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<title>&lt;unistd.h&gt;</title>
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<basefont size="3"> <a name="&lt;unistd.h&gt;"></a> <a name="tag_13_80"></a><!-- &lt;unistd.h&gt; -->
<!--header start-->
<center><font size="2">The Open Group Base Specifications Issue 6<br>
IEEE Std 1003.1-2001<br>
Copyright &copy; 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
<!--header end-->
<hr size="2" noshade>
<h4><a name="tag_13_80_01"></a>NAME</h4>
<blockquote>unistd.h - standard symbolic constants and types</blockquote>
<h4><a name="tag_13_80_02"></a>SYNOPSIS</h4>
<blockquote class="synopsis">
<p><tt>#include &lt;unistd.h&gt;</tt></p>
</blockquote>
<h4><a name="tag_13_80_03"></a>DESCRIPTION</h4>
<blockquote>
<p>The <i>&lt;unistd.h&gt;</i> header defines miscellaneous symbolic constants and types, and declares miscellaneous functions. The
actual values of the constants are unspecified except as shown. The contents of this header are shown below.</p>
<h5><a name="tag_13_80_03_01"></a>Version Test Macros</h5>
<p>The following symbolic constants shall be defined:</p>
<dl compact>
<dt>_POSIX_VERSION</dt>
<dd>
Integer value indicating version of IEEE&nbsp;Std&nbsp;1003.1 (C-language binding) to which the implementation conforms. For
implementations conforming to IEEE&nbsp;Std&nbsp;1003.1-2001, the value shall be 200112L.</dd>
<dt>_POSIX2_VERSION</dt>
<dd>
Integer value indicating version of the Shell and Utilities volume of IEEE&nbsp;Std&nbsp;1003.1 to which the implementation
conforms. For implementations conforming to IEEE&nbsp;Std&nbsp;1003.1-2001, the value shall be 200112L.</dd>
</dl>
<p>The following symbolic constant shall be defined only if the implementation supports the XSI option; see <a href=
"xbd_chap02.html#tag_02_01_04"><i>XSI Conformance</i></a> .</p>
<dl compact>
<dt>_XOPEN_VERSION</dt>
<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
Integer value indicating version of the X/Open Portability Guide to which the implementation conforms. The value shall be 600. <img
src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
</dl>
<h5><a name="tag_13_80_03_02"></a>Constants for Options and Option Groups</h5>
<p>The following symbolic constants, if defined in <i>&lt;unistd.h&gt;</i>, shall have a value of -1, 0, or greater, unless
otherwise specified below. If these are undefined, the <a href="../functions/fpathconf.html"><i>fpathconf</i>()</a>, <a href=
"../functions/pathconf.html"><i>pathconf</i>()</a>, or <a href="../functions/sysconf.html"><i>sysconf</i>()</a> functions can be
used to determine whether the option is provided for a particular invocation of the application.</p>
<p>If a symbolic constant is defined with the value -1, the option is not supported. Headers, data types, and function interfaces
required only for the option need not be supplied. An application that attempts to use anything associated only with the option is
considered to be requiring an extension.</p>
<p>If a symbolic constant is defined with a value greater than zero, the option shall always be supported when the application is
executed. All headers, data types, and functions shall be present and shall operate as specified.</p>
<p>If a symbolic constant is defined with the value zero, all headers, data types, and functions shall be present. The application
can check at runtime to see whether the option is supported by calling <a href=
"../functions/fpathconf.html"><i>fpathconf</i>()</a>, <a href="../functions/pathconf.html"><i>pathconf</i>()</a>, or <a href=
"../functions/sysconf.html"><i>sysconf</i>()</a> with the indicated <i>name</i> parameter.</p>
<p>Unless explicitly specified otherwise, the behavior of functions associated with an unsupported option is unspecified, and an
application that uses such functions without first checking <a href="../functions/fpathconf.html"><i>fpathconf</i>()</a>, <a href=
"../functions/pathconf.html"><i>pathconf</i>()</a>, or <a href="../functions/sysconf.html"><i>sysconf</i>()</a> is considered to be
requiring an extension.</p>
<p>For conformance requirements, refer to <a href="xbd_chap02.html#tag_02"><i>Conformance</i></a> .</p>
<dl compact>
<dt>_POSIX_ADVISORY_INFO</dt>
<dd><sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Advisory Information option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_ASYNCHRONOUS_IO</dt>
<dd><sup>[<a href="javascript:open_code('AIO')">AIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Asynchronous Input and Output option. If this symbol has a value other than -1 or 0, it shall have
the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_BARRIERS</dt>
<dd><sup>[<a href="javascript:open_code('BAR')">BAR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Barriers option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.
<img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_CHOWN_RESTRICTED</dt>
<dd>
The use of <a href="../functions/chown.html"><i>chown</i>()</a> and <a href="../functions/fchown.html"><i>fchown</i>()</a> is
restricted to a process with appropriate privileges, and to changing the group ID of a file only to the effective group ID of the
process or to one of its supplementary group IDs. This symbol shall always be set to a value other than -1.</dd>
<dt>_POSIX_CLOCK_SELECTION</dt>
<dd><sup>[<a href="javascript:open_code('CS')">CS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Clock Selection option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_CPUTIME</dt>
<dd><sup>[<a href="javascript:open_code('CPT')">CPT</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Process CPU-Time Clocks option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_FSYNC</dt>
<dd><sup>[<a href="javascript:open_code('FSC')">FSC</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the File Synchronization option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_JOB_CONTROL</dt>
<dd>
The implementation supports job control. This symbol shall always be set to a value greater than zero.</dd>
<dt>_POSIX_MAPPED_FILES</dt>
<dd><sup>[<a href="javascript:open_code('MF')">MF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Memory Mapped Files option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_MEMLOCK</dt>
<dd><sup>[<a href="javascript:open_code('ML')">ML</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Process Memory Locking option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_MEMLOCK_RANGE</dt>
<dd><sup>[<a href="javascript:open_code('MR')">MR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Range Memory Locking option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_MEMORY_PROTECTION</dt>
<dd><sup>[<a href="javascript:open_code('MPR')">MPR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Memory Protection option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_MESSAGE_PASSING</dt>
<dd><sup>[<a href="javascript:open_code('MSG')">MSG</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Message Passing option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_MONOTONIC_CLOCK</dt>
<dd><sup>[<a href="javascript:open_code('MON')">MON</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Monotonic Clock option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_NO_TRUNC</dt>
<dd>
Pathname components longer than {NAME_MAX} generate an error. This symbol shall always be set to a value other than -1.</dd>
<dt>_POSIX_PRIORITIZED_IO</dt>
<dd><sup>[<a href="javascript:open_code('PIO')">PIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Prioritized Input and Output option. If this symbol has a value other than -1 or 0, it shall have
the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_PRIORITY_SCHEDULING</dt>
<dd><sup>[<a href="javascript:open_code('PS')">PS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Process Scheduling option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_RAW_SOCKETS</dt>
<dd><sup>[<a href="javascript:open_code('RS')">RS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Raw Sockets option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.
