gmtime man page

Prolog

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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.1‐2008 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 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.

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.

See Also

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

The Base Definitions volume of POSIX.1‐2008, Section 4.15, Seconds Since the Epoch, <time.h>

Info

2013 IEEE/The Open Group POSIX Programmer's Manual