性能测试时间的计算

int main()
{

 LARGE_INTEGER m_nFreq;
 LARGE_INTEGER m_nBeginTime;
 LARGE_INTEGER nEndTime;
 QueryPerformanceFrequency(&m_nFreq); // 获取时钟周期
 QueryPerformanceCounter(&m_nBeginTime); // 获取时钟计数
 Sleep(100);
 QueryPerformanceCounter(&nEndTime);
 printf("%f",(nEndTime.QuadPart-m_nBeginTime.QuadPart)*1000.0/m_nFreq.QuadPart);
 return 0;
}