and `fstat` to compute the `st_ino` (inode number) field.
`_STAT_EXEC_EXT`
  Tells `stat` and `fstat` to compute the execute access bit from the file-name extension. `stat` and `fstat` know about many popular file-name extensions, to speed up the computation of the execute access bit.
`_STAT_EXEC_MAGIC`
  Tells `stat` and `fstat` to compute the execute access bit from magic signature (the first two bytes of the file), see _is_executable, if the file-name extension is not enough for this.

  Computing the execute access bit from the magic signature is by far the most expensive part of `stat` and `fstat` (because it requires to read the first two bytes of every file). If your application doesn't care about execute access bit, setting `_STAT_EXEC_MAGIC` will significantly speed it up.

  Note that if `_STAT_EXEC_MAGIC` is set, but `_STAT_EXEC_EXT` is not, some files which shouldn't be flagged as executables (e.g., COFF `*.o` object files) will have their execute bit set, because they have the magic number signature at their beginning. Therefore, only use the above combination if you want to debug the list of extensions provided in `is_exec.c` file.

`_STAT_DIRSIZE`
  Causes `stat` to compute directory size by counting the number of its entries (unless some friendly network redirector brought a true directory size with it). Also computes the number of subdirectories and sets the number of links `st_nlink` field.

  This computation is also quite expensive, especially for directories with large sub-directories. If your application doesn't care about size of directories and the `st_nlink` member, you should set the `_STAT_DIRSIZE` bit in `_djstat_flags`.

`_STAT_ROOT_TIME`
  Causes `stat` to try to get time stamp of root directory from its volume label entry, if there is one.
`_STAT_WRITEBIT`
  Tells `fstat` that file's write access bit is required (this needs special treatment only under some versions of Novell Netware).

Note that if you set a bit, some failure bits in `_djstat_fail_bits` (see _djstat_fail_bits) might not be set, because some computations which report failures are only done when they are required.

### Portability

not ANSI, not POSIX

Node:_doprnt, Next:_dos_close, Previous:_djstat_flags, Up:Alphabetical List

## _doprnt

### Syntax

    #include <stdio.h>

    int _doprnt(const char *format, void *params, FILE *file);

### Description

This is an internal function that is used by all the `printf` style functions, which simply pass their format, arguments, and stream to this function.

See printf, for a discussion of the allowed formats and arguments.

### Return Value

The number of characters generated is returned.

### Portability

not ANSI, not POSIX

### Example

    int args[] = { 1, 2, 3, 66 };
    _doprnt("%d %d %d %c\n", args, stdout);

Node:_dos_close, Next:_dos_commit, Previous:_doprnt, Up:Alphabetical List

## _dos_close

### Syntax

    #include <dos.h>

    unsigned int _dos_close(int handle);

### Description

This is a direct connection to the MS-DOS close function call (%ah = 0x3E). This function closes the specified file.

See _dos_open. See _dos_creat. See _dos_creatnew. See _dos_read. See _dos_write.

### Return Value

Returns 0 if successful or DOS error code on error (and sets errno).

### Portability

not ANSI, not POSIX

### Example

    int handle;

    _dos_creat("FOO.DAT", _A_ARCH, &handle);
    ...
    _dos_close(handle);

Node:_dos_commit, Next:_dos_creat, Previous:_dos_close, Up:Alphabetical List

## _dos_commit

### Syntax

    #include <dos.h>

    unsigned int _dos_commit(int handle);

### Description

This is a direct connection to the MS-DOS commit function call (%ah = 0x68). This function flushes DOS internal file buffers to disk.

### Return Value

Returns 0 if successful or DOS error code on error (and sets errno).

### Portability

not ANSI, not POSIX

### Example

    _dos_write(handle, buffer, 1000, &result);
    _dos_commit(handle);
    _dos_close(handle);

Node:_dos_creat, Next:_dos_creatnew, Previous:_dos_commit, Up:Alphabetical List

## _dos_creat

### Syntax

    #include <dos.h>

    unsigned int _dos_creat(const char *filename, unsigned short attr, int *handle);

### Description

This is a direct connection to the MS-DOS creat function call (%ah = 0x3C). This function creates the given file with the given attribute and puts file handle into handle if creating is successful. If the file already exists it truncates the file to zero length. Meaning of attr parameter is the following:

`_A_NORMAL (0x00)`
  Normal file (no read/write restrictions)
`_A_RDONLY (0x01)`
  Read only file
`_A_HIDDEN (0x02)`
  Hidden file
`_A_SYSTEM (0x04)`
  System file
`_A_ARCH (0x20)`
  Archive file

See also _dos_open, _dos_creatnew, _dos_read, _dos_write, and _dos_close.

This function does not support long filenames, even on systems where the LFN API (see LFN) is available. For LFN-aware functions with similar functionality see _creat, and _creatnew. Also see creat, and open, which are Posix-standard.

### Return Value

Returns 0 if successful or DOS error code on error (and sets errno)

### Portability

not ANSI, not POSIX

### Example

    int handle;

    if ( !_dos_creat("FOO.DAT", _A_ARCH, &handle) )
       puts("Creating was successful !");

Node:_dos_creatnew, Next:_dos_findfirst, Previous:_dos_creat, Up:Alphabetical List

## _dos_creatnew

### Syntax

    #include <dos.h>

    unsigned int _dos_creatnew(const char *filename, unsigned short attr, int *handle);

### Description

This is a direct connection to the MS-DOS create unique function call (%ah = 0x5B). This function creates the given file with the given attribute and puts file handle into handle if creating is successful. This function will fail if the specified file exists. Meaning of attr parameter is the following:

`_A_NORMAL (0x00)`
  Normal file (no read/write restrictions)
`_A_RDONLY (0x01)`
  Read only file
`_A_HIDDEN (0x02)`
  Hidden file
`_A_SYSTEM (0x04)`
  System file
`_A_ARCH (0x20)`
  Archive file

See also _dos_open, _dos_creat, _dos_read, _dos_write, and _dos_close.

This function does not support long filenames, even on systems where the LFN API (see LFN) is available. For LFN-aware functions with similar functionality see _creatnew, and _creat. Also see creat, and open, which are Posix-standard.

### Return Value

Returns 0 if successful or DOS error code on error (and sets errno).

### Portability

not ANSI, not POSIX

### Example

    int handle;

    if ( !_dos_creatnew("FOO.DAT", _A_NORMAL, &handle) )
       puts("Creating was successful !");

Node:_dos_findfirst, Next:_dos_findnext, Previous:_dos_creatnew, Up:Alphabetical List

## _dos_findfirst

### Syntax

    #include <dos.h>

    unsigned int _dos_findfirst(char *name, unsigned int attr,
                                struct find_t *result);

### Description

This function and the related `_dos_findnext` (see _dos_findnext) are used to scan directories for the list of files therein. The name is a wildcard that specifies the directory and files to search. result is a structure to hold the results and state of the search, and attr is a combination of the following:

`_A_NORMAL (0x00)`
  Normal file (no read/write restrictions)
`_A_RDONLY (0x01)`
  Read only file
`_A_HIDDEN (0x02)`
  Hidden file
`_A_SYSTEM (0x04)`
  System file
`_A_VOLID (0x08)`
  Volume ID file
`_A_SUBDIR (0x10)`
  Subdirectory
`_A_ARCH (0x20)`
  Archive file

The results are returned in a `struct find_t` defined on `<dos.h>` as follows:

    struct find_t {
      char reserved[21];
      unsigned char attrib;
      unsigned short wr_time;
      unsigned short wr_date;
      unsigned long size;
      char name[256];
    };

See _dos_findnext.

This function does not support long filenames, even on systems where the LFN API (see LFN) is available. For LFN-aware functions with similar functionality see findfirst, and findnext. Also see opendir, and readdir, which are Posix-standard.

### Return Value

Zero if a match is found, DOS error code if not found (and sets errno).

### Portability

not ANSI, not POSIX

### Example

    #include <dos.h>

    struct find_t f;

    if ( !_dos_findfirst("*.DAT", &f, _A_ARCH | _A_RDONLY) )
    {
      do
      {
        printf("%-14s %10u %02u:%02u:%02u %02u/%02u/%04u\n",
               f.name,
               f.size,
               (f.wr_time >> 11) & 0x1f,
               (f.wr_time >>  5) & 0x3f,
               (f.wr_time & 0x1f) * 2,
               (f.wr_date >>  5) & 0x0f,
               (f.wr_date & 0x1f),
               ((f.wr_date >> 9) & 0x7f) + 1980);
      } while( !_dos_findnext(&f) );
    }

Node:_dos_findnext, Next:_dos_getdate, Previous:_dos_findfirst, Up:Alphabetical List

## _dos_findnext

### Syntax

    #include <dos.h>

    unsigned int _dos_findnext(struct find_t *result);

### Description

This finds the next file in the search started by `_dos_findfirst`. See _dos_findfirst, for the description of `struct find_t`.

This function does not support long filenames, even on systems where the LFN API (see LFN) is available. For LFN-aware functions with similar functionality see findfirst, and findnext. Also see opendir, and readdir, which are Posix-standard.

### Return Value

Zero if a match is found, DOS error code if not found (and sets errno).

### Portability

not ANSI, not POSIX

Node:_dos_getdate, Next:_dos_getdiskfree, Previous:_dos_findnext, Up:Alphabetical List

## _dos_getdate

### Syntax

    #include <dos.h>

    void _dos_getdate(struct dosdate_t *date);

### Description

This function gets the current date and fills the date structure with these values.

    struct dosdate_t {
      unsigned char  day;       /* 1-31          */
      unsigned char  month;     /* 1-12          */
      unsigned short year;      /* 1980-2099     */
      unsigned char  dayofweek; /* 0-6, 0=Sunday */
    };

See _dos_setdate. See _dos_gettime. See _dos_settime.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    struct dosdate_t date;

    _dos_getdate(&date);

Node:_dos_getdiskfree, Next:_dos_getdrive, Previous:_dos_getdate, Up:Alphabetical List

## _dos_getdiskfree

### Syntax

    #include <dos.h>

    unsigned int _dos_getdiskfree(unsigned int drive,
                                  struct diskfree_t *diskspace);

### Description

This function determines the free space on drive drive (0=default, 1=A:, 2=B:, etc.) and fills diskspace structure. The members of `struct diskfree_t` are defined by `<dos.h>` as follows:

    struct diskfree_t {
      unsigned short total_clusters;
      unsigned short avail_clusters;
      unsigned short sectors_per_cluster;
      unsigned short bytes_per_sector;
    };

### Return Value

Returns with 0 if successful, non-zero on error (and sets `errno` to `EINVAL`).

### Portability

not ANSI, not POSIX

### Example

    struct diskfree_t df;
    unsigned long freebytes;

    if ( !_dos_getdiskfree(0, &df) )
    {
      freebytes = (unsigned long)df.avail_clusters *
                  (unsigned long)df.bytes_per_sector *
                  (unsigned long)df.sectors_per_cluster;
      printf("There is %lu free bytes on the current drive.\n", freebytes);
    }
    else
      printf("Unable to get free disk space.\n");

Node:_dos_getdrive, Next:_dos_getfileattr, Previous:_dos_getdiskfree, Up:Alphabetical List

## _dos_getdrive

### Syntax

    #include <dos.h>

    void _dos_getdrive(unsigned int *p_drive);

### Description

This function determine the current default drive and writes this value into p_drive (1=A:, 2=B:, etc.).

See _dos_setdrive.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned int drive;

    _dos_getdrive(&drive);
    printf("The current drive is %c:.\n", 'A' - 1 + drive);

Node:_dos_getfileattr, Next:_dos_getftime, Previous:_dos_getdrive, Up:Alphabetical List

## _dos_getfileattr

### Syntax

    #include <dos.h>

    unsigned int _dos_getfileattr(const char *filename, unsigned int *p_attr);

### Description

This function determines the attributes of given file and fills attr with it. Use the following constans (in DOS.H) to check this value.

`_A_NORMAL (0x00)`
  Normal file (no read/write restrictions)
`_A_RDONLY (0x01)`
  Read only file
`_A_HIDDEN (0x02)`
  Hidden file
`_A_SYSTEM (0x04)`
  System file
`_A_VOLID (0x08)`
  Volume ID file
`_A_SUBDIR (0x10)`
  Subdirectory
`_A_ARCH (0x20)`
  Archive file

See _dos_setfileattr.

This function does not support long filenames, even on systems where the LFN API (see LFN) is available. For LFN-aware functions with similar functionality see _chmod. Also see chmod, access, and stat, which are Posix-standard.

### Return Value

Returns with 0 if successful and DOS error value on error (and sets errno=ENOENT).

### Portability

not ANSI, not POSIX

### Example

    unsigned int attr;

    if ( !_dos_getfileattr("FOO.DAT", &attr) )
    {
      puts("FOO.DAT attributes are:");
      if ( attr & _A_ARCH )   puts("Archive");
      if ( attr & _A_RDONLY ) puts("Read only");
      if ( attr & _A_HIDDEN ) puts("Hidden");
      if ( attr & _A_SYSTEM ) puts("Is it part of DOS ?");
      if ( attr & _A_VOLID )  puts("Volume ID");
      if ( attr & _A_SUBDIR ) puts("Directory");
    }
    else
      puts("Unable to get FOO.DAT attributes.");

Node:_dos_getftime, Next:_dos_gettime, Previous:_dos_getfileattr, Up:Alphabetical List

## _dos_getftime

### Syntax

    #include <dos.h>

    unsigned int _dos_getftime(int handle, unsigned int *p_date, unsigned *p_time);

### Description

This function gets the date and time of the given file and puts these values into p_date and p_time variable. The meaning of DOS date in the p_date variable is the following:

    F   E   D   C   B   A   9   8   7   6   5   4   3   2   1   0  (bits)
    X   X   X   X   X   X   X   X   X   X   X   X   X   X   X   X
    *-----------------------*   *-----------*   *---------------*
            year                    month              day

    year  = 0-119 (relative to 1980)
    month = 1-12
    day   = 1-31

The meaning of DOS time in the p_time variable is the following:

    F   E   D   C   B   A   9   8   7   6   5   4   3   2   1   0
    X   X   X   X   X   X   X   X   X   X   X   X   X   X   X   X
    *---------------*   *-------------------*   *---------------*
          hours              minutes                seconds

    hours   = 0-23
    minutes = 0-59
    seconds = 0-29 in two-second intervals

See _dos_setftime.

This function cannot be used to return last access and creation date and time, even on systems where the LFN API (see LFN) is available. See _lfn_get_ftime, for a function that can be used to get the other two times. Also see fstat, which is Posix-standard.

### Return Value

Returns 0 if successful and return DOS error on error (and sets errno=EBADF).

### Portability

not ANSI, not POSIX

### Example

    unsigned int handle, date, time;

    _dos_open("FOO.DAT", O_RDWR, &handle);
    _dos_gettime(handle, &date, &time);
    _dos_close(handle);
    printf("FOO.DAT date and time is: %04u-%02u-%02u %02u:%02u:%02u.\n",
           /*       year                      month              day    */
           ((date >> 9) & 0x7F) + 1980U, (date >>  5) & 0x0F, date & 0x1F,
           /*       hour                minute           second         */
           (time >> 11) & 0x1F, (time >>  5) & 0x3F, (time & 0x1F) * 2);

Node:_dos_gettime, Next:_dos_lock, Previous:_dos_getftime, Up:Alphabetical List

## _dos_gettime

### Syntax

    #include <dos.h>

    void _dos_gettime(struct dostime_t *time);

### Description

This function gets the current time and fills the time structure with these values.

    struct dostime_t {
      unsigned char hour;     /* 0-23 */
      unsigned char minute;   /* 0-59 */
      unsigned char second;   /* 0-59 */
      unsigned char hsecond;  /* 0-99 */
    };

See _dos_settime. See _dos_getdate. See _dos_setdate.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    struct dostime_t time;

    _dos_gettime(&time);

Node:_dos_lock, Next:_dos_open, Previous:_dos_gettime, Up:Alphabetical List

## _dos_lock

### Syntax

    #include <io.h>

    int _dos_lock(int _fd, long _offset, long _length)

### Description

Adds an advisory lock to the specified region of the file.

### Return Value

Zero if the lock was added, nonzero otherwise.

### Portability

not ANSI, not POSIX

Node:_dos_open, Next:_dos_read, Previous:_dos_lock, Up:Alphabetical List

## _dos_open

### Syntax

    #include <fcntl.h>
    #include <share.h>
    #include <dos.h>

    unsigned int _dos_open(const char *filename, unsigned short mode, int *handle);

### Description

This is a direct connection to the MS-DOS open function call (%ah = 0x3D). This function opens the given file with the given mode and puts handle of file into handle if openning is successful. Meaning of mode parameter is the following:

Access mode bits (in FCNTL.H):

`O_RDONLY (_O_RDONLY) 0x00`
  Open for read only
`O_WRONLY (_O_WRONLY) 0x01`
  Open for write only
`O_RDWR (_O_RDWR) 0x02`
  Open for read and write

Sharing mode bits (in SHARE.H):

`SH_COMPAT (_SH_COMPAT) 0x00`
  Compatibility mode
`SH_DENYRW (_SH_DENYRW) 0x10`
  Deny read/write mode
`SH_DENYWR (_SH_DENYWR) 0x20`
  Deny write mode
`SH_DENYRD (_SH_DENYRD) 0x30`
  Deny read mode
`SH_DENYNO (_SH_DENYNO) 0x40`
  Deny none mode

Inheritance bits (in FCNTL.H):

`O_NOINHERIT (_O_NOINHERIT) 0x80`
  File is not inherited by child process

See also _dos_creat, _dos_creatnew, _dos_read, _dos_write, and _dos_close.

This function does not support long filenames, even on systems where the LFN API (see LFN) is available. For LFN-aware functions with similar functionality see _open, _creat, and _creatnew. Also see open, and creat, which are Posix-standard.

### Return Value

Returns 0 if successful or DOS error code on error (and sets errno to EACCES, EINVAL, EMFILE or ENOENT).

### Portability

not ANSI, not POSIX

### Example

    int handle;

    if ( !_dos_open("FOO.DAT", O_RDWR, &handle) )
       puts("Wow, file opening was successful !");

Node:_dos_read, Next:_dos_setdate, Previous:_dos_open, Up:Alphabetical List

## _dos_read

### Syntax

    #include <dos.h>

    unsigned int _dos_read(int handle, void *buffer, unsigned int count, unsigned int *result);

### Description

This is a direct connection to the MS-DOS read function call (%ah = 0x3F). No conversion is done on the data; it is read as raw binary data. This function reads from handle into buffer count bytes. count value may be arbitrary size (for example > 64KB). It puts number of bytes read into result if reading is successful.

See also _dos_open, _dos_creat, _dos_creatnew, _dos_write, and _dos_close.

### Return Value

Returns 0 if successful or DOS error code on error (and sets errno to EACCES or EBADF)

### Portability

not ANSI, not POSIX

### Example

    int handle;
    unsigned int result;
    char *filebuffer;

    if ( !_dos_open("FOO.DAT", O_RDONLY, &handle) )
    {
       puts("FOO.DAT openning was successful.");
       if ( (filebuffer = malloc(130000)) != NULL )
       {
         if ( !_dos_read(handle, buffer, 130000, &result) )
           printf("%u bytes read from FOO.DAT.\n", result);
         else
           puts("Reading error.");
         ...
         /* Do something with filebuffer. */
         ...
       }
       _dos_close(handle);
    }

Node:_dos_setdate, Next:_dos_setdrive, Previous:_dos_read, Up:Alphabetical List

## _dos_setdate

### Syntax

    #include <dos.h>

    unsigned int _dos_setdate(struct dosdate_t *date);

### Description

This function sets the current date. The dosdate_t structure is as follows:

    struct dosdate_t {
      unsigned char  day;       /* 1-31          */
      unsigned char  month;     /* 1-12          */
      unsigned short year;      /* 1980-2099     */
      unsigned char  dayofweek; /* 0-6, 0=Sunday */
    };

dayofweek field has no effect at this function call.

See _dos_getdate. See _dos_gettime. See _dos_settime.

### Return Value

Returns 0 if successful and non-zero on error (and sets errno=EINVAL).

### Portability

not ANSI, not POSIX

### Example

    struct dosdate_t date;

    date->year  = 1999;
    date->month = 12;
    date->day   = 31;
    if ( !_dos_setdate(&date) )
      puts("It was a valid date.");

Node:_dos_setdrive, Next:_dos_setfileattr, Previous:_dos_setdate, Up:Alphabetical List

## _dos_setdrive

### Syntax

    #include <dos.h>

    void _dos_setdrive(unsigned int drive, unsigned int *p_drives);

### Description

This function set the current default drive based on drive (1=A:, 2=B:, etc.) and determines the number of available logical drives and fills p_drives with it.

See _dos_getdrive.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned int available_drives;

    /* The current drive will be A: */
    _dos_setdrive(1, &available_drives);
    printf("Number of available logical drives %u.\n", available_drives);

Node:_dos_setfileattr, Next:_dos_setftime, Previous:_dos_setdrive, Up:Alphabetical List

## _dos_setfileattr

### Syntax

    #include <dos.h>

    unsigned int _dos_setfileattr(const char *filename, unsigned int attr);

### Description

This function sets the attributes of given file. Use the following constans in DOS.H to create attr parameter:

`_A_NORMAL (0x00)`
  Normal file (no read/write restrictions)
`_A_RDONLY (0x01)`
  Read only file
`_A_HIDDEN (0x02)`
  Hidden file
`_A_SYSTEM (0x04)`
  System file
`_A_VOLID (0x08)`
  Volume ID file
`_A_SUBDIR (0x10)`
  Subdirectory
`_A_ARCH (0x20)`
  Archive file

See _dos_getfileattr.

This function does not support long filenames, even on systems where the LFN API (see LFN) is available. For LFN-aware functions with similar functionality see _chmod. Also see chmod, which is Posix-standard.

### Return Value

Returns with 0 if successful and DOS error value on error (and sets errno to ENOENT or EACCES).

### Portability

not ANSI, not POSIX

### Example

    if ( !_dos_setfileattr("FOO.DAT", _A_RDONLY | _A_HIDDEN) )
       puts("FOO.DAT is hidden now.");

Node:_dos_setftime, Next:_dos_settime, Previous:_dos_setfileattr, Up:Alphabetical List

## _dos_setftime

### Syntax

    #include <dos.h>

    unsigned int _dos_setftime(int handle, unsigned int date, unsigned time);

### Description

This function sets the date and time of the given file. The meaning of DOS date in the date variable is the following:

    F E D C B A 9 8 7 6 5 4 3 2 1 0 (bits)
    x x x x x x x x x x x x x x x x
    *-----------* *-----* *-------*
        year       month     day

    year  = 0-119 (relative to 1980)
    month = 1-12
    day   = 1-31

The meaning of DOS time in the time variable is the following:

    F E D C B A 9 8 7 6 5 4 3 2 1 0 (bits)
    x x x x x x x x x x x x x x x x
    *-------* *---------* *-------*
      hours     minutes    seconds

    hours   = 0-23
    minutes = 0-59
    seconds = 0-29 in two-second intervals

See _dos_getftime.

This function cannot be used to set the last access date and time, even on systems where the LFN API (see LFN) is available. For LFN-aware functions with similar functionality see utime, which is Posix-standard, and see utimes.

### Return Value

Returns 0 if successful and return DOS error on error (and sets errno=EBADF).

### Portability

not ANSI, not POSIX

### Example

    struct dosdate_t d;
    struct dostime_t t;
    unsigned int handle, date, time;

    _dos_open("FOO.DAT", O_RDWR, &handle);
    _dos_getdate(&d);
    _dos_gettime(&t);
    date = ((d.year - 1980) << 9) | (d.month << 5) | d.day;
    time = (t.hour << 11) | (t.minute << 5) | (t.second / 2);
    _dos_settime(handle, date, time);
    _dos_close(handle);

Node:_dos_settime, Next:_dos_unlock, Previous:_dos_setftime, Up:Alphabetical List

## _dos_settime

### Syntax

    #include <dos.h>

    void _dos_settime(struct dostime_t *time);

### Description

This function sets the current time. The time structure is as follows:

    struct dostime_t {
      unsigned char hour;     /* 0-23 */
      unsigned char minute;   /* 0-59 */
      unsigned char second;   /* 0-59 */
      unsigned char hsecond;  /* 0-99 */
    };

See _dos_gettime. See _dos_getdate. See _dos_setdate.

### Return Value

Returns 0 if successful and non-zero on error (and sets errno=EINVAL).

### Portability

not ANSI, not POSIX

### Example

    struct dostime_t time;

    time->hour    = 23;
    time->minute  = 59;
    time->second  = 59;
    time->hsecond = 99;
    if ( !_dos_settime(&time) )
      puts("It was a valid time.");

Node:_dos_unlock, Next:_dos_write, Previous:_dos_settime, Up:Alphabetical List

## _dos_unlock

### Syntax

    #include <io.h>

    _dos_unlock(int _fd, long _offset, long _length)

### Description

Removes an advisory lock to the specified region of the file.

### Return Value

Zero if the lock was removed, nonzero otherwise.

### Portability

not ANSI, not POSIX

Node:_dos_write, Next:_doscan, Previous:_dos_unlock, Up:Alphabetical List

## _dos_write

### Syntax

    #include <dos.h>

    unsigned int _dos_write(int handle, const void *buffer, unsigned int count,
                            unsigned int *result);

### Description

This is a direct connection to the MS-DOS write function call (%ah = 0x40). No conversion is done on the data; it is written as raw binary data. This function writes count bytes from buffer to handle. count value may be arbitrary size (e.g. > 64KB). It puts the number of bytes written into result if writing is successful.

See also _dos_open, _dos_creat, _dos_creatnew, _dos_read, and _dos_close.

### Return Value

Returns 0 if successful or DOS error code on error (and sets errno to EACCES or EBADF)

### Portability

not ANSI, not POSIX

### Example

    int handle;
    unsigned int result;
    char *filebuffer;

    if ( !_dos_creat("FOO.DAT", _A_ARCH, &handle) )
    {
       puts("FOO.DAT creating was successful.");
       if ( (filebuffer = malloc(130000)) != NULL )
       {
         ...
         /* Put something into filebuffer. */
         ...
         if ( !_dos_write(handle, buffer, 130000, &result) )
           printf("%u bytes written into FOO.DAT.", result);
         else
           puts("Writing error.");
       }
       _dos_close(handle);
    }

Node:_doscan, Next:_doserrno, Previous:_dos_write, Up:Alphabetical List

## _doscan

### Syntax

    #include <stdio.h>

    int _doscan(FILE *file, const char *format, void **ptrs_to_args);

### Description

This is an internal function that is used by all the `scanf` style functions, which simply pass their format, arguments, and stream to this function.

See scanf, for a discussion of the allowed formats and arguments.

### Return Value

The number of characters successfully scanned is returned, or -1 on error.

### Portability

not ANSI, not POSIX

### Example

    int x, y;
    int *args[2];
    args[0] = &x;
    args[1] = &y;
    _doscan(stdin, "%d %d", args);

Node:_doserrno, Next:dosexterr, Previous:_doscan, Up:Alphabetical List

## _doserrno

### Syntax

    #include <errno.h>

    extern int _doserrno;

### Description

Whenever a DOS call returns a failure indication, this variable is assigned the value of the error code returned by the failed DOS call.

For a list of the error codes and their short descriptions, see dosexterr.

### Portability

not ANSI, not POSIX

### Example

     _doserrno = 0;
     fprintf (stdprn, "Hello, world!\r\n\f");
     if (_doserrno == 0x1c)
       fprintf (stderr, "The printer is out of paper!\n");

Node:dosexterr, Next:dosmemget, Previous:_doserrno, Up:Alphabetical List

## dosexterr

### Syntax

    #include <dos.h>

    int dosexterr(struct DOSERROR *p_error);

### Description

This function reads extended error information from DOS and fills p_error structure.

    struct _DOSERROR {
      int  exterror;
      char class;
      char action;
      char locus;
    };

Values for extended error code (exterror field):

    00h (0)   no error
    01h (1)   function number invalid
    02h (2)   file not found
    03h (3)   path not found
    04h (4)   too many open files (no handles available)
    05h (5)   access denied
    06h (6)   invalid handle
    07h (7)   memory control block destroyed
    08h (8)   insufficient memory
    09h (9)   memory block address invalid
    0Ah (10)  environment invalid (usually >32K in length)
    0Bh (11)  format invalid
    0Ch (12)  access code invalid
    0Dh (13)  data invalid
    0Eh (14)  reserved
    0Fh (15)  invalid drive
    10h (16)  attempted to remove current directory
    11h (17)  not same device
    12h (18)  no more files
    13h (19)  disk write-protected
    14h (20)  unknown unit
    15h (21)  drive not ready
    16h (22)  unknown command
    17h (23)  data error (CRC)
    18h (24)  bad request structure length
    19h (25)  seek error
    1Ah (26)  unknown media type (non-DOS disk)
    1Bh (27)  sector not found
    1Ch (28)  printer out of paper
    1Dh (29)  write fault
    1Eh (30)  read fault
    1Fh (31)  general failure
    20h (32)  sharing violation
    21h (33)  lock violation
    22h (34)  disk change invalid (ES:DI -> media ID structure)(see below)
    23h (35)  FCB unavailable
    24h (36)  sharing buffer overflow
    25h (37)  (DOS 4+) code page mismatch
    26h (38)  (DOS 4+) cannot complete file operation (out of input)
    27h (39)  (DOS 4+) insufficient disk space
    28h-31h   reserved
    32h (50)  network request not supported
    33h (51)  remote computer not listening
    34h (52)  duplicate name on network
    35h (53)  network name not found
    36h (54)  network busy
    37h (55)  network device no longer exists
    38h (56)  network BIOS command limit exceeded
    39h (57)  network adapter hardware error
    3Ah (58)  incorrect response from network
    3Bh (59)  unexpected network error
    3Ch (60)  incompatible remote adapter
    3Dh (61)  print queue full
    3Eh (62)  queue not full
    3Fh (63)  not enough space to print file
    40h (64)  network name was deleted
    41h (65)  network: Access denied
    42h (66)  network device type incorrect
    43h (67)  network name not found
    44h (68)  network name limit exceeded
    45h (69)  network BIOS session limit exceeded
    46h (70)  temporarily paused
    47h (71)  network request not accepted
    48h (72)  network print/disk redirection paused
    49h (73)  network software not installed
              (LANtastic) invalid network version
    4Ah (74)  unexpected adapter close
              (LANtastic) account expired
    4Bh (75)  (LANtastic) password expired
    4Ch (76)  (LANtastic) login attempt invalid at this time
    4Dh (77)  (LANtastic v3+) disk limit exceeded on network node
    4Eh (78)  (LANtastic v3+) not logged in to network node
    4Fh (79)  reserved
    50h (80)  file exists
    51h (81)  reserved
    52h (82)  cannot make directory
    53h (83)  fail on INT 24h
    54h (84)  (DOS 3.3+) too many redirections
    55h (85)  (DOS 3.3+) duplicate redirection
    56h (86)  (DOS 3.3+) invalid password
    57h (87)  (DOS 3.3+) invalid parameter
    58h (88)  (DOS 3.3+) network write fault
    59h (89)  (DOS 4+) function not supported on network
    5Ah (90)  (DOS 4+) required system component not installed
    64h (100) (MSCDEX) unknown error
    65h (101) (MSCDEX) not ready
    66h (102) (MSCDEX) EMS memory no longer valid
    67h (103) (MSCDEX) not High Sierra or ISO-9660 format
    68h (104) (MSCDEX) door open

Values for error class (class field):

    01h  out of resource (storage space or I/O channels)
    02h  temporary situation (file or record lock)
    03h  authorization (denied access)
    04h  internal (system software bug)
    05h  hardware failure
    06h  system failure (configuration file missing or incorrect)
    07h  application program error
    08h  not found
    09h  bad format
    0Ah  locked
    0Bh  media error
    0Ch  already exists
    0Dh  unknown

Values for suggested action (action field):

    01h  retry
    02h  delayed retry
    03h  prompt user to reenter input
    04h  abort after cleanup
    05h  immediate abort
    06h  ignore
    07h  retry after user intervention

Values for error locus (locus field):

    01h  unknown or not appropriate
    02h  block device (disk error)
    03h  network related
    04h  serial device (timeout)
    05h  memory related

### Return Value

Returns with the extended error code.

### Portability

not ANSI, not POSIX

### Example

    #include <stdio.h>
    #include <dos.h>

    void main(void)
    {
      FILE *fp;
      struct _DOSERROR de;

      fp = fopen("EXAMPLE.DAT","r");
      if ( fp == NULL )
      {
        puts("Unable to open file for reading.");
        _dosexterr(&de);
        printf("Extended DOS error information:\n");
        printf("Extended error: %i\n",de.exterror);
        printf("Class:          %x\n",de.class);
        printf("Action:         %x\n",de.action);
        printf("Error Locus:    %x\n",de.locus);
      }
    }

Node:dosmemget, Next:dosmemgetb, Previous:dosexterr, Up:Alphabetical List

## dosmemget

### Syntax

    #include <sys/movedata.h>

    void dosmemget(int offset, int length, void *buffer);

### Description

This function transfers data from MS-DOS's conventional memory space to the program's virtual address space. The offset is a physical address, which can be computed from a real-mode segment/offset pair as follows:

    offset = segment * 16 + offset;

The length is the number of bytes to transfer, and buffer is a pointer to somewhere in your virtual address space (such as memory obtained from `malloc`) where the data will go.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned short shift_state;
    dosmemget(0x417, 2, &shift_state);
    if (shift_state & 0x0004)
      /* Ctrl key pressed */;

Node:dosmemgetb, Next:dosmemgetl, Previous:dosmemget, Up:Alphabetical List

## dosmemgetb

### Syntax

    #include <sys/movedata.h>

    void _dosmemgetb(unsigned long offset, size_t xfers, void *buffer);

### Description

This function transfers data from MS-DOS's conventional memory space to the program's virtual address space, using only byte transfers. The offset is a physical address, which can be computed from a real-mode segment/offset pair as follows:

    offset = segment * 16 + offset;

The xfers is the number of bytes to transfer, and buffer is a pointer to somewhere in your virtual address space (such as memory obtained from `malloc`) where the data will go.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned short shift_state;
    _dosmemgetb(0x417, 2, &shift_state);
    if (shift_state & 0x0004)
      /* Ctrl key pressed */;

Node:dosmemgetl, Next:dosmemgetw, Previous:dosmemgetb, Up:Alphabetical List

## dosmemgetl

### Syntax

    #include <sys/movedata.h>

    void _dosmemgetl(unsigned long offset, size_t xfers, void *buffer);

### Description

This function transfers data from MS-DOS's conventional memory space to the program's virtual address space, using only long-word (32-bit) transfers. The offset is a physical address, which can be computed from a real-mode segment/offset pair as follows:

    offset = segment * 16 + offset;

The count is the number of long-words to transfer, and buffer is a pointer to somewhere in your virtual address space (such as memory obtained from `malloc`) where the data will go.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned long shift_state;
    _dosmemgetl(0x417, 1, &shift_state);
    if (shift_state & 0x0004)
      /* Ctrl key pressed */;

Node:dosmemgetw, Next:dosmemput, Previous:dosmemgetl, Up:Alphabetical List

## dosmemgetw

### Syntax

    #include <sys/movedata.h>

    void _dosmemgetw(unsigned long offset, size_t xfers, void *buffer);

### Description

This function transfers data from MS-DOS's conventional memory space to the program's virtual address space, using only short-word (16-bit) transfers. The offset is a physical address, which can be computed from a real-mode segment/offset pair as follows:

    offset = segment * 16 + offset;

The xfers is the number of words to transfer, and buffer is a pointer to somewhere in your virtual address space (such as memory obtained from `malloc`) where the data will go.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned short shift_state;
    _dosmemgetw(0x417, 1, &shift_state);
    if (shift_state & 0x0004)
      /* Ctrl key pressed */;

Node:dosmemput, Next:dosmemputb, Previous:dosmemgetw, Up:Alphabetical List

## dosmemput

### Syntax

    #include <sys/movedata.h>

    void dosmemput(const void *buffer, int length, int offset);

### Description

This function transfers data from the program's virtual address space to MS-DOS's conventional memory space. The offset is a physical address, which can be computed from a real-mode segment/offset pair as follows:

    offset = segment * 16 + offset;

The length is the number of bytes to transfer, and buffer is a pointer to somewhere in your virtual address space (such as memory obtained from `malloc`) where the data will come from.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned short save_screen[25][80];
    dosmemput(save_screen, 80*2*25, 0xb8000);

Node:dosmemputb, Next:dosmemputl, Previous:dosmemput, Up:Alphabetical List

## dosmemputb

### Syntax

    #include <sys/movedata.h>

    void _dosmemputb(const void *buffer, size_t xfers, unsigned long offset);

### Description

This function transfers data from the program's virtual address space to MS-DOS's conventional memory space, using only byte (8-bit) transfers. The offset is a physical address, which can be computed from a real-mode segment/offset pair as follows:

    offset = segment * 16 + offset;

The xfers is the number of bytes to transfer, and buffer is a pointer to somewhere in your virtual address space (such as memory obtained from `malloc`) where the data will come from.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned short save_screen[25][80];
    _dosmemputb(save_screen, 0xb8000, 80*2*25);

Node:dosmemputl, Next:dosmemputw, Previous:dosmemputb, Up:Alphabetical List

## dosmemputl

### Syntax

    #include <sys/movedata.h>

    void _dosmemputl(const void *buffer, size_t xfers, unsigned long offset);

### Description

This function transfers data from the program's virtual address space to MS-DOS's conventional memory space, using only long-word (32-bit) transfers. The offset is a physical address, which can be computed from a real-mode segment/offset pair as follows:

    offset = segment * 16 + offset;

The xfers is the number of long-words to transfer, and buffer is a pointer to somewhere in your virtual address space (such as memory obtained from `malloc`) where the data will come from.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned short save_screen[25][80];
    _dosmemputl(save_screen, 40*25, 0xb8000);

Node:dosmemputw, Next:DPMI Overview, Previous:dosmemputl, Up:Alphabetical List

## dosmemputw

### Syntax

    #include <sys/movedata.h>

    void _dosmemputw(const void *buffer, size_t xfers, unsigned long offset);

### Description

This function transfers data from the program's virtual address space to MS-DOS's conventional memory space, using only short-word (16-bit) transfers. The offset is a physical address, which can be computed from a real-mode segment/offset pair as follows:

    offset = segment * 16 + offset;

The xfers is the number of short-words to transfer, and buffer is a pointer to somewhere in your virtual address space (such as memory obtained from `malloc`) where the data will come from.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned short save_screen[25][80];
    _dosmemputw(save_screen, 0xb8000, 80*25);

Node:DPMI Overview, Next:DPMI Specification, Previous:dosmemputw, Up:Alphabetical List

## DPMI Overview

    extern unsigned short __dpmi_error;

For most functions, the error returned from the DPMI server is stored in this variable.

    typedef struct {
      unsigned short offset16;
      unsigned short segment;
    } __dpmi_raddr;

This structure is used to hold a real-mode address, which consists of a segment:offset pair.

    typedef struct {
      unsigned long  offset32;
      unsigned short selector;
    } __dpmi_paddr;

This structure is used to hold a protected-mode address, which consists of a selector:offset pair.

    typedef struct {
      unsigned long handle;			/* 0, 2 */
      unsigned long size; 	/* or count */	/* 4, 6 */
      unsigned long address;		/* 8, 10 */
    } __dpmi_meminfo;

This structure is used by many functions that need to refer to blocks of 32-bit memory. The `size` field doubles as a count for those operations that want a count of something, or return a count.

    typedef union {
      struct {
        unsigned long edi;
        unsigned long esi;
        unsigned long ebp;
        unsigned long res;
        unsigned long ebx;
        unsigned long edx;
        unsigned long ecx;
        unsigned long eax;
      } d;
      struct {
        unsigned short di, di_hi;
        unsigned short si, si_hi;
        unsigned short bp, bp_hi;
        unsigned short res, res_hi;
        unsigned short bx, bx_hi;
        unsigned short dx, dx_hi;
        unsigned short cx, cx_hi;
        unsigned short ax, ax_hi;
        unsigned short flags;
        unsigned short es;
        unsigned short ds;
        unsigned short fs;
        unsigned short gs;
        unsigned short ip;
        unsigned short cs;
        unsigned short sp;
        unsigned short ss;
      } x;
      struct {
        unsigned char edi[4];
        unsigned char esi[4];
        unsigned char ebp[4];
        unsigned char res[4];
        unsigned char bl, bh, ebx_b2, ebx_b3;
        unsigned char dl, dh, edx_b2, edx_b3;
        unsigned char cl, ch, ecx_b2, ecx_b3;
        unsigned char al, ah, eax_b2, eax_b3;
      } h;
    } __dpmi_regs;

This structure is used by functions that pass register information, such as simulating real-mode calls.

    typedef struct {
      unsigned char  major;
      unsigned char  minor;
      unsigned short flags;
      unsigned char  cpu;
      unsigned char  master_pic;
      unsigned char  slave_pic;
    } __dpmi_version_ret;

This structure is used to return version information to the program.

    typedef struct {
      unsigned long largest_available_free_block_in_bytes;
      unsigned long maximum_unlocked_page_allocation_in_pages;
      unsigned long maximum_locked_page_allocation_in_pages;
      unsigned long linear_address_space_size_in_pages;
      unsigned long total_number_of_unlocked_pages;
      unsigned long total_number_of_free_pages;
      unsigned long total_number_of_physical_pages;
      unsigned long free_linear_address_space_in_pages;
      unsigned long size_of_paging_file_partition_in_pages;
      unsigned long reserved[3];
    } __dpmi_free_mem_info;

This structure is used to return information about the state of virtual memory in the system.

    typedef struct {
      unsigned long total_allocated_bytes_of_physical_memory_host;
      unsigned long total_allocated_bytes_of_virtual_memory_host;
      unsigned long total_available_bytes_of_virtual_memory_host;
      unsigned long total_allocated_bytes_of_virtual_memory_vcpu;
      unsigned long total_available_bytes_of_virtual_memory_vcpu;
      unsigned long total_allocated_bytes_of_virtual_memory_client;
      unsigned long total_available_bytes_of_virtual_memory_client;
      unsigned long total_locked_bytes_of_memory_client;
      unsigned long max_locked_bytes_of_memory_client;
      unsigned long highest_linear_address_available_to_client;
      unsigned long size_in_bytes_of_largest_free_memory_block;
      unsigned long size_of_minimum_allocation_unit_in_bytes;
      unsigned long size_of_allocation_alignment_unit_in_bytes;
      unsigned long reserved[19];
    } __dpmi_memory_info;

This is also used to return memory information, but by a different function.

    typedef struct {
      unsigned long data16[2];
      unsigned long code16[2];
      unsigned short ip;
      unsigned short reserved;
      unsigned long data32[2];
      unsigned long code32[2];
      unsigned long eip;
    } __dpmi_callback_info;

This structure is used to install TSR programs.

    typedef struct {
      unsigned long size_requested;
      unsigned long size;
      unsigned long handle;
      unsigned long address;
      unsigned long name_offset;
      unsigned short name_selector;
      unsigned short reserved1;
      unsigned long reserved2;
    } __dpmi_shminfo;

This structure is used to manipulate shared memory regions.

Node:DPMI Specification, Next:__dpmi_allocate_dos_memory, Previous:DPMI Overview, Up:Alphabetical List

## DPMI Specification

To obtain the DPMI specification, Contact Intel and order document number 240977-001. Also, try ftp.qdeck.com:/pub/memory/dpmi* and http://www.delorie.com/djgpp/doc/dpmi/.

Node:__dpmi_allocate_dos_memory, Next:__dpmi_allocate_ldt_descriptors, Previous:DPMI Specification, Up:Alphabetical List

## __dpmi_allocate_dos_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_allocate_dos_memory(int _paragraphs, int *_ret_selector_or_max);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0100

This function allocates DOS memory. You pass it the number of paragraphs ((bytes+15)>>4) to allocate. If it succeeds, it returns a segment (dos-style) and fills in _ret_selector_or_max with a selector (protected-mode) that you can use to reference the same memory. Note that it's the selector you use to free the block, not the segment.

### Return Value

-1 on error, else the segment [0000..FFFF].

### Portability

not ANSI, not POSIX

Node:__dpmi_allocate_ldt_descriptors, Next:__dpmi_allocate_linear_memory, Previous:__dpmi_allocate_dos_memory, Up:Alphabetical List

## __dpmi_allocate_ldt_descriptors

### Syntax

    #include <dpmi.h>

    int __dpmi_allocate_ldt_descriptors(int count);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0000

Allocates count descriptors.

### Return Value

-1 on error, else the first descriptor. Use __dpmi_get_selector_increment_value to figure out the remaining selectors.

### Portability

not ANSI, not POSIX

### Example

    short sel = __dpmi_allocate_ldt_descriptors(1);

Node:__dpmi_allocate_linear_memory, Next:__dpmi_allocate_memory, Previous:__dpmi_allocate_ldt_descriptors, Up:Alphabetical List

## __dpmi_allocate_linear_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_allocate_linear_memory(__dpmi_meminfo *info, int commit);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0504 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This allocates a block of page-aligned linear address space. Pass a desired address (or zero for any) and a size. commit is 1 for committed pages, else they are uncommitted. It returns a handle and the actual address.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_allocate_memory, Next:__dpmi_allocate_real_mode_callback, Previous:__dpmi_allocate_linear_memory, Up:Alphabetical List

## __dpmi_allocate_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_allocate_memory(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0501

This allocates virtual memory. Fill in size, returns handle and address.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_allocate_real_mode_callback, Next:__dpmi_allocate_shared_memory, Previous:__dpmi_allocate_memory, Up:Alphabetical List

## __dpmi_allocate_real_mode_callback

### Syntax

    #include <dpmi.h>

    int __dpmi_allocate_real_mode_callback(void (*_handler)(void), __dpmi_regs *_regs, __dpmi_raddr *_ret);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0303

This function gives you a real-mode address to pass to TSRs that gets reflected to your protected-mode handler. You pass it a register block to use; it gets filled in with the real-mode registers when your handler is called, and the registers are set from it when the handler returns.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_allocate_shared_memory, Next:__dpmi_allocate_specific_ldt_descriptor, Previous:__dpmi_allocate_real_mode_callback, Up:Alphabetical List

## __dpmi_allocate_shared_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_allocate_shared_memory(__dpmi_shminfo *info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0d00 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function allocates a shared memory block that can be accessed from different virtual machines. Fill the required length in `info->size_requested`. The function fills the rest of the structure: allocated length in `info->size`, block handle in `info->handle`, linear address in `info->address`, and the selector:offset of an ASCIIZ block name (up to 128 bytes long) in `info->name_selector` and `info->name_offset`, respectively.

The access to the shared memory block can be serialized by calling the `__dpmi_serialize_on_shared_memory` function (see __dpmi_serialize_on_shared_memory).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_allocate_specific_ldt_descriptor, Next:__dpmi_clear_debug_watchpoint, Previous:__dpmi_allocate_shared_memory, Up:Alphabetical List

## __dpmi_allocate_specific_ldt_descriptor

### Syntax

    #include <dpmi.h>

    int __dpmi_allocate_specific_ldt_descriptor(int _selector);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x000d

This allocates the specific selector given.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_clear_debug_watchpoint, Next:__dpmi_create_alias_descriptor, Previous:__dpmi_allocate_specific_ldt_descriptor, Up:Alphabetical List

## __dpmi_clear_debug_watchpoint

### Syntax

    #include <dpmi.h>

    int __dpmi_clear_debug_watchpoint(unsigned long _handle);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0b01

Clear a debug watchpoint.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_create_alias_descriptor, Next:__dpmi_discard_page_contents, Previous:__dpmi_clear_debug_watchpoint, Up:Alphabetical List

## __dpmi_create_alias_descriptor

### Syntax

    #include <dpmi.h>

    int __dpmi_create_alias_descriptor(int _selector);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x000a

Create a new selector with the same parameters as the given one.

### Return Value

-1 on error, else the new selector.

### Portability

not ANSI, not POSIX

Node:__dpmi_discard_page_contents, Next:__dpmi_free_dos_memory, Previous:__dpmi_create_alias_descriptor, Up:Alphabetical List

## __dpmi_discard_page_contents

### Syntax

    #include <dpmi.h>

    int __dpmi_discard_page_contents(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0703

Advises the server that the given pages are no longer needed and may be reclaimed. Fill in address and size (in bytes).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_free_dos_memory, Next:__dpmi_free_ldt_descriptor, Previous:__dpmi_discard_page_contents, Up:Alphabetical List

## __dpmi_free_dos_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_free_dos_memory(int _selector);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0101

This function frees the dos memory allocated by __dpmi_allocate_dos_memory. Remember to pass the selector and not the segment.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_free_ldt_descriptor, Next:__dpmi_free_memory, Previous:__dpmi_free_dos_memory, Up:Alphabetical List

## __dpmi_free_ldt_descriptor

### Syntax

    #include <dpmi.h>

    int __dpmi_free_ldt_descriptor(int descriptor);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0001

This function frees a single descriptor, even if it was allocated as one of many.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

### Example

    __dpmi_free_ldt_descriptor(sel);

Node:__dpmi_free_memory, Next:__dpmi_free_physical_address_mapping, Previous:__dpmi_free_ldt_descriptor, Up:Alphabetical List

## __dpmi_free_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_free_memory(unsigned long _handle);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0502

This frees a block of virtual memory.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_free_physical_address_mapping, Next:__dpmi_free_real_mode_callback, Previous:__dpmi_free_memory, Up:Alphabetical List

## __dpmi_free_physical_address_mapping

### Syntax

    #include <dpmi.h>

    int __dpmi_free_physical_address_mapping(__dpmi_meminfo *info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0801 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function unmaps a physical device mapped with __dpmi_physical_address_mapping. Fill in the linear address.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_free_real_mode_callback, Next:__dpmi_free_serialization_on_shared_memory, Previous:__dpmi_free_physical_address_mapping, Up:Alphabetical List

## __dpmi_free_real_mode_callback

### Syntax

    #include <dpmi.h>

    int __dpmi_free_real_mode_callback(__dpmi_raddr *_addr);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0303

This function frees the real-mode callback address.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_free_serialization_on_shared_memory, Next:__dpmi_free_shared_memory, Previous:__dpmi_free_real_mode_callback, Up:Alphabetical List

## __dpmi_free_serialization_on_shared_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_free_serialization_on_shared_memory(unsigned long handle,
                                                   int flags);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0d03 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function frees the serialization on shared memory block specified by its handle handle. The bit-mapped variable flags defines the following bits:

bit 0
  If set, release shared serialization (as opposed to exclusive serialization).
bit 1
  If set, free pending serialization.
bits 2-15
  Reserved (should be zero).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_free_shared_memory, Next:__dpmi_get_and_disable_virtual_interrupt_state, Previous:__dpmi_free_serialization_on_shared_memory, Up:Alphabetical List

## __dpmi_free_shared_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_free_shared_memory(unsigned long handle);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0d01 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function frees the shared memory block specified by the given handle. The handle becomes invalid after this call.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_and_disable_virtual_interrupt_state, Next:__dpmi_get_and_enable_virtual_interrupt_state, Previous:__dpmi_free_shared_memory, Up:Alphabetical List

## __dpmi_get_and_disable_virtual_interrupt_state

### Syntax

    #include <dpmi.h>

    int __dpmi_get_and_disable_virtual_interrupt_state(void);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0900

This function disables interrupts, and returns the previous setting.

### Return Value

The previous setting.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_and_enable_virtual_interrupt_state, Next:__dpmi_get_and_set_virtual_interrupt_state, Previous:__dpmi_get_and_disable_virtual_interrupt_state, Up:Alphabetical List

## __dpmi_get_and_enable_virtual_interrupt_state

### Syntax

    #include <dpmi.h>

    int __dpmi_get_and_enable_virtual_interrupt_state(void);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0901

This function enables interrupts, and returns the previous setting.

### Return Value

The previous setting.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_and_set_virtual_interrupt_state, Next:__dpmi_get_capabilities, Previous:__dpmi_get_and_enable_virtual_interrupt_state, Up:Alphabetical List

## __dpmi_get_and_set_virtual_interrupt_state

### Syntax

    #include <dpmi.h>

    int __dpmi_get_and_set_virtual_interrupt_state(int _old_state);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AH = 0x09

This function restores the interrupt state from a previous call to __dpmi_get_and_disable_virtual_interrupt_state or __dpmi_get_and_enable_virtual_interrupt_state.

### Return Value

The previous setting.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_capabilities, Next:__dpmi_get_coprocessor_status, Previous:__dpmi_get_and_set_virtual_interrupt_state, Up:Alphabetical List

## __dpmi_get_capabilities

### Syntax

    #include <dpmi.h>

    int __dpmi_get_capabilities(int *flags, char *vendor_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0401 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

Gets the capabilities of the server. flags are as follows:

    ---- ---X = 1="page accessed/dirty" supported
    ---- --X- = 1="exceptions restartble" supported
    ---- -X-- = 1="device mapping" supported
    ---- X--- = 1="map conventional memory" supported
    ---X ---- = 1="demand zero-fill" supported
    --X- ---- = 1="write-protect client" supported
    -X-- ---- = 1="write-protect host" supported

The vendor info is a 128-byte buffer:

    [0] host major number
    [1] host minor number
    [2..127] vendor name

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_coprocessor_status, Next:__dpmi_get_descriptor, Previous:__dpmi_get_capabilities, Up:Alphabetical List

## __dpmi_get_coprocessor_status

### Syntax

    #include <dpmi.h>

    int __dpmi_get_coprocessor_status(void);

### Description

Please refer to DPMI Specification, for details on DPMI function call operation. Also see DPMI Overview, for general information.

DPMI function AX = 0x0e00 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

### Return Value

-1 on error, else returns the processor status flags. Here's the meaning of each set bit:

bit 0
  If set, co-processor is enabled. If reset, co-processor is disabled.
bit 1
  If set, the application is emulating the co-processor.
bit 2
  If set, the numeric co-processor is present.
bit 3
  If set, the DPMI host is emulating the co-processor.
bits 4-7
  The co-processor type:
  `0000`
    none
  `0010`
    80287
  `0011`
    80387
  `0100`
    80486 with a numeric processor

### Portability

not ANSI, not POSIX

Node:__dpmi_get_descriptor, Next:__dpmi_get_descriptor_access_rights, Previous:__dpmi_get_coprocessor_status, Up:Alphabetical List

## __dpmi_get_descriptor

### Syntax

    #include <dpmi.h>

    int __dpmi_get_descriptor(int _selector, void *_buffer);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x000b

This function fills the 8-byte buffer pointed to by _buffer with the parameters of the descriptor whose selector is passed in _selector. The data has the following format:

    [0] XXXX XXXX = segment limit [7:0]
    [1] XXXX XXXX = segment limit [15:8]
    [2] XXXX XXXX = base address [7:0]
    [3] XXXX XXXX = base address [15:8]
    [4] XXXX XXXX = base address [23:16]
    [5] ---- XXXX = type; see details below
    [5] ---X ---- = 0=system, 1=application (must be 1)
    [5] -XX- ---- = privilege level, usually 3 (binary 11)
    [5] X--- ---- = 0=absent, 1=present; usually 1
    [6] ---- XXXX = segment limit [19:16]
    [6] ---X ---- = available for user; see details below
    [6] --0- ---- = must be zero
    [6] -X-- ---- = 0=16-bit 1=32-bit; usually 1
    [6] X--- ---- = 0=byte-granular (small) 1=page-granular (big)
    [7] XXXX XXXX = base address [31:24]

Here's an alternative view of the layout that treats the buffer as an array of 4 16-bit words (i.e., `unsigned short`s):

    [0] XXXX XXXX XXXX XXXX = segment limit [15:0]
    [1] XXXX XXXX XXXX XXXX = base address  [15:0]
    [2] ---- ---- XXXX XXXX = base address [23:16]
    [2] ---- XXXX ---- ---- = type; see details below
    [2] ---1 ---- ---- ---- = 0=system, 1=application; must be 1
    [2] -XX- ---- ---- ---- = privilege level, usually 3 (binary 11)
    [2] X--- ---- ---- ---- = 0=absent, 1=present; usually 1
    [3] ---- ---- ---- XXXX = segment limit [19:16]
    [3] ---- ---- ---X ---- = available for user; see details below
    [3] ---- ---- --0- ---- = must be zero
    [3] ---- ---- -X-- ---- = 0=16-bit 1=32-bit; usually 1
    [3] ---- ---- X--- ---- = 0=byte-granular (small) 1=page-granular (big)
    [3] XXXX XXXX ---- ---- = base address [31:24]

Special considerations apply to some of the fields:

Segment Limit fields
  The segment limit is specified as a 20-bit number. This number is interpreted as a number of bytes if the granularity bit (bit 7 of byte 6) is not set, and as a number of 4KB pages if the granularity bit is set. Offsets larger than the limit will generate a GPF, the General Protection Fault exception.

  For expand-down data segments (see below), the segment limit is the lower limit of the segment; the upper limit is either 0xffffffff or 0xffff, depending on whether the size bit is set (32-bit default size) or not (16-bit default size). For expand-down segments, values of offset less than the segment limit result in a GPF.

Base Address fields
  Segment base address should generally be 16-byte aligned. This is not required, but it maximizes performance by aligning code and data on 16-byte boundaries.
Type field
  This field has different meanings depending on whether the descriptor is for code or data segment. For code segments, the meaning is as follows:

      ---X = 0=not accessed, 1=accessed
      --1- = 0=execute only, 1=execute/read; must be 1
      -0-- = 0=non-conforming, 1=conforming; must be 0
      1--- = 0=data segment, 1=code segment

  The accessed/not accessed bit indicates whether the segment has been accessed since the last time the bit was cleared. This bit is set whenever the segment selector is loaded into a segment register, and the bit then remains set until explicitly cleared. This bit can be used for debugging purposes.

  The read bit must be set to allow reading data from the code segment, which is done in several cases by the library. The DPMI spec (see DPMI Specification) requires this bit to be 1 for code segments.

  The conforming bit must be cleared so that transfer of execution into this segment from a less-privileged segment will result in a GPF. The DPMI spec (see DPMI Specification) requires this bit to be 0 for code segments.

  For data segments, the meaning of the `type` field is as follows:

      ---X = 0=not accessed, 1=accessed
      --X- = 0=read-only, 1=read/write
      -X-- = 0=expand-up, 1=expand-down; usually 0
      0--- = 0=data segment, 1=code segment

  The accessed/not accessed bit has the same meaning as for code segments. The expand up/down bit is meant to be 1 for stack segments whose size should be changed dynamically, whereby changing the limit adds the additional space to the bottom of the stack; for data segments and statically-sized stack segments, this bit is usually zero.

Present bit
  If this bit is clear, a segment-not-present exception will be generated when the selector is loaded into a segment register, and all the fields of the descriptor except the privilege level and the system/application bit are available for CPU/OS to store their own data. Don't clear this bit unless you know what you are doing.
Available bit
  This bit is left for the application's use. It is neither set nor cleared by the DPMI server.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_descriptor_access_rights, Next:__dpmi_get_extended_exception_handler_vector_pm, Previous:__dpmi_get_descriptor, Up:Alphabetical List

## __dpmi_get_descriptor_access_rights

### Syntax

    #include <dpmi.h>

    int __dpmi_get_descriptor_access_rights(int _selector);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

This function returns the access rights byte from the `lar` opcode.

### Return Value

The access byte. See __dpmi_set_descriptor_access_rights, for the details about the access information returned. Also see __dpmi_get_descriptor.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_extended_exception_handler_vector_pm, Next:__dpmi_get_extended_exception_handler_vector_rm, Previous:__dpmi_get_descriptor_access_rights, Up:Alphabetical List

## __dpmi_get_extended_exception_handler_vector_pm

### Syntax

    #include <dpmi.h>

    int __dpmi_get_extended_exception_handler_vector_pm(int vector,
                                                        __dpmi_paddr *address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0210 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This gets the function that handles protected mode exceptions.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_extended_exception_handler_vector_rm, Next:__dpmi_get_free_memory_information, Previous:__dpmi_get_extended_exception_handler_vector_pm, Up:Alphabetical List

## __dpmi_get_extended_exception_handler_vector_rm

### Syntax

    #include <dpmi.h>

    int __dpmi_get_extended_exception_handler_vector_rm(int vector,
                                                        __dpmi_paddr *address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0211 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function gets the handler for real-mode exceptions.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_free_memory_information, Next:__dpmi_get_memory_block_size_and_base, Previous:__dpmi_get_extended_exception_handler_vector_rm, Up:Alphabetical List

## __dpmi_get_free_memory_information

### Syntax

    #include <dpmi.h>

    int __dpmi_get_free_memory_information(__dpmi_free_mem_info *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0500

This function returns information about available memory. Unsupported fields will have -1 (0xfffffff) in them.

### Return Value

Zero. This always works.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_memory_block_size_and_base, Next:__dpmi_get_memory_information, Previous:__dpmi_get_free_memory_information, Up:Alphabetical List

## __dpmi_get_memory_block_size_and_base

### Syntax

    #include <dpmi.h>

    int __dpmi_get_memory_block_size_and_base(__dpmi_meminfo *info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x050a (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

Pass the handle. It fills in the address and size.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_memory_information, Next:__dpmi_get_multiple_descriptors, Previous:__dpmi_get_memory_block_size_and_base, Up:Alphabetical List

## __dpmi_get_memory_information

### Syntax

    #include <dpmi.h>

    int __dpmi_get_memory_information(__dpmi_memory_info *buffer);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x050b (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function returns virtual memory information, as follows:

`total_allocated_bytes_of_physical_memory_host`
  The total amount of allocated physical memory controlled by the DPMI host.
`total_allocated_bytes_of_virtual_memory_host`
  The total amount of allocated virtual memory controlled by the DPMI host.
`total_available_bytes_of_virtual_memory_host`
  The total amount of available virtual memory controlled by the DPMI host.
`total_allocated_bytes_of_virtual_memory_vcpu`
  The amount of virtual memory allocated by the DPMI host for the current virtual machine.
`total_available_bytes_of_virtual_memory_vcpu`
  The amount of virtual memory available for the current virtual machine.
`total_allocated_bytes_of_virtual_memory_client`
  The amount of virtual memory allocated by the DPMI host for the current client (that is, for the calling program).
`total_available_bytes_of_virtual_memory_client`
  The amount of virtual memory available to the current client.
`total_locked_bytes_of_memory_client`
  The amount of memory locked by the calling program.
`max_locked_bytes_of_memory_client`
  Maximum locked memory for the current client.
`highest_linear_address_available_to_client`
  The highest linear address available to the calling program.
`size_in_bytes_of_largest_free_memory_block`
  Size of the largest available memory block.
`size_of_minimum_allocation_unit_in_bytes`
  Size of the smallest block that can be allocated.
`size_of_allocation_alignment_unit_in_bytes`
  The alignment of allocated memory blocks.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_multiple_descriptors, Next:__dpmi_get_page_attributes, Previous:__dpmi_get_memory_information, Up:Alphabetical List

## __dpmi_get_multiple_descriptors

### Syntax

    #include <dpmi.h>

    int __dpmi_get_multiple_descriptors(int count, void *buffer);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x000e (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function gets a list of selectors' parameters. The buffer pointed to by buffer must be prefilled with selector values, and will contain the parameters on return:

    [0x00:2] selector #1 (pass)
    [0x02:8] parameters #1 (returned)
    [0x0a:2] selector #2 (pass)
    [0x0c:8] parameters #2 (returned)
    ...

### Return Value

Returns count if successful, the negative of the number of descriptors copied if failure.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_page_attributes, Next:__dpmi_get_page_size, Previous:__dpmi_get_multiple_descriptors, Up:Alphabetical List

## __dpmi_get_page_attributes

### Syntax

    #include <dpmi.h>

    int __dpmi_get_page_attributes(__dpmi_meminfo *info, short *buffer);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0506 (DPMI 1.0 only). Supported by CWSDPMI, but not by Windows.

This function retrieves the attributes of a number of pages. Pass the handle in `info->handle`, offset of first page (relative to start of block) in `info->address`, and number of pages in `info->count`. The buffer buffer gets filled in with the attributes. For each page, a 16-bit attribute word in buffer defines the attributes of that page as follows:

bits 0-2
  Page type:
  `000`
    uncommitted
  `001`
    committed
  `010`
    mapped
bit 3
  If set, the page is read/write. If cleared, the page is read-only.
bit 4
  If set, bits 5 and 6 specify accessed and dirty bits.
bit 5
  The page has been accessed (only valid if bit 4 is set).
bit 6
  The page has been written (is dirty). Only valid if bit 4 is set.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_page_size, Next:__dpmi_get_processor_exception_handler_vector, Previous:__dpmi_get_page_attributes, Up:Alphabetical List

## __dpmi_get_page_size

### Syntax

    #include <dpmi.h>

    int __dpmi_get_page_size(unsigned long *_size);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0604

Fills in the page size.

### Return Value

-1 on error (16-bit host), else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_processor_exception_handler_vector, Next:__dpmi_get_protected_mode_interrupt_vector, Previous:__dpmi_get_page_size, Up:Alphabetical List

## __dpmi_get_processor_exception_handler_vector

### Syntax

    #include <dpmi.h>

    int __dpmi_get_processor_exception_handler_vector(int _vector, __dpmi_paddr *_address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0202

This function gets the current protected-mode exception handler (not interrupts) for the exception _vector. It will return a selector:offset pair in the members of the _address variable.

### Return Value

-1 on error (invalid vector), else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_protected_mode_interrupt_vector, Next:__dpmi_get_raw_mode_switch_addr, Previous:__dpmi_get_processor_exception_handler_vector, Up:Alphabetical List

## __dpmi_get_protected_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int __dpmi_get_protected_mode_interrupt_vector(int _vector, __dpmi_paddr *_address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0204

This function gets the address of the current protected mode interrupt (not exception) handler. It returns a selector:offset pair.

### Return Value

Zero. This always works.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_raw_mode_switch_addr, Next:__dpmi_get_real_mode_interrupt_vector, Previous:__dpmi_get_protected_mode_interrupt_vector, Up:Alphabetical List

## __dpmi_get_raw_mode_switch_addr

### Syntax

    #include <dpmi.h>

    int __dpmi_get_raw_mode_switch_addr(__dpmi_raddr *_rm, __dpmi_paddr *_pm);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0306

Read the spec for more info.

### Return Value

Zero. This always works.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_real_mode_interrupt_vector, Next:__dpmi_get_segment_base_address, Previous:__dpmi_get_raw_mode_switch_addr, Up:Alphabetical List

## __dpmi_get_real_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int __dpmi_get_real_mode_interrupt_vector(int _vector, __dpmi_raddr *_address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0200

This function stores the real-mode interrupt vector address in _address. This is the same as the DOS get vector call, and returns a real-mode segment:offset pair.

Bits [31:8] in the vector number are silently ignored.

### Return Value

Zero. This function always works.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_segment_base_address, Next:__dpmi_get_segment_limit, Previous:__dpmi_get_real_mode_interrupt_vector, Up:Alphabetical List

## __dpmi_get_segment_base_address

### Syntax

    #include <dpmi.h>

    int __dpmi_get_segment_base_address(int _selector, unsigned long *_addr);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0006

The physical base address of the selector is stored in *addr.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

### Example

    unsigned long addr;
    if (__dpmi_get_segment_base_address(selector, &addr))
      ...

Node:__dpmi_get_segment_limit, Next:__dpmi_get_selector_increment_value, Previous:__dpmi_get_segment_base_address, Up:Alphabetical List

## __dpmi_get_segment_limit

### Syntax

    #include <dpmi.h>

    unsigned __dpmi_get_segment_limit(int _selector);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

### Return Value

The limit of the segment, as returned by the `lsl` opcode.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_selector_increment_value, Next:__dpmi_get_state_of_debug_watchpoint, Previous:__dpmi_get_segment_limit, Up:Alphabetical List

## __dpmi_get_selector_increment_value

### Syntax

    #include <dpmi.h>

    int __dpmi_get_selector_increment_value(void);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0003

### Return Value

The value to add to each selector allocated by __dpmi_allocate_ldt_descriptors to get the next one.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_state_of_debug_watchpoint, Next:__dpmi_get_state_save_restore_addr, Previous:__dpmi_get_selector_increment_value, Up:Alphabetical List

## __dpmi_get_state_of_debug_watchpoint

### Syntax

    #include <dpmi.h>

    int __dpmi_get_state_of_debug_watchpoint(unsigned long _handle, int *_status);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0b02

Gets the state of the watchpoint. Pass handle, fills in status (0=not encountered, 1=encountered).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_state_save_restore_addr, Next:__dpmi_get_vendor_specific_api_entry_point, Previous:__dpmi_get_state_of_debug_watchpoint, Up:Alphabetical List

## __dpmi_get_state_save_restore_addr

### Syntax

    #include <dpmi.h>

    int __dpmi_get_state_save_restore_addr(__dpmi_raddr *_rm, __dpmi_paddr *_pm);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0305

Read the spec for info.

