Updated: 2025/Dec/31

Please read Privacy Policy. It's for your privacy.

UNISTD(3)                  Library Functions Manual                  UNISTD(3)

NAME
     unistd - standard symbolic constants and types

SYNOPSIS
     #include <unistd.h>

DESCRIPTION
     The <unistd.h> header forms the basis of the Portable Operating System
     Interface for Unix (POSIX) API.  It includes definitions for numerous
     functions, symbolic constants, and types.  Among these are:

           ⊕   The implementation-defined NULL pointer constant.

           ⊕   Types such as size_t, ssize_t, pid_t, and intptr_t.

           ⊕   Various limits and other symbolic constants described in
               pathconf(2) and sysconf(3).

           ⊕   Prototypes for several important system calls and library
               routines such as chown(2), dup(2), execl(3), fork(2), pipe(2),
               rmdir(2), setuid(2), and write(2).

           ⊕   The symbolic constant _POSIX_VERSION that defines the version
               of the POSIX standard to which the implementation conforms.

           ⊕   Various other _POSIX -prefixed symbolic constants that indicate
               whether the system implements some optional part of the
               standard.  Examples include such constants as _POSIX_IPV6 for
               inet6(4) functionality and _POSIX_ASYNCHRONOUS_IO for aio(3).

SEE ALSO
     limits(3), stddef(3), stdint(3), stdlib(3), types(3)

STANDARDS
     The <unistd.h> header conforms to IEEE Std 1003.1-2001 ("POSIX.1").

NetBSD 11.99                    August 9, 2011                    NetBSD 11.99