272 lines
7.1 KiB
HTML
272 lines
7.1 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>alarm()--Set Schedule for Alarm Signal</title>
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Begin Header Records ========================================== -->
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<!-- UNIX5 SCRIPT J converted by B2H R4.1 (346) (CMS) by V2KEA304 -->
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<!-- at RCHVMW2 on 17 Feb 1999 at 11:05:09 -->
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<!--End Header Records -->
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<!-- Edited by Kersten Feb 02 -->
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<!-- This file has undergone html cleanup May 2002 by JET -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<a name="Top_Of_Page"></a>
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<!-- Java sync-link -->
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<script type="text/javascript" language="Javascript" src="../rzahg/synch.js">
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</script>
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<h2>alarm()--Set Schedule for Alarm Signal</h2>
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<div class="box" style="width: 60%;">
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<br>
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Syntax<br>
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<pre>
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#include <unistd.h>
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unsigned int alarm( unsigned int <em>seconds</em> );
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</pre>
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<br>
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Service Program Name: QPOSSRV1<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>alarm()</strong> function generates a SIGALRM signal after the
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number of seconds specified by the <em>seconds</em> parameter have elapsed. The
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delivery of the SIGALRM signal is directed at the calling process.</p>
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<p><em>seconds</em> is the number of real seconds to elapse before the SIGALRM
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is generated. Because of processor delays, the SIGALRM may be generated
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slightly later than this specified time. If <em>seconds</em> is zero, any
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previously set alarm request is canceled.</p>
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<p>Only one such alarm can be active at a time for the process. If a new alarm
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time is set, any previous alarm is canceled.</p>
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<br>
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<!-- Please NOTE: DO NOT DELETE THIS SECTION if this API has no authorities and locks. -->
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<!-- Instead, use the commented out coding below to indicate NONE. -->
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<h3>Authorities and Locks</h3>
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<!-- Use this if there are no authorities and locks. -->
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<p>None.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong><em>seconds</em></strong></dt>
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<dd>(Input) The number of real seconds to elapse before generating the
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signal.</dd>
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</dl>
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<h3>Return Value</h3>
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<table cellpadding="5">
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<!-- cols="10 90" -->
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<tr>
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<td align="left" valign="top"><em>value</em></td>
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<td align="left" valign="top"><strong>alarm()</strong> was successful. The
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value returned is one of the following:
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<ul>
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<li>A nonzero value that is the number of real seconds until the previous
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<strong>alarm()</strong> request would have generated a SIGALRM signal.</li>
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<li>A value of zero if there was no previous <strong>alarm()</strong> request
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with time remaining.</li>
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</ul>
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</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>-1</em></td>
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<td align="left" valign="top"><strong>alarm()</strong> was not successful. The
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<em>errno</em> variable is set to indicate the error.</td>
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</tr>
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</table>
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<h3>Error Conditions</h3>
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<p>If <strong>alarm()</strong> is not successful, <em>errno</em> usually
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indicates the following error. Under some conditions, <em>errno</em> could
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indicate an error other than that listed here.</p>
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<dl>
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<dt><em>[ENOTSIGINIT]</em></dt>
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<dd>
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<p>Process not enabled for signals.</p>
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<p>An attempt was made to call a signal function under one of the following
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conditions:</p>
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<ul>
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<li>The signal function is being called for a process that is not enabled for
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asynchronous signals.</li>
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<li>The signal function is being called when the system signal controls have
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not been initialized.</li>
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</ul>
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<br>
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</dd>
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</dl>
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<h3>Usage Notes</h3>
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<p>The <strong>alarm()</strong> function enables a process for signals if the
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process is not already enabled for signals. For details, see <a href=
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"sigesig.htm">Qp0sEnableSignals()--Enable Process for Signals</a>. If the
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system has not been enabled for signals, <strong>alarm()</strong> is not
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successful, and an [ENOTSIGINIT] error is returned.</p>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li>The <<strong>signal.h</strong>> file (see <a href="unix13.htm">Header
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Files for UNIX-Type Functions</a>)<br>
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<br>
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</li>
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<li>The <<strong>unistd.h</strong>> file<br>
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<br>
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</li>
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<li><a href="sigpause.htm">pause()</a>--Suspend Process Until Signal
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Received<br>
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<br>
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</li>
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<li><a href="sigdsig.htm">Qp0sDisableSignals()</a>--Disable Process for
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Signals<br>
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<br>
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</li>
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<li><a href="sigesig.htm">Qp0sEnableSignals()</a>--Enable Process for
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Signals<br>
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<br>
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</li>
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<li><a href="setitime.htm">setitimer()</a>--Set Value for Interval Timer<br>
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<br>
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</li>
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<li><a href="sigactn.htm">sigaction()</a>--Examine and Change Signal Action<br>
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<br>
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</li>
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<li><a href="sigsusp.htm">sigsuspend()</a>--Wait for Signal<br>
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<br>
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</li>
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<li><a href="sigsleep.htm">sleep()</a>--Suspend Processing for Interval of
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Time<br>
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<br>
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</li>
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<li><a href="usleep.htm">usleep()</a>--Suspend Processing for Interval of
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Time</li>
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</ul>
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<br>
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<h3>Example</h3>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<p>The following example generates a SIGALRM signal using the <strong>
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alarm()</strong> function:</p>
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<pre>
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#include <signal.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <time.h>
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#include <errno.h>
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#define LOOP_LIMIT 1E6
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volatile int sigcount=0;
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void catcher( int sig ) {
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printf( "Signal catcher called for signal %d\n", sig );
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sigcount = 1;
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}
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int main( int argc, char *argv[] ) {
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struct sigaction sact;
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volatile double count;
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time_t t;
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sigemptyset( &sact.sa_mask );
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sact.sa_flags = 0;
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sact.sa_handler = catcher;
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sigaction( SIGALRM, &sact, NULL );
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alarm(5); /* timer will pop in five seconds */
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time( &t );
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printf( "Before loop, time is %s", ctime(&t) );
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for( count=0; ((count<LOOP_LIMIT) && (sigcount==0)); count++ );
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time( &t );
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printf( "After loop, time is %s\n", ctime(&t) );
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if( sigcount == 0 )
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printf( "The signal catcher never gained control\n" );
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else
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printf( "The signal catcher gained control\n" );
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printf( "The value of count is %.0f\n", count );
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return( 0 );
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}
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</pre>
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<br>
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<h3>Output:</h3>
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<pre>
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Before loop, time is Sun Jan 22 10:14:00 1995
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Signal catcher called for signal 14
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After loop, time is Sun Jan 22 10:14:05 1995
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The signal catcher gained control
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The value of count is 290032
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</pre>
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<br>
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<hr>
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API introduced: V3R6
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
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"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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