Question

I want to measure the speed of a function within a loop. But why my way of doing it always print ‘0’ instead of high-res timing with 9 digits decimal precision (i.e. in nano/micro seconds)?

What’s the correct way to do it?

#include <iomanip> #include <iostream> #include <time.h> int main() {    for (int i = 0; i <100; i++) {     std::clock_t startTime = std::clock();      // a very fast function in the middle     cout << 'Time: ' << setprecision(9) << (clock() - startTime + 0.00)/CLOCKS_PER_SEC << endl;  }   return 0; } 

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Answer 1

Move your time calculation functions outside for () { .. } statement then devide total execution time by the number of operations in your testing loop.

#include <iostream> #include <ctime> #define NUMBER 10000 // the number of operations  // get the difference between start and end time and devide by // the number of operations double diffclock(clock_t clock1, clock_t clock2) {     double diffticks = clock1 - clock2;     double diffms = (diffticks) / (CLOCKS_PER_SEC / NUMBER);     return diffms; }  int main() {     // start a timer here     clock_t begin = clock();      // execute your functions several times (at least 10'000)     for (int i = 0; i < NUMBER; i++) {         // a very fast function in the middle         func()     }      // stop timer here     clock_t end = clock();      // display results here     cout << 'Execution time: ' << diffclock(end, begin) << ' ms.' << endl;     return 0; } 

Note: std::clock() lacks sufficient precision for profiling. Reference.