unistd.h - standard symbolic constants and types
#include <unistd.h>
The <unistd.h> header defines miscellaneous symbolic constants and types, and declares miscellaneous functions. The contents of this header are shown below.Version Test Macros
The following symbolic constants are defined:
- _POSIX_VERSION
- Integer value indicating version of the ISO POSIX-1 standard (C language binding).
- _POSIX2_VERSION
- Integer value indicating version of the ISO POSIX-2 standard (Commands).
- _POSIX2_C_VERSION
- Integer value indicating version of the ISO POSIX-2 standard (C language binding).
- _XOPEN_VERSION
- Integer value indicating version of the X/Open Portability Guide to which the implementation conforms.
_POSIX_VERSION is defined in the ISO POSIX-1 standard. It changes with each new version of the ISO POSIX-1 standard.
_POSIX2_VERSION is defined to have the value of the ISO POSIX-2 standard's POSIX2_VERSION limit. It changes with each new version of the ISO POSIX-2 standard.
_POSIX2_C_VERSION is defined in the ISO POSIX-2 standard. It changes with each new version of the ISO POSIX-2 standard. When the C language binding option of the ISO POSIX-2 standard and therefore the X/Open POSIX2 C-language Binding Feature Group is not supported, _POSIX2_C_VERSION will be set to -1.
_XOPEN_VERSION is defined as an integer value equal to 500.
_XOPEN_XCU_VERSION is defined as an integer value indicating the version of the XCU specification to which the implementation conforms. If the value is -1, no commands and utilities are provided on the implementation. If the value is greater than or equal to 4, the functionality associated with the following symbols is also supported (see
Mandatory Symbolic Constants andConstants for Options and Feature Groups ):_POSIX2_C_BIND _POSIX2_C_VERSION _POSIX2_CHAR_TERM _POSIX2_LOCALEDEF _POSIX2_UPE _POSIX2_VERSIONIf this constant is not defined use the sysconf() function to determine which features are supported.
Each of the following symbolic constants is defined only if the implementation supports the indicated issue of the X/Open Portability Guide:
- _XOPEN_XPG2
- X/Open Portability Guide, Volume 2, January 1987, XVS System Calls and Libraries (ISBN: 0-444-70175-3).
- _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).
Mandatory Symbolic Constants
Although all implementations conforming to this specification support all of the FIPS features described below, there may be system-dependent or file-system-dependent configuration procedures that can remove or modify any or all of these features. Such configurations should not be made if strict FIPS compliance is required. 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(), pathconf() or fpathconf() functions to determine which features are present on the system at that time or for the particular pathname in question.
- _POSIX_CHOWN_RESTRICTED
- The use of chown() is restricted to a process with appropriate privileges, and to changing the group ID of a file only to the effective group ID of the process or to one of its supplementary group IDs.
- _POSIX_NO_TRUNC
- Pathname components longer than {NAME_MAX} generate an error.
- _POSIX_VDISABLE
- Terminal special characters defined in <termios.h> can be disabled using this character value.
- _POSIX_SAVED_IDS
- Each process has a saved set-user-ID and a saved set-group-ID.
- _POSIX_JOB_CONTROL
- Implementation supports job control.
_POSIX_CHOWN_RESTRICTED, _POSIX_NO_TRUNC and _POSIX_VDISABLE will have values other than -1.
The following symbolic constants are always defined to unspecified values to indicate that this functionality from the POSIX Threads Extension is always present on XSI-conformant systems:
- _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 synchronisation option.
- _POSIX_THREAD_SAFE_FUNCTIONS
- The implementation supports the thread-safe functions option.
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. This will always have a value other than -1.
- _POSIX2_C_DEV
- Implementation supports the C Language Development Utilities option.
- _POSIX2_CHAR_TERM
- Implementation supports at least one terminal type.
- _POSIX2_FORT_DEV
- Implementation supports the FORTRAN Development Utilities option.