### Return Value

The number of bytes required to save state.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_vendor_specific_api_entry_point, Next:__dpmi_get_version, Previous:__dpmi_get_state_save_restore_addr, Up:Alphabetical List

## __dpmi_get_vendor_specific_api_entry_point

### Syntax

    #include <dpmi.h>

    int __dpmi_get_vendor_specific_api_entry_point(char *_id, __dpmi_paddr *_api);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0a00

Look up a vendor-specific function, given the name of the function.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_version, Next:__dpmi_get_virtual_interrupt_state, Previous:__dpmi_get_vendor_specific_api_entry_point, Up:Alphabetical List

## __dpmi_get_version

### Syntax

    #include <dpmi.h>

    int __dpmi_get_version(__dpmi_version_ret *_ret);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0400

Fills in version information. The flags are as follows:

    ---- ---X = 0=16-bit host  1=32-bit host
    ---- --X- = 0=V86 used for reflected ints, 1=real mode
    ---- -X-- = 0=no virtual memory, 1=virtual memory supported

The cpu is 2=80286, 3=80386, 4=80486, etc.

DPMI 0.9 returns major=0 and minor=0x5a.

### Return Value

Zero. This always works.

### Portability

not ANSI, not POSIX

Node:__dpmi_get_virtual_interrupt_state, Next:__dpmi_install_resident_service_provider_callback, Previous:__dpmi_get_version, Up:Alphabetical List

## __dpmi_get_virtual_interrupt_state

### Syntax

    #include <dpmi.h>

    int __dpmi_get_virtual_interrupt_state(void);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0902

### Return Value

This function returns the current interrupt flag (1=enabled).

### Portability

not ANSI, not POSIX

Node:__dpmi_install_resident_service_provider_callback, Next:__dpmi_int, Previous:__dpmi_get_virtual_interrupt_state, Up:Alphabetical List

## __dpmi_install_resident_service_provider_callback

### Syntax

    #include <dpmi.h>

    int
    __dpmi_install_resident_service_provider_callback(__dpmi_callback_info *info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0c00 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function installs a resident service provider callback and declares an intent to provide resident protected-mode services after terminating with a call to `__dpmi_terminate_and_stay_resident` (see __dpmi_terminate_and_stay_resident).

The various members of info should be filled as follows:

`data16`
  An 8-byte descriptor for the 16-bit data segment.
`code16`
  An 8-byte descriptor for the 16-bit code segment (zeros if not supported).
`ip`
  A 16-bit offset of the 16-bit callback procedure.
`data32`
  An 8-byte descriptor for 32-bit data segment.
`code32`
  An 8-byte descriptor for 32-bit code segment (zeros if not supported).
`eip`
  A 32-bit offset of the 32-bit callback procedure.

See __dpmi_get_descriptor, for the details about the layout of the 8-byte segment descriptor.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_int, Next:__dpmi_lock_linear_region, Previous:__dpmi_install_resident_service_provider_callback, Up:Alphabetical List

## __dpmi_int

### Syntax

    #include <dpmi.h>

    int __dpmi_int(int _vector, __dpmi_regs *_regs);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0300

This function performs a software interrupt in real mode after filling in most the registers from the given structure. %ss, %esp, and %eflags are automatically taken care of, unlike __dpmi_simulate_real_mode_interrupt.

The following variables can be used to tune this function. By default, these variables are all zero.

`__dpmi_int_ss`
`__dpmi_int_sp`
`__dpmi_int_flags`
  These hold the values stored in the appropriate field in the `__dpmi_regs` structure.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_lock_linear_region, Next:__dpmi_map_conventional_memory_in_memory_block, Previous:__dpmi_int, Up:Alphabetical List

## __dpmi_lock_linear_region

### Syntax

    #include <dpmi.h>

    int __dpmi_lock_linear_region(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0600

This function locks virtual memory, to prevent page faults during hardware interrupts. Pass address and size (in bytes).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_map_conventional_memory_in_memory_block, Next:__dpmi_map_device_in_memory_block, Previous:__dpmi_lock_linear_region, Up:Alphabetical List

## __dpmi_map_conventional_memory_in_memory_block

### Syntax

    #include <dpmi.h>

    int __dpmi_map_conventional_memory_in_memory_block(__dpmi_meminfo *info,
                                                       unsigned long physaddr);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0509 (DPMI 1.0 only). Supported by CWSDPMI, but not by Windows.

This function maps conventional memory (even when virtualized) to virtual memory. Pass the handle, offset, and number of pages.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_map_device_in_memory_block, Next:__dpmi_mark_page_as_demand_paging_candidate, Previous:__dpmi_map_conventional_memory_in_memory_block, Up:Alphabetical List

## __dpmi_map_device_in_memory_block

### Syntax

    #include <dpmi.h>

    int __dpmi_map_device_in_memory_block(__dpmi_meminfo *info,
                                          unsigned long *physaddr);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0508 (DPMI 1.0 only). Supported by CWSDPMI, but not by Windows.

This function maps a physical address range to virtual memory. Pass the handle, offset relative to the start of the block, and number of pages to map.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_mark_page_as_demand_paging_candidate, Next:__dpmi_mark_real_mode_region_as_pageable, Previous:__dpmi_map_device_in_memory_block, Up:Alphabetical List

## __dpmi_mark_page_as_demand_paging_candidate

### Syntax

    #include <dpmi.h>

    int __dpmi_mark_page_as_demand_paging_candidate(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0702

Advises the server that certain pages are unlikely to be used soon. Set address and size (in bytes).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_mark_real_mode_region_as_pageable, Next:__dpmi_physical_address_mapping, Previous:__dpmi_mark_page_as_demand_paging_candidate, Up:Alphabetical List

## __dpmi_mark_real_mode_region_as_pageable

### Syntax

    #include <dpmi.h>

    int __dpmi_mark_real_mode_region_as_pageable(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0602

This function advises the host that the given pages are suitable for page-out. Pass address and size (in bytes).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_physical_address_mapping, Next:__dpmi_relock_real_mode_region, Previous:__dpmi_mark_real_mode_region_as_pageable, Up:Alphabetical List

## __dpmi_physical_address_mapping

### Syntax

    #include <dpmi.h>

    int __dpmi_physical_address_mapping(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0800

Maps a physical device (like a graphics buffer) to linear memory. Fill in the physical address and size (in bytes). On return, the address is the linear address to use.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_relock_real_mode_region, Next:__dpmi_reset_debug_watchpoint, Previous:__dpmi_physical_address_mapping, Up:Alphabetical List

## __dpmi_relock_real_mode_region

### Syntax

    #include <dpmi.h>

    int __dpmi_relock_real_mode_region(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0603

This function relocks the pages unlocked with __dpmi_mark_real_mode_region_as_pageable. Pass address and size (in bytes).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_reset_debug_watchpoint, Next:__dpmi_resize_dos_memory, Previous:__dpmi_relock_real_mode_region, Up:Alphabetical List

## __dpmi_reset_debug_watchpoint

### Syntax

    #include <dpmi.h>

    int __dpmi_reset_debug_watchpoint(unsigned long _handle);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0b03

Resets a watchpoint given its handle in _handle.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_resize_dos_memory, Next:__dpmi_resize_linear_memory, Previous:__dpmi_reset_debug_watchpoint, Up:Alphabetical List

## __dpmi_resize_dos_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_resize_dos_memory(int _selector, int _newpara, int *_ret_max);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0102

This function resizes a dos memory block. Remember to pass the selector, and not the segment. If this call fails, _ret_max contains the largest number of paragraphs available.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_resize_linear_memory, Next:__dpmi_resize_memory, Previous:__dpmi_resize_dos_memory, Up:Alphabetical List

## __dpmi_resize_linear_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_resize_linear_memory(__dpmi_meminfo *info, int commit);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0505 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function resizes a memory block. Pass the handle and new size. Bit 0 of commit is 1 for committed pages; bit 1 is 1 to automatically update descriptors. It returns a new handle and base address.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_resize_memory, Next:__dpmi_segment_to_descriptor, Previous:__dpmi_resize_linear_memory, Up:Alphabetical List

## __dpmi_resize_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_resize_memory(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0503

This function changes the size of a virtual memory block. You must pass the handle and size fields. It may change the base address also; beware of debugging breakpoints and locked memory. It will return a new handle.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_segment_to_descriptor, Next:__dpmi_serialize_on_shared_memory, Previous:__dpmi_resize_memory, Up:Alphabetical List

## __dpmi_segment_to_descriptor

### Syntax

    #include <dpmi.h>

    int __dpmi_segment_to_descriptor(int _segment);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0002

This function returns a selector that maps to what the real-mode segment provided would have referenced. Warning: this is a scarce resource.

### Return Value

-1 on error, else the selector.

### Portability

not ANSI, not POSIX

### Example

    short video = __dpmi_segment_to_descriptor(0xa000);
    movedata(_my_ds(), buffer, video, 0, 320*200);

Node:__dpmi_serialize_on_shared_memory, Next:__dpmi_set_coprocessor_emulation, Previous:__dpmi_segment_to_descriptor, Up:Alphabetical List

## __dpmi_serialize_on_shared_memory

### Syntax

    #include <dpmi.h>

    int __dpmi_serialize_on_shared_memory(unsigned long handle, int flags);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0d02 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function serializes access to a shared memory block whose handle is given in handle. The bit-mapped variable flags defines the following bits:

bit 0
  If set, return immediately if serialization is unavailable. If cleared, the program is suspended until the serialization becomes available.
bit 1
  If set, perform shared serialization. If cleared, perform exclusive serialization.
bits 2-15
  Reserved (should be zero).

An exclusive serialization blocks any serialization attempts for the same memory block from other virtual machines. A shared serialization blocks only exclusive serialization attempts from other virtual machines.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_coprocessor_emulation, Next:__dpmi_set_debug_watchpoint, Previous:__dpmi_serialize_on_shared_memory, Up:Alphabetical List

## __dpmi_set_coprocessor_emulation

### Syntax

    #include <dpmi.h>

    int __dpmi_set_coprocessor_emulation(int flags);

### Description

Please refer to DPMI Specification, for details on DPMI function call operation. Also see DPMI Overview, for general information.

DPMI function AX = 0x0e01 (DPMI v1.0 only, but supported by most DPMI v0.9 servers, including CWSDPMI, Windows, and QDPMI).

This function sets the co-processor emulation state as specified by flags. The only two used bits in flags are:

`bit 0`
  If set, enable the co-processor. If reset, disable the co-processor.
`bit 1`
  If set, the emulation of the floating-point instructions will be done by the calling application.

DJGPP programs using one of the provided emulators should generally call this functions with an argument of 2. (The DJGPP startup code does that automatically if no co-processor is detected.)

### Return Value

-1 on errors, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_debug_watchpoint, Next:__dpmi_set_descriptor, Previous:__dpmi_set_coprocessor_emulation, Up:Alphabetical List

## __dpmi_set_debug_watchpoint

### Syntax

    #include <dpmi.h>

    int __dpmi_set_debug_watchpoint(__dpmi_meminfo *_info, int _type);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0b00

Set a debug breakpoint. Type is 0 for execute, 1 for write, and 2 for access. Fill in address and size (1,2,4 bytes). Server fills in handle.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_descriptor, Next:__dpmi_set_descriptor_access_rights, Previous:__dpmi_set_debug_watchpoint, Up:Alphabetical List

## __dpmi_set_descriptor

### Syntax

    #include <dpmi.h>

    int __dpmi_set_descriptor(int _selector, void *_buffer);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x000c

This function sets the parameters of the selector _selector by copying the contents of the 8-byte buffer pointed to by _buffer into the LDT entry of the selector's descriptor. See __dpmi_get_descriptor, for the description of the contents of the 8-byte buffer.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_descriptor_access_rights, Next:__dpmi_set_extended_exception_handler_vector_pm, Previous:__dpmi_set_descriptor, Up:Alphabetical List

## __dpmi_set_descriptor_access_rights

### Syntax

    #include <dpmi.h>

    int __dpmi_set_descriptor_access_rights(int _selector, int _rights);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0009

This sets the access rights of _selector to _rights.

The meaning of the individual bit fields of _rights is described below. For more details, please refer to __dpmi_get_descriptor.

    ---- ---- ---- ---X = 0=not accessed, 1=accessed
    ---- ---- ---- --X- = data: 0=read, 1=r/w; code: 1=readable
    ---- ---- ---- -X-- = data: 0=expand-up, 1=expand-down; code: 0=non-conforming
    ---- ---- ---- X--- = 0=data, 1=code
    ---- ---- ---1 ---- = must be 1
    ---- ---- -XX- ---- = priviledge level (must equal CPL)
    ---- ---- X--- ---- = 0=absent, 1=present
    ---X ---- ---- ---- = available for the user
    --0- ---- ---- ---- = must be 0
    -X-- ---- ---- ---- = 0=16-bit 1=32-bit
    X--- ---- ---- ---- = 0=byte granular (small) 1=page-granular (big)

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_extended_exception_handler_vector_pm, Next:__dpmi_set_extended_exception_handler_vector_rm, Previous:__dpmi_set_descriptor_access_rights, Up:Alphabetical List

## __dpmi_set_extended_exception_handler_vector_pm

### Syntax

    #include <dpmi.h>

    int __dpmi_set_extended_exception_handler_vector_pm(int vector,
                                                        __dpmi_paddr *address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0212 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function installs a handler for protected-mode exceptions.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_extended_exception_handler_vector_rm, Next:__dpmi_set_multiple_descriptors, Previous:__dpmi_set_extended_exception_handler_vector_pm, Up:Alphabetical List

## __dpmi_set_extended_exception_handler_vector_rm

### Syntax

    #include <dpmi.h>

    int __dpmi_set_extended_exception_handler_vector_rm(int vector,
                                                        __dpmi_paddr *address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0213 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function installs a handler for real-mode exceptions.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_multiple_descriptors, Next:__dpmi_set_page_attributes, Previous:__dpmi_set_extended_exception_handler_vector_rm, Up:Alphabetical List

## __dpmi_set_multiple_descriptors

### Syntax

    #include <dpmi.h>

    int __dpmi_set_multiple_descriptors(int count, void *buffer);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x000f (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function sets multiple descriptors. Buffer usage is like in `__dpmi_get_multiple_descriptors` (see __dpmi_get_multiple_descriptors), but the caller fills in everything before calling.

### Return Value

Returns count if successful, the negative of the number of descriptors set if failure.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_page_attributes, Next:__dpmi_set_processor_exception_handler_vector, Previous:__dpmi_set_multiple_descriptors, Up:Alphabetical List

## __dpmi_set_page_attributes

### Syntax

    #include <dpmi.h>

    int __dpmi_set_page_attributes(__dpmi_meminfo *info, short *buffer);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0507 (DPMI 1.0 only). Supported by CWSDPMI, but not by Windows.

This function sets attributes of a number of pages. Pass handle in `info->handle`, offset within block in `info->address`, and number of pages in `info->count`. buffer points to an array of 16-bit words which specify the new attributes. See __dpmi_get_page_attributes, for the definition of the page attribute word.

The DJGPP startup code calls this function to uncommit the so-called null page, the first 4KB of the program's address space. This causes `NULL` pointer dereferences, a frequent programmatic error, to trigger a Page Fault exception, rather than go unnoticed.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_processor_exception_handler_vector, Next:__dpmi_set_protected_mode_interrupt_vector, Previous:__dpmi_set_page_attributes, Up:Alphabetical List

## __dpmi_set_processor_exception_handler_vector

### Syntax

    #include <dpmi.h>

    int __dpmi_set_processor_exception_handler_vector(int _vector, __dpmi_paddr *_address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0203

This function installs a handler for protected mode exceptions (not interrupts). You must pass a selector:offset pair.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_protected_mode_interrupt_vector, Next:__dpmi_set_real_mode_interrupt_vector, Previous:__dpmi_set_processor_exception_handler_vector, Up:Alphabetical List

## __dpmi_set_protected_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int __dpmi_set_protected_mode_interrupt_vector(int _vector, __dpmi_paddr *_address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0205

This function installs a protected-mode interrupt (not exception) handler. You must pass a selector:offset pair. Hardware interrupts will always be reflected to protected mode if you install a handler. You must explicitely `sti` before `iret` because `iret` won't always restore interrupts in a virtual environment.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_real_mode_interrupt_vector, Next:__dpmi_set_segment_base_address, Previous:__dpmi_set_protected_mode_interrupt_vector, Up:Alphabetical List

## __dpmi_set_real_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int __dpmi_set_real_mode_interrupt_vector(int _vector, __dpmi_raddr *_address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0201

This function sets a real-mode interrupt vector. You must pass a segment:offset pair, not a selector.

Bits [31:8] in the vector number are silently ignored.

### Return Value

Zero. This function always works.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_segment_base_address, Next:__dpmi_set_segment_limit, Previous:__dpmi_set_real_mode_interrupt_vector, Up:Alphabetical List

## __dpmi_set_segment_base_address

### Syntax

    #include <dpmi.h>

    int __dpmi_set_segment_base_address(int _selector, unsigned _address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0007

This function sets the base address of the _selector to _address.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_set_segment_limit, Next:__dpmi_simulate_real_mode_interrupt, Previous:__dpmi_set_segment_base_address, Up:Alphabetical List

## __dpmi_set_segment_limit

### Syntax

    #include <dpmi.h>

    int __dpmi_set_segment_limit(int _selector, unsigned _address);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0008

This function sets the highest valid address in the segment referenced by _selector. For example, if you pass 0xfffff, the highest valid address is 0xfffff. Note: if you pass a number <= 64K, the segment changes to "non-big", and may cause unexpected problems. Limits for segments larger than 1MB must have their low 12 bits set.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_simulate_real_mode_interrupt, Next:__dpmi_simulate_real_mode_procedure_iret, Previous:__dpmi_set_segment_limit, Up:Alphabetical List

## __dpmi_simulate_real_mode_interrupt

### Syntax

    #include <dpmi.h>

    int __dpmi_simulate_real_mode_interrupt(int _vector, __dpmi_regs *_regs);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0300

This function performs a software interrupt in real mode after filling in all the registers from the given structure. You must set %ss, %esp, and %eflags to valid real-mode values or zero, unlike __dpmi_int.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_simulate_real_mode_procedure_iret, Next:__dpmi_simulate_real_mode_procedure_retf, Previous:__dpmi_simulate_real_mode_interrupt, Up:Alphabetical List

## __dpmi_simulate_real_mode_procedure_iret

### Syntax

    #include <dpmi.h>

    int __dpmi_simulate_real_mode_procedure_iret(__dpmi_regs *_regs);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0302

This function switches to real mode, filling in all the registers from the structure. ss:sp and flags must be valid or zero. The called function must return with an `iret`.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_simulate_real_mode_procedure_retf, Next:__dpmi_simulate_real_mode_procedure_retf_stack, Previous:__dpmi_simulate_real_mode_procedure_iret, Up:Alphabetical List

## __dpmi_simulate_real_mode_procedure_retf

### Syntax

    #include <dpmi.h>

    int __dpmi_simulate_real_mode_procedure_retf(__dpmi_regs *_regs);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0301

This function switches to real mode with all the registers set from the structure, including cs:ip. The function called should return with a `retf`. ss:sp and flags must be set to valid values or zero.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_simulate_real_mode_procedure_retf_stack, Next:__dpmi_terminate_and_stay_resident, Previous:__dpmi_simulate_real_mode_procedure_retf, Up:Alphabetical List

## __dpmi_simulate_real_mode_procedure_retf_stack

### Syntax

    #include <dpmi.h>

    int __dpmi_simulate_real_mode_procedure_retf_stack(__dpmi_regs *_regs, int stack_words_to_copy, const void *stack_data);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0301

This function switches to real mode with all the registers set from the structure, including cs:ip. The function called should return with a `retf`. ss:sp and flags must be set to valid values or zero.

You may optionally specify data to be copied to the real-mode stack, to pass arguments to real-mode procedures with stack-based calling conventions. If you don't want to copy data to the real mode stack, pass 0 for stack_words_to_copy, and `NULL` for stack_bytes.

Note that the amount of stack data to be copied should be given in units of 16-bit words, not in bytes. This is defined by the underlying DPMI function.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_terminate_and_stay_resident, Next:__dpmi_unlock_linear_region, Previous:__dpmi_simulate_real_mode_procedure_retf_stack, Up:Alphabetical List

## __dpmi_terminate_and_stay_resident

### Syntax

    #include <dpmi.h>

    int __dpmi_terminate_and_stay_resident(int return_code,
                                           int paragraphs_to_keep);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0c01 (DPMI 1.0 only). Not supported by CWSDPMI and Windows.

This function terminates the calling program, but leaves it resident in memory. return_code specifies which value to return to the OS. paragraphs_to_keep specifies the number of paragraphs of DOS (conventional) memory to keep; it should be either zero or 6 or more. Note that any protected-mode memory remains allocated to the program unless explicitly freed before calling this function.

The calling program must call the function `__dpmi_install_resident_service_provider_callback` before this one, otherwise it will be terminated instead of going TSR. See __dpmi_install_resident_service_provider_callback.

### Return Value

This call does not return.

### Portability

not ANSI, not POSIX

Node:__dpmi_unlock_linear_region, Next:__dpmi_yield, Previous:__dpmi_terminate_and_stay_resident, Up:Alphabetical List

## __dpmi_unlock_linear_region

### Syntax

    #include <dpmi.h>

    int __dpmi_unlock_linear_region(__dpmi_meminfo *_info);

### Description

Please refer to DPMI Specification for details on DPMI function call operation. Also see DPMI Overview for general information.

DPMI function AX = 0x0601

This function unlocks virtual memory. Pass address and size (in bytes).

### Return Value

-1 on error, else zero.

### Portability

not ANSI, not POSIX

Node:__dpmi_yield, Next:dup, Previous:__dpmi_unlock_linear_region, Up:Alphabetical List

## __dpmi_yield

### Syntax

    #include <dpmi.h>

    void __dpmi_yield(void);

### Description

`__dpmi_yield` calls function 1680h of the interrupt 2Fh, which tells the task manager in a multitasking environment that the calling program doesn't need the rest of its time slice. The task manager will then preempt the calling program and switch to another task that is ready to run.

This function should be called in busy-wait loops, like when a program waits for user input via keyboard, after it finds the keyboard buffer empty, to enhance overall performance in a multitasking environment.

### Return Value

None. If the call isn't supported by the environment, like when running on plain DOS, `errno` is set to `ENOSYS`.

### Portability

not ANSI, not POSIX

Node:dup, Next:dup2, Previous:__dpmi_yield, Up:Alphabetical List

## dup

### Syntax

    #include <unistd.h>

    int dup(int old_handle);

### Description

This function duplicates the given file handle. Both handles refer to the same file and file pointer.

### Return Value

The new file handle, or -1 if error.

### Portability

not ANSI, POSIX

### Example

    do_file(dup(fileno(stdin)));

Node:dup2, Next:_dxe_load, Previous:dup, Up:Alphabetical List

## dup2

### Syntax

    #include <unistd.h>

    int dup2(int existing_handle, int new_handle);

### Description

This call causes new_handle to refer to the same file and file pointer as existing_handle. If new_handle is an open file, it is closed.

### Return Value

The new handle, or -1 on error.

### Portability

not ANSI, POSIX

### Example

    /* copy new file to stdin stream */
    close(0);
    dup2(new_stdin, 0);
    close(new_stdin);

Node:_dxe_load, Next:ecvt, Previous:dup2, Up:Alphabetical List

## _dxe_load

### Syntax

    #include <sys/dxe.h>

    void *_dxe_load(char *dxe_filename);

### Description

This function loads a dynamic executable image, whose file name is pointed to by dxe_filename, into memory and returns the entry point for the symbol associated with the image. The symbol may point to a structure or a function.

### Return Value

0 on failure, the address of the loaded symbol on success.

### Portability

not ANSI, not POSIX

### Example

      static int (*add)(int a, int b);

      add = _dxe_load("add.dxe");
      if (add == 0)
        printf("Cannot load add.dxe\n");
      else
        printf("Okay, 3 + 4 = %d\n", add(3,4));

Node:ecvt, Next:ecvtbuf, Previous:_dxe_load, Up:Alphabetical List

## ecvt

### Syntax

    #include <stdlib.h>

    char * ecvt (double value, int ndigits, int *decpt, int *sign)

### Description

This function converts the value into a null-terminated string, and returns a pointer to that string.

`ecvt` works exactly like `ecvtbuf` (see ecvtbuf), except that it generates the string in an internal static buffer which is overwritten on each call.

### Return Value

A pointer to the generated string.

### Portability

not ANSI, not POSIX

Node:ecvtbuf, Next:edi_init, Previous:ecvt, Up:Alphabetical List

## ecvtbuf

### Syntax

    #include <stdlib.h>

    char * ecvtbuf (double value, int ndigits, int *decpt, int *sign, char *buf)

### Description

This function converts its argument value into a null-terminated string of ndigits digits in buf. buf should have enough space to hold at least `ndigits + 1` characters.

The produced string in buf does not include the decimal point. Instead, the position of the decimal point relative to the beginning of buf is stored in an integer variable whose address is passed in decpt. Thus, if buf is returned as "1234" and *decpt as 1, this corresponds to a value of 1.234; if *decpt is -1, this corresponds to a value of 0.01234, etc.

The sign is also not included in buf's value. If value is negative, `ecvtbuf` puts a nonzero value into the variable whose address is passed in sign; otherwise it stores zero in *sign.

The least-significant digit in buf is rounded.

`ecvtbuf` produces the string "NaN" if value is a NaN, and "Inf" or "Infinity" if value is an infinity (the longer form is produced when ndigits is 8 or more).

### Return Value

A pointer to buf.

### Portability

not ANSI, not POSIX

### Example

      #include <stdlib.h>
      #include <stdio.h>
      #include <math.h>

      char vbuf[20];
      int esign, edecpt;

      ecvtbuf (M_PI, 5, &edecpt, &esign, buf)
      /* This will print " 31416".  */
      printf ("%c%s", esign ? '-' : ' ', buf);

Node:edi_init, Next:enable, Previous:ecvtbuf, Up:Alphabetical List

## edi_init

### Syntax

    #include <debug/dbgcom.h>

    void edi_init (jmp_buf start_state);

### Description

This function is part of the DJGPP debugging support. It should be called after a call to `v2loadimage` (see v2loadimage) which loads an executable program as a debuggee. `edi_init` then takes care of initializing the data structures which need to be set before the debugger can set breakpoints and run the debuggee.

The argument start_state is usually set by a preceding call to `v2loadimage`.

### Portability

not ANSI, not POSIX

### Example

     if (v2loadimage (exec_file, cmdline, start_state))
       {
          printf ("Load failed for image %s\n", exec_file);
          exit (1);
       }

      edi_init (start_state);

Node:enable, Next:endgrent, Previous:edi_init, Up:Alphabetical List

## enable

### Syntax

    #include <dos.h>

    int enable(void);

### Description

This function enables interrupts.

See disable.

### Return Value

Returns nonzero if the interrupts were already enabled, zero if they had been disabled before this call.

### Portability

not ANSI, not POSIX

### Example

    int ints_were_enabled;

    ints_were_enabled = enable();
    . . . do some stuff . . .
    if (!ints_were_enabled)
      disable();

Node:endgrent, Next:endmntent, Previous:enable, Up:Alphabetical List

## endgrent

### Syntax

    #include <grp.h>

    void endgrent(void);

### Description

This function should be called after all calls to `getgrent`, `getgrgid`, or `getgrnam`.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

See getgrent.

Node:endmntent, Next:endpwent, Previous:endgrent, Up:Alphabetical List

## endmntent

### Syntax

    #include <mntent.h>

    int endmntent(FILE *filep);

### Description

This function should be called after the last call to `getmntent` (see getmntent).

### Return Value

This function always returns one.

### Portability

not ANSI, not POSIX

Node:endpwent, Next:errno, Previous:endmntent, Up:Alphabetical List

## endpwent

### Syntax

    #include <pwd.h>

    void endpwent(void);

### Description

This function should be called after the last call to getpwent (see getpwent).

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:errno, Next:exec*, Previous:endpwent, Up:Alphabetical List

## errno

### Syntax

    #include <errno.h>

    extern int errno;

### Description

This variable is used to hold the value of the error of the last function call. The value might be one of the following:

`0`
  No Error. Library functions never set `errno` to zero, but the startup code does that just before calling `main` (this is ANSI C requirement).
`1`
  EDOM - Numerical input to a function is out of range.
`2`
  ERANGE - Numerical output of a function is out of range.
`3`
  E2BIG - Argument list too long. `system` and the functions from the `spawn` family assign this to `errno` when the command line is too long (longer than 126-character limit when invoking non-DJGPP programs, or longer than the transfer buffer size when invoking DJGPP programs).
`4`
  EACCES - Permission denied. Attempt to write to a read-only file, or remove a non-empty directory, or open a directory as if it were a file, etc. In essence, it's a DOS way of saying "You can't do that, but I'm too stupid to know why."
`5`
  EAGAIN - Resource temporarily unavailable, try again later. Almost never used in DJGPP, except when DOS returns error code 3Dh ("network print queue full") 81h (NetWare4 "CWait children still running") or 9Bh (NetWare4 "unable to create another TCB").
`6`
  EBADF - Bad file descriptor: an invalid file handle passed to a library function.
`7`
  EBUSY - Resource busy. Attempt to remove current directory (including current directory on another drive), or when a networked resource, such as a drive, is in use by another process.
`8`
  ECHILD - No child processes. Returned by `wait` and `waitpid`, and by NetWare-related calls.
`9`
  EDEADLK - Resource deadlock avoided. Never used in DJGPP.
`10`
  EEXIST - File exists. Returned by `open` and `mkdir` when a file or directory by that name already exists.
`11`
  EFAULT - Bad address. A function was passed a bad pointer (like a `NULL` pointer).
`12`
  EFBIG - File too large. Never used in DJGPP.
`13`
  EINTR - Interrupted system call. `system` and the functions of the `spawn` family use that when the child program was interrupted by `Ctrl-<C>`. Also, when DOS returns the "fail on INT 24h" error code.
`14`
  EINVAL - Invalid argument. Any case when any argument to a library function is found to be invalid. Examples include invalid drive number, "." or ".." as one of the arguments to `rename`, syntax errors in the command line passed to `system`, etc.
`15`
  EIO - Input or output error. Low-level error in I/O operation, like bad disk block, damaged FAT, etc.
`16`
  EISDIR - Is a directory: an attempt to do something with a directory which is only allowed with regular files. DOS usually returns `EACCES` in these cases, but DJGPP sometimes assigns `EISDIR` to `errno`, like when `rename` is called to move a regular file over a directory, or when `system` or one of the `spawn*` functions are passed a name of a directory instead of an executable program.
`17`
  EMFILE - Too many open files in system (no more handles available). This usually means that the number specified by the `FILES=` directive in `CONFIG.SYS` is too small.
`18`
  EMLINK - Too many links. Not used in DJGPP (as DOS doesn't support links).
`19`
  ENAMETOOLONG - File name too long (longer than `FILENAME_MAX`, defined in `stdio.h`).
`20`
  ENFILE - Too many open files. Never used in DJGPP.
`21`
  ENODEV - No such device. Attempt to access an invalid drive, or an invalid operation for the type of drive.
`22`
  ENOENT - No such file or directory.
`23`
  ENOEXEC - Unable to execute file. Returned by `_dxe_load` (when the argument names a file that isn't a valid DXE), and by NetWare-related calls which run programs remotely.
`24`
  ENOLCK - No locks available. Returned when the DOS file-locking functions cannot lock more files (due to overflow of the sharing buffer).
`25`
  ENOMEM - Not enough memory. Note that, unlike your expectations, `malloc` does NOT set `errno` to `ENOMEM`; however, several library functions that use `malloc` will do that when it returns a `NULL` pointer.
`26`
  ENOSPC - No space left on drive. DOS usually doesn't return this error, but `write` and `_write` do this for it, when they detect a full disk condition.
`27`
  ENOSYS - Function not implemented. Any system call that isn't supported by the underlying OS, like an LFN function when running on plain DOS.
`28`
  ENOTDIR - Not a directory. DOS never returns this code, but some library functions, like `rename` and `_truename`, do that if they expect a valid directory pathname, but get either an invalid (e.g. empty) pathname or a file that is not a directory.
`29`
  ENOTEMPTY - Directory not empty. DOS never returns this code, but `rename` does, when it is called to move a directory over an existing non-empty directory.
`30`
  ENOTTY - Inappropriate I/O control operation. The termios functions set `errno` to this when called on a device that is not a TTY.
`31`
  ENXIO - No such device or address. An operation attempted to reference a device (not a disk drive) that is invalid, or non-existent, or access a disk drive that exists but is empty.
`32`
  EPERM - Operation not permitted. Examples include: sharing or file lock violations; denial of access to networked resources; expired password or illegal login attempts via a network; too many or duplicate network redirections; etc.
`33`
  EPIPE - Broken pipe: attempt to write to a pipe with nobody to read it. This never happens in DJGPP.
`34`
  EROFS - Read-only file system: attempt to write to a read-only disk. Unfortunately, DOS almost never returns this code.
`35`
  ESPIPE - Invalid seek: attempt to seek on a pipe. Never happens in DJGPP, except for NetWare-related operations, since pipes are simulated with regular files in MS-DOS, and therefore are always seekable.
`36`
  ESRCH - No such process. Not used in DJGPP.
`37`
  EXDEV - Improper link. An attempt to rename a file across drives, or create a "symlink" to a file that is not an executable DJGPP v2.x program.
`38`
  ENMFILE - No more files. `findfirst` and `findnext` assign this to `errno` when they exhaust the files in the directory. `readdir` does that as well.

See perror.

### Portability

ANSI, POSIX

Node:exec*, Next:__exit, Previous:errno, Up:Alphabetical List

## exec*

### Syntax

    #include <unistd.h>

    int execl(const char *path, const char *argv0, ...);
    int execle(const char *path, const char *argv0, ... /*, char *const envp[] */);
    int execlp(const char *path, const char *argv0, ...);
    int execlpe(const char *path, const char *argv0, ... /*, char *const envp[] */);

    int execv(const char *path, char *const argv[]);
    int execve(const char *path, char *const argv[], char *const envp[]);
    int execvp(const char *path, char *const argv[]);
    int execvpe(const char *path, char *const argv[], char *const envp[]);

### Description

These functions operate by calling `spawn*` with a type of `P_OVERLAY`. Refer to spawn* for a full description.

### Return Value

If successful, these functions do not return. If there is an error, these functions return -1 and set `errno` to indicate the error.

### Portability

not ANSI, POSIX

### Example

    execlp("gcc", "gcc", "-v", "hello.c", 0);

Node:__exit, Next:_exit, Previous:exec*, Up:Alphabetical List

## __exit

### Syntax

    #include <unistd.h>

    void __exit(int exit_code);

### Description

This is an internal library function which exits the program, returning exit_code to the calling process. No additional processing is done, and any `atexit` functions are not called. Since hardware interrupts are not unhooked, this can cause crashes after the program exits. This function is normally called only by `_exit`; do not call it directly.

### Return Value

This function does not return.

### Portability

not ANSI, POSIX

Node:_exit, Next:exit, Previous:__exit, Up:Alphabetical List

## _exit

### Syntax

    #include <unistd.h>

    void _exit(int exit_code);

### Description

This function exits the program, returning exit_code to the calling process. No additional processing (such as closing file descriptors or calls to the static destructor functions) is done, and any `atexit` functions are not called; only the hardware interrupt handlers are unhooked, to prevent system crashes e.g. after a call to `abort`. This function is normally called only by `exit` and `abort`.

### Return Value

This function does not return.

### Portability

not ANSI, not POSIX

Node:exit, Next:exp, Previous:_exit, Up:Alphabetical List

## exit

### Syntax

    #include <stdlib.h>

    void exit(int exit_code);

### Description

This function exits the program, returning exit_code to the calling process. Before exiting, all open files are closed and all `atexit` and `on_exit` requests are processed.

### Return Value

This function does not return.

### Portability

ANSI, POSIX

### Example

    if (argc < 4)
    {
      print_usage();
      exit(1);
    }

Node:exp, Next:exp10, Previous:exit, Up:Alphabetical List

## exp

### Syntax

    #include <math.h>

    double exp(double x);

### Description

This function computes the exponential of x, e^x, where e is the base of the natural system of logarithms, approximately 2.718281828.

### Return Value

e to the x power. If the value of x is finite, but so large in magnitude that its exponential cannot be accurately represented by a `double`, the return value is the nearest representable `double` (possibly, an `Inf`), and `errno` is set to `ERANGE`. If x is either a positive or a negative infinity, the result is either `+Inf` or zero, respectively, and `errno` is not changed. If x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:exp10, Next:exp2, Previous:exp, Up:Alphabetical List

## exp10

### Syntax

    #include <math.h>

    double exp10(double x);

### Description

This function computes 10 to the power of x, 10^x.

### Return Value

10 to the x power. If the value of x is finite, but so large in magnitude that 10^x cannot be accurately represented by a `double`, the return value is the nearest representable `double` (possibly, an `Inf`), and `errno` is set to `ERANGE`. If x is either a positive or a negative infinity, the result is either `+Inf` or zero, respectively, and `errno` is not changed. If x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:exp2, Next:expm1, Previous:exp10, Up:Alphabetical List

## exp2

### Syntax

    #include <math.h>

    double exp2(double x);

### Description

This function computes 2 to the power of x, 2^x.

### Return Value

2 to the x power. If the value of x is finite, but so large in magnitude that 2^x cannot be accurately represented by a `double`, the return value is is the nearest representable `double` (possibly, an `Inf`), and `errno` is set to `ERANGE`. If x is either a positive or a negative infinity, the result is either `+Inf` or zero, respectively, and `errno` is not changed. If x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:expm1, Next:fabs, Previous:exp2, Up:Alphabetical List

## expm1

### Syntax

    #include <math.h>

    double expm1(double x);

### Description

This function computes the value of e^x - 1, the exponential of x minus 1, where e is the base of the natural system of logarithms, approximately 2.718281828. The result is more accurate than `exp(x) - 1` for small values of x, where the latter method would lose many significant digits.

### Return Value

e raised to the power x, minus 1. If the value of x is finite, but so large that its exponent would overflow a `double`, the return value is `Inf`, and `errno` is set to `ERANGE`. If x is either a positive or a negative infinity, the result is either `+Inf` or -1, respectively, and `errno` is not changed. If x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:fabs, Next:_far*, Previous:expm1, Up:Alphabetical List

## fabs

### Syntax

    #include <math.h>

    double fabs(double x);

### Description

This function computes the absolute value of its argument x.

### Return Value

x if x is positive, else -x. Note that in this context, +0.0 is positive and -0.0 is negative. Infinities and `NaN`s are returned unchanged, except for the sign.

### Portability

ANSI, POSIX

Node:_far*, Next:fclose, Previous:fabs, Up:Alphabetical List

## _far*

### Syntax

    #include <sys/farptr.h>

    unsigned char _farpeekb(unsigned short selector, unsigned long offset);
    unsigned short _farpeekw(unsigned short selector, unsigned long offset);
    unsigned long _farpeekl(unsigned short selector, unsigned long offset);

    void _farpokeb(unsigned short sel, unsigned long off, unsigned char val);
    void _farpokew(unsigned short sel, unsigned long off, unsigned short val);
    void _farpokel(unsigned short sel, unsigned long off, unsigned long val);

    void _farsetsel(unsigned short selector);
    unsigned short _fargetsel(void);

    void _farnspokeb(unsigned long offset, unsigned char value);
    void _farnspokew(unsigned long offset, unsigned short value);
    void _farnspokel(unsigned long offset, unsigned long value);

    unsigned char _farnspeekb(unsigned long offset);
    unsigned short _farnspeekw(unsigned long offset);
    unsigned long _farnspeekl(unsigned long offset);

### Description

These functions provide the equivalent functionality of "far pointers" to peek or poke an absolute memory addresses, even though gcc doesn't understand the keyword "far". They come in handy when you need to access memory-mapped devices (like VGA) or some address in lower memory returned by a real-mode service. These functions are provided as inline assembler functions, so when you optimize your program they reduce to only a few opcodes (only one more than a regular memory access), resulting in very optimal code.

The first two groups of functions take a selector and an offset. This selector is not a dos segment. If you want to access dos memory, pass _go32_info_block.selector_for_linear_memory (or just _dos_ds) as the selector, and seg*16+ofs as the offset. For functions which poke the memory, you should also provide the value to put there.

The last two groups assume that you've used `_farsetsel` to specify the selector. You should avoid making any function calls between `_farsetsel` and using these other functions, unless you're absolutely sure that they won't modify that selector. This allows you to optimize loops by setting the selector once outside the loop, and using the shorter functions within the loop. You can use `_fargetsel` if you want to temporary change the selector with `_farsetsel` and restore it afterwards.

### Return Value

Functions which peek the address return the value at given address. `_fargetsel` returns the current selector.

### Portability

not ANSI, not POSIX

Node:fclose, Next:fcntl, Previous:_far*, Up:Alphabetical List

## fclose

### Syntax

    #include <stdio.h>

    int fclose(FILE *file);

### Description

This function closes the given file.

### Return Value

Zero on success, else `EOF`.

### Portability

ANSI, POSIX

### Example

    FILE *f = fopen("data", "r");
    fprintf(f, "Hello\n");
    fclose(f);

Node:fcntl, Next:fcvt, Previous:fclose, Up:Alphabetical List

## fcntl

### Syntax

    #include <fcntl.h>

    int fcntl (int fd, int cmd, ...);

### Description

This function performs the operation specified by cmd on the file open on handle fd. The following operations are defined by the header `fcntl.h`:

`F_DUPFD`
  Returns a file handle that duplicates fd like `dup` does (see dup), except that `fcntl` also makes sure the returned handle is the lowest available handle greater than or equal to the integer value of the third argument.
`F_GETFD`
  Get the `FD_CLOEXEC` close-on-exec (a.k.a. no-inherit) status of fd. If the returned value has its least-significant bit set, the file will not be inherited by programs invoked by this process; otherwise, the file will remain open in the child processes.

  Note that only the first 20 handles can be passed to child processes by DOS/Windows; handles beyond that cannot be inherited. In addition, the stub loader of the child DJGPP program will forcibly close handles 19 and 18 (since otherwise it will be unable to read the COFF executable information and enter protected mode). Therefore, the current implementation always returns 0 for handles below 18, meaning that all those handles are inherited, and `FD_CLOEXEC` for handles 18 and above.

  The no-inherit bit can be set when the file is open, by using the `O_NOINHERIT` in the open flags; see open.

`F_SETFD`
  Set the close-on-exec flag for the handle fd using the LSB of the integer value supplied as the third argument. Currently, `fcntl` always fails this call and sets `errno` to `ENOSYS`, since DOS/Windows don't support changing the no-inherit status of an open file.
`F_GETFL`
  Get the open mode and status flags associated with the handle fd. The flags are those supported by `open` and `creat` functions, like `O_READONLY`, `O_APPEND`, etc. Currently, this command always returns zero, with no flags set.
`F_SETFL`
  Set the open mode and status flags associated with the handle fd. This always fails and sets `errno` to `ENOSYS`, since DOS and Windows don't allow to change the descriptor flags after the file is open.
`F_GETLK`
  Get a description of a file segment lock as specified in the structure pointed to by the third argument. This is unsupported and will always fail.
`F_SETLK`
  Set or clear a file segment lock according to the structure pointed to by the third argument. This is unsupported and will always fail.
`F_SETLKW`
  Same as `F_SETLK`, but if the lock is blocked, the call will wait until it is unblocked and the lock can be applied. This is unsupported and will always fail.

This function can be hooked by the Filesystem extensions, see File System Extensions. If you don't want this, and you are calling `fcntl` with the `F_DUPFD` command, you should use `dup2` instead, see dup2.

### Return Value

If an invalid or unsupported value is passed in cmd, or fd is an invalid file handle, the function returns -1 and sets `errno` to the appropriate value. Unsupported values of cmd cause `ENOSYS` to be stored in `errno`. If cmd is `F_DUPFD`, the function returns the new descriptor or -1 in case of a failure.

### Portability

not ANSI, POSIX (see note 1)

Notes:

1. Contrary to Posix requirement, the handle returned by `F_DUPFD` shares the `FD_CLOEXEC` flag with fd (unless they are on different sides of the 20-handle mark), since DOS/Windows only maintain a single set of bits for all the handles associated with the same call to `open`.

### Example

     /* Save the handle in a way that it won't be passed
        to child processes.  */
      int saved_fd = fcntl (fd, F_DUPFD, 20);

Node:fcvt, Next:fcvtbuf, Previous:fcntl, Up:Alphabetical List

## fcvt

### Syntax

    #include <stdlib.h>

    char * fcvt (double value, int ndigits, int *decpt, int *sign)

### Description

This function converts the value into a null-terminated string, and returns a pointer to that string.

`fcvt` works exactly like `fcvtbuf` (see fcvtbuf), except that it generates the string in an internal static buffer which is overwritten on each call.

### Return Value

A pointer to the generated string.

### Portability

not ANSI, not POSIX

Node:fcvtbuf, Next:fdopen, Previous:fcvt, Up:Alphabetical List

## fcvtbuf

### Syntax

    #include <stdlib.h>

    char * fcvtbuf (double value, int ndigits, int *decpt, int *sign, char *buf)

### Description

This function converts its argument value into a null-terminated string in buf with ndigits digits to the right of the decimal point. ndigits can be negative to indicate rounding to the left of the decimal point. buf should have enough space to hold at least `310+max(0,ndigits)` characters.

Note that, unlike `ecvtbuf` (see ecvtbuf), `fcvtbuf` only counts the digits to the right of the decimal point. Thus, if value is 123.45678 and ndigits is 4, then `ecvtbuf` will produce "1235", but `fcvtbuf` will produce "1234568" (and *decpt will be 3 in both cases).

The produced string in buf does not include the decimal point. Instead, the position of the decimal point relative to the beginning of buf is stored in an integer variable whose address is passed in decpt. Thus, if buf is returned as "1234" and *decpt as 1, this corresponds to a value of 1.234; if *decpt is -1, this corresponds to a value of 0.01234, etc.

The sign is also not included in buf's value. If value is negative, `ecvtbuf` puts a nonzero value into the variable whose address is passed in sign; otherwise it stores zero in *sign.

The least-significant digit in buf is rounded.

`ecvtbuf` produces the string "NaN" if value is a NaN, and "Inf" or "Infinity" if value is an infinity (the longer form is produced when ndigits is 8 or more).

### Return Value

A pointer to buf.

### Portability

not ANSI, not POSIX

### Example

      #include <stdlib.h>
      #include <stdio.h>
      #include <math.h>

      char vbuf[20];
      int fsign, fdecpt;

      fcvtbuf (M_PI, 5, &fdecpt, &fsign, buf)
      /* This will print " 314159".  */
      printf ("%c%s", fsign ? '-' : ' ', buf);

Node:fdopen, Next:feof, Previous:fcvtbuf, Up:Alphabetical List

## fdopen

### Syntax

    #include <stdio.h>

    FILE *fdopen(int fd, const char *mode);

### Description

This function opens a stream-type file that uses the given fd file, which must already be open. The file is opened with the modes specified by mode, which is the same as for `fopen`. See fopen.

### Return Value

The newly created `FILE *`, or `NULL` on error.

### Portability

not ANSI, POSIX

### Example

    FILE *stdprn = fdopen(4, "w");

Node:feof, Next:ferror, Previous:fdopen, Up:Alphabetical List

## feof

### Syntax

    #include <stdio.h>

    int feof(FILE *file);

### Description

This function can be used to indicate if the given file is at the end-of-file or not.

### Return Value

Nonzero at end-of-file, zero otherwise.

### Portability

ANSI, POSIX

### Example

    while (!feof(stdin))
      gets(line);

Node:ferror, Next:fflush, Previous:feof, Up:Alphabetical List

## ferror

### Syntax

    #include <stdio.h>

    int ferror(FILE *file);

### Description

This function can be used to indicate if the given file has encountered an error or not. See clearerr.

### Return Value

Nonzero for an error, zero otherwize.

### Portability

ANSI, POSIX

### Example

    if (ferror(stdin))
      exit(1);

Node:fflush, Next:ffs, Previous:ferror, Up:Alphabetical List

## fflush

### Syntax

    #include <stdio.h>

    int fflush(FILE *file);

### Description

If file is not a `NULL` pointer, this function causes any unwritten buffered data to be written out to the given file. This is useful in cases where the output is line buffered and you want to write a partial line.

If file is a `NULL` pointer, `fflush` writes any buffered output to all files opened for output.

Note that `fflush` has no effect for streams opened for reading only. Also note that the operating system can further buffer/cache writes to disk files; a call to `fsync` (see fsync) or `sync` (see sync) is typically required to actually deliver data to the file(s).

### Return Value

Zero on success, -1 on error. When called with a `NULL` pointer, -1 will be returned if an error happened while flushing some of the streams (but `fflush` will still try to flush all the rest before it returns).

### Portability

ANSI, POSIX

### Example

    printf("Enter value : ");
    fflush(stdout);
    scanf(result);

Node:ffs, Next:fgetc, Previous:fflush, Up:Alphabetical List

## ffs

### Syntax

    #include <string.h>

    int ffs(int _mask);

### Description

This function find the first (least significant) bit set in the input value.

### Return Value

Bit position (1..32) of the least significant set bit, or zero if the input value is zero.

### Portability

not ANSI, not POSIX

### Example

    ffs(0) = 0
    ffs(1) = 1
    ffs(5) = 1
    ffs(96) = 6

Node:fgetc, Next:fgetgrent, Previous:ffs, Up:Alphabetical List

## fgetc

### Syntax

    #include <stdio.h>

    int fgetc(FILE *file);

### Description

Returns the next character in the given file as an unsigned char.

### Return Value

The given char (value 0..255) or `EOF` at end-of-file.

### Portability

ANSI, POSIX

### Example

    int c;
    while((c=fgetc(stdin)) != EOF)
      fputc(c, stdout);

Node:fgetgrent, Next:fgetpos, Previous:fgetc, Up:Alphabetical List

## fgetgrent

### Syntax

    #include <grp.h>

    struct group *fgetgrent(FILE *file);

### Description

This function, in MS-DOS, is exactly the same as `getgrent` (see getgrent).

### Portability

not ANSI, not POSIX

Node:fgetpos, Next:fgets, Previous:fgetgrent, Up:Alphabetical List

## fgetpos

### Syntax

    #include <stdio.h>

    int fgetpos(FILE *file, fpos_t *offset);

### Description

This function records the current file pointer for file, for later use by `fsetpos`.

See fsetpos. See ftell.

### Return Value

Zero if successful, nonzero if not.

### Portability

ANSI, POSIX

Node:fgets, Next:File System Extensions, Previous:fgetpos, Up:Alphabetical List

## fgets

### Syntax

    #include <stdio.h>

    char *fgets(char *buffer, int maxlength, FILE *file);

### Description

This function reads as much of a line from a file as possible, stopping when the buffer is full (maxlength-1 characters), an end-of-line is detected, or `EOF` or an error is detected. It then stores a `NULL` to terminate the string.

### Return Value

The address of the buffer is returned on success, if `EOF` is encountered before any characters are stored, or if an error is detected, `NULL` is returned instead.

### Portability

ANSI, POSIX

### Example

    char buf[100];
    while (fgets(buf, 100, stdin))
      fputs(buf, stdout);

Node:File System Extensions, Next:__file_exists, Previous:fgets, Up:Alphabetical List

## File System Extensions

### Description

The File System Extensions are a part of the lowest level of I/O operations in the C runtime library of DJGPP. These extensions are provided to allow for cases where Unix uses a file descriptor to access such items as serial ports, memory, and the network, but DOS does not. It allows a set of functions (called an extension) to gain control when one of these low-level functions is called on a file descriptor set up by the extension.

Each extension must provide one or two handler functions. All handler functions take the same arguments:

      int function(__FSEXT_Fnumber func_number, int *rv, va_list args);

The func_number identifies which function is to be emulated. The file `<sys/fsext.h>` defines the function numbers as follows:

`__FSEXT_nop`
  A no-op. This is currently unused by the library functions.
`__FSEXT_open`
  An open handler. This is called just before the library is about to issue the DOS OpenFile call on behalf of your program.
`__FSEXT_creat`
  A create handler. Called when a file needs to be created. Note that the handler should both create the "file" and open it.
`__FSEXT_read`
  A read handler. Called when data should be read from a "file".
`__FSEXT_write`
  A write handler. Called to write data to a "file". On "text" files it receives the ORIGINAL (unconverted) buffer.
`__FSEXT_ready`
  A ready handler. It is called by `select` library function (see select) when it needs to know whether a handle used to reference the "file" is ready for reading or writing, or has an error condition set. The handler should return an OR'ed bit mask of the following bits (defined on `<sys/fsext.h>`):
  `__FSEXT_ready_read`
    The "file" is ready for reading.
  `__FSEXT_ready_write`
    The "file" is ready for writing.
  `__FSEXT_ready_error`
    The "file" has an error condition set.
`__FSEXT_close`
  A close handler. Called when the "file" should be closed.
`__FSEXT_fcntl`
  A file fcntl handler.
`__FSEXT_ioctl`
  A file ioctl handler.
`__FSEXT_lseek`
  A file lseek handler (see lseek).
`__FSEXT_link`
  A file link handler (see link). This is most relevant to file system extensions that emulate a directory structure.
`__FSEXT_unlink`
  A file unlink handler (see unlink). This is most relevant to file system extensions that emulate a directory structure.
`__FSEXT_dup`
  A file dup handler (see dup). This is called when a new descriptor is needed to refer to an existing descriptor.
`__FSEXT_dup2`
  A file dup2 handler (see dup2). This is called when two different file descriptors are used to refer to the same open file.
`__FSEXT_fstat`
  A file fstat handler (see fstat). The extension should fill in various status information about the emulated file.

rv points to a temporary return value pointer. If the function is emulated by the handler, the return value should be stored here, and the handler should return a nonzero value. If the handler returns zero, it is assumed to have not emulated the call, and the regular DOS I/O function will happen. The args represent the arguments passed to the original function; these point to the actual arguments on the stack, so the emulation may choose to modify them and return zero to the regular function, which will then act on the modified arguments.

A normal extension would provide these parts:

- Some function to create a connection to the extension. This may be a custom function (such as `socket` for networking) or an extension to open (such as `/dev/ttyS0` to access the serial port).
- Initialization code that adds the open handler, if any.
- Overrides for the basic I/O functions, such as `read` and `write`. This is a single function in the extension that uses the function number parameter to select an extension function.
- The core functionality of the extension, if any.

Please note that the special Unix filenames `/dev/null` and `/dev/tty` are already mapped to the appropriate DOS names `NUL` and `CON`, respectively, so you don't need to write extensions for these.

Node:__file_exists, Next:__file_tree_walk, Previous:File System Extensions, Up:Alphabetical List

## __file_exists

### Syntax

    #include <unistd.h>

    int __file_exists(const char *_fn);

### Description

This function provides a fast way to ask if a given file exists. Unlike access(), this function does not cause other objects to get linked in with your program, so is used primarily by the startup code to keep minimum code size small.

### Return Value

Zero if the file does not exist, nonzero if it does. Note that this is the opposite of what access() returns.

### Portability

not ANSI, not POSIX

### Example

    if (__file_exists(fname))
      process_file(fname);

Node:__file_tree_walk, Next:filelength, Previous:__file_exists, Up:Alphabetical List

## __file_tree_walk

### Syntax

    #include <dir.h>

    int __file_tree_walk(const char *dir,
                       int (*func)(const char *path, const struct ffblk *ff));

### Description

This function recursively descends the directory hierarchy which starts with dir. For each file in the hierarchy, `__file_tree_walk` calls the user-defined function func which is passed a pointer to a `NULL`-terminated character array in path holding the full pathname of the file, a pointer to a `ffblk` structure (see findfirst) ff with a DOS filesystem information about that file.

This function always visits a directory before any of its siblings. The argument dir must be a directory, or `__file_tree_walk` will fail and set errno to `ENOTDIR`. The directory dir itself is never passed to func.

The tree traversal continues until one of the following events:

(1) The tree is exhausted (i.e., all descendants of dir are processed). In this case, `__file_tree_walk` returns 0, meaning a success.

(2) An invocation of func returns a non-zero value. In this case, `__file_tree_walk` stops the tree traversal and returns whatever func returned.

(3) An error is detected within `__file_tree_walk`. In that case, `ftw` returns -1 and sets errno (see errno) to a suitable value.

### Return Value

Zero in case the entire tree was successfully traversed, -1 if `__file_tree_walk` detected some error during its operation, or any other non-zero value which was returned by the user-defined function func.

### Portability

not ANSI, not POSIX

### Example

    #include <stdlib.h>

    int
    ff_walker(const char *path, const struct ffblk *ff)
    {
      printf("%s:\t%lu\t", path, ff->ff_fsize);
      if (ff->ff_attrib & 1)
        printf("R");
      if (ff->ff_attrib & 2)
        printf("H");
      if (ff->ff_attrib & 4)
        printf("S");
      if (ff->ff_attrib & 8)
        printf("V");
      if (ff->ff_attrib & 0x10)
        printf("D");
      if (ff->ff_attrib & 0x20)
        printf("A");
      printf("\n");

      if (strcmp(ff->ff_name, "XXXXX") == 0)
        return 42;
      return 0;
    }

    int
    main(int argc, char *argv[])
    {
      if (argc > 1)
        {
          char msg[80];

          sprintf(msg, "__file_tree_walk: %d",
                       __file_tree_walk(argv[1], ff_walker));
          if (errno)
            perror(msg);
          else
            puts(msg);
        }
      else
        printf("Usage: %s dir\n", argv[0]);

      return 0;
    }

Node:filelength, Next:fileno, Previous:__file_tree_walk, Up:Alphabetical List

## filelength

### Syntax

    #include <io.h>

    long filelength(int fhandle);

### Description

This function returns the size, in bytes, of a file whose handle is specified in the argument fhandle. To get the handle of a file opened by fopen or freopen, you can use fileno macro.

### Return Value

The size of the file in bytes, or (if any error occured) -1L and errno set to a value describing the cause of the failure.

### Portability

not ANSI, not POSIX

### Example

      printf("Size of file to which STDIN is redirected is %ld\n",
              filelength(0));

Node:fileno, Next:findfirst, Previous:filelength, Up:Alphabetical List

## fileno

### Syntax

    #include <stdio.h>

    int fileno(FILE *file);

### Description

This function returns the raw file descriptor number that file uses for I/O.

### Return Value

The file descriptor number.

### Portability

not ANSI, POSIX

Node:findfirst, Next:findnext, Previous:fileno, Up:Alphabetical List

## findfirst

### Syntax

    #include <dir.h>

    int findfirst(const char *pathname, struct ffblk *ffblk, int attrib);

### Description

This function and the related `findnext` (see findnext) are used to scan directories for the list of files therein. The pathname is a wildcard that specifies the directory and files to search for (such as `subdir/*.c`), ffblk is a structure to hold the results and state of the search, and attrib is a combination of the following:

`FA_RDONLY`
  Include read-only files in the search (Ignored.)
`FA_HIDDEN`
  Include hidden files in the search
`FA_SYSTEM`
  Include system files in the search
`FA_LABEL`
  Include the volume label in the search
`FA_DIREC`
  Include subdirectories in the search
`FA_ARCH`
  Include modified files in the search (Ignored.)

If a file has flag bits that are not specified in the attrib parameter, the file will be excluded from the results. Thus, if you specified `FA_DIREC` and `FA_LABEL`, subdirectories and the volume label will be included in the results. Hidden and system files will be excluded.

Since `findfirst` calls DOS function 4eh, it is not possible to exclude read-only files or archive files from the results. Even if the FA_ARCH and FA_RDONLY bits are not specified in the attrib parameter, the results will include any read-only and archive files in the directory searched.

This function supports long file names.

The results of the search are stored in ffblk, which is extended when the LFN API (see LFN) is supported. Fields marked LFN are only valid if the `lfn_magic` member is set to "LFN32".

    struct ffblk {
      char lfn_magic[6];	    /* LFN: the magic "LFN32" signature */
      short lfn_handle;	    /* LFN: the handle used by findfirst/findnext */
      unsigned short lfn_ctime; /* LFN: file creation time */
      unsigned short lfn_cdate; /* LFN: file creation date */
      unsigned short lfn_atime; /* LFN: file last access time (usually 0) */
      unsigned short lfn_adate; /* LFN: file last access date */
      char ff_reserved[5];      /* used to hold the state of the search */
      unsigned char ff_attrib;  /* actual attributes of the file found */
      unsigned short ff_ftime;  /* hours:5, minutes:6, (seconds/2):5 */
      unsigned short ff_fdate;  /* (year-1980):7, month:4, day:5 */
      unsigned long ff_fsize;   /* size of file */
      char ff_name[260];        /* name of file as ASCIIZ string */
    }

### Return Value

Zero if a match is found, nonzero if none found.

### Portability

not ANSI, not POSIX

### Example

    struct ffblk f;
    int done = findfirst("*.exe", &f, FA_HIDDEN | FA_SYSTEM);
    while (!done)
    {
      printf("%10u %2u:%02u:%02u %2u/%02u/%4u %s\n",
        f.ff_fsize,
        (f.ff_ftime >> 11) & 0x1f,
        (f.ff_ftime >>  5) & 0x3f,
        (f.ff_ftime & 0x1f) * 2,
        (f.ff_fdate >>  5) & 0x0f,
        (f.ff_fdate & 0x1f),
        ((f.ff_fdate >> 9) & 0x7f) + 1980,
        f.ff_name);
      done = findnext(&f);
    }

Node:findnext, Next:_fixpath, Previous:findfirst, Up:Alphabetical List

## findnext

### Syntax

    #include <dir.h>

    int findnext(struct ffblk *ffblk);

### Description

This finds the next file in the search started by `findfirst`. See findfirst.

### Return Value

Zero if there was a match, else nonzero.

### Portability

not ANSI, not POSIX

Node:_fixpath, Next:floor, Previous:findnext, Up:Alphabetical List

## _fixpath

### Syntax

    #include <sys/stat.h>

    void _fixpath(const char *in_path, char *out_path);

### Description

This function canonicalizes the input path in_path and stores the result in the buffer pointed to by out_path.

The path is fixed by removing consecutive and trailing slashes, making the path absolute if it's relative by prepending the current drive letter and working directory, removing "." components, collapsing ".." components, adding a drive specifier if needed, and converting all slashes to '/'. DOS-style 8+3 names of directories which are part of the pathname, as well as its final filename part, are returned lower-cased in out_path, but long filenames are left intact. See _preserve_fncase, for more details on letter-case conversions in filenames.

Since the returned path name can be longer than the original one, the caller should ensure there is enough space in the buffer pointed to by out_path. Using ANSI-standard constant `FILENAME_MAX` (defined on `stdio.h`) or Posix-standard constant `PATH_MAX` (defined on `limits.h`) is recommended.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    char oldpath[100], newpath[FILENAME_MAX];
    scanf(oldpath);
    _fixpath(oldpath, newpath);
    printf("that really is %s\n", newpath);

Node:floor, Next:_flush_disk_cache, Previous:_fixpath, Up:Alphabetical List

## floor

### Syntax

    #include <math.h>

    double floor(double x);

### Description

This function computes the largest integer not greater than x.

### Return Value

The largest integer value less than or equal to x. Infinities and `NaN`s are returned unchanged.

### Portability

ANSI, POSIX

Node:_flush_disk_cache, Next:fmod, Previous:floor, Up:Alphabetical List

## _flush_disk_cache

### Syntax

    #include <io.h>

    void _flush_disk_cache (void);

### Description

Attempts to update the disk with the data cached in the write-behind disk caches (such as `SmartDrv` and the built-in Windows 95 disk cache).

Note that this does not flushes the DOS buffers. You need to call `fsync` (see fsync) or `close` (see close) to force DOS to commit the file data to the disk; `sync` (see sync) does that for all open files.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

      /* Make sure all files are actually written to disk.  */
      sync ();
      _flush_disk_cache ();

Node:fmod, Next:_fmode, Previous:_flush_disk_cache, Up:Alphabetical List

## fmod

### Syntax

    #include <math.h>

    double fmod(double x, double y);

### Description

This function computes the remainder of `x/y`, which is x - iy for some integer i such that iy < x < (i+1)y.

### Return Value

The remainder of x/y. If x is `Inf` or `NaN`, the return value is `NaN` and `errno` is set to `EDOM`. If y is zero, the return value is zero (but `errno` is not changed).

### Portability

ANSI, POSIX

Node:_fmode, Next:fnmatch, Previous:fmod, Up:Alphabetical List

## _fmode

### Syntax

    #include <fcntl.h>

    extern int _fmode;

### Description

This variable may be set to `O_TEXT` or `O_BINARY` to specify the mode that newly opened files should be opened in if the open call did not specify. See open. See fopen.

The default value is `O_TEXT`.

### Portability

not ANSI, not POSIX

### Example

    _fmode = O_BINARY;

Node:fnmatch, Next:fnmerge, Previous:_fmode, Up:Alphabetical List

## fnmatch

### Syntax

    #include <fnmatch.h>

    int fnmatch(const char *pattern, const char *string, int flags);

### Description

This function indicates if string matches the pattern. The pattern may include the following special characters:

`*`
  Matches zero of more characters.
`?`
  Matches exactly one character.
`[...]`
  Matches one character if it's in a range of characters. If the first character is `!`, matches if the character is not in the range. Between the brackets, the range is specified by listing the characters that are in the range, or two characters separated by `-` to indicate all characters in that range. For example, `[a-d]` matches `a`, `b`, `c`, or `d`. If you want to include the literal `-` in the range, make it the first character, like in `[-afz]`.
`\`
  Causes the next character to not be treated as a wildcard. For example, `\*` matches an asterisk. This feature is not available if flags includes `FNM_NOESCAPE`, in which case `\` is treated as a directory separator.

The value of flags is a combination of zero of more of the following:

`FNM_PATHNAME`
  This means that the string should be treated as a pathname, in that the slash characters `/` and `\` in string never match any of the wildcards in pattern.
`FNM_NOESCAPE`
  If this flag is not set, the backslash `\` may be used in pattern for quoting special characters. If this flag is set, `\` is treated as a directory separator.
`FNM_NOCASE`
  If this flag is set, `fnmatch` matches characters case-insensitively, including in character ranges like `[a-f]`. Note that the case-folding is done by calling `toupper` (see toupper), and thus might be sensitive to the current locale.
`FNM_PERIOD`
  This flag is accepted and ignored in the current implementation. (This is the right thing to do on non-LFN platforms, where leading dots in file names are forbidden.)

  In the Posix specification, if this flag is set, leading dots in file names will not match any wildcards. If `FNM_PATHNAME` is set, a dot after a slash also doesn't match any wildcards.

The DJGPP implementation treats forward slashes and backslashes as equal when `FNM_NOESCAPE` is set, since on DOS/Windows these two characters are both used as directory separators in file names.

### Return Value

Zero if the string matches, `FNM_NOMATCH` if it does not. Posix defines an additional `FNM_ERROR` code that's returned in case of an error, but the current implementation never returns it.

### Portability

not ANSI, POSIX (see note 1)

Notes:

1. The equal handling of `\` and `/` is DJGPP-specific.

### Example

    if (fnmatch("*.[ch]", filename, FNM_PATHNAME|FNM_NOCASE))
      do_source_file(filename);

Node:fnmerge, Next:fnsplit, Previous:fnmatch, Up:Alphabetical List

## fnmerge

### Syntax

    #include <dir.h>

    void fnmerge (char *path, const char *drive, const char *dir,
    		const char *name, const char *ext);

### Description

This function constructs a file path from its components drive, dir, name, and ext. If any of these is a `NULL` pointer, it won't be used. Usually, the drive string should include the trailing colon ``:'`, the dir string should include the trailing slash ``/'` or backslash ``\'`, and the ext string should include the leading dot ``.'`. However, if any of these isn't present, `fnmerge` will add them.

