8 Time Functions (time.h)

This chapter groups functions used either for reporting on time (elapsed, current, or compute time) or to perform calculations based on time.

The header file time.h defines three types. clock_t and time_t are both used for representations of time particularly suitable for arithmetic. (In this implementation, quantities of type clock_t have the highest resolution possible on your machine, and quantities of type time_t resolve to seconds.) size_t is also defined if necessary for quantities representing sizes.

time.h also defines the structure tm for the traditional representation of Gregorian calendar time as a series of numbers, with the following fields:

tm_sec

Seconds, between 0 and 60 inclusive (60 allows for leap seconds).

tm_min

Minutes, between 0 and 59 inclusive.

tm_hour

Hours, between 0 and 23 inclusive.

tm_mday

Day of the month, between 1 and 31 inclusive.

tm_mon

Month, between 0 (January) and 11 (December).

tm_year

Year (since 1900), can be negative for earlier years.

tm_wday

Day of week, between 0 (Sunday) and 6 (Saturday).

tm_yday

Number of days elapsed since last January 1, between 0 and 365 inclusive.

tm_isdst

Daylight Savings Time flag: positive means DST in effect, zero means DST not in effect, negative means no information about DST is available. Although for mktime(), negative means that it should decide if DST is in effect or not.