- _POSIX2_FORT_RUN
- Implementation supports the FORTRAN Run-time Utilities option.
- _POSIX2_LOCALEDEF
- Implementation supports the creation of locales by the localedef utility.
- _POSIX2_SW_DEV
- Implementation supports the Software Development Utilities option.
- _POSIX2_UPE
- The implementation supports the User Portability Utilities option.
- _XOPEN_CRYPT
- The implementation supports the X/Open Encryption Feature Group.
- _XOPEN_ENH_I18N
- The implementation supports the Issue 4, Version 2 Enhanced Internationalisation Feature Group. This is always set to a value other than -1.
- _XOPEN_LEGACY
- The implementation supports the Legacy Feature Group.
- _XOPEN_REALTIME
- The implementation supports the X/Open Realtime Feature Group.
- _XOPEN_REALTIME_THREADS
- The implementation supports the X/Open Realtime Threads Feature Group.
- _XOPEN_SHM
- The implementation supports the Issue 4, Version 2 Shared Memory Feature Group. This is always set to a value other than -1.
- _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 Synchronised 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.
The following symbolic constant will be defined if the option is supported; otherwise, it will be undefined:
- _POSIX_PRIORITIZED_IO
- Implementation supports the Prioritized Input and Output option.
If _XOPEN_REALTIME_THREADS 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_THREAD_PRIORITY_SCHEDULING
- The implementation supports the thread execution scheduling option.
- _POSIX_THREAD_PRIO_INHERIT
- The implementation supports the priority inheritance option.
- _POSIX_THREAD_PRIO_PROTECT
- The implementation supports the priority 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
- Synchronised input or output operations may be performed for the associated file.
Constants for Functions
The following symbolic constant is defined:
- NULL
- Null pointer
The following symbolic constants are defined for the access() 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 confstr() function:
- _CS_PATH
- If the ISO POSIX-2 standard is supported, this is the value for the environment variable that finds all standard utilities. Otherwise the meaning of this value is unspecified.
- _CS_XBS5_ILP32_OFF32_CFLAGS
- If sysconf(_SC_XBS5_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the cc and c89 utilities to build an application using a programming model with 32-bit int, long, pointer, and off_t types.
- _CS_XBS5_ILP32_OFF32_LDFLAGS
- If sysconf(_SC_XBS5_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the cc and c89 utilities to build an application using a programming model with 32-bit int, long, pointer, and off_t types.
- _CS_XBS5_ILP32_OFF32_LIBS
- If sysconf(_SC_XBS5_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the cc and c89 utilities to build an application using a programming model with 32-bit int, long, pointer, and off_t types.
- _CS_XBS5_ILP32_OFF32_LINTFLAGS
- If sysconf(_SC_XBS5_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of options to be given to the lint utility to check application source using a programming model with 32-bit int, long, pointer, and off_t types.
- _CS_XBS5_ILP32_OFFBIG_CFLAGS
- If sysconf(_SC_XBS5_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the cc and c89 utilities to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.
- _CS_XBS5_ILP32_OFFBIG_LDFLAGS
- If sysconf(_SC_XBS5_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the cc and c89 utilities to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.
- _CS_XBS5_ILP32_OFFBIG_LIBS
- If sysconf(_SC_XBS5_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the cc and c89 utilities to build an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.
- _CS_XBS5_ILP32_OFFBIG_LINTFLAGS
- If sysconf(_SC_XBS5_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of options to be given to the lint utility to check an application using a programming model with 32-bit int, long, and pointer types, and an off_t type using at least 64 bits.
- _CS_XBS5_LP64_OFF64_CFLAGS
- If sysconf(_SC_XBS5_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the cc and c89 utilities to build an application using a programming model with 64-bit int, long, pointer, and off_t types.
- _CS_XBS5_LP64_OFF64_LDFLAGS
- If sysconf(_SC_XBS5_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the cc and c89 utilities to build an application using a programming model with 64-bit int, long, pointer, and off_t types.
