QFatal where is the problem

[grastvei]

I've got a software that suddenly gives me a qFatal from qlist::at but there is no stacktrace that tell me what caused it. Is there a god method to get the stacktrace or similar from the crash?

[sierdzio]

Run in debug mode if possible.

A shot in the dark (but ion case of QList it's really very possible) is that somebody is trying to access an index outside of the list (index > QList::size()). Normally that crashes with a failed assertion.

[grastvei]

I run in debug, and I know something is trying to access outside the list. But it is hard to detect from where this call is.

[sierdzio]

No stacktrace in debug mode? Have you compiled Qt yourself only in release mode, perhaps?

[grastvei]

It is qt5.1 for mingw.
When i recive qFatal the application keeps running in the background, but it is not possible to interact with it anymore.

[grastvei]

The solution for me is to use: qInstallMessageHandler
Install a new handler and break when the qFatal occurs.

[Jeroentjehome]

Hi, just for your information, but a QList index is size() - 1 as maximum. It works like arrays in C, so with index 0, not 1!
That might explain a crash.

[grastvei]

The crash was QString::number sometimes convert a double incorrectly. It work maybe a million times and the suddenly dropped everything after the decimal, and coursed the a split operation to fail.

[grastvei]

When we first are writing error handlers to capture errors. Is there an easy way to capture a stack trace? That would make it easier to debug a crash that is done by a customer.

[Jeroentjehome]

Hi,
In Qt5 you are able to install an event message handler. There your are able to store any data into a errorLog file etc before the crash really aborts the program (qFatal).
Maybe that would add functionality to your program for debugging.