CLOCK(3) Linux Programmer's Manual CLOCK(3)
clock - determine processor time
The clock() function returns an approximation of processor time used by the program.
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 collected 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 preferable.
clock_gettime(2), getrusage(2), times(2)
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.