2.1 tm

The tm structure contains a representation of time 'broken down' into components of the Gregorian calendar.

The value of tm_isdst is zero if Daylight Saving Time is not in effect, and is negative if the information is not available.

When Daylight Saving Time is in effect, the value represents the number of seconds the clock is advanced.

See the set_dst() function for more information about Daylight Saving.