UNISTD(3) BSD Library Functions Manual UNISTD(3)
unistd -- standard symbolic constants and types
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:
o The implementation-defined NULL pointer constant.
o Types such as size_t, ssize_t, pid_t, and intptr_t.
o Various limits and other symbolic constants described in pathconf(2) and
o 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).
o The symbolic constant _POSIX_VERSION that defines the version of the POSIX stan-
dard to which the implementation conforms.
o 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).
limits(3), stddef(3), stdint(3), stdlib(3), types(3)
The <unistd.h> header conforms to IEEE Std 1003.1-2001 (``POSIX.1'').
BSD August 9, 2011 BSD