Defined in header <ctime>  

typedef /* unspecified */ time_t; 
Arithmetic type capable of representing times.
Although not defined, this is almost always an integral value holding the number of seconds (not counting leap seconds) since 00:00, Jan 1 1970 UTC, corresponding to POSIX time.
returns the current time of the system as time since epoch (function) 

converts time since epoch to calendar time expressed as local time (function) 

converts time since epoch to calendar time expressed as Universal Coordinated Time (function) 

C documentation for time_t 
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