Why is CLOCKS_PER_SEC not the actual number of clocks per second?

Question

I have just written this short C++ program to approximate the actual number of clock ticks per second.

#include 
#include 

usi         


        

Answer 1

When you set int first_time = time(NULL);, time(NULL) might be "1 nanosecond away", (because it is truncated), from turning +1. Therefore, the: while(time(NULL) <= first_time) {} can be jumped over faster than 1 second, quicker than you expected.

That's why there are less clocks in that "1 second" of yours.