mktime assumes the time at timp is a local time, and converts its representation from the traditional representation defined by struct tm into a representation suitable for arithmetic.
localtime is the inverse of mktime.### Returns
If the contents of the structure at timp do not form a valid calendar time representation, the result is -1. Otherwise, the result is the time, converted to a time_t value.
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**Authoritative source**: BUSMASTER DITA help source `mktime.dita`, compiled into `BUSMASTER.CHM` with the application.
