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:
- 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).
The <unistd.h>
header conforms
to IEEE Std 1003.1-2001 (“POSIX.1”).