How to time event in C++?

Question

I'd like to be able to get number of nanoseconds it takes to do something in my C++ program.

Object creation, time for a function to do it's thing etc.

In Java, we'd do something along the lines of:

    long now = System.currentTimeMillis();
    // stuff
    long diff = (System.currentTimeMillis() - now);

How would you do the same in C++?

I wrote [this](https://gist.github.com/3287323) timer class a little while ago - it's far from perfect but it could be helpful. — Gordon Bailey, Aug 07 '12 at 17:08

score 9 · Accepted Answer · answered Aug 07 '12 at 19:35

9

The <chrono> library in standard C++ provides the best way to do this. This library provides a standard, type safe, generic API for clocks.

#include <chrono>
#include <iostream>

int main() {
    using std::chrono::duration_cast;
    using std::chrono::nanoseconds;
    typedef std::chrono::high_resolution_clock clock;

    auto start = clock::now();
    // stuff
    auto end = clock::now();
    std::cout << duration_cast<nanoseconds>(end-start).count() << "ns\n";
}

The actual resolution of the clock will vary between implementations, but this code will always show results in nanoseconds, as accurately as possible given the implementation's tick period.

answered Aug 07 '12 at 19:35

bames53

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I am getting `error: ‘std::chrono’ has not been declared` error. What might be going on please? – James Raitsev Aug 08 '12 at 00:49
@Jam You may be using a standard library implementation from before C++11. What compiler version and standard library are you using? – bames53 Aug 08 '12 at 01:08
`i686-apple-darwin11-llvm-g++-4.2 (GCC) 4.2.1`, not sure about the version of standard library. How can i find it out? – James Raitsev Aug 08 '12 at 14:04
gcc 4.2 is far too old to support this. I'm guessing you're at least on OS X 10.6, in which case you should be able to use clang++ with the arguments -std=c++11 and -stdlib=libc++ to enable C++11 including the chrono library. – bames53 Aug 08 '12 at 15:32
Hmm ... I just updated the command line dev tools a few days ago. I am on OSX10.8, mountain lion. How can i upgrade the compiler please? Also, is this feature an exclusive feature of c11? – James Raitsev Aug 08 '12 at 21:17
Yes, chrono was introduced with C++11, but many implementations have it even before being completely C++11 compliant. The llvm-gcc compiler is not going to be updated past 4.2, and I think it has been removed starting with Xcode 4.4 (though a previous install may remain), so you have to switch to a different compiler. Use the command clang++ instead of g++ or whatever command you've been using. Also enable C++11 mode with the compiler flags -std=c++11 and -stdlib=libc++. – bames53 Aug 08 '12 at 22:06

SChepurin · Answer 2 · 2012-08-07T18:05:00.457

2

In C++11 you can do it using chrono library where -

Class template std::chrono::duration represents a time interval. It consists of a count of ticks of type Rep and a tick period, where the tick period is a compile-time rational constant representing the number of seconds from one tick to the next.

Currently implemented in GCC 4.5.1. (not yet in VC++). See sample code from cppreference.com on Ideone.com execution time of a function call

edited Aug 07 '12 at 18:05

answered Aug 07 '12 at 17:55

SChepurin

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`` is in the VS2012 RC although I think the high_resolution_clock's tick is only 100ns. It should be better on other platforms. libc++ on OS X has ns resolution. I'm not sure about gcc or libstdc++. – bames53 Aug 07 '12 at 18:43

score 1 · Answer 3 · answered Aug 07 '12 at 17:03

1

Take a look at clock and clock_t. For the resolution you're talking about, I don't think there's native support in C++. To get meaningful values, you'll have to time multiple calls or constructions, or use a profiler (desired).

answered Aug 07 '12 at 17:03

Luchian Grigore

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score 0 · Answer 4 · edited May 23 '17 at 10:28

0

Asked and answered many times.

If you're using C++11 you can consider chrono.

edited May 23 '17 at 10:28

Community

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answered Aug 07 '12 at 17:02

Jonathon Reinhart

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Unfortunately none of those give the right answer, ``. – bames53 Aug 07 '12 at 18:45
What do you mean "the right answer"? That is a C++11 feature, which the OP did not mention supporting. – Jonathon Reinhart Aug 07 '12 at 18:46
Chrono is standard, provides type safety for both time points vs. durations and for units, and won't require a new API as higher resolutions become available, so in most cases I'd consider it a mistake to use clock_gettime(), clock(), gettimeofday(), QueryPerformanceFrequency(), etc. – bames53 Aug 07 '12 at 18:58
The latest versions of all the major compilers support chrono. If someone needs to support an older compiler then they can mention that requirement. It's 2012 so IMO C++ == C++11 now. – bames53 Aug 07 '12 at 19:01

score 0 · Answer 5 · answered Aug 07 '12 at 17:45

I asked this exact question earlier today. The best solution I have at the moment is to use SDL, and call:

uint32 a_time = SDL_GetTicks(); // Return uint32 count of milliseconds since SDL_Init was called

Although this is probably going to give you lots of overhead, even if you just init SDL with the timer functionality. (SDL_Init(SDL_INIT_TIMER).

Hope this helps you - I settled for this as a solution because it is portable.

How to time event in C++?

5 Answers5