The value returned is the CPU time used so far as a clock_t; to get the number of seconds used, divide by CLOCKS_PER_SEC. If the
processor time used is not available or its value cannot be represented, the function returns the value (clock_t) -1.
C89, C99, POSIX.1-2001. POSIX requires that CLOCKS_PER_SEC equals 1000000 independent of the actual resolution.
The C standard allows for arbitrary values at the start of the program; subtract the value returned from a call to clock() at the
start of the program to get maximum portability.
Note that the time can wrap around. On a 32-bit system where CLOCKS_PER_SEC equals 1000000 this function will return the same value
approximately every 72 minutes.
On several other implementations, the value returned by clock() also includes the times of any children whose status has been col‐
lected via wait(2) (or another wait-type call). Linux does not include the times of waited-for children in the value returned by
clock(). The times(2) function, which explicitly returns (separate) information about the caller and its children, may be prefer‐