201 lines
7.5 KiB
HTML
201 lines
7.5 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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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>time</title>
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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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<basefont size="3"> <a name="time"></a> <a name="tag_03_775"></a><!-- time -->
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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_775_01"></a>NAME</h4>
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<blockquote>time - get time</blockquote>
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<h4><a name="tag_03_775_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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time_t time(time_t *</tt><i>tloc</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_775_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>time</i>() function shall return the value of time <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src=
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"../images/opt-start.gif" alt="[Option Start]" border="0"> in seconds since the Epoch. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></p>
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<p>The <i>tloc</i> argument points to an area where the return value is also stored. If <i>tloc</i> is a null pointer, no value is
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stored.</p>
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</blockquote>
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<h4><a name="tag_03_775_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>time</i>() shall return the value of time. Otherwise, (<b>time_t</b>)-1 shall be returned.</p>
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</blockquote>
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<h4><a name="tag_03_775_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_775_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_775_06_01"></a>Getting the Current Time</h5>
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<p>The following example uses the <i>time</i>() function to calculate the time elapsed, in seconds, since the Epoch, <a href=
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"../functions/localtime.html"><i>localtime</i>()</a> to convert that value to a broken-down time, and <a href=
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"../functions/asctime.html"><i>asctime</i>()</a> to convert the broken-down time values into a printable string.</p>
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<pre>
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<tt>#include <stdio.h>
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#include <time.h>
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<br>
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int main(void)
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{
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time_t result;
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<br>
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result = time(NULL);
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printf("%s%ju secs since the Epoch\n",
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asctime(localtime(&result)),
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(uintmax_t)result);
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return(0);
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}
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</tt>
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</pre>
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<p>This example writes the current time to <i>stdout</i> in a form like this:</p>
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<pre>
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<tt>Wed Jun 26 10:32:15 1996
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835810335 secs since the Epoch
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</tt>
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</pre>
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<h5><a name="tag_03_775_06_02"></a>Timing an Event</h5>
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<p>The following example gets the current time, prints it out in the user's format, and prints the number of minutes to an event
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being timed.</p>
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<pre>
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<tt>#include <time.h>
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#include <stdio.h>
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...
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time_t now;
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int minutes_to_event;
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...
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time(&now);
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minutes_to_event = ...;
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printf("The time is ");
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puts(asctime(localtime(&now)));
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printf("There are %d minutes to the event.\n",
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minutes_to_event);
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...
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_775_07"></a>APPLICATION USAGE</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_775_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>time</i>() function returns a value in seconds (type <b>time_t</b>) while <a href=
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"../functions/times.html"><i>times</i>()</a> returns a set of values in clock ticks (type <b>clock_t</b>). Some historical
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implementations, such as 4.3 BSD, have mechanisms capable of returning more precise times (see below). A generalized timing scheme
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to unify these various timing mechanisms has been proposed but not adopted.</p>
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<p>Implementations in which <b>time_t</b> is a 32-bit signed integer (many historical implementations) fail in the year 2038.
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IEEE Std 1003.1-2001 does not address this problem. However, the use of the <b>time_t</b> type is mandated in order to
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ease the eventual fix.</p>
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<p>The use of the <a href="../basedefs/time.h.html"><i><time.h></i></a> header instead of <a href=
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"../basedefs/sys/types.h.html"><i><sys/types.h></i></a> allows compatibility with the ISO C standard.</p>
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<p>Many historical implementations (including Version 7) and the 1984 /usr/group standard use <b>long</b> instead of <b>time_t</b>.
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This volume of IEEE Std 1003.1-2001 uses the latter type in order to agree with the ISO C standard.</p>
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<p>4.3 BSD includes <i>time</i>() only as an alternate function to the more flexible <a href=
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"../functions/gettimeofday.html"><i>gettimeofday</i>()</a> function.</p>
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</blockquote>
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<h4><a name="tag_03_775_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>In a future version of this volume of IEEE Std 1003.1-2001, <b>time_t</b> is likely to be required to be capable of
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representing times far in the future. Whether this will be mandated as a 64-bit type or a requirement that a specific date in the
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future be representable (for example, 10000 AD) is not yet determined. Systems purchased after the approval of this volume of
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IEEE Std 1003.1-2001 should be evaluated to determine whether their lifetime will extend past 2038.</p>
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</blockquote>
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<h4><a name="tag_03_775_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="clock.html"><i>clock</i>()</a> , <a href="ctime.html"><i>ctime</i>()</a>
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, <a href="difftime.html"><i>difftime</i>()</a> , <a href="gettimeofday.html"><i>gettimeofday</i>()</a> , <a href=
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"gmtime.html"><i>gmtime</i>()</a> , <a href="localtime.html"><i>localtime</i>()</a> , <a href="mktime.html"><i>mktime</i>()</a> ,
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<a href="strftime.html"><i>strftime</i>()</a> , <a href="strptime.html"><i>strptime</i>()</a> , <a href=
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"utime.html"><i>utime</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/time.h.html"><i><time.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_775_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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<h4><a name="tag_03_775_12"></a>Issue 6</h4>
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<blockquote>
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<p>Extensions beyond the ISO C standard are marked.</p>
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<p>The EXAMPLES, RATIONALE, and FUTURE DIRECTIONS sections are added.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<center><font size="2"><!--footer start-->
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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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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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