[Interest] Construction of QObjects before QApplication or something else brings SEGV

[Etienne Sandré-Chardonnal]

About the first problem, that's normal, since the documentation says:
"Since the QApplication object does so much initialization, it *must* be
created before any other objects related to the user interface are created."

QApplication is created in main() in most cases. Then, the GUI is created.
Then, the main returns a->exec().

Could you post the code? Otherwise, check Qt examples about how to
initialize an application.

And if you have a segfault situation, this means the behavior is likely
undefined. So making trivial changes, changing the compiler version, eating
a pizza, and even doing nothing may change the code's behavior.

Etienne


2013/9/11 Olivier BARTHELEMY <barthelemy at geovariances.com>

> I am having SEGFAULTS in some code just by making trivial changes that
> should not influence the behaviour.
> The code simply creates a QTextEdit in a QDIalog, and segfaults somewhere
> in child calls of show() on the QDialog
> Running valgrind, i noticed warnings about 'conditional jump or move
> depending on uninitialized value'. Strangely, the warning has an almost
> identical call stack than the segv.
> The warning is apparently triggered because the class that builds the
> QApplication and the dialog is a child of QObject, so the QObject
> constructed before the QApplication must mess something up. Removing that
> inheritance to QOBject, of manually creating the QApplication before
> creating the class object removes the valgrind warning, but does not clear
> the SEGV.
> I have had some mixed success to remove the segv by trying multiple G++
> versions. Older G++ versions seem to crash less (no crash in 4.1, little
> crashes in 4.4, almost always crash in 4.6), but the results are
> inconsistent. It seems more like the difference of generated code triggers
> more or less the error, but what is messed up is still there.
>
> People there (https://code.google.com/p/eiskaltdc/issues/detail?id=601)
> and on some other sites (google 'QWidgetPrivate::create_sys conditional
> jump' for example) have been having similar problems of either the warning
> or the SEGV with call stacks indicating the same problem, but without
> solution.
>
> Any suggestion?
>
> I'm using QT4.8.5
>
>
> --
> Olivier BARTHELEMY
>
> _______________________________________________
> Interest mailing list
> Interest at qt-project.org
> http://lists.qt-project.org/mailman/listinfo/interest
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.qt-project.org/pipermail/interest/attachments/20130911/bf5b5adb/attachment.html>