1GMTIME(3P)                 POSIX Programmer's Manual                GMTIME(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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11

NAME

13       gmtime, gmtime_r — convert a time value to a broken-down UTC time
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SYNOPSIS

16       #include <time.h>
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18       struct tm *gmtime(const time_t *timer);
19       struct tm *gmtime_r(const time_t *restrict timer,
20           struct tm *restrict result);
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DESCRIPTION

23       For gmtime(): The functionality described on  this  reference  page  is
24       aligned  with the ISO C standard. Any conflict between the requirements
25       described here and the ISO C standard is unintentional. This volume  of
26       POSIX.1‐2008 defers to the ISO C standard.
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28       The gmtime() function shall convert the time in seconds since the Epoch
29       pointed to by timer into a broken-down time, expressed  as  Coordinated
30       Universal Time (UTC).
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32       The  relationship  between a time in seconds since the Epoch used as an
33       argument to gmtime() and the tm  structure  (defined  in  the  <time.h>
34       header)  is  that  the  result  shall be as specified in the expression
35       given in the definition of seconds since the Epoch (see the Base  Defi‐
36       nitions volume of POSIX.1‐2008, Section 4.15, Seconds Since the Epoch),
37       where the names in the structure and in the expression correspond.
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39       The same relationship shall apply for gmtime_r().
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41       The gmtime() function need not be thread-safe.
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43       The asctime(),  ctime(),  gmtime(),  and  localtime()  functions  shall
44       return  values  in one of two static objects: a broken-down time struc‐
45       ture and an array of type char.  Execution of any of the functions  may
46       overwrite the information returned in either of these objects by any of
47       the other functions.
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49       The gmtime_r() function shall convert the time  in  seconds  since  the
50       Epoch  pointed to by timer into a broken-down time expressed as Coordi‐
51       nated Universal Time (UTC).  The broken-down  time  is  stored  in  the
52       structure  referred  to  by result.  The gmtime_r() function shall also
53       return the address of the same structure.
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RETURN VALUE

56       Upon successful  completion,  the  gmtime()  function  shall  return  a
57       pointer to a struct tm.  If an error is detected, gmtime() shall return
58       a null pointer and set errno to indicate the error.
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60       Upon successful completion, gmtime_r() shall return the address of  the
61       structure  pointed to by the argument result.  If an error is detected,
62       gmtime_r() shall return a null pointer and set errno  to  indicate  the
63       error.
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ERRORS

66       The gmtime() and gmtime_r() functions shall fail if:
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68       EOVERFLOW
69              The result cannot be represented.
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71       The following sections are informative.
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EXAMPLES

74       None.
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APPLICATION USAGE

77       The  gmtime_r()  function  is thread-safe and returns values in a user-
78       supplied buffer instead of possibly using a static data area  that  may
79       be overwritten by each call.
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RATIONALE

82       None.
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FUTURE DIRECTIONS

85       None.
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SEE ALSO

88       asctime(),  clock(),  ctime(), difftime(), localtime(), mktime(), strf‐
89       time(), strptime(), time(), utime()
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91       The Base Definitions volume  of  POSIX.1‐2008,  Section  4.15,  Seconds
92       Since the Epoch, <time.h>
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95       Portions  of  this text are reprinted and reproduced in electronic form
96       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
97       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
98       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
99       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
100       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  In  the
101       event of any discrepancy between this version and the original IEEE and
102       The Open Group Standard, the original IEEE and The Open Group  Standard
103       is  the  referee document. The original Standard can be obtained online
104       at http://www.unix.org/online.html .
105
106       Any typographical or formatting errors that appear  in  this  page  are
107       most likely to have been introduced during the conversion of the source
108       files to man page format. To report such errors,  see  https://www.ker‐
109       nel.org/doc/man-pages/reporting_bugs.html .
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113IEEE/The Open Group                  2013                           GMTIME(3P)
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