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The GNU C Library

21.4 Calendar Time

This section describes facilities for keeping track of calendar time. See section 21.1 Time Basics.

The GNU C library represents calendar time three ways:

• Simple time (the time_t data type) is a compact representation, typically giving the number of seconds of elapsed time since some implementation-specific base time.

• There is also a "high-resolution time" representation. Like simple time, this represents a calendar time as an elapsed time since a base time, but instead of measuring in whole seconds, it uses a struct timeval data type, which includes fractions of a second. Use this time representation instead of simple time when you need greater precision.

• Local time or broken-down time (the struct tm data type) represents a calendar time as a set of components specifying the year, month, and so on in the Gregorian calendar, for a specific time zone. This calendar time representation is usually used only to communicate with people.

21.4.1 Simple Calendar Time		Facilities for manipulating calendar time.
21.4.2 High-Resolution Calendar		A time representation with greater precision.
21.4.3 Broken-down Time		Facilities for manipulating local time.
21.4.4 High Accuracy Clock		Maintaining a high accuracy system clock.
21.4.5 Formatting Calendar Time		Converting times to strings.
21.4.6 Convert textual time and date information back		Convert textual time and date information back into broken-down time values.
21.4.7 Specifying the Time Zone with TZ		How users specify the time zone.
21.4.8 Functions and Variables for Time Zones		Functions to examine or specify the time zone.
21.4.9 Time Functions Example		An example program showing use of some of the time functions.