This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
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.1‐2008 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.1‐2008, Section 4.15, Seconds Since theEpoch), where the names in the structure and in the expression
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.
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.
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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
IEEE/The Open Group 2013 GMTIME(3P)