See fnsplit.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    char buf[MAXPATH];
    fnmerge(buf, "d:", "/foo/", "data", ".txt");

Node:fnsplit, Next:fopen, Previous:fnmerge, Up:Alphabetical List

## fnsplit

### Syntax

    #include <dir.h>

    int fnsplit (const char *path, char *drive, char *dir,
    		char *name, char *ext);

### Description

This function decomposes a path into its components. It is smart enough to know that `.` and `..` are directories, and that file names with a leading dot, like `.emacs`, are not all extensions.

The drive, dir, name and ext arguments should all be passed, but some or even all of them might be `NULL` pointers. Those of them which are non-`NULL` should point to buffers which have enough room for the strings they would hold. The constants `MAXDRIVE`, `MAXDIR`, `MAXFILE` and `MAXEXT`, defined on dir.h, define the maximum length of these buffers.

See fnmerge.

### Return Value

A flag that indicates which components were found:

`DRIVE`
  The drive letter was found.
`DIRECTORY`
  A directory or subdirectories was found.
`FILENAME`
  A filename was found.
`EXTENSION`
  An extension was found.
`WILDCARDS`
  The path included `*` or `?`.

### Portability

not ANSI, not POSIX

### Example

    char d[MAXDRIVE], p[MAXDIR], f[MAXFILE], e[MAXEXT];
    int which = fnsplit("d:/djgpp/bin/gcc.exe", d, p, f, e);
    d = "d:"
    p = "/djgpp/bin/"
    f = "gcc"
    e = ".exe"

Node:fopen, Next:fork, Previous:fnsplit, Up:Alphabetical List

## fopen

### Syntax

    #include <stdio.h>

    FILE *fopen(const char *filename, const char *mode);

### Description

This function opens a stream corresponding to the named filename with the given mode. The mode can be one of the following:

`r`
  Open an existing file for reading.
`w`
  Create a new file (or truncate an existing file) and open it for writing.
`a`
  Open an existing file (or create a new one) for writing. The file pointer is positioned to the end of the file before every write.

Followed by any of these characters:

`b`
  Force the file to be open in binary mode instead of the default mode.

  When called to open the console in binary mode, `fopen` will disable the generation of `SIGINT` when you press `Ctrl-C` (`Ctrl-Break` will still cause `SIGINT`), because many programs that use binary reads from the console will also want to get the `^C` characters. You can use the `__djgpp_set_ctrl_c` library function (see __djgpp_set_ctrl_c) if you want `Ctrl-C` to generate interrupts while console is read in binary mode.

`t`
  Force the file to be open in text mode instead of the default mode.
`+`
  Open the file as with `O_RDWR` so that both reads and writes can be done to the same file.

If the file is open for both reading and writing, you must call `fflush`, `fseek`, or `rewind` before switching from read to write or from write to read.

The open file is set to line buffered if the underlying object is a device (stdin, stdout, etc), or is fully buffered if the underlying object is a disk file (data.c, etc).

If `b` or `t` is not specified in mode, the file type is chosen by the value of `fmode` (see _fmode).

If you need to specify the DOS share flags use the `__djgpp_share_flags`. See __djgpp_share_flags.

### Return Value

A pointer to the `FILE` object, or `NULL` if there was an error.

### Portability

ANSI, POSIX

### Example

    FILE *f = fopen("foo", "rb+"); /* open existing file for read/write, binary mode */

Node:fork, Next:fpathconf, Previous:fopen, Up:Alphabetical List

## fork

### Syntax

    #include <unistd.h>

    pid_t fork(void);

### Description

This function always returns -1 and sets `errno` to ENOMEM, as MS-DOS does not support multiple processes. It exists only to assist in porting Unix programs.

### Portability

not ANSI, POSIX

Node:fpathconf, Next:_fpreset, Previous:fork, Up:Alphabetical List

## fpathconf

### Syntax

    #include <unistd.h>

    long fpathconf(int fd, int name);

### Description

Returns configuration information on the filesystem that the open file resides on. See pathconf. If the filesystem cannot be determined from the file handle fd (e.g., for character devices), `fpathconf` will return the info for the current drive.

### Return Value

The configuration value; for details, see pathconf.

### Portability

not ANSI, POSIX

Node:_fpreset, Next:fprintf, Previous:fpathconf, Up:Alphabetical List

## _fpreset

### Syntax

    #include <float.h>

    void _fpreset(void);

### Description

Resets the FPU completely.

### Portability

not ANSI, not POSIX

Node:fprintf, Next:fpurge, Previous:_fpreset, Up:Alphabetical List

## fprintf

### Syntax

    #include <stdio.h>

    int fprintf(FILE *file, const char *format, ...);

### Description

Prints formatted output to the named file. See printf.

### Return Value

The number of characters written.

### Portability

ANSI, POSIX

Node:fpurge, Next:fputc, Previous:fprintf, Up:Alphabetical List

## fpurge

### Syntax

    #include <stdio.h>

    int fpurge(FILE *file);

### Description

If file designates a buffered stream open for writing or for both reading and writing, this function purges the stream's buffer without writing it to disk. Otherwise, it does nothing (so it has no effect on read-only streams such as `stdin`).

### Return Value

Zero on success, -1 on failure.

### Portability

not ANSI, not POSIX

Node:fputc, Next:fputs, Previous:fpurge, Up:Alphabetical List

## fputc

### Syntax

    #include <stdio.h>

    int fputc(int character, FILE *file);

### Description

This function writes the given character to the given `file`.

### Return Value

The given character [0..255] or `EOF`.

### Portability

ANSI, POSIX

### Example

    fputc('\n', stdout);

Node:fputs, Next:fread, Previous:fputc, Up:Alphabetical List

## fputs

### Syntax

    #include <stdio.h>

    int fputs(const char *string, FILE *file);

### Description

This function all the characters of string (except the trailing `NULL`) to the given file.

### Return Value

A nonnegative number on success, `EOF` on error.

### Portability

ANSI, POSIX

### Example

    fputs("Hello\n", stdout);

Node:fread, Next:free, Previous:fputs, Up:Alphabetical List

## fread

### Syntax

    #include <stdio.h>

    size_t fread(void *buffer, size_t size, size_t number, FILE *file);

### Description

This function reads size*number characters from file to buffer.

### Return Value

The number of items of size size read, or less if there was an error.

### Portability

ANSI, POSIX

### Example

    int foo[10];
    fread(foo, sizeof(int), 10, stdin);

Node:free, Next:freopen, Previous:fread, Up:Alphabetical List

## free

### Syntax

    #include <stdlib.h>

    void free(void *ptr);

### Description

Returns the allocated memory to the heap (see malloc). If the ptr is `NULL`, it does nothing.

### Return Value

None.

### Portability

ANSI, POSIX

### Example

    char *q = (char *)malloc(20);
    free(q);

Node:freopen, Next:frexp, Previous:free, Up:Alphabetical List

## freopen

### Syntax

    #include <stdio.h>

    FILE *freopen(const char *filename, const char *mode, FILE *file);

### Description

This function closes file if it was open, then opens a new file like `fopen(filename, mode)` but it reuses file.

This is useful to, for example, associate `stdout` with a new file.

### Return Value

The new file, or `NULL` on error.

### Portability

ANSI, POSIX

### Example

    freopen("/tmp/stdout.dat", "wb", stdout);

Node:frexp, Next:fscanf, Previous:freopen, Up:Alphabetical List

## frexp

### Syntax

    #include <math.h>

    double frexp(double x, int *pexp);

### Description

This function separates the given value x into a mantissa m in the range `[0.5,1)` and an exponent e, such that m*2^e = x. It returns the value of the mantissa and stores the integer exponent in *pexp.

### Return Value

The mantissa. If the value of x is `NaN` or `Inf`, the return value is `NaN`, zero is stored in `*pexp`, and `errno` is set to `EDOM`. If x is zero, *pexp and the return value are also both zero.

### Portability

ANSI, POSIX

Node:fscanf, Next:fseek, Previous:frexp, Up:Alphabetical List

## fscanf

### Syntax

    #include <stdio.h>

    int fscanf(FILE *file, const char *format, ...);

### Description

This function scans formatted text from file and stores it in the variables pointed to by the arguments. See scanf.

### Return Value

The number of items successfully scanned.

### Portability

ANSI, POSIX

Node:fseek, Next:fsetpos, Previous:fscanf, Up:Alphabetical List

## fseek

### Syntax

    #include <stdio.h>

    int fseek(FILE *file, long offset, int mode);

### Description

This function moves the file pointer for file according to mode:

`SEEK_SET`
  The file pointer is moved to the offset specified.
`SEEK_CUR`
  The file pointer is moved relative to its current position.
`SEEK_END`
  The file pointer is moved to a position offset bytes from the end of the file. The offset is usually nonpositive in this case.

Warning! The ANSI standard only allows values of zero for offset when mode is not `SEEK_SET` and the file has been opened as a text file. Although this restriction is not enforced, beware that there is not a one-to-one correspondence between file characters and text characters under MS-DOS, so some `fseek` operations may not do exactly what you expect.

Also, since `lseek` under DOS does not return an error indication when you try to move the file pointer before the beginning of the file, neither will `fseek`. Portable programs should call `ftell` after `fseek` to get the actual position of the file pointer.

Note that DOS does not mind if you seek before the beginning of the file, like seeking from the end of the file by more than the file's size. Therefore, `lseek` will not return with an error in such cases either.

### Return Value

Zero if successful, nonzero if not.

### Portability

ANSI, POSIX

### Example

    fseek(stdin, 12, SEEK_CUR); /* skip 12 bytes */

Node:fsetpos, Next:__FSEXT_add_open_handler, Previous:fseek, Up:Alphabetical List

## fsetpos

### Syntax

    #include <stdio.h>

    int fsetpos(FILE *file, const fpos_t *offset);

### Description

This function moves the file pointer for file to position offset, as recorded by `fgetpos`.

See fgetpos. See fseek.

### Return Value

Zero if successful, nonzero if not.

### Portability

ANSI, POSIX

Node:__FSEXT_add_open_handler, Next:__FSEXT_alloc_fd, Previous:fsetpos, Up:Alphabetical List

## __FSEXT_add_open_handler

### Syntax

    #include <sys/fsext.h>

    int __FSEXT_add_open_handler(__FSEXT_Function *_function);

### Description

This function is part of the File System Extensions. It is used to add a handler for functions that do not get passed descriptors, such as `_open` and `_creat`.

### Portability

not ANSI, not POSIX

### Example

    static int
    _my_handler(__FSEXT_Fnumber n, int *rv, va_list args)
    {
      . . .
    }

    int main()
    {
      __FSEXT_add_open_handler(_my_handler);
    }

Node:__FSEXT_alloc_fd, Next:__FSEXT_call_open_handlers, Previous:__FSEXT_add_open_handler, Up:Alphabetical List

## __FSEXT_alloc_fd

### Syntax

    #include <sys/fsext.h>

    int __FSEXT_alloc_fd(__FSEXT_Function *_function);

### Description

This function is part of the File System Extensions. It is used by extensions that fully emulate the I/O functions, and thus don't have a corresponding DOS file handle. Upon the first call, this function opens DOS's `NUL` device, so as to allocate a handle that DOS won't then reuse. Upon subsequent calls, that handle is duplicated by calling the DOS `dup` function; this makes all of the handles use a single entry in the System File Table, and thus be independent of what the `FILES=` parameter of `CONFIG.SYS` says. `__FSEXT_alloc_fd` also assigns the handler function for the handle it returns.

The module is responsible for calling `_close` on the descriptor after setting the handler function to zero in the extended close handler.

### Return Value

If successful, a new file descriptor is returned. On error, a negative number is returned and errno is set to indicate the error.

### Portability

not ANSI, not POSIX

### Example

    int socket()
    {
      int fd = __FSEXT_alloc_fd(socket_handler);
      init_socket(fd);
      return fd;
    }

Node:__FSEXT_call_open_handlers, Next:__FSEXT_get_data, Previous:__FSEXT_alloc_fd, Up:Alphabetical List

## __FSEXT_call_open_handlers

### Syntax

    #include <sys/fsext.h>

    int __FSEXT_call_open_handlers(__FSEXT_Fnumber _function_number,
    			       int *rv, va_list _args);

### Description

This function is part of the File System Extensions. It is used internally to libc.a to allow extensions to get an opportunity to override the `_open` and `_creat` functions.

### Portability

not ANSI, not POSIX

Node:__FSEXT_get_data, Next:__FSEXT_get_function, Previous:__FSEXT_call_open_handlers, Up:Alphabetical List

## __FSEXT_get_data

### Syntax

    #include <sys/fsext.h>

    void *__FSEXT_get_data(int _fd);

### Description

This function is part of the File System Extensions. It is used to retrieve a descriptor-specific pointer that was previously stored by `__FSEXT_set_data` (see __FSEXT_set_data). The pointer is not otherwise used.

See __FSEXT_set_data, for an example of how this may be used.

### Return Value

Returns the stored pointer, or NULL if there was an error (or no pointer had been stored).

### Portability

not ANSI, not POSIX

Node:__FSEXT_get_function, Next:__FSEXT_set_data, Previous:__FSEXT_get_data, Up:Alphabetical List

## __FSEXT_get_function

### Syntax

    #include <sys/fsext.h>

    __FSEXT_Function *__FSEXT_get_function(int _fd);

This function is part of the File System Extensions. It is used internal to libc.a to redirect I/O requests to the appropriate extensions.

### Portability

not ANSI, not POSIX

### Example

    _read(int fd, void *buf, int len)
    {
      __FSEXT_Function *func = __FSEXT_get_function(fd);
      if (func)
      {
        int rv;
        if (func(__FSEXT_read, &rv, &fd))
          return rv;
      }
      /* rest of read() */
    }

Node:__FSEXT_set_data, Next:__FSEXT_set_function, Previous:__FSEXT_get_function, Up:Alphabetical List

## __FSEXT_set_data

### Syntax

    #include <sys/fsext.h>

    void * __FSEXT_set_data(int _fd, void *_data);

### Description

This function is part of the File System Extensions. It is used to store a descriptor-specific pointer that can later be retrieved by `__FSEXT_get_data` (see __FSEXT_get_data). The pointer is not otherwise used.

This is useful when writing an extension that may be handling several open pseudo-files. `__FSEXT_set_data` can be used when creating or opening the file to store a pointer to data about the specific file. Later, when specific operation needs to be done (e.g. read, write, etc.) a pointer to pseudo-file associated with the file descriptor can be fetched with `__FSEXT_get_data`.

### Return Value

Returns the pointer you passed it, or NULL if there was an error.

### Portability

not ANSI, not POSIX

### Example

    typedef struct
    {
       void* Ptr;
       off_t Current_Ofs;
       size_t Size;
    } _mem_file_t;

    int my_fsext(__FSEXT_Fnumber Op, int* RV, va_list Args)
    {
       const char* Path;
       void* Buffer;
       size_t Size;
       int fd;
       _mem_file_t* MPtr;

       switch (Op)
       {
          case __FSEXT_creat:
           /* Create a new memory file */

           Path = va_list(Args, const char*);

           /* Check to see if we should create a new file */
           if (strnicmp("/tmp/", Path, 5) != 0) return 0;

           /* Allocate some memory to keep info on our fake file */
           MPtr = malloc(sizeof(_mem_file_t));
           if (!MPtr) return 0;

           memset(MPtr, 0, sizeof(_mem_file_t));

           /* Get a file descriptor we can use */
           fd = __FSEXT_alloc_fd(my_fsext);
           if (fd < 0)
           {
              free(MPtr);
              return 0;
           }

           /* Now store our note about this file descriptor so we can lookup it
              up quickly later. */
           __FSEXT_set_data(fd, MPtr);

           /* Return the file descriptor
           *RV = fd;
           return 1;

          case __FSEXT_read:
           /* Read from our memory file. */
           fd = va_list(Args, int);
           Buffer = va_list(Args, void*);
           Size = va_list(Args, size_t);

           /* Look up the information about this file */
           MPtr = __FSEXT_get_data(fd);
           if (!MPtr)
           {
               *RV = -1;
               return 1;
           }

           if (MPtr->Current_Ofs >= MPtr->Size)
           {
               *RV = 0;
               return 1;
           }

           if (Size > (MPtr->Size - MPtr->Current_Ofs))
            Size = MPtr->Size - MPtr->Current_Ofs;

           memcpy(Buffer, (char*) MPtr->Ptr+MPtr->Current_Ofs, Size);
           MPtr->Current_Ofs += Size;

           *RV = Size;
           return 1;

           ...
        }
    }

Node:__FSEXT_set_function, Next:fstat, Previous:__FSEXT_set_data, Up:Alphabetical List

## __FSEXT_set_function

### Syntax

    #include <sys/fsext.h>

    int __FSEXT_set_function(int _fd, __FSEXT_Function *_function);

### Description

This function is part of the File System Extensions. It is used to set the handler function for those extensions that use DOS files for I/O. One situation where you might need this is when you must catch output to the terminal and play some tricks with it, like colorize it or redirect it to another device.

### Return Value

Zero in case of success, non-zero in case of failure (like if _fd is negative).

### Portability

not ANSI, not POSIX

### Example

    #include <sys/fsext.h>
    #include <conio.h>

    /* A simple example of a write handler which converts DOS I/O to the
       screen into direct writes to video RAM.  */
    static int
    my_screen_write (__FSEXT_Fnumber func, int *retval, va_list rest_args)
    {
      char *buf, *mybuf;
      size_t buflen;
      int fd = va_arg (rest_args, int);

      if (func != __FSEXT_write || !isatty (fd))
        return 0;  /* and the usual DOS call will be issued */

      buf = va_arg (rest_args, char *);
      buflen = va_arg (rest_args, size_t);
      mybuf = alloca (buflen + 1);
      memcpy (mybuf, buf, buflen);
      mybuf[buflen] = '\0';
      cputs (mybuf);
      *retval = buflen;
      return 1;  /* meaning that we handled the call */
    }

    /* Install our handler.  The `attribute constructor' causes this
       function to be called by the startup code.  */
    static void __attribute__((constructor))
    install_screen_write_handler (void)
    {
      __FSEXT_set_function (fileno (stdout), my_screen_write);
    }

Node:fstat, Next:fsync, Previous:__FSEXT_set_function, Up:Alphabetical List

## fstat

### Syntax

    #include <sys/stat.h>

    int fstat(int file, struct stat *sbuf);

### Description

This function obtains the status of the open file file and stores it in sbuf. See stat, for the description of members of `struct stat`.

Some members of `struct stat` are very expensive to compute. If your application is a heavy user of `fstat` and is too slow, you can disable computation of the members your application doesn't need, as described in _djstat_flags.

### Return Value

Zero on success, nonzero on failure (and errno set).

### Portability

not ANSI, POSIX

### Example

    struct stat s;
    fstat(fileno(stdin), &s);
    if (S_ISREG(s.st_mode))
      puts("STDIN is a redirected disk file");
    else if (S_ISCHR(s.st_mode))
      puts("STDIN is a character device");

### Bugs

If a file was open in write-only mode, its execute mode bits might be incorrectly reported as if the file were non-executable. This is because some executables are only recognized by reading their first two bytes, which cannot be done for files open in write-only mode.

For `fstat` to return correct info, you should make sure that all the data written to the file has been delivered to the operating system, e.g. by calling both `fflush` and `fsync`. Otherwise, the buffering of the library I/O functions and the OS might cause stale info to be returned.

### Implementation Notes

Supplying a 100% Unix-compatible `fstat` function under DOS is an implementation nightmare. The following notes describe some of the obscure points specific to `fstat`s behavior in DJGPP.

1. The `drive` for character devices (like `con`, `/dev/null` and others is returned as -1. For drives networked by Novell Netware, it is returned as -2.

2. The starting cluster number of a file serves as its inode number. For files whose starting cluster number is inaccessible (empty files, files on networked drives, etc.) the `st_inode` field will be invented in a way which guarantees that no two different files will get the same inode number (thus it is unique). This invented inode will also be different from any real cluster number of any local file. However, only for local, non-empty files/directories the inode is guaranteed to be consistent between `stat` and `fstat` function calls.

3. The WRITE access mode bit is set only for the user (unless the file is read-only, hidden or system). EXECUTE bit is set for directories, files which can be executed from the DOS prompt (batch files, .com, .dll and .exe executables) or run by `go32-v2.exe`. For files which reside on networked drives under Novell Netware, this can sometimes fail, in which case only the read access bit is set.

4. The variable `_djstat_flags` (see _djstat_flags) controls what hard-to-get fields of `struct stat` are needed by the application.

Node:fsync, Next:ftell, Previous:fstat, Up:Alphabetical List

## fsync

### Syntax

    #include <unistd.h>

    int fsync(int file);

### Description

Forces all information about the file with the given descriptor to be synchronized with the disk image. Works by calling DOS function 0x68. Warning: External disk caches are not flushed by this function.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    fsync(fileno(stdout));

Node:ftell, Next:ftime, Previous:fsync, Up:Alphabetical List

## ftell

### Syntax

    #include <stdio.h>

    long ftell(FILE *file);

### Description

Returns the current file position for `file`. This is suitable for a future call to `fseek`.

### Return Value

The file position, or -1 on error.

### Portability

ANSI, POSIX

### Example

    long p = ftell(stdout);

Node:ftime, Next:ftruncate, Previous:ftell, Up:Alphabetical List

## ftime

### Syntax

    #include <sys/timeb.h>

    int ftime(struct timeb *buf);

### Description

This function stores the current time in the structure buf. The format of `struct timeb` is:

    struct timeb {
      time_t         time;     /* seconds since 00:00:00 GMT 1/1/1970 */
      unsigned short millitm;  /* milliseconds */
      short          timezone; /* difference between GMT and local, minutes */
      short          dstflag;  /* set if daylight savings time in affect */
    };

### Return Value

Zero on success, nonzero on error.

### Portability

not ANSI, not POSIX

### Example

    struct timeb t;
    ftime(&t);

Node:ftruncate, Next:ftw, Previous:ftime, Up:Alphabetical List

## ftruncate

### Syntax

    #include <unistd.h>

    int ftruncate(int handle, off_t where);

### Description

This function truncates the file open on handle at byte position where. The file pointer associated with handle is not changed.

Note that this function knows nothing about buffering by stdio functions like `fwrite` and `fprintf`, so if handle comes from a `FILE` object, you need to call `fflush` before calling this function.

### Return Value

Zero for success, nonzero for failure.

### Portability

not ANSI, not POSIX

### Example

    int x = open("data", O_WRONLY);
    ftruncate(x, 1000);
    close(x);

Node:ftw, Next:_fwalk, Previous:ftruncate, Up:Alphabetical List

## ftw

### Syntax

    #include <ftw.h>

    int ftw(const char *dir,
            int (*func)(const char *path, struct stat *stbuf, int flag),
            int depth);

### Description

This function recursively descends the directory hierarchy which starts with dir. For each file in the hierarchy, `ftw` calls the user-defined function func which is passed a pointer to a `NULL`-terminated character array in path holding the full pathname of the file, a pointer to a `stat` structure (see stat) stbuf with a filesystem information about that file, and an integer flag. Possible values of flag are:

`FTW_F`
  This is a regular file.
`FTW_D`
  This is a directory.
`FTW_VL`
  This is a volume label.
`FTW_DNR`
  This is a directory which cannot be read with `readdir()`. (This will never happen in DJGPP.)
`FTW_NS`
  This file exists, but `stat` fails for it.

If flag is `FTW_DNR`, the descendants of that directory won't be processed. If flag is `FTW_NS`, then stbuf will be garbled.

This function always visits a directory before any of its siblings. The argument dir must be a directory, or `ftw` will fail and set errno to `ENOTDIR`. The function func is called with dir as its argument before the recursive descent begins.

The depth argument has no meaning in the DJGPP implementation and is always ignored.

The tree traversal continues until one of the following events:

(1) The tree is exhausted (i.e., all descendants of dir are processed). In this case, `ftw` returns 0, meaning a success.

(2) An invocation of func returns a non-zero value. In this case, `ftw` stops the tree traversal and returns whatever func returned.

(3) An error is detected within `ftw`. In that case, `ftw` returns -1 and sets errno (see errno) to a suitable value.

### Return Value

Zero in case the entire tree was successfully traversed, -1 if `ftw` detected some error during its operation, or any other non-zero value which was returned by the user-defined function func.

### Implementation Notes

This function uses `malloc` (see malloc) for dynamic memory allocation during its operation. If func disrupts the normal flow of code execution by e.g. calling `longjump` or if an interrupt handler which never returns is executed, this memory will remain permanently allocated.

This function calls `opendir()` and `readdir()` functions to read the directory entries. Therefore, you can control what files will your func get by setting the appropriate bits in the external variable __opendir_flags. See opendir, for description of these bits.

This function also calls `stat` for every directory entry it passes to func. If your application only needs some part of the information returned in the `stat` structure, you can make your application significantly faster by setting bits in the external variable _djstat_flags (see _djstat_flags for details). The most expensive `stat` features are `_STAT_EXEC_MAGIC` and `_STAT_DIRSIZE`.

### Portability

not ANSI, not POSIX

### Example

    #include <stdlib.h>

    int
    file_walker(const char *path, struct stat *sb, int flag)
    {
      char *base;

      printf("%s:\t%u\t", path, sb->st_size);
      if (S_ISLABEL(sb->st_mode))
        printf("V");
      if (S_ISDIR(sb->st_mode))
        printf("D");
      if (S_ISCHR(sb->st_mode))
        printf("C");
      if (sb->st_mode & S_IRUSR)
        printf("r");
      if (sb->st_mode & S_IWUSR)
        printf("w");
      if (sb->st_mode & S_IXUSR)
        printf("x");

      if (flag == FTW_NS)
        printf("  !!no_stat!!");
      printf("\n");

      base = strrchr(path, '/');
      if (base == 0)
        base = strrchr(path, '\\');
      if (base == 0)
        base = strrchr(path, ':');
      if (strcmp(base == 0 ? path : base + 1, "xxxxx") == 0)
        return 42;
      return 0;
    }

    int
    main(int argc, char *argv[])
    {
      if (argc > 1)
        {
          char msg[80];

          sprintf(msg, "file_tree_walk: %d",
                       ftw(argv[1], file_walker, 0));
          if (errno)
            perror(msg);
          else
            puts(msg);
        }
      else
        printf("Usage: %s dir\n", argv[0]);

      return 0;
    }

Node:_fwalk, Next:fwrite, Previous:ftw, Up:Alphabetical List

## _fwalk

### Syntax

    #include <libc/file.h>

    void _fwalk(void (*function)(FILE *file));

### Description

For each open file in the system, the given function is called, passing the file pointer as its only argument.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    void pfile(FILE *x)
    { printf("FILE at %p\n", x); }

    _fwalk(pfile);

Node:fwrite, Next:gcvt, Previous:_fwalk, Up:Alphabetical List

## fwrite

### Syntax

    #include <stdio.h>

    size_t fwrite(void *buffer, size_t size, size_t number, FILE *file);

### Description

This function writes size*number characters from buffer to file.

### Return Value

The number of items of size size written, or less if there was an error.

### Portability

ANSI, POSIX

### Example

    int foo[10];
    fwrite(foo, sizeof(int), 10, stdin);

Node:gcvt, Next:_get_dev_info, Previous:fwrite, Up:Alphabetical List

## gcvt

### Syntax

    #include <stdlib.h>

    char * gcvt (double value, int ndigits, char *buf)

### Description

This function converts its argument value into a null-terminated string of ndigits significant digits in buf. buf should have enough space to hold at least `ndigits + 7` characters. The result roughly corresponds to what is obtained by the following snippet:

     (void) sprintf(buf, "%.*g", ndigits, value);

except that trailing zeros and trailing decimal point are suppressed.

The least-significant digit in buf is rounded.

`ecvtbuf` produces the string "NaN" if value is a NaN, and "Inf" if value is an infinity.

### Return Value

A pointer to buf.

### Portability

not ANSI, not POSIX

### Example

      #include <stdlib.h>
      #include <stdio.h>
      #include <math.h>

      char vbuf[20];

      /* This will print " 3.14159".  */
      printf ("%s", gcvt (M_PI, 5, buf));

Node:_get_dev_info, Next:_get_dos_version, Previous:gcvt, Up:Alphabetical List

## _get_dev_info

### Syntax

    #include <io.h>

    short _get_dev_info(int handle);

### Description

Given a file handle in handle, this function returns the info word from DOS IOCTL function 0 (Int 21h/AX=4400h). handle must refer to an open file or device, otherwise the call will fail (and set errno to `EBADF`).

In case of success, the returned value is the coded information from the system about the character device or the file which is referenced by the file handle handle. The following table shows the meaning of the individual bits in the return value:

For a character device:

Bit(s) | Description
14 | Device can process IOCTL functions 02h and 03h
13 | Device supports output-until-busy
11 | Device supports OPEN/CLOSE calls
8 | Unknown; set by MS-DOS 6.2x `KEYBxx.COM`
7 | Always set for character devices
6 | End of file on input
5 | Device is in raw (binary) mode
4 | Device uses Int 29h
3 | Clock device
2 | NUL device
1 | Standard output device
0 | Standard input device

For a block device (a disk file):

Bit(s) | Description
15 | Device is remote (networked drive)
14 | Don't set file time stamp on close
11 | If set, non-removable media
11 | If clear, media is removable (e.g. floppy disk)
8 | Generate Int 24h if full disk or read past EOF
7 | Always clear for disk files
6 | File has not been written to
5-0 | Drive number (0 = A:)

Note that the functionality indicated by bit 8 for the block devices is only supported by DOS version 4.

Cooked mode means that on input `C-<C>`, `C-<P>`, `C-<S>` and `C-<Z>` are processed, on output `TAB`s are expanded into spaces and `CR` character is added before each `LF`, and input is terminated when the <RET> key is pressed. In contrast, in raw mode, all the special characters are passed verbatim, and the read operation waits until the specified number of characters has been read.

### Return Value

The device information word described above. In case of error, -1 is returned and errno is set to `EBADF`.

### Portability

not ANSI, not POSIX

### Example

     int fd = open ("CLOCK$", O_RDONLY | O_BINARY);
     int clock_info = _get_dev_info (fd);

Node:_get_dos_version, Next:_get_volume_info, Previous:_get_dev_info, Up:Alphabetical List

## _get_dos_version

### Syntax

    #include <dos.h>

    extern unsigned short   _osmajor, _osminor;
    extern const    char  * _os_flavor;

    unsigned short _get_dos_version(int true_version);

### Description

This function gets the host OS version and flavor. If the argument true_version is non-zero, it will return a true version number, which is unaffected by possible tinkering with SETVER TSR program. (This is only available in DOS 5.0 or later.)

The external variables `_osmajor` and `_osminor` will always be set to the major and minor parts of the advertised version number, possibly changed by SETVER, even if true_version is non-zero. You typically need the true version when you need an intimate knowledge of the host OS internals, like when using undocumented features. Note that some DOS clones (notably, DR-DOS) do not support DOS function required to report the true DOS version; for these, the version reported might be affected by SETVER even if true_version is non-zero.

The external variable `_os_flavor` will point to a string which describes the OEM name of the host OS variety.

### Return Value

`_get_dos_version()` returns the version number (true version number, if true_version is non-zero) as a 16-bit number: the major part of the version in the upper 8 bits, the minor part in the lower 8 bits. For instance, DOS version 6.20 will be returned as 0x0614.

### Portability

not ANSI, not POSIX

### Example

      unsigned short true_dos_version = _get_dos_version(1);

      if (true_dos_version < 0x0614)   /* require DOS 6.20 or later */
        puts("This program needs DOS 6.20 or later to run");
      else
        printf("You are running %s variety of DOS\n", _os_flavor);

Node:_get_volume_info, Next:getc, Previous:_get_dos_version, Up:Alphabetical List

## _get_volume_info

### Syntax

    #include <fcntl.h>

    unsigned _get_volume_info (const char *path,
                               int *max_file_len, int *max_path_len,
                               char *fsystype);

### Description

This function returns filesystem information about the volume where path resides. Only the root directory name part is actually used; if path does not specify the drive explicitly, or is a `NULL` pointer, the current drive is used. Upon return, the variable pointed to by max_file_len contains the maximum length of a filename (including the terminating zero), the variable pointed to by max_path_len contains the maximum length of a pathname (including the terminating zero), and a string that identifies the filesystem type (e.g., "FAT", "NTFS" etc.) is placed into the buffer pointed to by fsystype, which should be long enough (32 bytes are usually enough). If any of these pointers is a `NULL` pointer, it will be ignored. The function returns various flags that describe features supported by the given filesystem as a bit-mapped number. The following bits are currently defined:

`_FILESYS_CASE_SENSITIVE`
  Specifies that file searches are case-sensitive.
`_FILESYS_CASE_PRESERVED`
  Filename letter-case is preserved in directory entries.
`_FILESYS_UNICODE`
  Filesystem uses Unicode characters in file and directory names.
`_FILESYS_LFN_SUPPORTED`
  Filesystem supports the Long File Name (LFN) API.
`_FILESYS_VOL_COMPRESSED`
  This volume is compressed.
`_FILESYS_UNKNOWN`
  The underlying system call failed. This usually means that the drive letter is invalid, like when a floppy drive is empty or a drive with that letter doesn't exist.

### Return value

A combination of the above bits if the LFN API is supported, or 0 (and `errno` set to `ENOSYS`) if the LFN API is not supported by the OS. If the drive letter is invalid, the function returns `_FILESYS_UNKNOWN` and sets `errno` to either `ENODEV` or `ENXIO`.

### Portability

not ANSI, not POSIX

Node:getc, Next:getcbrk, Previous:_get_volume_info, Up:Alphabetical List

## getc

### Syntax

    #include <stdio.h>

    int getc(FILE *file);

### Description

Get one character from file.

### Return Value

The character ([0..255]) or `EOF` if eof or error.

### Portability

ANSI, POSIX

### Example

    int c;
    while ((c=getc(stdin)) != EOF)
      putc(c, stdout);

Node:getcbrk, Next:getch, Previous:getc, Up:Alphabetical List

## getcbrk

### Syntax

    #include <dos.h>

    int getcbrk(void);

### Description

Get the setting of the Ctrl-C checking flag in MS-DOS.

See setcbrk.

### Return Value

0 if not checking, 1 if checking.

### Portability

not ANSI, not POSIX

Node:getch, Next:getchar, Previous:getcbrk, Up:Alphabetical List

## getch

### Syntax

    #include <conio.h>

    int     getch(void);

### Description

A single character from the predefined standard input handle is read and returned. The input is not buffered. If there is a character pending from `ungetch` (see ungetch), it is returned instead. The character is not echoed to the screen. This function doesn't check for special characters like `Ctrl-<C>`.

If the standard input handle is connected to the console, any pending output in the `stdout` and `stderr` streams is flushed before reading the input, if these streams are connected to the console.

### Return Value

The character.

### Portability

not ANSI, not POSIX

Node:getchar, Next:getche, Previous:getch, Up:Alphabetical List

## getchar

### Syntax

    #include <stdio.h>

    int getchar(void);

### Description

The same as `fgetc(stdin)` (see fgetc).

### Return Value

The character, or `EOF`.

### Portability

ANSI, POSIX

Node:getche, Next:getcwd, Previous:getchar, Up:Alphabetical List

## getche

### Syntax

    #include <conio.h>

    int getche(void);

### Description

A single character from the predefined standard input handle is read and returned. The input is not buffered. If there is a character pending from `ungetch` (see ungetch), it is returned instead. The character is echoed to the screen. This function doesn't check for special characters like `Ctrl-<C>`.

If the standard input handle is connected to the console, any pending output in the `stdout` and `stderr` streams is flushed before reading the input, if these streams are connected to the console.

### Return Value

The character.

### Portability

not ANSI, not POSIX

Node:getcwd, Next:getdate, Previous:getche, Up:Alphabetical List

## getcwd

### Syntax

    #include <unistd.h>

    char *getcwd(char *buffer, int max);

### Description

Get the current directory. The return value includes the drive specifier. If buffer is `NULL`, `getcwd` allocates memory with `malloc`. This call fails if more than max characters are required to specify the current directory.

### Return Value

The buffer, either buffer or a newly-allocated buffer, or `NULL` on error.

### Portability

not ANSI, POSIX

### Example

    char *buf = (char *)malloc(PATH_MAX);
    if (buf && getcwd(buf, PATH_MAX))
    {
      printf("cwd is %s\n", buf);
      free(buf);
    }

Node:getdate, Next:getdfree, Previous:getcwd, Up:Alphabetical List

## getdate

### Syntax

    #include <dos.h>

    void getdate(struct date *);

### Description

This function gets the current date. The return structure is as follows:

    struct date {
      short da_year;
      char  da_day;
      char  da_mon;
    };

See setdate. See gettime.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    struct date d;
    getdate(&d);

Node:getdfree, Next:getdisk, Previous:getdate, Up:Alphabetical List

## getdfree

### Syntax

    #include <dos.h>

    void getdfree(unsigned char drive, struct dfree *ptr);

### Description

This function gets information about the size and fullness of the given drive (0=default, 1=A:, etc). The return structure is as follows:

    struct dfree {
      unsigned df_avail; /* number of available clusters */
      unsigned df_total; /* total number of clusters */
      unsigned df_bsec;  /* bytes per sector */
      unsigned df_sclus; /* sectors per cluster */
    };

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    struct dfree d;
    getdfree(3, &d); /* drive C: */

Node:getdisk, Next:getdtablesize, Previous:getdfree, Up:Alphabetical List

## getdisk

### Syntax

    #include <dir.h>

    int getdisk(void);

### Description

Gets the current disk (0=A).

See setdisk.

### Return Value

The current disk number.

### Portability

not ANSI, not POSIX

### Example

    printf("This drive is %c:\n", getdisk() + 'A');

Node:getdtablesize, Next:getegid, Previous:getdisk, Up:Alphabetical List

## getdtablesize

### Syntax

    #include <unistd.h>

    int getdtablesize(void);

### Description

Get the maximum number of open file descriptors the system supports.

### Return Value

255

### Portability

not ANSI, not POSIX

Node:getegid, Next:getenv, Previous:getdtablesize, Up:Alphabetical List

## getegid

### Syntax

    #include <unistd.h>

    int getegid(void);

### Description

Get the effective group id.

### Return Value

42

### Portability

not ANSI, POSIX

Node:getenv, Next:geteuid, Previous:getegid, Up:Alphabetical List

## getenv

### Syntax

    #include <stdlib.h>

    char *getenv(const char *name);

### Description

Get the setting of the environment variable name. Do not alter or free the returned value.

### Return Value

The value, or `NULL` if that variable does not exist.

### Portability

ANSI, POSIX

### Example

    char *term = getenv("TERM");

Node:geteuid, Next:getftime, Previous:getenv, Up:Alphabetical List

## geteuid

### Syntax

    #include <unistd.h>

    int geteuid(void);

### Description

Gets the effective UID.

### Return Value

42

### Portability

not ANSI, POSIX

Node:getftime, Next:getgid, Previous:geteuid, Up:Alphabetical List

## getftime

### Syntax

    #include <dos.h>

    int getftime(int handle, struct ftime *ptr);

### Description

Get the timestamp for the given file handle. The return structure is as follows:

    struct ftime {
      unsigned ft_tsec:5;	/* 0-29, double to get real seconds */
      unsigned ft_min:6;	/* 0-59 */
      unsigned ft_hour:5;	/* 0-23 */
      unsigned ft_day:5;	/* 1-31 */
      unsigned ft_month:4;	/* 1-12 */
      unsigned ft_year:7;	/* since 1980 */
    }

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    struct ftime t;
    getftime(fd, &t);

Node:getgid, Next:getgrent, Previous:getftime, Up:Alphabetical List

## getgid

### Syntax

    #include <unistd.h>

    int getgid(void);

### Description

Get the current group id.

### Return Value

42

### Portability

not ANSI, POSIX

Node:getgrent, Next:getgrgid, Previous:getgid, Up:Alphabetical List

## getgrent

### Syntax

    #include <grp.h>

    struct group *getgrent(void);

### Description

This function returns the next available group entry. Note that for MS-DOS, this is simulated. If the environment variable GROUP is set, that is the name of the only group returned, else the only group is "dos". Thus, under DOS, `getgrent` will always fail on the second and subsequent calls.

The return type of this and related function is as follows:

    struct group {
      gid_t    gr_gid;    /* result of getgid() */
      char  ** gr_mem;    /* gr_mem[0] points to
                              getenv("USER"/"LOGNAME") or "user" */
      char  *  gr_name;   /* getenv("GROUP") or "dos" */
    };

### Return Value

The next structure, or `NULL` at the end of the list.

### Portability

not ANSI, not POSIX

### Example

    struct group *g;
    setgrent();
    while ((g = getgrent()) != NULL)
    {
      printf("group %s gid %d\n", g->gr_name, g->gr_gid);
    }
    endgrent();

Node:getgrgid, Next:getgrnam, Previous:getgrent, Up:Alphabetical List

## getgrgid

### Syntax

    #include <grp.h>

    extern struct group *getgrgid(int gid);

### Description

This function returns the group entry that matches gid. See getgrent, for the description of `struct group`.

### Return Value

The matching group, or `NULL` if none match.

### Portability

not ANSI, POSIX

Node:getgrnam, Next:getgroups, Previous:getgrgid, Up:Alphabetical List

## getgrnam

### Syntax

    #include <grp.h>

    struct group *getgrnam(char *name);

### Description

This function returns the group entry for the group named name. See getgrent, for the description of `struct group`.

### Return Value

The matching group, or `NULL` if none match.

### Portability

not ANSI, POSIX

Node:getgroups, Next:gethostname, Previous:getgrnam, Up:Alphabetical List

## getgroups

### Syntax

    #include <unistd.h>

    int getgroups(int size, gid_t *grouplist);

### Description

This function always returns zero. It exists to assist porting from Unix.

### Return Value

Zero.

### Portability

not ANSI, POSIX

Node:gethostname, Next:getitimer, Previous:getgroups, Up:Alphabetical List

## gethostname

### Syntax

    #include <unistd.h>
    #include <sys/param.h>

    int gethostname (char *buf, int size);

### Description

Get the name of the host the program is executing on. This name is obtained from the network software, if present, otherwise from the `"HOSTNAME"` environment variable, if present, finally defaulting to `"pc"`.

The call fails if more than size characters are required to specify the host name. A buffer size of `MAXGETHOSTNAME` is guaranteed to be enough.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    char *buf = (char *) malloc (MAXGETHOSTNAME);
    if (buf && 0 == gethostname (buf, MAXGETHOSTNAME))
      printf ("We're on %s\n", buf);
    if (buf) free(buf);

Node:getitimer, Next:getkey, Previous:gethostname, Up:Alphabetical List

## getitimer

### Syntax

    #include <sys/time.h>

    int getitimer(int which, struct itimerval *value);

### Description

This function gets the current value of the interval timer specified by which into structure value. Variable which can have the value of `ITIMER_REAL` or `ITIMER_PROF`. See setitimer, for more details about timers.

Upon return, the `it_value` member of value will hold the amount of time left until timer expiration, or zero if the timer has expired or was stopped by a previous call to `setitimer`. The `it_interval` member will hold the interval between two successive alarms as set by the last call to `setitimer` (but note that interval values less than the system clock granularity are rounded up to that granularity). The value returned in `it_interval` member is not set to zero when the timer is stopped, it always retains the interval that was last in use.

### Return Value

Returns 0 on success, -1 on failure (and sets `errno`).

### Portability

not ANSI, not POSIX

Node:getkey, Next:getlogin, Previous:getitimer, Up:Alphabetical List

## getkey

### Syntax

    #include <pc.h>
    #include <keys.h>

    int getkey(void);

### Description

Waits for the user to press one key, then returns that key. Alt-key combinations have 0x100 added to them. Extended keys return their non-extended codes.

The file `keys.h` has symbolic names for many of the keys.

See getxkey.

### Return Value

The key pressed.

### Portability

not ANSI, not POSIX

### Example

    while (getkey() != K_Alt_3)
      do_something();

Node:getlogin, Next:getlongpass, Previous:getkey, Up:Alphabetical List

## getlogin

### Syntax

    #include <unistd.h>

    char *getlogin(void);

### Description

Get the login ID of the user.

### Return Value

Returns the value of the `USER` environment variable, else the `LOGNAME` environment variable, else `"dosuser"`.

### Portability

not ANSI, POSIX

### Example

    printf("I am %s\n", getlogin());

Node:getlongpass, Next:getmntent, Previous:getlogin, Up:Alphabetical List

## getlongpass

### Syntax

    #include <stdlib.h>

    int  getlongpass(const char *prompt, char *password, int max_length)

### Description

This function reads up to a Newline (CR or LF) or EOF (Ctrl-D or Ctrl-Z) from the standard input, without an echo, after prompting with a null-terminated string prompt. It puts a null-terminated string of at most max_length - 1 first characters typed by the user into a buffer pointed to by password. Pressing Ctrl-C or Ctrl-Break will cause the calling program to `exit(1)`.

### Return Value

Zero if successful, -1 on error (and errno is set to an appropriate value).

### Portability

not ANSI, not POSIX

### Example

    char password[MAX_PASS];

    (void)getlongpass("Password: ", password, MAX_PASS);

Node:getmntent, Next:getopt, Previous:getlongpass, Up:Alphabetical List

## getmntent

### Syntax

    #include <mntent.h>

    struct mntent *getmntent(FILE *filep);

### Description

This function returns information about the various drives that are available to your program. Beginning with drive `A:`, information is retrieved for successive drives with successive calls to `getmntent`. Note that drives `A:` and `B:` will only be returned if there is an MS-DOS formatted disk in the drive; empty drives are skipped. For systems with a single floppy drive, it is returned as if it were mounted on `A:/` or `B:/`, depending on how it was last referenced (and if there is a disk in the drive).

For each drive scanned, a pointer to a static structure of the following type is returned:

    struct mntent
    {
        char * mnt_fsname;  /* The name of this file system */
        char * mnt_dir;     /* The root directory of this file system */
        char * mnt_type;	/* Filesystem type */
        char * mnt_opts;    /* Options, see below */
        int    mnt_freq;    /* -1 */
        int    mnt_passno;  /* -1 */
        long   mnt_time;    /* -1 */
    };

DJGPP implementation returns the following in the first 4 fields of `struct mntent`:

`mnt_fsname`
  For networked and CD-ROM drives, this is the name of root directory in the form `\\HOST\PATH` (this is called a UNC name).

  For drives compressed with DoubleSpace, `mnt_fsname` is the string `X:\DBLSPACE.NNN`, where X is the drive letter of the host drive and NNN is the sequence number of the Compressed Volume File.

  For drives compressed with Stacker, `mnt_fsname` is the string `X:\STACVOL.NNN`, where X and NNN are as for DoubleSpace drives.

  For drives compressed with Jam (a shareware disk compression software), `mnt_fsname` is the full name of the Jam archive file.

  For SUBSTed drives, `mnt_fsname` is the actual directory name that that was SUBSTed to emulate a drive.

  JOINed drives get their `mnt_fsname` as if they were NOT JOINed (i.e., either the label name or the default `Drive X:`).

  For drives with a volume label, `mnt_fsname` is the name of the label; otherwise the string `Drive X:`, where X is the drive letter.

`mnt_dir`
  For most drives, this is the name of its root directory `X:/` (where X is the drive letter), except that JOINed drives get `mnt_dir` as the name of the directory to which they were JOINed.

  For systems with a single floppy drive (which can be referenced as either `a:/` or `b:/`), the mount directory will be returned as one of these, depending on which drive letter was last used to reference that drive.

`mnt_type`

       "fd"     for floppy disks
       "hd"     for hard disks
       "dblsp"  for disks compressed with DoubleSpace
       "stac"   for disks compressed with Stacker
       "jam"    for disks compressed with Jam
       "cdrom"  for CD-ROM drives
       "ram"    for RAM disks
       "subst"  for SUBSTed directories
       "join"   for JOINed disks
       "net"    for networked drives

`mnt_opts`
  The string `ro,dev=XX` for CD-ROM drives, `rw,dev=XX` for all the others, where XX is the hexadecimal drive number of the REAL drive on which this filesystem resides. That is, if you call `stat` on mnt_fsname, you will get the numeric equivalent of XX in `st_dev` member of `struct stat`. E.g., for drive `C:` you will get `rw,dev=02`. Note that SUBSTed and JOINed drives get the drive numbers as if SUBST and JOIN were not in effect.

### Return Value

This function returns a pointer to a `struct mntent`, or `NULL` if there are no more drives to report on.

### Portability

not ANSI, not POSIX

### Example

    struct mntent *m;
    FILE *f;
    f = setmntent("/etc/mnttab", "r");
    while ((m = getmntent(f)))
      printf("Drive %s, name %s\n", m->mnt_dir, m->mnt_fsname);
    endmntent(f);

Node:getopt, Next:getpagesize, Previous:getmntent, Up:Alphabetical List

## getopt

### Syntax

    #include <unistd.h>

    int getopt(int argc, char * const *argv, const char *options);
    extern char *optarg;
    extern int optind, opterr, optopt;

### Description

Parse options from the command line. The options are a string of valid option characters. If a given option takes a parameter, that character should be followed by a colon.

For each valid switch, this function sets `optarg` to the argument (if the switch takes one), sets `optind` to the index in argv that it is using, sets `optopt` to the option letter found, and returns the option letter found.

If an unexpected option is found, `getopt` will return `?`, and if `opterr` is nonzero, will print an error message to stderr.

The special option `--` indicates that no more options follow on the command line, and cause `getopt` to stop looking.

### Return Value

The option found, or -1 if no more options.

### Portability

not ANSI, POSIX

### Example

    int c;
    opterr = 0;
    while ((c=getopt(argc, argv, "vbf:")) != -1)
    {
      switch (c)
      {
        case 'v':
          verbose_flag ++;
          break;
        case 'b':
          binary_flag ++;
          break;
        case 'f':
          output_filename = optarg;
          break;
        case '?':
          printf("Unknown option %c\n", optopt);
          usage();
          exit(1);
      }
    }

Node:getpagesize, Next:getpass, Previous:getopt, Up:Alphabetical List

## getpagesize

### Syntax

    #include <unistd.h>

    int getpagesize(void);

### Description

Return the size of the native virtual memory page size.

### Return Value

4096 for the i386 and higher processors.

### Portability

not ANSI, not POSIX

Node:getpass, Next:getpgrp, Previous:getpagesize, Up:Alphabetical List

## getpass

### Syntax

    #include <stdlib.h>

    char * getpass(const char *prompt)

### Description

This function reads up to a Newline (CR or LF) or EOF (Ctrl-D or Ctrl-Z) from the standard input, without an echo, after prompting with a null-terminated string prompt. It returns the string of at most 8 characters typed by the user. Pressing Ctrl-C or Ctrl-Break will cause the calling program to `exit(1)`.

### Return Value

A pointer to a static buffer which holds the user's response. The buffer will be overwritten by each new call. In case of any error in the lower I/O routines, a NULL pointer will be returned.

### Portability

not ANSI, not POSIX

### Example

    char *password = getpass("Password: ");

Node:getpgrp, Next:getpid, Previous:getpass, Up:Alphabetical List

## getpgrp

### Syntax

    #include <unistd.h>

    int getpgrp(void);

### Description

Gets the process group, which is currently the same as the pid.

### Return Value

The process group.

### Portability

not ANSI, POSIX

Node:getpid, Next:getpwent, Previous:getpgrp, Up:Alphabetical List

## getpid

### Syntax

    #include <unistd.h>

    int getpid(void);

### Description

Get the process ID, which uniquely identifies each program running on the system.

### Return Value

The process ID.

### Portability

not ANSI, POSIX

Node:getpwent, Next:getpwnam, Previous:getpid, Up:Alphabetical List

## getpwent

### Syntax

    #include <pwd.h>

    struct passwd *getpwent(void);

### Description

This function retrieves the next available password file entry. For MS-DOS, this is simulated by providing exactly one entry:

    struct passwd {
      char * pw_name;    /* getlogin() */
      int    pw_uid;     /* getuid() */
      int    pw_gid;     /* getgid() */
      char * pw_dir;     /* "/" or getenv("HOME") */
      char * pw_shell;   /* "/bin/sh" or getenv("SHELL") */
    };

The `pw_name` member is returned as described under `getlogin` (see getlogin). The `pw_uid` member is returned as described under `getuid` (see getuid). `pw_gid` is returned as described under `getgid` (see getgid). The `pw_dir` member is set to the value of the environment variable `HOME` if it is defined, or to `/` otherwise. `pw_shell` is set as follows:

- If the environment variable `SHELL` is set, the value of `SHELL`.
- If `SHELL` is not set, but `COMSPEC` is, the value of `COMSPEC`.
- If neither of the above variables is defined, `pw_shell` is set to `"sh"`.

### Return Value

The next passwd entry, or `NULL` if there are no more.

### Portability

not ANSI, not POSIX

### Example

    struct passwd *p;
    setpwent();
    while ((p = getpwent()) != NULL)
    {
      printf("user %s name %s\n", p->pw_name, p->pw_gecos);
    }
    endpwent();

Node:getpwnam, Next:getpwuid, Previous:getpwent, Up:Alphabetical List

## getpwnam

### Syntax

    #include <pwd.h>

    struct passwd *getpwnam(const char *name);

### Description

This function gets the password file entry matching name. See getpwent, for the description of `struct passwd`.

### Return Value

The matching record, or `NULL` if none match.

### Portability

not ANSI, POSIX

Node:getpwuid, Next:getrlimit, Previous:getpwnam, Up:Alphabetical List

## getpwuid

### Syntax

    #include <pwd.h>

    struct passwd *getpwuid(uid_t uid);

### Description

This function gets the password file entry matching uid. See getpwent, for the description of `struct passwd`.

### Return Value

The matching record, or `NULL` if none match.

### Portability

not ANSI, POSIX

Node:getrlimit, Next:getrusage, Previous:getpwuid, Up:Alphabetical List

## getrlimit

### Syntax

    #include <sys/resource.h>

    int getrlimit (int rltype, struct rlimit *rlimitp);

### Description

This function gets the resource limit specified by rltype and stores it in the buffer pointed to by rlimitp. The `rlimit` structure is defined on `sys/resource.h` as follows:

    struct rlimit {
      long rlim_cur;  /* current (soft) limit */
      long rlim_max;  /* maximum value for rlim_cur */
    };

The following resource types can be passed in rltype:

`RLIMIT_CPU`
  CPU time in milliseconds.
`RLIMIT_FSIZE`
  Maximum file size.
`RLIMIT_DATA`
  Data size.
`RLIMIT_STACK`
  Stack size.
`RLIMIT_CORE`
  Core file size.
`RLIMIT_RSS`
  Resident set size.
`RLIMIT_MEMLOCK`
  Locked-in-memory address space.
`RLIMIT_NPROC`
  Number of processes.
`RLIMIT_NOFILE`
  Number of open files.

Currently, only the `RLIMIT_STACK` and `RLIMIT_NOFILE` are meaningful: the first returns the value of `_stklen` (see _stklen), the second the value returned by `sysconf(_SC_OPEN_MAX)` (see sysconf). All other members of the `rlimit` structure are set to `RLIM_INFINITY`, defined in `sys/resource.h` as `2^31 - 1`.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    struct rlimit rlimitbuf;
    int rc = getrlimit (RLIMIT_STACK, &rlimitbuf);

Node:getrusage, Next:gets, Previous:getrlimit, Up:Alphabetical List

## getrusage

### Syntax

    #include <sys/time.h>
    #include <sys/resource.h>

    int getrusage(int who, struct rusage *rusage);

### Description

This function returns information about the running process. The structure `struct rusage` is defined on `<sys/resource.h>` as follows:

      struct rusage {
        struct timeval ru_utime;	/* user time used */
        struct timeval ru_stime;	/* system time used */
        long ru_maxrss;		/* integral max resident set size */
        long ru_ixrss;		/* integral shared text memory size */
        long ru_idrss;		/* integral unshared data size */
        long ru_isrss;		/* integral unshared stack size */
        long ru_minflt;		/* page reclaims */
        long ru_majflt;		/* page faults */
        long ru_nswap;		/* swaps */
        long ru_inblock;		/* block input operations */
        long ru_oublock;		/* block output operations */
        long ru_msgsnd;		/* messages sent */
        long ru_msgrcv;		/* messages received */
        long ru_nsignals;		/* signals received */
        long ru_nvcsw;		/* voluntary context switches */
        long ru_nivcsw;		/* involuntary context switches */
      };

Currently, the only field that is computed is `ru_utime`. It is computed as the total elapsed time used by the calling program. The remainder of the fields are set to zero.

The who parameter must be `RUSAGE_SELF` or `RUSAGE_CHILDREN`.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    struct rusage r;
    getrusage(RUSAGE_SELF, &r);

Node:gets, Next:gettext, Previous:getrusage, Up:Alphabetical List

## gets

### Syntax

    #include <stdio.h>

    char *gets(char *buffer);

### Description

Reads characters from `stdin`, storing them in buffer, until either end of file or a newline is encountered. If any characters were stored, the buffer is then `NULL` terminated and its address is returned, else `NULL` is returned.

### Return Value

The address of the buffer, or `NULL`.

### Portability

ANSI, POSIX

### Example

    char buf[1000];
    while (gets(buf))
      puts(buf);

Node:gettext, Next:gettextinfo, Previous:gets, Up:Alphabetical List

## gettext

### Syntax

    #include <conio.h>

    int     gettext(int _left, int _top, int _right, int _bottom, void *_destin);

### Description

Retrieve a block of screen characters into a buffer.

### Return Value

1

### Portability

not ANSI, not POSIX

Node:gettextinfo, Next:gettime, Previous:gettext, Up:Alphabetical List

## gettextinfo

### Syntax

    #include <conio.h>

    void    gettextinfo(struct text_info *_r);

### Description

This function returns the parameters of the current window on the screen. The return structure is this:

    struct text_info {
        unsigned char winleft;
        unsigned char wintop;
        unsigned char winright;
        unsigned char winbottom;
        unsigned char attribute;
        unsigned char normattr;
        unsigned char currmode;
        unsigned char screenheight;
        unsigned char screenwidth;
        unsigned char curx;
        unsigned char cury;
    };

The `normattr` field is the text attribute which was in effect before the program started.

### Portability

not ANSI, not POSIX

Node:gettime, Next:gettimeofday, Previous:gettextinfo, Up:Alphabetical List

## gettime

### Syntax

    #include <dos.h>

    void gettime(struct time *);

### Description

This function gets the current time. The return structure is as follows:

    struct time {
      unsigned char ti_min;
      unsigned char ti_hour;
      unsigned char ti_hund;
      unsigned char ti_sec;
    };

See settime. See getdate.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    struct time t;
    gettime(&t);

Node:gettimeofday, Next:getuid, Previous:gettime, Up:Alphabetical List

## gettimeofday

### Syntax

    #include <time.h>

    int gettimeofday(struct timeval *tp, struct timezone *tzp);

### Description

Gets the current GMT time and the local timezone information. The return structures are as follows:

    struct timeval {
      long tv_sec;  /* seconds since 00:00:00 GMT 1/1/1970 */
      long tv_usec; /* microseconds */
    };
    struct timezone {
      int tz_minuteswest; /* west of GMT */
      int tz_dsttime;     /* set if daylight saving time in affect */
    };

If either tp or tzp are `NULL`, that information is not provided.

Note that although this function returns microseconds for compatibility reasons, the values are precise to less than 1/20 of a second only. The underlying DOS function has 1/20 second granularity, as it is calculated from the 55 ms timer tick count, so you won't get better than that with gettimeofday().

See settimeofday.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

Node:getuid, Next:getw, Previous:gettimeofday, Up:Alphabetical List

## getuid

### Syntax

    #include <unistd.h>

    int getuid(void);

### Description

Returns the user ID.

### Return Value

42

### Portability

not ANSI, POSIX

Node:getw, Next:getwd, Previous:getuid, Up:Alphabetical List

## getw

### Syntax

    #include <stdio.h>

    int getw(FILE *file);

### Description

Reads a single binary word in native format from file.

See putw.

### Return Value

The value read, or `EOF` for end-of-file or error. Since `EOF` is a valid integer, you should use `feof` or `ferror` to detect this situation.

### Portability

not ANSI, not POSIX

### Example

    int i = getw(stdin);

Node:getwd, Next:getxkey, Previous:getw, Up:Alphabetical List

## getwd

### Syntax

    #include <unistd.h>

    char *getwd(char *buffer);

### Description

Get the current directory and put it in buffer. The return value includes the drive specifier.

### Return Value

buffer is returned.

### Portability

not ANSI, not POSIX

### Example

    char buf[PATH_MAX];
    getwd(buf);

Node:getxkey, Next:glob, Previous:getwd, Up:Alphabetical List

## getxkey

### Syntax

    #include <pc.h>
    #include <keys.h>

    int getxkey(void);

### Description

Waits for the user to press one key, then returns that key. Alt-key combinations have 0x100 added to them, and extended keys have 0x200 added to them.

The file `keys.h` has symbolic names for many of the keys.

See getkey.

### Return Value

The key pressed.

### Portability

not ANSI, not POSIX

### Example

    while (getxkey() != K_EEnd)
      do_something();

Node:glob, Next:globfree, Previous:getxkey, Up:Alphabetical List

## glob

### Syntax

    #include <glob.h>

    int  glob(const char *pattern, int flags,
              int (*errfunc)(const char *epath, int eerrno), glob_t *pglob);

### Description

This function expands a filename wildcard which is passed as pattern. The pattern may include these special characters:

`*`
  Matches zero of more characters.
`?`
  Matches exactly one character (any character).
`[...]`
  Matches one character from a group of characters. If the first character is `!`, matches any character not in the group. A group is defined as a list of characters between the brackets, e.g. `[dkl_]`, or by two characters separated by `-` to indicate all characters between and including these two. For example, `[a-d]` matches `a`, `b`, `c`, or `d`, and `[!a-zA-Z0-9]` matches any character that is not alphanumeric.
`...`
  Matches all the subdirectories, recursively (VMS aficionados, rejoice!).
`\`
  Causes the next character to not be treated as special. For example, `\[` matches a literal `[`. If flags includes `GLOB_NOESCAPE`, this quoting is disabled and `\` is handled as a simple character.

The variable flags controls certain options of the expansion process. Possible values for _flags are as follows:

`GLOB_APPEND`
  Append the matches to those already present in the array `pglob->gl_pathv`. By default, `glob` discards all previous contents of `pglob->gl_pathv` and allocates a new memory block for it. If you use `GLOB_APPEND`, `pglob` should point to a structure returned by a previous call to `glob`.
`GLOB_DOOFFS`
  Skip `pglob->gl_offs` entries in `gl_pathv` and put new matches after that point. By default, `glob` puts the new matches beginning at `pglob->gl_pathv[0]`. You can use this flag both with `GLOB_APPEND` (in which case the new matches will be put after the first `pglob->gl_offs` matches from previous call to `glob`), or without it (in which case the first `pglob->gl_offs` entries in `pglob->gl_pathv` will be filled by `NULL` pointers).
`GLOB_ERR`
  Stop when an unreadable directory is encountered and call user-defined function errfunc. This cannot happen under DOS (and thus errfunc is never used).
`GLOB_MARK`
  Append a slash to each pathname that is a directory.
`GLOB_NOCHECK`
  If no matches are found, return the pattern itself as the only match. By default, `glob` doesn't change `pglob` if no matches are found.
`GLOB_NOESCAPE`
  Disable blackslash as an escape character. By default, backslash quotes special meta-characters in wildcards described above.
`GLOB_NOSORT`
  Do not sort the returned list. By default, the list is sorted alphabetically. This flag causes the files to be returned in the order they were found in the directory.

Given the pattern and the flags, `glob` expands the pattern and returns a list of files that match the pattern in a structure a pointer to which is passed via pglob. This structure is like this:

    typedef struct {
      size_t gl_pathc;
      char **gl_pathv;
      size_t gl_offs;
    } glob_t;

In the structure, the `gl_pathc` field holds the number of filenames in `gl_pathv` list; this includes the filenames produced by this call, plus any previous filenames if `GLOB_APPEND` or `GLOB_DOOFFS` were set in flags. The list of matches is returned as an array of pointers to the filenames; `gl_pathv` holds the address of the array. Thus, the filenames which match the pattern can be accessed as `gl_pathv[0]`, `gl_pathv[1]`, etc. If `GLOB_DOOFFS` was set in flags, the new matches begin at offset given by `gl_offs`.

### Return Value

Zero on success, or one of these codes:

`GLOB_ABORTED`
  Not used in DJGPP implementation.
`GLOB_NOMATCH`
  No files matched the given pattern.
`GLOB_NOSPACE`
  Not enough memory to accomodate expanded filenames.
`GLOB_ERR`
  Never happens on MSDOS, see above.

### Notes

`glob` will not match names of volume labels.

On MSDOS, filenames are always matched case-insensitively. On filesystems that preserve letter-case in filenames (such as Windows 9x), matches are case-insensitive unless the pattern includes uppercase characters.

On MSDOS, the list of expanded filenames will be returned in lower case, if all the characters of the pattern (except those between brackets [...]) are lower-case; if some of them are upper-case, the expanded filenames will be also in upper case. On filesystems that preserve letter-case in filenames, long filenames are returned as they are found in the directory entry; DOS-style 8+3 filenames are returned as on MSDOS (in lower case if the pattern doesn't include any upper-case letters, in upper case otherwise).

When the environment variable `LFN` is set to `n`, `glob` behaves on Windows 9x exactly as it does on MSDOS.

Setting the environment variable `FNCASE` to `y`, or setting the `_CRT0_FLAG_PRESERVE_FILENAME_CASE` bit in the `_crt0_startup_flags` variable (see _crt0_startup_flags) suppresses any letter-case conversions in filenames and forces case-sensitive filename matching. See _preserve_fncase.

### Portability

not ANSI, POSIX

### Example

    #include <stdlib.h>
    #include <string.h>
    #include <glob.h>

    /* Convert a wildcard pattern into a list of blank-separated
       filenames which match the wildcard.  */

    char * glob_pattern(char *wildcard)
    {
      char *gfilename;
      size_t cnt, length;
      glob_t glob_results;
      char **p;

      glob(wildcard, GLOB_NOCHECK, 0, &glob_results);

      /* How much space do we need?  */
      for (p = glob_results.gl_pathv, cnt = glob_results.gl_pathc;
           cnt; p++, cnt--)
        length += strlen(*p) + 1;

      /* Allocate the space and generate the list.  */
      gfilename = (char *) calloc(length, sizeof(char));
      for (p = glob_results.gl_pathv, cnt = glob_results.gl_pathc;
           cnt; p++, cnt--)
        {
          strcat(gfilename, *p);
          if (cnt > 1)
            strcat(gfilename, " ");
        }

      globfree(&glob_results);
      return gfilename;
    }

Node:globfree, Next:gmtime, Previous:glob, Up:Alphabetical List

## globfree

### Syntax

    #include <glob.h>

    void globfree(glob_t *_pglob);

### Description

Frees the memory associated with `_pglob`.

### Portability

not ANSI, POSIX

Node:gmtime, Next:_go32_conventional_mem_selector, Previous:globfree, Up:Alphabetical List

## gmtime

### Syntax

    #include <time.h>

    struct tm *gmtime(const time_t *tod);

### Description

Converts the time represented by tod into a structure.

The return structure has this format:

    struct tm {
      int    tm_sec;    /* seconds after the minute [0-60] */
      int    tm_min;    /* minutes after the hour [0-59] */
      int    tm_hour;   /* hours since midnight [0-23] */
      int    tm_mday;   /* day of the month [1-31] */
      int    tm_mon;    /* months since January [0-11] */
      int    tm_year;   /* years since 1900 */
      int    tm_wday;   /* days since Sunday [0-6] */
      int    tm_yday;   /* days since January 1 [0-365] */
      int    tm_isdst;  /* Daylight Savings Time flag */
      long   tm_gmtoff; /* offset from GMT in seconds */
      char * tm_zone;   /* timezone abbreviation */
    };

### Return Value

A pointer to a static structure which is overwritten with each call.

### Portability

ANSI, POSIX

### Example

    time_t x;
    struct tm *t;
    time(&x);
    t = gmtime(&t);

Node:_go32_conventional_mem_selector, Next:_go32_dpmi_allocate_dos_memory, Previous:gmtime, Up:Alphabetical List

## _go32_conventional_mem_selector

### Syntax

    #include <go32.h>

    u_short _go32_conventional_mem_selector();

### Description

This function returns a selector which has a physical base address corresponding to the beginning of conventional memory. This selector can be used as a parameter to `movedata` (see movedata) to manipulate memory in the conventional address space.

