C#vs C++用于循环性能测量

Question

对于踢,我想看看C#for-loop的速度与C++ for循环的速度相比如何.我的测试是简单地遍历for循环100000次,100000次,并对结果取平均值.

这是我的C#实现:

 static void Main(string[] args) {

    var numberOfMeasurements = 100000;
    var numberOfLoops = 100000;
    var measurements = new List < long > ();
    var stopwatch = new Stopwatch();

    for (var i = 0; i < numberOfMeasurements; i++) {
       stopwatch.Start();
       for (int j = 0; j < numberOfLoops; j++) {}
       measurements.Add(stopwatch.ElapsedMilliseconds);
    }

    Console.WriteLine("Average runtime = " + measurements.Average() + " ms.");
    Console.Read();
 }

结果: Average runtime = 10301.92929 ms.

这是我的C++实现:

void TestA()
{
    auto numberOfMeasurements = 100000;
    auto numberOfLoops = 100000;
    std::vector<long> measurements;

    for (size_t i = 0; i < numberOfMeasurements; i++)
    {
        auto start = clock();
        for (size_t j = 0; j < numberOfLoops; j++){}
        auto duration = start - clock();
        measurements.push_back(duration);
    }

    long avg = std::accumulate(measurements.begin(), measurements.end(), 0.0) / measurements.size();
    std::cout << "TestB: Time taken in milliseconds: " << avg << std::endl;

}

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

结果: TestA: Time taken in milliseconds: 0

当我看到里面的东西时measurements,我注意到它充满了零......所以,它是什么,这里有什么问题？是clock吗？有没有更好/正确的方法来测量for循环？

Answer 1

没有"问题".能够优化无用的代码是C++的关键特性之一.由于内部循环什么都不做,所以每个理智的编译器都应该删除它.

每日提示:仅描述有意义的代码.

如果您想了解一些关于微基准测试,你可能有兴趣在此.