SYSTEMTIME 与 time_t 之间的转换，计算2个SYSTEMTIME的时间差

1. time_t systemtime_to_time_t(const SYSTEMTIME& st)
2. {
3. struct tm gm = {st.wSecond, st.wMinute, st.wHour, st.wDay, st.wMonth-1, st.wYear-1900, st.wDayOfWeek, 0, 0};
4. return mktime(&gm);
5. }
6. SYSTEMTIME time_t_to_systemtime(time_t t)
7. {
8. tm temptm = *localtime(&t);
9. SYSTEMTIME st = {1900 + temptm.tm_year,
10. 1 + temptm.tm_mon,
11. temptm.tm_wday,
12. temptm.tm_mday,
13. temptm.tm_hour,
14. temptm.tm_min,
15. temptm.tm_sec,
16. 0};
17. return st;
18. }

https://blog.csdn.net/hellokandy/article/details/51329446

MFC版本的计算两个SYSTEMTIME之间的时间差，返回毫秒：

1. __int64 TimeDiff(SYSTEMTIME left, SYSTEMTIME right)
2. {
3. CTime tmLeft(left.wYear, left.wMonth, left.wDay, 0, 0, 0);
4. CTime tmRight(right.wYear, right.wMonth, right.wDay, 0, 0, 0);
5. CTimeSpan sp = tmLeft - tmRight;
6. long MillisecondsL = (left.wHour*3600 + left.wMinute*60 + left.wSecond)*1000 + left.wMilliseconds;
7. long MillisecondsR = (right.wHour*3600 + right.wMinute*60 + right.wSecond)*1000 + right.wMilliseconds;
8. return  (__int64)sp.GetDays()*86400000 + (MillisecondsL - MillisecondsR);//此处返回毫秒
9. }

https://blog.csdn.net/hellokandy/article/details/51329183