### Return Value

The selector.

### Portability

not ANSI, not POSIX

### Example

    short blank_row_buf[ScreenCols()];
    /* scroll screen */
    movedata(_go32_conventional_mem_selector(), 0xb8000 + ScreenCols()*2,
             _go32_conventional_mem_selector(), 0xb8000,
             ScreenCols() * (ScreenRows()-1) * 2);
    /* fill last row */
    movedata(_go32_my_ds, (int)blank_row_buf,
             _go32_conventional_mem_selector(),
                0xb8000 + ScreenCols()*(ScreenRows()-1)*2,
              ScreenCols() * 2);

Node:_go32_dpmi_allocate_dos_memory, Next:_go32_dpmi_allocate_iret_wrapper, Previous:_go32_conventional_mem_selector, Up:Alphabetical List

## _go32_dpmi_allocate_dos_memory

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_allocate_dos_memory(_go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

Allocate a part of the conventional memory area (the first 640K). Set the `size` field of info to the number of paragraphs requested (this is (size in bytes + 15)/16), then call. The `rm_segment` field of info contains the segment of the allocated memory.

The memory may be resized with `_go32_dpmi_resize_dos_memory` and must be freed with `_go32_dpmi_free_dos_memory`.

If there isn't enough memory in the system, the `size` field of info has the largest available size, and an error is returned.

See also dosmemput, and dosmemget.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    _go32_dpmi_seginfo info;
    info.size = (want_size+15) / 16;
    _go32_dpmi_allocate_dos_memory(&info);
    dosmemput(buffer, want_size, info.rm_segment*16);
    _go32_dpmi_free_dos_memory(&info);

Node:_go32_dpmi_allocate_iret_wrapper, Next:_go32_dpmi_allocate_real_mode_callback_iret, Previous:_go32_dpmi_allocate_dos_memory, Up:Alphabetical List

## _go32_dpmi_allocate_iret_wrapper

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_allocate_iret_wrapper(_go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function creates a small assembler function that handles the overhead of servicing an interrupt. To use, put the address of your servicing function in the `pm_offset` field of info and call this function. The `pm_field` will get replaced with the address of the wrapper function, which you pass to both `_go32_dpmi_set_protected_mode_interrupt_vector` and `_go32_dpmi_free_iret_wrapper`.

See also _go32_dpmi_set_protected_mode_interrupt_vector, and _go32_dpmi_free_iret_wrapper.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    _go32_dpmi_seginfo info;
    info.pm_offset = my_handler;
    _go32_dpmi_allocate_iret_wrapper(&info);
    _go32_dpmi_set_protected_mode_interrupt_handler(0x75, &info);
    ...
    _go32_dpmi_free_iret_wrapper(&info);

Node:_go32_dpmi_allocate_real_mode_callback_iret, Next:_go32_dpmi_allocate_real_mode_callback_retf, Previous:_go32_dpmi_allocate_iret_wrapper, Up:Alphabetical List

## _go32_dpmi_allocate_real_mode_callback_iret

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_allocate_real_mode_callback_iret(_go32_dpmi_seginfo *info, _go32_dpmi_registers *regs);

### Description

See DPMI Overview.

This function allocates a "real-mode callback". Fill in the `pm_offset` field of info and call this function. It will fill in the `rm_segment` and `rm_offset` fields. Any time a real-mode program calls the real-mode address, your function gets called. The registers in effect will be stored in regs, which should be a global, and will be passed to your function. Any changes in regs will be reflected back into real mode. A wrapper will be added to your function to simulate the effects of an `iret` instruction, so this function is useful for trapping real-mode software interrupts (like 0x1b - `Ctrl-<Break>` hit).

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    _go32_dpmi_registers regs;

    my_handler(_go32_dpmi_registers *r)
    {
      r->d.eax = 4;
    }

    setup()
    {
      _go32_dpmi_seginfo info;
      _go32_dpmi_seginfo old_vector;
      _go32_dpmi_get_real_mode_interrupt_vector(0x84, &old_vector);
      info.pm_offset = my_handler;
      _go32_dpmi_allocate_real_mode_callback_iret(&info, &regs);
      _go32_dpmi_set_real_mode_interrupt_vector(0x84, &info);
      do_stuff();
      _go32_dpmi_set_real_mode_interrupt_vector(0x84, &old_vector);
      _go32_dpmi_free_real_mode_callback(&info);
    }

Node:_go32_dpmi_allocate_real_mode_callback_retf, Next:_go32_dpmi_chain_protected_mode_interrupt_vector, Previous:_go32_dpmi_allocate_real_mode_callback_iret, Up:Alphabetical List

## _go32_dpmi_allocate_real_mode_callback_retf

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_allocate_real_mode_callback_retf(_go32_dpmi_seginfo *info, _go32_dpmi_registers *regs);

### Description

See DPMI Overview.

This function allocates a "real-mode callback". Fill in the `pm_offset` field of info and call this function. It will fill in the `rm_segment` and `rm_offset` fields. Any time a real-mode program calls the real-mode address, your function gets called. The registers in effect will be stored in regs, which should be a global, and will be passed to your function. Any changes in regs will be reflected back into real mode. A wrapper will be added to your function to simulate the effects of a far return, such as the callback for the packet driver receiver.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

See _go32_dpmi_allocate_real_mode_callback_iret, for an example of usage.

Node:_go32_dpmi_chain_protected_mode_interrupt_vector, Next:_go32_dpmi_free_dos_memory, Previous:_go32_dpmi_allocate_real_mode_callback_retf, Up:Alphabetical List

## _go32_dpmi_chain_protected_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_chain_protected_mode_interrupt_vector(int vector, _go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function is used to chain a protected mode interrupt. It will build a suitable wrapper that will call your function and then jump to the next handler. Your function need not perform any special handling.

Warning! Because of the way DPMI works, you may not `longjmp` out of an interrupt handler or perform any system calls (such as `printf`) from within an interrupt handler.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

See _go32_dpmi_set_protected_mode_interrupt_vector.

Node:_go32_dpmi_free_dos_memory, Next:_go32_dpmi_free_iret_wrapper, Previous:_go32_dpmi_chain_protected_mode_interrupt_vector, Up:Alphabetical List

## _go32_dpmi_free_dos_memory

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_free_dos_memory(_go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function frees the conventional memory allocated by `_go32_dpmi_allocate_real_mode_memory`. You should pass it the same structure as was used to allocate it.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    _go32_dpmi_seginfo info;
    info.size = 100;
    _go32_dpmi_allocate_dos_memory(&info);
    _go32_dpmi_free_dos_memory(&info);

Node:_go32_dpmi_free_iret_wrapper, Next:_go32_dpmi_free_real_mode_callback, Previous:_go32_dpmi_free_dos_memory, Up:Alphabetical List

## _go32_dpmi_free_iret_wrapper

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_free_iret_wrapper(_go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function frees the memory used by the wrapper created by `_go32_dpmi_allocate_iret_wrapper`. You should not free a wrapper that is still in use.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

See _go32_dpmi_allocate_iret_wrapper.

Node:_go32_dpmi_free_real_mode_callback, Next:_go32_dpmi_get_free_memory_information, Previous:_go32_dpmi_free_iret_wrapper, Up:Alphabetical List

## _go32_dpmi_free_real_mode_callback

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_free_real_mode_callback(_go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function frees the real-mode callbacks and wrappers allocated by `_go32_dpmi_allocate_real_mode_callback_iret` and `_go32_dpmi_allocate_real_mode_callback_retf`.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

See _go32_dpmi_allocate_real_mode_callback_iret, for an example of usage.

Node:_go32_dpmi_get_free_memory_information, Next:_go32_dpmi_get_protected_mode_interrupt_vector, Previous:_go32_dpmi_free_real_mode_callback, Up:Alphabetical List

## _go32_dpmi_get_free_memory_information

### Syntax

    #include <dpmi.h

    int _go32_dpmi_get_free_memory_information(_go32_dpmi_meminfo *info);

### Description

This function fills in the following structure:

    typedef struct {
      u_long available_memory;
      u_long available_pages;
      u_long available_lockable_pages;
      u_long linear_space;
      u_long unlocked_pages;
      u_long available_physical_pages;
      u_long total_physical_pages;
      u_long free_linear_space;
      u_long max_pages_in_paging_file;
      u_long reserved[3];
    } _go32_dpmi_meminfo;

The only field that is guaranteed to have useful data is `available_memory`. Any unavailable field has -1 in it.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    int phys_mem_left()
    {
      _go32_dpmi_meminfo info;
      _go32_dpmi_get_free_memory_information(&info);
      if (info.available_physical_pages != -1)
        return info.available_physical_pages * 4096;
      return info.available_memory;
    }

Node:_go32_dpmi_get_protected_mode_interrupt_vector, Next:_go32_dpmi_get_real_mode_interrupt_vector, Previous:_go32_dpmi_get_free_memory_information, Up:Alphabetical List

## _go32_dpmi_get_protected_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_get_protected_mode_interrupt_vector(int vector, _go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function puts the selector and offset of the specified interrupt vector into the `pm_selector` and `pm_offset` fields of info. This structure can be saved and later passed to `_go32_dpmi_get_protected_mode_interrupt_vector` to restore a vector.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

See _go32_dpmi_set_protected_mode_interrupt_vector, for an example of usage.

Node:_go32_dpmi_get_real_mode_interrupt_vector, Next:_go32_dpmi_lock_code, Previous:_go32_dpmi_get_protected_mode_interrupt_vector, Up:Alphabetical List

## _go32_dpmi_get_real_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_get_real_mode_interrupt_vector(int vector, _go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function gets the real-mode interrupt vector specified into the address in the `rm_segment` and `rm_offset` fields in info.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

See _go32_dpmi_allocate_real_mode_callback_iret, for an example of usage.

Node:_go32_dpmi_lock_code, Next:_go32_dpmi_lock_data, Previous:_go32_dpmi_get_real_mode_interrupt_vector, Up:Alphabetical List

## _go32_dpmi_lock_code

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_lock_code( void *lockaddr, unsigned long locksize);

### Description

Locks the given region of code, starting at lockaddr for locksize bytes. lockaddr is a regular pointer in your program, such as the address of a function.

### Return Value

0 if success, -1 if failure.

### Portability

not ANSI, not POSIX

### Example

    void my_handler()
    {
    }

    void lock_my_handler()
    {
      _go32_dpmi_lock_code(my_handler, (unsigned long)(lock_my_handler - my_handler));
    }

Node:_go32_dpmi_lock_data, Next:_go32_dpmi_remaining_physical_memory, Previous:_go32_dpmi_lock_code, Up:Alphabetical List

## _go32_dpmi_lock_data

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_lock_data( void *lockaddr, unsigned long locksize);

### Description

Locks the given region of data, starting at lockaddr for locksize bytes. lockaddr is a regular pointer in your program, such as the address of a variable.

### Return Value

0 if success, -1 if failure.

### Portability

not ANSI, not POSIX

### Example

    int semaphore=0;

    void lock_my_handler()
    {
      _go32_dpmi_lock_data(&semaphore, 4);
    }

Node:_go32_dpmi_remaining_physical_memory, Next:_go32_dpmi_remaining_virtual_memory, Previous:_go32_dpmi_lock_data, Up:Alphabetical List

## _go32_dpmi_remaining_physical_memory

### Syntax

    #include <dpmi.h>

    unsigned long _go32_dpmi_remaining_physical_memory(void);

### Description

Returns the amount of physical memory that is still available in the system.

### Return Value

The amount in bytes.

### Portability

not ANSI, not POSIX

Node:_go32_dpmi_remaining_virtual_memory, Next:_go32_dpmi_resize_dos_memory, Previous:_go32_dpmi_remaining_physical_memory, Up:Alphabetical List

## _go32_dpmi_remaining_virtual_memory

### Syntax

    #include <dpmi.h>

    unsigned long _go32_dpmi_remaining_virtual_memory(void);

### Description

Returns the amount of virtual memory that is still available in the system.

### Return Value

The amount in bytes.

### Portability

not ANSI, not POSIX

Node:_go32_dpmi_resize_dos_memory, Next:_go32_dpmi_set_protected_mode_interrupt_vector, Previous:_go32_dpmi_remaining_virtual_memory, Up:Alphabetical List

## _go32_dpmi_resize_dos_memory

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_resize_dos_memory(_go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

The info structure is the same one used to allocate the memory. Fill in a new value for `size` and call this function. If there is not enough memory to satisfy the request, the largest size is filled in to the `size` field, the memory is not resized, and this function fails.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    _go32_dpmi_seginfo info;
    info.size = 10;
    _go32_dpmi_allocate_dos_memory(&info);
    info.size = 20;
    _go32_dpmi_resize_dos_memory(&info);
    _go32_dpmi_free_dos_memory(&info);

Node:_go32_dpmi_set_protected_mode_interrupt_vector, Next:_go32_dpmi_set_real_mode_interrupt_vector, Previous:_go32_dpmi_resize_dos_memory, Up:Alphabetical List

## _go32_dpmi_set_protected_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_set_protected_mode_interrupt_vector(int vector, _go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function sets the protected mode interrupt vector specified to point to the given function. The `pm_offset` and `pm_selector` fields of info must be filled in (see _go32_my_cs). The following should be noted:

- You may not `longjmp` out of an interrupt handler.
- You may not make any function calls that require system calls, such as `printf`.
- This function will not wrap the handler for you. The `_go32_dpmi_allocate_iret_wrapper` and `_go32_dpmi_chain_protected_mode_interrupt_vector` functions can wrap your function if you want.
- You must set the pm_selector field of info. Use `_go32_my_cs` to get a selector valid for your functions.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    volatile int tics = 0;

    timer_handler()
    {
      tics++;
    }

    int main()
    {
      _go32_dpmi_seginfo old_handler, new_handler;

      printf("grabbing timer interrupt\n");
      _go32_dpmi_get_protected_mode_interrupt_vector(8, &old_handler);

      new_handler.pm_offset = (int)tic_handler;
      new_handler.pm_selector = _go32_my_cs();
      _go32_dpmi_chain_protected_mode_interrupt_vector(8, &new_handler);

      getkey();

      printf("releasing timer interrupt\n");
      _go32_dpmi_set_protected_mode_interrupt_vector(8, &old_handler);

      return 0;
    }

Node:_go32_dpmi_set_real_mode_interrupt_vector, Next:_go32_dpmi_simulate_fcall, Previous:_go32_dpmi_set_protected_mode_interrupt_vector, Up:Alphabetical List

## _go32_dpmi_set_real_mode_interrupt_vector

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_set_real_mode_interrupt_vector(int vector, _go32_dpmi_seginfo *info);

### Description

See DPMI Overview.

This function sets the real-mode interrupt vector specified to point to the address in the `rm_segment` and `rm_offset` fields in info.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

See _go32_dpmi_allocate_real_mode_callback_iret, for an example of usage.

Node:_go32_dpmi_simulate_fcall, Next:_go32_dpmi_simulate_fcall_iret, Previous:_go32_dpmi_set_real_mode_interrupt_vector, Up:Alphabetical List

## _go32_dpmi_simulate_fcall

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_simulate_fcall(_go32_dpmi_registers *regs);

### Description

See DPMI Overview.

This function simulates a real-mode far call to a function that returns with a far return. The registers are set up from regs, including `CS` and `IP`, which indicate the address of the call. Any registers the function modifies are reflected in regs on return.

If `SS` and `SP` are both zero, a small temporary stack is used when in real mode. If not, they are used as is. It's a good idea to use `memset` to initialize the register structure before using it.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    _go32_dpmi_registers r;
    r.x.ax = 47;
    r.x.cs = some_segment;
    r.x.ip = some_offset;
    r.x.ss = r.x.sp = 0;
    _go32_dpmi_simulate_fcall(&r);
    printf("returns %d\n", r.x.ax);

Node:_go32_dpmi_simulate_fcall_iret, Next:_go32_dpmi_simulate_int, Previous:_go32_dpmi_simulate_fcall, Up:Alphabetical List

## _go32_dpmi_simulate_fcall_iret

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_simulate_fcall_iret(_go32_dpmi_registers *regs);

### Description

See DPMI Overview.

This function simulates a real-mode far call to a function that returns with an `iret` instruction. The registers are set up from regs, including `CS` and `IP`, which indicate the address of the call. Any registers the function modifies are reflected in regs on return.

If `SS` and `SP` are both zero, a small temporary stack is used when in real mode. If not, they are used as is. It's a good idea to use `memset` to initialize the register structure before using it.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    _go32_dpmi_registers r;
    r.x.ax = 47;
    r.x.cs = some_segment;
    r.x.ip = some_offset;
    r.x.ss = r.x.sp = 0;
    _go32_dpmi_simulate_fcall_iret(&r);
    printf("returns %d\n", r.x.ax);

Node:_go32_dpmi_simulate_int, Next:_go32_info_block, Previous:_go32_dpmi_simulate_fcall_iret, Up:Alphabetical List

## _go32_dpmi_simulate_int

### Syntax

    #include <dpmi.h>

    int _go32_dpmi_simulate_int(int vector, _go32_dpmi_registers *regs);

### Description

See DPMI Overview.

This function simulates a real-mode interrup. The registers are set up from regs, including `CS` and `IP`, which indicate the address of the call. Any registers the function modifies are reflected in regs on return.

If `SS` and `SP` are both zero, a small temporary stack is used when in real mode. If not, they are used as is. It's a good idea to use `memset` to initialize the register structure before using it.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    _go32_dpmi_registers r;
    r.h.ah = 0x08;
    r.h.dl = 0x80; /* drive C: */
    r.x.ss = r.x.sp = 0;
    _go32_dpmi_simulate_int(0x13, &r);
    printf("disk is %d cyl, %d head, %d sect\n",
           r.h.ch | ((r.x.cl<<2)&0x300),
           r.h.dh, r.h.cl & 0x3f));

Node:_go32_info_block, Next:_go32_interrupt_stack_size, Previous:_go32_dpmi_simulate_int, Up:Alphabetical List

## _go32_info_block

### Syntax

    #include <go32.h>

    extern __Go32_Info_Block _go32_info_block;

### Description

The go32 information block is a mechanism for `go32` to pass information to the application. Some of this information is generally useful, such as the pid or the transfer buffer, while some is used internally to `libc.a` only.

The structure has this format:

    typedef struct {
      unsigned long  size_of_this_structure_in_bytes;
      unsigned long  linear_address_of_primary_screen;
      unsigned long  linear_address_of_secondary_screen;
      unsigned long  linear_address_of_transfer_buffer;
      unsigned long  size_of_transfer_buffer;
      unsigned long  pid;
      unsigned char  master_interrupt_controller_base;
      unsigned char  slave_interrupt_controller_base;
      unsigned short selector_for_linear_memory;
      unsigned long  linear_address_of_stub_info_structure;
      unsigned long  linear_address_of_original_psp;
      unsigned short run_mode;
      unsigned short run_mode_info;
    } Go32_Info_Block;

The linear address fields provide values that are suitable for `dosmemget`, `dosmemput`, and `movedata`. The selector_for_linear_memory is suitable for `<sys/farptr.h>` selector parameters.

Due to the length of these fields, and their popularity, the following macros are available:

`_dos_ds`
  This expands to _go32_info_block.selector_for_linear_memory
`__tb`
  This expands to _go32_info_block.linear_address_of_transfer_buffer

The `run_mode` field indicates the mode that the program is running in. The following modes are defined:

`_GO32_RUN_MODE_UNDEF`
  This indicates that the extender did not (or could not) determine or provide the mode information. The most probable reason is that it's an older extender that does not support this field. The program should not assume anything about the run mode if it is this value.
`_GO32_RUN_MODE_RAW`
  This indicates that no CPU manager is being used, and no XMS manager is present. The CPU is being managed directly from the extender, and memory was allocated from the extended memory pool.
`_GO32_RUN_MODE_XMS`
  This indicates that the extender is managing the CPU, but an XMS driver is managing the memory pool.
`_GO32_RUN_MODE_VCPI`
  This indicates that a VCPI server (like `emm386` or `qemm`) is managing both the CPU and the memory.
`_GO32_RUN_MODE_DPMI`
  This indicates that a DPMI server (like `qdpmi` or Windows) is managing both the CPU and memory. Programs may rely on this value to determine if it is safe to use DPMI 0.9 functions.

  If this value is set, the `run_mode_info` field has the DPMI specification version, in hex, shifted eight bits. For example, DPMI 0.9 has 0x005A in the `run_mode_info` field.

Note that the program should not assume that the value will be one of the listed values. If the program is running with an extender that provides some other mode (say, a newly released extender) then the program should be able to handle that case gracefully.

### Portability

not ANSI, not POSIX

### Example

    dosmemget(_go32_info_block.linear_address_of_primary_screen, 80*25*2, buf);

Node:_go32_interrupt_stack_size, Next:_go32_my_cs, Previous:_go32_info_block, Up:Alphabetical List

## _go32_interrupt_stack_size

### Syntax

    #include <dpmi.h>

    extern unsigned long _go32_interrupt_stack_size;

### Description

The default size of the interrupt handler's stack. Defaults to 32k.

### Portability

not ANSI, not POSIX

Node:_go32_my_cs, Next:_go32_my_ds, Previous:_go32_interrupt_stack_size, Up:Alphabetical List

## _go32_my_cs

### Syntax

    #include <go32.h>

    u_short _go32_my_cs();

### Description

Returns the current `CS`. This is useful for setting up interrupt vectors and such.

### Return Value

`CS`

### Portability

not ANSI, not POSIX

Node:_go32_my_ds, Next:_go32_my_ss, Previous:_go32_my_cs, Up:Alphabetical List

## _go32_my_ds

### Syntax

    #include <go32.h>

    u_short _go32_my_ds();

### Description

Returns the current `DS`. This is useful for moving memory and such.

### Return Value

`DS`

### Portability

not ANSI, not POSIX

Node:_go32_my_ss, Next:_go32_rmcb_stack_size, Previous:_go32_my_ds, Up:Alphabetical List

## _go32_my_ss

### Syntax

    #include <go32.h>

    u_short _go32_my_ss();

### Description

Returns the current `SS`. This is useful for moving memory and such.

### Return Value

`SS`

### Portability

not ANSI, not POSIX

Node:_go32_rmcb_stack_size, Next:_go32_want_ctrl_break, Previous:_go32_my_ss, Up:Alphabetical List

## _go32_rmcb_stack_size

### Syntax

    #include <dpmi.h>

    extern unsigned long _go32_rmcb_stack_size;

### Description

The default size of the real mode callback handler's stack. Defaults to 32k.

### Portability

not ANSI, not POSIX

Node:_go32_want_ctrl_break, Next:_go32_was_ctrl_break_hit, Previous:_go32_rmcb_stack_size, Up:Alphabetical List

## _go32_want_ctrl_break

### Syntax

    #include <go32.h>

    void   _go32_want_ctrl_break(int yes);

### Description

This function tells go32 whether or not it wants `Ctrl-Break` to be an exception or passed to the application. If you pass a nonzero value for yes, pressing `Ctrl-Break` will set a flag that can be detected with `_go32_was_ctrl_break_hit` (see _go32_was_ctrl_break_hit). If you pass zero for yes, when you press `Ctrl-Break` the program will be terminated.

Note that if you call `_go32_was_ctrl_break_hit`, this function automatically gets called to ask for `Ctrl-Break` events.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    _g32_want_ctrl_break(1);
    do_something_long();
    _g32_want_ctrl_break(0);

Node:_go32_was_ctrl_break_hit, Next:gotoxy, Previous:_go32_want_ctrl_break, Up:Alphabetical List

## _go32_was_ctrl_break_hit

### Syntax

    #include <go32.h>

    unsigned _go32_was_ctrl_break_hit(void);

### Description

This function returns the number of times that `Ctrl-Break` was hit since the last call to this function or `_go32_want_ctrl_break` (see _go32_want_ctrl_break).

### Return Value

Zero if `Ctrl-Break` hasn't been hit, nonzero to indicate how many times if it has been hit.

Note that `_go32_want_ctrl_break` is automatically called to request these events, so you don't have to set up for this call.

### Portability

not ANSI, not POSIX

### Example

    while (!_go32_was_ctrl_break_hit())
      do_something();

Node:gotoxy, Next:gppconio_init, Previous:_go32_was_ctrl_break_hit, Up:Alphabetical List

## gotoxy

### Syntax

    #include <conio.h>

    void gotoxy(int x, int y);

### Description

Move the cursor to row y, column x. The upper left corner of the current window is (1,1).

### Portability

not ANSI, not POSIX

Node:gppconio_init, Next:hasmntopt, Previous:gotoxy, Up:Alphabetical List

## gppconio_init

### Syntax

    #include <conio.h>

    void gppconio_init(void);

### Description

Initialize the screen. This is called automatically at program start-up if you use any of the `conio` functions, but there may be times when you need to call it again, typically after calling some video BIOS function which affects screen parameters.

### Portability

not ANSI, not POSIX

Node:hasmntopt, Next:highvideo, Previous:gppconio_init, Up:Alphabetical List

## hasmntopt

### Syntax

    #include <mntent.h>

    char *hasmntopt(const struct mntent *mnt, const char *opt);

### Description

This function scans the `mnt_opts` field of the `mntent` structure pointed to by mnt for a substring that matches opt. See getmntent.

### Return Value

This function returns the address of the substring if a match is found, or `NULL` otherwise.

### Portability

not ANSI, not POSIX

Node:highvideo, Next:htonl, Previous:hasmntopt, Up:Alphabetical List

## highvideo

### Syntax

    #include <conio.h>

    void highvideo(void);

### Description

Causes any new characters put on the screen to be bright.

### Portability

not ANSI, not POSIX

Node:htonl, Next:htons, Previous:highvideo, Up:Alphabetical List

## htonl

### Syntax

    #include <netinet/in.h>

    unsigned long htonl(unsigned long val);

### Description

This function converts from host formatted longs to network formatted longs. For the i386 and higher processors, this means that the bytes are swapped from 1234 order to 4321 order.

### Return Value

The network-order value.

### Portability

not ANSI, not POSIX

### Example

    packet.ipaddr = htonl(ip);

Node:htons, Next:hypot, Previous:htonl, Up:Alphabetical List

## htons

### Syntax

    #include <netinet/in.h>

    unsigned short htons(unsigned short val);

### Description

This function converts from host formatted shorts to network formatted shorts. For the i386 and higher processors, this means that the bytes are swapped from 12 order to 21 order.

### Return Value

The network-order value.

### Portability

not ANSI, not POSIX

### Example

    tcp.port = htons(port);

Node:hypot, Next:inb, Previous:htons, Up:Alphabetical List

## hypot

### Syntax

    #include <math.h>

    double hypot(double x, double y);

### Description

This function computes `sqrt(x*x + y*y)`, the length of a hypotenuse of a right triangle whose shorter sides are x and y. In other words, it computes the Euclidean distance between the points `(0,0)` and `(x,y)`. Since the computation is done in extended precision, there is no danger of overflow or underflow when squaring the arguments, whereas direct computation of `sqrt(x*x + y*y)` could cause overflow or underflow for extreme (very large or very small) values of x and y.

### Return Value

The value of `sqrt(x*x + y*y)`. If both arguments are finite, but the result is so large that it would overflow a `double`, the return value is `Inf`, and `errno` is set to `ERANGE`. If one of the arguments is `Inf`, the return value is `Inf` and the value of `errno` is left unchanged. If one of the arguments is `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:inb, Next:index, Previous:hypot, Up:Alphabetical List

## inb

### Syntax

    #include <pc.h>

    unsigned char inb(unsigned short _port);

### Description

Calls inportb. Provided only for compatibility.

### Portability

not ANSI, not POSIX

Node:index, Next:initstate, Previous:inb, Up:Alphabetical List

## index

### Syntax

    #include <strings.h>

    char *index(const char *string, int ch);

### Description

Returns a pointer to the first occurrence of ch in string. Note that the `NULL` character counts, so if you pass zero as ch you'll get a pointer to the end of the string back.

### Return Value

A pointer to the character, or `NULL` if it wasn't found.

### Portability

not ANSI, not POSIX

### Example

    if (index(path, '*'))
      do_wildcards(path);

Node:initstate, Next:inp, Previous:index, Up:Alphabetical List

## initstate

### Syntax

    #include <stdlib.h>

    char *initstate(unsigned seed, char *arg_state, int n);

### Description

Initializes the random number generator (see random) with pointer arg_state to array of n bytes, then calls `srandom` with seed.

### Return Value

Pointer to old state information.

### Portability

not ANSI, not POSIX

Node:inp, Next:inportb, Previous:initstate, Up:Alphabetical List

## inp

### Syntax

    #include <pc.h>

    unsigned char inp(unsigned short _port);

### Description

Calls inportb. Provided only for compatibility.

### Portability

not ANSI, not POSIX

Node:inportb, Next:inportl, Previous:inp, Up:Alphabetical List

## inportb

### Syntax

    #include <pc.h>

    unsigned char inportb(unsigned short _port);

### Description

Read a single 8-bit I/O port.

This function is provided as an inline assembler macro, and will be optimized down to a single opcode when you optimize your program.

### Return Value

The value returned through the port.

### Portability

not ANSI, not POSIX

Node:inportl, Next:inportsb, Previous:inportb, Up:Alphabetical List

## inportl

### Syntax

    #include <pc.h>

    unsigned long inportl(unsigned short _port);

### Description

This function reads a single 32-bit I/O port.

This function is provided as an inline assembler macro, and will be optimized down to a single opcode when you optimize your program.

### Return Value

The value returned from the port.

### Portability

not ANSI, not POSIX

Node:inportsb, Next:inportsl, Previous:inportl, Up:Alphabetical List

## inportsb

### Syntax

    #include <pc.h>

    void inportsb(unsigned short _port, unsigned char *_buf, unsigned _len);

### Description

Reads the 8-bit _port _len times, and stores the bytes in buf.

### Portability

not ANSI, not POSIX

Node:inportsl, Next:inportsw, Previous:inportsb, Up:Alphabetical List

## inportsl

### Syntax

    #include <pc.h>

    void inportsl(unsigned short _port, unsigned long *_buf, unsigned _len);

### Description

Reads the 32-bit _port _len times, and stores the bytes in buf.

### Portability

not ANSI, not POSIX

Node:inportsw, Next:inportw, Previous:inportsl, Up:Alphabetical List

## inportsw

### Syntax

    #include <pc.h>

    void inportsw(unsigned short _port, unsigned short *_buf, unsigned _len);

### Description

Reads the 16-bit _port _len times, and stores the bytes in buf.

### Portability

not ANSI, not POSIX

Node:inportw, Next:inpw, Previous:inportsw, Up:Alphabetical List

## inportw

### Syntax

    #include <pc.h>

    unsigned short inportw(unsigned short _port);

### Description

Read a single 16-bit I/O port.

This function is provided as an inline assembler macro, and will be optimized down to a single opcode when you optimize your program.

### Return Value

The value returned through the port.

### Portability

not ANSI, not POSIX

Node:inpw, Next:insline, Previous:inportw, Up:Alphabetical List

## inpw

### Syntax

    #include <pc.h>

    unsigned short inpw(unsigned short _port);

### Description

Calls inportw. Provided only for compatibility.

### Portability

not ANSI, not POSIX

Node:insline, Next:insque, Previous:inpw, Up:Alphabetical List

## insline

### Syntax

    #include <conio.h>

    void insline(void);

### Description

A blank line is inserted at the current cursor position. The previous line and lines below it scroll down.

### Portability

not ANSI, not POSIX

Node:insque, Next:int386, Previous:insline, Up:Alphabetical List

## insque

### Syntax

    #include <search.h>

    void insque(struct qelem *elem, struct qelem *pred);

### Description

This function manipulates queues built from doubly linked lists. Each element in the queue must be in the form of `struct qelem` which is defined thus:

    struct qelem {
      struct qelem *q_forw;
      struct qelem *q_back;
      char q_data[0];
    }

This function inserts elem in a queue immediately after pred.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:int386, Next:int386x, Previous:insque, Up:Alphabetical List

## int386

### Syntax

    #include <dos.h>

    int int386(int ivec, union REGS *in, union REGS *out);

### Description

This function is equal to `int86` function. See int86, for further description.

### Return Value

The returned value of `EAX`.

### Portability

not ANSI, not POSIX

Node:int386x, Next:int86, Previous:int386, Up:Alphabetical List

## int386x

### Syntax

    #include <dos.h>

    int int386x(int ivec, union REGS *in, union REGS *out, struct SREGS *seg);

### Description

This function is equal to `int86x`. See int86, for further description.

### Return Value

The value of `EAX` is returned.

### Portability

not ANSI, not POSIX

Node:int86, Next:int86x, Previous:int386x, Up:Alphabetical List

## int86

### Syntax

    #include <dos.h>

    int int86(int ivec, union REGS *in, union REGS *out);

### Description

The `union REGS` is defined by `<dos.h>` as follows:

    struct DWORDREGS {
      unsigned long edi;
      unsigned long esi;
      unsigned long ebp;
      unsigned long cflag;
      unsigned long ebx;
      unsigned long edx;
      unsigned long ecx;
      unsigned long eax;
      unsigned short eflags;
    };

    struct DWORDREGS_W {
      unsigned long di;
      unsigned long si;
      unsigned long bp;
      unsigned long cflag;
      unsigned long bx;
      unsigned long dx;
      unsigned long cx;
      unsigned long ax;
      unsigned short flags;
    };

    struct WORDREGS {
      unsigned short di, _upper_di;
      unsigned short si, _upper_si;
      unsigned short bp, _upper_bp;
      unsigned short cflag, _upper_cflag;
      unsigned short bx, _upper_bx;
      unsigned short dx, _upper_dx;
      unsigned short cx, _upper_cx;
      unsigned short ax, _upper_ax;
      unsigned short flags;
    };

    struct BYTEREGS {
      unsigned short di, _upper_di;
      unsigned short si, _upper_si;
      unsigned short bp, _upper_bp;
      unsigned long cflag;
      unsigned char bl;
      unsigned char bh;
      unsigned short _upper_bx;
      unsigned char dl;
      unsigned char dh;
      unsigned short _upper_dx;
      unsigned char cl;
      unsigned char ch;
      unsigned short _upper_cx;
      unsigned char al;
      unsigned char ah;
      unsigned short _upper_ax;
      unsigned short flags;
    };

    union REGS {
      struct DWORDREGS d;
    #ifdef _NAIVE_DOS_REGS
      struct WORDREGS x;
    #else
    #ifdef _BORLAND_DOS_REGS
      struct DWORDREGS x;
    #else
      struct DWORDREGS_W x;
    #endif
    #endif
      struct WORDREGS w;
      struct BYTEREGS h;
    };

Note: The `.x.` branch is a problem generator. Most programs expect the `.x.` branch to have e.g. "`.x.ax`" members, and that they are 16-bit. If you know you want 32-bit values, use the `.d.eax` members. If you know you want 16-bit values, use the `.w.ax` members. The `.x.` members behave according to `#defines`, as follows:

`default`
  If you specify no `#define`, the `.x.` branch has "`ax`" members and is 32-bit. This is compatible with previous versions of djgpp.
`_NAIVE_DOS_REGS`
  This define gives you `.x.ax`, but they are 16-bit. This is probably what most programs ported from 16-bit dos compilers will want.
`_BORLAND_DOS_REGS`
  This define gives you `.x.eax` which are 32-bit. This is compatible with Borland's 32-bit compilers.

This function simulates a software interrupt. Note that, unlike the `__dpmi_int` function, requests that go through `int86` and similar functions are specially processed to make them suitable for invoking real-mode interrupts from protected-mode programs. For example, if a particular routine takes a pointer in `BX`, `int86` expects you to put a (protected-mode) pointer in `EBX`. Therefore, `int86` should have specific support for every interrupt and function you invoke this way. Currently, it supports only a subset of all available interrupts and functions:

1) All functions of any interrupt which expects only scalar arguments registers (i.e., no pointers to buffers).

2) In addition, the following functions of interrupt 21h are supported: 9, 39h, 3Ah, 3Bh, 3Ch, 3Dh, 3Fh, 40h, 41h, 43h, 47h, 56h.

When the interrupt is invoked, the CPU registers are copied from in. After the interrupt, the CPU registers are copied to out.

This function is just like `int86x` (see int86x) except that suitable default values are used for the segment registers.

See also int86x, intdos, and bdos.

### Return Value

The returned value of `EAX`.

### Portability

not ANSI, not POSIX

### Example

    union REGS r;
    r.x.ax = 0x0100;
    r.h.dl = 'c';
    int86(0x21, &r, &r);

Node:int86x, Next:intdos, Previous:int86, Up:Alphabetical List

## int86x

### Syntax

    #include <dos.h>

    int int86x(int ivec, union REGS *in, union REGS *out, struct SREGS *seg);

### Description

This function is just like `int86` (see int86) except that values you pass in SREGS are used for the segment registers instead of the defaults.

See also int86, intdos, and bdos.

### Return Value

The value of `EAX` is returned.

### Portability

not ANSI, not POSIX

### Example

    union REGS r;
    struct SREGS s;
    r.h.ah = 0x31;
    r.h.dl = 'c';
    r.x.si = si_val;
    s.ds = ds_val;
    int86x(0x21, &r, &r, &s);

Node:intdos, Next:intdosx, Previous:int86x, Up:Alphabetical List

## intdos

### Syntax

    #include <dos.h>

    int intdos(union REGS *in, union REGS *out);

### Description

This function is just like `int86` (see int86x) except that the interrupt vector is 0x21.

### Return Value

`EAX`

### Portability

not ANSI, not POSIX

Node:intdosx, Next:intensevideo, Previous:intdos, Up:Alphabetical List

## intdosx

### Syntax

    #include <dos.h>

    int intdosx(union REGS *in, union REGS *out, struct SREGS *s);

### Description

This function is just like `int86x` (see int86x) except that the interrupt vector is 0x21.

### Return Value

`EAX`

### Portability

not ANSI, not POSIX

Node:intensevideo, Next:_invent_inode, Previous:intdosx, Up:Alphabetical List

## intensevideo

### Syntax

    #include <conio.h>

    void intensevideo(void);

### Description

Bit 7 (`MSB`) of the character attribute byte has two possible effects on EGA and VGA displays: it can either make the character blink or change the background color to bright (thus allowing for 16 background colors as opposed to the usual 8). This function sets that bit to display bright background colors. After a call to this function, every character written to the screen with bit 7 of the attribute byte set, will have a bright background color. The companion function `blinkvideo` (see blinkvideo) has the opposite effect.

Note that there is no BIOS function to get the current status of this bit, but bit 5 of the byte at `0040h:0065h` in the BIOS area indicates the current state: if it's 1 (the default), blinking characters will be displayed.

### Portability

not ANSI, not POSIX

Node:_invent_inode, Next:ioctl (DOS), Previous:intensevideo, Up:Alphabetical List

## _invent_inode

### Syntax

    ino_t
    _invent_inode(const char *name, unsigned time_stamp, unsigned long fsize)

### Description

This invents an inode number for those files which don't have valid DOS cluster number. These could be:

- devices like `/dev/null` or file system extensions (see File System Extensions)
- empty files which were not allocated disk space yet
- or files on networked drives, for which the redirector doesn't bring the cluster number.

To ensure proper operation of this function, you must call it with a filename in some canonical form. E.g., with a name returned by `truename()` (see _truename), or that returned by `_fixpath()` (see _fixpath). The point here is that the entire program must abide by these conventions through its operation, or else you risk getting different inode numbers for the same file.

### Return Value

0 on error, otherwise the invented inode number for the file

### Portability

not ANSI, not POSIX

Node:ioctl (DOS), Next:ioctl (General description), Previous:_invent_inode, Up:Alphabetical List

## ioctl (DOS)

The DOSish version of `ioctl` performs an interrupt 0x21, function 0x44. It takes care of supplying transfer buffers in low address regions, if they are needed. For an exhaustive description of the various commands and subcommands, see Ralf Brown's interrupt list.

It is highly recommended to use only the DOS_* functions listed in `sys/ioctl.h`.

### Syntax

    #include <sys/ioctl.h>

    int ioctl(int fd, int cmd, ... );

### Description

The parameter `fd` must refer to a file descriptor for character device functions, or the number of a block device (usually current=0, A:=1, ...).

The following constants can be used for the `cmd` parameter:

`DOS_GETDEVDATA`
  Get device information. Returns the device information word from `DX`. The call to `ioctl` should look like this:

       int ret_val = ioctl (fd, DOS_GETDEVDATA);

  For another way of achieving the same effect, see _get_dev_info.

`DOS_SETDEVDATA`
  Set device information. Returns the new device information word form `DX` or -1. The call to `ioctl` should look like this:

       int ret_val = ioctl (fd, DOS_SETDEVDATA, 0, dev_info);

`DOS_RCVDATA`
  Read from character device control channel. After `cmd` must follow the number of requested bytes to read and a pointer to a buffer. Returns the number of bytes actually read or -1 on error. The call to `ioctl` should look like this:

       unsigned char buf[bytes_to_read];
       int ret_val = ioctl (fd, DOS_RCVDATA, bytes_to_read, &buf);

`DOS_SNDDATA`
  Write to character device control channel. After `cmd` must follow the number of bytes to write and a pointer to a buffer holding the data. Returns the number of bytes actually written. An example of a call:

       unsigned char buf[bytes_to_write];
       int ret_val = ioctl (fd, DOS_SNDDATA, bytes_to_write, &buf);

`DOS_RCVCTLDATA`
  Read from block device control channel. See `DOS_RCVDATA`.
`DOS_SNDCTLDATA`
  Write to block device control channel. See `DOS_SNDDATA`.
`DOS_CHKINSTAT`
  Check the input status of a file. Returns 0 if not ready of at EOF, `0xff` if file is ready. Here's an example of how to call:

       int ret_val = ioctl (fd, DOS_CHKINSTAT);

  A more portable way of doing this is by calling `select`. See select.

`DOS_CHKOUTSTAT`
  Check the output status of a file. Returns 0 if not ready of at EOF, `0xff` if file is ready. `select` (see select) is another, more portable way of doing the same.
`DOS_ISCHANGEABLE`
  Check if a block device is changeable. Returns 0 for removable or 1 for fixed. An example of a call:

       int ret_val = ioctl (fd, DOS_ISCHANGEABLE);

`DOS_ISREDIRBLK`
  Check if a block device is remote o local. The function `_is_remote_drive` (see _is_remote_drive) is another way of returning the same info.
`DOS_ISREDIRHND`
  Check if a file handle refers to a local or remote device. See _is_remote_handle for another way of doing this.
`DOS_SETRETRY`
  Set the sharing retry count. The first extra parameter specifies the pause between retries, the second number of retries. An example:

       int ret_val = ioctl (fd, DOS_SETRETRY, pause_between_retries, max_retries);

`DOS_GENCHARREQ`
  Generic character device request. Example:

       int ret_val = ioctl (fd, DOS_GENCHARREQ, category_and_function,
                            &param_block, si_value, di_value, param_block_size);

  Refer to Ralf Brown's Interrupt List for the details about each function and relevant parameter block layout.

`DOS_GENBLKREQ`
  Generic block device request. Example of the call:

       int ret_val = ioctl (drive_no, DOS_GENBLKREQ, category_and_function,
                            &param_block, si_value, di_value, param_block_size);

  Note that instead of the handle, the first argument is the disk drive number (0 = default, 1 = A:, etc.).

`DOS_GLDRVMAP`
  Get logical drive map. A call like the following:

       int ret_val = ioctl (drive_no, DOS_GLDRVMAP);

  will return 0 if the block device has only one logical drive assigned, or a number in the range 1..26 which is the last drive numer used to reference that drive (1 = A:, etc.). Thus, on a machine which has a single floppy drive, calling `ioctl (1, DOS_GLDRVMAP);` will return 2 if the floppy was last refered to as B:. This function and the next one can be used together to prevent DOS from popping the ugly prompt saying "Insert diskette for drive B: and press any key when ready".

`DOS_SLDRVMAP`
  Set logical drive map. For example, a call like this:

       ioctl (1, DOS_SLDRVMAP);

  will cause drive A: to be mapped to drive B:.

`DOS_QGIOCTLCAPH`
  Query generic ioctl capability (handle). Test if a handle supports ioctl functions beyond those in the standard DOS 3.2 set. Call like this:

       int ret_val = ioctl (fd, DOS_QGIOCTLCAPH, category_and_function);

  This will return zero if the specified IOCTL function is supported, 1 if not.

`DOS_QGIOCTLCAPD`
  Query generic ioctl capability (drive). Test if a drive supports ioctl functions beyond those in the standard DOS 3.2 set. Used same as DOS_QGIOCTLCAPH, but the first argument is a drive number (0 = default, 1 = A:, etc.), not a handle.

If your specific device driver requires different commands, they must be or'ed together with the flags listed in `<sys/ioctl.h>` to tell the drive about transfer buffers and what to return.

### Return Value

See description above.

### Device information word

The bits of the device information word have the following meaning:\\ Character device:

14 Device driver can process IOCTL request

13 output until busy supported

11 driver supports OPEN/CLOSE calls

7 set (indicates device)

6 EOF on input

5 raw (binary) mode

4 device is special (uses INT 29)

3 clock device

2 NUL device

1 standard output

0 standard input

Disk file:

15 file is remote (DOS 3.0+)

14 don't set file date/time on closing (DOS 3.0+)

11 media not removable

8 (DOS 4 only) generate INT 24 if no disk space on write or read past end of file

7 clear (indicates file)

6 file has not been written

5-0 drive number (0 = A:)

### Example

    #include <sys/ioctl.h>
    int main(int argc, char **argv){
       char buf[6];
       short *s;

       open(fd,"EMMQXXX0",O_RDONLY);
       mybuf[0] = '\0';
       s = mybuf;
       ioctl(fd,DOS_SNDDATA,6, (int) &mybuf);
       if(*s ==0x25 )printf("EMM386 >= 4.45\n");
       mybuf[0]='\x02';
       ioctl(fd,DOS_SNDDATA,2,(int )&mybuf);
       printf("EMM Version %d.%d\n",(int )mybuf[0],(int) mybuf[1]);
       close(fd);
    }

Node:ioctl (General description), Next:ioctl (UNIX), Previous:ioctl (DOS), Up:Alphabetical List

## ioctl (General description)

`ioctl` performs low level calls to communicate with device drivers. As there are lots of different device drivers, no really general description is possible.

The DJGPP version tries to cope with two different flavors of `ioctl`, a DOSish and a UNIXish way. To distinguish between DOS-like and UNIX-like calls, all valid DOS commands have all 3 MSB set to 0, the UNIX command have at least one of the 3 MSB set to 1.

Node:ioctl (UNIX), Next:_is_executable, Previous:ioctl (General description), Up:Alphabetical List

## ioctl (UNIX)

The UNIX version first checks if an FSE handler is associated to the file descriptor. If so, it calls the handler in the usual way File System Extensions. Otherwise it sets errno to `ENOTTY` and returns -1.

As this part is still under development, it should not be used exhaustively.

Node:_is_executable, Next:_is_remote_drive, Previous:ioctl (UNIX), Up:Alphabetical List

## _is_executable

### Syntax

    #include <sys/stat.h>

    int _is_executable(const char *path, int fhandle, const char *extension);

### Description

This function determines if a file is executable under DOS/DJGPP environment. The file may be given either by its path or its file handle fhandle. If extension is non-NULL and non-empty, it is used first to look up in a list of known extensions which determine whether the file is executable. (If the `_STAT_EXEC_EXT` bit of the `_djstat_flags` global variable (see _djstat_flags) is not set, this step is skipped.) If extension is unavailable or not enough to determine the result, the first 2 bytes of the file are checked to contain one of the known magic numbers identifying the file as executable. If the file's 2 first bytes need to be read but the read fails, 0 is returned and errno is set. (The file is only searched for magic number if the `_STAT_EXEC_MAGIC` bit of the `_djstat_flags` variable is set.)

Note that if `_STAT_EXEC_MAGIC` is set, but `_STAT_EXEC_EXT` is not, some files which shouldn't be flagged as executables (e.g., COFF `*.o` object files) will have their execute bit set, because they have the magic number signature at their beginning. Therefore, only use the above combination if you want to debug the list of extensions provided in `is_exec.c` file from the library sources.

If the file passed by its handle was open as write-only, and the extension alone isn't enough to determine whether the file is executable, then this function returns 0, because it cannot look at the magic number.

This function is used internally by `f?stat`; you are not supposed to call it directly.

### Return Value

1 for executable file, 0 otherwise (including in case of errors in accessing the file).

### Portability

not ANSI, not POSIX

Node:_is_remote_drive, Next:_is_remote_handle, Previous:_is_executable, Up:Alphabetical List

## _is_remote_drive

### Syntax

    int _is_remote_drive(int drv);

### Description

Given the drive number in drv (A: = 0, B: = 1, etc.), this function returns non-zero if the drive is treated by DOS as a remote (networked) drive, or zero otherwise. It does so by calling subfunction 09h of the DOS IOCTL function (interrupt 21h, AX=4409h) and looking at bit 12 of the device attribute word returned in the DX register.

Note that DOS treats CD-ROM drives as remote.

### Return Value

Zero for local drives, non-zero for remote and CD-ROM drives.

### Portability

not ANSI, not POSIX

Node:_is_remote_handle, Next:isalnum, Previous:_is_remote_drive, Up:Alphabetical List

## _is_remote_handle

### Syntax

    int _is_remote_handle(int fhandle);

### Description

Given the file handle of an open file in fhandle, this function returns non-zero if the drive where that file resides is treated by DOS as a remote (networked) drive, or zero otherwise. It does so by calling subfunction 0Ah of the DOS IOCTL function (interrupt 21h, AX=440Ah) and looking at bit 15 of the device attribute word returned in the DX register.

Note that DOS treats CD-ROM drives as remote.

### Return Value

Zero for files on local drives, non-zero for files on remote and CD-ROM drives.

### Portability

not ANSI, not POSIX

Node:isalnum, Next:isalpha, Previous:_is_remote_handle, Up:Alphabetical List

## isalnum

### Syntax

    #include <ctype.h>

    int isalnum(int c);

### Description

Tells if c is any letter or digit.

### Return Value

Nonzero if c is a letter or digit, else zero.

### Portability

ANSI, POSIX

Node:isalpha, Next:isascii, Previous:isalnum, Up:Alphabetical List

## isalpha

### Syntax

    #include <ctype.h>

    int isalpha(int c);

### Description

Tells if c is a letter.

### Return Value

Nonzero if c is a letter, else zero.

### Portability

ANSI, POSIX

Node:isascii, Next:isatty, Previous:isalpha, Up:Alphabetical List

## isascii

### Syntax

    #include <ctype.h>

    int isascii(int c);

### Description

Tells if c is an ASCII character (0x00 to 0x7f).

### Return Value

Nonzero if c is ASCII, else zero.

### Portability

not ANSI, not POSIX

Node:isatty, Next:iscntrl, Previous:isascii, Up:Alphabetical List

## isatty

### Syntax

    #include <unistd.h>

    int isatty(int fd);

### Description

Tells if the file descriptor refers to a terminal device or not.

### Return Value

Nonzero if fd is a terminal device, zero otherwise.

### Portability

not ANSI, POSIX

### Example

    if (isatty(1))
      fflush(stdout);

Node:iscntrl, Next:isdigit, Previous:isatty, Up:Alphabetical List

## iscntrl

### Syntax

    #include <ctype.h>

    int iscntrl(int c);

### Description

Tells if c is a control character.

### Return Value

Nonzero if c is a control character, else zero.

### Portability

ANSI, POSIX

Node:isdigit, Next:isgraph, Previous:iscntrl, Up:Alphabetical List

## isdigit

### Syntax

    #include <ctype.h>

    int isdigit(int c);

### Description

Tells if c is a digit.

### Return Value

Nonzero if c is a digit, else zero.

### Portability

ANSI, POSIX

Node:isgraph, Next:islower, Previous:isdigit, Up:Alphabetical List

## isgraph

### Syntax

    #include <ctype.h>

    int isgraph(int c);

### Description

Tells if c is a visible printing character. Space is not included.

### Return Value

Nonzero if c is a visible printing character, else zero.

### Portability

ANSI, POSIX

Node:islower, Next:isprint, Previous:isgraph, Up:Alphabetical List

## islower

### Syntax

    #include <ctype.h>

    int islower(int c);

### Description

Tells if c is lower case or not.

### Return Value

Nonzero if c is lower case, else zero.

### Portability

ANSI, POSIX

Node:isprint, Next:ispunct, Previous:islower, Up:Alphabetical List

## isprint

### Syntax

    #include <ctype.h>

    int isprint(int c);

### Description

Tells if c is a printing character, which includes the space character.

### Return Value

Nonzero if c is a printing character, else zero.

### Portability

ANSI, POSIX

Node:ispunct, Next:isspace, Previous:isprint, Up:Alphabetical List

## ispunct

### Syntax

    #include <ctype.h>

    int ispunct(int c);

### Description

Tells if c is any printing character except space and those indicated by `isalnum`.

### Return Value

Nonzero if c is punctuation, else zero.

### Portability

ANSI, POSIX

Node:isspace, Next:isupper, Previous:ispunct, Up:Alphabetical List

## isspace

### Syntax

    #include <ctype.h>

    int isspace(int c);

### Description

Tells if c is whitespace, that is, carriage return, newline, form feed, tab, vertical tab, or space.

### Return Value

Nonzero if c is whitespace, else zero.

### Portability

ANSI, POSIX

Node:isupper, Next:isxdigit, Previous:isspace, Up:Alphabetical List

## isupper

### Syntax

    #include <ctype.h>

    int isupper(int c);

### Description

Tells if c is an upper case character or not.

### Return Value

Nonzero if c is upper case, else zero.

### Portability

ANSI, POSIX

Node:isxdigit, Next:itoa, Previous:isupper, Up:Alphabetical List

## isxdigit

### Syntax

    #include <ctype.h>

    int isxdigit(int c);

### Description

Tells if c is a valid hexadecimal digit or not. This includes `[0-9a-fA-F]`.

### Return Value

Nonzero if c is a hex digit, else zero.

### Portability

ANSI, POSIX

Node:itoa, Next:kbhit, Previous:isxdigit, Up:Alphabetical List

## itoa

### Syntax

    #include <stdlib.h>

    char * itoa(int value, char *string, int radix)

### Description

This function converts its argument value into a null-terminated character string using radix as the base of the number system. The resulting string with a length of upto 33 bytes (including the optional sign and the terminating `NULL` is put into the buffer whose address is given by string. For radixes other than 10, value is treated as an unsigned int (i.e., the sign bit is not interpreted as such). The argument radix should specify the base, between 2 and 36, in which the string reprsentation of value is requested.

### Return Value

A pointer to string.

### Portability

not ANSI, not POSIX

### Example

    char binary_str[33];

    (void)itoa(num, binary_str, 2);

Node:kbhit, Next:kill, Previous:itoa, Up:Alphabetical List

## kbhit

### Syntax

    #include <pc.h>

    int kbhit(void);

### Description

If the user has hit a key, this function will detect it. This function is very fast when there is no key waiting, so it may be used inside loops as needed.

If you test shift/alt/ctrl status with bios calls (e.g., using `bioskey (2)` or `bioskey (0x12)`) then you should also use bios calls for testing for keys. This can be done with by `bioskey (1)` or `bioskey (0x11)`. Failing to do so can cause trouble in multitasking environments like DESQview/X.

### Return Value

Nonzero if a key has been hit, else zero.

### Portability

not ANSI, not POSIX

### Example

    while (!kbhit())
      do_stuff();

Node:kill, Next:labs, Previous:kbhit, Up:Alphabetical List

## kill

### Syntax

    #include <signal.h>

    int	kill(pid_t _pid, int _sig);

### Description

If _pid is the current `getpid()`, the given _sig is raised with raise.

### Return Value

-1 on error, else zero.

### Portability

not ANSI, POSIX

Node:labs, Next:ldexp, Previous:kill, Up:Alphabetical List

## labs

### Syntax

    #include <stdlib.h>

    long labs(long x);

### Description

This function takes the absolute value of x. See abs.

### Return Value

|x|

### Portability

ANSI, POSIX

Node:ldexp, Next:ldiv, Previous:labs, Up:Alphabetical List

## ldexp

### Syntax

    #include <math.h>

    double ldexp(double val, int exp);

### Description

This function computes val*2^exp.

### Return Value

val*2^exp. `ldexp(0., exp)` returns 0 for all values of `exp`, without setting `errno`. For non-zero values of val, `errno` is set to `ERANGE` if the result cannot be accurately represented by a `double`, and the return value is then the nearest representable `double` (possibly, an `Inf`). If val is a `NaN` or `Inf`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

### Example

    ldexp(3.5,4) == 3.5 * (2^4) == 56.0

Node:ldiv, Next:_lfn_gen_short_fname, Previous:ldexp, Up:Alphabetical List

## ldiv

### Syntax

    #include <stdlib.h>

    ldiv_t ldiv(long numerator, long denominator);

### Description

Returns the quotient and remainder of the division numerator divided by denominator. The return type is as follows:

    typedef struct {
      long quot;
      long rem;
    } ldiv_t;

### Return Value

The results of the division are returned.

### Portability

ANSI, POSIX

### Example

    ldiv_t l = ldiv(42, 3);
    printf("42 = %ld x 3 + %ld\n", l.quot, l.rem);

    ldiv(+40, +3) = { +13, +1 }
    ldiv(+40, -3) = { -13, -1 }
    ldiv(-40, +3) = { -13, -1 }
    ldiv(-40, -3) = { +13, -1 }

Node:_lfn_gen_short_fname, Next:_lfn_get_ftime, Previous:ldiv, Up:Alphabetical List

## _lfn_gen_short_fname

### Syntax

    #include <fcntl.h>

    char * _lfn_gen_short_fname (const char *long_fname, char *short_fname);

### Description

This function generates a short (8+3) filename alias for the long filename pointed to by long_fname and puts it into the buffer pointed to by short_fname. It uses the same algorithm that Windows 9x uses, with the exception that the returned short name will never have a numeric tail, because this function doesn't check the directory to see whether the generated short name will collide with any other file in the directory. Note that long_fname must contain only the name part of a file; elements of a full pathname (like `:` or `/` are not allowed (they will cause the function to fail). short_fname will be returned upper-cased, since that is how 8+3 filenames are stored in directory entries.

When the LFN API is not supported (see _use_lfn), the function simply converts up to 12 characters of long_fname to upper-case and returns that. It will do the same if long_fname includes any characters illegal in a filename.

You might need to call this function if you want to know whether a given filename is valid on MSDOS: if a case-sensitive string comparison function such as `strcmp` (see strcmp) returns a 0 when it compares the original long filename with the short one returned by `_lfn_gen_short_fname`, then the filename is a valid DOS name. (Note that if long_fname is in lower case, it might not compare equal with short_fname because of the case difference.)

### Return value

The function returns a pointer to short_fname.

### Portability

not ANSI, not POSIX

### Example

    #include <stdio.h>
    #include <string.h>
    #include <fcntl.h>

    int dos_check (char *fname)
    {
      char fshort[13];
      int retval;

      if (stricmp (_lfn_gen_short_fname (fname, fshort), fname) == 0)
      {
        printf ("%s is a valid MSDOS 8+3 filename\n", fname);
        retval = 1;
      }
      else
      {
        printf ("%s will have to be changed for MSDOS\n", fname);
        retval = 0;
      }
      return retval;
    }

Node:_lfn_get_ftime, Next:__libc_termios_init, Previous:_lfn_gen_short_fname, Up:Alphabetical List

## _lfn_get_ftime

### Syntax

    #include <fcntl.h>

    char _lfn_get_ftime (int fhandle, int flag);

### Description

This function returns creation and access time for files that reside on a filesystem which supports long filenames (such as Windows 95). Files which reside on native FAT filesystems will cause this function to fail. The fhandle parameter is the file handle as returned by one of the functions which open or create files. The flag parameter determines which time (creation or access) is returned. It can be set to one of the following:

`_LFN_ATIME`
  Causes `_lfn_get_ftime` to return the time when the file was last accessed. (Currently, it actually only returns the date of last access; the time bits are all zeroed.)
`_LFN_CTIME`
  Causes `_lfn_get_ftime` to return the time when the file was created. Note that if the file was created by a program which doesn't support long filenames, this time will be zero.

### Return value

The file time stamp, as a packed unsigned int value:

`Bits 0-4`
  seconds divided by 2
`Bits 5-10`
  minutes (0-59)
`Bits 11-15`
  hours (0-23)
`Bits 16-20`
  day of the month (1-31)
`Bits 21-24`
  month (1 = January)
`Bits 25-31`
  year offset from 1980 (add 1980 to get the actual year)

If the underlying system calls fail, the function will return 0 and set `errno` to an appropriate value.

### Portability

not ANSI, not POSIX

### Example

     unsigned file_stamp = _lfn_get_ftime (handle, _LFN_CTIME);

Node:__libc_termios_init, Next:libm, Previous:_lfn_get_ftime, Up:Alphabetical List

## __libc_termios_init

### Syntax

    #include <libc/ttyprvt.h>

    void __libc_termios_init (void);

### Description

This function sets read/write hooks for the termios emulation and import parameters. Currently importing parameters is not supported, the emulation is resolved by only internal(static) parameters. Note that this function is called by tcXXX function automatically.

### Portability

not ANSI, not POSIX

Node:libm, Next:link, Previous:__libc_termios_init, Up:Alphabetical List

## libm

### Syntax

    #include <libm/math.h>

    enum fdversion {fdlibm_ieee = -1, fdlibm_svid, fdlibm_xopen, fdlibm_posix};

    #define _LIB_VERSION_TYPE enum fdversion
    #define _LIB_VERSION _fdlib_version

    extern  _LIB_VERSION_TYPE  _LIB_VERSION;

    #define _IEEE_  fdlibm_ieee
    #define _SVID_  fdlibm_svid
    #define _XOPEN_ fdlibm_xopen
    #define _POSIX_ fdlibm_posix

    _LIB_VERSION_TYPE _LIB_VERSION = _IEEE_;

### Description

The alternate math library, `libm.a`, originally written by Cygnus support, provides versions of mathematical functions which comply to several different standards of behavior in abnormal cases, and are sometimes more accurate than those included in the default `libc.a` library, in particular when elaborate argument reduction is required to avoid precision loss. Functions in `libm.a` allow to create programs with well-defined and standard-compliant behavior when numerical errors occur, and provide the application with a means to control their behavior in abnormal cases via the `matherr` callback. They almost never rely on the features specific to the x87 FPU, and are thus slower and sometimes slightly less accurate than the functions from `libc.a`.

In contrast, the functions in the default `libc.a` library are written for maximum speed and exploitation of the x87 FPU features, do not call `matherr`, and are therefore much faster and sometimes more accurate (due to the extended 80-bit precision with which the x87 FPU carries its calculations).

Another aspect of differences between functions in `libc.a` and in `libm.a` is the value returned when the result overflows a `double`. The functions from `libc.a` always return a suitably signed infinity, `Inf`, whereas for functions from `libm.a` an application can arrange for a large but finite value to be returned. Getting finite return values might be important in certain kinds of mathematical computations where the special rules defined for infinities (e.g., Inf + a = Inf) might be inappropriate.

Refer to Math, for detailed documentation of the individual functions from `libm.a`. This section explains the general setup of using those functions from DJGPP programs.

To use the alternate math library with your program, you need to do the following:

- Include the header `<libm/math.h>`. Alternatively, you can include `<math.h>` as usual and compile with `-D_USE_LIBM_MATH_H` option to `gcc`, which will cause it to use `libm/math.h` instead of the default `math.h`. (The second possibility leaves the source ANSI-compliant.)
- Set the global variable `_fdlib_version` to a value other than the default `_IEEE_`. The possible values are listed and explained below.
- At the beginning of your `main` function, set the FPU to a predictable state by calling `_clear87` (see _clear87) and `_fpreset` (see _fpreset) library functions. (Another possibility is to make these calls in a function declared with `__attribute__((constructor))`, so it will be called before `main`.)
- Link your program with the `libm.a` library, e.g. by specifying `-lm` on the link command line.

The functions in `libm.a` can emulate different standards. You can select to which standard your program will comply by setting the global variable `_fdlib_version` (or the macro `_LIB_VERSION` which evaluates to it) to one of the values below. This will only affect the behavior of the math functions when an error is signaled by the FPU.

`_IEEE_`
  The default value, specifies IEEE-compliant operation. In case of an error, this version will immediately return whatever result is computed by the FPU, and will not set `errno`. If the result overflows, an `Inf` is returned. This version gives the fastest code.
`_POSIX_`
  In case of an error, this version will set `errno` to the appropriate value (`EDOM` or `ERANGE`) and return to the caller, without calling the `matherr` function (see matherr). If the result overflows, an `Inf` is returned. This version should be used for maximum POSIX- and ANSI-compliance.
`_SVID_`
  This version is compliant with the System V Interface Definition. This is the slowest version. In case of an error, it calls the `matherr` function (see matherr), which can be customized to the specific application needs. If `matherr` returns zero, a message is printed to the standard error stream which states the name of the function that generated the error and the error type, and `errno` is set. If `matherr` returns non-zero, there will be no message and `errno` will be left unaltered. If the result overflows, this version returns `HUGE`, a large but finite value defined by `libm/math.h`.
`_XOPEN_`
  Complies to the X/Open specifications. It behaves exactly like `_SVID_`, but it never prints an error message, even if `matherr` returns zero, and `Inf` us returned when a result overflows.

### Portability

not ANSI, not POSIX

### Example

    /*  Testing errno == EDOM after sqrt(-1).

        !!!  MUST compile with -lm  !!!  */

    #include <assert.h>
    #include <errno.h>
    #include <stdio.h>
    #include <libm/math.h>	/* or #define _USE_LIBM_MATH_H and #include <math.h> */
    #include <float.h>

    /* Setting _LIB_VERSION to anything but _IEEE_ will turn on errno handling. */
    _LIB_VERSION_TYPE _LIB_VERSION = _POSIX_;

    int main (void)
    {
      /* Reset the FPU (possible previous FP problems).  */
      _clear87 ();
      _fpreset ();

      /* Run the test.  */
      errno = 0;
      assert(errno == 0);
      sqrt(-1.0);
      assert(errno == EDOM); /* this line should NOT cause the assertion to fail */

      return(0);
    }

Node:link, Next:llabs, Previous:libm, Up:Alphabetical List

## link

### Syntax

    #include <unistd.h>

    int link(const char *exists, const char *new);

### Description

Because of limitations of MS-DOS, this function doesn't really link two files together. However, it simulates a real `link` by copying the file at exists to new.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

### Example

    link("foo.c", "foo.bak");

Node:llabs, Next:lldiv, Previous:link, Up:Alphabetical List

## llabs

### Syntax

    #include <stdlib.h>

    long long llabs(long long x);

### Description

This function takes the absolute value of x. See abs.

### Return Value

|x|

### Portability

not ANSI, not POSIX

Node:lldiv, Next:load_npx, Previous:llabs, Up:Alphabetical List

## lldiv

### Syntax

    #include <stdlib.h>

    lldiv_t lldiv(long long numerator, long long denominator);

### Description

Returns the quotient and remainder of the division numerator divided by denominator. The return type is as follows:

    typedef struct {
      long long quot;
      long long rem;
    } lldiv_t;

### Return Value

The results of the division are returned.

### Portability

not ANSI, not POSIX

### Example

    lldiv_t l = lldiv(42, 3);
    printf("42 = %lld x 3 + %lld\n", l.quot, l.rem);

    lldiv(+40, +3) = { +13, +1 }
    lldiv(+40, -3) = { -13, -1 }
    lldiv(-40, +3) = { -13, -1 }
    lldiv(-40, -3) = { +13, -1 }

Node:load_npx, Next:localeconv, Previous:lldiv, Up:Alphabetical List

## load_npx

### Syntax

    #include <debug/dbgcom.h>

    extern NPX npx;
    void load_npx (void);

### Description

This function restores the state of the x87 numeric processor from the data saved in the external variable `npx`. This variable is a structure defined as follows in the header `debug/dbgcom.h`:

    typedef struct {
      unsigned short sig0;
      unsigned short sig1;
      unsigned short sig2;
      unsigned short sig3;
      unsigned short exponent:15;
      unsigned short sign:1;
    } NPXREG;

    typedef struct {
      unsigned long control;
      unsigned long status;
      unsigned long tag;
      unsigned long eip;
      unsigned long cs;
      unsigned long dataptr;
      unsigned long datasel;
      NPXREG reg[8];
      long double st[8];
      char st_valid[8];
      long double mmx[8];
      char in_mmx_mode;
      char top;
    } NPX;

`load_npx` should be called immediately after `run_child` (see run_child) is called to begin or resume the debugged program, and provided that a call to `save_npx` was issued before `run_child` was called. See save_npx.

