man3/timegm.3

   1 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .TH TIMEGM 3 2021-03-22 "Linux man-pages (unreleased)"
   6 .SH NAME
   7 timegm, timelocal \- inverses of gmtime and localtime
   8 .SH LIBRARY
   9 Standard C library
  10 .RI ( libc ", " \-lc )
  11 .SH SYNOPSIS
  12 .nf
  13 .B #include <time.h>
  14 .PP
  15 .BI "time_t timelocal(struct tm *" tm );
  16 .BI "time_t timegm(struct tm *" tm );
  17 .PP
  18 .fi
  19 .RS -4
  20 Feature Test Macro Requirements for glibc (see
  21 .BR feature_test_macros (7)):
  22 .RE
  23 .PP
  24 .BR timelocal (),
  25 .BR timegm ():
  26 .nf
  27     Since glibc 2.19:
  28         _DEFAULT_SOURCE
  29     Glibc 2.19 and earlier:
  30         _BSD_SOURCE || _SVID_SOURCE
  31 .fi
  32 .SH DESCRIPTION
  33 The functions
  34 .BR timelocal ()
  35 and
  36 .BR timegm ()
  37 are the inverses of
  38 .BR localtime (3)
  39 and
  40 .BR gmtime (3).
  41 Both functions take a broken-down time and convert it to calendar time
  42 (seconds since the Epoch, 1970-01-01 00:00:00 +0000, UTC).
  43 The difference between the two functions is that
  44 .BR timelocal ()
  45 takes the local timezone into account when doing the conversion, while
  46 .BR timegm ()
  47 takes the input value to be Coordinated Universal Time (UTC).
  48 .SH RETURN VALUE
  49 On success,
  50 these functions return the calendar time (seconds since the Epoch),
  51 expressed as a value of type
  52 .IR time_t .
  53 On error, they return the value
  54 .I (time_t)\ \-1
  55 and set
  56 .I errno
  57 to indicate the error.
  58 .SH ERRORS
  59 .TP
  60 .B EOVERFLOW
  61 The result cannot be represented.
  62 .SH ATTRIBUTES
  63 For an explanation of the terms used in this section, see
  64 .BR attributes (7).
  65 .ad l
  66 .nh
  67 .TS
  68 allbox;
  69 lbx lb lb
  70 l l l.
  71 Interface       Attribute       Value
  72 T{
  73 .BR timelocal (),
  74 .BR timegm ()
  75 T}      Thread safety   MT-Safe env locale
  76 .TE
  77 .hy
  78 .ad
  79 .sp 1
  80 .SH STANDARDS
  81 These functions are nonstandard GNU extensions
  82 that are also present on the BSDs.
  83 .SH NOTES
  84 The
  85 .BR timelocal ()
  86 function is equivalent to the POSIX standard function
  87 .BR mktime (3).
  88 There is no reason to ever use it.
  89 .SH SEE ALSO
  90 .BR gmtime (3),
  91 .BR localtime (3),
  92 .BR mktime (3),
  93 .BR tzset (3)