128 lines
5.0 KiB
HTML
128 lines
5.0 KiB
HTML
<!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 name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>clock</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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</script>
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<basefont size="3"> <a name="clock"></a> <a name="tag_03_74"></a><!-- clock -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_74_01"></a>NAME</h4>
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<blockquote>clock - report CPU time used</blockquote>
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<h4><a name="tag_03_74_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/time.h.html">time.h</a>><br>
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<br>
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clock_t clock(void);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_74_03"></a>DESCRIPTION</h4>
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<blockquote>
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<div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
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requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to
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the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div>
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<p>The <i>clock</i>() function shall return the implementation's best approximation to the processor time used by the process since
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the beginning of an implementation-defined era related only to the process invocation.</p>
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</blockquote>
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<h4><a name="tag_03_74_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>To determine the time in seconds, the value returned by <i>clock</i>() should be divided by the value of the macro
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CLOCKS_PER_SEC. <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> CLOCKS_PER_SEC is defined to be one million in <a href="../basedefs/time.h.html"><i><time.h></i></a>. <img
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src="../images/opt-end.gif" alt="[Option End]" border="0"> If the processor time used is not available or its value cannot be
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represented, the function shall return the value ( <b>clock_t</b>)-1.</p>
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</blockquote>
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<h4><a name="tag_03_74_05"></a>ERRORS</h4>
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<blockquote>
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<p>No errors are defined.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_74_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_74_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>In order to measure the time spent in a program, <i>clock</i>() should be called at the start of the program and its return
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value subtracted from the value returned by subsequent calls. The value returned by <i>clock</i>() is defined for compatibility
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across systems that have clocks with different resolutions. The resolution on any particular system need not be to microsecond
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accuracy.</p>
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<p>The value returned by <i>clock</i>() may wrap around on some implementations. For example, on a machine with 32-bit values for
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<b>clock_t</b>, it wraps after 2147 seconds or 36 minutes.</p>
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</blockquote>
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<h4><a name="tag_03_74_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_74_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_74_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="asctime.html"><i>asctime</i>()</a> , <a href="ctime.html"><i>ctime</i>()</a> , <a href=
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"difftime.html"><i>difftime</i>()</a> , <a href="gmtime.html"><i>gmtime</i>()</a> , <a href="localtime.html"><i>localtime</i>()</a>
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, <a href="mktime.html"><i>mktime</i>()</a> , <a href="strftime.html"><i>strftime</i>()</a> , <a href=
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"strptime.html"><i>strptime</i>()</a> , <a href="time.html"><i>time</i>()</a> , <a href="utime.html"><i>utime</i>()</a> , the Base
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Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/time.h.html"><i><time.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_74_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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