小心GetTickCount的溢出和误差问题

GetTickCount

MSDN里有这么一句：The elapsed time is stored as a DWORD value. Therefore, the time will wrap around to zero if the system is run continuously for 49.7 days.

就是说系统启动49.7天以后，就又从0开始了

而且这个数值时间越久，误差越大。