GMTIME(3P) POSIX Programmer's Manual GMTIME(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
gmtime, gmtime_r - convert a time value to a broken-down UTC time
struct tm *gmtime(const time_t *timer);
struct tm *gmtime_r(const time_t *restrict timer,
struct tm *restrict result);
For gmtime(): The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the require-
ments 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 Coordi-
nated 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 Defini-
tions volume of IEEE Std 1003.1-2001, Section 4.14, Seconds Since the Epoch), where the names in the structure and in the expression corre-
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 Coordi-
nated 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.
The gmtime() function shall fail if:
The result cannot be represented.
The following sections are informative.
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.
asctime(), clock(), ctime(), difftime(), localtime(), mktime(), strftime(), strptime(), time(), utime(), the Base Definitions volume of
IEEE Std 1003.1-2001, <time.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- 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 .
/The Open Group 2003 GMTIME(3P)