[Qt-interest] Strange problem storing and retrieving and comparing QTime/QDataTime

[Thiago Macieira]

Em Terça-feira 17 Novembro 2009, às 12:55:57, você escreveu:
> timeSpec() on both returns 0 (Qt::LocalTime)
> 
> converting both toTimeSpec(Qt::UTC), just for a try, and comparison again
>  failed.
> 
> However "converting" toTime_t(), actually made the test pass!

Now that's weird. The time_t value is basically the number of seconds since 
Jan 1, 1970, 0:00 UTC. It's calculated by converting the QDateTime to UTC then 
calculating the number of seconds:

static uint toTime_tHelper(const QDate &utcDate, const QTime &utcTime)
{
    int days = QDate(1970, 1, 1).daysTo(utcDate);
    int secs = QTime().secsTo(utcTime);
    if (days < 0 || (days == 0 && secs < 0))
        return uint(-1);

    qlonglong retval = (qlonglong(days) * SECS_PER_DAY) + secs;
    if (retval >= Q_INT64_C(0xFFFFFFFF))
        return uint(-1);
    return uint(retval);
}

Now, remember that QDateTime keeps the time precision in *milliseconds*, 
whereas time_t has a resolution of seconds. My guess is your roundtrip through 
the database discarded the millisecond component (your source was 
file.lastModified(), which does have millisecond resolution).

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Senior Product Manager - Nokia, Qt Development Frameworks
      PGP/GPG: 0x6EF45358; fingerprint:
      E067 918B B660 DBD1 105C  966C 33F5 F005 6EF4 5358
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