- _CS_XBS5_LP64_OFF64_LIBS
- If sysconf(_SC_XBS5_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the cc and c89 utilities to build an application using a programming model with 64-bit int, long, pointer, and off_t types.
- _CS_XBS5_LP64_OFF64_LINTFLAGS
- If sysconf(_SC_XBS5_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of options to be given to the lint utility to check application source using a programming model with 64-bit int, long, pointer, and off_t types.
- _CS_XBS5_LPBIG_OFFBIG_CFLAGS
- If sysconf(_SC_XBS5_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of initial options to be given to the cc and c89 utilities to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
- _CS_XBS5_LPBIG_OFFBIG_LDFLAGS
- If sysconf(_SC_XBS5_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of final options to be given to the cc and c89 utilities to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
- _CS_XBS5_LPBIG_OFFBIG_LIBS
- If sysconf(_SC_XBS5_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of libraries to be given to the cc and c89 utilities to build an application using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
- _CS_XBS5_LPBIG_OFFBIG_LINTFLAGS
- If sysconf(_SC_XBS5_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of options to be given to the lint utility to check application source using a programming model with an int type using at least 32 bits and long, pointer, and off_t types using at least 64 bits.
The following symbolic constants are defined for the lseek() and fcntl() 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 sysconf():
_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_ARG_MAX _SC_AIO_LISTIO_MAX _SC_AIO_MAX _SC_AIO_PRIO_DELTA_MAX _SC_ASYNCHRONOUS_IO _SC_ATEXIT_MAX _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_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_OPEN_MAX _SC_PAGESIZE _SC_PAGE_SIZE _SC_PASS_MAX (LEGACY) _SC_PRIORITIZED_IO _SC_PRIORITY_SCHEDULING _SC_RE_DUP_MAX
_SC_REALTIME_SIGNALS _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_THREADS _SC_THREAD_ATTR_STACKADDR _SC_THREAD_ATTR_STACKSIZE _SC_THREAD_DESTRUCTOR_ITERATIONS _SC_THREAD_KEYS_MAX _SC_THREAD_PRIORITY_SCHEDULING _SC_THREAD_PRIO_INHERIT _SC_THREAD_PRIO_PROTECT _SC_THREAD_PROCESS_SHARED _SC_THREAD_SAFE_FUNCTIONS _SC_THREAD_STACK_MIN _SC_THREAD_THREADS_MAX _SC_TIMERS _SC_TIMER_MAX _SC_TTY_NAME_MAX _SC_TZNAME_MAX _SC_VERSION _SC_XOPEN_VERSION _SC_XOPEN_CRYPT _SC_XOPEN_ENH_I18N _SC_XOPEN_SHM _SC_XOPEN_UNIX _SC_XOPEN_XCU_VERSION _SC_XOPEN_LEGACY _SC_XOPEN_REALTIME _SC_XOPEN_REALTIME_THREADS _SC_XBS5_ILP32_OFF32 _SC_XBS5_ILP32_OFFBIG _SC_XBS5_LP64_OFF64 _SC_XBS5_LPBIG_OFFBIGThe two constants _SC_PAGESIZE and _SC_PAGE_SIZE may be defined to have the same value.
The following symbolic constants are defined as possible values for the function argument to the lockf() function:
- F_LOCK
Lock a section for exclusive use. - F_ULOCK
Unlock locked sections. - F_TEST
Test section for locks by other processes. - F_TLOCK
Test and lock a section for exclusive use. The following symbolic constants are defined for pathconf():
_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_VDISABLEThe following symbolic constants are defined for file streams:
- STDIN_FILENO
- File number of stdin. It is 0.
- STDOUT_FILENO
- File number of stdout. It is 1.
- STDERR_FILENO
- File number of stderr. It is 2.
Type Definitions
The size_t, ssize_t, uid_t, gid_t, off_t and pid_t types are defined as described in <sys/types.h>.The useconds_t type is defined as described in <sys/types.h>.