<img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_READER_WRITER_LOCKS</dt>
<dd><sup>[<a href="javascript:open_code('THR')">THR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Read-Write Locks option. This is always set to a value greater than zero if the Threads option is
supported. If this symbol has a value other than -1 or 0, it shall have the value 200112L. <img src="../images/opt-end.gif" alt=
"[Option End]" border="0"></dd>
<dt>_POSIX_REALTIME_SIGNALS</dt>
<dd><sup>[<a href="javascript:open_code('RTS')">RTS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Realtime Signals Extension option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_REGEXP</dt>
<dd>
The implementation supports the Regular Expression Handling option. This symbol shall always be set to a value greater than
zero.</dd>
<dt>_POSIX_SAVED_IDS</dt>
<dd>
Each process has a saved set-user-ID and a saved set-group-ID. This symbol shall always be set to a value greater than zero.</dd>
<dt>_POSIX_SEMAPHORES</dt>
<dd><sup>[<a href="javascript:open_code('SEM')">SEM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Semaphores option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.
<img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_SHARED_MEMORY_OBJECTS</dt>
<dd><sup>[<a href="javascript:open_code('SHM')">SHM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Shared Memory Objects option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_SHELL</dt>
<dd>
The implementation supports the POSIX shell. This symbol shall always be set to a value greater than zero.</dd>
<dt>_POSIX_SPAWN</dt>
<dd><sup>[<a href="javascript:open_code('SPN')">SPN</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Spawn option. If this symbol has a value other than -1 or 0, it shall have the value 200112L. <img
src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_SPIN_LOCKS</dt>
<dd><sup>[<a href="javascript:open_code('SPI')">SPI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Spin Locks option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.
<img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_SPORADIC_SERVER</dt>
<dd><sup>[<a href="javascript:open_code('SS')">SS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Process Sporadic Server option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_SYNCHRONIZED_IO</dt>
<dd><sup>[<a href="javascript:open_code('SIO')">SIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Synchronized Input and Output option. If this symbol has a value other than -1 or 0, it shall have
the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_ATTR_STACKADDR</dt>
<dd><sup>[<a href="javascript:open_code('TSA')">TSA</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread Stack Address Attribute option. If this symbol has a value other than -1 or 0, it shall have
the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_ATTR_STACKSIZE</dt>
<dd><sup>[<a href="javascript:open_code('TSS')">TSS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread Stack Address Size option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_CPUTIME</dt>
<dd><sup>[<a href="javascript:open_code('TCT')">TCT</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread CPU-Time Clocks option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_PRIO_INHERIT</dt>
<dd><sup>[<a href="javascript:open_code('TPI')">TPI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread Priority Inheritance option. If this symbol has a value other than -1 or 0, it shall have
the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_PRIO_PROTECT</dt>
<dd><sup>[<a href="javascript:open_code('TPP')">TPP</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread Priority Protection option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_PRIORITY_SCHEDULING</dt>
<dd><sup>[<a href="javascript:open_code('TPS')">TPS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread Execution Scheduling option. If this symbol has a value other than -1 or 0, it shall have
the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_PROCESS_SHARED</dt>
<dd><sup>[<a href="javascript:open_code('TSH')">TSH</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread Process-Shared Synchronization option. If this symbol has a value other than -1 or 0, it
shall have the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_SAFE_FUNCTIONS</dt>
<dd><sup>[<a href="javascript:open_code('TSF')">TSF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread-Safe Functions option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREAD_SPORADIC_SERVER</dt>
<dd><sup>[<a href="javascript:open_code('TSP')">TSP</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Thread Sporadic Server option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_THREADS</dt>
<dd><sup>[<a href="javascript:open_code('THR')">THR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Threads option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.
<img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_TIMEOUTS</dt>
<dd><sup>[<a href="javascript:open_code('TMO')">TMO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Timeouts option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.
<img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_TIMERS</dt>
<dd><sup>[<a href="javascript:open_code('TMR')">TMR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Timers option. If this symbol has a value other than -1 or 0, it shall have the value 200112L. <img
src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_TRACE</dt>
<dd><sup>[<a href="javascript:open_code('TRC')">TRC</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Trace option. If this symbol has a value other than -1 or 0, it shall have the value 200112L. <img
src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_TRACE_EVENT_FILTER</dt>
<dd><sup>[<a href="javascript:open_code('TEF')">TEF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Trace Event Filter option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_TRACE_INHERIT</dt>
<dd><sup>[<a href="javascript:open_code('TRI')">TRI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Trace Inherit option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_TRACE_LOG</dt>
<dd><sup>[<a href="javascript:open_code('TRL')">TRL</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Trace Log option. If this symbol has a value other than -1 or 0, it shall have the value 200112L.
<img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_TYPED_MEMORY_OBJECTS</dt>
<dd><sup>[<a href="javascript:open_code('TYM')">TYM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Typed Memory Objects option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX_VDISABLE</dt>
<dd>
This symbol shall be defined to be the value of a character that shall disable terminal special character handling as described in
<a href="termios.h.html"><i>&lt;termios.h&gt;</i></a> . This symbol shall always be set to a value other than -1.</dd>
<dt>_POSIX2_C_BIND</dt>
<dd>
The implementation supports the C-Language Binding option. This symbol shall always have the value 200112L.</dd>
