problem with clock()

[killbill689]

I want to calculate the time elapsed since the execution of take_forks() but the value of "b" and "end"are always 0.Why this happens?

clock_t start,end;
	start=clock();//clocks before taking the forks
	take_forks(i);
	end=clock();//clocks after taking forks
	
	
        double b=(double)(end-start)/(double)(CLOCKS_PER_SEC);

tmesos=tmesos+(b/counter)/n;
printf("waiting time is %f",b);