Correct way of portably timing code using C++11

Question

I\'m in the midst of writing some timing code for a part of a program that has a low latency requirement.

Looking at whats available in the std::chrono library, I\'m

Answer 1

Use steady_clock. On all implementations its precision is nanoseconds. You can check this yourself for your platform by printing out steady_clock::period::num and steady_clock::period::den.

Now that doesn't mean that it will actually measure nanosecond precision. But platforms do their best. For me, two consecutive calls to steady_clock (with optimizations enabled) will report times on the order of 100ns apart.

#include "chrono_io.h"
#include <chrono>
#include <iostream>

int
main()
{
    using namespace std::chrono;
    using namespace date;
    auto t0 = steady_clock::now();
    auto t1 = steady_clock::now();
    auto t2 = steady_clock::now();
    auto t3 = steady_clock::now();
    std::cout << t1-t0 << '\n';
    std::cout << t2-t1 << '\n';
    std::cout << t3-t2 << '\n';
}

The above example uses this free, open-source, header-only library only for convenience of formatting the duration. You can format things yourself (I'm lazy). For me this just output:

287ns
116ns
75ns

YMMV.