NAME
unistd: unistd.h — standard structures and symbolic constants
DESCRIPTION
The header
<unistd.h>
defines the following structures and symbolic constants:
Symbolic constants 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.
Symbolic constant representing a null pointer:
Symbolic constants for the
lseek()
and
fcntl()
functions (the following constants 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".
Symbolic constants (with fixed values):
- _POSIX_VERSION
Integer value indicating version of
IEEE Std 1003.1
standard implemented.
The current value is 199009L,
indicating the (4-digit) year and (2-digit) month
that the standard was approved by the
IEEE
Standards Board.
However, if any of the symbols
_AES_SOURCE,
_XPG3,
or
_POSIX1_1988
is defined before
<unistd.h>
is included, the value of this symbol will be 198808L.
- _POSIX2_VERSION
Integer value indicating version of
IEEE
Std1003.2
standard implemented.
The current value is 199209L,
indicating the (4-digit) year and (2-digit) month
that the standard was approved by the
IEEE Standards Board.
- _POSIX2_C_VERSION
Integer value indicating version of
IEEE Std 1003.2
C-Language Binding Option implemented.
The current value is 199209L,
indicating the (4-digit) year and (2-digit) month
that the standard was approved by the
IEEE
Standards Board.
- _XOPEN_VERSION
Integer value indicating issue number of the
X/Open Portability Guide implemented.
The current value is 4, indicating Issue 4.
However, if the symbol
_XPG3
is defined before
<unistd.h>
is included, the value of this symbol will be 3.
The following symbolic constants are defined in this header
if the state of the corresponding option or restriction
does not vary after compilation.
If a symbol is absent from this header,
the value or presence of the corresponding option or restriction
should be determined at execution time through
sysconf()
or
pathconf():
- _POSIX_CHOWN_RESTRICTED
The use of
chown()
is restricted to processes that have appropriate privileges.
- _POSIX_JOB_CONTROL
Implementation supports job control (true of all
HP-UX implementations).
- _POSIX_NO_TRUNC
Pathname components longer than
NAME_MAX
generate an error.
- _POSIX_REALTIME_SIGNALS
Implementation supports Realtime Signals Extensions
(true of all HP-UX implementations).
- _POSIX_SAVED_IDS
Effective user and group are saved across an
exec()
call (true of all HP-UX implementations).
- _POSIX_FSYNC
Implementation supports File Synchronization (true of all
HP-UX implementations).
See
open(2).
- _POSIX_SYNCHRONIZED_IO
Implementation supports Synchronized IO (true of all
HP-UX implementations).
See
open(2).
- _POSIX_VDISABLE
Terminal special characters can be disabled using this character (see
termio(7)).
- _POSIX_THREADS
Implementation supports POSIX threads.
- _POSIX2_C_BIND
All POSIX.2 C-language functionality is provided
in the default libraries used by the
c89
C compiler (see
cc(1)).
- _POSIX2_LOCALEDEF
New locales can be defined by using the
localedef
command (see
localedef(1M)).
- _POSIX2_UPE
The system supports
IEEE
Std1003.2a
(POSIX
User Portability Utilities Option).
- _POSIX2_CHAR_TERM
At least one terminal exists that supports all required POSIX.2a commands.
All symbolic constants whose names begin
_CS,
_PC,
and
_SC
(see
confstr(3C),
pathconf(2),
and
sysconf(2))
are defined.
The following symbolic constants for file streams are defined:
- STDIN_FILENO
File number of standard input
(stdin).
- STDOUT_FILENO
File number of standard output
(stdout).
- STDERR_FILENO
File number of standard error
(stderr).
The types
size_t,
ssize_t,
uid_t,
gid_t,
off_t,
and
pid_t
are defined.
Declarations are provided for the following functions:
AUTHOR
unistd
was developed by HP.
SEE ALSO
access(2),
chown(2),
exit(2),
fcntl(2),
kill(2),
lseek(2),
open(2),
pathconf(2),
sysconf(2),
confstr(3C),
limits(5),
stdsyms(5),
termio(7).
STANDARDS CONFORMANCE
<unistd.h>: AES, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, POSIX.2, POSIX.4