`mktime`

---convert time to arithmetic representation#include <time.h> time_t mktime(struct tm *timp);

**Description**

`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.

**Portability**

ANSI C requires `mktime`

.

`mktime`

requires no supporting OS subroutines.

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