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unistd.h

, unistd

- standard symbolic constants and types

Synopsis

#include <unistd.h>

Description

The <unistd.h> header defines the symbolic constants and structures which are notalready defined or declared in some other header. The contents of thisheader 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). Seestandards(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 thesysconf(3C) function to determine which features are supported. This constant is not defined for the SUSv3 environment.

Mandatory Symbolic Constants

The following symbolic constants, if defined in <unistd.h>, have a value of-1, 0, or greater, unless otherwise specified below. If these are undefined,thefpathconf(2),pathconf(2), orsysconf(3C) functions can be used to determine whetherthe option is provided for a particular invocation of the application.

If a symbolic constant is defined with the value -1, the optionis not supported. Headers, data types, and function interfaces required only forthe option need not be supplied. An application that attempts to useanything associated only with the option is considered to be requiring an extension.

If a symbolic constant is defined with a value greater than zero,the option is always supported when the application is executed. All headers,data types, and functions are present and operate as specified.

If a symbolic constant is defined with the value zero, all headers,data types, and functions are present. The application can check at runtimeto see whether the option is supported by callingfpathconf(),pathconf(), orsysconf() with the indicatedname parameter.

Unless explicitly specified otherwise, the behavior of functions associated with an unsupportedoption is unspecified, and an application that uses such functions without firstcheckingfpathconf(),pathconf(), orsysconf() is considered to be requiring an extension.

_POSIX_ADVISORY_INFO: Implementation supports the Advisory Information option.
_POSIX_ASYNCHRONOUS_IO: Implementation supports the Asynchronous Input and Output option.
_POSIX_BARRIERS: Implementation supports the Barriers option.
_POSIX_CLOCK_SELECTION: Implementation supports the Clock Selection option.
_POSIX_CPUTIME: Implementation supports the Process CPU-Time Clocks option.
_POSIX_FSYNC: Implementation supports the File Synchronisation option.
_POSIX_IPV6: Implementation supports the IPv6 option.
_POSIX_JOB_CONTROL: Implementation supports job control.
_POSIX_MAPPED_FILES: Implementation supports the Memory Mapped Files option.
_POSIX_MEMLOCK: Implementation supports the Process Memory Locking option.
_POSIX_MEMLOCK_RANGE: Implementation supports the Range Memory Locking option.
_POSIX_MEMORY_PROTECTION: Implementation supports the Memory Protection option.
_POSIX_MESSAGE_PASSING: Implementation supports the Message Passing option.
_POSIX_MONOTONIC_CLOCK: Implementation supports the Monotonic Clock option.
_POSIX_PRIORITY_SCHEDULING: Implementation supports the Process Scheduling option.
_POSIX_RAW_SOCKETS: Implementation supports the Raw Sockets option.
_POSIX_READER_WRITER_LOCKS: Implementation supports the Read-Write Locks option.
_POSIX_REALTIME_SIGNALS: Implementation supports the Realtime Signals Extension option.
_POSIX_REGEXP: Implementation supports the Regular Expression Handling option.
_POSIX_SAVED_IDS: The exec functions (seeexec(2)) save the effective user and group.
_POSIX_SEMAPHORES: Implementation supports the Semaphores option.
_POSIX_SHARED_MEMORY_OBJECTS: Implementation supports the Shared Memory Objects option.
_POSIX_SHELL: Implementation supports the POSIX shell.
_POSIX_SPAWN: Implementation supports the Spawn option.
_POSIX_SPIN_LOCKS: Implementation supports the Spin Locks option.
_POSIX_SPORADIC_SERVER: Implementation supports the Process Sporadic Server option.
_POSIX_SYNCHRONIZED_IO: Implementation supports the Synchronized Input and Output option.
_POSIX_THREAD_ATTR_STACKADDR: Implementation supports the thread stack address attribute option.
_POSIX_THREAD_ATTR_STACKSIZE: Implementation supports the thread stack size attribute option.
_POSIX_THREAD_CPUTIME: Implementation supports the Thread CPU-Time Clocks option.
_POSIX_THREAD_PROCESS_SHARED: Implementation supports the process-shared synchronization option.
_POSIX_THREAD_SAFE_FUNCTIONS: Implementation supports the thread-safe functions option.
_POSIX_THREAD_SPORADIC_SERVER: Implementation supports the Thread Sporadic Server option.
_POSIX_THREADS: Implementation supports the threads option.
_POSIX_TIMERS: Implementation supports the Timers option.
_POSIX_TIMEOUTS: Implementation supports the Timeouts option.
_POSIX_TRACE: Implementation supports the Trace option.
_POSIX_TRACE_EVENT_FILTER: Implementation supports the Trace Event Filter option.
_POSIX_TRACE_INHERIT: Implementation supports the Trace Inherit option.
_POSIX_TRACE_LOG: Implementation supports the Trace Log option.
_POSIX_TYPED_MEMORY_OBJECTS: Implementation supports the Typed Memory Objects option.
_POSIX_V6_ILP32_OFF32: Implementation provides a C-language compilation environment with 32-bitint,long, andpointer types and anoff_t type using at least 64 bits.
_POSIX_V6_ILP32_OFFBIG: Implementation provides a C-language compilation environment with 32-bitint, long, andpointer types and anoff_t type using at least 64 bits.
_POSIX_V6_LP64_OFF64: Implementation provides a C-language compilation environment with 32-bitint and 64-bitlong,pointer, andoff_t types.
_POSIX_V6_LPBIG_OFFBIG: Implementation provides a C-language compilation environment with anint type using at least 32 bits andlong,pointer, andoff_t types using at least 64 bits.
_POSIX_XOPEN_STREAMS: Implementation supports the XSI STREAMS Option Group.
_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 thelocaledef(1) utility.
_POSIX2_PBS: Implementation supports the Batch Environment Services and Utilities option.
_POSIX2_PBS_ACCOUNTING: Implementation supports the Batch Accounting option.
_POSIX2_PBS_CHECKPOINT: Implementation supports the Batch Checkpoint/Restart option.
_POSIX2_PBS_LOCATE: Implementation supports the Locate Batch Job Request option.
_POSIX2_PBS_MESSAGE: Implementation supports the Batch Job Message Request option.
_POSIX2_PBS_TRACK: Implementation supports the Track Batch Job Request option.
_POSIX2_SW_DEV: Implementation supports the Software Development Utilities option.
_POSIX2_UPE: Implementation supports the User Portability Utilities option.
_XBS5_ILP32_OFF32: Implementation provides a C-language compilation environment with 32-bitint,long,pointer andoff_t types.
_XBS5_ILP32_OFFBIG: Implementation provides a C-language compilation environment with 32-bitint,long andpointer types and anoff_t type using at least 64 bits.
_XBS5_LP64_OFF64: Implementation provides a C-language compilation environment with 32-bitint and 64-bitlong,pointer andoff_t types.
_XBS5_LPBIG_OFFBIG: Implementation provides a C-language compilation environment with anint type using at least 32 bits andlong,pointer andoff_t types using at least 64 bits.
_XOPEN_ENH_I18N: Implementation supports the Issue 4, Version 2 Enhanced Internationalization Feature Group.
_XOPEN_LEGACY: Implementation supports the Legacy Feature Group.
_XOPEN_REALTIME: Implementation supports the X/Open Realtime Feature Group.
_XOPEN_SHM: Implementation supports the Issue 4, Version 2 Shared Memory Feature Group.
_XOPEN_UNIX: X/Open CAE Specification, January 1997, System Interfaces and Headers, Issue 5 (ISBN: 1-85912-181-0, C606).
_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).