### Portability

not ANSI, not POSIX

### Example

     save_npx ();
     run_child ();
     load_npx ();

Node:localeconv, Next:localtime, Previous:load_npx, Up:Alphabetical List

## localeconv

### Syntax

    #include <locale.h>

    struct lconv *localeconv(void);

### Description

This function returns a pointer to a static structure that contains information about the current locale. The structure contains these fields:

`char *currency_symbol`
  A string that should be used when printing local currency.
`char *decimal_point`
  A string that is used to separate the integer and fractional portions of real numbers in `printf`. Currently, only the first character is significant.
`char *grouping`
  An array of numbers indicating the size of groupings for non-monetary values to the left of the decimal point. The first number is the size of the grouping just before the decimal point. A number of zero means to repeat the previous number indefinitely. A number of `CHAR_MAX` means to group the remainder of the digits together.
`char *int_curr_symbol`
  A string that should be used when formatting monetary values for local currency when the result will be used internationally.
`char *mon_decimal_point`
  A string that separates the interger and fractional parts of monetary values.
`char *mon_grouping`
  Same as grouping, but for monetary values.
`char *negative_sign`
  A string that is used to represent negative monetary values.
`char *positive_sign`
  A string that is used to represent positive monetary values.
`char *thousands_sep`
  The grouping separator for non-monetary values.
`char frac_digits`
  The number of digits to the right of the decimal point for monetary values.
`char int_frac_digits`
  Like frac_digits, but when formatting for international use.
`char n_cs_precedes`
  If nonzero, the currency string should precede the monetary value if the monetary value is negative.
`char n_sep_by_space`
  If nonzero, the currency string and the monetary value should be separated by a space if the monetary value is negative.
`char n_sign_posn`
  Determines the placement of the negative indication string if the monetary value is negative.
  0
    ($value), (value$)
  1
    -$value, -value$
  2
    $value-, value$-
  3
    -$value, value-$
  4
    $-value, value$-
`char p_cs_precedes`
`char p_sep_by_space`
`char p_sign_posn`
  These are the same as n_*, but for when the monetary value is positive.

Note that any numeric field may have a value of `CHAR_MAX`, which indicates that no information is available.

### Return Value

A pointer to the `struct lconv` structure.

### Portability

ANSI, POSIX

### Example

    struct lconv *l = localeconv;
    printf("%s%d\n", l->negative_sign, value);

Node:localtime, Next:lock, Previous:localeconv, Up:Alphabetical List

## localtime

### Syntax

    #include <time.h>

    struct tm *localtime(const time_t *tod);

### Description

Converts the time represented by tod into a structure, correcting for the local timezone. See gmtime, for the description of `struct tm`.

### Return Value

A pointer to a static structure which is overwritten with each call.

### Portability

ANSI, POSIX

Node:lock, Next:log, Previous:localtime, Up:Alphabetical List

## lock

### Syntax

    #include <io.h>

    int lock(int fd, long offset, long length);

### Description

Locks a region in file fd using MS-DOS file sharing interface. The region of length bytes, starting from offset, will become entirely inaccessible to other processes. If multiple locks are used on a single file they must be non-overlapping. The lock must be removed before the file is closed.

This function will fail unless SHARE, or a network software providing similar interface, is installed. This function is compatible with Borland C++ function of the same name.

See unlock.

### Return Value

Zero if successful, nonzero if not.

### Portability

not ANSI, not POSIX

Node:log, Next:log10, Previous:lock, Up:Alphabetical List

## log

### Syntax

    #include <math.h>

    double log(double x);

### Description

This function computes the natural logarithm of x.

### Return Value

The natural logarithm of x. If x is zero, a negative infinity is returned and `errno` is set to `ERANGE`. If x is negative or `+Inf` or a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:log10, Next:log1p, Previous:log, Up:Alphabetical List

## log10

### Syntax

    #include <math.h>

    double log10(double x);

### Description

This function computes the base-10 logarithm of x.

### Return Value

The logarithm base 10 of x. If x is zero, a negative infinity is returned and `errno` is set to `ERANGE`. If x is negative or `+Inf` or a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:log1p, Next:log2, Previous:log10, Up:Alphabetical List

## log1p

### Syntax

    #include <math.h>

    double log1p(double x);

### Description

This function computes the natural logarithm of 1 + x. It is more accurate than `log(1 + x)` for small values of x.

### Return Value

The natural logarithm of 1 + x. If x is -1, a negative infinity is returned and `errno` is set to `ERANGE`. If x is less than -1 or `+Inf` or a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:log2, Next:longjmp, Previous:log1p, Up:Alphabetical List

## log2

### Syntax

    #include <math.h>

    double log2(double x);

### Description

This function computes the base-2 logarithm of x.

### Return Value

The base-2 logarithm of x. If x is zero, a negative infinity is returned and `errno` is set to `ERANGE`. If x is negative or `+Inf` or a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:longjmp, Next:lowvideo, Previous:log2, Up:Alphabetical List

## longjmp

### Syntax

    #include <setjmp.h>

    void longjmp(jmp_buf env, int val);

### Description

This function reverts back to a CPU state that was stored in env by `setjmp` (see setjmp). The state includes all CPU registers, so any variable in a register when `setjmp` was called will be preserved, and all else will be indeterminate.

The value passed as val will be the return value of `setjmp` when it resumes processing there. If val is zero, the return value will be one.

### Return Value

This function does not return.

### Portability

ANSI, POSIX

### Example

    jmp_buf j;
    if (setjmp(j))
      return;
    do_something();
    longjmp(j, 1);

Node:lowvideo, Next:lseek, Previous:longjmp, Up:Alphabetical List

## lowvideo

### Syntax

    #include <conio.h>

    void    lowvideo(void);

### Description

Causes any new characters put on the screen to be dim.

### Portability

not ANSI, not POSIX

Node:lseek, Next:malloc, Previous:lowvideo, Up:Alphabetical List

## lseek

### Syntax

    #include <unistd.h>

    off_t lseek(int fd, off_t offset, int whence);

### Description

This function moves the file pointer for handle fd according to whence:

`SEEK_SET`
  The file pointer is moved to the offset specified.
`SEEK_CUR`
  The file pointer is moved offset bytes relative to its current position.
`SEEK_END`
  The file pointer is moved to a position offset bytes from the end of the file. The value of offset is usually nonpositive in this case.

### Return Value

The new offset is returned.

### Portability

not ANSI, POSIX

### Example

    lseek(fd, 12, SEEK_CUR); /* skip 12 bytes */

Node:malloc, Next:matherr, Previous:lseek, Up:Alphabetical List

## malloc

### Syntax

    #include <stdlib.h>

    void *malloc(size_t size);

### Description

This function allocates a chunk of memory from the heap large enough to hold any object that is size bytes in length. This memory must be returned to the heap with `free` (see free).

Note: this version of malloc is designed to reduce memory usage. A faster but less efficient version is available in the libc sources (djlsr*.zip) in src/libc/ansi/stdlib/fmalloc.c

### Return Value

A pointer to the allocated memory, or `NULL` if there isn't enough free memory to satisfy the request.

### Portability

ANSI, POSIX

### Example

    char *c = (char *)malloc(100);

Node:matherr, Next:mblen, Previous:malloc, Up:Alphabetical List

## matherr

### Syntax

    #include <libm/math.h>

    enum fdversion _fdlib_version = _SVID_;

    int matherr(struct exception *exc);

### Description

`matherr` is a user-definable handler for errors in math library functions. It is only supported in the alternate math library (link with `-lm`), and will only be called if the global variable `_fdlib_version` is set to either `_SVID_` or `_XOPEN_` (see libm). You also need to mask the Invalid Operation exception in the x87 control word (see _control87) or install a handler for signal `SIGFPE` (see signal), or else some exceptions will generate `SIGFPE` and your program will be terminated before it gets a chance to call `matherr`. DJGPP versions 2.02 and later mask all FP exceptions at startup, so this consideration applies only to programs that unmask FP exceptions at run time.

If the above conditions are met, every math function will call `matherr` when a numerical exception is detected. The default version of `matherr`, supplied with `libm.a`, does nothing and returns zero (the `_SVID_` version will then print an error message to the standard error stream and set `errno`).

This default behavior is inappropriate in some cases. For example, an interactive program which runs in a windowed environment might want the error message to go to a particular window, or pop up a dialog box; a fault-tolerant program might want to fall back to backup procedures so that meaningful results are returned to the application code, etc. In such cases, you should include your own version of `matherr` in your program.

`matherr` is called with a single argument exc which is a pointer to a structure defined on `<libm/math.h>` like this:

    struct exception {
    	int type;
    	char *name;
    	double arg1, arg2, retval;
    };

The member `type` is an integer code describing the type of exception that has occured. It can be one of the following:

`DOMAIN`
  Argument(s) are outside the valid function domain (e.g., `log(-1)`).
`SING`
  Argument(s) would result in a singularity (e.g., `log(0)`).
`OVERFLOW`
  The result causes overflow, like in `exp(10000)`.
`UNDERFLOW`
  The result causes underflow, like in `exp(-10000)`.
`TLOSS`
  The result loses all significant digits, like in `sin(10e100)`.

These codes are defined on `<libm/math.h>`.

The member `name` points to the string that is the name of the function which generated the exception. The members `arg1` and `arg2` are the values of the arguments with which the function was called (`arg2` is undefined if the function only accepts a single argument). The member `retval` is set to the default value that will be returned by the math library function; `matherr` can change it to return a different value.

### Return Value

`matherr` should return zero if it couldn't handle the exception, or non-zero if the exception was handled.

If `matherr` returns zero, under `_SVID_` version an error message is printed which includes the name of the function and the exception type, and under `_SVID_` and `_XOPEN_` `errno` is set to an appropriate value. If `matherr` returns non-zero, no error message is printed and `errno` is left unchanged.

### Portability

not ANSI, not POSIX

### Example

      #include <libm/math.h>

      int matherr(register struct exception *x)
      {
        switch (x->type) {
          case DOMAIN:
            /* change sqrt to return sqrt(-arg1), not NaN */
            if (!strcmp(x->name, "sqrt")) {
              x->retval = sqrt(-x->arg1);
              return 1; /* be silent: no message, don't set errno */
            } /* FALL THROUGH */
          case SING:
            /* all other domain or sing exceptions, print message and abort */
            fprintf(stderr, "domain exception in %s\n", x->name);
            abort();
            break;
        }
        return 0; /* all other exceptions, execute default procedure */
      }

Node:mblen, Next:mbstowcs, Previous:matherr, Up:Alphabetical List

## mblen

### Syntax

    #include <stdlib.h>

    int mblen(const char *s, size_t n);

### Description

This function returns the number of characters of string s that make up the next multibyte character. No more than n characters are checked.

If s is `NULL`, the internal shift state is reset.

### Return Value

The number of characters that comprise the next multibyte character.

### Portability

ANSI, POSIX

### Example

    int n = mblen(string, INT_MAX);
    string += n;

Node:mbstowcs, Next:mbtowc, Previous:mblen, Up:Alphabetical List

## mbstowcs

### Syntax

    #include <stdlib.h>

    size_t mbstowcs(wchar_t *wcs, const char *s, size_t n);

### Description

Converts a multibyte string to a wide character string. The result will be no more than n wide characters.

### Return Value

The number of wide characters stored.

### Portability

ANSI, POSIX

### Example

    int wlen = mbtowcs(wbuf, string, sizeof(wbuf)/sizeof(wchar_t));

Node:mbtowc, Next:memccpy, Previous:mbstowcs, Up:Alphabetical List

## mbtowc

### Syntax

    #include <stdlib.h>

    int mbtowc(wchar_t *pwc, const char *s, size_t n);

### Description

Convert the first multibyte sequence in s to a wide character. At most n characters are checked. If pwc is not `NULL`, the result is stored there. If s is null, the internal shift state is reset.

### Return Value

The number of characters used by the multibyte sequence.

### Portability

ANSI, POSIX

### Example

    string += mbtowc(&wc, string, strlen(string));

Node:memccpy, Next:memchr, Previous:mbtowc, Up:Alphabetical List

## memccpy

### Syntax

    #include <string.h>

    void * memccpy(void *to, const void *from, int ch, size_t nbytes)

### Description

This function copies characters from memory area from into to, stopping after the first occurrence of character ch has been copied, or after nbytes characters have been copied, whichever comes first. The buffers should not overlap.

### Return Value

A pointer to the character after the copy of ch in to, or a `NULL` pointer if ch was not found in the first nbytes characters of from.

### Portability

not ANSI, not POSIX

### Example

    char inpbuf[256], dest[81];

    printf("Enter a path: ");
    fflush(stdout);
    gets(inpbuf);
    memset(dest, 0, sizeof(dest));
    if (memccpy(dest, inpbuf, '\\', 80))
      printf("The first directory in path is %s\n", dest);
    else
      printf("No explicit directory in path\n");

Node:memchr, Next:memcmp, Previous:memccpy, Up:Alphabetical List

## memchr

### Syntax

    #include <string.h>

    void *memchr(const void *string, int ch, size_t num);

### Description

This function searches num bytes starting at string, looking for the first occurence of ch.

### Return Value

A pointer to the first match, or `NULL` if it wasn't found.

### Portability

ANSI, POSIX

### Example

    if (memchr(path, '/', strlen(path))
      do_slash();

Node:memcmp, Next:memcpy, Previous:memchr, Up:Alphabetical List

## memcmp

### Syntax

    #include <string.h>

    int memcmp(const void *s1, const void *s2, size_t num);

### Description

This function compares two regions of memory, at s1 and s2, for num bytes.

### Return Value

zero
  s1 == s2
positive
  s1 > s2
negative
  s1 < s2

### Portability

ANSI, POSIX

Node:memcpy, Next:memicmp, Previous:memcmp, Up:Alphabetical List

## memcpy

### Syntax

    #include <string.h>

    void *memcpy(void *dest, const void *src, int num);

### Description

This function copies num bytes from source to dest. It assumes that the source and destination regions don't overlap; if you need to copy overlapping regions, use `memmove` instead. See memmove.

### Return Value

dest

### Portability

ANSI, POSIX

### Example

    memcpy(buffer, temp_buffer, BUF_MAX);

Node:memicmp, Next:memmove, Previous:memcpy, Up:Alphabetical List

## memicmp

### Syntax

    #include <string.h>

    int memicmp(const void *s1, const void *s2, size_t num);

### Description

This function compares two regions of memory, at s1 and s2, for num bytes, disregarding case.

### Return Value

Zero if they're the same, nonzero if different, the sign indicates "order".

### Portability

not ANSI, not POSIX

### Example

    if (memicmp(arg, "-i", 2) == 0)   /* '-I' or '-include' etc. */
      do_include();

Node:memmove, Next:memset, Previous:memicmp, Up:Alphabetical List

## memmove

### Syntax

    #include <string.h>

    void *memmove(void *dest, const void *source, int num);

### Description

This function copies num bytes from source to dest. The copy is done in such a way that if the two regions overlap, the source is always read before that byte is changed by writing to the destination.

### Return Value

dest

### Portability

ANSI, POSIX

### Example

    memmove(buf+1, buf, 99);
    memmove(buf, buf+1, 99);

Node:memset, Next:mkdir, Previous:memmove, Up:Alphabetical List

## memset

### Syntax

    #include <string.h>

    void *memset(void *buffer, int ch, size_t num);

### Description

This function stores num copies of ch, starting at buffer. This is often used to initialize objects to a known value, like zero.

Note that, although ch is declared `int` in the prototype, `memset` only uses its least-significant byte to fill buffer.

### Return Value

buffer

### Portability

ANSI, POSIX

### Example

    struct tm t;
    memset(&t, 0, sizeof(t));

Node:mkdir, Next:mkfifo, Previous:memset, Up:Alphabetical List

## mkdir

### Syntax

    #include <sys/stat.h>

    int mkdir(const char *path, mode_t mode);

### Description

This function creates a subdirectory.

All the bits except `S_IWUSR` in the mode argument are ignored under MS-DOS. If `S_IWUSR` is not set in mode, the directory is created with read-only attribute bit set. Note that DOS itself ignores the read-only bit of directories, but some programs do not.

### Return Value

Zero if the subdirectory was created, nonzero on failure.

### Portability

not ANSI, POSIX

### Example

    mkdir("/usr/tmp", S_IWUSR);

Node:mkfifo, Next:mknod, Previous:mkdir, Up:Alphabetical List

## mkfifo

### Syntax

    #include <sys/stat.h>

    int mkfifo(const char *path, mode_t mode);

### Description

This function is provided only to assist in porting from Unix. It always returns an error condition.

### Portability

not ANSI, POSIX

Node:mknod, Next:mkstemp, Previous:mkfifo, Up:Alphabetical List

## mknod

### Syntax

    #include <sys/stat.h>

    int mknod(const char *path, mode_t mode, dev_t dev);

### Description

This function is provided to assist in porting from Unix. If mode specifies a regular file, `mknod` creates a file using path as its name. If mode specifies a character device, and if the device whose name is given by path exists and its device specification as returned by `stat` or `fstat` is equal to dev, `mknod` returns -1 and sets `errno` to `EEXIST`. In all other cases, -1 is returned `errno` is set to `EACCES`.

The argument dev is ignored if mode does not specify a character device.

### Return Value

Zero on success, -1 on failure.

### Portability

not ANSI, not POSIX

Node:mkstemp, Next:mktemp, Previous:mknod, Up:Alphabetical List

## mkstemp

### Syntax

    #include <stdio.h>

    int mkstemp(char *template);

### Description

template is a file specification that ends with six trailing `X` characters. This function replaces the `XXXXXX` with a set of characters such that the resulting file name names a nonexisting file. It then creates and opens the file in a way which guarantees that no other process can access this file.

Note that since MS-DOS is limited to eight characters for the file name, and since none of the `X`'s get replaced by a dot, you can only have two additional characters before the `X`'s.

Note also that the path you give will be modified in place.

### Return Value

The open file descriptor.

### Portability

not ANSI, not POSIX

### Example

    char path[100];
    strcpy(path, "/tmp/ccXXXXXX");
    int fd = mkstemp(path);

Node:mktemp, Next:mktime, Previous:mkstemp, Up:Alphabetical List

## mktemp

### Syntax

    #include <stdio.h>

    char *mktemp(char *template);

### Description

template is a file specification that ends with six trailing `X` characters. This function replaces the `XXXXXX` with a set of characters such that the resulting file name names a nonexisting file.

Note that since MS-DOS is limited to eight characters for the file name, and since none of the `X`'s get replaced by a dot, you can only have two additional characters before the `X`'s.

### Return Value

The resulting filename.

### Portability

not ANSI, not POSIX

### Example

    char template[] = "/tmp/ccXXXXXX";
    mktemp(template);
    FILE *q = fopen(template, "w");

Node:mktime, Next:modf, Previous:mktemp, Up:Alphabetical List

## mktime

### Syntax

    #include <time.h>

    time_t mktime(struct tm *tptr);

### Description

This function converts a time structure into the number of seconds since 00:00:00 GMT 1/1/1970. It also attempts to normalize the fields of tptr. The layout of a `struct tm` is as follows:

    struct tm {
      int    tm_sec;    /* seconds after the minute [0-60] */
      int    tm_min;    /* minutes after the hour [0-59] */
      int    tm_hour;   /* hours since midnight [0-23] */
      int    tm_mday;   /* day of the month [1-31] */
      int    tm_mon;    /* months since January [0-11] */
      int    tm_year;   /* years since 1900 */
      int    tm_wday;   /* days since Sunday [0-6] */
      int    tm_yday;   /* days since January 1 [0-365] */
      int    tm_isdst;  /* Daylight Savings Time flag */
      long   tm_gmtoff; /* offset from GMT in seconds */
      char * tm_zone;   /* timezone abbreviation */
    };

If you don't know whether daylight saving is in effect at the moment specified by the contents of tptr, set the `tm_isdst` member to -1, which will cause `mktime` to compute the DST flag using the data base in the `zoneinfo` subdirectory of your main DJGPP installation. This requires that you set the environment variable `TZ` to a file in that directory which corresponds to your geographical area.

### Return Value

The resulting time, or -1 if the time in tptr cannot be described in that format.

### Portability

ANSI, POSIX

Node:modf, Next:modfl, Previous:mktime, Up:Alphabetical List

## modf

### Syntax

    #include <math.h>

    double modf(double x, double *pint);

### Description

`modf` breaks down x into its integer portion (which it stores in *pint) and the remaining fractional portion, which it returns. Both integer and fractional portions have the same sign as x, except if x is a negative zero, in which case the integer part is a positive zero.

### Return Value

The fractional portion. If x is `Inf` or `NaN`, the return value is zero, the integer portion stored in *pint is the same as the value of x, and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:modfl, Next:_mono_clear, Previous:modf, Up:Alphabetical List

## modfl

### Syntax

    #include <math.h>

    long double modf(long double x, long double *pint);

### Description

`modfl` breaks down x into its integer portion (which it stores in *pint) and the remaining fractional portion, which it returns.

### Return Value

The fractional portion.

### Portability

not ANSI, not POSIX

Node:_mono_clear, Next:_mono_printf, Previous:modfl, Up:Alphabetical List

## _mono_clear

### Syntax

    #include <sys/mono.h>

    void _mono_clear(void);

### Description

Clears the monochrome monitor.

### Portability

not ANSI, not POSIX

Node:_mono_printf, Next:_mono_putc, Previous:_mono_clear, Up:Alphabetical List

## _mono_printf

### Syntax

    #include <sys/mono.h>

    void _mono_printf(const char *fmt, ...);

### Description

Like printf, but prints to the monochrome monitor.

### Portability

not ANSI, not POSIX

Node:_mono_putc, Next:movedata, Previous:_mono_printf, Up:Alphabetical List

## _mono_putc

### Syntax

    #include <sys/mono.h>

    void _mono_putc(int c);

### Description

Prints a single character to the monochrome monitor.

### Portability

not ANSI, not POSIX

Node:movedata, Next:movedatab, Previous:_mono_putc, Up:Alphabetical List

## movedata

### Syntax

    #include <sys/movedata.h>

    void movedata(unsigned source_selector, unsigned source_offset,
                  unsigned dest_selector, unsigned dest_offset,
                  size_t length);

### Description

This function allows the caller to directly transfer information between conventional and linear memory, and among each as well. The selectors passed are not segment values like in DOS. They are protected mode selectors that can be obtained by the `_my_ds` and `_go32_info_block.selector_for_linear_memory` (or just `_dos_ds`) functions (_my_ds, _go32_info_block). The offsets are linear offsets. If the selector is for the program's data area, this offset corresponds to the address of a buffer (like `(unsigned)&something`). If the selector is for the conventional memory area, the offset is the physical address of the memory, which can be computed from a traditional segment/offset pair as `segment`*16+`offset`. For example, the color text screen buffer is at offset 0xb8000.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    short blank_row_buf[ScreenCols()];
    /* scroll screen */
    movedata(_dos_ds, 0xb8000 + ScreenCols()*2,
             _dos_ds, 0xb8000,
             ScreenCols() * (ScreenRows()-1) * 2);
    /* fill last row */
    movedata(_my_ds(), (unsigned)blank_row_buf,
             _dos_ds, 0xb8000 + ScreenCols()*(ScreenRows()-1)*2,
              ScreenCols() * 2);

Node:movedatab, Next:movedatal, Previous:movedata, Up:Alphabetical List

## movedatab

### Syntax

    #include <sys/movedata.h>

    void _movedatab(unsigned, unsigned, unsigned, unsigned, size_t);

### Description

Just like movedata, but all transfers are always 8-bit transfers.

### Portability

not ANSI, not POSIX

Node:movedatal, Next:movedataw, Previous:movedatab, Up:Alphabetical List

## movedatal

### Syntax

    #include <sys/movedata.h>

    void _movedatal(unsigned, unsigned, unsigned, unsigned, size_t);

### Description

Just like movedata, but all transfers are always 32-bit transfers, and the count is a count of transfers, not bytes.

### Portability

not ANSI, not POSIX

Node:movedataw, Next:movetext, Previous:movedatal, Up:Alphabetical List

## movedataw

### Syntax

    #include <sys/movedata.h>

    void _movedataw(unsigned, unsigned, unsigned, unsigned, size_t);

### Description

Just like movedata, but all transfers are always 16-bit transfers, and the count is a count of transfers, not bytes.

### Portability

not ANSI, not POSIX

Node:movetext, Next:mprotect, Previous:movedataw, Up:Alphabetical List

## movetext

### Syntax

    #include <conio.h>

    int movetext(int _left, int _top, int _right, int _bottom,
                 int _destleft, int _desttop);

### Description

Moves a block of text on the screen.

### Return Value

1 on success, zero on error.

### Portability

not ANSI, not POSIX

Node:mprotect, Next:_my_cs, Previous:movetext, Up:Alphabetical List

## mprotect

### Syntax

    #include <sys/types.h>
    #include <sys/mman.h>

    int mprotect(void *addr, size_t len, int prot);

### Description

This function modifies the access protection of a memory region. Protection occurs in 4Kbyte regions (pages) aligned on 4Kbyte boundaries. All pages in the region will be changed, so addr and len should be multiples of 4096.

The protection prot for each page is specified with the values: PROT_NONE Region can not be touched (if or'ed is ignored). PROT_READ Region can be read (can be or'ed with PROT_WRITE). PROT_WRITE Region can be written (implies read access).

This function is only supported on DPMI hosts which provide some V1.0 extensions on V0.9 memory blocks.

### Return Value

The function returns 0 if successful and the value -1 if all the pages could not be set.

### Portability

not ANSI, not POSIX

### Example

    mprotect(readonly_buffer,8192,PROT_READ);
    mprotect(guard_area,4096,PROT_NONE);
    mprotect(NULL,4096,PROT_WRITE);	/* Let NULL pointers not generate exceptions */

Node:_my_cs, Next:_my_ds, Previous:mprotect, Up:Alphabetical List

## _my_cs

### Syntax

    #include <sys/segments.h>

    unsigned short _my_cs();

### Description

Returns the current `CS`. This is useful for setting up interrupt vectors and such.

### Return Value

`CS`

### Portability

not ANSI, not POSIX

Node:_my_ds, Next:_my_ss, Previous:_my_cs, Up:Alphabetical List

## _my_ds

### Syntax

    #include <sys/segments.h>

    unsigned short _my_ds();

### Description

Returns the current `DS`. This is useful for setting up interrupt vectors and such.

### Return Value

`DS`

### Portability

not ANSI, not POSIX

Node:_my_ss, Next:nice, Previous:_my_ds, Up:Alphabetical List

## _my_ss

### Syntax

    #include <sys/segments.h>

    unsigned short _my_ss();

### Description

Returns the current `SS`. This is useful for setting up interrupt vectors and such.

### Return Value

`SS`

### Portability

not ANSI, not POSIX

Node:nice, Next:normvideo, Previous:_my_ss, Up:Alphabetical List

## nice

### Syntax

    #include <unistd.h>

    int nice(int _increment);

### Description

Adjusts the priority of the process. Provided for Unix compatibility only.

### Return Value

The new nice value.

### Portability

not ANSI, not POSIX

Node:normvideo, Next:nosound, Previous:nice, Up:Alphabetical List

## normvideo

### Syntax

    #include <conio.h>

    void normvideo(void);

### Description

Resets the text attribute to what it was before the program started.

### Portability

not ANSI, not POSIX

Node:nosound, Next:ntohl, Previous:normvideo, Up:Alphabetical List

## nosound

### Syntax

    #include <pc.h>

    void nosound(void);

### Description

Disable the PC speaker.

### Portability

not ANSI, not POSIX

Node:ntohl, Next:ntohs, Previous:nosound, Up:Alphabetical List

## ntohl

### Syntax

    #include <netinet/in.h>

    unsigned long ntohl(unsigned long val);

### Description

This function converts from network formatted longs to host formatted longs. For the i386 and higher processors, this means that the bytes are swapped from 1234 order to 4321 order.

### Return Value

The host-order value.

### Portability

not ANSI, not POSIX

### Example

    ip = ntohl(packet.ipaddr);

Node:ntohs, Next:open, Previous:ntohl, Up:Alphabetical List

## ntohs

### Syntax

    #include <netinet/in.h>

    unsigned short ntohs(unsigned short val);

### Description

This function converts from network formatted shorts to host formatted shorts. For the i386 and higher processors, this means that the bytes are swapped from 12 order to 21 order.

### Return Value

The host-order value.

### Portability

not ANSI, not POSIX

### Example

    port = ntohs(tcp.port);

Node:open, Next:_open, Previous:ntohs, Up:Alphabetical List

## open

### Syntax

    #include <fcntl.h>
    #include <sys/stat.h> /* for mode definitions */

    int open(const char *file, int mode /*, int permissions */);

### Description

This function opens the named file in the given mode, which is any combination of the following:

`O_RDONLY`
  The file is opened for reading.
`O_WRONLY`
  The file is opened for writing.
`O_RDWR`
  The file is opened for both reading and writing.
`O_CREAT`
  If the file does not exist, it is created. See creat.
`O_TRUNC`
  If the file does exist, it is truncated to zero bytes.
`O_EXCL`
  If the file exists, and `O_CREAT` is also specified, the `open` call will fail.
`O_APPEND`
  The file pointer is positioned at the end of the file before each write.
`O_TEXT`
  The file is opened in text mode, meaning that Ctrl-M characters are stripped on reading and added on writing as needed. The default mode is specified by the `_fmode` variable _fmode.
`O_BINARY`
  The file is opened in binary mode.

  When called to open the console in binary mode, `open` will disable the generation of `SIGINT` when you press `Ctrl-C` (`Ctrl-Break` will still cause `SIGINT`), because many programs that use binary reads from the console will also want to get the `^C` characters. You can use the `__djgpp_set_ctrl_c` library function (see __djgpp_set_ctrl_c) if you want `Ctrl-C` to generate interrupts while console is read in binary mode.

If the file is created by this call, it will be given the read/write permissions specified by permissions, which may be any combination of these values:

`S_IRUSR`
  The file is readable. This is always true for MS-DOS.
`S_IWUSR`
  The file is writable.

Other `S_I*` values may be included, but they will be ignored.

You can specify the share flags (a DOS specific feature) in mode. And you can indicate default values for the share flags in `__djgpp_share_flags`. See __djgpp_share_flags.

### Return Value

If successful, the file descriptor is returned. On error, a negative number is returned and `errno` is set to indicate the error.

### Portability

not ANSI, POSIX

### Example

    int q = open("/tmp/foo.dat", O_RDONLY|O_BINARY);

Node:_open, Next:opendir, Previous:open, Up:Alphabetical List

## _open

### Syntax

    #include <io.h>

    int _open(const char *path, int attrib);

### Description

This is a direct connection to the MS-DOS open function call, int 0x21, %ah = 0x3d. (When long file names are supported, `_open` calls function 0x716c of Int 0x21.) The file is set to binary mode.

This function can be hooked by the File System Extensions (see File System Extensions). If you don't want this, you should use `_dos_open` (see _dos_open) (but note that the latter doesn't support long file names).

### Return Value

The new file descriptor, else -1 on error.

### Portability

not ANSI, not POSIX

Node:opendir, Next:outb, Previous:_open, Up:Alphabetical List

## opendir

### Syntax

    #include <dirent.h>

    extern int __opendir_flags;

    DIR *opendir(char *name);

### Description

This function "opens" a directory so that you can read the list of file names in it. The pointer returned must be passed to `closedir` when you are done with it. See readdir.

The global variable `__opendir_flags` can be set to include the following values to control the operation of `opendir`:

`__OPENDIR_PRESERVE_CASE`
  Do not change the case of files to lower case. Just in case Micros*ft decides to support case-sensitive file systems some day.

  You can also use this flag if you want the names of files like `README` and `FAQ` from Unix distributions to be returned in upper-case on Windows 9X filesystems. See _preserve_fncase, for other ways of achieving this and for more detailed description of the automatic letter-case conversion by DJGPP library functions.

`__OPENDIR_NO_HIDDEN`
  Do not include hidden files and directories in the search. By default, all files and directories are included.
`__OPENDIR_FIND_HIDDEN`
  Provided for back-compatibility with previous DJGPP versions, where hidden files and directories were by default skipped. In versions 2.02 and later, this flag has no effect.
`__OPENDIR_FIND_LABEL`
  Include volume labels in the search. By default, these are skipped.

You can simply put `int __opendir_flags = ...;` in your code. The default is to let it get set to zero as an uninitialized variable.

### Return Value

The open directory structure, or `NULL` on error.

### Portability

not ANSI, POSIX (see note 1)

Notes:

1. The `__opendir_flags` variable is DJGPP-specific.

### Example

    DIR *d = opendir(".");
    closedir(d);

Node:outb, Next:outp, Previous:opendir, Up:Alphabetical List

## outb

### Syntax

    #include <pc.h>

    void outb(unsigned short _port, unsigned char _data);

### Description

Calls outportb. Provided only for compatibility.

### Portability

not ANSI, not POSIX

Node:outp, Next:outportb, Previous:outb, Up:Alphabetical List

## outp

### Syntax

    #include <pc.h>

    void outp(unsigned short _port, unsigned char  _data);

### Description

Calls outportb. Provided only for compatibility.

### Portability

not ANSI, not POSIX

Node:outportb, Next:outportl, Previous:outp, Up:Alphabetical List

## outportb

### Syntax

    #include <pc.h>

    void outportb(unsigned short _port, unsigned char  _data);

### Description

Write a single byte to an 8-bit port.

This function is provided as an inline assembler macro, and will be optimized down to a single opcode when you optimize your program.

### Portability

not ANSI, not POSIX

Node:outportl, Next:outportsb, Previous:outportb, Up:Alphabetical List

## outportl

### Syntax

    #include <pc.h>

    void outportl(unsigned short _port, unsigned long _data);

### Description

Write a single long to an 32-bit port.

This function is provided as an inline assembler macro, and will be optimized down to a single opcode when you optimize your program.

### Portability

not ANSI, not POSIX

Node:outportsb, Next:outportsl, Previous:outportl, Up:Alphabetical List

## outportsb

### Syntax

    #include <pc.h>

    void outportsb(unsigned short _port, const unsigned char *_buf, unsigned _len);

### Description

Writes the _len bytes in _buf to the 8-bit _port.

### Portability

not ANSI, not POSIX

Node:outportsl, Next:outportsw, Previous:outportsb, Up:Alphabetical List

## outportsl

### Syntax

    #include <pc.h>

    void outportsl(unsigned short _port, const unsigned long *_buf, unsigned _len);

### Description

Writes the _len longs in _buf to the 32-bit _port.

### Portability

not ANSI, not POSIX

Node:outportsw, Next:outportw, Previous:outportsl, Up:Alphabetical List

## outportsw

### Syntax

    #include <pc.h>

    void outportsw(unsigned short _port, const unsigned short *_buf, unsigned _len);

### Description

Writes the _len shorts in _buf to the 16-bit _port.

### Portability

not ANSI, not POSIX

Node:outportw, Next:outpw, Previous:outportsw, Up:Alphabetical List

## outportw

### Syntax

    #include <pc.h>

    void outportw(unsigned short _port, unsigned short _data);

### Description

Write a single short to an 16-bit port.

This function is provided as an inline assembler macro, and will be optimized down to a single opcode when you optimize your program.

### Portability

not ANSI, not POSIX

Node:outpw, Next:pathconf, Previous:outportw, Up:Alphabetical List

## outpw

### Syntax

    #include <pc.h>

    void outpw(unsigned short _port, unsigned short _data);

### Description

Calls outportw. Provided only for compatibility.

### Portability

not ANSI, not POSIX

Node:pathconf, Next:pause, Previous:outpw, Up:Alphabetical List

## pathconf

### Syntax

    #include <unistd.h>

    long pathconf(const char *filename, int name);

### Description

This function returns various system-dependent configuration values. The name is one of the following:

`_PC_LINK_MAX`
  The maximum number of directory entries that can refer to a single real file. Always 1 in DJGPP.
`_PC_MAX_CANON`
  The maximum number of bytes in an editable input line. In DJGPP, this is 126 (DOS restriction).
`_PC_MAX_INPUT`
  The maximum number of bytes in a non-editable input line. Also 126 in DJGPP.
`_PC_NAME_MAX`
  The maximum length of an individual file name. If the filesystem where filename resides supports long file names, the result is whatever `_get_volume_info` returns (usually 255); otherwise 12 will be returned. See _use_lfn.
`_PC_PATH_MAX`
  The maximum length of a complete path name. If the filesystem where filename resides supports long file names, the result is whatever `_get_volume_info` returns (usually 260); otherwise 80 will be returned. See _use_lfn.
`_PC_PIPE_BUF`
  The size of a pipe's internal buffer. In DJGPP, this returns 512.
`_PC_CHOWN_RESTRICTED`
  If non-zero, only priviledged user can change the ownership of files by calling `chown`, otherwise anyone may give away files. The DJGPP version always returns zero, since MS-DOS files can be freely given away.
`_PC_NO_TRUNC`
  If zero is returned, filenames longer than what `pathconf (filename, _PC_NAME_MAX)` returns are truncated, otherwise an error occurs if you use longer names. In DJGPP, this returns 0, since DOS always silently truncates long names.
`_PC_VDISABLE`
  A character to use to disable tty special characters. DJGPP currently doesn't support special characters, so this returns -1.

### Return Value

The selected configuration value is returned.

### Portability

not ANSI, POSIX

### Example

    char *buf = malloc(pathconf("c:/", _PC_MAX_PATH)+1);

Node:pause, Next:pclose, Previous:pathconf, Up:Alphabetical List

## pause

### Syntax

    #include <unistd.h>

    int pause(void);

### Description

This function just calls `__dpmi_yield()` (see __dpmi_yield) to give up a slice of the CPU.

### Return Value

Zero.

### Portability

not ANSI, POSIX

Node:pclose, Next:perror, Previous:pause, Up:Alphabetical List

## pclose

### Syntax

    #include <stdio.h>

    int pclose(FILE *pipe);

### Description

This function closes a pipe opened with `popen` (see popen). Note that since MS-DOS is not multitasking, this function will actually run the program specified in `popen` if the pipe was opened for writing.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

### Example

    FILE *f = popen("sort", "w");
    write_to_pipe(f);
    pclose(f);

Node:perror, Next:pipe, Previous:pclose, Up:Alphabetical List

## perror

### Syntax

    #include <stdio.h>

    void perror(const char *string);

### Description

This function formats an error message and prints it to `stderr`. The message is the string, a colon, and a message suitable for the error condition indicated by `errno`.

### Return Value

None.

### Portability

ANSI, POSIX

### Example

    int x = open("foo", O_RDONLY);
    if (x < 0)
    {
      perror("foo");
      exit(1);
    }

Node:pipe, Next:popen, Previous:perror, Up:Alphabetical List

## pipe

### Syntax

    #include <unistd.h>

    int pipe(int fildes[2]);

### Description

This function is provided only to assist in porting from Unix. It always returns an error condition.

### Portability

not ANSI, POSIX

Node:popen, Next:pow, Previous:pipe, Up:Alphabetical List

## popen

### Syntax

    #include <stdio.h>

    FILE *popen(const char *program, const char *mode);

### Description

This function executes the named `program` and attaches either its input stream or its output stream to the returned file. While the file is open, the calling program can write to the program (if the program was open for writing) or read the program's output (if the program was opened for reading). When the program is done, or if you have no more input for it, pass the file pointer to `pclose` (see pclose), which terminates the program.

Since MS-DOS does not support multitasking, this function actually runs the entire program when the program is opened for reading, and stores the output in a temporary file. `pclose` then removes that file. Similarly, when you open a program for writing, a temp file holds the data and `pclose` runs the entire program.

The mode is the same as for `fopen` (see fopen).

### Return Value

An open file which can be used to read the program's output or write to the program's input.

### Portability

not ANSI, POSIX

### Example

    FILE *p = popen("dir", "r");
    read_program(p);
    pclose(p);

Node:pow, Next:pow10, Previous:popen, Up:Alphabetical List

## pow

### Syntax

    #include <math.h>

    double pow(double x, double y);

### Description

This function computes x^y, x raised to the power y.

### Return Value

x raised to the power y. If the result overflows a `double` or underflows, `errno` is set to `ERANGE`. If y is `NaN`, the return value is `NaN` and `errno` is set to `EDOM`. If x and y are both 0, the return value is 1, but `errno` is set to `EDOM`. If y is a positive or a negative Infinity, the following results are returned, depending on the value of x:

x negative
  the return value is `NaN` and `errno` is set to `EDOM`.
absolute value of x less than 1 and y is `+Inf`
absolute value of x greater than 1 and y is `-Inf`
  the return value is zero.
absolute value of x less than 1 and y is `-Inf`
absolute value of x greater than 1 and y is `+Inf`
  the return value is `+Inf`.
absolute value of x is 1
  the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:pow10, Next:pow2, Previous:pow, Up:Alphabetical List

## pow10

### Syntax

    #include <math.h>

    double pow10(double x);

### Description

This function computes 10 to the power of x, 10^x.

### Return Value

10 to the x power. If the value of x is finite, but so large in magnitude that 10^x cannot be accurately represented by a `double`, the return value is the nearest representable ! `double` (possibly, an `Inf`), and `errno` is set to `ERANGE`. If x is either a positive or a negative infinity, the result is either `+Inf` or zero, respectively, and `errno` is not changed. If x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:pow2, Next:powi, Previous:pow10, Up:Alphabetical List

## pow2

### Syntax

    #include <math.h>

    double pow2(double x);

### Description

This function computes 2 to the power of x, 2^x.

### Return Value

2 to the x power. If the value of x is finite, but so large in magnitude that 2^x cannot be accurately represented by a `double`, the return value is the nearest representable `double` (possibly, an `Inf`), and `errno` is set to `ERANGE`. If x is either a positive or a negative infinity, the result is either `+Inf` or zero, respectively, and `errno` is not changed. If x is a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

not ANSI, not POSIX

Node:powi, Next:_preserve_fncase, Previous:pow2, Up:Alphabetical List

## powi

### Syntax

    #include <math.h>

    double powi(double x, int iy);

### Description

This function computes x^iy, where iy is an integer number. It does so by an optimized sequence of squarings and multiplications. For integer values of exponent, it is always faster to call `powi` than to call `pow` with the same arguments, even if iy has a very large value. For small values of iy, `powi` is much faster than `pow`.

### Return Value

x raised to the iy power. If x and iy are both zero, the return value is 1. If x is equal to zero, and iy is negative, the return value is `Inf`. This function never sets `errno`.

### Portability

not ANSI, not POSIX

Node:_preserve_fncase, Next:printf, Previous:powi, Up:Alphabetical List

## _preserve_fncase

### Syntax

    #include <fcntl.h>

    char _preserve_fncase (void);

### Description

This function returns a non-zero value if letter-case in filenames should be preserved. It is used by library functions that get filenames from the operating system (like `readdir`, `_fixpath` and others). The usual behavior of these functions (when `_preserve_fncase` returns zero) is to down-case 8+3 DOS-style filenames, but leave alone the letter-case in long filenames when these are supported (see _use_lfn). This can be changed by either setting `_CRT0_FLAG_PRESERVE_FILENAME_CASE` bit in the `_crt0_startup_flags` variable (see _crt0_startup_flags), or by setting the `FNCASE` environment variable to `Y` at run time. You might need such a setup e.g. on Windows 95 if you want to see files with names like `README` and `FAQ` listed in upper-case (for this to work, you will have to manually rename all the other files with 8+3 DOS-style names to lower-case names). When the case in filenames is preserved, all filenames will be returned in upper case on MSDOS (and other systems that don't support long filenames), or if the environment variable `LFN` is set to `N` on systems that support LFN. That is because this is how filenames are stored in the DOS directory entries.

### Return value

Zero when 8+3 filenames should be converted to lower-case, non-zero otherwise.

### Portability

not ANSI, not POSIX

Node:printf, Next:psignal, Previous:_preserve_fncase, Up:Alphabetical List

## printf

### Syntax

    #include <stdio.h>

    int printf(const char *format, ...);

### Description

Sends formatted output from the arguments (...) to `stdout`.

The format string contains regular characters to print, as well as conversion specifiers, which begin with a percent symbol. Each conversion speficier contains the following fields:

- an optional flag, which may alter the conversion:
  `-`
    left-justify the field.
  `+`
    Force a `+` sign on positive numbers.
  `space`
    To leave a blank space where a plus or minus sign would have been.
  `#`
    Alternate conversion - prefix octal numbers with `0`, hexadecimal numbers with `0x` or `0X`, or force a trailing decimal point if a floating point conversion would have omitted it.
  `0`
    To pad numbers with leading zeros.
- A field width specifier, which specifies the minimum width of the field. This may also be an asterisk (`*`), which means that the actual width will be obtained from the next argument. If the argument is negative, it supplies a `-` flag and a positive width.
- An optional decimal point and a precision. This may also be an asterisk, but a negative argument for it indicates a precision of zero. The precision specifies the minimum number of digits to print for an integer, the number of fraction digits for a floating point number (max for `g` or `G`, actual for others), or the maximum number of characters for a string.
- An optional conversion qualifier, which may be `h` to specify `short`, `l` to specify long ints, or `L` to specify long doubles. Long long type can be specified by `L` or `ll`.
- The conversion type specifier:
  `c`
    A single character
  `d`
    A signed integer
  `D`
    A signed long integer
  `e`
  `E`
    A floating point number (double or long double). The exponent case matches the specifier case. The representation always has an exponent.
  `f`
    A floating point number (double or long double). The representation never has an exponent.
  `g`
  `G`
    A floating point number (double or long double). The exponent case matches the specifier case. The representation has an exponent if it needs one.
  `i`
    A signed integer.
  `n`
    The next argument is a pointer to an integer, and the number of characters generated so far is stored in that integer.
  `o`
    A unsigned integer, printed in base 8 instead of base 10.
  `p`
    A pointer. This is printed with an `x` specifier.
  `s`
    A `NULL`-terminated string.
  `u`
    An unsigned integer.
  `U`
    An unsigned long integer.
  `x`
  `X`
    An unsigned integer, printed in base 16 instead of base 10. The case of the letters used matches the specifier case.
  `%`
    A single percent symbol is printed.

### Return Value

The number of characters written.

### Portability

ANSI, POSIX

### Example

    printf("%-3d %10.2f%% Percent of %s\n", index, per[index], name[index]);

Node:psignal, Next:_put_path, Previous:printf, Up:Alphabetical List

## psignal

### Syntax

    #include <signal.h>

    extern char *sys_siglist[];
    void psignal (int sig, const char *msg);

### Description

This function produces a message on the standard error stream describing the signal given by its number in sig. It prints the string pointed to by msg, then the name of the signal, and a newline.

The names of signals can be retrieved using the array `sys_siglist`, with the signal number serving as an index into this array.

### Portability

not ANSI, not POSIX

### Example

      #include <signal.h>

      void sig_catcher (int sig)
      {
        psignal (progname, sig);
        return;
      }

Node:_put_path, Next:putc, Previous:psignal, Up:Alphabetical List

## _put_path

### Syntax

    #include <libc/dosio.h>

    int _put_path(const char *path);
    int _put_path2(const char *path, int offset);

### Description

These functions are used internally by all low-level library functions that need to pass file names to DOS. `_put_path` copies its argument path to the transfer buffer (see _go32_info_block) starting at the beginning of the transfer buffer; `_put_path2` does the same except that it puts the file name starting at offset bytes from the beginning of the transfer buffer.

These functions are meant to be called by low-level library functions, not by applications. You should only call them if you know what you are doing. In particular, if you call any library function between a call to `_put_path` or `_put_path2` and the call to a DOS function that uses the file name, the file name in the transfer buffer could be wiped out, corrupted or otherwise changed. You have been warned!

Some constructs in file names are transformed while copying them, to allow transparent support for nifty features. Here's the list of these transformations:

- Multiple forward slashes are collapsed into a single slash.

  Unix treats multiple slashes as a single slash, so some ported programs pass names like `c:/foo//bar` to library functions. DOS functions choke on such file names, so collapsing the slashes prevents these names from failing.

- Trailing slashes are removed, except for root directories.

  Various DOS calls cannot cope with file names like `c:/foo/`; this feature solves this problem.

- Translation of Unix device names.

  Unix `/dev/null` is mapped to DOS-standard `NUL`, and Unix `/dev/tty` to DOS-standard `CON`. This provides for transparent support of these special devices, e.g. in Unix shell scripts.

- Translation of DOS device names.

  Any file name which begins with `/dev/` or `x:/dev/` (where x: is any valid DOS drive letter) has the `/dev/` or `x:/dev/` prefix removed, and the rest is passed to DOS. This is because some DOS functions don't recognize device names unless they are devoid of the drive and directory specifications, and programs could add a drive and a directory if they convert a name like `/dev/con` to a fully-qualified path name.

- `/dev/x/` is translated into `x:/`.

  This allows to use Unix-style absolute path names that begin with a slash, instead of DOS-style names with a drive letter. Some Unix programs and shell scripts fail for file names that include colons, which are part of the drive letter specification; this feature allows to work around such problems by using e.g. `/dev/c/` where `c:/` would fail.

- `/dev/env/foo/` is replaced by the value of the environment variable foo.

  (In other words, you can think of environment variables as if they were sub-directories of a fictitious directory `/dev/env`.)

  This allows to use environment variable names inside path names compiled into programs, and have them transparently expanded at run time. For example, `/dev/env/DJDIR/include` will expand to the exact path name of the DJGPP include directory, no matter where DJGPP is installed on the machine where the program runs. (The value of `DJDIR` is computed by the DJGPP startup code and pushed into the environment of every DJGPP program before `main` is called.)

  Note that environment variables are case-sensitive, so `/dev/env/foo` and `/dev/env/FOO` are not the same. DOS shells usually upcase the name of the environment variable if you set it with the built-in command `SET`, so if you type e.g. `SET foo=bar`, the shell defines a variable named `FOO`.

  If the environment variable is undefined, it will expand into an empty string. The expansion is done recursively, so environment variables may reference other environment variables using the same `/dev/env/` notation. For example, if the variable `HOME` is set to `/dev/env/DJDIR/home`, and DJGPP is installed in `c:/software/djgpp`, then `/dev/env/HOME/sources` will expand to `c:/software/djgpp/home/sources`.

  It is possible to supply a default value, to be used if the variable is not defined, or has an empty value. To this end, put the default value after the name of the variable and delimit it by `~`, like in `/dev/env/DJDIR~c:/djgpp~/include`.

  If you need to include a literal character `~` in either the environment variable name or in the default value that replaces it, use two `~`s in a row. For example, `/dev/env/FOO~~` will expand to the value of the variable `FOO~`. Likewise, `/dev/env/FOO~~BAR~foo~~baz~` will expand to the value of the variable `FOO~BAR` if it is defined and nonempty, and to `foo~baz` otherwise. Leading `~` in the default value isn't supported (it is interpreted as part of the preceding variable name).

  The default value may also reference (other) environment variables, but nested default values can get tricky. For example, `/dev/env/foo~/dev/env/bar~` will work, but `/dev/env/foo~/dev/env/bar~baz~~` will not. To use nested default values, you need to double the quoting of the `~` characters, like in `/dev/env/foo~/dev/env/bar~~baz~~~`.

### Return Value

Both functions return the offset into the transfer buffer of the terminating null character that ends the file name.

not ANSI, not POSIX

### Example

These functions are meant to be called by low-level library functions, not by applications. You should only call them if you know what you are doing. In particular, if you call any library function between a call to `_put_path` or `_put_path2` and the call to a DOS function that uses the file name, the file name in the transfer buffer could be wiped out, corrupted and otherwise changed. You have been warned!

     __dpmi_regs r;

     _put_path("/dev/c/djgpp/bin/");
     r.x.ax = 0x4300;  /* get file attributes */
     r.x.ds = __tb >> 4;
     r.x.dx = __tb & 0x0f;
     __dpmi_int(0x21, &r);

Node:putc, Next:putch, Previous:_put_path, Up:Alphabetical List

## putc

### Syntax

    #include <stdio.h>

    int putc(int c, FILE *file);

### Description

This function writes one character to the given file.

### Return Value

The character written.

### Portability

ANSI, POSIX

### Example

    while ((c=getc(stdin)) != EOF)
      putc(c, stdout);

Node:putch, Next:putchar, Previous:putc, Up:Alphabetical List

## putch

### Syntax

    #include <conio.h>

    int putch(int _c);

### Description

Put the character _c on the screen at the current cursor position. The special characters return, linefeed, bell, and backspace are handled properly, as is line wrap and scrolling. The cursor position is updated.

### Return Value

The character is returned.

### Portability

not ANSI, not POSIX

Node:putchar, Next:putenv, Previous:putch, Up:Alphabetical List

## putchar

### Syntax

    #include <stdio.h>

    int putchar(int c);

### Description

This is the same as `fputc(c, stdout)`. See fputc.

### Return Value

The character written.

### Portability

ANSI, POSIX

### Example

    while ((c = getchar()) != EOF)
      putchar(c);

Node:putenv, Next:puts, Previous:putchar, Up:Alphabetical List

## putenv

### Syntax

    #include <stdlib.h>

    int putenv(const char *env);

### Description

This function adds an entry to the program's environment. The string passed must be of the form `NAME`=`VALUE`. Any existing value for the environment variable is gone.

`putenv` will copy the string passed to it, and will automatically free any existing string already in the environment. Keep this in mind if you alter the environment yourself. The string you pass is still your responsibility to free. Note that most implementations will not let you free the string you pass, resulting in memory leaks.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    putenv("SHELL=ksh.exe");

Node:puts, Next:puttext, Previous:putenv, Up:Alphabetical List

## puts

### Syntax

    #include <stdio.h>

    int puts(const char *string);

### Description

This function writes string to `stdout`, and then writes a newline character.

### Return Value

Nonnegative for success, or `EOF` on error.

### Portability

ANSI, POSIX

### Example

    puts("Hello, there");

Node:puttext, Next:putw, Previous:puts, Up:Alphabetical List

## puttext

### Syntax

    #include <conio.h>

    int puttext(int _left, int _top, int _right, int _bottom, void *_source);

### Description

The opposite of gettext.

### Return Value

1 on success, zero on error.

### Portability

not ANSI, not POSIX

Node:putw, Next:qsort, Previous:puttext, Up:Alphabetical List

## putw

### Syntax

    #include <stdio.h>

    int putw(int x, FILE *file);

### Description

Writes a single binary word in native format to file.

### Return Value

The value written, or `EOF` for end-of-file or error. Since `EOF` is a valid integer, you should use `feof` or `ferror` to detect this situation.

### Portability

not ANSI, not POSIX

### Example

    putw(12, stdout);

Node:qsort, Next:raise, Previous:putw, Up:Alphabetical List

## qsort

### Syntax

    #include <stdlib.h>

    void qsort(void *base, size_t numelem, size_t size,
               int (*cmp)(const void *e1, const void *e2));

### Description

This function sorts the given array in place. base is the address of the first of numelem array entries, each of size size bytes. `qsort` uses the supplied function cmp to determine the sort order for any two elements by passing the address of the two elements and using the function's return address.

The return address of the function indicates the sort order:

Negative
  Element e1 should come before element e2 in the resulting array.
Positive
  Element e1 should come after element e2 in the resulting array.
Zero
  It doesn't matter which element comes first in the resulting array.

### Return Value

None.

### Portability

ANSI, POSIX

### Example

    typedef struct {
      int size;
      int sequence;
    } Item;

    int qsort_helper_by_size(const void *e1, const void *e2)
    {
      return ((const Item *)e2)->size - ((const Item *)e1)->size;
    }

    Item list[100];

    qsort(list, 100, sizeof(Item), qsort_helper_by_size);

    int qsort_stringlist(const void *e1, const void *e2)
    {
      return strcmp(*(char **)e1, *(char **)e2);
    }

    char *slist[10];

    /* alphabetical order */
    qsort(slist, 10, sizeof(char *), qsort_stringlist);

Node:raise, Next:rand, Previous:qsort, Up:Alphabetical List

## raise

### Syntax

    #include <signal.h>

    int	raise(int sig);

### Description

This function raises the given signal sig. See the list of possible signals.

### Return Value

0 on success, -1 for illegal value of sig.

### Portability

ANSI, POSIX

Node:rand, Next:rand48, Previous:raise, Up:Alphabetical List

## rand

### Syntax

    #include <stdlib.h>

    int rand(void);

### Description

Returns a pseudo-random number between zero and `RAND_MAX` (defined on `stdlib.h`).

By default, this function always generates the same sequence of numbers each time you run the program. (This is usually desirable when debugging, or when comparing two different runs.) If you need to produce a different sequence on every run, you must seed `rand` by calling `srand` (see srand) before the first call to `rand`, and make sure to use a different argument to `srand` each time. The usual technique is to get the argument to `srand` from a call to the `time` library function (see time), whose return value changes every second.

To get a random number in the range 0..N, use `rand()%(N+1)`. Note that the low bits of the `rand`'s return value are not very random, so `rand()%N` for small values of N could be not enough random. The alternative, but non-ANSI, function `random` is better if N is small. See random.

### Return Value

The number.

### Portability

ANSI, POSIX

### Example

    /* random pause */
    srand(time(0));
    for (i=rand(); i; i--);

Node:rand48, Next:random, Previous:rand, Up:Alphabetical List

## rand48

### Syntax

    #include <stdlib.h>

    double drand48(void);
    double erand48(unsigned short state[3]);
    unsigned long lrand48(void);
    unsigned long nrand48(unsigned short state[3]);
    long mrand48(void);
    long jrand48(unsigned short state[3]);
    void srand48(long seed);
    unsigned short *seed48(unsigned short state_seed[3]);
    void lcong48(unsigned short param[7]);

### Description

This is the family of `*rand48` functions. The basis for these functions is the linear congruential formula X[n+1] = (a*X[n] + c) mod 2^48, n >= 0. a = 0x5deece66d and c = 0xb at start and after a call to either `srand48` or `seed48`. A call to `lcong48` changes a and c (and the internal state).

`drand48` and `erand48` return `double`s uniformly distributed in the interval [0.0, 1.0).

`lrand48` and `nrand48` return `unsigned long`s uniformly distributed in the interval [0, 2^31).

`mrand48` and `jrand48` return `long`s uniformly distributed in the interval [-2^31, 2^31).

`erand48`, `jrand48` and `nrand48` requires the state of the random generator to be passed.

`drand48`, `lrand48` and `mrand48` uses an internal state (common with all three functions) which should be initialized with a call to one of the functions `srand48`, `seed48` or `lcong48`.

`srand48` sets the high order 32 bits to the argument seed. The low order 16 bits are set to the arbitrary value 0x330e.

`seed48` sets the internal state according to the argument state_seed (`state_seed[0]` is least significant). The previous state of the random generator is saved in an internal (static) buffer, to which a pointer is returned.

`lcong48` sets the internal state to `param[0-2]`, a to `param[3-5]` (`param[0]` and `param[3]` are least significant) and c to `param[6]`.

### Return Value

A random number.

### Portability

not ANSI, not POSIX

### Example

    #include <stdio.h>
    #include <stdlib.h>
    #include <time.h>

    int main(void)
    {

      srand48(time(NULL));
      printf("%.12f is a random number in [0.0, 1.0).\n", drand48());

      exit(0);
    }

Node:random, Next:rawclock, Previous:rand48, Up:Alphabetical List

## random

### Syntax

    #include <stdlib.h>

    long random(void);

### Description

Returns a random number in the range 0..MAXINT.

### Return Value

0 .. MAXINT

### Portability

not ANSI, not POSIX

### Example

     /* Produce a random integer between 0 and 199.  */
     int random_number = random () % 200;

Node:rawclock, Next:read, Previous:random, Up:Alphabetical List

## rawclock

### Syntax

    #include <time.h>

    unsigned long rawclock(void);

### Description

Returns the number of clock tics (18.2 per second) since midnight.

### Return Value

The number of tics.

### Portability

not ANSI, not POSIX

### Example

    /* wait 1/4 second */
    int i = rawclock()+5;
    while (rawclock()<i);

Node:read, Next:_read, Previous:rawclock, Up:Alphabetical List

## read

### Syntax

    #include <unistd.h>

    ssize_t read(int fd, void *buffer, size_t length);

### Description

This function reads at most length bytes from file fd into buffer. Note that in some cases, such as end-of-file conditions and text files, it may read less than the requested number of bytes. At end-of-file, `read` will read exactly zero bytes.

### Return Value

The number of bytes read, zero meaning end-of-file, or -1 for an error.

### Portability

not ANSI, POSIX

### Example

    char buf[10];
    int r = read(0, buf, 10);

Node:_read, Next:read_child, Previous:read, Up:Alphabetical List

## _read

### Syntax

    #include <io.h>

    ssize_t _read(int fildes, void *buf, size_t nbyte);

### Description

This is a direct connection to the MS-DOS read function call, int 0x21, %ah = 0x3f. No conversion is done on the data; it is read as raw binary data. This function can be hooked by the See File System Extensions. If you don't want this, you should use See _dos_read.

### Return Value

The number of bytes read.

### Portability

not ANSI, not POSIX

Node:read_child, Next:read_sel_addr, Previous:_read, Up:Alphabetical List

## read_child

### Syntax

    #include <debug/dbgcom.h>

    void read_child (unsigned child_addr, void *buf, unsigned len);

### Description

This function reads the memory of the debugged process starting at address child_addr for len bytes, and copies the data read to the buffer pointed to by buf. It is used primarily to save the original instruction at the point where a breakpoint instruction is inserted (to trigger a trap when the debuggee's code gets to that point). See write_child.

### Return Value

The function return zero if it has successfully transferred the data, non-zero otherwise (e.g., if the address in child_addr is outside the limits of the debuggee's code segment.

### Portability

not ANSI, not POSIX

Node:read_sel_addr, Next:readdir, Previous:read_child, Up:Alphabetical List

## read_sel_addr

### Syntax

    #include <debug/dbgcom.h>

    void read_sel_addr (unsigned offset, void *buf, unsigned len, unsigned sel);

### Description

This function reads the memory starting at offset offset in selector sel for len bytes, and copies the data read to the buffer pointed to by buf. See write_sel_addr.

### Return Value

The function return zero if it has successfully transferred the data, non-zero otherwise (e.g., if the address in offset is outside the limits of the segment whose selector is sel).

### Portability

not ANSI, not POSIX

Node:readdir, Next:realloc, Previous:read_sel_addr, Up:Alphabetical List

## readdir

### Syntax

    #include <dirent.h>

    struct dirent *readdir(DIR *dir);

### Description

This function reads entries from a directory opened by `opendir` (see opendir). It returns the information in a static buffer with this format:

    struct dirent {
      unsigned short d_namlen;  /* The length of the name (like strlen) */
      char d_name[MAXNAMLEN+1]; /* The name */
    };

Note that some directory entries might be skipped by `readdir`, depending on the bits set in the global variable `__opendir_flags`. See __opendir_flags.

### Return Value

A pointer to a static buffer that is overwritten with each call.

### Portability

not ANSI, POSIX (see note 1)

Notes:

1. The `__opendir_flags` variable is DJGPP-specific.

### Example

    DIR *d = opendir(".");
    struct dirent *de;
    while (de = readdir(d))
      puts(de->d_name);
    closedir(d);

Node:realloc, Next:redir_cmdline_delete, Previous:readdir, Up:Alphabetical List

## realloc

### Syntax

    #include <stdlib.h>

    void *realloc(void *ptr, size_t size);

### Description

This function changes the size of the region pointed to by ptr. If it can, it will reuse the same memory space, but it may have to allocate a new memory space to satisfy the request. In either case, it will return the pointer that you should use to refer to the (possibly new) memory area. The pointer passed may be `NULL`, in which case this function acts just like `malloc` (see malloc).

### Return Value

A pointer to the memory you should now refer to.

### Portability

ANSI, POSIX

### Example

    if (now+new > max)
    {
      max = now+new;
      p = realloc(p, max);
    }

Node:redir_cmdline_delete, Next:redir_cmdline_parse, Previous:realloc, Up:Alphabetical List

## redir_cmdline_delete

### Syntax

    #include <debug/redir.h>

    void redir_cmdline_delete (cmdline_t *cmd);

### Description

For the rationale and general description of the debugger redirection issue, see redir_debug_init.

This function serves as a destructor for a `cmdline_t` object. It frees storage used for the command-line arguments associated with cmd, closes any open handles stored in it, and frees memory used to store the file handles and the file names of the files where standard handles were redirected.

The function is safe to use even if cmd might be a `NULL` pointer, or if some of members of the `cmdline_t` structure are `NULL` pointers. See redir_debug_init, for detailed description of the `cmdline_t` structure.

### Portability

not ANSI, not POSIX

### Example

     redir_cmdline_delete (&child_cmd);

Node:redir_cmdline_parse, Next:redir_debug_init, Previous:redir_cmdline_delete, Up:Alphabetical List

## redir_cmdline_parse

### Syntax

    #include <debug/redir.h>

    int  redir_cmdline_parse (const char *args, cmdline_t *cmd);

### Description

For the rationale and general description of the debugger redirection issue, see redir_debug_init.

This function parses a command-line tail (i.e., without the program to be invoked) passed as a string in args. For every redirection directive in args, like `>> foo`, it opens the file that is the target of the redirection, and records in cmd the information about these redirections. (See redir_debug_init, for details of the `cmdline_t` structure that is used to hold this information.) The command line with redirections removed is placed into `cmd->command` (typically, it will be used to call `v2loadimage`, see v2loadimage), while the rest of information is used by `redir_to_child` and `redir_to_debugger` to redirect standard handles before and after calling `run_child`.

### Return Value

The function returns zero in case of success, -1 otherwise. Failure usually means some kind of syntax error, like `>` without a file name following it; or a file name that isn't allowed by the underlying OS, like `lost+found` on DOS.

### Portability

not ANSI, not POSIX

### Example

      /* Init command line storage.  */
      if (redir_debug_init (&child_cmd) == -1)
        fatal ("Cannot allocate redirection storage: not enough memory.\n");

      /* Parse the command line and create redirections.  */
      if (strpbrk (args, "<>"))
        {
          if (redir_cmdline_parse (args, &child_cmd) == 0)
    	args = child_cmd.command;
          else
    	error ("Syntax error in command line.");
        }
      else
        child_cmd.command = strdup (args);

      cmdline = (char *) alloca (strlen (args) + 4);
      cmdline[0] = strlen (args);
      strcpy (cmdline + 1, args);
      cmdline[strlen (args) + 1] = 13;

      if (v2loadimage (exec_file, cmdline, start_state))
        {
          printf ("Load failed for image %s\n", exec_file);
          exit (1);
        }

Node:redir_debug_init, Next:redir_to_child, Previous:redir_cmdline_parse, Up:Alphabetical List

## redir_debug_init

### Syntax

    #include <debug/redir.h>

    int redir_debug_init (cmdline_t *cmd);

### Description

This function initializes the data structure in the cmd variable required to save and restore debugger's standard handles across invocations of `run_child` (see run_child). The debugger will then typically call `redir_to_child` and `redir_to_debugger`.

These functions are needed when a debugger wants to redirect standard handles of the debuggee, or if the debuggee redirects some of its standard handles, because the debuggee is not a separate process, we just pretend it is by jumping between two threads of execution. But, as far as DOS is concerned, the debugger and the debuggee are a single process, and they share the same Job File Table (JFT). The JFT is a table maintained by DOS in the program's PSP where, for each open handle, DOS stores the index into the SFT, the System File Table. (The SFT is an internal data structure where DOS maintains everything it knows about a certain open file/device.) A handle that is returned by `open`, `_open` and other similar functions is simply an index into the JFT where DOS stored the SFT entry index for the file or device that the program opened.

When a program starts, the first 5 entries in the JFT are preconnected to the standard devices. Any additional handles opened by either the debugger or the debuggee use handles beyond the first 5 (unless one of the preconnected handles is deliberately closed). Here we mostly deal with handles 0, 1 and 2, the standard input, standard output, and standard error; they all start connected to the console device (unless somebody redirects the debugger's I/O from the command line).

Since both the debugger and the debuggee share the same JFT, their handles 0, 1 and 2 point to the same JFT entries and thus are connected to the same files/devices. Therefore, if the debugger redirects its standard output, the standard output of the debuggee is also automagically redirected to the same file/device! Similarly, if the debuggee redirects its stdout to a file, you won't be able to see debugger's output (it will go to the same file where the debuggee has its output); and if the debuggee closes its standard input, you will lose the ability to talk to debugger!

