精确时间计时有时候是非常必要比如播放多媒体时视频和音频时间同步还有在测试代码性能时也需要使用到非常精确时间计时还有测试硬件性能时也需要精确时间计时这时就需要使用QueryPerformanceCounter来查询定时器计数值如果硬件里有定时器它就会启动这个定时器并且不断获取定时器值这样定时器精度就跟硬件时钟晶振样精确
QueryPerformanceCounter和QueryPerformanceFrequency声明如下:
WINBASEAPI
BOOL
WINAPI
QueryPerformanceCounter(
__out LARGE_INTEGER *lpPerformanceCount
);
WINBASEAPI
BOOL
WINAPI
QueryPerformanceFrequency(
__out LARGE_INTEGER *lpFrequency
);
lpPerformanceCount是返回定时器当前计数值
QueryPerformanceFrequency是返回定时器频率
例子如下:
#001 //精确时钟查询
#002 //蔡军生 2007/11/08 QQ:9073204 深圳
#003 void TestHighTimer(void)
#004 {
#005 //
#006 LARGE_INTEGER nFreq;
#007 LARGE_INTEGER nLastTime1;
#008 LARGE_INTEGER nLastTime2;
#009
#010 //获取是否支持精确定时器
#011 (QueryPerformanceFrequency(&nFreq))
#012 {
#013 //
#014 const nBufSize = 256;
#015 TCHAR chBuf[nBufSize];
#016
#017 //显示定时器频率
#018 wsprf(chBuf,_T("LastTime=%I64d\r\n"),nFreq);
#019 OutputDebugString(chBuf);
#020
#021 //获取定时器值
#022 QueryPerformanceCounter(&nLastTime1);
#023 wsprf(chBuf,_T("LastTime=%I64d\r\n"),nLastTime1);
#024 OutputDebugString(chBuf);
#025
#026 Sleep(0);
#027
#028 //获取定时器值
#029 QueryPerformanceCounter(&nLastTime2);
#030 wsprf(chBuf,_T("LastTime=%I64d\r\n"),nLastTime2);
#031 OutputDebugString(chBuf);
#032
#033
#034 //计算时间是花费多少秒
#035 float fInterval = nLastTime2.QuadPart - nLastTime1.QuadPart;
#036 swprf(chBuf,nBufSize,_T("花费:%f\r\n"),fInterval/(float)nFreq.QuadPart);
#037 OutputDebugString(chBuf);
#038 }
#039
#040 }
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