一个精确的定时器

typedef union _LARGE_INTEGER
{
　struct
　{
　　DWORD LowPart ;// 4字节整型数
　　LONG HighPart;// 4字节整型数
　};
　LONGLONG QuadPart ;// 8字节整型数

}LARGE_INTEGER ;

LARGE_INTEGER litmp;
LONGLONG QPart1,QPart2;
double dfMinus, dfFreq, dfTim;
QueryPerformanceFrequency(&litmp);
dfFreq = (double)litmp.QuadPart;// 获得计数器的时钟频率
QueryPerformanceCounter(&litmp);
QPart1 = litmp.QuadPart;// 获得初始值
Sleep(100);
QueryPerformanceCounter(&litmp);
QPart2 = litmp.QuadPart;//获得中止值
dfMinus = (double)(QPart2-QPart1);
dfTim = dfMinus / dfFreq;// 获得对应的时间值，单位为秒

LARGE_INTEGER litmp;
LONGLONG QPart1,QPart2;
double dfMinus, dfFreq, dfTim;
QueryPerformanceFrequency(&litmp);
dfFreq = (double)litmp.QuadPart;// 获得计数器的时钟频率
QueryPerformanceCounter(&litmp);
QPart1 = litmp.QuadPart;// 获得初始值
do
{
　QueryPerformanceCounter(&litmp);
　QPart2 = litmp.QuadPart;//获得中止值
　dfMinus = (double)(QPart2-QPart1);
　dfTim = dfMinus / dfFreq;// 获得对应的时间值，单位为秒
}while(dfTim)

LARGE_INTEGER litmp;
LONGLONG QPart1,QPart2;
double dfMinus, dfFreq, dfTim;
QueryPerformanceFrequency(&litmp);
dfFreq = (double)litmp.QuadPart;// 获得计数器的时钟频率
QueryPerformanceCounter(&litmp);
QPart1 = litmp.QuadPart;// 获得初始值
do
{
　QueryPerformanceCounter(&litmp);
　QPart2 = litmp.QuadPart;//获得中止值
　dfMinus = (double)(QPart2-QPart1);
　dfTim = dfMinus / dfFreq;// 获得对应的时间值，单位为秒
}while(dfTim)