The debugger redirection support attempts to solve all these problems by creating an illusion of two separate sets of standard handles. Each time the debuggee is about to be run or resumed, it should call `redir_to_child` to redirect debugger's own standard handles to the file specified in the command-line (as given by e.g. the "run" command of GDB) before running the debuggee, then call `redir_to_debugger` to redirect them back to the debugger's original input/output when the control is returned from the debuggee (e.g. after a breakpoint is hit). Although the debugger and the debuggee have two separate copies of the file-associated data structures, the debugger still can redirect standard handles of the debuggee because they use the same JFT entries as debugger's own standard handles.

The `cmdline_t` structure is declared in the header `debug/redir.h` as follows:

    struct dbg_redirect {
      int inf_handle;   /* debuggee's handle */
      int our_handle;   /* debugger's handle */
      char *file_name;  /* file name where debuggee's handle is redirected */
      int mode;         /* mode used to open() the above file */
      off_t filepos;    /* file position of debuggee's handle; unused */
    };

    typedef struct _cmdline {
      char *command;		    /* command line with redirection removed */
      int redirected;		    /* 1 if handles redirected for child */
      struct dbg_redirect **redirection;/* info about redirected handles */
    } cmdline_t;

In the `cmdline_t` structure, the `redirection` member points to an array of 3 `dbg_redirect` structures, one each for each one of the 3 standard handles. The `inf_handle` and `our_handle` members of those structures are used to save the handle used, respectively, by the debuggee (a.k.a. the inferior process) and by the debugger.

The cmd variable is supposed to be defined by the debugger's application code. `redir_debug_init` is called to initialize that variable. It calls `redir_cmdline_delete` to close any open handles held in cmd and to free any allocated storage; then it fills cmd with the trivial information (i.e., every standard stream is connected to the usual handles 0, 1, and 2).

### Return Value

`redir_debug_init` returns zero in case of success, or -1 otherwise.

### Portability

not ANSI, not POSIX

### Example

     if (redir_debug_init (&child_cmd) == -1)
       fatal ("Cannot allocate redirection storage: not enough memory.\n");

Node:redir_to_child, Next:redir_to_debugger, Previous:redir_debug_init, Up:Alphabetical List

## redir_to_child

### Syntax

    #include <debug/redir.h>

    int redir_to_child (cmdline_t *cmd);

### Description

For the rationale and general description of the debugger redirection issue, see redir_debug_init.

This function redirects all 3 standard streams so that they point to the files/devices where the child (a.k.a. debuggee) process connected them. All three standard handles point to the console device by default, but this could be changed, either because the command line for the child requested redirection, like in `prog > foo`, or because the child program itself redirected one of its standard handles e.g. with a call to `dup2`.

`redir_to_child` uses information stored in the `cmdline_t` variable pointed to by the cmd argument to redirect the standard streams as appropriate for the debuggee, while saving the original debugger's handles to be restored by `redir_to_debugger`.

### Return Value

The function returns zero in case of success, -1 in case of failure. Failure usually means the process has run out of available file handles.

### Portability

not ANSI, not POSIX

### Example

      errno = 0;
      if (redir_to_child (&child_cmd) == -1)
        {
          redir_to_debugger (&child_cmd);
          error ("Cannot redirect standard handles for program: %s.",
                 strerror (errno));
        }

Node:redir_to_debugger, Next:regcomp, Previous:redir_to_child, Up:Alphabetical List

## redir_to_debugger

### Syntax

    #include <debug/redir.h>

    int redir_to_debugger (cmdline_t *cmd);

### Description

For the rationale and general description of the debugger redirection issue, see redir_debug_init.

This function redirects all 3 standard streams so that they point to the files/devices where the debugger process connected them. All three standard handles point to the console device by default, but this could be changed, either because the command line for the child requested redirection, like in `prog > foo`, or because the child program itself redirected one of its standard handles e.g. with a call to `dup2`.

`redir_to_debugger` uses information stored in the `cmdline_t` variable pointed to by the cmd argument to redirect the standard streams as appropriate for the debugger, while saving the original debuggee's handles to be restored by `redir_to_child`.

### Return Value

The function returns zero in case of success, -1 in case of failure. Failure usually means the process has run out of available file handles.

### Portability

not ANSI, not POSIX

### Example

     /* Restore debugger's standard handles.  */
     errno = 0;
     if (redir_to_debugger (&child_cmd) == -1)
       error ("Cannot redirect standard handles for debugger: %s.",
              strerror (errno));

Node:regcomp, Next:regerror, Previous:redir_to_debugger, Up:Alphabetical List

## regcomp

### Syntax

    #include <sys/types.h>
    #include <regex.h>

    int regcomp(regex_t *preg, const char *pattern, int cflags);

### Description

This function is part of the implementation of POSIX 1003.2 regular expressions (REs).

`regcomp` compiles the regular expression contained in the pattern string, subject to the flags in cflags, and places the results in the `regex_t` structure pointed to by preg. (The regular expression syntax, as defined by POSIX 1003.2, is described below.)

The parameter cflags is the bitwise OR of zero or more of the following flags:

`REG_EXTENDED`
  Compile modern (extended) REs, rather than the obsolete (basic) REs that are the default.
`REG_BASIC`
  This is a synonym for 0, provided as a counterpart to `REG_EXTENDED` to improve readability. This is an extension, compatible with but not specified by POSIX 1003.2, and should be used with caution in software intended to be portable to other systems.
`REG_NOSPEC`
  Compile with recognition of all special characters turned off. All characters are thus considered ordinary, so the RE in pattern is a literal string. This is an extension, compatible with but not specified by POSIX 1003.2, and should be used with caution in software intended to be portable to other systems. `REG_EXTENDED` and `REG_NOSPEC` may not be used in the same call to `regcomp`.
`REG_ICASE`
  Compile for matching that ignores upper/lower case distinctions. See the description of regular expressions below for details of case-independent matching.
`REG_NOSUB`
  Compile for matching that need only report success or failure, not what was matched.
`REG_NEWLINE`
  Compile for newline-sensitive matching. By default, newline is a completely ordinary character with no special meaning in either REs or strings. With this flag, `[^` bracket expressions and `.` never match newline, a `^` anchor matches the null string after any newline in the string in addition to its normal function, and the `$` anchor matches the null string before any newline in the string in addition to its normal function.
`REG_PEND`
  The regular expression ends, not at the first NUL, but just before the character pointed to by the `re_endp` member of the structure pointed to by preg. The `re_endp` member is of type `const char *`. This flag permits inclusion of NULs in the RE; they are considered ordinary characters. This is an extension, compatible with but not specified by POSIX 1003.2, and should be used with caution in software intended to be portable to other systems.

When successful, `regcomp` returns 0 and fills in the structure pointed to by preg. One member of that structure (other than `re_endp`) is publicized: `re_nsub`, of type `size_t`, contains the number of parenthesized subexpressions within the RE (except that the value of this member is undefined if the `REG_NOSUB` flag was used).

Note that the length of the RE does matter; in particular, there is a strong speed bonus for keeping RE length under about 30 characters, with most special characters counting roughly double.

### Return Value

If `regcomp` succeeds, it returns zero; if it fails, it returns a non-zero error code, which is one of these:

`REG_BADPAT`
  invalid regular expression
`REG_ECOLLATE`
  invalid collating element
`REG_ECTYPE`
  invalid character class
`REG_EESCAPE`
  `\` applied to unescapable character
`REG_ESUBREG`
  invalid backreference number (e.g., larger than the number of parenthesized subexpressions in the RE)
`REG_EBRACK`
  brackets [ ] not balanced
`REG_EPAREN`
  parentheses ( ) not balanced
`REG_EBRACE`
  braces { } not balanced
`REG_BADBR`
  invalid repetition count(s) in { }
`REG_ERANGE`
  invalid character range in [ ]
`REG_ESPACE`
  ran out of memory (an RE like, say, `((((a{1,100}){1,100}){1,100}){1,100}){1,100}'` will eventually run almost any existing machine out of swap space)
`REG_BADRPT`
  ?, *, or + operand invalid
`REG_EMPTY`
  empty (sub)expression
`REG_ASSERT`
  "can't happen" (you found a bug in `regcomp`)
`REG_INVARG`
  invalid argument (e.g. a negative-length string)

### Regular Expressions' Syntax

Regular expressions (REs), as defined in POSIX 1003.2, come in two forms: modern REs (roughly those of `egrep`; 1003.2 calls these extended REs) and obsolete REs (roughly those of `ed`; 1003.2 basic REs). Obsolete REs mostly exist for backward compatibility in some old programs; they will be discussed at the end. 1003.2 leaves some aspects of RE syntax and semantics open; `(*)' marks decisions on these aspects that may not be fully portable to other 1003.2 implementations.

A (modern) RE is one(*) or more non-empty(*) branches, separated by `|`. It matches anything that matches one of the branches.

A branch is one(*) or more pieces, concatenated. It matches a match for the first, followed by a match for the second, etc.

A piece is an atom possibly followed by a single(*) `*`, `+`, `?`, or bound. An atom followed by `*` matches a sequence of 0 or more matches of the atom. An atom followed by `+` matches a sequence of 1 or more matches of the atom. An atom followed by `?` matches a sequence of 0 or 1 matches of the atom.

A bound is `{` followed by an unsigned decimal integer, possibly followed by `,` possibly followed by another unsigned decimal integer, always followed by `}`. The integers must lie between 0 and `RE_DUP_MAX` (255(*)) inclusive, and if there are two of them, the first may not exceed the second. An atom followed by a bound containing one integer `i` and no comma matches a sequence of exactly `i` matches of the atom. An atom followed by a bound containing one integer `i` and a comma matches a sequence of `i` or more matches of the atom. An atom followed by a bound containing two integers `i` and `j` matches a sequence of `i` through `j` (inclusive) matches of the atom.

An atom is a regular expression enclosed in `()` (matching a match for the regular expression), an empty set of `()` (matching the null string(*)), a bracket expression (see below), `.` (matching any single character), `^` (matching the null string at the beginning of a line), `$` (matching the null string at the end of a line), a `\` followed by one of the characters `^.[$()|*+?{\\` (matching that character taken as an ordinary character), a `\` followed by any other character(*) (matching that character taken as an ordinary character, as if the `\` had not been present(*)), or a single character with no other significance (matching that character). A `{` followed by a character other than a digit is an ordinary character, not the beginning of a bound(*). It is illegal to end an RE with `\`.

A bracket expression is a list of characters enclosed in `[]`. It normally matches any single character from the list (but see below). If the list begins with `^`, it matches any single character (but see below) not from the rest of the list. If two characters in the list are separated by `-`, this is shorthand for the full range of characters between those two (inclusive) in the collating sequence, e.g. `[0-9]` in ASCII matches any decimal digit. It is illegal(*) for two ranges to share an endpoint, e.g. `a-c-e`. Ranges are very collating-sequence-dependent, and portable programs should avoid relying on them.

To include a literal `]` in the list, make it the first character (following a possible `^`). To include a literal `-`, make it the first or last character, or the second endpoint of a range. To use a literal `-` as the first endpoint of a range, enclose it in `[.` and `.]` to make it a collating element (see below). With the exception of these and some combinations using `[` (see next paragraphs), all other special characters, including `\`, lose their special significance within a bracket expression.

Within a bracket expression, a collating element (a character, a multi-character sequence that collates as if it were a single character, or a collating-sequence name for either) enclosed in `[.` and `.]` stands for the sequence of characters of that collating element. The sequence is a single element of the bracket expression's list. A bracket expression containing a multi-character collating element can thus match more than one character, e.g. if the collating sequence includes a `ch` collating element, then the RE `[[.ch.]]*c` matches the first five characters of "chchcc".

Within a bracket expression, a collating element enclosed in `[=` and `=]` is an equivalence class, standing for the sequences of characters of all collating elements equivalent to that one, including itself. (If there are no other equivalent collating elements, the treatment is as if the enclosing delimiters were `[.` and `.]`.) For example, if `o` and `^` are the members of an equivalence class, then `[[=o=]]`, `[[=^=]]`, and `[o^]` are all synonymous. An equivalence class may not be an endpoint of a range.

Within a bracket expression, the name of a character class enclosed in `[:` and `:]` stands for the list of all characters belonging to that class. Standard character class names are:

    alnum	digit	punct
    alpha	graph	space
    blank	lower	upper
    cntrl	print	xdigit

These stand for the character classes defined by `isalnum` (see isalnum), `isdigit` (see isdigit), `ispunct` (see ispunct), `isalpha` (see isalpha), `isgraph` (see isgraph), `isspace` (see isspace) (`blank` is the same as `space`), `islower` (see islower), `isupper` (see isupper), `iscntrl` (see iscntrl), `isprint` (see isprint), and `isxdigit` (see isxdigit), respectively. A locale may provide others. A character class may not be used as an endpoint of a range.

There are two special cases(*) of bracket expressions: the bracket expressions `[[:<:]]` and `[[:>:]]` match the null string at the beginning and end of a word respectively. A word is defined as a sequence of word characters which is neither preceded nor followed by word characters. A word character is an `alnum` character (as defined by `isalnum` library function) or an underscore. This is an extension, compatible with but not specified by POSIX 1003.2, and should be used with caution in software intended to be portable to other systems.

In the event that an RE could match more than one substring of a given string, the RE matches the one starting earliest in the string. If the RE could match more than one substring starting at that point, it matches the longest. Subexpressions also match the longest possible substrings, subject to the constraint that the whole match be as long as possible, with subexpressions starting earlier in the RE taking priority over ones starting later. Note that higher-level subexpressions thus take priority over their lower-level component subexpressions.

Match lengths are measured in characters, not collating elements. A null string is considered longer than no match at all. For example, `bb*` matches the three middle characters of "abbbc", `(wee|week)(knights|nights)` matches all ten characters of "weeknights", when `(.*).*` is matched against "abc" the parenthesized subexpression matches all three characters, and when `(a*)*` is matched against "bc" both the whole RE and the parenthesized subexpression match the null string.

If case-independent matching is specified, the effect is much as if all case distinctions had vanished from the alphabet. When an alphabetic that exists in multiple cases appears as an ordinary character outside a bracket expression, it is effectively transformed into a bracket expression containing both cases, e.g. `x` becomes `[xX]`. When it appears inside a bracket expression, all case counterparts of it are added to the bracket expression, so that (e.g.) `[x]` becomes `[xX]` and `[^x]` becomes `[^xX]`.

No particular limit is imposed on the length of REs(*). Programs intended to be portable should not employ REs longer than 256 bytes, as an implementation can refuse to accept such REs and remain POSIX-compliant.

Obsolete (basic) regular expressions differ in several respects. `|`, `+`, and `?` are ordinary characters and there is no equivalent for their functionality. The delimiters for bounds are `\{` and `\}`, with `{` and `}` by themselves ordinary characters. The parentheses for nested subexpressions are `\(` and `\)`, with `(` and `)` by themselves ordinary characters. `^` is an ordinary character except at the beginning of the RE or(*) the beginning of a parenthesized subexpression, `$` is an ordinary character except at the end of the RE or(*) the end of a parenthesized subexpression, and `*` is an ordinary character if it appears at the beginning of the RE or the beginning of a parenthesized subexpression (after a possible leading `^`). Finally, there is one new type of atom, a back reference: `\` followed by a non-zero decimal digit d matches the same sequence of characters matched by the dth parenthesized subexpression (numbering subexpressions by the positions of their opening parentheses, left to right), so that (e.g.) `\([bc]\)\1` matches "bb" or "cc" but not "bc".

### History

This implementation of the POSIX regexp functionality was written by Henry Spencer.

### Bugs

The locale is always assumed to be the default one of 1003.2, and only the collating elements etc. of that locale are available.

`regcomp` implements bounded repetitions by macro expansion, which is costly in time and space if counts are large or bounded repetitions are nested.

An RE like, say, `((((a{1,100}){1,100}){1,100}){1,100}){1,100}`, will (eventually) run almost any existing machine out of swap space.

There are suspected problems with response to obscure error conditions. Notably, certain kinds of internal overflow, produced only by truly enormous REs or by multiply nested bounded repetitions, are probably not handled well.

Due to a mistake in 1003.2, things like `a)b` are legal REs because `)` is a special character only in the presence of a previous unmatched `(`. This can't be fixed until the spec is fixed.

The standard's definition of back references is vague. For example, does `a\e(\e(b\e)*\e2\e)*d` match "abbbd"? Until the standard is clarified, behavior in such cases should not be relied on.

### Portability

not ANSI, POSIX

Node:regerror, Next:regexec, Previous:regcomp, Up:Alphabetical List

## regerror

### Syntax

    #include <sys/types.h>
    #include <regex.h>

    size_t regerror(int errcode, const regex_t *preg,
                    char *errbuf, size_t errbuf_size);

### Description

`regerror` maps a non-zero value of errcode from either `regcomp` (Return Value, see regcomp) or `regexec` (Return Value, see regexec) to a human-readable, printable message.

If preg is non-`NULL`, the error code should have arisen from use of the variable of the type `regex_t` pointed to by preg, and if the error code came from `regcomp`, it should have been the result from the most recent `regcomp` using that `regex_t` variable. (`regerror` may be able to supply a more detailed message using information from the `regex_t` than from errcode alone.) `regerror` places the `NUL`-terminated message into the buffer pointed to by errbuf, limiting the length (including the `NUL`) to at most errbuf_size bytes. If the whole message won't fit, as much of it as will fit before the terminating `NUL` is supplied. In any case, the returned value is the size of buffer needed to hold the whole message (including terminating `NUL`). If errbuf_size is 0, errbuf is ignored but the return value is still correct.

If the errcode given to `regerror` is first ORed with `REG_ITOA`, the "message" that results is the printable name of the error code, e.g. "REG_NOMATCH", rather than an explanation thereof. If errcode is `REG_ATOI`, then preg shall be non-NULL and the `re_endp` member of the structure it points to must point to the printable name of an error code (e.g. "REG_ECOLLATE"); in this case, the result in errbuf is the decimal representation of the numeric value of the error code (0 if the name is not recognized). `REG_ITOA` and `REG_ATOI` are intended primarily as debugging facilities; they are extensions, compatible with but not specified by POSIX 1003.2, and should be used with caution in software intended to be portable to other systems. Be warned also that they are considered experimental and changes are possible.

### Return Value

The size of buffer needed to hold the message (including terminating `NUL`) is always returned, even if errbuf_size is zero.

### Portability

not ANSI, POSIX

Node:regexec, Next:regfree, Previous:regerror, Up:Alphabetical List

## regexec

### Syntax

    #include <sys/types.h>
    #include <regex.h>

    int regexec(const regex_t *preg, const char *string,
                size_t nmatch, regmatch_t pmatch[], int eflags);

### Description

`regexec` matches the compiled RE pointed to by preg against the string, subject to the flags in eflags, and reports results using nmatch, pmatch, and the returned value. The RE must have been compiled by a previous invocation of `regcomp` (see regcomp). The compiled form is not altered during execution of `regexec`, so a single compiled RE can be used simultaneously by multiple threads.

By default, the NUL-terminated string pointed to by string is considered to be the text of an entire line, with the NUL indicating the end of the line. (That is, any other end-of-line marker is considered to have been removed and replaced by the NUL.)

The eflags argument is the bitwise OR of zero or more of the following flags:

`REG_NOTBOL`
  The first character of the string is not the beginning of a line, so the `^` anchor should not match before it. This does not affect the behavior of newlines under `REG_NEWLINE` (REG_NEWLINE, see regcomp).
`REG_NOTEOL`
  The NUL terminating the string does not end a line, so the `$` anchor should not match before it. This does not affect the behavior of newlines under `REG_NEWLINE` (REG_NEWLINE, see regcomp).
`REG_STARTEND`
  The string is considered to start at `string + pmatch[0].rm_so` and to have a terminating `NUL` located at `string + pmatch[0].rm_eo` (there need not actually be a `NUL` at that location), regardless of the value of nmatch. See below for the definition of pmatch and nmatch. This is an extension, compatible with but not specified by POSIX 1003.2, and should be used with caution in software intended to be portable to other systems. Note that a non-zero `rm_so` does not imply `REG_NOTBOL`; `REG_STARTEND` affects only the location of the string, not how it is matched.
`REG_TRACE`
  trace execution (printed to stdout)
`REG_LARGE`
  force large representation
`REG_BACKR`
  force use of backref code

Regular Expressions' Syntax, See regcomp, for a discussion of what is matched in situations where an RE or a portion thereof could match any of several substrings of string.

If `REG_NOSUB` was specified in the compilation of the RE (REG_NOSUB, see regcomp), or if nmatch is 0, `regexec` ignores the pmatch argument (but see below for the case where `REG_STARTEND` is specified). Otherwise, pmatch should point to an array of nmatch structures of type `regmatch_t`. Such a structure has at least the members `rm_so` and `rm_eo`, both of type `regoff_t` (a signed arithmetic type at least as large as an `off_t` and a `ssize_t`, containing respectively the offset of the first character of a substring and the offset of the first character after the end of the substring. Offsets are measured from the beginning of the string argument given to `regexec`. An empty substring is denoted by equal offsets, both indicating the character following the empty substring.

When `regexec` returns, the 0th member of the pmatch array is filled in to indicate what substring of string was matched by the entire RE. Remaining members report what substring was matched by parenthesized subexpressions within the RE; member `i` reports subexpression `i`, with subexpressions counted (starting at 1) by the order of their opening parentheses in the RE, left to right. Unused entries in the array--corresponding either to subexpressions that did not participate in the match at all, or to subexpressions that do not exist in the RE (that is, `i > preg->re_nsub`--have both `rm_so` and `rm_eo` set to `-1`. If a subexpression participated in the match several times, the reported substring is the last one it matched. (Note, as an example in particular, that when the RE `(b*)+` matches "bbb", the parenthesized subexpression matches the three `b`s and then an infinite number of empty strings following the last `b`, so the reported substring is one of the empties.)

If `REG_STARTEND` is specified in eflags, pmatch must point to at least one `regmatch_t` variable (even if nmatch is 0 or `REG_NOSUB` was specified in the compilation of the RE, REG_NOSUB, see regcomp), to hold the input offsets for `REG_STARTEND`. Use for output is still entirely controlled by nmatch; if nmatch is 0 or `REG_NOSUB` was specified, the value of `pmatch[0]` will not be changed by a successful `regexec`.

### Return Value

Normally, `regexec` returns 0 for success and the non-zero code `REG_NOMATCH` for failure. Other non-zero error codes may be returned in exceptional situations. The list of possible error return values is below:

`REG_ESPACE`
  ran out of memory
`REG_BADPAT`
  the passed argument preg doesn't point to an RE compiled by `regcomp`
`REG_INVARG`
  invalid argument(s) (e.g., `string + pmatch[0].rm_eo` is less than `string + pmatch[0].rm_so`)

### History

This implementation of the POSIX regexp functionality was written by Henry Spencer.

### Bugs

`regexec` performance is poor. nmatch exceeding 0 is expensive; nmatch exceeding 1 is worse. `regexec` is largely insensitive to RE complexity except that back references are massively expensive. RE length does matter; in particular, there is a strong speed bonus for keeping RE length under about 30 characters, with most special characters counting roughly double.

The implementation of word-boundary matching is a bit of a kludge, and bugs may lurk in combinations of word-boundary matching and anchoring.

### Portability

not ANSI, POSIX

Node:regfree, Next:remove, Previous:regexec, Up:Alphabetical List

## regfree

### Syntax

    #include <sys/types.h>
    #include <regex.h>

    void regfree(regex_t *preg);

### Description

`regfree` frees any dynamically-allocated storage associated with the compiled RE pointed to by preg. The remaining `regex_t` is no longer a valid compiled RE and the effect of supplying it to `regexec` or `regerror` is undefined.

### Portability

not ANSI, POSIX

Node:remove, Next:remque, Previous:regfree, Up:Alphabetical List

## remove

### Syntax

    #include <stdio.h>

    int remove(const char *file);

### Description

This function removes the named file from the file system. Unless you have an un-erase program, the file and its contents are gone for good.

### Return Value

Zero on success, nonzero on failure.

### Portability

ANSI, POSIX

### Example

    remove("/tmp/data.tmp");

Node:remque, Next:_rename, Previous:remove, Up:Alphabetical List

## remque

### Syntax

    #include <search.h>

    void remque(struct qelem *elem);

### Description

This function manipulates queues built from doubly linked lists. Each element in the queue must be in the form of `struct qelem` which is defined thus:

    struct qelem {
      struct qelem *q_forw;
      struct qelem *q_back;
      char q_data[0];
    }

This function removes the entry elem from a queue.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:_rename, Next:rename, Previous:remque, Up:Alphabetical List

## _rename

### Syntax

    #include <stdio.h>

    int _rename(const char *oldname, const char *newname);

### Description

This function renames an existing file or directory oldname to newname. It is much smaller that `rename` (see rename), but it can only rename a directory so it stays under the same parent, it cannot move directories between different branches of the directory tree. This means that in the following example, the first call will succeed, while the second will fail:

    _rename("c:/path1/mydir", "c:/path1/yourdir");
    _rename("c:/path1/mydir", "c:/path2");

On systems that support long filenames (see _use_lfn), `_rename` can also move directories (so that both calls in the above example succeed there), unless the `LFN` environment variable is set to `n`, or the `_CRT0_FLAG_NO_LFN` is set in the `_crt0_startup_flags` variable, See _crt0_startup_flags.

If you don't need the extra functionality offered by `rename` (which usually is only expected by Unix-born programs), you can use `_rename` instead and thus make your program a lot smaller.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

Node:rename, Next:rewind, Previous:_rename, Up:Alphabetical List

## rename

### Syntax

    #include <stdio.h>

    int rename(const char *oldname, const char *newname);

### Description

This function renames an existing file or directory oldname to newname. If newname exists, then it is first removed. If newname is a directory, it must be empty (or else errno will be set to `ENOTEMPTY`), and must not include oldname in its path prefix (otherwise, errno will be set to `EINVAL`). If newname exists, both oldname and newname must be of the same type (both directories or both regular files) (or else errno will be set to `ENOTDIR` or `EISDIR`), and must reside on the same logical device (otherwise, errno will be set to `EXDEV`). Wildcards are not allowed in either oldname or newname. DOS won't allow renaming a current directory even on a non-default drive (you will get the `EBUSY` or `EINVAL` in errno). `ENAMETOOLONG` will be returned for pathnames which are longer than the limit imposed by DOS. If oldname doesn't exist, errno will be set to `ENOENT`. For most of the other calamities, DOS will usually set errno to `EACCES`.

If anything goes wrong during the operation of `rename()`, the function tries very hard to leave the things as ther were before it was invoked, but it might not always succeed.

### Return Value

Zero on success, nonzero on failure.

### Portability

ANSI, POSIX

### Example

    rename("c:/mydir/some.doc", "c:/yourdir/some.sav");
    rename("c:/path1/mydir", "c:/path2");

Node:rewind, Next:rewinddir, Previous:rename, Up:Alphabetical List

## rewind

### Syntax

    #include <stdio.h>

    void rewind(FILE *file);

### Description

This function repositions the file pointer to the beginning of the file and clears the error indicator.

### Return Value

None.

### Portability

ANSI, POSIX

### Example

    rewind(stdin);

Node:rewinddir, Next:rindex, Previous:rewind, Up:Alphabetical List

## rewinddir

### Syntax

    #include <dirent.h>

    void rewinddir(DIR *dir);

### Description

This function resets the position of the dir so that the next call to `readdir` (see readdir) starts at the beginning again.

### Return Value

None.

### Portability

not ANSI, POSIX

### Example

    DIR *d = opendir(".");
    rewinddir(d);

Node:rindex, Next:rmdir, Previous:rewinddir, Up:Alphabetical List

## rindex

### Syntax

    #include <strings.h>

    char *rindex(const char *string, int ch);

### Description

Returns a pointer to the last occurrence of ch in string. Note that the `NULL` character counts, so if you pass zero as ch you'll get a pointer to the end of the string back.

### Return Value

A pointer to the character, or `NULL` if it wasn't found.

### Portability

not ANSI, not POSIX

### Example

    char *last_slash = rindex(filename, '/');

Node:rmdir, Next:run_child, Previous:rindex, Up:Alphabetical List

## rmdir

### Syntax

    #include <unistd.h>

    int rmdir(const char *dirname);

### Description

This function removes directory dirname. The directory must be empty.

### Return Value

Zero if the directory was removed, nonzero on failure.

### Portability

not ANSI, POSIX

### Example

    rmdir("/tmp/datadir");

Node:run_child, Next:save_npx, Previous:rmdir, Up:Alphabetical List

## run_child

### Syntax

    #include <debug/dbgcom.h>

    void run_child (void);

### Description

This function starts or resumes the debugged program, via a `longjmp` to the debuggee's code. When the debuggee hits a breakpoint, or exits normally, the exception handler that is called to service the breakpoint exception will `longjmp` back to `run_child`, and it will then return to the caller.

After `run_child` returns, the debugger usually examines the `a_tss` variable to find out the reason the debuggee stopped. The `a_tss` variable is defined by the header `debug/tss.h` as follows:

    typedef struct TSS {
    	unsigned short tss_back_link;
    	unsigned short res0;
    	unsigned long  tss_esp0;
    	unsigned short tss_ss0;
    	unsigned short res1;
    	unsigned long  tss_esp1;
    	unsigned short tss_ss1;
    	unsigned short res2;
    	unsigned long  tss_esp2;
    	unsigned short tss_ss2;
    	unsigned short res3;
    	unsigned long  tss_cr3;

    	unsigned long  tss_eip;
    	unsigned long  tss_eflags;
    	unsigned long  tss_eax;
    	unsigned long  tss_ecx;
    	unsigned long  tss_edx;
    	unsigned long  tss_ebx;
    	unsigned long  tss_esp;
    	unsigned long  tss_ebp;
    	unsigned long  tss_esi;
    	unsigned long  tss_edi;
    	unsigned short tss_es;
    	unsigned short res4;
    	unsigned short tss_cs;
    	unsigned short res5;
    	unsigned short tss_ss;
    	unsigned short res6;
    	unsigned short tss_ds;
    	unsigned short res7;
    	unsigned short tss_fs;
    	unsigned short res8;
    	unsigned short tss_gs;
    	unsigned short res9;
    	unsigned short tss_ldt;
    	unsigned short res10;
    	unsigned short tss_trap;
    	unsigned char  tss_iomap;
    	unsigned char  tss_irqn;
    	unsigned long  tss_error;
    } TSS;

    extern TSS a_tss;

See the example below for a typical tests after `run_child` returns.

Note that, generally, you'd need to save the standard handles before calling `run_child` and restore them after it returns. Otherwise, if the debuggee redirects one of its standard handles, the corresponding debugger's standard handle is redirected as well. See redir_to_child, and see redir_to_debugger.

### Portability

not ANSI, not POSIX

### Example

     save_npx ();
     run_child ();
     load_npx ();

     if (a_tss.tss_irqn == 0x21)
      {
         status = DEBUGGEE_EXITED;
         exit_code = a_tss.tss_eax & 0xff;
      }
     else
      {
         status = DEBUGGEE_GOT_SIGNAL
         if (a_tss.tss_irqn == 0x75)
           signal_number = SIGINT;
         else if (a_tss.tss_irqn == 1 || a_tss.tss_irqn == 3)
           signal_number = SIGTRAP;  /* a breakpoint */
      }

Node:save_npx, Next:sbrk, Previous:run_child, Up:Alphabetical List

## save_npx

### Syntax

    #include <debug/dbgcom.h>

    extern NPX npx;
    void save_npx (void);

### Description

This function saves the state of the x87 numeric processor in the external variable `npx`. This variable is a structure defined as follows in the header `debug/dbgcom.h`:

    typedef struct {
      unsigned short sig0;
      unsigned short sig1;
      unsigned short sig2;
      unsigned short sig3;
      unsigned short exponent:15;
      unsigned short sign:1;
    } NPXREG;

    typedef struct {
      unsigned long control;
      unsigned long status;
      unsigned long tag;
      unsigned long eip;
      unsigned long cs;
      unsigned long dataptr;
      unsigned long datasel;
      NPXREG reg[8];
      long double st[8];
      char st_valid[8];
      long double mmx[8];
      char in_mmx_mode;
      char top;
    } NPX;

`save_npx` should be called immediately before `run_child` (see run_child) is called to begin or resume the debugged program.

To restore the x87 state when control is returned to the debugger, call `load_npx`, see load_npx.

### Portability

not ANSI, not POSIX

### Example

     save_npx ();
     run_child ();
     load_npx ();

Node:sbrk, Next:scanf, Previous:save_npx, Up:Alphabetical List

## sbrk

### Syntax

    #include <unistd.h>

    void *sbrk(int delta)

### Description

This function changes the "break" of the program by adding delta to it. This is the highest address that your program can access without causing a violation. Since the heap is the region under the break, you can expand the heap (where `malloc` gets memory from) by increasing the break.

This function is normally accessed only by `malloc` (see malloc).

### Return Value

The address of the first byte outside of the previous valid address range, or -1 if no more memory could be accessed. In other words, a pointer to the chunk of heap you just allocated, if you had passed a positive number.

### Portability

not ANSI, not POSIX

### Example

    char *buf;
    buf = sbrk(1000); /* allocate space */

Node:scanf, Next:Screen Variables, Previous:sbrk, Up:Alphabetical List

## scanf

### Syntax

    #include <stdio.h>

    int scanf(const char *format, ...);

### Description

This function scans formatted text from `stdin` and stores it in the variables pointed to by the arguments. See scanf.

The format string contains regular characters which much match the input exactly as well as a conversion specifiers, which begin with a percent symbol. Any whitespace in the format string matches zero or more of any whitespace characters in the input. Thus, a single space may match a newline and two tabs in the input. All conversions except `c` and `[` also skip leading whitespace automatically. Each conversion specifier contains the following fields:

- An asterisk (`*`) which indicates that the input should be converted according to the conversion spec, but not stored anywhere. This allows to describe an input field that is to be skipped.
- A width specifier, which specifies the maximum number of input characters to use in the conversion.
- An optional conversion qualifier, which may be `h` to specify `short`, `l` to specify doubles or long ints, or `L` or `ll` (two lower-case ell letters) to specify long doubles and the long long type. If the `h` qualifier appears before a specifier that implies conversion to a `long` or `float` or `double`, like in `%hD` or `%hf`, it is generally ignored.
- The conversion type specifier:
  `c`
    Copy the next character (or width characters) to the given buffer. This conversion suppresses skipping of the leading whitespace; use `%1s` to read the next non-whitespace character. Unlike with `%s`, the copied characters are not terminated with a null character. If the width parameter is not specified, a width of one is implied.
  `d`
    Convert the input to a signed `int` using 10 as the base of the number representation.
  `hd`
    Convert the input to a signed `short` using 10 as the base.
  `ld`
  `D`
    Convert the input to a signed `long` using 10 as the base.
  `Ld`
  `lld`
  `lD`
    Convert the input to a signed `long long` using 10 as the base.
  `e`
  `E`
  `f`
  `F`
  `g`
  `G`
    Convert the input to a floating point number (a `float`).
  `le`
  `lE`
  `lf`
  `lF`
  `lg`
  `lG`
    Convert the input to a `double`.
  `Le`
  `LE`
  `lle`
  `llE`
  `Lf`
  `LF`
  `llf`
  `llF`
  `Lg`
  `LG`
  `llg`
  `llG`
    Convert the input to a `long double`.
  `i`
    Convert the input, determining base automatically by the presence of `0x` or `0` prefixes, and store in an `int`. See strtol.
  `hi`
    Like `i`, but stores the result in a `short`.
  `li`
  `I`
    Like `i`, but stores the result in a `long`.
  `Li`
  `lli`
  `lI`
    Like `i`, but stores the result in a `long long`.
  `n`
    Store the number of characters scanned so far into the `int` pointed to by the argument.
  `hn`
    Like `n`, but the argument should point to a `short`.
  `ln`
    Like `n`, but the argument should point to a `long`.
  `Ln`
  `lln`
    Like `n`, but the argument should point to a `long long`.
  `o`
    Convert the input to a signed `int`, using base 8.
  `ho`
    Convert the input to a signed `short`, using base 8.
  `lo`
  `O`
    Convert the input to a signed `long`, using base 8.
  `Lo`
  `llo`
  `lO`
    Convert the input to a signed `long long`, using base 8.
  `p`
    Convert the input to a pointer. This is like using the `x` format.
  `s`
    Copy the input to the given string, skipping leading whitespace and copying non-whitespace characters up to the next whitespace. The string stored is then terminated with a null character.
  `u`
    Convert the input to an unsigned `int` using 10 as the base.
  `hu`
    Convert the input to an unsigned `short` using 10 as the base.
  `lu`
  `U`
    Convert the input to an unsigned `long` using 10 as the base.
  `Lu`
  `llu`
  `lU`
    Convert the input to an unsigned `long long` using 10 as the base.
  `x`
  `X`
    Convert the input to an unsigned `int`, using base 16.
  `hx`
  `hX`
    Convert the input to an unsigned `short`, using base 16.
  `lx`
  `lX`
    Convert the input to an unsigned `long`, using base 16.
  `Lx`
  `LX`
  `llx`
  `llX`
    Convert the input to an unsigned `long long`, using base 16.
  `[...]`
    Stores the matched characters in a `char` array, followed by a terminating null character. If you do not specify the width parameter, `scanf` behaves as if width had a very large value. Up to width characters are consumed and assigned, provided that they match the specification inside the brackets. The characters between the brackets determine which characters are allowed, and thus when the copying stops. These characters may be regular characters (example: `[abcd]`) or a range of characters (example: `[a-d]`). If the first character is a caret (`^`), then the set specifies the set of characters that do not get copied (i.e. the set is negated). To specify that the set contains a close-bracket (`]`), put it immediately after `[` or `[^`. To specify a literal dash (`-`), write it either immediately after `[` or `[^`, or immediately before the closing `]`.
  `%`
    This must match a percent character in the input.

Integer formats make use of `strtol` or `strtoul` to perform the actual conversions. Floating-point conversions use `strtod` and `_strtold`.

### Return Value

The number of items successfully matched and assigned. If input ends, or if there is any input failure before the first item is converted and assigned, `EOF` is returned. Note that literal characters (including whitespace) in the format string which matched input characters count as "converted items", so input failure after such characters were read and matched will not cause `EOF` to be returned.

### Portability

ANSI (see note 1), POSIX

Notes:

1. The conversion specifiers `F`, `D`, `I`, `O`, and `U` are DJGPP extensions; they are provided for compatibility with Borland C and other compilers. The conversion specifiers for the `long long` data type are GCC extensions. The meaning of `[a-c]` as a range of characters is a very popular extension to ANSI (which merely says a dash "may have a special meaning" in that context).

### Example

    int x, y;
    char buf[100];
    scanf("%d %d %s", &x, &y, buf);

    /* read to end-of-line */
    scanf("%d %[^\n]\n", &x, buf);
    /* read letters only */
    scanf("[a-zA-Z]", buf);

Node:Screen Variables, Next:ScreenClear, Previous:scanf, Up:Alphabetical List

## Screen Variables

### Syntax

    #include <go32.h>
    #include <pc.h>

    unsigned long ScreenPrimary;
    unsigned long ScreenSecondary;
    extern unsigned char ScreenAttrib;

### Description

The first two variables (actually, they are #define'd aliases to fields in the _go32_info_block structure see _go32_info_block) allow access to the video memory of the primary and secondary screens as if they were arrays. To reference them, you must use dosmemget()/dosmemput() functions (dosmemget, dosmemput) or any one of the far pointer functions (see _far*), as the video memory is not mapped into your default address space.

The variable ScreenAttrib holds the current attribute which is in use by the text screen writes. The attribute is constructed as follows:

bits 0-3 - foreground color;

bits 4-6 - background color;

bit 7 - blink on (1) or off (0).

### Example

_farpokew(_dos_ds, ScreenPrimary, ( ((unsigned short) attr) << 8) + char ));

Node:ScreenClear, Next:ScreenCols, Previous:Screen Variables, Up:Alphabetical List

## ScreenClear

### Syntax

    #include <pc.h>

    void  ScreenClear(void);

### Description

This function clears the text screen. It overwrites it by blanks with the current background and foreground as specified by ScreenAttrib (see Screen Variables).

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    ScreenClear();

Node:ScreenCols, Next:ScreenGetChar, Previous:ScreenClear, Up:Alphabetical List

## ScreenCols

### Syntax

    #include <pc.h>

    int ScreenCols(void);

### Description

This function returns the number of columns of the screen. It does so by looking at the byte at the absolute address 40:4Ah in the BIOS area. In text modes, the meaning of number of columns is obvious; in graphics modes, this value is the number of columns of text available when using the video BIOS functions to write text.

### Return Value

The number of columns.

### Portability

not ANSI, not POSIX

### Example

    int available_columns = ScreenCols();

Node:ScreenGetChar, Next:ScreenGetCursor, Previous:ScreenCols, Up:Alphabetical List

## ScreenGetChar

### Syntax

    #include <pc.h>

    void  ScreenGetChar(int *ch, int *attr, int col, int row);

### Description

This function stores the character and attribute of the current primary screen at row given by row and column given by col (these are zero-based) into the integers whose address is specified by ch and attr. It does so by directly accessing the video memory, so it will only work when the screen is in text mode. You can pass the value `NULL` in each of the pointers if you do not want to retrieve the the corresponding information.

Warning: note that both the variables ch and attr are pointers to an `int`, not to a `char`! You must pass a pointer to an `int` there, or your program will crash or work erratically.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    int ch, attr;

    ScreenGetChar(&ch, &attr, 0, 0);

Node:ScreenGetCursor, Next:ScreenMode, Previous:ScreenGetChar, Up:Alphabetical List

## ScreenGetCursor

### Syntax

    #include <pc.h>

    void  ScreenGetCursor(int *row, int *column);

### Description

This function retrieves the current cursor position of the default video page by calling function 3 of the interrupt 10h, and stores it in the variables pointed by row and column.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    ScreenGetCursor(&wherex, &wherey);

Node:ScreenMode, Next:ScreenPutChar, Previous:ScreenGetCursor, Up:Alphabetical List

## ScreenMode

### Syntax

    #include <pc.h>

    int  ScreenMode(void);

### Description

This function reports the current video mode as known to the system BIOS. It does so by accessing the byte at absolute address 40:49h.

### Return Value

The video mode.

### Portability

not ANSI, not POSIX

### Example

    video_mode = ScreenMode();

Node:ScreenPutChar, Next:ScreenPutString, Previous:ScreenMode, Up:Alphabetical List

## ScreenPutChar

### Syntax

    #include <pc.h>

    void  ScreenPutChar(int ch, int attr, int col, int row);

### Description

This function writes the character whose value is specified in ch with an attribute attr at row given by row and column given by col, which are zero-based. It does so by directly accessing the video memory, so it will only work when the screen is in text mode.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    ScreenPutChar('R', (BLUE << 4) | LIGHTMAGENTA, 75, 0);

Node:ScreenPutString, Next:ScreenRetrieve, Previous:ScreenPutChar, Up:Alphabetical List

## ScreenPutString

### Syntax

    #include <pc.h>

    void  ScreenPutString(const char *str, int attr, int column, int row);

### Description

Beginning at screen position given by column and row, this function displays the string given by str. Each string character gets the attribute given by attr. If column or row have values outside legal range for current video mode, nothing happens. The variables row and column are zero-based (e.g., the topmost row is row 0).

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    ScreenPutString("Hello, world!", (BLUE << 4) | LIGHTBLUE, 20, 10);

Node:ScreenRetrieve, Next:ScreenRows, Previous:ScreenPutString, Up:Alphabetical List

## ScreenRetrieve

### Syntax

    #include <pc.h>

    void  ScreenRetrieve(void *buf);

### Description

This function stores a replica of the current primary screen contents in the buffer pointed to by buf. It assumes without checking that buf has enough storage to hold the data. The required storage can be computed as `ScreenRows()*ScreenCols()*2` (ScreenRows, ScreenCols).

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    unsigned *saved_screen = (unsigned *)alloca(ScreenRows()*ScreenCols()*2;

    ScreenRetrieve(saved_screen);

Node:ScreenRows, Next:ScreenSetCursor, Previous:ScreenRetrieve, Up:Alphabetical List

## ScreenRows

### Syntax

    #include <pc.h>

    int ScreenRows(void);

### Description

This function returns the number of rows of the text screen. It does so by looking at the byte at the absolute address 40:84h in the BIOS area. This method works only for video adapters with their own BIOS extensions, like EGA, VGA, SVGA etc.

### Return Value

The number of rows.

### Portability

not ANSI, not POSIX

### Example

    int rows = ScreenRows();

Node:ScreenSetCursor, Next:ScreenUpdate, Previous:ScreenRows, Up:Alphabetical List

## ScreenSetCursor

### Syntax

    #include <pc.h>

    void  ScreenSetCursor(int  row, int  column);

### Description

This function moves the cursor position on the default video page to the point given by (zero-based) row and column, by calling function 2 of interrupt 10h.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    ScreenSetCursor(0, 0);   /* home the cursor */

Node:ScreenUpdate, Next:ScreenUpdateLine, Previous:ScreenSetCursor, Up:Alphabetical List

## ScreenUpdate

### Syntax

    #include <pc.h>

    void  ScreenUpdate(void *buf);

### Description

This function writes the contents of the buffer buf to the primary screen. The buffer should contain an exact replica of the video memory, including the characters and their attributes.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    ScreenUpdate(saved_screen);

Node:ScreenUpdateLine, Next:ScreenVisualBell, Previous:ScreenUpdate, Up:Alphabetical List

## ScreenUpdateLine

### Syntax

    #include <pc.h>

    void  ScreenUpdateLine(void *buf, int row);

### Description

This function writes the contents of buf to the screen line number given in row (the topmost line is row 0), on the primary screen.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    ScreenUpdateLine(line_buf, 10);

Node:ScreenVisualBell, Next:searchpath, Previous:ScreenUpdateLine, Up:Alphabetical List

## ScreenVisualBell

### Syntax

    #include <pc.h>

    void  ScreenVisualBell(void);

### Description

This function flashes the screen colors to produce the effect of "visual bell'. It does so by momentarily inverting the colors of every character on the screen.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    ScreenVisualBell();

Node:searchpath, Next:seekdir, Previous:ScreenVisualBell, Up:Alphabetical List

## searchpath

### Syntax

    #include <dir.h>

    char * searchpath(const char *file);

### Description

Given a name of a file in file, searches for that file in a list of directories, including the current working directory and directories listed in the `PATH` environment variable, and if found, returns the file name with leading directories prepended, so that the result can be used to access the file (e.g. by calling `open` or `stat`).

If file includes a drive letter or leading directories, `searchpath` first tries that name unaltered, in case it is already a fully-qualified path, or is relative to the current working directory. If that fails, it tries every directory in `PATH` in turn. Note that this will find e.g. `c:/foo/bar/baz.exe` if you pass `bar/baz.exe` to `searchpath` and if `c:/foo` is mentioned in `PATH`.

### Return Value

When successfull, the function returns a pointer to a static buffer where the full pathname of the found file is stored. Otherwise, it returns `NULL`. (The static buffer is overwritten on each call.)

### Portability

not ANSI, not POSIX

This function is provided for compatibility with Borland's library. However, note that the Borland version disregards the leading directories altogether and searches for the basename only. Thus, it will happily find e.g. `c:/foo/bar/baz.exe`, even if the directory `c:/foo/bar` doesn't exist, provided that `baz.exe` is somewhere on your `PATH`. We think this is a bug, so DJGPP's implementation doesn't behave like that.

### Example

      printf("%s was found as %s\n", argv[1], searchpath(argv[1]));

Node:seekdir, Next:select, Previous:searchpath, Up:Alphabetical List

## seekdir

### Syntax

    #include <dirent.h>

    void seekdir(DIR *dir, long loc);

### Description

This function sets the location pointer in dir to the specified loc. Note that the value used for loc should be either zero or a value returned by `telldir` (see telldir). The next call to `readdir` (see readdir) will read whatever entry follows that point in the directory.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    int q = telldir(dir);
    do_stuff();
    seekdir(dir, q);

Node:select, Next:_set_screen_lines, Previous:seekdir, Up:Alphabetical List

## select

### Syntax

    #include <time.h>

    int
    select(int nfds,
    	fd_set *readfds,
    	fd_set *writefds,
    	fd_set *exceptfds,
    	struct timeval *timeout)

### Description

This function waits for files to be ready for input or output, or to have exceptional condition pending, or for a timeout.

Each `fd_set` variable is a bitmap representation of a set of file descriptors, one bit for every descriptor. The following macros shall be used to deal with these sets:

`FD_ZERO(p)`
  Initialize the set to all zeros.
`FD_SET(n, p)`
  Set member n in set p.
`FD_CLR(n, p)`
  Clear member n in set p.
`FD_ISSET(n, p)`
  Return the value of member n in set p.
`FD_SETSIZE`
  The maximum number of descriptors supported by the system.

The nfds parameter is the number of bits to be examined in each of the `fd_set` sets: the function will only check file descriptors `0` through `nfds - 1`, even if some bits are set for descriptors beyond that.

On input, some of the bits of each one of the `fd_set` sets for which the function should wait, should be set using the `FD_SET` macro. `select` examines only those descriptors whose bits are set.

Any of `readfds`, `writefds`, and `exceptfds` can be a `NULL` pointer, if the caller is not interested in testing the corresponding conditions.

On output, if `select` returns a non-negative value, each non-`NULL` argument of the three sets will be replaced with a subset in which a bit is set for every descriptor that was found to be, respectively, ready for input, ready for output, and pending an exceptional condition. Note that if `select` returns -1, meaning a failure, the descriptor sets are unchanged, so you should always test the return value before looking at the bits in the returned sets.

The timeout value may be a NULL pointer (no timeout, i.e., wait forever), a pointer to a zero-value structure (poll mode, i.e., test once and exit immediately), or a pointer to a `struct timeval` variable (timeout: `select` will repeatedly test all the descriptors until some of them become ready, or the timeout expires).

`struct timeval` is defined as follows:

    struct timeval {
      time_t tv_sec;
      long tv_usec;
    };

### Return Value

On successfull return, `select` returns the number of files ready, or 0, if the timeout expired. The input sets are replaced with subsets that describe which files are ready for which operations. If `select` returns 0 (i.e., the timeout has expired), all the non-`NULL` sets have all their bits reset to zero.

On failure, `select` returns -1, sets `errno` to a suitable value, and leaves the descriptor sets unchanged.

### Portability

not ANSI, not POSIX

### Example

      struct timeval timeout;
      fd_set read_fds, write_fds;
      int i, select_result;

      timeout.tv_sec = 5;  /* 5-second timeout */
      timeout.tv_usec = 0;

      /* Display status of the 5 files open by default.  */
      for (i = 0; i < 5; i++)
        {

          FD_ZERO (&read_fds);
          FD_SET (i, &read_fds);
          select_result = select (i + 1, &read_fds, 0, 0, &timeout);
          if (select_result == -1)
            {
              fprintf(stderr, "%d: Failure for input", i);
              perror("");
            }
          else
            fprintf(stderr,
                    "%d: %s ready for input\n", i, select_result ? "" : "NOT");
          FD_ZERO (&write_fds);
          FD_SET (i, &write_fds);
          select_result = select (i + 1, 0, &write_fds, 0, &timeout);
          if (select_result == -1)
            {
              fprintf(stderr, "%d: Failure for output", i);
              perror("");
            }
          else
            fprintf(stderr,
                    "%d: %s ready for output\n", i, select_result ? "" : "NOT");
        }

### Implementation Notes

The following notes describe some details pertinent to the DJGPP implementation of `select`:

- While `select` waits for the timeout to expire, it repeatedly calls the `__dpmi_yield` function (see __dpmi_yield), so that any other programs that run at the same time (e.g., on Windows) get more CPU time.
- A file handle that belongs to a `FILE` object created by `fopen` or `fdopen` (see fopen) for which `feof` or `ferror` return non-zero, will be reported in the `exceptfds` set; also, such a handle will be reported not input-ready if there are no pending buffered characters in the `FILE` object. This might be a feature or a bug, depending on your point of view; in particular, Unix implementations usually don't check buffered input. Portable programs should refrain from mixing `select` with buffered I/O.
- DOS doesn't support exceptional conditions, so file handles used for unbuffered I/O will never be marked in `exceptfds`.
- DOS always returns an output-ready indication for a file descriptor connected to a disk file. So use of `writefds` is only meaningful for character devices.
- The usual text-mode input from the keyboard and other character devices is line-buffered by DOS. This means that if you type one character, `select` will indicate that file handle 0 is ready for input, but a call to `getc` will still block until the <Enter> key is pressed. If you need to make sure that reading a single character won't block, you should read either with BIOS functions such as `getkey` (see getkey, or with raw input DOS functions such as `getch` (see getch), or switch the handle to binary mode with a call to `setmode` (see setmode).

Node:_set_screen_lines, Next:setbuf, Previous:select, Up:Alphabetical List

## _set_screen_lines

### Syntax

    #include <conio.h>

    void _set_screen_lines(int nlines);

### Description

This function sets the text screen width to 80 and its height to the value given by nlines, which can be one of the following: 25, 28, 35, 40, 43 or 50. On a CGA, only 25-line screen is supported. On an EGA, you can use 25, 35 and 43. VGA, PGA and MCGA support all of the possible dimensions. The number of columns (i.e., screen width) is 80 for all of the above resolutions, because the standard EGA/VGA has no way of changing it. After this function returns, calls to `gettextinfo()` will return the actual screen dimensions as set by `_set_screen_lines()`. That is, you can e.g. test whether `_set_screen_lines()` succeeded by checking the screen height returned by `gettextinfo()` against the desired height. This function has a side effect of erasing the screen contents, so application programs which use it should make their own arrangements to redisplay it.

### Portability

not ANSI, not POSIX

Node:setbuf, Next:setbuffer, Previous:_set_screen_lines, Up:Alphabetical List

## setbuf

### Syntax

    #include <stdio.h>

    void setbuf(FILE *file, char *buffer);

### Description

This function modifies the buffering characteristics of file. First, if the file already has a buffer, it is freed. If there was any pending data in it, it is lost, so this function should only be used immediately after a call to `fopen`.

If the buffer passed is `NULL`, the file is set to unbuffered. If a non-`NULL` buffer is passed, it must be at least `BUFSIZ` bytes in size, and the file is set to fully buffered.

See setbuffer. See setlinebuf. See setvbuf.

### Return Value

None.

### Portability

ANSI, POSIX

### Example

    setbuf(stdout, malloc(BUFSIZ));

Node:setbuffer, Next:setcbrk, Previous:setbuf, Up:Alphabetical List

## setbuffer

### Syntax

    #include <stdio.h>

    void setbuffer(FILE *file, char *buffer, int length);

### Description

This function modifies the buffering characteristics of file. First, if the file already has a buffer, it is freed. If there was any pending data in it, it is lost, so this function should only be used immediately after a call to `fopen`.

If the buffer passed is `NULL`, the file is set to unbuffered. If a non-`NULL` buffer is passed, it must be at least size bytes in size, and the file is set to fully buffered.

See setbuf. See setlinebuf. See setvbuf.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    setbuffer(stdout, malloc(10000), 10000);

Node:setcbrk, Next:_setcursortype, Previous:setbuffer, Up:Alphabetical List

## setcbrk

### Syntax

    #include <dos.h>

    void setcbrk(int check);

### Description

Set the setting of the Ctrl-Break checking flag in MS-DOS. If check is zero, checking is not done. If nonzero, checking is done.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:_setcursortype, Next:setdate, Previous:setcbrk, Up:Alphabetical List

## _setcursortype

### Syntax

    #include <conio.h>

    void _setcursortype(int _type);

### Description

Sets the cursor type. _type is one of the following:

`_NOCURSOR`
  No cursor is displayed.
`_SOLIDCURSOR`
  A solid block is displayed.
`_NORMALCURSOR`
  An underline cursor is displayed.

### Portability

not ANSI, not POSIX

Node:setdate, Next:setdisk, Previous:_setcursortype, Up:Alphabetical List

## setdate

### Syntax

    #include <dos.h>

    void setdate(struct date *ptr);

### Description

This function sets the current time.

For the description of `struct date`, see getdate. Also see settime.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    struct date d;
    setdate(&d);

Node:setdisk, Next:setenv, Previous:setdate, Up:Alphabetical List

## setdisk

### Syntax

    #include <dir.h>

    int setdisk(int drive);

### Description

This function sets the current disk (0=A).

See also getdisk.

### Return Value

The highest drive actually present that the system can reference.

### Portability

not ANSI, not POSIX

### Example

    printf("There are %d drives\n", setdisk(getdisk()));

Node:setenv, Next:setftime, Previous:setdisk, Up:Alphabetical List

## setenv

### Syntax

    #include <stdlib.h>

    int setenv(const char *name, const char *value, int rewrite);

### Description

This function sets the environment variable name to value. If rewrite is set, then this function will replace any existing value. If it is not set, it will only put the variable into the environment if that variable isn't already defined.

### Return Value

Zero on success, -1 on failure.

### Portability

not ANSI, not POSIX

Node:setftime, Next:setgid, Previous:setenv, Up:Alphabetical List

## setftime

### Syntax

    #include <dos.h>

    int setftime(int handle, struct ftime *ftimep);

### Description

This function sets the modification time of a file. Note that since writing to a file, and closing a file opened for writing, also sets the modification time, you should only use this function on files opened for reading.

See getftime, for the description of `struct ftime`.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    int q = open("data.txt", O_RDONLY);
    struct ftime f;
    f.ft_sec = f.ft_min = f.ft_hour = f.ft_day = f.ft_month = f.ft_year = 0;
    setftime(q, &f);
    close(q);

Node:setgid, Next:setgrent, Previous:setftime, Up:Alphabetical List

## setgid

### Syntax

    #include <unistd.h>

    int setgid(gid_t gid);

### Description

This function is simulated, since MS-DOS does not support group IDs.

### Return Value

If gid is equal to that returned by see getgid, returns zero. Otherwise, returns -1 and sets `errno` to EPERM.

### Portability

not ANSI, POSIX

Node:setgrent, Next:setitimer, Previous:setgid, Up:Alphabetical List

## setgrent

### Syntax

    #include <grp.h>

    void setgrent(void);

### Description

This function should be called before any call to `getgrent`, `getgrgid`, or `getgrnam`, to start searching the groups' list from the beginning. See getgrent.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:setitimer, Next:setjmp, Previous:setgrent, Up:Alphabetical List

## setitimer

### Syntax

    #include <sys/time.h>

    extern long __djgpp_clock_tick_interval;

    struct timeval {
      time_t tv_sec;
      long tv_usec;
    };

    struct itimerval {
      struct timeval it_interval;    /* timer interval */
      struct timeval it_value;       /* current value */
    };

    int setitimer(int which, struct itimerval *value, struct itimerval *ovalue);

### Description

Each process has two interval timers, `ITIMER_REAL` and `ITIMER_PROF`, which raise the signals `SIGALRM` and `SIGPROF`, respectively. These are typically used to provide `alarm` and profiling capabilities.

This function changes the current value of the interval timer specified by which to the values in structure value. The previous value of the timer is returned in ovalue if it is not a `NULL` pointer. When the timer expires, the appropriate signal is raised.

If value is a `NULL` pointer, `setitimer` stores the previous timer value in ovalue (if it is non-`NULL`), like `getitimer` does, but otherwise does nothing.

A timer is defined by the `itimerval` structure. If the `it_value` member is non-zero it specifies the time to the next timer expiration. If `it_interval` is non-zero, it specifies the value with which to reload the timer upon expiration. Setting `it_value` to zero disables a timer. Setting `it_interval` to zero causes the timer to stop after the next expiration (assuming that `it_value` is non-zero).

Although times can be given with microsecond resolution, the granularity is determined by the timer interrupt frequency. Time values smaller than the system clock granularity will be rounded up to that granularity, before they are used. This means that passing a very small but non-zero value in `value->it_interval.tv_usec` will cause the system clock granularity to be stored and returned by the next call to `getitimer`. See the example below.

If an application changes the system clock speed by reprogramming the timer chip, it should make the new clock speed known to `setitimer`, otherwise intervals smaller than the default PC clock speed cannot be set with a call to `setitimer` due to rounding up to clock granularity. To this end, an external variable `__djgpp_clock_tick_interval` is provided, which should be set to the number of microseconds between two timer ticks that trigger Interrupt 8. The default value of this variable is `-1`, which causes `setitimer` to work with 54926 microsecond granularity that corresponds to the standard 18.2Hz clock frequency. The library never changes the value of `__djgpp_clock_tick_interval`.

### Return Value

Returns 0 on success, -1 on failure (and sets `errno`).

### Portability

not ANSI, not POSIX

### Bugs

This version uses `uclock` (see uclock) to determine the time of expiration. Under Windows 3.X, this fails because the OS reprograms the timer. Under Windows 9X, `uclock` sometimes reports erratic (non-increasing) time values; in these cases the timer might fire at a wrong time.

A misfeature of Windows 9X prevents the timer tick interrupt from being delivered to programs that are in the background (i.e. don't have the focus), even though the program itself might continue to run, if you uncheck the Background: Always suspend property in the Property Sheets. Therefore, the timers will not work in background programs on Windows 9X.

Also, debuggers compiled with DJGPP v2.02 and earlier cannot cope with timers and report `SIGSEGV` or `SIGABRT`, since signals were not supported in a debugged program before DJGPP v2.03.

### Example

    /* Find out what is the system clock granularity.  */

      struct itimerval tv;

      tv.it_interval.tv_sec = 0;
      tv.it_interval.tv_usec = 1;
      tv.it_value.tv_sec = 0;
      tv.it_value.tv_usec = 0;
      setitimer (ITIMER_REAL, &tv, 0);
      setitimer (ITIMER_REAL, 0, &tv);
      printf ("System clock granularity: %ld microseconds.\n",
    	  tv.it_interval.tv_usec);

Node:setjmp, Next:setlinebuf, Previous:setitimer, Up:Alphabetical List

## setjmp

### Syntax

    #include <setjmp.h>

    int setjmp(jmp_buf j);

### Description

This function stores the complete CPU state into j. This information is complete enough that `longjmp` (see longjmp) can return the program to that state. It is also complete enough to implement coroutines.

### Return Value

This function will return zero if it is returning from it's own call. If longjmp is used to restore the state, it will return whatever value was passed to longjmp, except if zero is passed to longjmp it will return one.

### Portability

ANSI, POSIX

### Example

    jmp_buf j;
    if (setjmp(j))
      return;
    do_something();
    longjmp(j, 1);

Node:setlinebuf, Next:setlocale, Previous:setjmp, Up:Alphabetical List

## setlinebuf

### Syntax

    #include <stdio.h>

    void setlinebuf(FILE *file);

### Description

This function modifies the buffering characteristics of file. First, if the file already has a buffer, it is freed. If there was any pending data in it, it is lost, so this function should only be used immediately after a call to `fopen`.

Next, a buffer is allocated and the file is set to line buffering.

See setbuf. See setlinebuf. See setvbuf.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    setlinebuf(stderr);

Node:setlocale, Next:setmntent, Previous:setlinebuf, Up:Alphabetical List

## setlocale

### Syntax

    #include <locale.h>

    char *setlocale(int category, const char *locale);

### Description

This function sets part or all of the current locale. The category is one of the following:

`LC_ALL`
  Set all parts of the locale.
`LC_COLLATE`
  Set the collating information.
`LC_CTYPE`
  Set the character type information.
`LC_MONETARY`
  Set the monetary formatting information.
`LC_NUMERIC`
  Set the numeric formatting information.
`LC_TIME`
  Set the time formatting information.

The locale should be the name of the current locale. Currently, only the "C" and "POSIX" locales are supported. If the locale is NULL, no action is performed. If locale is "", the locale is identified by environment variables (currently not supported).

See localeconv.

### Return Value

A static string naming the current locale for the given category, or NULL if the requested locale is not supported.

### Portability

ANSI, POSIX

### Example

    setlocale(LC_ALL, "C");

Node:setmntent, Next:setmode, Previous:setlocale, Up:Alphabetical List

## setmntent

### Syntax

    #include <mntent.h>

    FILE *setmntent(char *filename, const char *mode);

### Description

This function returns an open FILE* pointer which can be used by getmntent (see getmntent). The arguments filename and mode are always ignored under MS-DOS, but for portability should be set, accordingly, to the name of the file which describes the mounted filesystems and the open mode of that file (like the mode argument to `fopen`, see fopen). (There is no single standard for the name of the file that keeps the mounted filesystems, but it is usually, although not always, listed in the header `<mntent.h>`.)

### Return Value

The `FILE*` pointer is returned. For MS-DOS, this `FILE*` is not a real pointer and may only be used by `getmntent`.

### Portability

not ANSI, not POSIX

### Example

    #include <mntent.h>
    #if defined(MNT_MNTTAB)
    #define MNTTAB_FILE MNT_MNTTAB
    #elif defined(MNTTABNAME)
    #define MNTTAB_FILE MNTTABNAME
    #else
    #define MNTTAB_FILE "/etc/mnttab"
    #endif

      FILE *mnt_fp = setmntent (MNTTAB_FILE, "r");

Node:setmode, Next:setpgid, Previous:setmntent, Up:Alphabetical List

## setmode

### Syntax

    #include <io.h>

    int setmode(int file, int mode);

### Description

This function sets the mode of the given file to mode, which is either `O_TEXT` or `O_BINARY`. It will also set the file into either cooked or raw mode accordingly, and set any `FILE*` objects that use this file into text or binary mode.

When called to put file that refers to the console into binary mode, `setmode` will disable the generation of the signals `SIGINT` and `SIGQUIT` when you press, respectively, `Ctrl-<C>` and `Ctrl-<\>` (`Ctrl-<BREAK>` will still cause `SIGINT`), because many programs that use binary reads from the console will also want to get the `^C` and `^\` keys. You can use the `__djgpp_set_ctrl_c` library function (see __djgpp_set_ctrl_c) if you want `Ctrl-<C>` and `Ctrl-<\>` to generate signals while console is read in binary mode.

Note that, for buffered streams (`FILE*`), you must call `fflush` (see fflush) before `setmode`, or call `setmode` before writing anything to the file, for proper operation.

### Return Value

When successful, the function will return the previous mode of the given file. In case of failure, -1 is returned and errno is set.

### Portability

not ANSI, not POSIX

### Example

    setmode(0, O_BINARY);

Node:setpgid, Next:setpwent, Previous:setmode, Up:Alphabetical List

## setpgid

### Syntax

    #include <unistd.h>

    int setpgid(pid_t _pid, pid_t _pgid);

### Return Value

-1 (EPERM) if _pgid is not your current pid, else zero.

### Portability

not ANSI, POSIX

Node:setpwent, Next:setrlimit, Previous:setpgid, Up:Alphabetical List

## setpwent

### Syntax

    #include <pwd.h>

    void setpwent(void);

### Description

This function reinitializes `getpwent` so that scanning will start from the start of the list. See getpwent.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:setrlimit, Next:setsid, Previous:setpwent, Up:Alphabetical List

## setrlimit

### Syntax

    #include <sys/resource.h>

    int setrlimit (int rltype, const struct rlimit *rlimitp);

### Description

This function sets new limit pointed to by rlimitp on the resource limit specified by rltype. Note that currently it always fails.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

Node:setsid, Next:setstate, Previous:setrlimit, Up:Alphabetical List

## setsid

### Syntax

    #include <unistd.h>

    pid_t setsid(void);

### Description

This function does not do anything. It exists to assist porting from Unix.

### Return Value

Return value of see getpid.

### Portability

not ANSI, POSIX

Node:setstate, Next:settime, Previous:setsid, Up:Alphabetical List

## setstate

### Syntax

    #include <stdlib.h>

    char *setstate(char *arg_state);

### Description

Restores the random number generator (see random) state from pointer arg_state to state array.

### Return Value

Pointer to old state information.

### Portability

not ANSI, not POSIX

Node:settime, Next:settimeofday, Previous:setstate, Up:Alphabetical List

## settime

### Syntax

    #include <dos.h>

    void settime(struct time *ptr);

### Description

This function sets the current time.

For the description of `struct time`, see gettime. Also see setdate.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

    struct time t;
    settime(&t);

Node:settimeofday, Next:setuid, Previous:settime, Up:Alphabetical List

## settimeofday

### Syntax

    #include <time.h>

    int settimeofday(struct timeval *tp, ...);

### Description

Sets the current GMT time. For compatibility, a second argument is accepted. See gettimeofday, for information on the structure types.

