Creating QDateTime from string

[SPlatten]

I am trying to create an instance of QDateTime from a string, the string I have is in the format:

yyyy/MM/dd hh:mm:ss.zzz

I've tried:

QDateTime dtmCreated(QDateTime::fromString(strValue));

Where strValue contains:

2021-08-20T06:45:18

I then output dtmCreated to the console:

qDebug() << strValue << dtmCreated.isValid();

isValid returns false, I've also tried:

QDateTime dtmCreated(QDateTime::fromString(strValue, "yyyy/MM/ddThh:mm:ss"));

Same result isValid is false.

Also tried:

QDateTime dtmCreated(QDateTime::fromString(strValue, "yyyy-MM-dd HH:mm:ss"));

Same result isValid is false.

[J.Hilk]

@SPlatten
T

int main(int argc, char *argv[])
{
    QDateTime td = QDateTime::fromString("2021-08-20T06:45:18", "yyyy-MM-ddThh:mm:ss");
    qDebug() << td.isValid() << td;
    return 0;
}

[J.Hilk]

@SPlatten said in Creating QDateTime from string:
So, your date string contains -as separators and your format is passed as /

2021-08-20T06:45:18

Do you see the discrepancy? 😉

[SPlatten]

@J-Hilk , edited post having tried something else, still not working.

[J.Hilk]

@SPlatten
T

int main(int argc, char *argv[])
{
    QDateTime td = QDateTime::fromString("2021-08-20T06:45:18", "yyyy-MM-ddThh:mm:ss");
    qDebug() << td.isValid() << td;
    return 0;
}

[SPlatten]

@J-Hilk Using "yyyy-MM-ddTHH:mm:ss" works, something minor, in the database using a length of 6 I store the date/timestamp to microsecond resolution, when converting to QDateTime, its only accurate to seconds.

[J.Hilk]

@SPlatten QDateTime should be able to handle milliseconds, because thats what QTime can handle, but nothing further.

[KroMignon]

@SPlatten said in Creating QDateTime from string:

when converting to QDateTime, its only accurate to seconds.

QDateTime accuracy is down to milliseconds:

// Read milliseconds time stamp
QDateTime td = QDateTime::fromString("2021-08-20T06:45:18.234", "yyyy-MM-ddThh:mm:ss.zzz");

// add milliseconds to QDateTime
dt = dt.addMSecs(998);

[SPlatten]

@KroMignon , it seems that although the database field is accurate to microseconds, when I read the data into the application the QSqlField:

QString strName(crField.name()), strValue(crField.value().toString());

crField is a constant reference passed in parameter of QSqlField. strValue when converting the TIMESTAMP(6) from the database which in the database contains 2021-08-20 06:46:18.832407 gets converted to 2021-08-20T06:46:18, this doesn't even contain milliseconds.

[KroMignon]

@SPlatten said in Creating QDateTime from string:

when converting the TIMESTAMP(6) from the database

According to QVariant documentation, QVariant::toDateTime() will useQt::ISODate and not Qt::ISODateWithMs. So with the default conversion, you will never got milliseconds.

Do you really need micro-seconds in DB? Is TIMESTAMP(3) (milliseconds) not enough for you?
With this type, you should be able to parse the DATETIME with milliseconds (with Qt::ISODateWithMs / yyyy-MM-ddThh:mm:ss.zzz).

[SPlatten]

@KroMignon , to be honest milliseconds is probably good enough, but the higher resolution the better in the database, from your post is there a way to get milliseconds is the conversion doesn't use Qt::ISODateWithMS ?

[KroMignon]

@SPlatten said in Creating QDateTime from string:

to be honest milliseconds is probably good enough, but the higher resolution the better in the database, from your post is there a way to get milliseconds is the conversion doesn't use Qt::ISODateWithMS ?

Yes, I think so:

QDateTime dt = QDateTime::fromString(crField.value().toString(), Qt::ISODateWithMS);

[SPlatten]

@KroMignon, I'm not sure that is going to work because the toString function already removes the fraction part of the time.