The GNU C Library - Simple Calendar Time

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. In the GNU C library and other POSIX-compliant implementations, time_t is equivalent to long int . 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.)

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 .

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.