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 isapplied.

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

All of the following constants, whether defined in<unistd.h> or not, canbe queried with respect to a specific file using thepathconf() orfpathconf() functions.

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

Constants for Functions

The following constant is defined:

NULL: Null pointer.

The following symbolic constants are defined for theaccess(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 constantsF_OK,R_OK,W_OK, andX_OK, and the expressionsR_OK | W_OK,R_OK | X_OK,andR_OK | W_OK | X_OK all have distinct values.

The following symbolic constants are defined for thelockf(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 thelseek(2) andfcntl(2)functions (they have distinct values):

SEEK_SET: Set file offset tooffset.
SEEK_CUR: Set file offset to current plusoffset.
SEEK_END: Set file offset to EOF plusoffset.

The following symbolic constants are defined for theconfstr(3C) function for bothSPARC 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_POSIX_V6_ILP32_OFF32_CFLAGS`
`_CS_POSIX_V6_ILP32_OFF32_LDFLAGS`	`_CS_POSIX_V6_ILP32_OFF32_LIBS`
`_CS_POSIX_V6_ILP32_OFF32_LINTFLAGS`	`_CS_POSIX_V6_ILP32_OFFBIG_CFLAGS`
`_CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS`	`_CS_POSIX_V6_ILP32_OFFBIG_LIBS`
`_CS_POSIX_V6_ILP32_OFFBIG_LINTFLAGS`	`_CS_POSIX_V6_WIDTH_RESTRICTED_ENV`
`_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 theconfstr() function for SPARConly:

`_CS_POSIX_V6_LP64_OFF64_CFLAGS`	`_CS_POSIX_V6_LP64_OFF64_LDFLAGS`
`_CS_POSIX_V6_LP64_OFF64_LIBS`	`_CS_POSIX_V6_LP64_OFF64_LINTFLAGS`
`_CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS`	`_CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS`
`_CS_POSIX_V6_LPBIG_OFFBIG_LIBS`	`_CS_POSIX_V6_LPBIG_OFFBIG_LINTFLAGS`
`_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 thesysconf(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_PBS`	`_SC_2_PBS_ACCOUNTING`
`_SC_2_PBS_CHECKPOINT`	`_SC_2_PBS_LOCATE`
`_SC_2_PBS_MESSAGE`	`_SC_2_PBS_TRACK`
`_SC_2_SW_DEV`	`_SC_2_UPE`
`_SC_2_VERSION`	`_SC_ADVISORY_INFO`
`_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_BARRIERS`
`_SC_BC_BASE_MAX`	`_SC_BC_DIM_MAX`
`_SC_BC_SCALE_MAX`	`_SC_BC_STRING_MAX`
`_SC_CHILD_MAX`	`_SC_CLK_TCK`
`_SC_CLOCK_SELECTION`	`_SC_COLL_WEIGHTS_MAX`
`_SC_CPUTIME`	`_SC_DELAYTIMER_MAX`
`_SC_EXPR_NEST_MAX`	`_SC_FSYNC`
`_SC_GETGR_R_SIZE_MAX`	`_SC_GETPW_R_SIZE_MAX`
`_SC_HOST_NAME_MAX`	`_SC_IOV_MAX`
`_SC_IPV6`	`_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_MONOTONIC_CLOCK`	`_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_RAW_SOCKETS`
`_SC_READER_WRITER_LOCKS`	`_SC_REALTIME_SIGNALS`
`_SC_REGEXP`	`_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_SHELL`	`_SC_SIGQUEUE_MAX`
`_SC_SPAWN`	`_SC_SPIN_LOCKS`
`_SC_SPORADIC_SERVER`	`_SC_SS_REPL_MAX`
`_SC_STREAM_MAX`	`_SC_SYMLOOP_MAX`
`_SC_SYNCHRONIZED_IO`	`_SC_THREAD_ATTR_STACKADDR`
`_SC_THREAD_ATTR_STACKSIZE`	`_SC_THREAD_CPUTIME`
`_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_THREAD_SPORADIC_SERVER`	`_SC_THREADS`
`_SC_THREAD_SAFE_FUNCTIONS`	`_SC_THREAD_STACK_MIN`
`_SC_THREAD_THREADS_MAX`	`_SC_TIMEOUTS`
`_SC_TIMER_MAX`	`_SC_TIMERS`
`_SC_TRACE`	`_SC_TRACE_EVENT_FILTER`
`_SC_TRACE_EVENT_NAME_MAX`	`_SC_TRACE_INHERIT`
`_SC_TRACE_LOG`	`_SC_TRACE_NAME_MAX`
`_SC_TRACE_SYS_MAX`	`_SC_TRACE_USER_EVENT_MAX`
`_SC_TTY_NAME_MAX`	`_SC_TYPED_MEMORY_OBJECTS`
`_SC_TZNAME_MAX`	`_SC_V6_ILP32_OFF32`
`_SC_V6_ILP32_OFFBIG`	`_SC_V6_LP64_OFF64`
`_SC_V6_LPBIG_OFFBIG`	`_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_STREAMS`
`_SC_XOPEN_UNIX`	`_SC_XOPEN_VERSION`
`_SC_XOPEN_XCU_VERSION`

The constants_SC_PAGESIZE and_SC_PAGE_SIZE can be defined to have the samevalue.

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

`_PC_2_SYMLINKS`	`_PC_ALLOC_SIZE_MIN`
`_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_REC_INCR_XFER_SIZE`
`_PC_REC_MAX_XFER_SIZE`	`_PC_REC_MIN_XFER_SIZE`
`_PC_REC_XFER_ALIGN`	`_PC_SYMLINK_MAX`
`_PC_SYNC_IO`	`_PC_TIMESTAMP_RESOLUTION`
`_PC_VDISABLE`	`_PC_XATTR_ENABLED`
`_PC_XATTR_EXISTS`

The following symbolic constants are defined for file streams:

STDIN_FILENO: File number (0) ofstdin.
STDOUT_FILENO: File number (1) ofstout.
STDERR_FILENO: File number (2) ofstderr.

The following pathnames are defined:

GF_PATH: Pathname of the group file.
PF_PATH: Pathname of the passwd file.

Attributes

Seeattributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Committed
Standard	See`standards`(5).

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