unistd.h.html

unix 下的C开发手册,还用详细的例程。

Implementation supports the Range Memory Locking option.

<dt>_POSIX_MESSAGE_PASSING<dd>

Implementation supports the Message Passing option.

<dt>_POSIX_PRIORITY_SCHEDULING<dd>

Implementation supports the Process Scheduling option.

<dt>_POSIX_REALTIME_SIGNALS<dd>

Implementation supports the Realtime Signals Extension option.

<dt>_POSIX_SEMAPHORES<dd>

Implementation supports the Semaphores option.

<dt>_POSIX_SHARED_MEMORY_OBJECTS<dd>

Implementation supports the Shared Memory Objects option.

<dt>_POSIX_SYNCHRONIZED_IO<dd>

Implementation supports the Synchronised Input and Output option.

<dt>_POSIX_TIMERS<dd>

Implementation supports the Timers option.

</dl>
<p>
The following symbolic constants are always defined to unspecified
values to indicate that the functionality is always present on
XSI-conformant systems.
<dl compact>

<dt>_POSIX_FSYNC<dd>

Implementation supports the File Synchronisation option.

<dt>_POSIX_MAPPED_FILES<dd>

Implementation supports the Memory Mapped Files option.

<dt>_POSIX_MEMORY_PROTECTION<dd>

Implementation supports the Memory Protection option.

</dl>
<p>
The following symbolic constant will be defined if the option is
supported; otherwise, it will be undefined:
<dl compact>

<dt>_POSIX_PRIORITIZED_IO<dd>

Implementation supports the Prioritized Input and Output option.

</dl>
<p>
If _XOPEN_REALTIME_THREADS is defined to have a value other than
-1, then the following symbolic constants will be defined to an
unspecified value to indicate that the features are supported:
<dl compact>

<dt>_POSIX_THREAD_PRIORITY_SCHEDULING<dd>

The implementation supports the thread execution scheduling option.

<dt>_POSIX_THREAD_PRIO_INHERIT<dd>

The implementation supports the priority inheritance option.

<dt>_POSIX_THREAD_PRIO_PROTECT<dd>

The implementation supports the priority protection option.

</dl>
<h5><a name = "tag_000_010_276_004">&nbsp;</a>Execution-time Symbolic Constants</h5>
<p>
If any of the following constants are not defined in the header
<i>&lt;unistd.h&gt;</i>,
the value varies depending on the file to which it is applied.
<p>
If any of the following constants are defined to have value -1
in the header
<i>&lt;unistd.h&gt;</i>,
the implementation will not provide the option on any file;
if any are defined to have a value other than -1 in the header
<i>&lt;unistd.h&gt;</i>,
the implementation will provide the option on all applicable files.
<p>
All of the following constants, whether defined in
<i>&lt;unistd.h&gt;</i>
or not, may be queried with respect to a specific file using the
<i><a href="pathconf.html">pathconf()</a></i>
or
<i><a href="fpathconf.html">fpathconf()</a></i>
functions.
<dl compact>

<dt>_POSIX_ASYNC_IO<dd>

Asynchronous input or output operations may be performed for the
associated file.

<dt>_POSIX_PRIO_IO<dd>

Prioritized input or output operations may be performed for the
associated file.

<dt>_POSIX_SYNC_IO<dd>

Synchronised input or output operations may be performed for the
associated file.

</dl>
<h5><a name = "tag_000_010_276_005">&nbsp;</a>Constants for Functions</h5>
The following symbolic constant is defined:
<dl compact>

<dt>NULL<dd>
Null pointer

</dl>
<p>
The following symbolic constants are defined for the
<i><a href="access.html">access()</a></i>
function:
<dl compact>

<dt>R_OK<dd>
Test for read permission.

<dt>W_OK<dd>
Test for write permission.

<dt>X_OK<dd>
Test for execute (search) permission.

<dt>F_OK<dd>
Test for existence of file.

</dl>
<p>
The constants F_OK, R_OK, W_OK and X_OK and the expressions
<i>R_OK|W_OK</i>,
<i>R_OK|X_OK</i>
and
<i>R_OK|W_OK|X_OK</i>
all have distinct values.
<p>
<p>
The following symbolic constants are defined for the
<i><a href="confstr.html">confstr()</a></i>
function:
<dl compact>

<dt>_CS_PATH<dd>

If the ISO POSIX-2 standard is supported, this is the value for the
environment variable that finds all standard utilities.  Otherwise
the meaning of this value is unspecified.

<dt>_CS_XBS5_ILP32_OFF32_CFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_ILP32_OFF32) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of initial options to be given to the
<i>cc</i> and <i>c89</i> utilities to build an application using a
programming model with 32-bit int, long, pointer, and
off_t types.

<dt>_CS_XBS5_ILP32_OFF32_LDFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_ILP32_OFF32) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of final options to be given to the <i>cc</i>
and <i>c89</i> utilities to build an application using a
programming model with 32-bit int, long, pointer, and
off_t types.

