Simple Calendar Time

This section describes the time_t data type for representing calendar time, and the functions which operate on calendar time objects. These facilities are declared in the header file `time.h'.

Data Type: time_t

This is the data type used to represent calendar time. When interpreted as an absolute time value, it represents the number of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated Universal Time. (This date is sometimes referred to as the epoch.) POSIX requires that this count ignore leap seconds, but on some hosts this count includes leap seconds if you set TZ to certain values (see section Specifying the Time Zone with TZ).

In the GNU C library, time_t is equivalent to long int. In other systems, time_t might be either an integer or floating-point type.

Function: double difftime (time_t time1, time_t time0)

The difftime function returns the number of seconds elapsed between time time1 and time time0, as a value of type double. The difference ignores leap seconds unless leap second support is enabled.

In the GNU system, you can simply subtract time_t values. But on other systems, the time_t data type might use some other encoding where subtraction doesn't work directly.

Function: time_t time (time_t *result)

The time function returns the current time as a value of type time_t. If the argument result is not a null pointer, the time value is also stored in *result. If the calendar time is not available, the value (time_t)(-1) is returned.

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