<dt>_POSIX2_C_DEV</dt>
<dd><sup>[<a href="javascript:open_code('CD')">CD</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the C-Language Development Utilities option. If this symbol has a value other than -1 or 0, it shall
have the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_CHAR_TERM</dt>
<dd>
The implementation supports at least one terminal type.</dd>
<dt>_POSIX2_FORT_DEV</dt>
<dd><sup>[<a href="javascript:open_code('FD')">FD</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the FORTRAN Development Utilities option. If this symbol has a value other than -1 or 0, it shall have
the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_FORT_RUN</dt>
<dd><sup>[<a href="javascript:open_code('FR')">FR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the FORTRAN Runtime Utilities option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_LOCALEDEF</dt>
<dd>
The implementation supports the creation of locales by the <a href="../utilities/localedef.html"><i>localedef</i></a> utility. If
this symbol has a value other than -1 or 0, it shall have the value 200112L.</dd>
<dt>_POSIX2_PBS</dt>
<dd><sup>[<a href="javascript:open_code('BE')">BE</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Batch Environment Services and Utilities option. If this symbol has a value other than -1 or 0, it
shall have the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_PBS_ACCOUNTING</dt>
<dd><sup>[<a href="javascript:open_code('BE')">BE</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Batch Accounting option. If this symbol has a value other than -1 or 0, it shall have the value
200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_PBS_CHECKPOINT</dt>
<dd><sup>[<a href="javascript:open_code('BE')">BE</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Batch Checkpoint/Restart option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_PBS_LOCATE</dt>
<dd><sup>[<a href="javascript:open_code('BE')">BE</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Locate Batch Job Request option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_PBS_MESSAGE</dt>
<dd><sup>[<a href="javascript:open_code('BE')">BE</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Batch Job Message Request option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_PBS_TRACK</dt>
<dd><sup>[<a href="javascript:open_code('BE')">BE</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Track Batch Job Request option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_SW_DEV</dt>
<dd><sup>[<a href="javascript:open_code('SD')">SD</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the Software Development Utilities option. If this symbol has a value other than -1 or 0, it shall have
the value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_POSIX2_UPE</dt>
<dd><sup>[<a href="javascript:open_code('UP')">UP</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the User Portability Utilities option. If this symbol has a value other than -1 or 0, it shall have the
value 200112L. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_V6_ILP32_OFF32</dt>
<dd>
The implementation provides a C-language compilation environment with 32-bit <b>int</b>, <b>long</b>, <b>pointer</b>, and
<b>off_t</b> types.</dd>
<dt>_V6_ILP32_OFFBIG</dt>
<dd>
The implementation provides a C-language compilation environment with 32-bit <b>int</b>, <b>long</b>, and <b>pointer</b> types and
an <b>off_t</b> type using at least 64 bits.</dd>
<dt>_V6_LP64_OFF64</dt>
<dd>
The implementation provides a C-language compilation environment with 32-bit <b>int</b> and 64-bit <b>long</b>, <b>pointer</b>, and
<b>off_t</b> types.</dd>
<dt>_V6_LPBIG_OFFBIG</dt>
<dd>
The implementation provides a C-language compilation environment with an <b>int</b> type using at least 32 bits and <b>long</b>,
<b>pointer</b>, and <b>off_t</b> types using at least 64 bits.</dd>
<dt>_XBS5_ILP32_OFF32 (<b>LEGACY</b>)</dt>
<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation provides a C-language compilation environment with 32-bit <b>int</b>, <b>long</b>, <b>pointer</b>, and
<b>off_t</b> types. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_XBS5_ILP32_OFFBIG (<b>LEGACY</b>)</dt>
<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation provides a C-language compilation environment with 32-bit <b>int</b>, <b>long</b>, and <b>pointer</b> types and
an <b>off_t</b> type using at least 64 bits. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_XBS5_LP64_OFF64 (<b>LEGACY</b>)</dt>
<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation provides a C-language compilation environment with 32-bit <b>int</b> and 64-bit <b>long</b>, <b>pointer</b>, and
<b>off_t</b> types. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_XBS5_LPBIG_OFFBIG (<b>LEGACY</b>)</dt>
<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation provides a C-language compilation environment with an <b>int</b> type using at least 32 bits and <b>long</b>,
<b>pointer</b>, and <b>off_t</b> types using at least 64 bits. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_XOPEN_CRYPT</dt>
<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the X/Open Encryption Option Group.</dd>
<dt>_XOPEN_ENH_I18N</dt>
<dd>
The implementation supports the Issue 4, Version 2 Enhanced Internationalization Option Group. This symbol shall always be set to a
value other than -1.</dd>
<dt>_XOPEN_LEGACY</dt>
<dd>
The implementation supports the Legacy Option Group.</dd>
<dt>_XOPEN_REALTIME</dt>
<dd>
The implementation supports the X/Open Realtime Option Group.</dd>
<dt>_XOPEN_REALTIME_THREADS</dt>
<dd>
The implementation supports the X/Open Realtime Threads Option Group.</dd>
<dt>_XOPEN_SHM</dt>
<dd>
The implementation supports the Issue 4, Version 2 Shared Memory Option Group. This symbol shall always be set to a value other
than -1.</dd>
<dt>_XOPEN_STREAMS</dt>
<dd>
The implementation supports the XSI STREAMS Option Group. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
<dt>_XOPEN_UNIX</dt>
<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
"0"><br>
The implementation supports the XSI extension. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
</dl>
<h5><a name="tag_13_80_03_03"></a>Execution-Time Symbolic Constants</h5>
<p>If any of the following constants are not defined in the <i>&lt;unistd.h&gt;</i> header, the value shall vary depending on the
file to which it is applied.</p>
<p>If any of the following constants are defined to have value -1 in the <i>&lt;unistd.h&gt;</i> header, the implementation shall
not provide the option on any file; if any are defined to have a value other than -1 in the <i>&lt;unistd.h&gt;</i> header, the
implementation shall provide the option on all applicable files.</p>
<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 <a href="../functions/pathconf.html"><i>pathconf</i>()</a> or <a href=
"../functions/fpathconf.html"><i>fpathconf</i>()</a> functions:</p>
<dl compact>
<dt>_POSIX_ASYNC_IO</dt>
<dd>
Asynchronous input or output operations may be performed for the associated file.</dd>