### Return Value

Zero if the time was set, nonzero on error.

### Portability

not ANSI, not POSIX

Node:setuid, Next:setvbuf, Previous:settimeofday, Up:Alphabetical List

## setuid

### Syntax

    #include <unistd.h>

    int setuid(uid_t uid);

### Description

This function is simulated, since MS-DOS does not support user IDs.

### Return Value

If uid is equal to that returned by see getuid, returns zero. Otherwise, returns -1 and sets `errno` to EPERM.

### Portability

not ANSI, POSIX

Node:setvbuf, Next:sigaction, Previous:setuid, Up:Alphabetical List

## setvbuf

### Syntax

    #include <stdio.h>

    int setvbuf(FILE *file, char *buffer, int type, int length);

### Description

This function modifies the buffering characteristics of file. First, if the file already has a buffer, it is freed. If there was any pending data in it, it is lost, so this function should only be used immediately after a call to `fopen`.

If the type is `_IONBF`, the buffer and length are ignored and the file is set to unbuffered mode.

If the type is `_IOLBF` or `_IOFBF`, then the file is set to line or fully buffered, respectively. If buffer is `NULL`, a buffer of size size is created and used as the buffer. If buffer is non-`NULL`, it must point to a buffer of at least size size and will be used as the buffer.

See setbuf. See setbuffer. See setlinebuf.

### Return Value

Zero on success, nonzero on failure.

### Portability

ANSI, POSIX

### Example

    setvbuf(stderr, NULL, _IOLBF, 1000);

Node:sigaction, Next:sigaddset, Previous:setvbuf, Up:Alphabetical List

## sigaction

### Syntax

    #include <signal.h>

    int sigaction (int sig, const struct sigaction *act, struct sigaction *oact);

### Description

This function allows to examine and/or change the action associated with a signal sig. The `struct sigaction` structure, defined by the header file `signal.h`, is declared as follows:

     struct sigaction {
       int sa_flags;             /* flags for the action; currently ignored */
       void (*sa_handler)(int);  /* the handler for the signal */
       sigset_t sa_mask;         /* additional signals to be blocked */
     };

The `sa_handler` member is a signal handler, see signal. The `sa_mask` member defines the signals, in addition to sig, which are to be blocked during the execution of `sa_handler`.

The `sigaction` function sets the structure pointed to by `oact` to the current action for the signal sig, and then sets the new action for sig as specified by act. If the act argument is `NULL`, `sigaction` returns the current signal action in oact, but doesn't change it. If the oact argument is a `NULL` pointer, it is ignored. Thus, passing `NULL` pointers for both `act` and `oact` is a way to see if sig is a valid signal number on this system (if not, `sigaction` will return -1 and set `errno`).

### Return Value

0 on success, -1 for illegal value of sig.

### Portability

not ANSI, POSIX

Node:sigaddset, Next:sigdelset, Previous:sigaction, Up:Alphabetical List

## sigaddset

### Syntax

    #include <signal.h>

    int sigaddset (sigset_t *set, int signo)

### Description

This function adds the individual signal specified by signo the set of signals pointed to by set.

### Return Value

0 upon success, -1 if set is a NULL pointer, or if signo is specifies an unknown signal.

### Portability

not ANSI, POSIX

Node:sigdelset, Next:sigemptyset, Previous:sigaddset, Up:Alphabetical List

## sigdelset

### Syntax

    #include <signal.h>

    int sigdelset (sigset_t *set, int signo)

### Description

This function removess the individual signal specified by signo from the set of signals pointed to by set.

### Return Value

0 upon success, -1 if set is a NULL pointer, or if signo is specifies an unknown signal.

### Portability

not ANSI, POSIX

Node:sigemptyset, Next:sigfillset, Previous:sigdelset, Up:Alphabetical List

## sigemptyset

### Syntax

    #include <signal.h>

    int sigemptyset (sigset_t *set)

### Description

This function initializes the set of signals pointed to by set to exclude all signals known to the DJGPP runtime system. Such an empty set, if passed to `sigprocmask` (see sigprocmask), will cause all signals to be passed immediately to their handlers.

### Return Value

0 upon success, -1 if set is a NULL pointer.

### Portability

not ANSI, POSIX

Node:sigfillset, Next:sigismember, Previous:sigemptyset, Up:Alphabetical List

## sigfillset

### Syntax

    #include <signal.h>

    int sigfillset (sigset_t *set)

### Description

This function initializes the set of signals pointed to by set to include all signals known to the DJGPP runtime system. Such a full set, if set by `sigprocmask` (see sigprocmask), will cause all signals to be blocked from delivery to their handlers. Note that the set returned by this function only includes signals in the range `SIGABRT..SIGTRAP`; software interrupts and/or user-defined signals aren't included.

### Return Value

0 upon success, -1 if set is a NULL pointer.

### Portability

not ANSI, POSIX

### Example

      sigset_t full_set, prev_set;

      sigfillset (&full_set);
      sigprocmask (SIG_UNBLOCK, &full_set, &prev_set);

Node:sigismember, Next:siglongjmp, Previous:sigfillset, Up:Alphabetical List

## sigismember

### Syntax

    #include <signal.h>

    int sigismember (sigset_t *set, int signo)

### Description

This function checks whether the signal specified by signo is a member of the set of signals pointed to by set.

### Return Value

1 if the specified signal is a member of the set, 0 if it isn't, or if signo specifies an unknown signal, -1 if set is a NULL pointer.

### Portability

not ANSI, POSIX

Node:siglongjmp, Next:signal, Previous:sigismember, Up:Alphabetical List

## siglongjmp

### Syntax

    #include <setjmp.h>

    int	siglongjmp(sigjmp_buf env, int val);

### Description

See longjmp.

### Portability

not ANSI, POSIX

Node:signal, Next:sigpending, Previous:siglongjmp, Up:Alphabetical List

## signal

### Syntax

    #include <signal.h>

    void	(*signal(int sig, void (*func)(int)))(int);

### Description

Signals are generated in response to some exceptional behavior of the program, such as division by 0. A signal can also report some asynchronous event outside the program, such as someone pressing a `Ctrl-<BREAK>` key combination.

Signals are numbered 0..255 for software interrupts and 256..287 for exceptions (exception number plus 256); other implementation-specific codes are specified in `<signal.h>` (see below). Every signal is given a mnemonic which you should use for portable programs.

By default, signal `SIGQUIT` is discarded. This is so programs ported from other DOS environments, where `SIGQUIT` is generally not supported, continue to work as they originally did. If you want `SIGQUIT` to abort with a traceback, install `__djgpp_traceback_exit` as its handler (see __djgpp_traceback_exit).

The default handling for the rest of the signals is to print a traceback (a stack dump which describes the sequence of function calls leading to the generation of the signal) and abort the program by calling `_exit` (see _exit). As an exception, the default handler for the signal `SIGINT` doesn't print the traceback, and calls `exit` instead of `_exit`, when the INTR key (`Ctrl-C` by default) is pressed, so that programs could be shut down safely in this manner. `SIGINT` raised by `Ctrl-<BREAK>` does generate the traceback.

The function `signal` allows you to change the default behavior for a specific signal. It registers func as a signal handler for signal number sig. After you register your function as the handler for a particular signal, it will be called when that signal occurs. The execution of the program will be suspended until the handler returns or calls `longjmp` (see longjmp).

You may pass `SIG_DFL` as the value of func to reset the signal handling for the signal sig to default (also See __djgpp_exception_toggle, for a quick way to restore all the signals' handling to default), `SIG_ERR` to force an error when that signal happens, or `SIG_IGN` to ignore that signal. Signal handlers that you write are regular C functions, and may call any function that the ANSI/POSIX specs say are valid for signal handlers. For maximum portability, a handler for hardware interrupts and processor exceptions should only make calls to `signal`, assign values to data objects of type `volatile sig_atomic_t` (defined as `int` on `<signal.h>`) and return. Handlers for hardware interrupts need also be locked in memory (so that the operation of virtual memory mechanism won't swap them out), See locking memory regions. Handlers for software interrupts can also terminate by calling `abort`, `exit` or `longjmp`.

The following signals are defined on `<signal.h>`:

`SIGABRT`
  The Abort signal. Currently only used by the `assert` macro to terminate the program when an assertion fails (see assert), and by the `abort` function (see abort).
`SIGFPE`
  The Floating Point Error signal. Generated in case of divide by zero exception (Int 00h), overflow exception (Int 04h), and any x87 co-processor exception, either generated by the CPU (Int 10h), or by the co-processor itself (Int 75h). The co-processor status word is printed by the default handler for this signal. See _status87, for the definition of the individual bits of the status word.

  The DJGPP startup code masks all numeric exceptions, so this signal is usually only triggered by an integer divide by zero operation. If you want to unmask some of the numeric exceptions, see _control87.

`SIGILL`
  The Invalid Execution signal. Currently only generated for unknown/invalid exceptions.
`SIGINT`
  The Interrupt signal. Generated when an INTR key (`Ctrl-C` by default) or `Ctrl-<BREAK>` (Int 1Bh) key is hit. Note that when you open the console in binary mode, or switch it to binary mode by a call to `setmode` (see setmode), generation of `SIGINT` as result of `Ctrl-C` key is disabled. This is so for programs (such as Emacs) which want to be able to read the `^C` character as any other character. Use the library function `__djgpp_set_ctrl_c` to restore `SIGINT` generation when `Ctrl-C` is hit, if you need this. See __djgpp_set_ctrl_c, for details on how this should be done. `Ctrl-<BREAK>` always generates `SIGINT`.

  DJGPP hooks the keyboard hardware interrupt (Int 09h) to be able to generate `SIGINT` in response to the INTR key; you should be aware of this when you install a handler for the keyboard interrupt.

  Note that the key which generates `SIGINT` can be changed with a call to `__djgpp_set_sigint_key` function. See __djgpp_set_sigint_key.

`SIGSEGV`
  The invalid storage access (Segmentation Violation) signal. Generated in response to any of the following exceptions: Bound range exceeded in BOUND instruction (Int 05h), Double Exception or an exception in the exception handler (Int 08h), Segment Boundary violation by co-processor (Int 09h), Invalid TSS (Int 0Ah), Segment Not Present (Int 0Bh), Stack Fault (Int 0Ch), General Protection Violation (Int 0Dh), or Page Fault (Int 0Eh). Note that Int 09h is only generated on 80386 processor; i486 and later CPUs cause Int 0Dh when the co-processor accesses memory out of bounds. The Double Exception, Invalid TSS, Segment Not Present, Stack Fault, GPF, and Page Fault exceptions will cause an error code to be printed, if it is non-zero.
`SIGTERM`
  The Termination Request signal. Currently unused.

  The signals below this are not defined by ANSI C, and cannot be used when compiling under `-ansi` option to `gcc`.

`SIGALRM`
  The Alarm signal. Generated after certain time period has passed after a call to `alarm` library function (see alarm).
`SIGHUP`
  The Hang-up signal. Currently unused.
`SIGKILL`
  The Kill signal. Currently unused.
`SIGPIPE`
  The Broken Pipe signal. Currently unused.
`SIGQUIT`
  The Quit signal. Generated when the QUIT key (`Ctrl-\` by default) is hit. The key that raises the signal can be changed with a call to `__djgpp_set_sigquit_key` function. See __djgpp_set_sigquit_key. By default, `SIGQUIT` is discarded, even if its handler is `SIG_DFL`, so that DOS programs which don't expect it do not break. You can change the effect of `SIGQUIT` to abort with traceback by installing `__djgpp_traceback_exit` as its handler. See __djgpp_traceback_exit.

  DJGPP hooks the keyboard hardware interrupt (Int 09h) to be able to generate `SIGQUIT` in response to the QUIT key; you should be aware of this when you install a handler for the keyboard interrupt.

`SIGUSR1`
  User-defined signal no. 1.
`SIGUSR2`
  User-defined signal no. 2.

  The signals below are not defined by ANSI C and POSIX, and cannot be used when compiling under either `-ansi` or `-posix` options to `gcc`.

`SIGTRAP`
  The Trap Instruction signal. Generated in response to the Debugger Exception (Int 01h) or Breakpoint Exception (Int 03h).
`SIGNOFP`
  The No Co-processor signal. Generated if a co-processor (floating-point) instruction is encountered when no co-processor is installed (Int 07h).
`SIGTIMR`
  The Timer signal. Used by the `setitimer` and `alarm` functions (See setitimer, and see alarm).
`SIGPROF`
  The Profiler signal. Used by the execution profile gathering code in a program compiled with `-pg` option to `gcc`.

### Return Value

The previous handler for signal sig, or `SIG_ERR` if the value of sig is outside legal limits.

### Signal Mechanism Implementation Notes

Due to subtle aspects of protected-mode programs operation under MS-DOS, signal handlers cannot be safely called from hardware interrupt handlers. Therefore, DJGPP exception-handling mechanism arranges for the signal handler to be called on the first occasion that the program is in protected mode and touches any of its data. This means that if the exception occurs while the processor is in real mode, like when your program calls some DOS service, the signal handler won't be called until that call returns. For instance, if you call `read` (or `scanf`, or `gets`) to read text from the console and press `Ctrl-C`, you will have to press `Enter` to terminate the `read` call to cause the signal handler for `SIGINT` to be called. Another significant implication of this implementation is that when the program isn't touching any of its data (like in very tight loops which only use values in the registers), it cannot be interrupted.

### Portability

ANSI, POSIX

Node:sigpending, Next:sigprocmask, Previous:signal, Up:Alphabetical List

## sigpending

### Syntax

    #include <signal.h>

    int sigpending (sigset_t *set)

### Description

This function retrieves the signals that have been sent to the program, but are being blocked from delivery by the program's signal mask (see sigprocmask). The bit-mapped value which describes the pending signals is stored in the structure pointed to by set. You can use the `sigismember` function (see sigismember) to see what individual signals are pending.

### Return Value

0 on success, -1 on failure (and errno set to `EFAULT`).

### Portability

not ANSI, POSIX

### Example

    #include <signal.h>

      sigset_t pending_signals;

      /* If SIGINT is pending, force it to be raised.  */
      if (sigpending (&pending_signals) == 0
          && sigismember (&pending_signals, SIGINT))
        {
          sigset_t new_set, old_set;
          sigemptyset (&new_set);
          sigaddset (&new_set, SIGINT);
          sigprocmask (SIG_UNBLOCK, &new_set, &old_set);  /* will raise SIGINT */
          sigprocmask (SIG_SETMASK, &old_set, &new_set);  /* restore mask */
        }

Node:sigprocmask, Next:sigsetjmp, Previous:sigpending, Up:Alphabetical List

## sigprocmask

### Syntax

    #include <signal.h>

    int sigprocmask (int how, const sigset_t *new_set, sigset_t *old_set)

### Description

This function is used to examine and/or change the program's current signal mask. The current signal mask determines which signals are blocked from being delivered to the program. A signal is blocked if its bit in the mask is set. (See sigismember, See sigaddset, See sigdelset, See sigemptyset, See sigfillset, for information about functions to manipulate the signal masks.) When a blocked signal happens, it is not delivered to the program until such time as that signal is unblocked by another call to `sigprocmask`. Thus blocking a signal is an alternative to ignoring it (by setting its handler to `SIG_IGN`, see signal), but has an advantage of not missing the signal entirely.

The value of the argument how determines the operation: if it is `SIG_BLOCK`, the set pointed to by the argument new_set is added to the current signal mask. If the value is `SIG_UNBLOCK`, the set pointed to by new_set is removed from the current signal mask. If the value is `SIG_SETMASK`, the current mask is replaced by the set pointed to by new_set.

If the argument old_set is not `NULL`, the previous mask is stored in the space pointed to by old_set. If the value of the argument new_set is `NULL`, the value of how is not significant and the process signal mask is unchanged; thus, the call with a zero new_set can be used to inquire about currently blocked signals, without changing the current set.

If the new set defined by the call causes some pending signals to be unblocked, they are all delivered (by calling `raise`) before the call to `sigprocmask` returns.

The DJGPP implementation only records a single occurrence of any given signal, so when the signal is unblocked, its handler will be called at most once.

It is not possible to block CPU exceptions such as Page Fault, General Protection Fault etc. (mapped to `SIGSEGV` signal); for these, `sigprocmask` will behave as if the call succeeded, but when an exception happens, the signal handler will be called anyway (the default handler will abort the program).

Also note that there are no provisions to save and restore any additional info about the signal beyond the fact that it happened. A signal handler might need such info to handle the signal intelligently. For example, a handler for `SIGFPE` might need to examine the status word of the FPU to see what exactly went wrong. But if the signal was blocked and is delivered after a call to `sigprocmask` has unblocked it, that information is lost. Therefore, if you need access to such auxiliary information in the signal handler, don't block that signal.

### Return Value

0 on success, -1 for illegal value of sig or illegal address in new_set or old_set.

### Portability

not ANSI, POSIX

### Example

    #include <conio.h>
    #include <signal.h>

    static void
    sig_catcher (int signo)
    {
      cprintf ("\r\nGot signal %d\r\n", signo);
    }

    int
    main (void)
    {
      sigset_t sigmask, prevmask;

      signal (SIGINT, sig_catcher);

      sigemptyset (&sigmask);

      sigaddset (&sigmask, SIGINT);
      if (sigprocmask (SIG_SETMASK, &sigmask, &prevmask) == 0)
        cputs ("SIGINT blocked.  Try to interrupt me now.\r\n");
      while (!kbhit ())
        ;
      cputs ("See?  I wasn't interrupted.\r\n");
      cputs ("But now I will unblock SIGINT, and then get the signal.\r\n");
      sigprocmask (SIG_UNBLOCK, &sigmask, &prevmask);
      return 0;
    }

Node:sigsetjmp, Next:sin, Previous:sigprocmask, Up:Alphabetical List

## sigsetjmp

### Syntax

    #include <setjmp.h>

    int	sigsetjmp(sigjmp_buf env, int savemask);

### Description

See setjmp.

### Portability

not ANSI, POSIX

Node:sin, Next:sincos, Previous:sigsetjmp, Up:Alphabetical List

## sin

### Syntax

    #include <math.h>

    double sin(double x);

### Description

This function computes the sine of x (which should be given in radians).

### Return Value

The sine of x. If the absolute value of x is finite but greater than or equal to 2^63, the value is 0 (since for arguments that large each bit of the mantissa is more than `Pi`). If the value of x is infinite or `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

### Accuracy

In general, this function's relative accuracy is about 1.7*10^(-16), which is close to the machine precision for a `double`. However, for arguments very close to `Pi` and its odd multiples, the relative accuracy can be many times worse, due to loss of precision in the internal FPU computations. Since sin(Pi) is zero, the absolute accuracy is still very good; but if your program needs to preserve high relative accuracy for such arguments, link with `-lm` and use the version of `sin` from `libm.a` which does elaborate argument reduction, but is about three times slower.

Node:sincos, Next:sinh, Previous:sin, Up:Alphabetical List

## sincos

### Syntax

    #include <math.h>

    void   sincos(double *cosine, double *sine, double x);

### Description

This function computes the cosine and the sine of x in a single call, and stores the results in the addresses pointed to by cosine and sine, respectively. Since the function exploits a machine instruction that computes both cosine and sine simultaneously, it is faster to call `sincos` than to call `cos` and `sin` for the same argument.

If the absolute value of x is finite but greater than or equal to 2^63, the value stored in *cosine is 1 and the value stored in *sine is 0 (since for arguments that large each bit of the mantissa is more than `Pi`). If the value of x is infinite or `NaN`, `NaN` is stored in both *cosine and *sine, and `errno` is set to `EDOM`.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:sinh, Next:sleep, Previous:sincos, Up:Alphabetical List

## sinh

### Syntax

    #include <math.h>

    double sinh(double x);

### Description

This function computes the hyperbolic sine of x.

### Return Value

The hyperbolic sine of x. If the absolute value of x is finite but so large that the result would overflow a `double`, the return value is `Inf` with the same sign as x, and `errno` is set to `ERANGE`. If x is either a positive or a negative infinity, the result is `+Inf` with the same sign as x, and `errno` is not changed. If x is `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:sleep, Next:sound, Previous:sinh, Up:Alphabetical List

## sleep

### Syntax

    #include <unistd.h>

    unsigned sleep(unsigned seconds);

### Description

This function causes the program to pause for seconds seconds.

### Return Value

The number of seconds that haven't passed (i.e. always zero)

### Portability

not ANSI, POSIX

### Example

    sleep(5);

Node:sound, Next:spawn*, Previous:sleep, Up:Alphabetical List

## sound

### Syntax

    #include <pc.h>

    void		sound(int _frequency);

### Description

Enables the PC speaker at the given frequency. The argument _frequency should be given in Hertz units.

### Portability

not ANSI, not POSIX

Node:spawn*, Next:sprintf, Previous:sound, Up:Alphabetical List

## spawn*

### Syntax

    #include <process.h>

    int spawnl(int mode, const char *path, const char *argv0, ..., NULL);
    int spawnle(int mode, const char *path, const char *argv0, ..., NULL /*, const char **envp */);
    int spawnlp(int mode, const char *path, const char *argv0, ..., NULL);
    int spawnlpe(int mode, const char *path, const char *argv0, ..., NULL /*, const char **envp */);

    int spawnv(int mode, const char *path, const char **argv);
    int spawnve(int mode, const char *path, const char **argv, const char **envp);
    int spawnvp(int mode, const char *path, const char **argv);
    int spawnvpe(int mode, const char *path, const char **argv, const char **envp);

### Description

These functions run other programs. The path points to the program to run, and may optionally include its extension. These functions will look for a file path with the extensions `.com`, `.exe`, `.bat`, `.btm`, `.sh`, `.ksh`, `.pl` and `.sed`; if none is found, neither in the current directory nor along the `PATH`, they will look for path itself.

`.com` programs are invoked via the usual DOS calls; DJGPP `.exe` programs are invoked in a way that allows long command lines to be passed; other `.exe` programs are invoked via DOS; `.bat` and `.btm` programs are invoked via the command processor given by the `COMSPEC` environment variable; `.sh`, `.ksh` programs and programs with any other extensions that have `#!` as their first two characters are assumed to be Unix-style scripts and are invoked by calling a program whose pathname immediately follows the first two characters. (If the name of that program is a Unix-style pathname, without a drive letter and without an extension, like `/bin/sh`, the `spawn` functions will additionally look them up on the `PATH`; this allows to run Unix scripts without editing, if you have a shell installed somewhere along your `PATH`.) Any non-recognizable files will be also invoked via DOS calls.

WARNING! DOS is rather stupid in invoking programs: if the file doesn't have the telltale "MZ" signature of the `.exe` style programs, DOS assumes it is a `.com` style image and tries to execute it directly. If the file is not really an executable program, your application will almost certainly crash. Applications that need to be robust in such situations should test whether the program file is indeed an executable, e.g. with calls to `stat` (see stat) or `_is_executable` (see _is_executable) library functions.

Note that built-in commands of the shells can not be invoked via these functions; use `system` instead, or invoke the appropriate shell with the built-in command as its argument.

The programs are invoked with the arguments given. The zeroth argument is normally not used, since MS-DOS cannot pass it separately, but for compatibility it should be the name of the program. There are two ways of passing arguments. The `l` functions (like `spawnl`) take a list of arguments, with a `NULL` at the end of the list. This is useful when you know how many argument there will be ahead of time. The `v` functions (like `spawnv`) take a pointer to a list of arguments, which also must be `NULL`-terminated. This is useful when you need to compute the number of arguments at runtime.

In either case, you may also specify `e` to indicate that you will be giving an explicit environment, else the current environment is used. You may also specify `p` to indicate that you would like `spawn*` to search the `PATH` (in either the environment you pass or the current environment) for the executable, else it will only check the explicit path given.

Note that these function understand about other DJGPP programs, and will call them directly, so that you can pass command lines longer than 126 characters to them without any special code. DJGPP programs called by these functions will not glob the arguments passed to them; other programs also won't glob the arguments if they suppress expansion when given quoted filenames.

When the calling program runs on Windows 9X or Windows 2000 and calls the system shell to run the child program, or if the child program is a native Windows program (in `PE-COFF` format), or when the system shell is `4DOS` or `NDOS` and the shell is called to run the command, command lines longer than 126 characters are passed via the environment variable `CMDLINE`.

See exec*.

### Return Value

If successful and `mode` is `P_WAIT`, these functions return the exit code of the child process in the lower 8 bits of the return value. Note that if the program is run by a command processor (e.g., if it's a batch file), the exit code of that command processor will be returned. `COMMAND.COM` is notorious for returning 0 even if it couldn't run the command.

If successful and mode is `P_OVERLAY`, these functions will not return.

If there is an error (e.g., the program specified as `argv[0]` cannot be run, or the command line is too long), these functions return -1 and set `errno` to indicate the error. If the child program was interrupted by <Ctrl-C> or a Critical Device error, `errno` is set to `EINTR` (even if the child's exit code is 0), and bits 8-17 of the return value are set to `SIGINT` or `SIGABRT`, accordingly. Note that you must set the signal handler for `SIGINT` to `SIG_IGN`, or arrange for the handler to return, or else your program will be aborted before it will get chance to set the value of the return code.

### Portability

not ANSI, not POSIX

### Example

    char *environ[] = {
      "PATH=c:\\dos;c:\\djgpp;c:\\usr\\local\\bin",
      "DJGPP=c:/djgpp",
      0
    };

    char *args[] = {
      "gcc",
      "-v",
      "hello.c",
      0
    };

    spawnvpe(P_WAIT, "gcc", args, environ);

Node:sprintf, Next:sqrt, Previous:spawn*, Up:Alphabetical List

## sprintf

### Syntax

    #include <stdio.h>

    int sprintf(char *buffer, const char *format, ...);

### Description

Sends formatted output from the arguments (...) to the buffer. See printf.

### Return Value

The number of characters written.

### Portability

ANSI, POSIX

Node:sqrt, Next:srand, Previous:sprintf, Up:Alphabetical List

## sqrt

### Syntax

    #include <math.h>

    double sqrt(double x);

### Description

This function computes the square root of x.

### Return Value

The square root of x. If x is negative or a `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:srand, Next:srandom, Previous:sqrt, Up:Alphabetical List

## srand

### Syntax

    #include <stdlib.h>

    void srand(unsigned seed);

### Description

Initializes the random number generator for `rand()`. If you pass the same seed, `rand()` will return the same sequence of numbers. You can seed from time or rawclock.

### Portability

ANSI, POSIX

### Example

    /* random pause */
    srand(time(0));
    for (i=rand(); i; i--);

Node:srandom, Next:sscanf, Previous:srand, Up:Alphabetical List

## srandom

### Syntax

    #include <stdlib.h>

    int srandom(int seed);

### Description

Initializes the random number generator (see random). Passing the same seed results in `random` returning predictable sequences of numbers, unless see initstate or see setstate are called.

### Return Value

Zero.

### Portability

not ANSI, not POSIX

### Example

    srandom(45);

Node:sscanf, Next:stackavail, Previous:srandom, Up:Alphabetical List

## sscanf

### Syntax

    #include <stdio.h>

    int sscanf(const char *string, const char *format, ...);

### Description

This function scans formatted text from the string and stores it in the variables pointed to by the arguments. See scanf.

### Return Value

The number of items successfully scanned.

### Portability

ANSI, POSIX

Node:stackavail, Next:stat, Previous:sscanf, Up:Alphabetical List

## stackavail

### Syntax

    #include <stdlib.h>

    int stackavail(void);

### Description

This function returns the number of bytes that are available on the stack.

### Portability

not ANSI, not POSIX

### Example

    printf("Available stack size is %d bytes\n", stackavail());

Node:stat, Next:statfs, Previous:stackavail, Up:Alphabetical List

## stat

### Syntax

    #include <sys/stat.h>

    int stat(const char *file, struct stat *sbuf);

### Description

This function obtains the status of the file file and stores it in sbuf, which has this structure:

    struct  stat {
            time_t   st_atime;     /* time of last access       */
            time_t   st_ctime;     /* time of file's creation   */
            dev_t    st_dev;       /* The drive number (0 = a:) */
            gid_t    st_gid;       /* what getgid() returns */
            ino_t    st_ino;       /* starting cluster or unique identifier */
            mode_t   st_mode;      /* file mode - S_IF* and S_IRUSR/S_IWUSR */
            time_t   st_mtime;     /* time that the file was last written */
            nlink_t  st_nlink;     /* 2 + number of subdirs, or 1 for files */
            off_t    st_size;      /* size of file in bytes */
            off_t    st_blksize;   /* the size of transfer buffer */
            uid_t    st_uid;       /* what getuid() returns */
    };

The `st_atime`, `st_ctime` and `st_mtime` have different values only when long file names are supported (e.g. on Windows 9X); otherwise, they all have the same value: the time that the file was last written1. Most Windows 9X VFAT filesystems only support the date of the file's last access (the time is set to zero); therefore, the DJGPP implementation of `stat` sets the `st_atime` member to the same value as `st_mtime` if the time part of `st_atime` returned by the filesystem is zero (to prevent the situation where the file appears to have been created after it was last accessed, which doesn't look good).

Some members of `struct stat` are very expensive to compute. If your application is a heavy user of `stat` and is too slow, you can disable computation of the members your application doesn't need, as described in _djstat_flags.

### Return Value

Zero on success, nonzero on failure (and errno set).

### Portability

not ANSI, POSIX

### Example

    struct stat s;
    stat("data.txt", &s);
    if (S_ISDIR(s.st_mode))
      printf("is directory\n");

### Implementation Notes

Supplying a 100% Unix-compatible `stat` function under DOS is an implementation nightmare. The following notes describe some of the obscure points specific to `stat`s behavior in DJGPP.

1. The `drive` for character devices (like `con`, `/dev/null` and others is returned as -1. For drives networked by Novell Netware, it is returned as -2.

2. The starting cluster number of a file serves as its inode number. For files whose starting cluster number is inaccessible (empty files, files on Windows 9X, on networked drives, etc.) the `st_inode` field will be invented in a way which guarantees that no two different files will get the same inode number (thus it is unique). This invented inode will also be different from any real cluster number of any local file. However, only on plain DOS, and only for local, non-empty files/directories the inode is guaranteed to be consistent between `stat` and `fstat` function calls.

3. The WRITE access mode bit is set only for the user (unless the file is read-only, hidden or system). EXECUTE bit is set for directories, files which can be executed from the DOS prompt (batch files, .com, .dll and .exe executables) or run by `go32-v2`.

4. Size of directories is reported as the number of its files (sans `.' and `..' entries) multiplied by 32 bytes (the size of directory entry). On FAT filesystems that support the LFN API (such as Windows 9X), the reported size of the directory accounts for additional space used to store the long file names.

5. Time stamp for root directories is taken from the volume label entry, if that's available; otherwise, it is reported as 1-Jan-1980.

6. The variable `_djstat_flags` (see _djstat_flags) controls what hard-to-get fields of `struct stat` are needed by the application.

7. `stat` should not be used to get an up-to-date info about a file which is open and has been written to, because `stat` will only return correct data after the file is closed. Use `fstat` (see fstat) while the file is open. Alternatively, you can call `fflush` and `fsync` to make the OS flush all the file's data to the disk, before calling `stat`.

8. The number of links `st_nlink` is always 1 for files other than directories. For directories, it is the number of subdirectories plus 2. This is so that programs written for Unix that depend on this to optimize recursive traversal of the directory tree, will still work.

Node:statfs, Next:_status87, Previous:stat, Up:Alphabetical List

## statfs

### Syntax

    #include <sys/vfs.h>

    int statfs(const char *filename, struct statfs *buf);

### Description

This function returns information about the given "filesystem". The drive letter of the given filename, or the default drive if none is given, is used to retrieve the following structure:

    struct statfs
    {
        long	f_type;   /* 0 */
        long	f_bsize;  /* bytes per cluster */
        long	f_blocks; /* clusters on drive */
        long	f_bfree;  /* available clusters */
        long	f_bavail; /* available clusters */
        long	f_files;  /* clusters on drive */
        long	f_ffree;  /* available clusters */
        fsid_t	f_fsid;   /* [0]=drive_number, [1]=MOUNT_UFS
        long	f_magic;  /* FS_MAGIC */
    };

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    struct statfs fs;
    statfs("anything", &fs);
    printf("%d bytes left\n", fs.f_bfree * fs.f_bsize);

Node:_status87, Next:_stklen, Previous:statfs, Up:Alphabetical List

## _status87

### Syntax

    #include <float.h>

    unsigned int _status87(void);

### Description

Returns the status word of the FPU, which indicate the results of the most recently completed FPU operation:

    ---- ---- ---- ---X = SW_INVALID - invalid operation
    ---- ---- ---- --X- = SW_DENORMAL - denormalized operand
    ---- ---- ---- -X-- = SW_ZERODIVIDE - division by zero
    ---- ---- ---- X--- = SW_OVERFLOW - overflow
    ---- ---- ---X ---- = SW_UNDERFLOW - underflow
    ---- ---- --X- ---- = SW_INEXACT - loss of precision
    ---- ---- -X-- ---- = SW_STACKFAULT - stack over/under flow
    ---- ---- X--- ---- = SW_ERRORSUMMARY - set if any errors
    -X-- -XXX ---- ---- = SW_COND - condition code
    ---- ---X ---- ---- = SW_C0
    ---- --X- ---- ---- = SW_C1
    ---- -X-- ---- ---- = SW_C2
    -X-- ---- ---- ---- = SW_C3
    --XX X--- ---- ---- = SW_TOP - top of stack (use SW_TOP_SHIFT to shift it)
    X--- ---- ---- ---- = SW_BUSY - fpu is busy

### Portability

not ANSI, not POSIX

Node:_stklen, Next:stpcpy, Previous:_status87, Up:Alphabetical List

## _stklen

### Syntax

    extern int _stklen;

### Description

This variable sets the minimum stack length that the program requires. Note that the stack may be much larger than this. This value should be set statically, as it is only used at startup.

### Portability

not ANSI, not POSIX

### Example

    int _stklen = 256000;

Node:stpcpy, Next:strcasecmp, Previous:_stklen, Up:Alphabetical List

## stpcpy

### Syntax

    #include <string.h>

    char *stpcpy(char *_dest, const char *_src);

### Description

Like `strcpy` (see strcpy), but return value different.

### Return Value

Returns a pointer to the trailing NUL in dest.

### Portability

not ANSI, not POSIX

Node:strcasecmp, Next:strcat, Previous:stpcpy, Up:Alphabetical List

## strcasecmp

### Syntax

    #include <string.h>

    int strcasecmp(const char *s1, const char *s2);

### Description

This function compares the two strings, disregarding case.

### Return Value

Zero if they're the same, nonzero if different, the sign indicates "order".

### Portability

not ANSI, not POSIX

### Example

    if (strcasecmp(arg, "-i") == 0)
      do_include();

Node:strcat, Next:strchr, Previous:strcasecmp, Up:Alphabetical List

## strcat

### Syntax

    #include <string.h>

    char *strcat(char *s1, const char *s2);

### Description

This function concatenates s2 to the end of s1.

### Return Value

s1

### Portability

ANSI, POSIX

### Example

    char buf[100] = "hello";
    strcat(buf, " there");

Node:strchr, Next:strcmp, Previous:strcat, Up:Alphabetical List

## strchr

### Syntax

    #include <string.h>

    char *strchr(const char *s, int c);

### Description

This function returns a pointer to the first occurrence of c in s. Note that if c is `NULL`, this will return a pointer to the end of the string.

### Return Value

A pointer to the character, or `NULL` if it wasn't found.

### Portability

ANSI, POSIX

### Example

    char *slash = strchr(filename, '/');

Node:strcmp, Next:strcoll, Previous:strchr, Up:Alphabetical List

## strcmp

### Syntax

    #include <string.h>

    int strcmp(const char *s1, const char *s2);

### Description

This function compares s1 and s2.

### Return Value

Zero if the strings are equal, a positive number if s1 comes after s2 in the ASCII collating sequense, else a negative number.

### Portability

ANSI, POSIX

### Example

    if (strcmp(arg, "-i") == 0)
      do_include();

Node:strcoll, Next:strcpy, Previous:strcmp, Up:Alphabetical List

## strcoll

### Syntax

    #include <string.h>

    int strcoll(const char *s1, const char *s2);

### Description

This function compares s1 and s2, using the collating sequences from the current locale.

### Return Value

Zero if the strings are equal, a positive number if s1 comes after s2 in the collating sequense, else a negative number.

### Portability

ANSI, POSIX

### Example

    while (strcoll(var, list[i]) < 0)
      i++;

Node:strcpy, Next:strcspn, Previous:strcoll, Up:Alphabetical List

## strcpy

### Syntax

    #include <string.h>

    char *strcpy(char *s1, const char *s2);

### Description

This function copies s2 into s1.

### Return Value

s1

### Portability

ANSI, POSIX

### Example

    char buf[100];
    strcpy(buf, arg);

Node:strcspn, Next:strdup, Previous:strcpy, Up:Alphabetical List

## strcspn

### Syntax

    #include <string.h>

    size_t strcspn(const char *s1, const char *set);

### Description

This function finds the first character in s1 that matches any character in set. Note that the `NULL` bytes at the end of each string counts, so you'll at least get a pointer to the end of the string if nothing else.

### Return Value

The index of the found character.

### Portability

ANSI, POSIX

### Example

    int i = strcspn(command, "<>|");
    if (command[i])
      do_redirection();

Node:strdup, Next:strerror, Previous:strcspn, Up:Alphabetical List

## strdup

### Syntax

    #include <string.h>

    char * strdup (const char *source);

### Description

Returns a newly allocated area of memory that contains a duplicate of the string pointed to by source. The memory returned by this call must be freed by the caller.

### Return Value

Returns the newly allocated string, or NULL if there is no more memory.

### Portability

not ANSI, not POSIX

### Example

    char *foo()
    {
      return strdup("hello");
    }

Node:strerror, Next:strftime, Previous:strdup, Up:Alphabetical List

## strerror

### Syntax

    #include <string.h>

    char *strerror(int error);

### Description

This function returns a string that describes the error.

### Return Value

A pointer to a static string that should not be modified or free'd.

### Portability

ANSI, POSIX

### Example

    if (f=fopen("foo", "r") == 0)
      printf("Error! %s: %s\n", "foo", strerror(errno));

Node:strftime, Next:stricmp, Previous:strerror, Up:Alphabetical List

## strftime

### Syntax

    #include <time.h>

    size_t strftime(char *buf, size_t n, const char *format,
                    const struct tm *time_info);

### Description

This function formats the time data in time_info according to the given format and stores it in buf, not exceeding n bytes.

The format string is like `printf` in that any character other than `%` is added to the output string, and for each character following a `%` a pattern is added to the string as follows, with the examples as if the time was Friday, October 1, 1993, at 03:30:34 PM EDT:

`%A`
  The full weekday name (`Friday`)
`%a`
  The abbreviated weekday name (`Fri`)
`%B`
  The full month name (`October`)
`%b`
`%h`
  The abbreviated month name (`Oct`)
`%C`
  Short for `%a %b %e %H:%M:%S %Y` (`Fri Oct 1 15:30:34 1993`)
`%c`
  Short for `%m/%d/%y %H:%M:%S` (`10/01/93 15:30:34`)
`%e`
  The day of the month, blank padded to two characters (`2`)
`%D`
  Short for `%m/%d/%y` (`10/01/93`)
`%d`
  The day of the month, zero padded to two characters (`02`)
`%H`
  The hour (0-24), zero padded to two characters (`15`)
`%I`
  The hour (1-12), zero padded to two characters (`03`)
`%j`
  The Julian day, zero padded to three characters (`275`)
`%k`
  The hour (0-24), space padded to two characters (`15`)
`%l`
  The hour (1-12), space padded to two characters(`3`)
`%M`
  The minutes, zero padded to two characters (`30`)
`%m`
  The month (1-12), zero padded to two characters (`10`)
`%n`
  A newline (`\n`)
`%p`
  AM or PM (`PM`)
`%R`
  Short for `%H:%M` (`15:30`)
`%r`
  Short for `%I:%M:%S %p` (`03:30:35 PM`)
`%S`
  The seconds, zero padded to two characters (`35`)
`%T`
`%X`
  Short for `%H:%M:%S` (`15:30:35`)
`%t`
  A tab (`\t`)
`%U`
  The week of the year, with the first week defined by the first Sunday of the year, zero padded to two characters (`39`)
`%u`
  The day of the week (1-7) (`6`)
`%W`
  The week of the year, with the first week defined by the first Monday of the year, zero padded to two characters (`39`)
`%w`
  The day of the week (0-6) (`5`)
`%x`
  Short for `%m/%d/%y` (`10/01/93`)
`%y`
  The year (00-99) of the century (`93`)
`%Y`
  The year, zero padded to four digits (`1993`)
`%Z`
  The timezone abbreviation (`EDT`)
`%%`
  A percent symbol (`%`)

### Return Value

The number of characters stored.

### Portability

ANSI, POSIX

### Example

    time_t now = time (NULL);
    struct tm *t = localtime (&now);
    char buf[100];
    /* Print today's date e.g. "January 31, 2001".  */
    strftime (buf, 100, "%B %d, %Y", t);

Node:stricmp, Next:strlen, Previous:strftime, Up:Alphabetical List

## stricmp

### Syntax

    #include <string.h>

    int stricmp(const char *s1, const char *s2);

### Description

This function compares the two strings, disregarding case.

### Return Value

Zero if they're the same, nonzero if different, the sign indicates "order".

### Portability

not ANSI, not POSIX

### Example

    if (stricmp(arg, "-i") == 0)
      do_include();

Node:strlen, Next:strlwr, Previous:stricmp, Up:Alphabetical List

## strlen

### Syntax

    #include <string.h>

    size_t strlen(const char *string);

### Description

This function returns the number of characters in string.

### Return Value

The length of the string.

### Portability

ANSI, POSIX

### Example

    if (strlen(fname) > PATH_MAX)
      invalid_file(fname);

Node:strlwr, Next:strncasecmp, Previous:strlen, Up:Alphabetical List

## strlwr

### Syntax

    #include <string.h>

    char *strlwr(char *string);

### Description

This function replaces all upper case letters in string with lower case letters.

### Return Value

The string.

### Portability

not ANSI, not POSIX

### Example

    char buf[100] = "Hello";
    strlwr(buf);

Node:strncasecmp, Next:strncat, Previous:strlwr, Up:Alphabetical List

## strncasecmp

### Syntax

    #include <string.h>

    int strncasecmp(const char *s1, const char *s2, size_t max);

### Description

This function compares s1 and s2, ignoring case, up to a maximum of max characters.

### Return Value

Zero if the strings are equal, a positive number if s1 comes after s2 in the ASCII collating sequense, else a negative number.

### Portability

not ANSI, not POSIX

### Example

    if (strncasecmp(foo, "-i", 2) == 0)
      do_include();

Node:strncat, Next:strncmp, Previous:strncasecmp, Up:Alphabetical List

## strncat

### Syntax

    #include <string.h>

    char *strncat(char *s1, const char *s2, size_t max);

### Description

This function concatenates up to max characters of s2 to the end of s1.

### Return Value

s1

### Portability

ANSI, POSIX

### Example

    strncat(fname, extension, 4);

Node:strncmp, Next:strncpy, Previous:strncat, Up:Alphabetical List

## strncmp

### Syntax

    #include <string.h>

    int strncmp(const char *s1, const char *s2, size_t max);

### Description

This function compares up to max characters of s1 and s2.

### Return Value

Zero if the strings are equal, a positive number if s1 comes after s2 in the ASCII collating sequense, else a negative number.

### Portability

ANSI, POSIX

### Example

    if (strncmp(arg, "-i", 2) == 0)
      do_include();

Node:strncpy, Next:strnicmp, Previous:strncmp, Up:Alphabetical List

## strncpy

### Syntax

    #include <string.h>

    char *strncpy(char *s1, const char *s2, size_t max);

### Description

This function copies up to max characters of s2 into s1.

### Return Value

s1

### Portability

ANSI, POSIX

### Example

    char buf[100];
    strncpy(buf, arg, 99);

Node:strnicmp, Next:strpbrk, Previous:strncpy, Up:Alphabetical List

## strnicmp

### Syntax

    #include <string.h>

    int strnicmp(const char *s1, const char *s2, size_t max);

### Description

This function compares s1 and s2, ignoring case, up to a maximum of max characters.

### Return Value

Zero if the strings are equal, a positive number if s1 comes after s2 in the ASCII collating sequense, else a negative number.

### Portability

not ANSI, not POSIX

### Example

    if (strnicmp(foo, "-i", 2) == 0)
      do_include();

Node:strpbrk, Next:strrchr, Previous:strnicmp, Up:Alphabetical List

## strpbrk

### Syntax

    #include <string.h>

    char *strpbrk(const char *s1, const char *set);

### Description

This function finds the first character in s1 that matches any character in set.

### Return Value

A pointer to the first match, or `NULL` if none are found.

### Portability

ANSI, POSIX

### Example

    if (strpbrk(command, "<>|"))
      do_redirection();

Node:strrchr, Next:strsep, Previous:strpbrk, Up:Alphabetical List

## strrchr

### Syntax

    #include <string.h>

    char *strrchr(const char *s1, int c);

### Description

This function finds the last occurrence of `c` in `s1`.

### Return Value

A pointer to the last match, or `NULL` if the character isn't in the string.

### Portability

ANSI, POSIX

### Example

    char *last_slash = strrchr(filename, '/');

Node:strsep, Next:strspn, Previous:strrchr, Up:Alphabetical List

## strsep

### Syntax

    #include <string.h>

    char *strsep(char **stringp, char *delim);

### Description

This function retrieves the next token from the given string, where stringp points to a variable holding, initially, the start of the string. Tokens are delimited by a character from delim. Each time the function is called, it returns a pointer to the next token, and sets *stringp to the next spot to check, or `NULL`.

### Return Value

The next token, or NULL.

### Portability

not ANSI, not POSIX

### Example

    main()
    {
      char *buf = "Hello  there,stranger";
      char **bp = &buf;
      char *tok;
      while (tok = strsep(bp, " ,"))
        printf("tok = `%s'\n", tok);
    }

    tok = `Hello'
    tok = `'
    tok = `there'
    tok = `stranger'

Node:strspn, Next:strstr, Previous:strsep, Up:Alphabetical List

## strspn

### Syntax

    #include <string.h>

    size_t strspn(const char *s1, const char *set);

### Description

This function finds the first character in s1 that does not match any character in set. Note that the `NULL` bytes at the end of s1 counts, so you'll at least get a pointer to the end of the string if nothing else.

### Return Value

The index of the found character.

### Portability

ANSI, POSIX

### Example

    int i = strspn(entry, " \t\b");
    if (entry[i])
      do_something();

Node:strstr, Next:strtod, Previous:strspn, Up:Alphabetical List

## strstr

### Syntax

    #include <string.h>

    char *strstr(const char *s1, const char *s2);

### Description

This function finds the first occurrence of s2 in s1.

### Return Value

A pointer within s1, or `NULL` if s2 wasn't found.

### Portability

ANSI, POSIX

### Example

    if (strstr(command, ".exe"))
      do_exe();

Node:strtod, Next:strtok, Previous:strstr, Up:Alphabetical List

## strtod

### Syntax

    #include <stdlib.h>

    double strtod(const char *s, char **endp);

### Description

This function converts as many characters of s as look like a floating point number into that number. If endp is not a null pointer, `*endp` is set to point to the first unconverted character.

### Return Value

The value the represented by s.

If a number represented by s doesn't fit into the range of values representable by the type `double`, the function returns either `-HUGE_VAL` (if s begins with the character `-`) or `+HUGE_VAL`, and sets `errno` to `ERANGE`.

### Portability

ANSI, POSIX

### Example

    char *buf = "123ret";
    char *bp;
    double x = strtod(buf, &bp);

Node:strtok, Next:strtol, Previous:strtod, Up:Alphabetical List

## strtok

### Syntax

    #include <string.h>

    char *strtok(char *s1, const char *s2);

### Description

This function retrieves tokens from s1 which are delimited by characters from s2.

To initiate the search, pass the string to be searched as s1. For the remaining tokens, pass `NULL` instead.

### Return Value

A pointer to the token, or `NULL` if no more are found.

### Portability

ANSI, POSIX

### Example

    main()
    {
      char *buf = "Hello there, stranger";
      char *tok;
      for (tok = strtok(buf, " ,");
           tok;
           tok=strtok(0, " ,"))
        printf("tok = `%s'\n", tok);
    }

    tok = `Hello'
    tok = `there'
    tok = `stranger'

Node:strtol, Next:_strtold, Previous:strtok, Up:Alphabetical List

## strtol

### Syntax

    #include <stdlib.h>

    long strtol(const char *s, char **endp, int base);

### Description

This function converts as much of s as looks like an appropriate number into the value of that number. If endp is not a null pointer, *endp is set to point to the first unused character.

The base argument indicates what base the digits (or letters) should be treated as. If base is zero, the base is determined by looking for `0x`, `0X`, or `0` as the first part of the string, and sets the base used to 16, 16, or 8 if it finds one. The default base is 10 if none of those prefixes are found.

### Return Value

The value.

### Portability

ANSI, POSIX

### Example

    printf("Enter a number: "); fflush(stdout);
    gets(buf);
    char *bp;
    printf("The value is %d\n", strtol(buf, &bp, 0));

Node:_strtold, Next:strtoll, Previous:strtol, Up:Alphabetical List

## _strtold

### Syntax

    #include <stdlib.h>

    long double _strtold(const char *s, char **endp);

### Description

This function converts as many characters of s that look like a floating point number into one, and sets *endp to point to the first unused character.

### Return Value

The value the string represented.

### Portability

not ANSI, not POSIX

### Example

    char *buf = "123ret";
    char *bp;
    long double x = _strtold(buf, &bp);

Node:strtoll, Next:strtoul, Previous:_strtold, Up:Alphabetical List

## strtoll

### Syntax

    #include <stdlib.h>

    long long strtoll(const char *s, char **endp, int base);

### Description

This function converts as much of s as looks like an appropriate number into the value of that number, and sets *endp to point to the first unused character.

The base argument indicates what base the digits (or letters) should be treated as. If base is zero, the base is determined by looking for `0x`, `0X`, or `0` as the first part of the string, and sets the base used to 16, 16, or 8 if it finds one. The default base is 10 if none of those prefixes are found.

### Return Value

The value.

### Portability

not ANSI, not POSIX

### Example

    printf("Enter a number: "); fflush(stdout);
    gets(buf);
    char *bp;
    printf("The value is %lld\n", strtoll(buf, &bp, 0));

Node:strtoul, Next:strtoull, Previous:strtoll, Up:Alphabetical List

## strtoul

### Syntax

    #include <stdlib.h>

    unsigned long strtoul(const char *s, char **endp, int base);

### Description

This is just like `strtol` (see strtol) except that the result is unsigned.

### Return Value

The value.

### Portability

ANSI, POSIX

### Example

    printf("Enter a number: "); fflush(stdout);
    gets(buf);
    char *bp;
    printf("The value is %u\n", strtoul(buf, &bp, 0));

Node:strtoull, Next:strupr, Previous:strtoul, Up:Alphabetical List

## strtoull

### Syntax

    #include <stdlib.h>

    unsigned long long strtoull(const char *s, char **endp, int base);

### Description

This is just like `strtoll` (see strtoll) except that the result is unsigned.

### Return Value

The value.

### Portability

not ANSI, not POSIX

### Example

    printf("Enter a number: "); fflush(stdout);
    gets(buf);
    char *bp;
    printf("The value is %llu\n", strtoull(buf, &bp, 0));

Node:strupr, Next:strxfrm, Previous:strtoull, Up:Alphabetical List

## strupr

### Syntax

    #include <string.h>

    char *strupr(char *string);

### Description

This function converts all lower case characters in string to upper case.

### Return Value

string

### Portability

not ANSI, not POSIX

### Example

    char buf[] = "Foo!";
    strupr(buf);

Node:strxfrm, Next:swab, Previous:strupr, Up:Alphabetical List

## strxfrm

### Syntax

    #include <string.h>

    size_t strxfrm(char *s1, const char *s2, size_t max);

### Description

This copies characters from s2 to s1, which must be able to hold max characters. Each character is transformed according to the locale such that `strcmp(s1b, s2b)` is just like `strcoll(s1, s2)` where `s1b` and `s2b` are the transforms of `s1` and `s2`.

### Return Value

The actual number of bytes required to transform s2, including the `NULL`.

### Portability

ANSI, POSIX

Node:swab, Next:symlink, Previous:strxfrm, Up:Alphabetical List

## swab

### Syntax

    #include <stdlib.h>

    void swab(const void *from, void *to, int nbytes);

### Description

This function copies nbytes bytes from the address pointed to by from to the address pointed by to, exchanging adjacent even and odd bytes. It is useful for carrying binary data between little-endian and big-endian machines. The argument nbytes should be even, and the buffers from and to should not overlap.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:symlink, Next:syms_init, Previous:swab, Up:Alphabetical List

## symlink

### Syntax

    #include <unistd.h>

    int symlink(const char *exists, const char *new);

### Description

MSDOS doesn't support symbolic links. However, DJGPP supports "symlinks" to DJGPP programs. This function simulates a symlink between two `.exe` files in the DJGPP style. It creates a program whose name is pointed to by new which, when run, will actually execute the program exists passing it the string pointed by new in `argv[0]` (some programs change their behavior depending on what's passed in `argv[0]`). The file referred to by exists doesn't really have to exist when this function is called. If exists points to an existing file, the function checks that it is a DJGPP executable; if not, the call will fail with `EXDEV`.

Both new and exists can point to a name with or without the `.exe` extension.

Note that both exists and new must specify file names which reside in the same directory (this is a restriction of the DJGPP "symlinks"); the function will fail and set `errno` to `EXDEV` if they aren't.

This functions runs the `stubify` and `stubedit` programs, so they should be somewhere on your `PATH` for the function to succeed. (These programs come with the DJGPP development distribution.)

### Return Value

Zero in case of success, -1 in case of failure (and `errno` set to the appropriate error code).

### Portability

not ANSI, not POSIX

### Example

    symlink ("c:/djgpp/bin/grep", "c:/djgpp/bin/fgrep");

Node:syms_init, Next:syms_line2val, Previous:symlink, Up:Alphabetical List

## syms_init

### Syntax

    #include <debug/syms.h>

    void syms_init (char *file);

### Description

This function reads debugging symbols from the named file, which should be an executable program (either a `.exe` file or a raw COFF image created by `ld.exe`, the linker). It then processes the symbols: classifies them by type, sorts them by name and value, and stores them in internal data structures used by other symbol-related functions, such as `syms_val2name`, `syms_val2line`, etc.

You must call `syms_init` before calling the other `syms_*` functions.

Currently, `syms_init` only supports COFF and AOUT debugging format, so programs compiled with `-gstabs` cannot be processed by it.

### Return Value

None.

not ANSI, not POSIX

### Example

      syms_init("c:/foo/bar/baz.exe");

Node:syms_line2val, Next:syms_listwild, Previous:syms_init, Up:Alphabetical List

## syms_line2val

### Syntax

    #include <debug/syms.h>

    unsigned long syms_line2val (char *filename, int lnum);

### Description

This function returns the address of the first instruction produced from the line lnum of the source file filename that was linked into a program whose symbols were read by a previous call to `syms_init`.

COFF debugging format does not support pathnames, so filename should not include leading directories, just the basename.

You must call `syms_init` (see syms_init) before calling any of the other `syms_*` functions for the first time.

### Return Value

The address of the first instruction produced from the line, or zero if filename is not found in the symbol table or if no executable code was generated for line lnum in filename.

### Portability

not ANSI, not POSIX

### Example

     syms_init ("foo.exe");
     printf ("Line 3 of foo.c is at address %lx\n",
              syms_line2val("foo.c", 3));

Node:syms_listwild, Next:syms_module, Previous:syms_line2val, Up:Alphabetical List

## syms_listwild

### Syntax

    #include <debug/syms.h>

    void syms_listwild (char *pattern,
                        void (*handler) (unsigned long addr, char type_c,
                                         char *name, char *file, int lnum));

### Description

This function walks through all the symbols that were read by a previous call to `syms_init` (see syms_init). For each symbol whose name matches pattern, it invokes the user-defined function handler, passing it information about that symbol:

`address`
  the address of the symbol.
`type_c`
  a letter that specifies the type of the symbol, as follows:
  `T`
  `t`
    "text", or code: usually a function.
  `D`
  `d`
    data: an initialized variable.
  `B`
  `b`
    "bss": an uninitialized variable.
  `F`
  `f`
    a function (in `a.out` file only).
  `V`
  `v`
    a set element or pointer (in `a.out` file only).
  `I`
  `i`
    an indirect symbol (in `a.out` file only).
  `U`
  `u`
    an undefined (a.k.a. unresolved) symbol.
  `A`
  `a`
    an absolute symbol.
`name`
  the name of the symbol.
`file`
  the source file name where the symbol is defined.
`lnum`
  the line number on which the symbol is defined in the source file.

Since variables and functions defined in C get prepended with an underscore `_`, begin pattern with `_` if you want it to match C symbols.

You must call `syms_init` (see syms_init) before calling any of the other `syms_*` functions for the first time.

### Return Value

None.

### Portability

not ANSI, not POSIX

### Example

      void print_sym (unsigned long addr, char type_c,
                      char *name, char *file, int lnum)
      {
        printf (file ? "%s: %lx %c %s:%d\n" : "%s: %lx %c\n",
                name, addr, type_c,
                file ? file : "", lnum );
      }

      int main (void)
      {
        syms_init ("foo.exe");
        /* List all the symbols which begin with "___djgpp".  */
        syms_listwild ("___djgpp*", print_sym);
        return 0;
      }

Node:syms_module, Next:syms_name2val, Previous:syms_listwild, Up:Alphabetical List

## syms_module

### Syntax

    #include <debug/syms.h>

    char *syms_module (int nfile);

### Description

This function returns the name of the source file (a.k.a. module) whose ordinal number in the symbol table is nfile.

You must call `syms_init` (see syms_init) before calling any of the other `syms_*` functions for the first time.

### Return Value

The name of the source file, or a `NULL` pointer if nfile is negative or larger than the total number of modules linked into the program whose symbols were read by `syms_init`.

### Portability

not ANSI, not POSIX

Node:syms_name2val, Next:syms_val2line, Previous:syms_module, Up:Alphabetical List

## syms_name2val

### Syntax

    #include <debug/syms.h>
    extern int undefined_symbol;
    extern int syms_printwhy;

    unsigned long syms_name2val (const char *string);

### Description

This function returns the address of a symbol specified by string. string may be one of the following:

- A number, with or without a sign, in which case the number specifies the address or an offset from an address.
- A file name and a line number: `file#[line]`, where file is the name of one of the source files linked into the program whose symbols were read by `syms_init`, and line is a line number in that file. If line is omitted, it defaults to zero.

  Note that the COFF format supported by DJGPP only stores the basename of the source files, so do not specify file with leading directories.

- A symbol name as a string. The name can be specified either with or without the leading underscore `_`.
- A register name `%reg`. reg specifies the value of one of the debuggee's registers saved in the external variable `a_tss` (see run_child).
- Any sensible combination of the above elements, see the example below.

`syms_name2val` looks up the specified file, line, and symbol in the symbol table prepared by `syms_init`, finds their addresses, adds the offset, if any, and returns the result.

If the specified file, line, or symbol cannot be found, `syms_name2val` returns zero and sets the global variable `undefined_symbol` to a non-zero value. If the global variable `syms_printwhy` is non-zero, an error message is printed telling which part of the argument string was invalid.

You must call `syms_init` (see syms_init) before calling any of the other `syms_*` functions for the first time.

### Return Value

The address specified by string, or zero, if none found.

### Portability

not ANSI, not POSIX

### Example

     unsigned long addr1, addr2, addr3;

     syms_init ("foo.exe");
     addr1 = syms_name2val ("foo.c#256+12");
     addr2 = syms_name2val ("_main");
     addr3 = syms_name2val ("struct_a_var+%eax+4");

Node:syms_val2line, Next:syms_val2name, Previous:syms_name2val, Up:Alphabetical List

## syms_val2line

### Syntax

    #include <debug/syms.h>

    char *syms_val2line (unsigned long addr, int *line, int exact);

### Description

This function takes an address addr and returns the source file name which correspond to that address. The line number in that source file is stored in the variable pointed by line. If exact is non-zero, the function succeeds only if addr is the first address which corresponds to some source line.

You must call `syms_init` (see syms_init) before calling any of the other `syms_*` functions for the first time.

### Return Value

The name of the source file which corresponds to addr, or `NULL` if none was found.

### Portability

not ANSI, not POSIX

### Example

      int lineno;
      char *file_name;
      syms_init ("foo.exe");
      file_name = syms_val2line (0x1c12, &lineno);
      printf ("The address %x is on %s, line %d\n", 0x1c12, file_name, line);

Node:syms_val2name, Next:sync, Previous:syms_val2line, Up:Alphabetical List

## syms_val2name

### Syntax

    #include <debug/syms.h>

    char *syms_val2name (unsigned long addr, unsigned long *offset);

### Description

This function takes an address addr and returns the name of the closest symbol whose address is less that addr. If offset is not a `NULL` pointer, the offset of addr from the symbol's address is stored in the variable pointed to by offset.

You must call `syms_init` (see syms_init) before calling any of the other `syms_*` functions for the first time.

This function is meant to be used to convert numerical addresses into function names and offsets into their code, like what `symify` does with the call frame traceback.

The function ignores several dummy symbols, like `_end` and `_etext`.

### Return Value

The name of the found symbol, or the printed hexadecimal representation of addr, if no symbol was found near addr. The return value is a pointer to a static buffer, so don't overwrite it and don't pass it to `free`!

### Portability

not ANSI, not POSIX

### Example

      unsigned long offs;
      char *symbol_name;
      syms_init ("foo.exe");
      symbol_name = syms_val2name (0x1c12, &offs);
      printf ("The address %x is at %s%+ld\n", 0x1c12, symbol_name, offs);

Node:sync, Next:sys_errlist, Previous:syms_val2name, Up:Alphabetical List

## sync

### Syntax

    #include <unistd.h>

    int sync(void);

### Description

Intended to assist porting Unix programs. Under Unix, `sync` flushes all caches of previously written data. In this implementation, `sync` calls `fsync` on every open file. See fsync. It also calls `_flush_disk_cache` (see _flush_disk_cache) to try to force cached data to the disk.

### Return Value

Always returns 0.

### Portability

not ANSI, not POSIX

### Example

    sync();

Node:sys_errlist, Next:sys_nerr, Previous:sync, Up:Alphabetical List

## sys_errlist

### Syntax

    #include <errno.h>

    extern char *sys_errlist[];

### Description

This array contains error messages, indexed by `errno`, that describe the errors.

### Portability

not ANSI, not POSIX

### Example

    printf("Error: %s\n", sys_errlist[errno]);

Node:sys_nerr, Next:sysconf, Previous:sys_errlist, Up:Alphabetical List

## sys_nerr

### Syntax

    #include <errno.h>

    extern int sys_nerr;

### Description

This variable gives the number of error messages in `sys_errlist` (see sys_errlist).

### Portability

not ANSI, not POSIX

### Example

    if (errno < sys_nerr)
      printf("Error: %s\n", sys_errlist[errno]);

Node:sysconf, Next:system, Previous:sys_nerr, Up:Alphabetical List

## sysconf

### Syntax

    #include <unistd.h>

    long sysconf(int which);

### Description

This function returns various system configuration values, based on which:

      case _SC_ARG_MAX:	return _go32_info_block.size_of_transfer_buffer;
      case _SC_CHILD_MAX:	return CHILD_MAX;
      case _SC_CLK_TCK:	return CLOCKS_PER_SEC;
      case _SC_NGROUPS_MAX:	return NGROUPS_MAX;
      case _SC_OPEN_MAX:	return 255;
      case _SC_JOB_CONTROL:	return -1;
      case _SC_SAVED_IDS:	return -1;
      case _SC_STREAM_MAX:	return _POSIX_STREAM_MAX;
      case _SC_TZNAME_MAX:	return TZNAME_MAX;
      case _SC_VERSION:	return _POSIX_VERSION;

### Return Value

The value.

### Portability

not ANSI, POSIX

Node:system, Next:tan, Previous:sysconf, Up:Alphabetical List

## system

### Syntax

    #include <stdlib.h>

    int system(const char *cmd);

### Description

This function runs the command or program specified by cmd. If cmd is a null pointer, `system` returns non-zero only if a shell is available. If cmd is an empty string, the command processor pointed to by `SHELL` or `COMSPEC` variables in the environment will be invoked interactively; type `exit <RET>` to return to the program which called `system`. (Note that some other DOS compilers treat a null pointer like an empty command line, contrary to ANSI C requirements.)

When calling programs compiled by DJGPP this function will not use `command.com` and so will not be subject to its 126 character limit on command lines.

When the calling program runs on Windows 9X or Windows 2000 and calls the system shell to run the child program, or if the child program is a native Windows program (in `PE-COFF` format), or when the system shell is `4DOS` or `NDOS`, command lines longer than 126 characters are passed via the environment variable `CMDLINE`.

Command lines and pipes( i.e., the use of "<", ">", ">>", and "|") will be simulated internally in this function; this means that you can have both long command lines and redirection/pipes when running DJGPP programs with this function.

By default, `command.com` will only be invoked to run commands internal to it, or to run batch files (but this can be changed, see below). In these cases, the returned error code will always be zero, since `command.com` always exits with code 0.

Certain commands internal to `command.com` that don't make sense or cause no effect in the context of `system` are ignored by this function. These are `REM`, `EXIT`, `GOTO`, `SHIFT`; `SET`, `PATH` and `PROMPT` are ignored only if called with an argument. You can disable this feature if you need, see below.

Some commands are emulated internally by `system`, because the emulation is better than the original. Currently, the only emulated command is `CD` or `CHDIR`: the emulation knows about forward slashes and also switches the current drive. This emulation can also be switched off, as explained below.

When `system` is presented with an internal shell command, it checks the environment variables `SHELL` and `COMSPEC` (in that order) and invokes the program that they point to. If the shell thus found is one of the DOS shells (`command.com`, `4DOS` or `NDOS`), they are called with the `/c` switch prepended to the command line. Otherwise, `system` assumes that the shell is a Unix-style shell and passes it the entire command line via a temporary file, invoking the shell with a single argument which is the name of that file.

Shell scripts and batch files are invoked by calling either the program whose name appears on the first line (like in `#! /bin/sh`), or the default shell if none is specified by the script. If the name of the shell specified by the script is a Unix-style pathname, without a drive letter and with no extension, `system` will additionally search for it on the `PATH`. This allows to invoke Unix shell scripts unmodified, if you have a ported shell installed on your system.

You can customize the behavior of `system` using a bit-mapped variable __system_flags, defined on `<stdlib.h>`. The following bits are currently defined:

`__system_redirect`
  When set (the default), specifies that `system` can use its internal redirection and pipe code. If reset, any command line that includes an unquoted redirection symbol will be passed to the shell.
`__system_call_cmdproc`
  When set, `system` will always call the shell to execute the command line. If reset (the default), the shell will only be called when needed, as described above.

  You should always set this bit if you use a real, Unix-style shell (also, set `__system_use_shell`, described below, and the `SHELL` environment variable).

`__system_use_shell`
  When set (the default), the `SHELL` environment variable will take precedence upon `COMSPEC`; this allows you to specify a special shell for `system` that doesn't affect the rest of DOS. If reset, only `COMSPEC` is used to find the name of the command processor.
`__system_allow_multiple_cmds`
  When set, you can put multiple commands together separated by the `;` character. If reset (the default), the command line passed to `system` is executed as a single command and `;` has no special meaning.
`__system_allow_long_cmds`
  When set (the default), `system` will handle command lines longer than the DOS 126-character limit; this might crash your program in some cases, as the low-level functions that invoke the child program will only pass them the first 126 characters. When reset, `system` will detect early that the command line is longer than 126 characters and refuse to run it, but you will not be able to call DJGPP programs with long command lines.
`__system_emulate_command`
  If reset (the default), `system` will pass the entire command line to the shell if its name is one of the following: `sh.exe`, `sh16.exe`, `sh32.exe`, `bash.exe`, `tcsh.exe`. When set, `system` will attempt to emulate redirection and pipes internally, even if `COMSPEC` or `SHELL` point to a Unix-style shell.
`__system_handle_null_commands`
  When set (the default), commands internal to `COMMAND.COM` and compatible shells which have no effect in the context of `system`, are ignored (the list of these commands was given above). If reset, these commands are processed as all others, which means `COMMAND.COM` will be called to execute them.

