Why Does GCC Generate Multiple Destructors in C ?

Why Does GNU GCC Generate Multiple Destructors?

In C , a class may have multiple destructors, each with a specific purpose:

Base Object Destructor (D2): Destroys the object itself, non-virtual base classes, and data members.

Complete Object Destructor (D1): Additionally destroys virtual base classes.

Deleting Object Destructor (D0): Calls operator delete to free the memory and performs the same actions as D1.

Origins of Multiple Destructors

When compiling, GCC generates these destructors for classes with virtual functions or virtual base classes. This is a requirement of the C ABI (Application Binary Interface) for the Itanium architecture.

Differences and Usage

D2 and D1 are functionally equivalent if there are no virtual base classes. GCC may alias their symbols to the same code on certain optimizations.

Impact on Unit Testing

To achieve 100% function coverage for classes with virtual methods or base classes, it is crucial to cover all the destructors (D2, D1, and D0) in unit tests to ensure adequate testing for the entire destruction process.

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