C++高精度计算代码运行时间(转载)

转载:http://blog.csdn.net/rrrfff/article/details/6583410

    //在定时前应该先调用QueryPerformanceFrequency()函数获得机器内部计时器的时钟频率.
    //接着在需要严格计时的事件发生前和发生之后分别调用QueryPerformanceCounter(),利用两次获得的计数之差和时钟频率,就可以计算出事件经历的精确时间,
    //供WIN9X使用的高精度定时器:QueryPerformanceFrequency()和QueryPerformanceCounter(),要求计算机从硬件上支持高精度定时器.
    //数据类型LARGEINTEGER既可以是一个作为8字节长的整数,也可以是作为两个4字节长的整数的联合结构,其具体用法根据编译器是否支持64位而定.
    LARGE_INTEGER Frequency = {0};
    QueryPerformanceFrequency(&Frequency);
    double F    = (double)Frequency.QuadPart;
    QueryPerformanceCounter(&Frequency);
    LONGLONG I  = Frequency.QuadPart;
    {
        //do sth here
    }
    QueryPerformanceCounter(&Frequency);
    CString result;
    result.Format(_T("Result: %f"), double(Frequency.QuadPart - I) / F);
    MessageBox(NULL, result, _T("测试报告"), MB_OK);