我想知道在我的c++程序中某个函数在Linux上执行需要多少时间。之后,我想做一个速度比较。我看到了几个时间函数,但最终从boost。空间:

process_user_cpu_clock, captures user-CPU time spent by the current process

现在,我不清楚如果我使用上述函数,我会得到哪个CPU在该函数上花费的唯一时间吗?

其次,我找不到任何使用上述功能的例子。请问有谁能告诉我如何使用上面的功能?

p.s.:现在,我使用std::chrono::system_clock::now()以秒为单位获得时间,但这给了我不同的结果,因为不同的CPU负载每次。


当前回答

因为没有一个提供的答案是非常准确的或可复制的结果,我决定添加一个链接到我的代码,具有亚纳秒的精度和科学统计。

Note that this will only work to measure code that takes a (very) short time to run (aka, a few clock cycles to a few thousand): if they run so long that they are likely to be interrupted by some -heh- interrupt, then it is clearly not possible to give a reproducable and accurate result; the consequence of which is that the measurement never finishes: namely, it continues to measure until it is statistically 99.9% sure it has the right answer which never happens on a machine that has other processes running when the code takes too long.

https://github.com/CarloWood/cwds/blob/master/benchmark.h#L40

其他回答

简单程序查找函数执行时间。

#include <iostream>
#include <ctime> // time_t
#include <cstdio>

void function()
{
     for(long int i=0;i<1000000000;i++)
     {
        // do nothing
     }
}

int main()
{

time_t begin,end; // time_t is a datatype to store time values.

time (&begin); // note time before execution
function();
time (&end); // note time after execution

double difference = difftime (end,begin);
printf ("time taken for function() %.2lf seconds.\n", difference );

return 0;
}

您可以使用一个简单的类来进行这种测量。

class duration_printer {
public:
    duration_printer() : __start(std::chrono::high_resolution_clock::now()) {}
    ~duration_printer() {
        using namespace std::chrono;
        high_resolution_clock::time_point end = high_resolution_clock::now();
        duration<double> dur = duration_cast<duration<double>>(end - __start);
        std::cout << dur.count() << " seconds" << std::endl;
    }
private:
    std::chrono::high_resolution_clock::time_point __start;
};

唯一需要做的是在函数的开始处创建一个对象

void veryLongExecutingFunction() {
    duration_calculator dc;
    for(int i = 0; i < 100000; ++i) std::cout << "Hello world" << std::endl;
}

int main() {
    veryLongExecutingFunction();
    return 0;
}

就是这样。可以修改该类以满足您的需求。

因为没有一个提供的答案是非常准确的或可复制的结果,我决定添加一个链接到我的代码,具有亚纳秒的精度和科学统计。

Note that this will only work to measure code that takes a (very) short time to run (aka, a few clock cycles to a few thousand): if they run so long that they are likely to be interrupted by some -heh- interrupt, then it is clearly not possible to give a reproducable and accurate result; the consequence of which is that the measurement never finishes: namely, it continues to measure until it is statistically 99.9% sure it has the right answer which never happens on a machine that has other processes running when the code takes too long.

https://github.com/CarloWood/cwds/blob/master/benchmark.h#L40

下面是一个优秀的仅头类模板,用于测量函数或任何代码块的运行时间:

#ifndef EXECUTION_TIMER_H
#define EXECUTION_TIMER_H

template<class Resolution = std::chrono::milliseconds>
class ExecutionTimer {
public:
    using Clock = std::conditional_t<std::chrono::high_resolution_clock::is_steady,
                                     std::chrono::high_resolution_clock,
                                     std::chrono::steady_clock>;
private:
    const Clock::time_point mStart = Clock::now();

public:
    ExecutionTimer() = default;
    ~ExecutionTimer() {
        const auto end = Clock::now();
        std::ostringstream strStream;
        strStream << "Destructor Elapsed: "
                  << std::chrono::duration_cast<Resolution>( end - mStart ).count()
                  << std::endl;
        std::cout << strStream.str() << std::endl;
    }    

    inline void stop() {
        const auto end = Clock::now();
        std::ostringstream strStream;
        strStream << "Stop Elapsed: "
                  << std::chrono::duration_cast<Resolution>(end - mStart).count()
                  << std::endl;
        std::cout << strStream.str() << std::endl;
    }

}; // ExecutionTimer

#endif // EXECUTION_TIMER_H

下面是它的一些用法:

int main() {
    { // empty scope to display ExecutionTimer's destructor's message
         // displayed in milliseconds
         ExecutionTimer<std::chrono::milliseconds> timer;

         // function or code block here

         timer.stop();

    } 

    { // same as above
        ExecutionTimer<std::chrono::microseconds> timer;

        // code block here...

        timer.stop();
    }

    {  // same as above
       ExecutionTimer<std::chrono::nanoseconds> timer;

       // code block here...

       timer.stop();

    }

    {  // same as above
       ExecutionTimer<std::chrono::seconds> timer;

       // code block here...

       timer.stop();

    }              

    return 0;
}

由于类是一个模板,我们可以很容易地指定real我们想要测量和显示的时间。这是一个非常方便的实用工具类模板,用于做基准标记,非常容易使用。

对于旧的c++或C来说很简单:

#include <time.h> // includes clock_t and CLOCKS_PER_SEC

int main() {

    clock_t start, end;

    start = clock();
    // ...code to measure...
    end = clock();

    double duration_sec = double(end-start)/CLOCKS_PER_SEC;
    return 0;
}

计时精度(秒)为1.0/CLOCKS_PER_SEC