两个SYSTEMTIME比较

转自：http://blog.youkuaiyun.com/windless0530/article/details/5431112

time_t FileTimeToTime_t(const FILETIME &ft)
{
ULARGE_INTEGER ui;
ui.LowPart = ft.dwLowDateTime;
ui.HighPart = ft.dwHighDateTime;
return ((LONGLONG)(ui.QuadPart - 116444736000000000) / 10000000);
}

int GetDiffSeconds(const SYSTEMTIME &t1, const SYSTEMTIME &t2)
{
FILETIME fTime1 = { 0, 0 };
FILETIME fTime2 = { 0, 0 };
SystemTimeToFileTime(&t1, &fTime1);
SystemTimeToFileTime(&t2, &fTime2);

time_t tt1 = FileTimeToTime_t(fTime1);
time_t tt2 = FileTimeToTime_t(fTime2);

return (int)(tt2 - tt1);
}

int GetDiffDays(const SYSTEMTIME &t1, const SYSTEMTIME &t2)
{
int diffSeconds = GetDiffSeconds(t1, t2);
return diffSeconds / (24 * 3600);
}

反推SYSTEMTIME隔N天之后的SYSTEMTIME

void Time_tToFileTime(FILETIME &ft, time_t time)
{
    ULARGE_INTEGER ui;
    ui.QuadPart = (LONGLONG)(time * 10000000) + (LONGLONG)(116444736000000000);
    ft.dwLowDateTime = ui.LowPart;
    ft.dwHighDateTime = ui.HighPart;
}


void GetOffsetDaysTime(const SYSTEMTIME &stSrc, int offDays, SYSTEMTIME &stDst)
{
    FILETIME fTimeSrc = { 0, 0 };
    SystemTimeToFileTime(&stSrc, &fTimeSrc);
    time_t tmSrc = FileTimeToTime_t(fTimeSrc);
    time_t tmDst = tmSrc + SEC_OF_DAY * offDays;
    FILETIME fTimeDst = { 0, 0 };
    Time_tToFileTime(fTimeDst, tmDst);
    FileTimeToSystemTime(&fTimeDst, &stDst);
}