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unistd(5)

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO

NAME

unistd- header for symbolic constants

SYNOPSIS

#include <unistd.h>

DESCRIPTION

The <unistd.h> header defines the symbolic constants and structures which are not already defined or declared in some other header. The contents of this header are shown below.

Version Test Macros

The following symbolic constants are defined (with fixed values):

_POSIX_VERSION: Integer value indicating version of the POSIX standard (C language binding). See standards(5).
_POSIX2_VERSION: Integer value indicating version of the POSIX.2 standard (Commands). _POSIX2_C_VERSION Integer value indicating version of the POSIX.2 standard (C language binding).
_XOPEN_VERSION: Integer value indicating version of the XPG to which system conforms.
_XOPEN_XCU_VERSION: Integer value indicating the version of the XCU specification to which the implementation conforms. If this constant is not defined, use the sysconf(3C) function to determine which features are supported.

Mandatory Symbolic Constants

The following symbolic constants are either undefined or defined with a value other than -1. If a constant is undefined, an application should use the sysconf(3C), pathconf(2), or fpathconf(2) functions to determine which features are present on the system at that time or for the particular pathname in question.

_POSIX_JOB_CONTROL: Implementation supports job control.
_POSIX_SAVED_IDS: The exec functions (see exec(2)) save the effective user and group.
_POSIX_THREADS: The implementation supports the threads option.
_POSIX_THREAD_ATTR_STACKADDR: The implementation supports the thread stack address attribute option.
_POSIX_THREAD_ATTR_STACKSIZE: The implementation supports the thread stack size attribute option.
_POSIX_THREAD_PROCESS_SHARED: The implementation supports the process-shared synchronization option.
_POSIX_THREAD_SAFE_FUNCTIONS: The implementation supports the thread-safe functions option.
_XOPEN_XPG3: X/Open Specification, February 1992, System Interfaces and Headers, Issue 3 (ISBN: 1-872630-37-5, C212); this specification was formerly X/Open Portability Guide, Issue 3, Volume 2, January 1989, XSI System Interface and Headers (ISBN: 0-13-685843-0, XO/XPG/89/003).
_XOPEN_XPG4: X/Open CAE Specification, July 1992, System Interfaces and Headers, Issue 4 (ISBN: 1-872630-47-2, C202).
_XOPEN_UNIX: X/Open CAE Specification, January 1997, System Interfaces and Headers, Issue 5 (ISBN: 1-85912-181-0, C606).

Constants for Options and Feature Groups

The following symbolic constants are defined to have the value -1 if the implementation will never provide the feature, and to have a value other than -1 if the implementation always provides the feature. If these are undefined, the sysconf() function can be used to determine whether the feature is provided for a particular invocation of the application.

_POSIX2_C_BIND: Implementation supports the C Language Binding option.
_POSIX2_C_DEV: Implementation supports the C Language Development Utilities option.
_POSIX2_CHAR_TERM: Implementation supports at least one terminal type.
_POSIX2_LOCALEDEF: Implementation supports the creation of locales by the localedef(1) utility.
_POSIX2_SW_DEV: Implementation supports the Software Development Utilities option.
_POSIX2_UPE: The implementation supports the User Portability Utilities option.
_XOPEN_ENH_I18N: The implementation supports the Issue 4, Version 2 Enhanced Internationalization Feature Group.
_XOPEN_LEGACY: The implementation supports the Legacy Feature Group.
_XOPEN_REALTIME: The implementation supports the X/Open Realtime Feature Group.
_XOPEN_SHM: The implementation supports the Issue 4, Version 2 Shared Memory Feature Group.
_XBS5_ILP32_OFF32: Implementation provides a C-language compilation environment with 32-bit int, long, pointer and off_t types.
_XBS5_ILP32_OFFBIG: Implementation provides a C-language compilation environment with 32-bit int, long and pointer types and an off_t type using at least 64 bits.
_XBS5_LP64_OFF64: Implementation provides a C-language compilation environment with 32-bit int and 64-bit long, pointer and off_t types.
_XBS5_LPBIG_OFFBIG: Implementation provides a C-language compilation environment with an int type using at least 32 bits and long, pointer and off_t types using at least 64 bits.

If _XOPEN_REALTIME is defined to have a value other than -1 then the following symbolic constants will be defined to an unspecified value to indicate that the features are supported.

_POSIX_ASYNCHRONOUS_IO: Implementation supports the Asynchronous Input and Output option.
_POSIX_MEMLOCK: Implementation supports the Process Memory Locking option.
_POSIX_MEMLOCK_RANGE: Implementation supports the Range Memory Locking option.
_POSIX_MESSAGE_PASSING: Implementation supports the Message Passing option.
_POSIX_PRIORITY_SCHEDULING: Implementation supports the Process Scheduling option.
_POSIX_REALTIME_SIGNALS: Implementation supports the Realtime Signals Extension option.
_POSIX_SEMAPHORES: Implementation supports the Semaphores option.
_POSIX_SHARED_MEMORY_OBJECTS: Implementation supports the Shared Memory Objects option.
_POSIX_SYNCHRONIZED_IO: Implementation supports the Synchronized Input and Output option.
_POSIX_TIMERS: Implementation supports the Timers option.

The following symbolic constants are always defined to unspecified values to indicate that the functionality is always present on XSI-conformant systems.

_POSIX_FSYNC: Implementation supports the File Synchronisation option.
_POSIX_MAPPED_FILES: Implementation supports the Memory Mapped Files option.
_POSIX_MEMORY_PROTECTION: Implementation supports the Memory Protection option.

Execution-time Symbolic Constants

If any of the following constants are not defined in the header <unistd.h>, the value varies depending on the file to which it is applied.

If any of the following constants are defined to have value -1 in the header <unistd.h>, the implementation will not provide the option on any file; if any are defined to have a value other than -1 in the header <unistd.h>, the implementation will provide the option on all applicable files.

All of the following constants, whether defined in <unistd.h> or not, may be queried with respect to a specific file using the pathconf() or fpathconf() functions.

_POSIX_ASYNC_IO: Asynchronous input or output operations may be performed for the associated file.
_POSIX_PRIO_IO: Prioritized input or output operations may be performed for the associated file.
_POSIX_SYNC_IO: Synchronized input or output operations may be performed for the associated file.

Constants for Functions

The following constant is defined:

NULL: Null pointer.

The following symbolic constants are defined for the access(2) function:

R_OK: Test for read permission.
W_OK: Test for write permission.
X_OK: Test for execute (search) permission.
F_OK: Test for existence of file. The constants F_OK, R_OK, W_OK, and X_OK, and the expressions R_OK|W_OK, R_OK|X_OK, and R_OK|W_OK|X_OK all have distinct values.

The following symbolic constants are defined for the lockf(3C) function:

F_ULOCK: Unlock a previously locked region.
F_LOCK: Lock a region for exclusive use.
F_TLOCK: Test and lock a region for exclusive use.
F_TEST: Test a region for other processes locks.

The following symbolic constants are defined for the lseek(2) and fcntl(2) functions (they have distinct values):

SEEK_SET: Set file offset to offset.
SEEK_CUR: Set file offset to current plus offset.
SEEK_END: Set file offset to EOF plus offset.

The following symbolic constants are defined for the confstr(3C) function for both SPARC and x86:

`_CS_LFS64_CFLAGS`	`_CS_LFS64_LDFLAGS`
`_CS_LFS64_LIBS`	`_CS_LFS64_LINTFLAGS`
`_CS_LFS_CFLAGS`	`_CS_LFS_LDFLAGS`
`_CS_LFS_LIBS`	`_CS_LFS_LINTFLAGS`
`_CS_PATH`	`_CS_XBS5_ILP32_OFF32_CFLAGS`
`_CS_XBS5_ILP32_OFF32_LDFLAGS`	`_CS_XBS5_ILP32_OFF32_LIBS`
`_CS_XBS5_ILP32_OFF32_LINTFLAGS`	`_CS_XBS5_ILP32_OFFBIG_CFLAGS`
`_CS_XBS5_ILP32_OFFBIG_LDFLAGS`	`_CS_XBS5_ILP32_OFFBIG_LIBS`
`_CS_XBS5_ILP32_OFFBIG_LINTFLAGS`

The followwing symbolic constants are defined for the confstr() function for SPARC only:

`_CS_XBS5_LP64_OFF64_CFLAGS`	`_CS_XBS5_LP64_OFF64_LDFLAGS`
`_CS_XBS5_LP64_OFF64_LIBS`	`_CS_XBS5_LP64_OFF64_LINTFLAGS`
`_CS_XBS5_LPBIG_OFFBIG_CFLAGS`	`_CS_XBS5_LPBIG_OFFBIG_LDFLAGS`
`_CS_XBS5_LPBIG_OFFBIG_LIBS`	`_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS`

The following symbolic constants are defined for the sysconf(3C) function:

`_SC_2_C_BIND`	`_SC_2_C_DEV`
`_SC_2_C_VERSION`	`_SC_2_FORT_DEV`
`_SC_2_FORT_RUN`	`_SC_2_LOCALEDEF`
`_SC_2_SW_DEV`	`_SC_2_UPE`
`_SC_2_VERSION`	`_SC_AIO_LISTIO_MAX`
`_SC_AIO_MAX`	`_SC_AIO_PRIO_DELTA_MAX`
`_SC_ARG_MAX`	`_SC_ASYNCHRONOUS_IO`
`_SC_ATEXIT_MAX`	`_SC_AVPHYS_PAGES`
`_SC_BC_BASE_MAX`	`_SC_BC_DIM_MAX`
`_SC_BC_SCALE_MAX`	`_SC_BC_STRING_MAX`
`_SC_CHILD_MAX`	`_SC_CLK_TCK`
`_SC_COLL_WEIGHTS_MAX`	`_SC_DELAYTIMER_MAX`
`_SC_EXPR_NEST_MAX`	`_SC_FSYNC`
`_SC_GETGR_R_SIZE_MAX`	`_SC_GETPW_R_SIZE_MAX`
`_SC_IOV_MAX`	`_SC_JOB_CONTROL`
`_SC_LINE_MAX`	`_SC_LOGIN_NAME_MAX`
`_SC_LOGNAME_MAX`	`_SC_MAPPED_FILES`
`_SC_MEMLOCK`	`_SC_MEMLOCK_RANGE`
`_SC_MEMORY_PROTECTION`	`_SC_MESSAGE_PASSING`
`_SC_MQ_OPEN_MAX`	`_SC_MQ_PRIO_MAX`
`_SC_NGROUPS_MAX`	`_SC_NPROCESSORS_CONF`
`_SC_NPROCESSORS_ONLN`	`_SC_OPEN_MAX`
`_SC_PAGESIZE`	`_SC_PAGE_SIZE`
`_SC_PASS_MAX`	`_SC_PHYS_PAGES`
`_SC_PRIORITIZED_IO`	`_SC_PRIORITY_SCHEDULING`
`_SC_REALTIME_SIGNALS`	`_SC_RE_DUP_MAX`
`_SC_RTSIG_MAX`	`_SC_SAVED_IDS`
`_SC_SEMAPHORES`	`_SC_SEM_NSEMS_MAX`
`_SC_SEM_VALUE_MAX`	`_SC_SHARED_MEMORY_OBJECTS`
`_SC_SIGQUEUE_MAX`	`_SC_STREAM_MAX`
`_SC_SYNCHRONIZED_IO`	`_SC_THREAD_ATTR_STACKADDR`
`_SC_THREAD_ATTR_STACKSIZE`	`_SC_THREAD_DESTRUCTOR_ITERATIONS`
`_SC_THREAD_KEYS_MAX`	`_SC_THREAD_PRIO_INHERIT`
`_SC_THREAD_PRIO_PROTECT`	`_SC_THREAD_PRIORITY_SCHEDULING`
`_SC_THREAD_PROCESS_SHARED`	`_SC_THREADS`
`_SC_THREAD_SAFE_FUNCTIONS`	`_SC_THREAD_STACK_MIN`
`_SC_THREAD_THREADS_MAX`	`_SC_TIMER_MAX`
`_SC_TIMERS`	`_SC_TTY_NAME_MAX`
`_SC_TZNAME_MAX`	`_SC_VERSION`
`_SC_XBS5_ILP32_OFF32`	`_SC_XBS5_ILP32_OFFBIG`
`_SC_XBS5_LP64_OFF64`	`_SC_XBS5_LPBIG_OFFBIG`
`_SC_XOPEN_CRYPT`	`_SC_XOPEN_ENH_I18N`
`_SC_XOPEN_SHM`	`_SC_XOPEN_UNIX`
`_SC_XOPEN_VERSION`	`_SC_XOPEN_XCU_VERSION`

The two constants _SC_PAGESIZE and _SC_PAGE_SIZE may be defined to have the same value.

The following symbolic constants are defined for the fpathconf(2) function:

`_PC_ASYNC_IO`	`_PC_CHOWN_RESTRICTED`
`_PC_FILESIZEBITS`	`_PC_LINK_MAX`
`_PC_MAX_CANON`	`_PC_MAX_INPUT`
`_PC_NAME_MAX`	`_PC_NO_TRUNC`
`_PC_PATH_MAX`	`_PC_PIPE_BUF`
`_PC_PRIO_IO`	`_PC_SYNC_IO`
`_PC_VDISABLE`

The following symbolic constants are defined for file streams:

STDIN_FILENO: File number (0) of stdin.
STDOUT_FILENO: File number (1) of stout.
STDERR_FILENO: File number (2) of stderr. The following pathnames are defined:
GF_PATH: Pathname of the group file.
PF_PATH: Pathname of the passwd file.