[Interest] Relashionship between time_t and QDateTime

Thiago Macieira thiago.macieira at intel.com
Mon Aug 26 19:30:00 CEST 2013

On segunda-feira, 26 de agosto de 2013 17:42:58, Calogero Mauceri wrote:
> QDateTime myDateTime = QDateTime::fromTime_t(f_mtime);
> The date time printed doing a myDateTime.toString() is
>      Wed Dec 5 12:36:18 2007
> Retrieving the last modified information using QFileInfo, the result is
> different
>      QFileInfo fi(filepath);
>      QDateTime myDateTime = fi.lastModified();
> I get this result
>      Wed Dec 5 11:36:18 2007
> That is there is one hour difference. I guess the difference is due to
> the daylight saving management,
> but I can not understand how that management is performed.
> Note: if I look at the file properties on Windows dialog, the last
> modified time is shown as
>      Wed Dec 5 12:36:18 2007

Ah, Windows...

The problem might be simply a matter of timezones. The timestamps on files on 
Windows are not stored with time_t, but with some Windows-specific data. We get 
a FILETIME back from Win32.

Anyway, up until Qt 5.2, you cannot trust the output of a QDateTime with 
qDebug since it does not include the timezone. You have to ensure that the 
dates you're comparing by text are in the same timezone:

	qDebug() << dt.toUTC();

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