<dt>_POSIX_PRIO_IO</dt>
<dd>
Prioritized input or output operations may be performed for the associated file.</dd>
<dt>_POSIX_SYNC_IO</dt>
<dd>
Synchronized input or output operations may be performed for the associated file.</dd>
</dl>
<h5><a name="tag_13_80_03_04"></a>Constants for Functions</h5>
<p>The following symbolic constant shall be defined:</p>
<dl compact>
<dt>NULL</dt>
<dd>Null pointer</dd>
</dl>
<p>The following symbolic constants shall be defined for the <a href="../functions/access.html"><i>access</i>()</a> function:</p>
<dl compact>
<dt>F_OK</dt>
<dd>Test for existence of file.</dd>
<dt>R_OK</dt>
<dd>Test for read permission.</dd>
<dt>W_OK</dt>
<dd>Test for write permission.</dd>
<dt>X_OK</dt>
<dd>Test for execute (search) permission.</dd>
</dl>
<p>The constants F_OK, R_OK, W_OK, and X_OK and the expressions <i>R_OK</i>|<i>W_OK</i>, <i>R_OK</i>|<i>X_OK</i>, and
<i>R_OK</i>|<i>W_OK</i>|<i>X_OK</i> shall all have distinct values.</p>
<p>The following symbolic constants shall be defined for the <a href="../functions/confstr.html"><i>confstr</i>()</a> function:</p>
<dl compact>
<dt>_CS_PATH</dt>
<dd>
This is the value for the <i>PATH</i> environment variable that finds all standard utilities.</dd>
<dt>_CS_POSIX_V6_ILP32_OFF32_CFLAGS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_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 <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a
programming model with 32-bit <b>int</b>, <b>long</b>, <b>pointer</b>, and <b>off_t</b> types.</dd>
<dt>_CS_POSIX_V6_ILP32_OFF32_LDFLAGS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_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 <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a programming
model with 32-bit <b>int</b>, <b>long</b>, <b>pointer</b>, and <b>off_t</b> types.</dd>
<dt>_CS_POSIX_V6_ILP32_OFF32_LIBS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_ILP32_OFF32) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of
libraries to be given to the <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a programming
model with 32-bit <b>int</b>, <b>long</b>, <b>pointer</b>, and <b>off_t</b> types.</dd>
<dt>_CS_POSIX_V6_ILP32_OFFBIG_CFLAGS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_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 <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a
programming model with 32-bit <b>int</b>, <b>long</b>, and <b>pointer</b> types, and an <b>off_t</b> type using at least 64
bits.</dd>
<dt>_CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_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 <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a programming
model with 32-bit <b>int</b>, <b>long</b>, and <b>pointer</b> types, and an <b>off_t</b> type using at least 64 bits.</dd>
<dt>_CS_POSIX_V6_ILP32_OFFBIG_LIBS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_ILP32_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of
libraries to be given to the <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a programming
model with 32-bit <b>int</b>, <b>long</b>, and <b>pointer</b> types, and an <b>off_t</b> type using at least 64 bits.</dd>
<dt>_CS_POSIX_V6_LP64_OFF64_CFLAGS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_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 <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a
programming model with 64-bit <b>int</b>, <b>long</b>, <b>pointer</b>, and <b>off_t</b> types.</dd>
<dt>_CS_POSIX_V6_LP64_OFF64_LDFLAGS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_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 <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a programming
model with 64-bit <b>int</b>, <b>long</b>, <b>pointer</b>, and <b>off_t</b> types.</dd>
<dt>_CS_POSIX_V6_LP64_OFF64_LIBS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_LP64_OFF64) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of
libraries to be given to the <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a programming
model with 64-bit <b>int</b>, <b>long</b>, <b>pointer</b>, and <b>off_t</b> types.</dd>
<dt>_CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_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 <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a
programming model with an <b>int</b> type using at least 32 bits and <b>long</b>, <b>pointer</b>, and <b>off_t</b> types using at
least 64 bits.</dd>
<dt>_CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_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 <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a programming
model with an <b>int</b> type using at least 32 bits and <b>long</b>, <b>pointer</b>, and <b>off_t</b> types using at least 64
bits.</dd>
<dt>_CS_POSIX_V6_LPBIG_OFFBIG_LIBS</dt>
<dd>
If <i>sysconf</i>(_SC_V6_LPBIG_OFFBIG) returns -1, the meaning of this value is unspecified. Otherwise, this value is the set of
libraries to be given to the <a href="../utilities/c99.html"><i>c99</i></a> utility to build an application using a programming
model with an <b>int</b> type using at least 32 bits and <b>long</b>, <b>pointer</b>, and <b>off_t</b> types using at least 64
bits.</dd>
<dt>_CS_POSIX_V6_WIDTH_RESTRICTED_ENVS</dt>
<dd>
This value is a &lt;newline&gt;-separated list of names of programming environments supported by the implementation in which the
widths of the <b>blksize_t</b>, <b>cc_t</b>, <b>mode_t</b>, <b>nfds_t</b>, <b>pid_t</b>, <b>ptrdiff_t</b>, <b>size_t</b>,
<b>speed_t</b>, <b>ssize_t</b>, <b>suseconds_t</b>, <b>tcflag_t</b>, <b>useconds_t</b>, <b>wchar_t</b>, and <b>wint_t</b> types are
no greater than the width of type <b>long</b>.</dd>
</dl>
<p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
The following symbolic constants are reserved for compatibility with Issue 5:</p>
<p><br>
_CS_XBS5_ILP32_OFF32_CFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_ILP32_OFF32_LDFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_ILP32_OFF32_LIBS (<b>LEGACY</b>)<br>
_CS_XBS5_ILP32_OFF32_LINTFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_ILP32_OFFBIG_CFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_ILP32_OFFBIG_LDFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_ILP32_OFFBIG_LIBS (<b>LEGACY</b>)<br>
_CS_XBS5_ILP32_OFFBIG_LINTFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_LP64_OFF64_CFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_LP64_OFF64_LDFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_LP64_OFF64_LIBS (<b>LEGACY</b>)<br>
_CS_XBS5_LP64_OFF64_LINTFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_LPBIG_OFFBIG_CFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_LPBIG_OFFBIG_LDFLAGS (<b>LEGACY</b>)<br>
_CS_XBS5_LPBIG_OFFBIG_LIBS (<b>LEGACY</b>)<br>
_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS (<b>LEGACY</b>)<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
</p>
<p>The following symbolic constants shall be defined for the <a href="../functions/lseek.html"><i>lseek</i>()</a> and <a href=
"../functions/fcntl.html"><i>fcntl</i>()</a> functions and shall have distinct values:</p>
<dl compact>
<dt>SEEK_CUR</dt>
<dd>Set file offset to current plus <i>offset</i>.</dd>
<dt>SEEK_END</dt>
<dd>Set file offset to EOF plus <i>offset</i>.</dd>
<dt>SEEK_SET</dt>
<dd>Set file offset to <i>offset</i>.</dd>
</dl>
<p>The following symbolic constants shall be defined as possible values for the <i>function</i> argument to the <a href=
"../functions/lockf.html"><i>lockf</i>()</a> function:</p>
<dl compact>
<dt>F_LOCK</dt>
<dd>Lock a section for exclusive use.</dd>
<dt>F_TEST</dt>
<dd>Test section for locks by other processes.</dd>
<dt>F_TLOCK</dt>
<dd>Test and lock a section for exclusive use.</dd>
<dt>F_ULOCK</dt>
<dd>Unlock locked sections.</dd>
</dl>
<p>The following symbolic constants shall be defined for <a href="../functions/pathconf.html"><i>pathconf</i>()</a>:</p>
<p><br>
<sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_PC_ALLOC_SIZE_MIN<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
<sup>[<a href="javascript:open_code('AIO')">AIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_PC_ASYNC_IO<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_PC_CHOWN_RESTRICTED<br>
_PC_FILESIZEBITS<br>
_PC_LINK_MAX<br>
_PC_MAX_CANON<br>
_PC_MAX_INPUT<br>
_PC_NAME_MAX<br>
_PC_NO_TRUNC<br>
_PC_PATH_MAX<br>
_PC_PIPE_BUF<br>
_PC_PRIO_IO<br>
<sup>[<a href="javascript:open_code('ADV')">ADV</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_PC_REC_INCR_XFER_SIZE<br>
_PC_REC_MAX_XFER_SIZE<br>
_PC_REC_MIN_XFER_SIZE<br>
_PC_REC_XFER_ALIGN<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_PC_SYNC_IO<br>
_PC_VDISABLE<br>
</p>
<p>The following symbolic constants shall be defined for <a href="../functions/sysconf.html"><i>sysconf</i>()</a>:</p>
<p><br>
_SC_2_C_BIND<br>
_SC_2_C_DEV<br>
_SC_2_C_VERSION<br>
_SC_2_CHAR_TERM<br>
_SC_2_FORT_DEV<br>
_SC_2_FORT_RUN<br>
_SC_2_LOCALEDEF<br>
_SC_2_PBS<br>
_SC_2_PBS_ACCOUNTING<br>
_SC_2_PBS_CHECKPOINT<br>
_SC_2_PBS_LOCATE<br>
_SC_2_PBS_MESSAGE<br>
_SC_2_PBS_TRACK<br>
_SC_2_SW_DEV<br>
_SC_2_UPE<br>
_SC_2_VERSION<br>
_SC_ADVISORY_INFO<br>
_SC_ARG_MAX<br>
_SC_AIO_LISTIO_MAX<br>
_SC_AIO_MAX<br>
_SC_AIO_PRIO_DELTA_MAX<br>
_SC_ASYNCHRONOUS_IO<br>
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_ATEXIT_MAX<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
<sup>[<a href="javascript:open_code('BAR')">BAR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_BARRIERS<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_BC_BASE_MAX<br>
_SC_BC_DIM_MAX<br>
_SC_BC_SCALE_MAX<br>
_SC_BC_STRING_MAX<br>
_SC_CHILD_MAX<br>
_SC_CLK_TCK<br>
<sup>[<a href="javascript:open_code('CS')">CS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_CLOCK_SELECTION<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_COLL_WEIGHTS_MAX<br>
_SC_CPUTIME<br>
_SC_DELAYTIMER_MAX<br>
_SC_EXPR_NEST_MAX<br>
_SC_FILE_LOCKING<br>
_SC_FSYNC<br>
_SC_GETGR_R_SIZE_MAX<br>
_SC_GETPW_R_SIZE_MAX<br>
_SC_HOST_NAME_MAX<br>
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_IOV_MAX<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_JOB_CONTROL<br>
_SC_LINE_MAX<br>
_SC_LOGIN_NAME_MAX<br>
_SC_MAPPED_FILES<br>
_SC_MEMLOCK<br>
_SC_MEMLOCK_RANGE<br>
_SC_MEMORY_PROTECTION<br>
_SC_MESSAGE_PASSING<br>
<sup>[<a href="javascript:open_code('MON')">MON</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_MONOTONIC_CLOCK<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_MQ_OPEN_MAX<br>
_SC_MQ_PRIO_MAX<br>
_SC_NGROUPS_MAX<br>
_SC_OPEN_MAX<br>
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_PAGE_SIZE<br>
_SC_PAGESIZE<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_PRIORITIZED_IO<br>
_SC_PRIORITY_SCHEDULING<br>
_SC_RE_DUP_MAX<br>
<sup>[<a href="javascript:open_code('THR')">THR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_READER_WRITER_LOCKS<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_REALTIME_SIGNALS<br>
_SC_REGEXP<br>
_SC_RTSIG_MAX<br>
_SC_SAVED_IDS<br>
_SC_SEMAPHORES<br>
_SC_SEM_NSEMS_MAX<br>
_SC_SEM_VALUE_MAX<br>
_SC_SHARED_MEMORY_OBJECTS<br>
_SC_SHELL<br>
_SC_SIGQUEUE_MAX<br>
_SC_SPAWN<br>
<sup>[<a href="javascript:open_code('SPI')">SPI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_SPIN_LOCKS<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_SPORADIC_SERVER<br>
_SC_STREAM_MAX<br>
_SC_SYNCHRONIZED_IO<br>
_SC_THREAD_ATTR_STACKADDR<br>
_SC_THREAD_ATTR_STACKSIZE<br>
_SC_THREAD_CPUTIME<br>
_SC_THREAD_DESTRUCTOR_ITERATIONS<br>
_SC_THREAD_KEYS_MAX<br>
_SC_THREAD_PRIO_INHERIT<br>
_SC_THREAD_PRIO_PROTECT<br>
_SC_THREAD_PRIORITY_SCHEDULING<br>
_SC_THREAD_PROCESS_SHARED<br>
_SC_THREAD_SAFE_FUNCTIONS<br>
_SC_THREAD_SPORADIC_SERVER<br>
_SC_THREAD_STACK_MIN<br>
_SC_THREAD_THREADS_MAX<br>
_SC_TIMEOUTS<br>
_SC_THREADS<br>
_SC_TIMER_MAX<br>
<br>
<br>
<br>
_SC_TIMERS<br>
<sup>[<a href="javascript:open_code('TRC')">TRC</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_TRACE<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
<sup>[<a href="javascript:open_code('TEF')">TEF</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_TRACE_EVENT_FILTER<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
<sup>[<a href="javascript:open_code('TRI')">TRI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_TRACE_INHERIT<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
<sup>[<a href="javascript:open_code('TRL')">TRL</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_TRACE_LOG<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_TTY_NAME_MAX<br>
<sup>[<a href="javascript:open_code('TYM')">TYM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_TYPED_MEMORY_OBJECTS<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
_SC_TZNAME_MAX<br>
_SC_V6_ILP32_OFF32<br>
_SC_V6_ILP32_OFFBIG<br>
_SC_V6_LP64_OFF64<br>
_SC_V6_LPBIG_OFFBIG<br>
_SC_VERSION<br>
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>
_SC_XBS5_ILP32_OFF32 (<b>LEGACY</b>)<br>
_SC_XBS5_ILP32_OFFBIG (<b>LEGACY</b>)<br>
_SC_XBS5_LP64_OFF64 (<b>LEGACY</b>)<br>
_SC_XBS5_LPBIG_OFFBIG (<b>LEGACY</b>)<br>
_SC_XOPEN_CRYPT<br>
_SC_XOPEN_ENH_I18N<br>
_SC_XOPEN_LEGACY<br>
_SC_XOPEN_REALTIME<br>
_SC_XOPEN_REALTIME_THREADS<br>
_SC_XOPEN_SHM<br>
_SC_XOPEN_STREAMS<br>
_SC_XOPEN_UNIX<br>
_SC_XOPEN_VERSION<br>
_SC_XOPEN_XCU_VERSION<br>
<img src="../images/opt-end.gif" alt="[Option End]" border="0"><br>
</p>
<p>The two constants _SC_PAGESIZE and _SC_PAGE_SIZE may be defined to have the same value.</p>
<p>The following symbolic constants shall be defined for file streams:</p>
<dl compact>
<dt>STDERR_FILENO</dt>
<dd>File number of <i>stderr</i>; 2.</dd>
<dt>STDIN_FILENO</dt>
<dd>File number of <i>stdin</i>; 0.</dd>
<dt>STDOUT_FILENO</dt>
<dd>File number of <i>stdout</i>; 1.</dd>
</dl>
<h5><a name="tag_13_80_03_05"></a>Type Definitions</h5>
<p>The <b>size_t</b>, <b>ssize_t</b>, <b>uid_t</b>, <b>gid_t</b>, <b>off_t</b>, <b>pid_t</b>, and <b>useconds_t</b> types shall be
defined as described in <a href="../basedefs/sys/types.h.html"><i>&lt;sys/types.h&gt;</i></a>.</p>
<p>The <b>intptr_t</b> type shall be defined as described in <a href=
"../basedefs/inttypes.h.html"><i>&lt;inttypes.h&gt;</i></a>.</p>
<h5><a name="tag_13_80_03_06"></a>Declarations</h5>
<p>The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.</p>
<pre>
<tt>int access(const char *, int);
unsigned alarm(unsigned);
int chdir(const char *);
int chown(const char *, uid_t, gid_t);
int close(int);
size_t confstr(int, char *, size_t);
<br>
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
char *crypt(const char *, const char *);
char *ctermid(char *);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
int dup(int);
<br>
int dup2(int, int);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
void encrypt(char[64], int);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
int execl(const char *, const char *, ...);
int execle(const char *, const char *, ...);
int execlp(const char *, const char *, ...);
int execv(const char *, char *const []);
int execve(const char *, char *const [], char *const []);
int execvp(const char *, char *const []);
void _exit(int);
int fchown(int, uid_t, gid_t);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
int fchdir(int);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
<sup>[<a href="javascript:open_code('SIO')">SIO</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
int fdatasync(int);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
pid_t fork(void);
long fpathconf(int, int);
int fsync(int);
int ftruncate(int, off_t);
char *getcwd(char *, size_t);
gid_t getegid(void);
uid_t geteuid(void);
gid_t getgid(void);
int getgroups(int, gid_t []);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
long gethostid(void);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
int gethostname(char *, size_t);
char *getlogin(void);
int getlogin_r(char *, size_t);
int getopt(int, char * const [], const char *);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
pid_t getpgid(pid_t);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
pid_t getpgrp(void);
pid_t getpid(void);
pid_t getppid(void);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
pid_t getsid(pid_t);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
uid_t getuid(void);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
char *getwd(char *); (</tt><b>LEGACY</b> <tt>)
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
int isatty(int);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
int lchown(const char *, uid_t, gid_t);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
int link(const char *, const char *);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
int lockf(int, int, off_t);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
off_t lseek(int, off_t, int);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
int nice(int);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
long pathconf(const char *, int);
int pause(void);
int pipe(int [2]);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
ssize_t pread(int, void *, size_t, off_t);
ssize_t pwrite(int, const void *, size_t, off_t);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
ssize_t read(int, void *, size_t);
ssize_t readlink(const char *restrict, char *restrict, size_t);
int rmdir(const char *);
int setegid(gid_t);
int seteuid(uid_t);
int setgid(gid_t);
<br>
int setpgid(pid_t, pid_t);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
pid_t setpgrp(void);
int setregid(gid_t, gid_t);
int setreuid(uid_t, uid_t);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
pid_t setsid(void);
int setuid(uid_t);
unsigned sleep(unsigned);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
void swab(const void *restrict, void *restrict, ssize_t);
int symlink(const char *, const char *);
void sync(void);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
long sysconf(int);
pid_t tcgetpgrp(int);
int tcsetpgrp(int, pid_t);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
int truncate(const char *, off_t);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
char *ttyname(int);
int ttyname_r(int, char *, size_t);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
useconds_t ualarm(useconds_t, useconds_t);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
int unlink(const char *);
<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup><img src="../images/opt-start.gif" alt="[Option Start]" border="0">
int usleep(useconds_t);
pid_t vfork(void);
<img src="../images/opt-end.gif" alt="[Option End]" border="0">
ssize_t write(int, const void *, size_t);
</tt>
</pre>
<p>Implementations may also include the <a href="../functions/pthread_atfork.html"><i>pthread_atfork</i>()</a> prototype as defined
in <a href="pthread.h.html"><i>&lt;pthread.h&gt;</i></a> .</p>
<p>The following external variables shall be declared:</p>
<pre>
<tt>extern char *optarg;
extern int optind, opterr, optopt;
</tt>
</pre>
</blockquote>
<hr>
<div class="box"><em>The following sections are informative.</em></div>
<h4><a name="tag_13_80_04"></a>APPLICATION USAGE</h4>
<blockquote>
<p>IEEE&nbsp;Std&nbsp;1003.1-2001 only describes the behavior of systems that claim conformance to it. However, application
developers who want to write applications that adapt to other versions of IEEE&nbsp;Std&nbsp;1003.1 (or to systems that do not
conform to any POSIX standard) may find it useful to code them so as to conditionally compile different code depending on the value
of _POSIX_VERSION, for example:</p>
<pre>
<tt>#if _POSIX_VERSION &gt;= 200112L
/* Use the newer function that copes with large files. */
off_t pos=ftello(fp);
#else
/* Either this is an old version of POSIX, or _POSIX_VERSION is
not even defined, so use the traditional function. */
long pos=ftell(fp);
#endif
</tt>
</pre>
<p>Earlier versions of IEEE&nbsp;Std&nbsp;1003.1 and of the Single UNIX Specification can be identified by the following
macros:</p>
<dl compact>
<dt>POSIX.1-1988 standard</dt>
<dd>
_POSIX_VERSION==198808L</dd>
<dt>POSIX.1-1990 standard</dt>
<dd>
_POSIX_VERSION==199009L</dd>
<dt>ISO&nbsp;POSIX-1:1996 standard</dt>
<dd>
_POSIX_VERSION==199506L</dd>
<dt>Single UNIX Specification, Version 1</dt>
<dd>
_XOPEN_UNIX and _XOPEN_VERSION==4</dd>
<dt>Single UNIX Specification, Version 2</dt>
<dd>
_XOPEN_UNIX and _XOPEN_VERSION==500</dd>
</dl>
<p>IEEE&nbsp;Std&nbsp;1003.1-2001 does not make any attempt to define application binary interaction with the underlying operating
system. However, application developers may find it useful to query _SC_VERSION at runtime via <a href=
"../functions/sysconf.html"><i>sysconf</i>()</a> to determine whether the current version of the operating system supports the
necessary functionality as in the following program fragment:</p>
<pre>
<tt>if (sysconf(_SC_VERSION) &lt; 200112L) {
fprintf(stderr, "POSIX.1-2001 system required, terminating \n");
exit(1);
}
</tt>
</pre>
</blockquote>
<h4><a name="tag_13_80_05"></a>RATIONALE</h4>
<blockquote>
<p>As IEEE&nbsp;Std&nbsp;1003.1-2001 evolved, certain options became sufficiently standardized that it was concluded that simply
requiring one of the option choices was simpler than retaining the option. However, for backwards-compatibility, the option flags
(with required constant values) are retained.</p>
