Time difference in C++

Question

Does anyone know how to calculate time difference in C++ in milliseconds? I used difftime but it doesn't have enough precision for what I'm trying to measure.

Answer 1

I know this is an old question, but there's an updated answer for C++0x. There is a new header called <chrono> which contains modern time utilities. Example use:

#include <iostream> #include <thread> #include <chrono>  int main() {     typedef std::chrono::high_resolution_clock Clock;     typedef std::chrono::milliseconds milliseconds;     Clock::time_point t0 = Clock::now();     std::this_thread::sleep_for(milliseconds(50));     Clock::time_point t1 = Clock::now();     milliseconds ms = std::chrono::duration_cast<milliseconds>(t1 - t0);     std::cout << ms.count() << "ms\n"; }  50ms 

More information can be found here:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2661.htm

There is also now a boost implementation of <chrono>.

Answer 2

You have to use one of the more specific time structures, either timeval (microsecond-resolution) or timespec (nanosecond-resolution), but you can do it manually fairly easily:

#include <time.h>

int diff_ms(timeval t1, timeval t2)
{
    return (((t1.tv_sec - t2.tv_sec) * 1000000) + 
            (t1.tv_usec - t2.tv_usec))/1000;
}

This obviously has some problems with integer overflow if the difference in times is really large (or if you have 16-bit ints), but that's probably not a common case.