Visual Studio C++ exception... weirdness

Question

Hi,

I have a Qt application that I compile in release configuration, run, and then perform operation X in the program. Everything runs fine.

I then compile it in debug configuration, run without debugging (so CTRL+F5), perform operation X in the program. Everything still runs dandy fine.

But when I try to run the debug configuration with debugging (so just F5) and then perform operation X, Visual Studio breaks in with a message that an exception has been thrown... in a completely unrelated part of the program (code being executed is far from the site where VS breaks, in the QHash template)... and then VS hangs and I have to kill it with the Task Manager. I can repeat this ad infinitum, and it always freaks out the same way.

Boost::exception is used for the exceptions. VS is 2008, SP1. Qt is 4.6.2, using the precompiled VS binaries from the Qt site.

Does anyone have a clue what is going on?

Answer 1

Visual Studio has a feature called "first chance exception handling" where, when running attached to the debugger, you can have the debugger break when exceptions of certain types are thrown.

You can change these settings by going to Debug -> Exceptions (Ctrl+Alt+E) and (un)checking the appropriate checkboxes.

When it breaks you should get a message in the Output window indicating what exception was thrown.

If you have _HAS_ITERATOR_DEBUGGING enabled (it is enabled by default in debug builds), it can cause a lot of iterator errors to throw exceptions instead of performing operations that would cause access violations. That's the only thing I can think of off the top of my head that would cause an exception to occur "randomly."