<h5><a name="tag_13_80_05_01"></a>Version Test Macros</h5>
<p>The standard developers considered altering the definition of _POSIX_VERSION and removing _SC_VERSION from the specification of
<a href="../functions/sysconf.html"><i>sysconf</i>()</a> since the utility to an application was deemed by some to be minimal, and
since the implementation of the functionality is potentially problematic. However, they recognized that support for existing
application binaries is a concern to manufacturers, application developers, and the users of implementations conforming to
IEEE&nbsp;Std&nbsp;1003.1-2001.</p>
<p>While the example using _SC_VERSION in the APPLICATION USAGE section does not provide the greatest degree of imaginable utility
to the application developer or user, it is arguably better than a <b>core</b> file or some other equally obscure result. (It is
also possible for implementations to encode and recognize application binaries compiled in various POSIX.1-conforming environments,
and modify the semantics of the underlying system to conform to the expectations of the application.) For the reasons outlined in
the preceding paragraphs and in the APPLICATION USAGE section, the standard developers elected to retain the _POSIX_VERSION and
_SC_VERSION functionality.</p>
<h5><a name="tag_13_80_05_02"></a>Compile-Time Symbolic Constants for System-Wide Options</h5>
<p>IEEE&nbsp;Std&nbsp;1003.1-2001 now includes support in certain areas for the newly adopted policy governing options and
stubs.</p>
<p>This policy provides flexibility for implementations in how they support options. It also specifies how conforming applications
can adapt to different implementations that support different sets of options. It allows the following:</p>
<ol>
<li>
<p>If an implementation has no interest in supporting an option, it does not have to provide anything associated with that option
beyond the announcement that it does not support it.</p>
</li>
<li>
<p>An implementation can support a partial or incompatible version of an option (as a non-standard extension) as long as it does
not claim to support the option.</p>
</li>
<li>
<p>An application can determine whether the option is supported. A strictly conforming application must check this announcement
mechanism before first using anything associated with the option.</p>
</li>
</ol>
<p>There is an important implication of this policy. IEEE&nbsp;Std&nbsp;1003.1-2001 cannot dictate the behavior of interfaces
associated with an option when the implementation does not claim to support the option. In particular, it cannot require that a
function associated with an unsupported option will fail if it does not perform as specified. However, this policy does not prevent
a standard from requiring certain functions to always be present, but that they shall always fail on some implementations. The <a
href="../functions/setpgid.html"><i>setpgid</i>()</a> function in the POSIX.1-1990 standard, for example, is considered
appropriate.</p>
<p>The POSIX standards include various options, and the C-language binding support for an option implies that the implementation
must supply data types and function interfaces. An application must be able to discover whether the implementation supports each
option.</p>
<p>Any application must consider the following three cases for each option:</p>
<ol>
<li>
<p>Option never supported.</p>
<p>The implementation advertises at compile time that the option will never be supported. In this case, it is not necessary for the
implementation to supply any of the data types or function interfaces that are provided only as part of the option. The
implementation might provide data types and functions that are similar to those defined by IEEE&nbsp;Std&nbsp;1003.1-2001, but
there is no guarantee for any particular behavior.</p>
</li>
<li>
<p>Option always supported.</p>
<p>The implementation advertises at compile time that the option will always be supported. In this case, all data types and
function interfaces shall be available and shall operate as specified.</p>
</li>
<li>
<p>Option might or might not be supported.</p>
<p>Some implementations might not provide a mechanism to specify support of options at compile time. In addition, the
implementation might be unable or unwilling to specify support or non-support at compile time. In either case, any application that
might use the option at runtime must be able to compile and execute. The implementation must provide, at compile time, all data
types and function interfaces that are necessary to allow this. In this situation, there must be a mechanism that allows the
application to query, at runtime, whether the option is supported. If the application attempts to use the option when it is not
supported, the result is unspecified unless explicitly specified otherwise in IEEE&nbsp;Std&nbsp;1003.1-2001.</p>
</li>
</ol>
</blockquote>
<h4><a name="tag_13_80_06"></a>FUTURE DIRECTIONS</h4>
<blockquote>
<p>None.</p>
</blockquote>
<h4><a name="tag_13_80_07"></a>SEE ALSO</h4>
<blockquote>
<p><a href="inttypes.h.html"><i>&lt;inttypes.h&gt;</i></a> , <a href="limits.h.html"><i>&lt;limits.h&gt;</i></a> , <a href=
"sys/socket.h.html"><i>&lt;sys/socket.h&gt;</i></a> , <a href="sys/types.h.html"><i>&lt;sys/types.h&gt;</i></a> , <a href=
"termios.h.html"><i>&lt;termios.h&gt;</i></a> , <a href="wctype.h.html"><i>&lt;wctype.h&gt;</i></a> , the System Interfaces volume
of IEEE&nbsp;Std&nbsp;1003.1-2001, <a href="../functions/access.html"><i>access</i>()</a>, <a href=
"../functions/alarm.html"><i>alarm</i>()</a>, <a href="../functions/chdir.html"><i>chdir</i>()</a>, <a href=
"../functions/chown.html"><i>chown</i>()</a>, <a href="../functions/close.html"><i>close</i>()</a>, <a href=
"../functions/crypt.html"><i>crypt</i>()</a>, <a href="../functions/ctermid.html"><i>ctermid</i>()</a>, <a href=
"../functions/dup.html"><i>dup</i>()</a>, <a href="../functions/encrypt.html"><i>encrypt</i>()</a>, <i>environ</i>, <i>exec</i>, <a
href="../functions/exit.html"><i>exit</i>()</a>, <a href="../functions/fchdir.html"><i>fchdir</i>()</a>, <a href=
"../functions/fchown.html"><i>fchown</i>()</a>, <a href="../functions/fcntl.html"><i>fcntl</i>()</a>, <a href=
"../functions/fork.html"><i>fork</i>()</a>, <a href="../functions/fpathconf.html"><i>fpathconf</i>()</a>, <a href=
"../functions/fsync.html"><i>fsync</i>()</a>, <a href="../functions/ftruncate.html"><i>ftruncate</i>()</a>, <a href=
"../functions/getcwd.html"><i>getcwd</i>()</a>, <a href="../functions/getegid.html"><i>getegid</i>()</a>, <a href=
"../functions/geteuid.html"><i>geteuid</i>()</a>, <a href="../functions/getgid.html"><i>getgid</i>()</a>, <a href=
"../functions/getgroups.html"><i>getgroups</i>()</a>, <a href="../functions/gethostid.html"><i>gethostid</i>()</a>, <a href=
"../functions/gethostname.html"><i>gethostname</i>()</a>, <a href="../functions/getlogin.html"><i>getlogin</i>()</a>, <a href=
"../functions/getpgid.html"><i>getpgid</i>()</a>, <a href="../functions/getpgrp.html"><i>getpgrp</i>()</a>, <a href=
