Stuck with Segmentation fault

Im in the middle of the implementation of the calculation of the Transform origin with all editmode objects (by now only acitve Object is taken into accont).
I implemented it for Armatures and it works fine. Also tried Curves but im now getting a Segmentation fault when I display a transform gizmo.
How can I debug a Segfault (in QT Creator)? Is it possible to set up a step by step debugging? The function seems to reach the end, the error occurs after the function.

I’m not familiar with QtCreator myself, but we seem to have some info on that here: