А почитать документацию какая-то религия не позволяет? :) time.h
There are two interfaces for using time_t and the associated functions time, ctime,
difftime, gmtime, localtime, and mktime:
* The 32-bit interface supports years from 1900 up to 2035 and uses a 32-bit integer
for time_t. The type and function have names like __time32_t, __time32, etc.
This variant is mainly available for backwards compatibility.
* The 64-bit interface supports years from -9999 up to 9999 and uses a signed
long longfor time_t. The type and function have names like __time64_t,
__time64, etc.
The interfaces are defined in the system header file time.h.