Calculating time taken in milliseconds for a sorting algorithm sorting an integer array

Question

I am trying to compare two sorting algorithms merge sort and quick sort by seeing which one takes the least amount of time sorting a small integer array like {8,7,6,5,4,3,2,1} I know I shouldnt use clock() and I've been trying time() but every time it keeps giving me 0 for the time taken. I've tried using Chrono as well and it also just gives me 0 Can someone help me out with this?

The sorts are already made and they work fine, this is how I have it setup.

int Quiarr[] = {8, 7, 6, 5, 4, 3, 2, 1};
int arr_size = sizeof(Quiarr)/sizeof(Quiarr[0]);
start = time();
mergeSort(Quiarr, 0, arr_size - 1);
end = time();
msecs = ((double) (end - start)) * 1000 / CLOCKS_PER_SEC;
cout << msecss2 << " " << endl;

Good timers here: https://stackoverflow.com/questions/5521146/what-is-the-best-most-accurate-timer-in-c — Eljay, Nov 24 '17 at 20:26
It's likely that sorting such a small array takes too short an amount of time for your timer to measure. You can try http://en.cppreference.com/w/cpp/chrono/high_resolution_clock — François Andrieux, Nov 24 '17 at 20:28
Sorting eight elements takes microseconds, at most. `time` usually measures seconds. — molbdnilo, Nov 24 '17 at 20:34

score 0 · Answer 1 · answered Nov 24 '17 at 21:10

try this

auto t0 = std::chrono::high_resolution_clock::now();
// your sorting function here
auto t1 = std::chrono::high_resolution_clock::now();
auto elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(t2-t1);

high_resolution_clock::now(), has a precise granularity.

NOTE: you need to run more than one trial of your function, that's because of the OS scheduler, the elapsed time is not constant, and you need to consider the smallest value you get. (run a loop that repeats the code above let say 1000 times, and print the elapsed time the smallest value that repeats the most is the more plausible one).

All outputs coming from the code even after the loop 1000 times is till 0 — user6088127, Nov 24 '17 at 21:19

Calculating time taken in milliseconds for a sorting algorithm sorting an integer array

1 Answers1