QDateTime UTC Time_t problem

[scieck]

Hello,
shouldn't line 2 and line 4 below print the same UTC time?
Line 2 prints the correct UTC time, but line 4 prints local time.

The variable utc is holding UTC time, then calling utc.toTime_t() should return number of seconds from epoch to UTC, is this right ?
Then on line 4, a new QDateTime is built using the number of seconds from epoch to UTC, so shouldn't this print UTC time again?

QDateTime utc = QDateTime::currentDateTimeUtc();
qDebug() << utc;
uint time = utc.toTime_t();
qDebug() << QDateTime::fromTime_t(time); // this prints local time which is UTC + 9 hours

QDateTime utc = QDateTime::currentDateTimeUtc();
qDebug() << utc;
uint time = utc.toTime_t();
qDebug() << QDateTime::fromTime_t(time); // this prints local time which is UTC + 9 hours

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output:

QDateTime("Mon Feb 6 04:00:48 2012") 
QDateTime("Mon Feb 6 13:00:48 2012")

QDateTime("Mon Feb 6 04:00:48 2012") 
QDateTime("Mon Feb 6 13:00:48 2012")

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[ChrisW67]

Line 2 and 4 do print the same time, i.e they have the same time_t value which is always UTC, they are just formatted for different time zones.

QDateTime::fromTime_t() returns a QDateTime set to the local time corresponding to specified seconds after the epoch, i.e. it has Qt::LocalTime as its time spec, and this drives the string representation.

Try this:

qDebug() << "Local:" << QDateTime::currentDateTime();
QDateTime utc = QDateTime::currentDateTimeUtc();
qDebug() << "UTC:" << utc;
uint time = utc.toTime_t();
 
QDateTime result(QDate(), QTime(), Qt::UTC);  // a null UTC time
result.setTime_t(time);
qDebug() << "Result:" << result;

qDebug() << "Local:" << QDateTime::currentDateTime();
QDateTime utc = QDateTime::currentDateTimeUtc();
qDebug() << "UTC:" << utc;
uint time = utc.toTime_t();

QDateTime result(QDate(), QTime(), Qt::UTC);  // a null UTC time
result.setTime_t(time);
qDebug() << "Result:" << result;

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Local: QDateTime("Mon Feb 6 15:29:30 2012") 
UTC: QDateTime("Mon Feb 6 05:29:30 2012") 
Result: QDateTime("Mon Feb 6 05:29:30 2012")

Local: QDateTime("Mon Feb 6 15:29:30 2012") 
UTC: QDateTime("Mon Feb 6 05:29:30 2012") 
Result: QDateTime("Mon Feb 6 05:29:30 2012")

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[scieck]

I see, thanks Chris,

as I feel that local time is a special case of UTC time, I would have used Qt::UTC as (default) time spec rather than Qt::LocalTime.

anyway thanks for the clarification
cheers