QT 5.2 bug of incorrect calling of QDateTime::fromString() ?

[abshaev]

Hi everybody!

I cannot understand the reason of my problem connected with calling of function QDateTime::fromString.
The result of it is always "invalid" independently on converting format and datetime string.

When i calling opposite function .toString everything is OK:

QDateTime local(QDateTime::currentDateTime());
QString format = "yyyy-MM-dd hh:mm:ss";
QString S = local.toString(format);

Result: S = "2016-09-04 13:35:29"

But if I call it with the same settings it fails:

QDateTime dateTime = QDateTime::fromString(S, format);

Result: dateTime = (invalid)

Is it a bug of QT, if yes how to improve it ?

I use:
- Linux Ubuntu 15.04 64 bit
- Qt Creator 3.0.0
Based on Qt 5.2.0 (GCC 4.6.1, 64 bit)
Built on Dec 10 2013 at 11:45:55
From revision 27d10d8dcd

[anda_skoa]

This works for me

#include <QDateTime>
#include <QDebug>
 
int main()
{
    QDateTime d = QDateTime::currentDateTime();
 
    const QString format = "yyyy-MM-dd hh:mm:ss";
    const QString formatted = d.toString(format);
    qDebug() << "d=" << d << ", formatted=" << formatted;
 
    QDateTime d2 = QDateTime::fromString(formatted, format);
    qDebug() << "d2=" << d2;
 
    return 0;
}

#include <QDateTime>
#include <QDebug>

int main()
{
    QDateTime d = QDateTime::currentDateTime();
    
    const QString format = "yyyy-MM-dd hh:mm:ss";
    const QString formatted = d.toString(format);
    qDebug() << "d=" << d << ", formatted=" << formatted;
    
    QDateTime d2 = QDateTime::fromString(formatted, format);
    qDebug() << "d2=" << d2;

    return 0;
}

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Output is

d= QDateTime(2016-09-04 18:51:28.549 CEST Qt::TimeSpec(LocalTime)) , formatted= "2016-09-04 18:51:28"
d2= QDateTime(2016-09-04 18:51:28.000 CEST Qt::TimeSpec(LocalTime))

d= QDateTime(2016-09-04 18:51:28.549 CEST Qt::TimeSpec(LocalTime)) , formatted= "2016-09-04 18:51:28"
d2= QDateTime(2016-09-04 18:51:28.000 CEST Qt::TimeSpec(LocalTime))

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Qt 5.5.1, Debian/Unstable

Cheers,
_

[abshaev]

It is interesting, your code outputs the correct result on my desktop, but the value of datetime variable d2 is still "invalid" !

Debugging starts
&"warning: GDB: Failed to set controlling terminal: Inappropriate ioctl for device\n"
d= QDateTime("2016-09-04 20:19:13.029 MSK Qt::LocalTime") , formatted= "2016-09-04 20:19:13"
d2= QDateTime("2016-09-04 20:19:13.000 MSK Qt::LocalTime")

[Lesiok]

It is interesting, your code outputs the correct result on my desktop, but the value of datetime variable d2 is still "invalid" !

Debugging starts
&"warning: GDB: Failed to set controlling terminal: Inappropriate ioctl for device\n"
d= QDateTime("2016-09-04 20:19:13.029 MSK Qt::LocalTime") , formatted= "2016-09-04 20:19:13"
d2= QDateTime("2016-09-04 20:19:13.000 MSK Qt::LocalTime")

This code does exactly what to do. Format string does not contain expressions for milliseconds. Try this :

const QString format = "yyyy-MM-dd hh:mm:ss.zzz";

const QString format = "yyyy-MM-dd hh:mm:ss.zzz";

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[abshaev]

This code does exactly what to do. Format string does not contain expressions for milliseconds. Try this :

const QString format = "yyyy-MM-dd hh:mm:ss.zzz";

const QString format = "yyyy-MM-dd hh:mm:ss.zzz";

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I have added milliseconds to the format string, but resulting qdatetime is still invalid !))
Debug output is normal.
So I suppose that there is the bug in my Qt or Qt Creator release.

[Lesiok]

What does it mean "is still invalid" ? d2.isValid() returns false or You see somewhere different value than you expect ?

[anda_skoa]

I've changed the second output to

qDebug() << "d2=" << d2 << ", d2.isValid=" << d2.isValid();

qDebug() << "d2=" << d2 << ", d2.isValid=" << d2.isValid();

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and the output is

d2= QDateTime(2016-09-05 12:25:39.000 CEST Qt::TimeSpec(LocalTime)) , d2.isValid= true

d2= QDateTime(2016-09-05 12:25:39.000 CEST Qt::TimeSpec(LocalTime)) , d2.isValid= true

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Cheers,
_

[Lesiok]

So change it to :

qDebug() << "d2=" << d2.toString(format) << ", d2.isValid=" << d2.isValid();

qDebug() << "d2=" << d2.toString(format) << ", d2.isValid=" << d2.isValid();

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P.S.
Look at qdatetime.cpp how operator << for qdebug is working for this class.
In Qt 4.8 it uses QDateTime::toString() for this, in 5.7 QDateTime::toString(QStringLiteral("yyyy-MM-dd HH:mm:ss.zzz t")).
So this is not a bug.