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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>sem_getvalue</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_008_288"> </a>NAME</h4><blockquote>sem_getvalue - get the value of a semaphore(<b>REALTIME</b>)</blockquote><h4><a name = "tag_000_008_289"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="semaphore.h.html">semaphore.h</a>>int sem_getvalue(sem_t *<i>sem</i>, int *<i>sval</i>);</code></pre></blockquote><h4><a name = "tag_000_008_290"> </a>DESCRIPTION</h4><blockquote>The<i>sem_getvalue()</i>function updates the location referenced by the<i>sval</i>argument to have the value of the semaphore referenced by<i>sem</i>without affecting the state of the semaphore.The updated value represents an actual semaphore valuethat occurred at some unspecified time during the call,but it need not be the actual value of the semaphorewhen it is returned to the calling process.<p>If<i>sem</i>is locked, then the value returned by<i>sem_getvalue()</i>is either zero or a negative numberwhose absolute value represents the number of processes waitingfor the semaphore at some unspecified time during the call.</blockquote><h4><a name = "tag_000_008_291"> </a>RETURN VALUE</h4><blockquote>Upon successful completion, the function returns a value of zero.Otherwise, the function returns a value of -1 and sets<i>errno</i>to indicate the error.</blockquote><h4><a name = "tag_000_008_292"> </a>ERRORS</h4><blockquote>The <i>sem_getvalue()</i>function will fail if:<dl compact><dt>[EINVAL]<dd>The<i>sem</i>argument does not refer to a valid semaphore.<dt>[ENOSYS]<dd>The function<i>sem_getvalue()</i>is not supported by this implementation.</dl></blockquote><h4><a name = "tag_000_008_293"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_008_294"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_008_295"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_008_296"> </a>SEE ALSO</h4><blockquote><i><a href="semctl.html">semctl()</a></i>,<i><a href="semget.html">semget()</a></i>,<i><a href="semop.html">semop()</a></i>,<i><a href="sem_post.html">sem_post()</a></i>,<i><a href="sem_trywait.html">sem_trywait()</a></i>,<i><a href="sem_wait.html">sem_wait()</a></i>,<i><a href="semaphore.h.html"><semaphore.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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