"../functions/getpid.html"><i>getpid</i>()</a>, <a href="../functions/getppid.html"><i>getppid</i>()</a>, <a href=
"../functions/getsid.html"><i>getsid</i>()</a>, <a href="../functions/getuid.html"><i>getuid</i>()</a>, <a href=
"../functions/isatty.html"><i>isatty</i>()</a>, <a href="../functions/lchown.html"><i>lchown</i>()</a>, <a href=
"../functions/link.html"><i>link</i>()</a>, <a href="../functions/lockf.html"><i>lockf</i>()</a>, <a href=
"../functions/lseek.html"><i>lseek</i>()</a>, <a href="../functions/nice.html"><i>nice</i>()</a>, <a href=
"../functions/pathconf.html"><i>pathconf</i>()</a>, <a href="../functions/pause.html"><i>pause</i>()</a>, <a href=
"../functions/pipe.html"><i>pipe</i>()</a>, <a href="../functions/read.html"><i>read</i>()</a>, <a href=
"../functions/readlink.html"><i>readlink</i>()</a>, <a href="../functions/rmdir.html"><i>rmdir</i>()</a>, <a href=
"../functions/setgid.html"><i>setgid</i>()</a>, <a href="../functions/setpgid.html"><i>setpgid</i>()</a>, <a href=
"../functions/setpgrp.html"><i>setpgrp</i>()</a>, <a href="../functions/setregid.html"><i>setregid</i>()</a>, <a href=
"../functions/setreuid.html"><i>setreuid</i>()</a>, <a href="../functions/setsid.html"><i>setsid</i>()</a>, <a href=
"../functions/setuid.html"><i>setuid</i>()</a>, <a href="../functions/sleep.html"><i>sleep</i>()</a>, <a href=
"../functions/swab.html"><i>swab</i>()</a>, <a href="../functions/symlink.html"><i>symlink</i>()</a>, <a href=
"../functions/sync.html"><i>sync</i>()</a>, <a href="../functions/sysconf.html"><i>sysconf</i>()</a>, <a href=
"../functions/tcgetpgrp.html"><i>tcgetpgrp</i>()</a>, <a href="../functions/tcsetpgrp.html"><i>tcsetpgrp</i>()</a>, <a href=
"../functions/truncate.html"><i>truncate</i>()</a>, <a href="../functions/ttyname.html"><i>ttyname</i>()</a>, <a href=
"../functions/ualarm.html"><i>ualarm</i>()</a>, <a href="../functions/unlink.html"><i>unlink</i>()</a>, <a href=
"../functions/usleep.html"><i>usleep</i>()</a>, <a href="../functions/vfork.html"><i>vfork</i>()</a>, <a href=
"../functions/write.html"><i>write</i>()</a></p>
</blockquote>
<h4><a name="tag_13_80_08"></a>CHANGE HISTORY</h4>
<blockquote>
<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
</blockquote>
<h4><a name="tag_13_80_09"></a>Issue 5</h4>
<blockquote>
<p>The DESCRIPTION is updated for alignment with the POSIX Realtime Extension and the POSIX Threads Extension.</p>
<p>The symbolic constants _XOPEN_REALTIME and _XOPEN_REALTIME_THREADS are added. _POSIX2_C_BIND, _XOPEN_ENH_I18N, and _XOPEN_SHM
must now be set to a value other than -1 by a conforming implementation.</p>
<p>Large File System extensions are added.</p>
<p>The type of the argument to <i>sbrk</i>() is changed from <b>int</b> to <b>intptr_t</b>.</p>
<p>_XBS_ constants are added to the list of constants for Options and Option Groups, to the list of constants for the <a href=
"../functions/confstr.html"><i>confstr</i>()</a> function, and to the list of constants to the <a href=
"../functions/sysconf.html"><i>sysconf</i>()</a> function. These are all marked EX.</p>
</blockquote>
<h4><a name="tag_13_80_10"></a>Issue 6</h4>
<blockquote>
<p>_POSIX2_C_VERSION is removed.</p>
<p>The Open Group Corrigendum U026/4 is applied, adding the prototype for <a href=
"../functions/fdatasync.html"><i>fdatasync</i>()</a>.</p>
<p>The Open Group Corrigendum U026/1 is applied, adding the symbols _SC_XOPEN_LEGACY, _SC_XOPEN_REALTIME, and
_SC_XOPEN_REALTIME_THREADS.</p>
<p>The symbols _XOPEN_STREAMS and _SC_XOPEN_STREAMS are added to support the XSI STREAMS Option Group.</p>
<p>Text in the DESCRIPTION relating to conformance requirements is moved elsewhere in IEEE&nbsp;Std&nbsp;1003.1-2001.</p>
<p>The legacy symbol _SC_PASS_MAX is removed.</p>
<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>
<ul>
<li>
<p>The _CS_POSIX_* and _CS_XBS5_* constants are added for the <a href="../functions/confstr.html"><i>confstr</i>()</a>
function.</p>
</li>
<li>
<p>The _SC_XBS5_* constants are added for the <a href="../functions/sysconf.html"><i>sysconf</i>()</a> function.</p>
</li>
<li>
<p>The symbolic constants F_ULOCK, F_LOCK, F_TLOCK, and F_TEST are added.</p>
</li>
<li>
<p>The <b>uid_t</b>, <b>gid_t</b>, <b>off_t</b>, <b>pid_t</b>, and <b>useconds_t</b> types are mandated.</p>
</li>
</ul>
<p>The <a href="../functions/gethostname.html"><i>gethostname</i>()</a> prototype is added for sockets.</p>
<p>A new section is added for System-Wide Options.</p>
<p>Function prototypes for <a href="../functions/setegid.html"><i>setegid</i>()</a> and <a href=
"../functions/seteuid.html"><i>seteuid</i>()</a> are added.</p>
<p>Option symbolic constants are added for _POSIX_ADVISORY_INFO, _POSIX_CPUTIME, _POSIX_SPAWN, _POSIX_SPORADIC_SERVER,
_POSIX_THREAD_CPUTIME, _POSIX_THREAD_SPORADIC_SERVER, and _POSIX_TIMEOUTS, and <a href=
"../functions/pathconf.html"><i>pathconf</i>()</a> variables are added for _PC_ALLOC_SIZE_MIN, _PC_REC_INCR_XFER_SIZE,
_PC_REC_MAX_XFER_SIZE, _PC_REC_MIN_XFER_SIZE, and _PC_REC_XFER_ALIGN for alignment with IEEE&nbsp;Std&nbsp;1003.1d-1999.</p>
<p>The following are added for alignment with IEEE&nbsp;Std&nbsp;1003.1j-2000:</p>
<ul>
<li>
<p>Option symbolic constants _POSIX_BARRIERS, _POSIX_CLOCK_SELECTION, _POSIX_MONOTONIC_CLOCK, _POSIX_READER_WRITER_LOCKS,
_POSIX_SPIN_LOCKS, and _POSIX_TYPED_MEMORY_OBJECTS</p>
</li>
<li>
<p><a href="../functions/sysconf.html"><i>sysconf</i>()</a> variables _SC_BARRIERS, _SC_CLOCK_SELECTION, _SC_MONOTONIC_CLOCK,
_SC_READER_WRITER_LOCKS, _SC_SPIN_LOCKS, and _SC_TYPED_MEMORY_OBJECTS</p>
</li>
</ul>
<p>The _SC_XBS5 macros associated with the ISO/IEC&nbsp;9899:1990 standard are marked LEGACY, and new equivalent _SC_V6 macros
associated with the ISO/IEC&nbsp;9899:1999 standard are introduced.</p>
<p>The <a href="../functions/getwd.html"><i>getwd</i>()</a> function is marked LEGACY.</p>
<p>The <b>restrict</b> keyword is added to the prototypes for <a href="../functions/readlink.html"><i>readlink</i>()</a> and <a
href="../functions/swab.html"><i>swab</i>()</a>.</p>
<p>Constants for options are now harmonized, so when supported they take the year of approval of IEEE&nbsp;Std&nbsp;1003.1-2001 as
the value.</p>
<p>The following are added for alignment with IEEE&nbsp;Std&nbsp;1003.1q-2000:</p>
<ul>
<li>
<p>Optional symbolic constants _POSIX_TRACE, _POSIX_TRACE_EVENT_FILTER, _POSIX_TRACE_LOG, and _POSIX_TRACE_INHERIT</p>
</li>
<li>
<p>The <a href="../functions/sysconf.html"><i>sysconf</i>()</a> symbolic constants _SC_TRACE, _SC_TRACE_EVENT_FILTER,
_SC_TRACE_LOG, and _SC_TRACE_INHERIT.</p>
</li>
</ul>
<p>The <i>brk</i>() and <i>sbrk</i>() legacy functions are removed.</p>
<p>The Open Group Base Resolution bwg2001-006 is applied, which reworks the XSI versioning information.</p>
<p>The Open Group Base Resolution bwg2001-008 is applied, changing the <i>namelen</i> parameter for <a href=
"../functions/gethostname.html"><i>gethostname</i>()</a> from <b>socklen_t</b> to <b>size_t</b>.</p>
</blockquote>
<div class="box"><em>End of informative text.</em></div>
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