std::chrono multiplies durations

Question

Consider this example of code:

#include <chrono>
#include <iostream>

int main ( )
{
   using namespace std::chrono;

   system_clock::time_point s = system_clock::now();

   for (int i = 0; i < 1000000; ++i)
      std::cout << duration_cast<duration<double>>(system_clock::now() - s).count() << "\n";
}

I expect this to print the elapsed time in seconds. But it actually prints time in thousands of second (the expected result multiplied by 0.001). Am I doing something wrong?

Edit

Since seconds is equivalent to duration<some-int-type>, duration_cast<seconds> gives the same result.

I used gcc-4.7.3-r1

@DaveF: Only if you want to round to a whole number of seconds, since `seconds` is a convenience typedef for `duration`. `duration` should also have a period of one second. — Mike Seymour, Feb 26 '14 at 11:21
How are you determining that it's printing milliseconds? If I compile and run that code, and watch the output, it increases by 1 each second as expected (that's with a slightly different version of GCC though). — Mike Seymour, Feb 26 '14 at 11:39
[This](http://stackoverflow.com/questions/17405997/c-chrono-duration-cast-to-milliseconds-results-in-seconds) may help. — maverik, Feb 26 '14 at 11:43
@maverik: that seems to be the right explanation. Thanks a lot. — lisyarus, Feb 26 '14 at 14:54

score 2 · Answer 1 · answered Feb 26 '14 at 11:43

2

You program works as expected using both gcc 4.8.2 and VS2013. I think it might be a compiler bug in your old gcc 4.7

answered Feb 26 '14 at 11:43

GabiMe

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score 0 · Accepted Answer · edited May 23 '17 at 11:44

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maverik guessed this right: the problem was with binary incompatibility inside std::chrono - gcc-4.8 version of libstdc++ and gcc-4.7 did not agree on internal units of time.

edited May 23 '17 at 11:44

Community

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answered Apr 25 '16 at 22:51

lisyarus

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score -2 · Answer 3 · answered Feb 26 '14 at 11:20

-2

You could use duration_cast < seconds > instead of duration_cast < duration < double > >

answered Feb 26 '14 at 11:20

const_ref

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`seconds` is just a typedef for `duration`. `duration` should also have a period of one second. – Mike Seymour Feb 26 '14 at 11:22
I've already tried. seconds seem to act exactly like duration>, and duration_cast(...) in fact gives me seconds. – lisyarus Feb 26 '14 at 11:23
I get different results when using Ideone with C++11 compiler between the two(seconds and duration). Seconds only prints seconds(at least on that compiler). I cant test it on any other compiler atm however – const_ref Feb 26 '14 at 11:26

std::chrono multiplies durations

3 Answers3