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”).