mirror of https://github.com/mkerrisk/man-pages
87 lines
2.1 KiB
Groff
87 lines
2.1 KiB
Groff
.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH TIMEGM 3 2001-12-26 "GNU" "Linux Programmer's Manual"
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.SH NAME
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timegm, timelocal \- inverses for gmtime and localtime
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.SH SYNOPSIS
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.nf
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.B #include <time.h>
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.sp
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.BI "time_t timelocal (struct tm *" tm );
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.sp
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.BI "time_t timegm (struct tm *" tm );
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.SH DESCRIPTION
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The functions
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.B timelocal()
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and
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.B timegm()
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are the inverses to
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.BR localtime (3)
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and
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.BR gmtime (3).
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.SH NOTES
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These functions are GNU extensions.
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The
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.B timelocal()
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function is equivalent to the POSIX standard function
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.BR mktime (3).
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There is no reason to ever use it.
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.LP
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For a portable version of
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.BR timegm() ,
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set the
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.B TZ
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environment variable to UTC, call
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.B mktime()
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and restore the value of
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.BR TZ .
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Something like
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.RS
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.nf
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#include <time.h>
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#include <stdlib.h>
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time_t my_timegm (struct tm *tm) {
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time_t ret;
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char *tz;
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tz = getenv("TZ");
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setenv("TZ", "", 1);
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tzset();
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ret = mktime(tm);
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if (tz)
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setenv("TZ", tz, 1);
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else
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unsetenv("TZ");
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tzset();
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return ret;
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}
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.fi
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.RE
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.SH "SEE ALSO"
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.BR gmtime (3),
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.BR localtime (3),
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.BR mktime (3),
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.BR tzset (3)
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