The intptr_t type is defined as described in <inttypes.h>.
Declarations
The following are declared as functions and may also be defined as macros. Function prototypes must be provided for use with an ISO C compiler.int access(const char *, int); unsigned int alarm(unsigned int); int brk(void *); int chdir(const char *); int chroot(const char *); (LEGACY) int chown(const char *, uid_t, gid_t); int close(int); size_t confstr(int, char *, size_t); char *crypt(const char *, const char *); char *ctermid(char *); char *cuserid(char *s); (LEGACY) int dup(int); int dup2(int, int); void encrypt(char[64], int); int execl(const char *, const char *, ...); int execle(const char *, const char *, ...); int execlp(const char *, const char *, ...); int execv(const char *, char *const []); int execve(const char *, char *const [], char *const []); int execvp(const char *, char *const []); void _exit(int); int fchown(int, uid_t, gid_t); int fchdir(int); int fdatasync(int); pid_t fork(void); long int fpathconf(int, int); int fsync(int); int ftruncate(int, off_t); char *getcwd(char *, size_t); int getdtablesize(void); (LEGACY) gid_t getegid(void); uid_t geteuid(void); gid_t getgid(void); int getgroups(int, gid_t []); long gethostid(void); char *getlogin(void); int getlogin_r(char *, size_t); int getopt(int, char * const [], const char *); int getpagesize(void); (LEGACY) char *getpass(const char *); (LEGACY) pid_t getpgid(pid_t); pid_t getpgrp(void); pid_t getpid(void); pid_t getppid(void); pid_t getsid(pid_t); uid_t getuid(void); char *getwd(char *); int isatty(int); int lchown(const char *, uid_t, gid_t); int link(const char *, const char *); int lockf(int, int, off_t); off_t lseek(int, off_t, int); int nice(int); long int pathconf(const char *, int); int pause(void); int pipe(int [2]); ssize_t pread(int, void *, size_t, off_t); int pthread_atfork(void (*)(void), void (*)(void), void(*)(void)); ssize_t pwrite(int, const void *, size_t, off_t); ssize_t read(int, void *, size_t); int readlink(const char *, char *, size_t); int rmdir(const char *); void *sbrk(intptr_t); int setgid(gid_t); int setpgid(pid_t, pid_t); pid_t setpgrp(void); int setregid(gid_t, gid_t); int setreuid(uid_t, uid_t); pid_t setsid(void); int setuid(uid_t); unsigned int sleep(unsigned int); void swab(const void *, void *, ssize_t); int symlink(const char *, const char *); void sync(void); long int sysconf(int); pid_t tcgetpgrp(int); int tcsetpgrp(int, pid_t); int truncate(const char *, off_t); char *ttyname(int); int ttyname_r(int, char *, size_t); useconds_t ualarm(useconds_t, useconds_t); int unlink(const char *); int usleep(useconds_t); pid_t vfork(void); ssize_t write(int, const void *, size_t);
The following external variables are declared:
extern char *optarg; extern int optind, opterr, optopt;
None.
None.
access(), alarm(), chdir(), chown(), close(), crypt(), ctermid(), dup(), encrypt(), environ(), exec, exit(), fchdir(), fchown(), fcntl(), fork(), fpathconf(), fsync(), ftruncate(), getcwd(), getegid(), geteuid(), getgid(), getgroups(), gethostid(), getlogin(), getpgid(), getpgrp(), getpid(), getppid(), getsid(), getuid(), getwd(), isatty(), lchown(), link(), lockf(), lseek(), nice(), pathconf(), pause(), pipe(), read(), readlink(), rmdir(), setgid(), setpgid(), setpgrp(), setregid(), setreuid(), setsid(), setuid(), sleep(), swab(), symlink(), sync(), sysconf(), tcgetpgrp(), tcsetpgrp(), truncate(), ttyname(), ualarm(), unlink(), usleep(), vfork(), write(), <limits.h>, <sys/types.h>, <termios.h>,.