Crash in QString destructor (while fetching reference count).

Bart_Vandewoestyne

I have a class Bar with a member variable of type QString. When the destructor of this class is called, I get a crash with the error message:

Exception thrown: read access violation.

_q_value was 0x58A0620.

If there is a handler for this exception, the program may be safely continued.

The top of the call stack looks as follows:

Qt5Cored.dll!QGenericAtomicOps<QAtomicOpsBySize<4> >::load<int>(const int & _q_value) Line 90   C++
Qt5Cored.dll!QBasicAtomicInteger<int>::load() Line 103  C++
Qt5Cored.dll!QtPrivate::RefCount::deref() Line 66       C++
Qt5Cored.dll!QString::~QString() Line 1135      C++
Foo.dll!Bar::~Bar()     C++
... irrelevant stuff ...

So I think what happens is the following:

QString destructor is called, so the reference count to the shared data must be decreased by one.
To decrease the reference count, the current reference count value is loaded (atomically).
Loading the current reference count (_q_value) fails.

I have no idea why this happens and am looking for suggestions for what I could possibly doing wrong in my code (certain anti-patterns related to QString and implicit data sharing???)

Any hint on what to look for in order to diagnose and fix this problem is very welcome. I cannot share any code due to company restrictions. Qt version we are using is our own build of Qt 5.12.2.

Christian Ehrlicher

I would guess you're deleting your class 'Bar' twice but it's only a guess without a reproducible minimal example.