如何使用chrono库测试C++程序执行时间

原创已于 2023-07-13 22:05:46 修改 · 1.2k 阅读

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于 2020-12-16 10:51:43 首次发布

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本文展示了如何利用C++的std::chrono库来记录和计算程序执行的时间，包括 fibonacci 函数的计算时间和循环操作的耗时，并以不同时间单位展示结果。示例中还涉及到高精度时钟的选择和时间间隔的转换，以及通过std::this_thread::sleep_for函数模拟耗时操作。

使用C++标准库std::chrono

记录程序段开始执行时间，结束执行时间，相减后转换成某个时间单位。

example：

#include <iostream>
#include <chrono>
 
long fibonacci(unsigned n)
{
    if (n < 2) return n;
    return fibonacci(n-1) + fibonacci(n-2);
}
 
int main()
{
    auto start = std::chrono::steady_clock::now();
    std::cout << "f(42) = " << fibonacci(42) << '\n';
    auto end = std::chrono::steady_clock::now();
    std::chrono::duration<double> elapsed_seconds = end-start;
    std::cout << "elapsed time: " << elapsed_seconds.count() << "s\n";
}

output:

f(42) = 267914296
elapsed time: 1.88232s

example2:

#include <iostream>
#include <chrono>

void function()
{
    long long number = 0;

    for( long long i = 0; i != 2000000; ++i )
    {
       number += 5;
    }
}

int main()
{
    auto t1 = std::chrono::high_resolution_clock::now();
    function();
    auto t2 = std::chrono::high_resolution_clock::now();

    auto duration = std::chrono::duration_cast<std::chrono::microseconds>( t2 - t1 ).count();

    std::cout << duration;
    return 0;
}

更新：打印毫秒间隔时间

#include <iostream>
#include <chrono>
#include <ratio>
#include <thread>
 
void f()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
int main()
{
    auto t1 = std::chrono::high_resolution_clock::now();
    f();
    auto t2 = std::chrono::high_resolution_clock::now();
 
    // floating-point duration: no duration_cast needed
    std::chrono::duration<double, std::milli> fp_ms = t2 - t1;
 
    // integral duration: requires duration_cast
    auto int_ms = std::chrono::duration_cast<std::chrono::milliseconds>(t2 - t1);
 
    // converting integral duration to integral duration of shorter divisible time unit:
    // no duration_cast needed
    std::chrono::duration<long, std::micro> int_usec = int_ms;
 
    std::cout << "f() took " << fp_ms.count() << " ms, "
              << "or " << int_ms.count() << " whole milliseconds "
              << "(which is " << int_usec.count() << " whole microseconds)" << std::endl;
}