[no subject]

       The clock() function returns an approximation of processor
       time used by the program.

what makes you think that your program is using 100% of the CPU 100%
of the time (the only possible way that clock(2) could return a time
value that changed at the same rate as the wall clock time)?

To measure wall-clock time, use time(2) or gettimeofday(2).

--p