206 lines
5.0 KiB
HTML
206 lines
5.0 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of TIME</TITLE>
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</HEAD><BODY>
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<H1>TIME</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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time - get time in seconds
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/time.h">time.h</A>></B>
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<P>
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<B>time_t time(time_t *</B><I>tloc</I><B>);</B>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>time</B>()
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returns the time as the number of seconds since the
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Epoch, 1970-01-01 00:00:00 +0000 (UTC).
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<P>
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If
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<I>tloc</I>
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is non-NULL,
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the return value is also stored in the memory pointed to by
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<I>tloc</I>.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, the value of time in seconds since the Epoch is returned.
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On error, <I>((time_t) -1)</I> is returned, and <I>errno</I> is set
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appropriately.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="1"><B>EFAULT</B>
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<DD>
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<I>tloc</I>
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points outside your accessible address space (but see BUGS).
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<DT id="2"><DD>
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On systems where the C library
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<B>time</B>()
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wrapper function invokes an implementation provided by the
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<B><A HREF="/cgi-bin/man/man2html?7+vdso">vdso</A></B>(7)
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(so that there is no trap into the kernel),
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an invalid address may instead trigger a
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<B>SIGSEGV</B>
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signal.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>CONFORMING TO</H2>
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SVr4, 4.3BSD, C89, C99, POSIX.1-2001.
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POSIX does not specify any error conditions.
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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POSIX.1 defines
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<I>seconds since the Epoch</I>
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using a formula that approximates the number of seconds between a
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specified time and the Epoch.
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This formula takes account of the facts that
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all years that are evenly divisible by 4 are leap years,
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but years that are evenly divisible by 100 are not leap years
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unless they are also evenly divisible by 400,
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in which case they are leap years.
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This value is not the same as the actual number of seconds between the time
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and the Epoch, because of leap seconds and because system clocks are not
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required to be synchronized to a standard reference.
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The intention is that the interpretation of seconds since the Epoch values be
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consistent; see POSIX.1-2008 Rationale A.4.15 for further rationale.
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<P>
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On Linux, a call to
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<B>time</B>()
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with
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<I>tloc</I>
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specified as NULL cannot fail with the error
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<B>EOVERFLOW</B>,
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even on ABIs where
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<I>time_t</I>
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is a signed 32-bit integer and the clock ticks past the time 2**31
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(2038-01-19 03:14:08 UTC, ignoring leap seconds).
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(POSIX.1 permits, but does not require, the
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<B>EOVERFLOW</B>
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error in the case where the seconds since the Epoch will not fit in
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<I>time_t</I>.)
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Instead, the behavior on Linux is undefined when the system time is out of the
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<I>time_t</I>
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range.
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Applications intended to run after 2038 should use ABIs with
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<I>time_t</I>
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wider than 32 bits.
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<A NAME="lbAI"> </A>
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<H2>BUGS</H2>
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Error returns from this system call are indistinguishable from
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successful reports that the time is a few seconds
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<I>before</I>
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the Epoch, so the C library wrapper function never sets
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<I>errno</I>
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as a result of this call.
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<P>
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The
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<I>tloc</I>
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argument is obsolescent and should always be NULL in new code.
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When
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<I>tloc</I>
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is NULL, the call cannot fail.
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<A NAME="lbAJ"> </A>
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<H3>C library/kernel differences</H3>
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On some architectures, an implementation of
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<B>time</B>()
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is provided in the
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<B><A HREF="/cgi-bin/man/man2html?7+vdso">vdso</A></B>(7).
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<A NAME="lbAK"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+date">date</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?2+gettimeofday">gettimeofday</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?3+ctime">ctime</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+ftime">ftime</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+time">time</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+vdso">vdso</A></B>(7)
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<A NAME="lbAL"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="3"><A HREF="#lbAB">NAME</A><DD>
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<DT id="4"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="5"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="6"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="7"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="8"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="9"><A HREF="#lbAH">NOTES</A><DD>
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<DT id="10"><A HREF="#lbAI">BUGS</A><DD>
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<DL>
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<DT id="11"><A HREF="#lbAJ">C library/kernel differences</A><DD>
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</DL>
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<DT id="12"><A HREF="#lbAK">SEE ALSO</A><DD>
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<DT id="13"><A HREF="#lbAL">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:35 GMT, March 31, 2021
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</BODY>
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</HTML>
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