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Question

I'm trying to record the time my program takes to finish in seconds, with sub-second accuracy.

I'm not recording CPU time or cycles, I simply want to be able to mark a start point (Wall Clock time), then at the end of my program mark a finish (Wall Clock time), and calculate the delta.

Answer

You can use the clock() function to record the number of ticks taken and then convert this to seconds:

#include <time.h>
#include <stdio.h>
#include <math.h>
int main () {
   clock_t start_t = clock();
    
   double a=0;
   for(int i=0; i< 10000000; i++) {
     a+=sqrt(a);
   }
   clock_t end_t = clock();
   
   double total_t = (double)(end_t - start_t) / CLOCKS_PER_SEC;
   printf("Total time taken by CPU: %lf\n", total_t  );
   return(0);
}