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
IEEE Std 1003.1-2001 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 IEEE Std 1003.1-2001, Section 4.14, 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 reentrant. A function that is not
required to be reentrant is not required to 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.
ERRORS
The gmtime() function 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 IEEE Std 1003.1-2001, <time.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .