system time
Standard C library (libc)
Used for system time in clock ticks or CLOCKS_PER_SEC (defined in <time.h>). According to POSIX, it is an integer type or a real-floating type.
C11, POSIX.1-2008.
C89, POSIX.1-2001.
The following headers also provide this type: <sys/types.h> and <sys/times.h>.