GMTIME(3)                  POSIX Programmer's Manual                 GMTIME(3)



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

NAME
       gmtime, gmtime_r -- convert a time value to a broken-down UTC time

SYNOPSIS
       #include <time.h>

       struct tm *gmtime(const time_t *timer);
       struct tm *gmtime_r(const time_t *restrict timer,
           struct tm *restrict result);

DESCRIPTION
       For gmtime(): The functionality described on this reference page is
       aligned with the ISO C standard. Any conflict between the requirements
       described here and the ISO C standard is unintentional. This volume of
       POSIX.1-2017 defers to the ISO C standard.

       The gmtime() function shall convert the time in seconds since the Epoch
       pointed to by timer into a broken-down time, expressed as Coordinated
       Universal Time (UTC).

       The relationship between a time in seconds since the Epoch used as an
       argument to gmtime() and the tm structure (defined in the <time.h>
       header) is that the result shall be as specified in the expression
       given in the definition of seconds since the Epoch (see the Base
       Definitions volume of POSIX.1-2017, Section 4.16, Seconds Since the
       Epoch), where the names in the structure and in the expression
       correspond.

       The same relationship shall apply for gmtime___r().

       The gmtime() function need not be thread-safe.

       The asctime(), ctime(), gmtime(), and localtime() functions shall
       return values in one of two static objects: a broken-down time
       structure and an array of type char.  Execution of any of the functions
       may overwrite the information returned in either of these objects by
       any of the other functions.

       The gmtime___r() function shall convert the time in seconds since the
       Epoch pointed to by timer into a broken-down time expressed as
       Coordinated Universal Time (UTC).  The broken-down time is stored in
       the structure referred to by result.  The gmtime___r() function shall
       also return the address of the same structure.

RETURN VALUE
       Upon successful completion, the gmtime() function shall return a
       pointer to a struct tm.  If an error is detected, gmtime() shall return
       a null pointer and set errno to indicate the error.

       Upon successful completion, gmtime___r() shall return the address of the
       structure pointed to by the argument result.  If an error is detected,
       gmtime___r() shall return a null pointer and set errno to indicate the
       error.

ERRORS
       The gmtime() and gmtime___r() functions shall fail if:

       EOVERFLOW
              The result cannot be represented.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The gmtime___r() function is thread-safe and returns values in a user-
       supplied buffer instead of possibly using a static data area that may
       be overwritten by each call.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       asctime(), clock(), ctime(), difftime(), localtime(), mktime(),
       strftime(), strptime(), time(), utime()

       The Base Definitions volume of POSIX.1-2017, Section 4.16, Seconds
       Since the Epoch, <time.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                            GMTIME(3)
