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21.4 Calendar Time

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

• Simple Calendar Time
• High-Resolution Calendar
• Broken-down Time
• High Accuracy Clock
• Formatting Calendar Time
• Convert textual time and date information back
• Specifying the Time Zone with TZ
• Functions and Variables for Time Zones
• Time Functions Example