  Note that this bit shouldn't be used with a Unix-style shell, because it does the wrong thing then. With Unix-style shells, you are supposed to set the `__system_call_cmdproc` bit which will always call the shell.

`__system_ignore_chdir`
  If set, the `CD` and `CHDIR` commands are ignored. When reset (the default), the processing of these commands depends on the `__system_emulate_chdir` bit, see below.

  This bit is for compatibility with Unix, where a single `cd dir` command has no effect, because the current working directory there is not a global notion (as on MSDOS). Don't set this bit if you use multiple commands (see `__system_allow_multiple_cmds` above).

`__system_emulate_chdir`
  When set, the `CD` and `CHDIR` commands are emulated internally: they change the drive when the argument specifies a drive letter, and they support both forward slashes and backslashes in pathnames. When `CD` is called without an argument, it prints the current working directory with forward slashes and down-cases DOS 8+3 names. If this bit is reset (the default), `CD` and `CHDIR` are passed to the shell.

The behavior of `system` can be customized at run time by defining the variable `DJSYSFLAGS` in the environment. The value of that variable should be the numerical value of `__system_flags` that you'd like to set; it will override the value of `__system_flags` specified when the program was compiled.

### Return Value

If cmd is a null pointer, `system` returns non-zero if a shell is available. The actual test for the existence of an executable file pointed to by `SHELL` or `COMSPEC` is only performed if the shell is to be invoked to process the entire command line; if most of the work is to be done by `system` itself, passing a null pointer always yields a non-zero return value, since the internal emulation is always "available".

Otherwise, the return value is the exit status of the child process in its lower 8 bits; bits 8-17 of the return value will hold `SIGINT` or `SIGABRT` if the child process was aborted by `Ctrl-C` or Critical Device Error, respectively; otherwise it will be zero. If the child couldn't be run, `system` will return -1 and set `errno` to an appropriate value. Note that if `COMMAND.COM` was used to run the child, it will always return a 0 status, even if the command didn't run successfully. However, `system` only calls `COMMAND.COM` when it needs to run commands internal to it.

### Portability

ANSI, POSIX

### Example

    system("cc1plus.exe @cc123456.gp");

Node:tan, Next:tanh, Previous:system, Up:Alphabetical List

## tan

### Syntax

    #include <math.h>

    double tan(double x);

### Description

This function computes the tangent of x (which should be given in radians).

### Return Value

The tangent of x. If the absolute value of x is finite but greater than or equal to 2^63, the return value is 0 (since for arguments that large each bit of the mantissa is more than `Pi`). If the value of x is infinite or `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:tanh, Next:tcdrain, Previous:tan, Up:Alphabetical List

## tanh

### Syntax

    #include <math.h>

    double tanh(double x);

### Description

This function computes the hyperbolic tangent of x.

### Return Value

The hyperbolic tangent of x. If x is either a positive or a negative infinity, the result is unity with the same sign as x, and `errno` is not changed. If x is `NaN`, the return value is `NaN` and `errno` is set to `EDOM`.

### Portability

ANSI, POSIX

Node:tcdrain, Next:tcflow, Previous:tanh, Up:Alphabetical List

## tcdrain

### Syntax

    #include <termios.h>

    int tcdrain (int fd);

### Description

This function waits until all the output is written to the file/device referred to by the handle fd. In this implementation, this function does nothing except checking the validity of its arguments; it is provided for compatibility only. Note that the termios emulation handles console only.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

Node:tcflow, Next:tcflush, Previous:tcdrain, Up:Alphabetical List

## tcflow

### Syntax

    #include <termios.h>

    int tcflow (int fd, int action);

### Description

This function suspends transmission of data to, or reception of data from, the device/file open on handle fd. The action argument can take one of these values:

`TCOOFF`
  the output is suspended
`TCOON`
  the output is resumed
`TCIOFF`
  the STOP character is transmitted
`TCION`
  the START character is transmitted

The current START and STOP characters are stored in the `termios` structure that is currently in effect. See Termios functions, for more details about that.

Note that the DJGPP termios emulation handles console only.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

Node:tcflush, Next:tcgetattr, Previous:tcflow, Up:Alphabetical List

## tcflush

### Syntax

    #include <termios.h>

    int tcflush (int fd, int which);

### Description

This function clears the input and/or output queues on for the device/file open on handle fd. The which argument can take these values:

`TCIFLUSH`
  the unprocessed characters in the input buffer are discarded
`TCOFLUSH`
  no effect (provided for compatibility)
`TCIOFLUSH`
  has the combined effect of `TCIFLUSH` and `TCOFLUSH`

Note that the termios emulation handles console only.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

Node:tcgetattr, Next:tcgetpgrp, Previous:tcflush, Up:Alphabetical List

## tcgetattr

### Syntax

    #include <termios.h>

    int tcgetattr (int fd, struct termios *termiosp);

### Description

This function gets the parameters associated with the file/device referred to by the handle fd and stores them in the termios structure termiosp. See Termios functions, for the full description of `struct termios` and its members.

Note that the termios emulation handles console only.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

### Example

    struct termios termiosbuf;
    int rc = tcgetattr (0, &termiosbuf);

Node:tcgetpgrp, Next:tcsendbreak, Previous:tcgetattr, Up:Alphabetical List

## tcgetpgrp

### Syntax

    #include <termios.h>

    int tcgetpgrp (int fd);

### Description

This function returns the value of the process group ID for the foreground process associated with the terminal. The file descriptor fd must be connected to the terminal, otherwise the function will fail.

### Return Value

If fd is connected to the terminal, the function returns the process group ID, which is currently identical to the value returned by `getpgrp()` (see getpgrp). Otherwise, it returns -1 and sets `errno` to `ENOTTY`.

### Portability

not ANSI, POSIX

Node:tcsendbreak, Next:tcsetattr, Previous:tcgetpgrp, Up:Alphabetical List

## tcsendbreak

### Syntax

    #include <termios.h>

    int tcsendbreak (int fd, int duration);

### Description

This function generates a break condition for `duration*0.25` seconds. In the current implementation this function does nothing; it is provided for compatibility only. Note that the termios emulation handles console only.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

Node:tcsetattr, Next:tcsetpgrp, Previous:tcsendbreak, Up:Alphabetical List

## tcsetattr

### Syntax

    #include <termios.h>

    int tcsetattr (int fd, int action, const struct termios *termiosp);

### Description

This function sets termios structure for device open on the handle fd from the structure termiosp. Note that the termios emulation handles console only.

The action argument can accept the following values:

`TCSANOW`
`TCSADRAIN`
`TCSAFLUSH`

Currently, any of these values causes the values in termiosp to take effect immediately.

See Termios functions, for the description of the `struct termios` structure.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

### Example

    tcsetattr (0, TCSANOW, &termiosbuf);

Node:tcsetpgrp, Next:tell, Previous:tcsetattr, Up:Alphabetical List

## tcsetpgrp

### Syntax

    #include <termios.h>

    int tcsetpgrp (int fd, pid_t pgroup_id);

### Description

This function sets the foreground process group ID for the terminal connected to file descriptor fd. fd must be a valid handle connected to a terminal device, and pgroup_id must be the process group ID of the calling process, or the function will fail.

### Return Value

If fd is a valid handle connected to a terminal and pgroup_id is equal to what `getpgrp()` returns (see getpgrp), the function will do nothing and return zero. Otherwise, -1 will be returned and `errno` will be set to a suitable value. In particular, if the pgroup_id argument is different from what `getpgrp()` returns, `tcsetpgrp` sets `errno` to `ENOSYS`.

### Portability

not ANSI, POSIX

Node:tell, Next:telldir, Previous:tcsetpgrp, Up:Alphabetical List

## tell

### Syntax

    #include <io.h>

    off_t tell(int file);

### Description

This function returns the location of the file pointer for file.

### Return Value

The file pointer, or -1 on error.

### Portability

not ANSI, not POSIX

### Example

    off_t q = tell(fd);

Node:telldir, Next:tempnam, Previous:tell, Up:Alphabetical List

## telldir

### Syntax

    #include <dirent.h>

    long telldir(DIR *dir);

### Description

This function returns a value which indicates the position of the pointer in the given directory. This value is only useful as an argument to `seekdir` (see seekdir).

### Return Value

The directory pointer.

### Portability

not ANSI, not POSIX

### Example

    DIR *dir;
    long q = telldir(dir);
    do_something();
    seekdir(dir, q);

Node:tempnam, Next:Termios functions, Previous:telldir, Up:Alphabetical List

## tempnam

### Syntax

    #include <stdio.h>

    char * tempnam(const char *tmpdir, const char *prefix);

### Description

This function generates a file name which can be used for a temporary file, and makes sure that no other file by that name exists.

The caller has control on the choice of the temporary file's directory, and the initial letters of the file's basename. If the argument tmpdir points to the name of the directory in which the temporary file will be created, `tempnam` will ensure that the generate name is unique in that directory. If the argument prefix points to a string, then that string will be used as the first few characters of the file's basename. Due to limitations of the DOS 8.3 file namespace, only up to two first characters in prefix will be used.

If tmpdir is `NULL`, or empty, or points to a non-existent directory, `tempnam` will use a default directory. The default directory is determined by testing, in sequence, the directories defined by the values of environment variables `TMPDIR`, `TEMP` and `TMP`. The first variable that is found to point to an existing directory will be used. If none of these variables specify a valid directory, `tempnam` will use the static default path prefix defined by `P_tmpdir` on `<stdio.h>`, or `"c:/"`, in that order.

If prefix is `NULL` or empty, `tempnam` will supply its own default prefix `"tm"`.

`tempnam` puts the generated name into space allocated by `malloc`. It is up to the caller to free that space when it is no longer needed.

Note that `tempnam` does not actually create the file, nor does it ensure in any way that the file will be automatically deleted when it's no longer used. It is the user's responsibility to do that.

### Return Value

On success, `tempnam` returns a pointer to space (allocated with a call to `malloc`) where the file name is constructed. If `malloc` failed to provide sufficient memory buffer, or if no valid directory to hold the file was found, `tempnam` returns a `NULL` pointer.

### Portability

not ANSI, not POSIX

### Example

      #include <stdio.h>

        tempnam ("c:/tmp/", "foo");

Node:Termios functions, Next:textattr, Previous:tempnam, Up:Alphabetical List

## Termios functions

The `termios` functions allow to control terminals and asynchronous communications ports. The DJGPP implementation currently supports the `termios` functionality for console devices only. It does that by reading the keyboard via the BIOS Int 16h and writes to the screen via the direct output interrupt 29h. This I/O redirection is performed by the special hook internal to the library.

Many of the `termios` functions accept a termiosp argument which is a pointer to a `struct termios` variable. Here's the description of this structure:

     #define NCCS 12
     struct termios {
       cc_t	        c_cc[NCCS];  /* control characters */
       tcflag_t     c_cflag;     /* control modes */
       tcflag_t     c_iflag;     /* input modes */
       tcflag_t     c_lflag;     /* local modes */
       tcflag_t     c_oflag;     /* output modes */
       speed_t      c_ispeed;    /* input baudrate */
       speed_t      c_ospeed;    /* output baudrate */
     }

The array `c_cc[]` defines the special control characters. the following table lists the supported control functions the default characters which invoke those functions, and the default values for MIN and TIME parameters:

Index | Name | Function | Default Value
1 | VEOF | Signal End-Of-Input | Ctrl-D
2 | VEOL | Signal End-Of-Line | [Disabled]
3 | VERASE | Delete previous character | Backspace
4 | VINTR | Generate SIGINT | Ctrl-C
5 | VKILL | Erase current line | Ctrl-U
6 | VMIN | The MIN value | 1
7 | VQUIT | Generate SIGQUIT | Ctrl-\
8 | VSTART | Resume output | Ctrl-Q
9 | VSTOP | Suspend output | Ctrl-S
10 | VSUSP | Suspend program | Ctrl-Z
11 | VTIME | TIME value | 0

The special characters (like `VEOL`, `VKILL`, etc.) produce their effect only under the canonical input processing, that is, when the `ICANON` bit in the `c_lflag` member of `struct termios` (see below) is set. If `ICANON` is not set, all characters are processed as regular characters and returned to the caller; only the `VMIN` and `VTIME` parameters are meaningful in the non-canonical processing mode.

The `VEOL` character can be used to signal end of line (and thus end of input in the canonical mode) in addition to the normal `RET` key. In the non-canonical mode, input ends as soon as at least `VMIN` characters are received.

Note that the values of `VMIN` and `VTIME` are currently ignored; `termios` functions always work as if `VMIN` were 1 and `VTIME` were zero. Other parameters are supported (for console devices only), except that VSTOP and VSTART characters are not inserted to the input, but otherwise produce no effect.

The `c_cflag` member of `struct termios` describes the hardware terminal control, as follows:

Symbol | Function
B0 | Hang up
B50 | 50 baud
B75 | 75 baud
B110 | 110 baud
B134 | 134.5 baud
B150 | 150 baud
B200 | 200 baud
B300 | 300 baud
B600 | 600 baud
B1200 | 1200 baud
B1800 | 1800 baud
B2400 | 2400 baud
B4800 | 4800 baud
B9600 | 9600 baud
B19200 | 19200 baud
B38400 | 38400 baud
CSIZE | Character size:
CS5 | 5-bit characters
CS6 | 6-bit characters
CS7 | 7-bit characters
CS8 | 8-bit characters
CSTOPB | If set, send two stop bits
CREAD | Enable reading
PARENB | Enable parity
PARODD | If set, use odd parity
HUPCL | Hang up on last close
CLOCAL | If set, line is local

Note that since the DOS terminal doesn't use asynchronous ports, the above parameters are always ignored by the implementation. The default value of `c_cflag` is `(CS8|CREAD|CLOCAL)`.

The `c_lflag` member of `struct termios` defines the local modes that control the terminal functions:

Symbol | Function
ISIG | If set, enable signals SIGINT and SIGQUIT
ICANON | If set, enable canonical input processing
ECHO | If set, enable echoing
ECHOE | Erase character deletes
ECHOK | Output newline after the kill character
ECHONL | Echo the newline
NOFLSH | [Ignored]
TOSTOP | [Ignored]
ECHOCTL | Echo control characters as ^X
ECHOKE | Erase killed line
IEXTEN | [Ignored]

The default value of `c_lflag` is `(ISIG|ICANON|ECHO|IEXTEN|ECHOE|ECHOKE|ECHOCTL)`.

The `c_iflag` member of `struct termios` describes the input control:

Symbol | Function
IGNBRK | Ignore Ctrl-BREAK
BRKINT | Generate SIGINT on Ctrl-BREAK
IGNPAR | [Ignored]
PARMRK | [Ignored]
INPCK | [Ignored]
ISTRIP | Strip the 8th bit from input
INLCR | Map NL to CR on input
IGNCR | Ignore CR characters
ICRNL | Map CR to NL on input
IXON | [Ignored]
IXOFF | Enable start/stop input control
IMAXBEL | Ring the bell if input line too long

The default value of `c_iflag` is `(BRKINT|ICRNL|IMAXBEL)`.

The `c_oflag` member of `struct termios` specifies the output handling:

Symbol | Function
OPOST | If not set, output characters verbatim
ONLCR | Map newline to CR-LF pair on output
OCRNL | Map CR to NL on output
ONOEOT | Don't output EOT characters

Note that if the `OPOST` bit is not set, all the other flags are ignored and the characters are output verbatim. The default value of `c_oflag` is `(OPOST|ONLCR|ONOEOT)`.

The `c_ispeed` and `c_ospeed` members specify, respectively, the input and output baudrate of the terminal. They are set by default to 9600 baud, but the value is always ignored by this implementation, since no asynchronous ports are used.

Node:textattr, Next:textbackground, Previous:Termios functions, Up:Alphabetical List

## textattr

### Syntax

    #include <conio.h>

    void textattr(int _attr);

### Description

Sets the attribute used for future writes to the screen:

    ---- XXXX = foreground color
    -XXX ---- = background color
    X--- ---- = 1=blink 0=steady

The include file <conio.h> contains an enum COLORS that define the various values that can be used for these bitfields; light colors can only be used for the foreground.

### Portability

not ANSI, not POSIX

### Example

    /* blinking white on blue */
    textattr(BLINK | (BLUE << 4) | WHITE);

Node:textbackground, Next:textcolor, Previous:textattr, Up:Alphabetical List

## textbackground

### Syntax

    #include <conio.h>

    void textbackground(int _color);

### Description

Sets just the background of the text attribute. See textattr.

### Portability

not ANSI, not POSIX

Node:textcolor, Next:textmode, Previous:textbackground, Up:Alphabetical List

## textcolor

### Syntax

    #include <conio.h>

    void textcolor(int _color);

### Description

Sets just the foreground of the text attribute. See textattr.

### Portability

not ANSI, not POSIX

Node:textmode, Next:time, Previous:textcolor, Up:Alphabetical List

## textmode

### Syntax

    #include <conio.h>

    void textmode(int _mode);

### Description

Sets the text mode of the screen. _mode is one of the following:

`LASTMODE`
  The text mode which was in effect before the last call to `textmode()`.
`BW40`
  40-column black and white (on a color screen)
`C40`
  40-color color.
`BW80`
  80-column black and white (on a color screen)
`C80`
  80-column color
`MONO`
  The monochrome monitor
`C4350`
  80-column, 43- (on EGAs) or 50-row (on VGAs) color

See _set_screen_lines, for a more versatile method of setting text screen dimensions.

### Portability

not ANSI, not POSIX

Node:time, Next:times, Previous:textmode, Up:Alphabetical List

## time

### Syntax

    #include <time.h>

    time_t time(time_t *t);

### Description

If t is not `NULL`, the current time is stored in `*t`.

### Return Value

The current time is returned.

### Portability

ANSI, POSIX

### Example

    printf("Time is %d\n", time(0));

Node:times, Next:tmpfile, Previous:time, Up:Alphabetical List

## times

### Syntax

    #include <sys/times.h>

    clock_t times(struct tms *buf);

### Description

This function returns the number of clock ticks used by the current process and all of its children until the moment of call. The number of tics per second is `CLOCKS_PER_SEC`, defined on time.h.

This is the structure in which `times` returns its info:

    struct  tms {
      clock_t tms_cstime;
      clock_t tms_cutime;
      clock_t tms_stime;
      clock_t tms_utime;
    };

Currently, the elapsed time of the running program is returned in the `tms_utime` field, and all other fields return as zero.

### Return Value

The number of elapsed tics since the program started.

### Portability

not ANSI, POSIX

### Example

    printf("We used %d seconds of elapsed time\n", times(&buf)/CLOCKS_PER_SEC);

Node:tmpfile, Next:tmpnam, Previous:times, Up:Alphabetical List

## tmpfile

### Syntax

    #include <stdio.h>

    FILE *tmpfile(void);

### Description

This function opens a temporary file. It will automatically be removed if the file is closed or when the program exits. The name of the file is generated by the same algorithm as described under tmpnam() (see tmpnam).

### Return Value

A newly opened file.

### Portability

ANSI, POSIX

### Example

    FILE *tmp = tmpfile();

Node:tmpnam, Next:toascii, Previous:tmpfile, Up:Alphabetical List

## tmpnam

### Syntax

    #include <stdio.h>

    char *tmpnam(char *s);

### Description

This functions generates a string that is a valid file name and that is not the same as the name of an existing file. A different string is guaranteed to be produced each time it is called, up to `TMP_MAX` times (`TMP_MAX` is defined on stdio.h). If `tmpnam` is called more than TMP_MAX times, the behavior is implementation-dependent (ours just wraps around and tries to reuse the same file names from the beginning).

This function examines the environment to determine the directory in which the temporary file will be opened. It looks for one of the variables `"TMPDIR"`, `"TEMP"` and `"TMP"`, in that order. The first one which is found in the environment will be used on the assumption that it points to a directory. If neither of the above variables is defined, `tmpnam` defaults to the "c:/" directory (which under MS-DOS might mean that it fails to generate TMP_MAX unique names, because DOS root directories cannot grow beyond certain limits).

### Return Value

If s is a null pointer, `tmpnam` leaves its result in an internal static buffer and returns a pointer to that buffer. If s is not a null pointer, it is assumed to point to an array of at least `L_tmpnam` characters, and `tmpnam` writes its result in that array and returns a pointer to it as its value.

### Portability

ANSI, POSIX

### Example

    char buf[L_tmpnam];
    char *s = tmpnam(buf);

Node:toascii, Next:tolower, Previous:tmpnam, Up:Alphabetical List

## toascii

### Syntax

    #include <ctype.h>

    int toascii(int c);

### Description

This function strips the high bit of c, forcing it to be an ASCII character.

### Return Value

The ASCII character.

### Portability

not ANSI, not POSIX

### Example

    for (i=0; buf[i]; i++)
      buf[i] = toascii(buf[i]);

Node:tolower, Next:toupper, Previous:toascii, Up:Alphabetical List

## tolower

### Syntax

    #include <ctype.h>

    int tolower(int c);

### Description

This function returns c, converting it to lower case if it is upper case. See toupper.

### Return Value

The lower case letter.

### Portability

ANSI, POSIX

### Example

    for (i=0; buf[i]; i++)
      buf[i] = tolower(buf[i]);

Node:toupper, Next:_truename, Previous:tolower, Up:Alphabetical List

## toupper

### Syntax

    #include <ctype.h>

    int toupper(int c);

### Description

This function returns c, converting it to upper case if it is lower case. See tolower.

### Return Value

The upper case letter.

### Portability

ANSI, POSIX

### Example

    for (i=0; buf[i]; i++)
      buf[i] = toupper(buf[i]);

Node:_truename, Next:truncate, Previous:toupper, Up:Alphabetical List

## _truename

### Syntax

    #include <sys/stat.h>

    char * _truename(const char *path, char *true_path);

### Description

Given a path of a file, returns in true_path its canonicalized pathname, with all letters uppercased, default drive and directory made explicit, forward slashes converted to backslashes, asterisks converted to appropriate number of of question marks, file and directory names truncated to 8.3 if necessary, "." and ".." resolved, extra slashes (but the last, if present) removed, SUBSTed, JOINed and ASSIGNed drives resolved. Character devices return as "X:/DEVNAME" (note the forward slash!), where X is the CURRENT drive and DEVNAME is the device name (e.g. CON). This is exactly what DOS TRUENAME command does. See Ralph Brown's Interrupt List for more details.

The named path doesn't have to exist, but the drive, if given as part of it, should be a legal DOS drive, as this function hits the disk.

The function will fail if given a path which (1) is an empty string; or (2) contains only the drive letter (e.g. "c:"); or (3) has leading whitespace. It will also fail if it couldn't allocate memory required for its communication with DOS or for true_path (see below).

Upon success, the function will place the result in true_path, if that's non-NULL; the buffer should be large enough to contain the largest possible pathname (PATH_MAX characters). If true_path is a NULL pointer, the space to hold the result will be allocated by calling malloc; it is up to the caller to release the buffer by calling free.

### Return Value

The function returns the pointer to the result. In case of any failure, a NULL pointer is returned, and errno is set.

### Portability

not ANSI, not POSIX

### Example

      fprintf(stderr,
              "True name of %s is %s\n", path, _truename(path, (char *)0));

Node:truncate, Next:ttyname, Previous:_truename, Up:Alphabetical List

## truncate

### Syntax

    #include <unistd.h>

    int truncate(const char *file, off_t size);

### Description

This function truncates file to size bytes.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    truncate("/tmp/data.txt", 400);

Node:ttyname, Next:tzset, Previous:truncate, Up:Alphabetical List

## ttyname

### Syntax

    #include <unistd.h>

    char *ttyname(int file);

### Description

Gives the name of the terminal associated with file.

### Return Value

Returns "con" if file is a device, else `NULL`.

### Portability

not ANSI, POSIX

### Example

    char *tty = ttyname(0);

Node:tzset, Next:tzsetwall, Previous:ttyname, Up:Alphabetical List

## tzset

### Syntax

    #include <time.h>

    extern char *tzname[2];
    void tzset(void);

### Description

This function initializes the global variable `tzname` according to environment variable `TZ`. After the call, `tzname` holds the specifications for the time zone for the standard and daylight-saving times.

### Return Value

None.

### Portability

not ANSI, POSIX

Node:tzsetwall, Next:uclock, Previous:tzset, Up:Alphabetical List

## tzsetwall

### Syntax

    #include <time.h>

    void tzsetwall(void);

### Description

This function sets up the time conversion information used by `localtime` (see localtime) so that `localtime` returns the best available approximation of the local wall clock time.

### Return Value

None.

### Portability

not ANSI, not POSIX

Node:uclock, Next:umask, Previous:tzsetwall, Up:Alphabetical List

## uclock

### Syntax

    #include <time.h>

    uclock_t uclock(void);

### Description

This function returns the number of uclock ticks since an arbitrary time, actually, since the first call to `uclock`, which itself returns zero. The number of tics per second is `UCLOCKS_PER_SEC` (declared in the `time.h` header file.

`uclock` is provided for very high-resulution timing. It is currently accurate to better than 1 microsecond (actually about 840 nanoseconds). You cannot time across two midnights with this implementation, giving a maximum useful period of 48 hours and an effective limit of 24 hours. Casting to a 32-bit integer limits its usefulness to about an hour before 32 bits will wrap.

Note that `printf` will only print a value of type `uclock_t` correctly if you use format specifiers for `long long` data, such as `%Ld` or `%lld`, because `uclock_t` is a 64-bit integer. See printf.

Also note that `uclock` reprograms the interval timer in your PC to act as a rate generator rather than a square wave generator. I've had no problems running in this mode all the time, but if you notice strange things happening with the clock (losing time) after using `uclock`, check to see if this is the cause of the problem.

Windows 3.X doesn't allow to reprogram the timer, so the values returned by `uclock` there are incorrect. DOS and Windows 9X don't have this problem.

### Return Value

The number of tics.

### Portability

not ANSI, not POSIX

### Example

    printf("%Ld seconds have elapsed\n", (long long)(uclock()/UCLOCKS_PER_SEC));

Node:umask, Next:uname, Previous:uclock, Up:Alphabetical List

## umask

### Syntax

    #include <sys/stat.h>

    mode_t umask(mode_t cmask);

### Description

This function does nothing. It exists to assist porting.

### Portability

not ANSI, POSIX

Node:uname, Next:ungetc, Previous:umask, Up:Alphabetical List

## uname

### Syntax

    #include <sys/utsname.h>

    #int uname(struct utsname *u);

### Description

Fills in the structure with information about the system.

    struct utsname {
      char machine[9];
      char nodename[32];
      char release[9];
      char sysname[9];
      char version[9];
    };

`machine`
  "pc"
`nodename`
  The name of your PC (if networking is installed), else "pc".
`release`
  The minor release of dos. For example, dos 1.23 would return "23" here.
`sysname`
  The flavor of the OS.
`version`
  The major release of dos. For example, dos 1.23 would return "1" here.

### Return Value

Zero on success, else nonzero.

### Portability

not ANSI, POSIX

Node:ungetc, Next:ungetch, Previous:uname, Up:Alphabetical List

## ungetc

### Syntax

    #include <stdio.h>

    int ungetc(int c, FILE *file);

### Description

This function pushes c back into the file. You can only push back one character at a time.

### Return Value

The pushed-back character, or `EOF` on error.

### Portability

ANSI, POSIX

### Example

    int q;
    while (q = getc(stdin) != 'q');
    ungetc(q);

Node:ungetch, Next:unlink, Previous:ungetc, Up:Alphabetical List

## ungetch

### Syntax

    #include <conio.h>

    int ungetch(int);

### Description

Puts a character back, so that getch will return it instead of actually reading the console.

### Return Value

The charater is returned.

### Portability

not ANSI, not POSIX

Node:unlink, Next:unlock, Previous:ungetch, Up:Alphabetical List

## unlink

### Syntax

    #include <unistd.h>

    int unlink(const char *file);

### Description

This function removes a file from the file system.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, POSIX

### Example

    unlink("data.txt");

Node:unlock, Next:_use_lfn, Previous:unlink, Up:Alphabetical List

## unlock

### Syntax

    #include <io.h>

    int unlock(int fd, long offset, long length);

### Description

Unlocks a region previously locked by `lock`.

See lock.

### Return Value

Zero if successful, nonzero if not.

### Portability

not ANSI, not POSIX

Node:_use_lfn, Next:usleep, Previous:unlock, Up:Alphabetical List

## _use_lfn

### Syntax

    #include <fcntl.h>

    char _use_lfn(const char *path);

### Description

The `_use_lfn` function returns a nonzero value if the low level libc routines will use the Long File Name (LFN) functions provided with Windows 9x (and other advanced filesystems), when accessing files and directories on the same filesystem as path. path may be any legal pathname; however, the function only needs the name of the root directory on the particular drive in question. If path is a `NULL` pointer, the function assumes that all the filesystems support (or do not support) LFN in the same manner, and returns the info pertinent to the last filesystem that was queried; this usually makes the call faster. Note that on Windows 95 you don't need to distinguish between different drives: they all support LFN API. If path does not specify the drive explicitly, the current drive is used.

The header `fcntl.h` defines a macro `_USE_LFN`; applications should use this macro instead of calling `_use_lfn` directly. That is so this routine could be replaced with one which always returns 0 to disable using long file names. Calling `_USE_LFN` also makes the code more portable to other operating systems, where the macro can be redefined to whatever is appropriate for that environment (e.g., it should be a constant 1 on Unix systems and constant 0 for environments that don't support LFN API, like some other MSDOS compilers). Currently, `_USE_LFN` assumes that LFN API does not depend on a drive.

Long file names can also be disabled by setting the flag `_CRT0_FLAG_NO_LFN` in `_crt0_startup_flags` for an image which should not allow use of long file names. Long names can be suppressed at runtime on a global basis by setting the environment variable `LFN` to `N`, i.e. `SET LFN=N`. This might be needed if a distribution expected the truncation of long file names to 8.3 format to work. For example, if a C source routine included the file exception.h (9 letters) and the file was unzipped as exceptio.h, then GCC would not find the file unless you set `LFN=n`. The environment variable can be set in the `DJGPP.ENV` file to always disable LFN support on any system, or can be set in the DOS environment for a short term (single project) basis. If you dual boot a system between Windows 95 and DOS, you probably should set `LFN=n` in your `DJGPP.ENV` file, since long file names would not be visible under DOS, and working with the short names under DOS will damage the long names when returning to Windows 95.

### Return Value

If LFN APIs are supported and should be used, it returns 1, else 0.

Note that if the `_CRT0_FLAG_NO_LFN` bit is set, or `LFN` is set to `N` or `n` in the environment, both `_use_lfn` and `_USE_LFN` will always return 0 without querying the filesystem. You can reset the `_CRT0_FLAG_NO_LFN` bit at runtime to force filesystem to be queried.

### Portability

not ANSI, not POSIX

### Example

    #include <fcntl.h>
    #include <sys/stat.h>

      int fd = creat (_USE_LFN ? "MyCurrentJobFile.Text" : "currjob.txt",
                      S_IRUSR | S_IWUSR);

Node:usleep, Next:utime, Previous:_use_lfn, Up:Alphabetical List

## usleep

### Syntax

    #include <unistd.h>

    unsigned usleep(unsigned usec);

### Description

This function pauses the program for usec microseconds. Note that, since `usleep` calls `clock` internally, and the latter has a 55-msec granularity, any argument less than 55msec will result in a pause of random length between 0 and 55 msec. Any argument less than 11msec (more precisely, less than 11264 microseconds), will always result in zero-length pause (because `clock` multiplies the timer count by 5). See clock.

### Return Value

The number of unslept microseconds (i.e. zero).

### Portability

not ANSI, not POSIX

### Example

    usleep(500000);

Node:utime, Next:utimes, Previous:usleep, Up:Alphabetical List

## utime

### Syntax

    #include <utime.h>

    int utime(const char *file, const struct utimbuf *time);

### Description

This function sets the modification timestamp on the file. The new time is stored in this structure:

    struct utimbuf
    {
        time_t  actime;  /* access time (unused on FAT filesystems) */
        time_t  modtime; /* modification time */
    };

Note that, as under DOS a file only has a single timestamp, the `actime` field of `struct utimbuf` is ignored by this function, and only `modtime` field is used. On filesystems which support long filenames, both fields are used and both access and modification times are set.

### Return Value

Zero for success, nonzero for failure.

### Portability

not ANSI, POSIX

### Example

    struct utimbuf t;
    t.modtime = time(0);
    utime("data.txt", &t);

Node:utimes, Next:v2loadimage, Previous:utime, Up:Alphabetical List

## utimes

### Syntax

    #include <sys/time.h>

    int utimes(const char *file, struct timeval tvp[2]);

### Description

This function sets the file access time as specified by `tvp[0]`, and its modification time as specified by `tvp[1]`. `struct timeval` is defined as follows:

    struct timeval {
      time_t tv_sec;
      long tv_usec;
    };

Note that DOS and Windows maintain the file times with 2-second granularity. Therefore, the `tv_usec` member of the argument is always ignored, and the underlying filesystem truncates (or sometimes rounds) the actual file time stamp to the multiple of 2 seconds.

On plain DOS, only one file time is maintained, which is arbitrarily taken from `tvp[1].tv_sec`. On Windows 9X, both times are used, but note that most versions of Windows only use the date part and ignore the time.

Due to limitations of DOS and Windows, you cannot set times of directories.

### Return Value

Zero on success, nonzero on failure.

### Portability

not ANSI, not POSIX

### Example

    time_t now;
    struct timeval tvp[2];
    time(&now);
    tvp[1].tv_sec = now + 100;
    utimes("foo.dat", tvp);

Node:v2loadimage, Next:varargs, Previous:utimes, Up:Alphabetical List

## v2loadimage

### Syntax

    #include <debug/v2load.h>

    int v2loadimage (const char *program, const char *cmdline, jmp_buf load_state);

### Description

This function loads an executable image of a DJGPP v2.x program and prepares it for debugging. program should point to the file name of the executable program. `v2loadimage` does not search the `PATH` and does not try any executable extensions, so program should point to a fully-qualified path, complete with the drive, directory, and file-name extension; otherwise the call will fail.

cmdline should point to the command-line arguments to be passed to the program. The format of the command line should be exactly like the command tail DOS passes to programs: the first byte gives the length of the command tail, the tail itself begins with the second byte, and the tail is terminated by a CR character (decimal code 13); the length byte does not include the CR. The command-line arguments should look as if they were to be passed to the library function `system`. In particular, all special characters like wildcards and whitespace should be quoted as if they were typed at the DOS prompt.

Note that currently, this function doesn't support command lines longer than the DOS 126-character limit.

After the function loads the image and sets up the necessary memory segments for it to be able to run, it sets load_state so that it can be used to `longjmp` to the debuggee's entry point. This information is typically used by `run_child` (see run_child).

### Return Value

Zero in case of success, non-zero otherwise.

### Portability

not ANSI, not POSIX

### Example

     cmdline = (char *) alloca (strlen (args) + 4);
     cmdline[0] = strlen (args);
     strcpy (cmdline + 1, args);
     cmdline[strlen (args) + 1] = 13;

     if (v2loadimage (exec_file, cmdline, start_state))
      {
        printf ("Load failed for image %s\n", exec_file);
        exit (1);
      }

      edi_init (start_state);

Node:varargs, Next:vfork, Previous:v2loadimage, Up:Alphabetical List

## varargs

### Syntax

    #include <stdarg.h>

    void va_start(va_list ap, LAST_REQUIRED_ARG);
    TYPE va_arg(va_list ap, TYPE);
    void va_end(va_list ap);

### Description

Used to write functions taking a variable number of arguments. Note that these are actually macros, and not functions. You must prototype the function with `...' in its argument list. Then, you do the following:

- Create a variable of type `va_list`.
- Initialize it by calling `va_start` with it and the name of the last required (i.e. non-variable) argument.
- Retrieve the arguments by calling `va_arg` with the `va_list` variable and the type of the argument. As another alternative, you can pass the `va_list` to another function, which may then use `va_arg` to get at the arguments. `vprintf` is an example of this.
- Call `va_end` to destroy the `va_list`.

Be aware that your function must have some way to determine the number and types of the arguments. Usually this comes from one of the required arguments. Some popular ways are to pass a count, or to pass some special value (like `NULL`) at the end.

Also, the variable arguments will be promoted according to standard C promotion rules. Arguments of type `char` and `short` will be promoted to `int`, and you should retrieve them as such. Those of type `float` will be promoted to `double`.

### Return Value

`va_arg` returns the argument it fetched, the other macros return nothing.

### Portability

ANSI, POSIX

### Example

    int find_the_sum(int count, ...)
    {
      va_list ap;
      int i;
      int total = 0;

      va_start(ap, count);
      for (i = 0; i < count; i++)
          total += va_arg(ap, int);
      va_end(ap);
      return total;
    }

    int other_function(void)
    {
      return find_the_sum(6, 1, 2, 3, 4, 5, 6);
    }

Node:vfork, Next:vfprintf, Previous:varargs, Up:Alphabetical List

## vfork

### Syntax

    #include <unistd.h>

    pid_t vfork(void);

### Description

This function always returns -1 and sets `errno' to ENOMEM, as MS-DOS does not support multiple processes. It exists only to assist in porting Unix programs.

### Portability

not ANSI, not POSIX

Node:vfprintf, Next:vfscanf, Previous:vfork, Up:Alphabetical List

## vfprintf

### Syntax

    #include <stdio.h>
    #include <stdarg.h>

    int vfprintf(FILE *file, const char *format, va_list arguments);

### Description

Sends formatted output from the arguments to the file. See printf.

### Return Value

The number of characters written.

### Portability

ANSI, POSIX

### Example

    void my_errmsg(char *format, ...)
    {
      va_list arg;

      va_start(arg, format);
      fprintf(stderr, "my_errmsg: ");
      vfprintf(stderr, format, arg);
      va_end(arg);
    }

Node:vfscanf, Next:vprintf, Previous:vfprintf, Up:Alphabetical List

## vfscanf

### Syntax

    #include <stdio.h>

    int vfscanf(FILE *file, const char *format, va_list arguments);

### Description

This function scans formatted text from file and stores it in the variables pointed to by the arguments. See scanf.

### Return Value

The number of items successfully scanned.

### Portability

not ANSI, not POSIX

Node:vprintf, Next:vscanf, Previous:vfscanf, Up:Alphabetical List

## vprintf

### Syntax

    #include <stdio.h>
    #include <stdarg.h>

    int vprintf(const char *format, va_list arguments);

### Description

Sends formatted output from the arguments to `stdout`. See printf. See vfprintf.

### Return Value

The number of characters written.

### Portability

ANSI, POSIX

Node:vscanf, Next:vsprintf, Previous:vprintf, Up:Alphabetical List

## vscanf

### Syntax

    #include <stdio.h>

    int vscanf(const char *format, va_list arguments);

### Description

This function scans formatted text from `stdin` and stores it in the variables pointed to by the arguments. See scanf. See vfscanf.

### Return Value

The number of items successfully scanned.

### Portability

not ANSI, not POSIX

Node:vsprintf, Next:vsscanf, Previous:vscanf, Up:Alphabetical List

## vsprintf

### Syntax

    #include <stdio.h>
    #include <stdarg.h>

    int vsprintf(char *buffer, const char *format, va_list arguments);

### Description

Sends formatted output from the arguments to the buffer. See printf. See vfprintf.

### Return Value

The number of characters written.

### Portability

ANSI, POSIX

Node:vsscanf, Next:wait, Previous:vsprintf, Up:Alphabetical List

## vsscanf

### Syntax

    #include <stdio.h>

    int vsscanf(const char *string, const char *format, va_list arguments);

### Description

This function scans formatted text from the string and stores it in the variables pointed to by the arguments. See scanf. See vfscanf.

### Return Value

The number of items successfully scanned.

### Portability

not ANSI, not POSIX

Node:wait, Next:waitpid, Previous:vsscanf, Up:Alphabetical List

## wait

### Syntax

    #include <sys/wait.h>

    pid_t pid = wait(int *status);

### Description

This function causes its caller to delay its execution until a signal is received or one of its child processes terminates. If any child has terminated, return is immediate, returning the process ID and its exit status, if that's available. If no children processes were called since the last call, then -1 is returned and `errno` is set.

### Return Value

If successful, this function returns the exit status of the child. If there is an error, these functions return -1 and set `errno` to indicate the error type.

### Bugs

Currently, this function always fails.

### Portability

not ANSI, POSIX

Node:waitpid, Next:wcstombs, Previous:wait, Up:Alphabetical List

## waitpid

### Syntax

    #include <sys/wait.h>

    pid_t pid = waitpid((pid_t pid, int *status, int options);

### Description

Currently, this function always fails. A -1 is returned and `errno` is set to indicate there are no children.

### Return Value

If successful, this function returns the exit status of the child. If there is an error, these functions return -1 and set `errno` to indicate the error type.

### Bugs

Currently, this function always fails.

### Portability

not ANSI, POSIX

Node:wcstombs, Next:wctomb, Previous:waitpid, Up:Alphabetical List

## wcstombs

### Syntax

    #include <stdlib.h>

    size_t wcstombs(char *s, const wchar_t *wcs, size_t n);

### Description

Converts a wide character string to a multibyte string. At most n characters are stored.

### Return Value

The number of characters stored.

### Portability

ANSI, POSIX

### Example

    int len = wcstombs(buf, wstring, sizeof(buf));

Node:wctomb, Next:wherex, Previous:wcstombs, Up:Alphabetical List

## wctomb

### Syntax

    #include <stdlib.h>

    int wctomb(char *s, wchar_t wchar);

### Description

Convert a wide character to a multibyte character. The string s must be at least `MB_LEN_MAX` bytes long.

### Return Value

The number of characters stored.

### Portability

ANSI, POSIX

### Example

    char s[MB_LEN_MAX];
    int mlen = wctomb(s, wc);

Node:wherex, Next:wherey, Previous:wctomb, Up:Alphabetical List

## wherex

### Syntax

    #include <conio.h>

    int wherex(void);

### Return Value

The column the cursor is on. The leftmost column is 1.

### Portability

not ANSI, not POSIX

Node:wherey, Next:wild, Previous:wherex, Up:Alphabetical List

## wherey

### Syntax

    #include <conio.h>

    int     wherey(void);

### Return Value

The row the cursor is on. The topmost row is 1.

### Portability

not ANSI, not POSIX

Node:wild, Next:window, Previous:wherey, Up:Alphabetical List

## wild

### Syntax

    #include <debug/wild.h>

    int wild (char *pattern, char *string);

### Description

This function matches a string pointed to by string against a pattern pointed to by pattern. pattern may include wildcard characters `?` and `*`, meaning, respectively, any single character and any string of characters. The function returns non-zero if the string matches the pattern, zero otherwise.

This functions is meant to be used for simple matching of patterns, such as if a debugger needs to allow specification of symbols using wildcards.

### Return Value

The function returns non-zero if the string matches the pattern, zero otherwise.

### Portability

not ANSI, not POSIX

Node:window, Next:write, Previous:wild, Up:Alphabetical List

## window

### Syntax

    #include <conio.h>

    void    window(int _left, int _top, int _right, int _bottom);

### Description

Specifies the window on the screen to be used for future output requests. The upper left corner of the physical screen is (1,1).

### Portability

not ANSI, not POSIX

Node:write, Next:_write, Previous:window, Up:Alphabetical List

## write

### Syntax

    #include <unistd.h>

    int write(int file, const void *buffer, size_t count);

### Description

This function writes count bytes from buffer to file. It returns the number of bytes actually written. It will return zero or a number less than count if the disk is full, and may return less than count even under valid conditions.

Note that if file is a text file, `write` may write more bytes than it reports.

If count is zero, the function does nothing and returns zero. Use `_write` if you want to actually ask dos to write zero bytes.

The precise behavior of `write` when the target filesystem is full are somewhat troublesome, because DOS doesn't fail the underlying system call. If your application needs to rely on `errno` being set to `ENOSPC` in such cases, you need to invoke `write` as shown in the example below. In a nutshell, the trick is to call `write` one more time after it returns a value smaller than the count parameter; then it will always set `errno` if the disk is full.

### Return Value

The number of bytes written, zero at EOF, or -1 on error.

### Portability

not ANSI, POSIX

### Example

This example shows how to call `write` in a way which ensures that `errno` will be set to `ENOSPC` if the target filesystem is or becomes full:

      char *buf_ptr;    /* the buffer to write */
      size_t buf_len;   /* the number of bytes to write */
      int desc;         /* the file descriptor to write to */

      while (buf_len > 0)
      {
        int written = write (desc, buf_ptr, buf_len);
        if (written <= 0)
          break;

        buf_ptr += written;
        buf_len -= written;
      }

Node:_write, Next:write_child, Previous:write, Up:Alphabetical List

## _write

### Syntax

    #include <io.h>

    ssize_t _write(int fildes, void *buf, size_t nbyte);

### Description

This is a direct connection to the MS-DOS write function call, int 0x21, %ah = 0x40. No conversion is done on the data; it is written as raw binary data. This function can be hooked by the File-system extensions, see File System Extensions. If you don't want this, you should use `_dos_write` instead, see _dos_write.

### Return Value

The number of bytes written, or -1 (and `errno` set) in case of failure.

Note that DOS doesn't return an error indication when the target disk is full; therefore if the disk fills up while the data is written, `_write` does not return -1, it returns the number of bytes it succeeded to write. If you need to detect the disk full condition reliably, call `_write` again to try to write the rest of the data. This will cause DOS to return zero as the number of written bytes, and then `_write` will return -1 and set `errno` to `ENOSPC`. The example below shows one way of doing this.

### Portability

not ANSI, not POSIX

### Example

This example shows how to call `_write` in a way which ensures that `errno` will be set to `ENOSPC` if the target filesystem is or becomes full:

      char *buf_ptr;    /* the buffer to write */
      size_t buf_len;   /* the number of bytes to write */
      int desc;         /* the file descriptor to write to */

      while (buf_len > 0)
      {
        int written = _write (desc, buf_ptr, buf_len);
        if (written <= 0)
          break;

        buf_ptr += written;
        buf_len -= written;
      }

Node:write_child, Next:write_sel_addr, Previous:_write, Up:Alphabetical List

## write_child

### Syntax

    #include <debug/dbgcom.h>

    void write_child (unsigned child_addr, void *buf, unsigned len);

### Description

This function transfers len bytes from the buffer pointed to by buf in the debugger's data segment to the memory of the debugged process starting at the address child_addr. It is used primarily to insert a breakpoint instruction into the debugged process (to trigger a trap when the debuggee's code gets to that point). The companion function `read_child` (see read_child) is usually called before `write_child` to save the original code overwritten by the breakpoint instruction.

### Return Value

The function return zero if it has successfully transferred the data, non-zero otherwise (e.g., if the address in child_addr is outside the limits of the debuggee's code segment.

### Portability

not ANSI, not POSIX

Node:write_sel_addr, Next:xfree, Previous:write_child, Up:Alphabetical List

## write_sel_addr

### Syntax

    #include <debug/dbgcom.h>

    void write_sel_addr (unsigned sel, unsigned offset, void *buf, unsigned len);

### Description

This function transfers len bytes from the buffer pointed to by buf in the data segment whose selector is sel, at offset offset. The companion function `read_sel_addr` (see read_sel_addr) is usually called before `write_sel_addr` to save the original contents, if needed.

### Return Value

The function return zero if it has successfully transferred the data, non-zero otherwise (e.g., if the address in offset is outside the limits of the sels segment).

### Portability

not ANSI, not POSIX

Node:xfree, Next:xmalloc, Previous:write_sel_addr, Up:Alphabetical List

## xfree

### Syntax

    #include <stdlib.h>

    void xfree(void *ptr);

### Description

Frees memory allocated by `xmalloc` (see xmalloc). This function guarantees that a NULL pointer is handled gracefully.

Note that, currently, the header `stdlib.h` does not declare a prototype for `xfree`, because many programs declare its prototype in different and conflicting ways. If you use `xfree` in your own code, you might need to provide your own prototype explicitly.

### Portability

not ANSI, not POSIX

### Example

    void *f = xmalloc(100);
    xfree(f);

Node:xmalloc, Next:xrealloc, Previous:xfree, Up:Alphabetical List

## xmalloc

### Syntax

    #include <stdlib.h>

    void *xmalloc(size_t size);

### Description

This function is just like `malloc` (see malloc), except that if there is no more memory, it prints an error message and exits.

Note that, currently, the header `stdlib.h` does not declare a prototype for `xmalloc`, because many programs declare its prototype in different and conflicting ways. If you use `xmalloc` in your own code, you might need to provide your own prototype explicitly.

### Return Value

A pointer to the newly allocated memory.

### Portability

not ANSI, not POSIX

### Example

    char *f = xmalloc(100);

Node:xrealloc, Previous:xmalloc, Up:Alphabetical List

## xrealloc

### Syntax

    #include <stdlib.h>

    void *xrealloc(void *ptr, size_t size);

### Description

This function is just like `realloc` (see realloc), except that if there is no more memory, it prints an error message and exits. It can also properly handle ptr being `NULL`.

Note that, currently, the header `stdlib.h` does not declare a prototype for `xrealloc`, because many programs declare its prototype in different and conflicting ways. If you use `xrealloc` in your own code, you might need to provide your own prototype explicitly.

### Return Value

A pointer to a possibly new block.

### Portability

not ANSI, not POSIX

### Example

    char *buf;
    buf = (char *)xrealloc(buf, new_size);

Node:Unimplemented, Next:Master Index, Previous:Alphabetical List, Up:Top

# Unimplemented Functions

The DJGPP standard C library is ANSI- and POSIX-compliant, and provides many additional functions for compatibility with Unix/Linux systems. However, some of the functions needed for this compatibility are very hard or impossible to implement using DOS facilities.

Therefore, a small number of library functions are really just stubs: they are provided because POSIX requires them to be present in a compliant library, or because they are widely available on Unix systems, but they either always fail, or handle only the trivial cases and fail for all the others. An example of the former behavior is the function `fork`: it always returns a failure indication; an example of the latter behavior is the function `mknode`: it handles the cases of regular files and existing character devices, but fails for all other file types.

This chapter lists all such functions. This list is here for the benefit of programmers who write portable programs or port Unix packages to DJGPP.

Each function below is labeled as either "always fails" or "trivial", depending on which of the two classes described above it belongs to. An additional class, labeled "no-op", includes functions which pretend to succeed, but have no real effect, since the underlying functionality is either always available or always ignored.

- addmntent: Always fails.
- cfgetispeed: No-op.
- cfgetospeed: No-op.
- cfsetispeed: No-op.
- cfsetospeed: No-op.
- chown: Trivial.
- fcntl: Always fails for all operations except `F_DUPFD` and `F_GETFD`.
- fork: Always fails.
- getgrgid: Trivial.
- getgrnam: Trivial.
- getgroups: Trivial.
- getpwnam: Trivial.
- getpwuid: Trivial.
- mkfifo: Always fails.
- mknod: Trivial.
- nice: No-op.
- pipe: Always fails.
- setgid: Trivial.
- setpgid: Trivial.
- setsid: Trivial.
- setuid: Trivial.
- tcdrain: No-op.
- tcsendbreak: No-op.
- tcsetpgrp: Trivial.
- umask: Trivial.
- vfork: Always fails.
- wait: Always fails.
- waitpid: Always fails.

Node:Master Index, Previous:Unimplemented, Up:Top

See Alphabetical List.

# Table of Contents

- Introduction
- Functional Categories
  - bios functions
  - conio functions
  - cpu functions
  - ctype functions
  - debugging functions
  - dos functions
  - dpmi functions
  - environment functions
  - file system functions
  - go32 functions
  - io functions
  - locale functions
  - math functions
  - memory functions
  - misc functions
  - mono functions
  - posix functions
  - process functions
  - random number functions
  - shell functions
  - signal functions
  - sound functions
  - startup functions
  - stdio functions
  - string functions
  - termios functions
  - time functions
  - unix functions
- Alphabetical List
  - _8087
  - abort
  - abs
  - access
  - acos
  - acosh
  - addmntent
  - alarm
  - alloca
  - asctime
  - asin
  - asinh
  - assert
  - atan
  - atan2
  - atanh
  - atexit
  - atof
  - atoi
  - atol
  - _atold
  - basename
  - bcmp
  - bcopy
  - bdos
  - bdosptr
  - _bios_disk
  - _bios_equiplist
  - _bios_keybrd
  - _bios_memsize
  - _bios_printer
  - _bios_serialcom
  - _bios_timeofday
  - bioscom
  - biosdisk
  - biosequip
  - bioskey
  - biosmemory
  - biosprint
  - biostime
  - blinkvideo
  - brk
  - bsearch
  - bzero
  - calloc
  - cbrt
  - ceil
  - cfgetispeed
  - cfgetospeed
  - cfmakeraw
  - cfree
  - cfsetispeed
  - cfsetospeed
  - cfsetspeed
  - cgets
  - chdir
  - _check_v2_prog
  - chmod
  - _chmod
  - chown
  - chsize
  - cleanup_client
  - _clear87
  - clearerr
  - clock
  - close
  - _close
  - closedir
  - clreol
  - clrscr
  - _conio_kbhit
  - _control87
  - cos
  - cosh
  - cprintf
  - cputs
  - creat
  - _creat
  - _creatnew
  - crlf2nl
  - __crt0_glob_function
  - __crt0_load_environment_file
  - __crt0_setup_arguments
  - _crt0_startup_flags
  - cscanf
  - ctermid
  - ctime
  - delay
  - delline
  - _detect_80387
  - difftime
  - dirname
  - disable
  - div
  - __djgpp_exception_toggle
  - __djgpp_map_physical_memory
  - __djgpp_memory_handle
  - __djgpp_memory_handle_list
  - __djgpp_nearptr_disable
  - __djgpp_nearptr_enable
  - __djgpp_set_ctrl_c
  - __djgpp_set_page_attributes
  - __djgpp_set_sigint_key
  - __djgpp_set_sigquit_key
  - __djgpp_share_flags
  - __djgpp_traceback_exit
  - _djstat_describe_lossage
  - _djstat_fail_bits
  - _djstat_flags
  - _doprnt
  - _dos_close
  - _dos_commit
  - _dos_creat
  - _dos_creatnew
  - _dos_findfirst
  - _dos_findnext
  - _dos_getdate
  - _dos_getdiskfree
  - _dos_getdrive
  - _dos_getfileattr
  - _dos_getftime
  - _dos_gettime
  - _dos_lock
  - _dos_open
  - _dos_read
  - _dos_setdate
  - _dos_setdrive
  - _dos_setfileattr
  - _dos_setftime
  - _dos_settime
  - _dos_unlock
  - _dos_write
  - _doscan
  - _doserrno
  - dosexterr
  - dosmemget
  - dosmemgetb
  - dosmemgetl
  - dosmemgetw
  - dosmemput
  - dosmemputb
  - dosmemputl
  - dosmemputw
  - DPMI Overview
  - DPMI Specification
  - __dpmi_allocate_dos_memory
  - __dpmi_allocate_ldt_descriptors
  - __dpmi_allocate_linear_memory
  - __dpmi_allocate_memory
  - __dpmi_allocate_real_mode_callback
  - __dpmi_allocate_shared_memory
  - __dpmi_allocate_specific_ldt_descriptor
  - __dpmi_clear_debug_watchpoint
  - __dpmi_create_alias_descriptor
  - __dpmi_discard_page_contents
  - __dpmi_free_dos_memory
  - __dpmi_free_ldt_descriptor
  - __dpmi_free_memory
  - __dpmi_free_physical_address_mapping
  - __dpmi_free_real_mode_callback
  - __dpmi_free_serialization_on_shared_memory
  - __dpmi_free_shared_memory
  - __dpmi_get_and_disable_virtual_interrupt_state
  - __dpmi_get_and_enable_virtual_interrupt_state
  - __dpmi_get_and_set_virtual_interrupt_state
  - __dpmi_get_capabilities
  - __dpmi_get_coprocessor_status
  - __dpmi_get_descriptor
  - __dpmi_get_descriptor_access_rights
  - __dpmi_get_extended_exception_handler_vector_pm
  - __dpmi_get_extended_exception_handler_vector_rm
  - __dpmi_get_free_memory_information
  - __dpmi_get_memory_block_size_and_base
  - __dpmi_get_memory_information
  - __dpmi_get_multiple_descriptors
  - __dpmi_get_page_attributes
  - __dpmi_get_page_size
  - __dpmi_get_processor_exception_handler_vector
  - __dpmi_get_protected_mode_interrupt_vector
  - __dpmi_get_raw_mode_switch_addr
  - __dpmi_get_real_mode_interrupt_vector
  - __dpmi_get_segment_base_address
  - __dpmi_get_segment_limit
  - __dpmi_get_selector_increment_value
  - __dpmi_get_state_of_debug_watchpoint
  - __dpmi_get_state_save_restore_addr
  - __dpmi_get_vendor_specific_api_entry_point
  - __dpmi_get_version
  - __dpmi_get_virtual_interrupt_state
  - __dpmi_install_resident_service_provider_callback
  - __dpmi_int
  - __dpmi_lock_linear_region
  - __dpmi_map_conventional_memory_in_memory_block
  - __dpmi_map_device_in_memory_block
  - __dpmi_mark_page_as_demand_paging_candidate
  - __dpmi_mark_real_mode_region_as_pageable
  - __dpmi_physical_address_mapping
  - __dpmi_relock_real_mode_region
  - __dpmi_reset_debug_watchpoint
  - __dpmi_resize_dos_memory
  - __dpmi_resize_linear_memory
  - __dpmi_resize_memory
  - __dpmi_segment_to_descriptor
  - __dpmi_serialize_on_shared_memory
  - __dpmi_set_coprocessor_emulation
  - __dpmi_set_debug_watchpoint
  - __dpmi_set_descriptor
  - __dpmi_set_descriptor_access_rights
  - __dpmi_set_extended_exception_handler_vector_pm
  - __dpmi_set_extended_exception_handler_vector_rm
  - __dpmi_set_multiple_descriptors
  - __dpmi_set_page_attributes
  - __dpmi_set_processor_exception_handler_vector
  - __dpmi_set_protected_mode_interrupt_vector
  - __dpmi_set_real_mode_interrupt_vector
  - __dpmi_set_segment_base_address
  - __dpmi_set_segment_limit
  - __dpmi_simulate_real_mode_interrupt
  - __dpmi_simulate_real_mode_procedure_iret
  - __dpmi_simulate_real_mode_procedure_retf
  - __dpmi_simulate_real_mode_procedure_retf_stack
  - __dpmi_terminate_and_stay_resident
  - __dpmi_unlock_linear_region
  - __dpmi_yield
  - dup
  - dup2
  - _dxe_load
  - ecvt
  - ecvtbuf
  - edi_init
  - enable
  - endgrent
  - endmntent
  - endpwent
  - errno
  - exec*
  - __exit
  - _exit
  - exit
  - exp
  - exp10
  - exp2
  - expm1
  - fabs
  - _far*
  - fclose
  - fcntl
  - fcvt
  - fcvtbuf
  - fdopen
  - feof
  - ferror
  - fflush
  - ffs
  - fgetc
  - fgetgrent
  - fgetpos
  - fgets
  - File System Extensions
  - __file_exists
  - __file_tree_walk
  - filelength
  - fileno
  - findfirst
  - findnext
  - _fixpath
  - floor
  - _flush_disk_cache
  - fmod
  - _fmode
  - fnmatch
  - fnmerge
  - fnsplit
  - fopen
  - fork
  - fpathconf
  - _fpreset
  - fprintf
  - fpurge
  - fputc
  - fputs
  - fread
  - free
  - freopen
  - frexp
  - fscanf
  - fseek
  - fsetpos
  - __FSEXT_add_open_handler
  - __FSEXT_alloc_fd
  - __FSEXT_call_open_handlers
  - __FSEXT_get_data
  - __FSEXT_get_function
  - __FSEXT_set_data
  - __FSEXT_set_function
  - fstat
  - fsync
  - ftell
  - ftime
  - ftruncate
  - ftw
  - _fwalk
  - fwrite
  - gcvt
  - _get_dev_info
  - _get_dos_version
  - _get_volume_info
  - getc
  - getcbrk
  - getch
  - getchar
  - getche
  - getcwd
  - getdate
  - getdfree
  - getdisk
  - getdtablesize
  - getegid
  - getenv
  - geteuid
  - getftime
  - getgid
  - getgrent
  - getgrgid
  - getgrnam
  - getgroups
  - gethostname
  - getitimer
  - getkey
  - getlogin
  - getlongpass
  - getmntent
  - getopt
  - getpagesize
  - getpass
  - getpgrp
  - getpid
  - getpwent
  - getpwnam
  - getpwuid
  - getrlimit
  - getrusage
  - gets
  - gettext
  - gettextinfo
  - gettime
  - gettimeofday
  - getuid
  - getw
  - getwd
  - getxkey
  - glob
  - globfree
  - gmtime
  - _go32_conventional_mem_selector
  - _go32_dpmi_allocate_dos_memory
  - _go32_dpmi_allocate_iret_wrapper
  - _go32_dpmi_allocate_real_mode_callback_iret
  - _go32_dpmi_allocate_real_mode_callback_retf
  - _go32_dpmi_chain_protected_mode_interrupt_vector
  - _go32_dpmi_free_dos_memory
  - _go32_dpmi_free_iret_wrapper
  - _go32_dpmi_free_real_mode_callback
  - _go32_dpmi_get_free_memory_information
  - _go32_dpmi_get_protected_mode_interrupt_vector
  - _go32_dpmi_get_real_mode_interrupt_vector
  - _go32_dpmi_lock_code
  - _go32_dpmi_lock_data
  - _go32_dpmi_remaining_physical_memory
  - _go32_dpmi_remaining_virtual_memory
  - _go32_dpmi_resize_dos_memory
  - _go32_dpmi_set_protected_mode_interrupt_vector
  - _go32_dpmi_set_real_mode_interrupt_vector
  - _go32_dpmi_simulate_fcall
  - _go32_dpmi_simulate_fcall_iret
  - _go32_dpmi_simulate_int
  - _go32_info_block
  - _go32_interrupt_stack_size
  - _go32_my_cs
  - _go32_my_ds
  - _go32_my_ss
  - _go32_rmcb_stack_size
  - _go32_want_ctrl_break
  - _go32_was_ctrl_break_hit
  - gotoxy
  - gppconio_init
  - hasmntopt
  - highvideo
  - htonl
  - htons
  - hypot
  - inb
  - index
  - initstate
  - inp
  - inportb
  - inportl
  - inportsb
  - inportsl
  - inportsw
  - inportw
  - inpw
  - insline
  - insque
  - int386
  - int386x
  - int86
  - int86x
  - intdos
  - intdosx
  - intensevideo
  - _invent_inode
  - ioctl (DOS)
  - ioctl (General description)
  - ioctl (UNIX)
  - _is_executable
  - _is_remote_drive
  - _is_remote_handle
  - isalnum
  - isalpha
  - isascii
  - isatty
  - iscntrl
  - isdigit
  - isgraph
  - islower
  - isprint
  - ispunct
  - isspace
  - isupper
  - isxdigit
  - itoa
  - kbhit
  - kill
  - labs
  - ldexp
  - ldiv
  - _lfn_gen_short_fname
  - _lfn_get_ftime
  - __libc_termios_init
  - libm
  - link
  - llabs
  - lldiv
  - load_npx
  - localeconv
  - localtime
  - lock
  - log
  - log10
  - log1p
  - log2
  - longjmp
  - lowvideo
  - lseek
  - malloc
  - matherr
  - mblen
  - mbstowcs
  - mbtowc
  - memccpy
  - memchr
  - memcmp
  - memcpy
  - memicmp
  - memmove
  - memset
  - mkdir
  - mkfifo
  - mknod
  - mkstemp
  - mktemp
  - mktime
  - modf
  - modfl
  - _mono_clear
  - _mono_printf
  - _mono_putc
  - movedata
  - movedatab
  - movedatal
  - movedataw
  - movetext
  - mprotect
  - _my_cs
  - _my_ds
  - _my_ss
  - nice
  - normvideo
  - nosound
  - ntohl
  - ntohs
  - open
  - _open
  - opendir
  - outb
  - outp
  - outportb
  - outportl
  - outportsb
  - outportsl
  - outportsw
  - outportw
  - outpw
  - pathconf
  - pause
  - pclose
  - perror
  - pipe
  - popen
  - pow
  - pow10
  - pow2
  - powi
  - _preserve_fncase
  - printf
  - psignal
  - _put_path
  - putc
  - putch
  - putchar
  - putenv
  - puts
  - puttext
  - putw
  - qsort
  - raise
  - rand
  - rand48
  - random
  - rawclock
  - read
  - _read
  - read_child
  - read_sel_addr
  - readdir
  - realloc
  - redir_cmdline_delete
  - redir_cmdline_parse
  - redir_debug_init
  - redir_to_child
  - redir_to_debugger
  - regcomp
  - regerror
  - regexec
  - regfree
  - remove
  - remque
  - _rename
  - rename
  - rewind
  - rewinddir
  - rindex
  - rmdir
  - run_child
  - save_npx
  - sbrk
  - scanf
  - Screen Variables
  - ScreenClear
  - ScreenCols
  - ScreenGetChar
  - ScreenGetCursor
  - ScreenMode
  - ScreenPutChar
  - ScreenPutString
  - ScreenRetrieve
  - ScreenRows
  - ScreenSetCursor
  - ScreenUpdate
  - ScreenUpdateLine
  - ScreenVisualBell
  - searchpath
  - seekdir
  - select
  - _set_screen_lines
  - setbuf
  - setbuffer
  - setcbrk
  - _setcursortype
  - setdate
  - setdisk
  - setenv
  - setftime
  - setgid
  - setgrent
  - setitimer
  - setjmp
  - setlinebuf
  - setlocale
  - setmntent
  - setmode
  - setpgid
  - setpwent
  - setrlimit
  - setsid
  - setstate
  - settime
  - settimeofday
  - setuid
  - setvbuf
  - sigaction
  - sigaddset
  - sigdelset
  - sigemptyset
  - sigfillset
  - sigismember
  - siglongjmp
  - signal
  - sigpending
  - sigprocmask
  - sigsetjmp
  - sin
  - sincos
  - sinh
  - sleep
  - sound
  - spawn*
  - sprintf
  - sqrt
  - srand
  - srandom
  - sscanf
  - stackavail
  - stat
  - statfs
  - _status87
  - _stklen
  - stpcpy
  - strcasecmp
  - strcat
  - strchr
  - strcmp
  - strcoll
  - strcpy
  - strcspn
  - strdup
  - strerror
  - strftime
  - stricmp
  - strlen
  - strlwr
  - strncasecmp
  - strncat
  - strncmp
  - strncpy
  - strnicmp
  - strpbrk
  - strrchr
  - strsep
  - strspn
  - strstr
  - strtod
  - strtok
  - strtol
  - _strtold
  - strtoll
  - strtoul
  - strtoull
  - strupr
  - strxfrm
  - swab
  - symlink
  - syms_init
  - syms_line2val
  - syms_listwild
  - syms_module
  - syms_name2val
  - syms_val2line
  - syms_val2name
  - sync
  - sys_errlist
  - sys_nerr
  - sysconf
  - system
  - tan
  - tanh
  - tcdrain
  - tcflow
  - tcflush
  - tcgetattr
  - tcgetpgrp
  - tcsendbreak
  - tcsetattr
  - tcsetpgrp
  - tell
  - telldir
  - tempnam
  - Termios functions
  - textattr
  - textbackground
  - textcolor
  - textmode
  - time
  - times
  - tmpfile
  - tmpnam
  - toascii
  - tolower
  - toupper
  - _truename
  - truncate
  - ttyname
  - tzset
  - tzsetwall
  - uclock
  - umask
  - uname
  - ungetc
  - ungetch
  - unlink
  - unlock
  - _use_lfn
  - usleep
  - utime
  - utimes
  - v2loadimage
  - varargs
  - vfork
  - vfprintf
  - vfscanf
  - vprintf
  - vscanf
  - vsprintf
  - vsscanf
  - wait
  - waitpid
  - wcstombs
  - wctomb
  - wherex
  - wherey
  - wild
  - window
  - write
  - _write
  - write_child
  - write_sel_addr
  - xfree
  - xmalloc
  - xrealloc
- Unimplemented Functions

#### Footnotes

1. Even when long file names are supported, the three time values returned by `stat` might be identical if the file was last written by a program which used legacy DOS functions that don't know about long file names.