QueryPerformanceCounter

windows的Sleep函數，睡眠線程指定毫秒數，能夠用來作毫秒延時。 對於微秒延時，沒有一個現成的函數，可是能夠經過 QueryPerformanceFrequency QueryPerformanceCounter 來間接實現。原理就是用循環查詢的方式不斷調用QueryPerformanceCounter（在Winbase.h中）

LARGE_INTEGER freq;
LARGE_INTEGER start, end;
QueryPerformanceFrequency(&freq);
unsigned int us = 100000;
LONGLONG count = (us * freq.QuadPart) / (1000 * 1000);
QueryPerformanceCounter(&start);
count = count + startQuadPart ;
do
{
   QueryPerformanceCounter(&end);
}while(end.QuadPart< count);
printf("us %u, elaps %u ms\r\n", us, tpend-tpstart);```