QDate conversions from/to string inconsistent for QLocale::ShortFormat (issue with the century)

Jacques L.

Looks like a wrong feature in Qt (to avoid to call it a bug).

Code:

   QDate qdate(2020,12,05);
   QString qstring = QLocale::system().toString(qdate, QLocale::ShortFormat);

   QDate qdate2 = QDate::fromString(qstring, QLocale::system().dateFormat(QLocale::ShortFormat));
   QString qstring2 = QLocale::system().toString(qdate, QLocale::ShortFormat);

    #define __DV(x) qDebug() << #x " =" << x

   __DV(qdate);
   __DV(qstring);
   __DV(qdate2);
   __DV(qstring2);

Output:

qdate = QDate("2020-12-05")
qstring = "05-12-20"
qdate2 = QDate("1920-12-05")
qstring2 = "05-12-20"

So, in the above code, I do not encode date strings myself, I'm just letting Qt to generate strings using QLocale::ShortFormat and interpreting its own result back to QDate, still using QLocale::ShortFormat. And Qt is mishandling the century.

Please note that I only need to work in the 21st century here. That's Qt that transform it in 20th century's date

The long format is too much for me but mm-dd-yyyy would be OK. I need to keep using QLocale. I need to save the date in a text file(i.e. as a string), and later read it back. Also I need to show it the shortest possible way in a QTableWidget.

The problem is that QDate string formatting in connection to QLocale is not very flexible, and Qt doesn't have a consistent interpretation in both direction of the QDate to/from QString conversions.

Of course, I may for sure solve this the long way (in terms of coding and runtime), but I wonder if there something that I'm doing wrong and that could be solved easily and a more clean way?

Christian Ehrlicher

The problem comes from https://code.woboq.org/qt5/qtbase/src/corelib/time/qdatetimeparser.cpp.html#1988 - can't change it for Qt5 anymore since it may break existing implementations but maybe it's not too late for Qt6.
See https://bugreports.qt.io/browse/QTBUG-89147