[Interest] Relashionship between time_t and QDateTime

Thiago Macieira thiago.macieira at intel.com
Tue Aug 27 19:57:32 CEST 2013

On terça-feira, 27 de agosto de 2013 21:40:29, Constantin Makshin wrote:
> When converting time from UTC to local time, Windows uses the *current*
> state of daylight saving, not one that was active at the time the
> original timestamp is "pointing" to.

Hmm... we have two versions of the code: FileTimeToSystemTime and gmtime. Are 
you saying that gmtime is broken and does not apply the correct historical 
daylight saving settings?

#if defined(Q_OS_WINCE)
    tm res;
    FILETIME localTime = time_tToFt(secsSince1Jan1970UTC);
    SYSTEMTIME sysTime;
    FileTimeToSystemTime(&localTime, &sysTime);
    FILETIME resultTime;
    LocalFileTimeToFileTime(&localTime , &resultTime);
    FileTimeToSystemTime(&resultTime , &sysTime);
    res.tm_sec = sysTime.wSecond;
    res.tm_min = sysTime.wMinute;
    res.tm_hour = sysTime.wHour;
    res.tm_mday = sysTime.wDay;
    res.tm_mon = sysTime.wMonth - 1;
    res.tm_year = sysTime.wYear - 1900;
    res.tm_isdst = (int)isdst;
    brokenDown = &res;
#elif !defined(QT_NO_THREAD) && defined(_POSIX_THREAD_SAFE_FUNCTIONS)
    // use the reentrant version of gmtime() where available
    tm res;
    brokenDown = gmtime_r(&secsSince1Jan1970UTC, &res);
#elif defined(_MSC_VER) && _MSC_VER >= 1400
    tm res;
    if (!_gmtime64_s(&res, &secsSince1Jan1970UTC))
        brokenDown = &res;
    brokenDown = gmtime(&secsSince1Jan1970UTC);

Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
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