Fork ,excel and time

Hello everyone.

I use in my programme a fork() and excel() to call another programme. In my main programme i want to know the time it needs to run (including the programme i call with excel ) but i made a test and print clock() (from time.h) before and after excel and the value i got was the same. Why does this happening ? I mean clock get its value from the system it doesn't depend on the programme. What i was expecting was this clock (before excel)< clock (after excel).

Thanks in advance