Why Are Multiple Destructors Generated in GNU GCC (g )?
GNU GCC (g ): Multiple Dtors Explained
Problem:
While investigating code coverage in a C project, it was observed that multiple destructors (dtors) were being generated for some classes. This article aims to explain why and how these multiple dtors are created.
Understanding Dtor Variations
In the Itanium C ABI, there are three types of destructors:
- D2 (Base Object Destructor): Destroys the object itself, along with non-virtual base classes and data members.
- D1 (Complete Object Destructor): Destroys virtual base classes in addition to D2's functionality.
- D0 (Deleting Destructor): Performs the same tasks as D1, but also calls operator delete to release memory.
Multiple Dtor Generation
Multiple dtors are generated for classes that have virtual base classes. This is because virtual base classes need to be destroyed in a specific order to ensure proper memory management.
Selective Usage of Dtors
The choice of which dtors to use depends on the code context:
- If a class has no virtual base classes, D2 and D1 are identical.
- To destroy an object of a specific base class, the dtors with matching types (D2 or D1) are used.
- To completely destroy an object of a derived class, D1 is used.
- To destroy an object and release its associated memory, D0 is called.
Coverage Considerations
When striving for complete function coverage in unit testing, it's crucial to consider all forms of dtors to ensure that their execution is adequately tested.
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