How to measure execution time of a function? - c++

Question

I've searched SO and found relevant questions answered but I'm confused about the three different clock definitions. Considering I compile with Mingw on Windows;
I wonder whether the code below is OK or not? (I do not really need nanoseconds or microseconds precision; just testing...)
Which one should I use?
std::chrono::high_resolution_clock
std::chrono::system_clock
std::chrono::steady_clock
#include <iostream>
#include <chrono>
...
...
...
void printTimeElapsed(
std::chrono::high_resolution_clock::time_point t0,
std::chrono::high_resolution_clock::time_point t1)
{
int64_t hh; // hour
int64_t mm; // min
int64_t ss; // sec
int64_t ml; // millisec
int64_t mc; // microsec
int64_t ns; // nanosec
ns = std::chrono::duration_cast<std::chrono::nanoseconds>(t1 - t0).count();
std::cout << ns << std::endl;
mc = ns / 1000;
ns %= 1000;
ml = mc / 1000;
mc %= 1000;
ss = ml / 1000;
ml %= 1000;
mm = ss / 60;
ss %= 60;
hh = mm / 60;
mm %= 60;
std::cout
<< std::setfill('0') << std::setw(3) << hh << ":"
<< std::setfill('0') << std::setw(2) << mm << ":"
<< std::setfill('0') << std::setw(2) << ss << "."
<< std::setfill('0') << std::setw(3) << ml << "."
<< std::setfill('0') << std::setw(3) << mc << "."
<< std::setfill('0') << std::setw(3) << ns << std::endl;
return;
}
...
...
...
int main(
int argc,
char *argv[])
{
std::chrono::high_resolution_clock::time_point t0;
std::chrono::high_resolution_clock::time_point t1;
...
...
t0 = std::chrono::high_resolution_clock::now();
/* call the function to be measured */
t1 = std::chrono::high_resolution_clock::now();
printTimeElapsed(t0, t1);
...
...
return (0);
}

Answer 1

system_clock is not steady: is subject to time adjustments.
high_resolution_clock is not guaranteed to be steady.
It means for users to use steady_clock for measurement, and because of this, implementers need to make the steady_clock of a high resolution.
Windows implementation of steady_clock should be based on QueryPerformanceCounter / QueryPerformanceFrequency, which is highest resolution of available API. This is true for MSVC, need to check for MinGW.