c++定时事件控制台错误

Question

我正试图写一个类，将能够使用QueryPerformanceCounter在c++时间事件。这个想法是，你创建一个计时器对象，给一个函数一个双格式的时间，它计数直到时间过去，然后做一些事情。这个类最适合用于游戏中的计时(游戏邦注:例如，拥有一个每秒计数60次的计时器)。当我编译这段代码时，它只是向控制台输出0，似乎永远都是这样。但我注意到一些我无法理解的bug。如果我点击控制台窗口的滚动条并按住它，计时器就会正确计数。例如，如果我输入5.0，然后快速点击并按住滚动条5秒或更长时间，当我放手时，程序将打印"完成!!"那么，当我让它将经过的时间打印到控制台时，为什么它不能正确计数呢?打印东西到控制台是否有故障，或者我的定时代码是否有问题?下面是代码:

   #include <iostream>
#include <iomanip>
#include "windows.h"
using namespace std;

int main()
{
    setprecision(10); // i tried to see if precision in the stream was the problem but i don't think it is
    cout << "hello! lets time something..." << endl;
    bool timing = 0;                // a switch to turn the timer on and off
    LARGE_INTEGER T1, T2;           // the timestamps to count
    LARGE_INTEGER freq;             // the frequency per seccond for measuring the difference between the stamp values
    QueryPerformanceFrequency(&freq); // gets the frequency from the computer
    // mil.QuadPart = freq.QuadPart / 1000; // not used

    double ellapsedtime = 0, desiredtime; // enter a value to count up to in secconds
    // if you entered 4.5 for example, then it should wait for 4.5 secconds
    cout << "enter the amount of time you would like to wait for in seconds (in double format.)!!" << endl;
    cin >> desiredtime;
    QueryPerformanceCounter(&T1);   // gets the first stamp value
    timing = 1;                    // switches the timer on
    while(timing)
    {
        QueryPerformanceCounter(&T2);      // gets another stamp value
        ellapsedtime += (T2.QuadPart - T1.QuadPart) / freq.QuadPart;   // measures the difference between the two stamp
        //values and then divides them by the frequency to get how many secconds has ellapsed
        cout << ellapsedtime << endl;
        T1.QuadPart = T2.QuadPart; // assigns the value of the second stamp to the first one, so that we can measure the
        // difference between them again and again
        if(ellapsedtime>=desiredtime) // checks if the elapsed time is bigger than or equal to the desired time,
        // and if it is prints done and turns the timer off
        {
            cout << "done!!!" << endl;
            timing = 0; // breaks the loop
        }
    }

    return 0;
}

Answer 1

应该在ellapsedtime中存储自第一次调用QueryPerformanceCounter以来经过的微秒数，并且不应该覆盖第一个时间戳。

工作代码:

// gets another stamp value
QueryPerformanceCounter(&T2);     
// measures the difference between the two stamp
ellapsedtime += (T2.QuadPart - T1.QuadPart);
cout << "number of tick " << ellapsedtime << endl;
ellapsedtime *= 1000000.;
ellapsedtime /= freq.QuadPart;
cout << "number of Microseconds " << ellapsedtime << endl;
// checks if the elapsed time is bigger than or equal to the desired time
if(ellapsedtime/1000000.>=desiredtime)         {
   cout << "done!!!" << endl;
   timing = 0; // breaks the loop
}

请务必阅读:获取高分辨率时间戳