QObject destructors not being called

Question

I have two QObject child classes in my Qt application. One object from each of these classes was instantiated on the stack. Previously, my application would exit cleanly. However, since I've updated to Qt5.1.0, their destructors are not being called. I get the following warning twice when I launch the debugger.

the debug information found in "/usr/lib/debug//lib64/libfreebl3.so.debug" 
does not match "/lib64/libfreebl3.so" (CRC mismatch)

Is this a bug in Qt or in my code?

Answer 1

See the documentation of QCoreApplication::exec:

We recommend that you connect clean-up code to the aboutToQuit() signal, instead of putting it in your application's main() function because on some platforms the QCoreApplication::exec() call may not return. For example, on Windows when the user logs off, the system terminates the process after Qt closes all top-level windows. Hence, there is no guarantee that the application will have time to exit its event loop and execute code at the end of the main() function after the QCoreApplication::exec() call.

You're using it incorrectly. It is not guaranteed that exec will be terminated after windows are closed. You should use aboutToQuit signal to stop other threads. If this signal is not emitted either, you need to call QApplication::quit() explicitly when your window is closed.

Answer 2

I'm not exactly sure in this case if this is a bug in your code or not, but anyway it is not recommended to create QObjects in the stack.

The reason is that the parent object (if any) will automatically call delete when destroyed, but then the object will also be automatically destroyed when it goes out of scope. Hence the object is destroyed twice which is Undefined Behaviour. That may explained why it worked well in one case, and not in another, since you can't rely on any consistent behaviour.

(But in your case it is weird that you say the destructor is not called at all...)