<dt>_CS_XBS5_ILP32_OFF32_LIBS<dd>

If <i>sysconf</i>(_SC_XBS5_ILP32_OFF32) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of libraries to be given to the <i>cc</i> and
<i>c89</i> utilities to build an application using a
programming model with 32-bit int, long, pointer, and
off_t types.

<dt>_CS_XBS5_ILP32_OFF32_LINTFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_ILP32_OFF32) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of options to be given to the <i>lint</i>
utility to check application source using a programming
model with 32-bit int, long, pointer, and off_t types.

<dt>_CS_XBS5_ILP32_OFFBIG_CFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_ILP32_OFFBIG) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of initial options to be given to the
<i>cc</i> and <i>c89</i> utilities to build an application using a
programming model with 32-bit int, long, and pointer
types, and an off_t type using at least 64 bits.

<dt>_CS_XBS5_ILP32_OFFBIG_LDFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_ILP32_OFFBIG) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of final options to be given to the 
<i>cc</i> and <i>c89</i> utilities to build an application using a
programming model with 32-bit int, long, and pointer
types, and an off_t type using at least 64 bits.

<dt>_CS_XBS5_ILP32_OFFBIG_LIBS<dd>

If <i>sysconf</i>(_SC_XBS5_ILP32_OFFBIG) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of libraries to be given to the <i>cc</i> and
<i>c89</i> utilities to build an application using a
programming model with 32-bit int, long, and pointer
types, and an off_t type using at least 64 bits.

<dt>_CS_XBS5_ILP32_OFFBIG_LINTFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_ILP32_OFFBIG) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of options to be given to the <i>lint</i>
utility to check an application using a programming
model with 32-bit int, long, and pointer types, and an
off_t type using at least 64 bits.

<dt>_CS_XBS5_LP64_OFF64_CFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_LP64_OFF64) returns -1, the meaning
of this value is unspecified.  Otherwise, this value is
the set of initial options to be given to the <i>cc</i> and
<i>c89</i> utilities to build an application using a
programming model with 64-bit int, long, pointer, and
off_t types.

<dt>_CS_XBS5_LP64_OFF64_LDFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_LP64_OFF64) returns -1, the meaning
of this value is unspecified.  Otherwise, this value is
the set of final options to be given to the <i>cc</i> and <i>c89</i>
utilities to build an application using a programming
model with 64-bit int, long, pointer, and off_t types.

<dt>_CS_XBS5_LP64_OFF64_LIBS<dd>

If <i>sysconf</i>(_SC_XBS5_LP64_OFF64) returns -1, the meaning
of this value is unspecified.  Otherwise, this value is
the set of libraries to be given to the <i>cc</i> and <i>c89</i>
utilities to build an application using a programming
model with 64-bit int, long, pointer, and off_t types.

<dt>_CS_XBS5_LP64_OFF64_LINTFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_LP64_OFF64) returns -1, the meaning
of this value is unspecified.  Otherwise, this value is
the set of options to be given to the <i>lint</i> utility to
check application source using a programming model with
64-bit int, long, pointer, and off_t types.

<dt>_CS_XBS5_LPBIG_OFFBIG_CFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_LPBIG_OFFBIG) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of initial options to be given to the
<i>cc</i> and <i>c89</i> utilities to build an application using a
programming model with an int type using at least 32
bits and long, pointer, and off_t types using at least
64 bits.

<dt>_CS_XBS5_LPBIG_OFFBIG_LDFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_LPBIG_OFFBIG) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of final options to be given to the <i>cc</i>
and <i>c89</i> utilities to build an application using a
programming model with an int type using at least 32
bits and long, pointer, and off_t types using at least
64 bits.

<dt>_CS_XBS5_LPBIG_OFFBIG_LIBS<dd>

If <i>sysconf</i>(_SC_XBS5_LPBIG_OFFBIG) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of libraries to be given to the <i>cc</i> and
<i>c89</i> utilities to build an application using a
programming model with an int type using at least 32
bits and long, pointer, and off_t types using at least
64 bits.

<dt>_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS<dd>

If <i>sysconf</i>(_SC_XBS5_LPBIG_OFFBIG) returns -1, the
meaning of this value is unspecified.  Otherwise, this
value is the set of options to be given to the <i>lint</i>
utility to check application source using a programming
model with an int type using at least 32 bits and long,
pointer, and off_t types using at least 64 bits.

</dl>
<p>
The following symbolic constants are defined for the
<i><a href="lseek.html">lseek()</a></i>
and
<i><a href="fcntl.html">fcntl()</a></i>
functions (they have distinct values):
<dl compact>

<dt>SEEK_SET<dd>
Set file offset to <i>offset</i>.

<dt>SEEK_CUR<dd>
Set file offset to current plus <i>offset</i>.

<dt>SEEK_END<dd>
Set file offset to EOF plus <i>offset</i>.

</dl>
<p>
The following symbolic constants are defined for <i>sysconf</i>():
<p>
<pre>
_SC_2_C_BIND
_SC_2_C_DEV
_SC_2_C_VERSION
_SC_2_FORT_DEV
_SC_2_FORT_RUN
_SC_2_LOCALEDEF
_SC_2_SW_DEV
_SC_2_UPE
_SC_2_VERSION
_SC_ARG_MAX