measuring the performance of some fragments of codes
 

Hi FOAMers,
I added some lines of code to a solver and would like to measure the performance of each part, e.g pressure solver, momentum solver and so on, Would it be the EXACT way of measuring?

double a = clock::getTime();
THE CODE;
double b = clock::getTime();
elapsed cpu time for that part of code EXACTLY is : (b-a) ?

(
I expected to get nearly same value, but using the above method,sometimes provides strange results.
e.g for a particular fragment of code, it gives performance of 9%, and sometimes 15% (the simulation is converged)
actually when i print out the value of the scalar/double a or b, it seems that it can be 9 precision number ,so subtraction may lead to some errors due to that range of accuracy
)

Thanks in advance.

UPDATE : using 'elapsedCpuTime' gave accurate time and solved the problem.