使用QueryPerformanceFrequency 计算程序执行时间

/////////////////////////////////////////////////
#include <iostream>
#include <windows.h>
using namespace    std;
////////////////////////////////////////////////
void main()
{
    _LARGE_INTEGER time_start;    /*开始时间*/
    _LARGE_INTEGER time_over;        /*结束时间*/
    double dqFreq;                /*计时器频率*/
    LARGE_INTEGER f;            /*计时器频率*/
    QueryPerformanceFrequency(&f);
    dqFreq=(double)f.QuadPart;
    QueryPerformanceCounter(&time_start);
    Sleep(1000);/*循环耗时*/
    QueryPerformanceCounter(&time_over); 
    cout<<((time_over.QuadPart-time_start.QuadPart)/dqFreq)<<endl;//单位为秒，精度为1000 000/（cpu主频）微秒
}