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);
[TSF] struct tm *gmtime_r(const time_t *restrict timer,
struct tm *restrict result);
DESCRIPTION
For gmtime (): [CX] 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 (“POSIX.1”) 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).
[CX] 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 (“POSIX.1”),
xbd_chap04(7)), where the names in the structure and in
the expression correspond.
[TSF] The same relationship shall apply for gmtime_r ().
[CX] 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(3),
ctime(3), gmtime (), and
localtime(3) 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.
[TSF] 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
The gmtime () function shall return a
pointer to a struct tm.
[TSF] Upon successful completion, gmtime_r () shall return the address of the structure pointed to by the argument result. If an error is detected, or UTC is not available, gmtime_r () shall return a null pointer.
ERRORS
No errors are defined.
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(3) , clock(3) , ctime(3) , difftime(3) , localtime(3) , mktime(3) , strftime(3) , strptime(3) , time(3) , utime(3) , the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <time.h>
CHANGE HISTORY
First released in Issue 1. Derived from Issue 1 of the SVID.
Issue 5
A note indicating that the gmtime ()
function need not be reentrant is added to the DESCRIPTION.
The gmtime_r () function is included for alignment with the POSIX Threads Extension.
Issue 6
The gmtime_r () function is marked as part of the Thread-Safe Functions option.
Extensions beyond the ISO C standard are marked.
The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using a static data area.
The restrict keyword is added to the gmtime_r () prototype for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.
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