How Can Constructor Ambiguity in C Virtual Inheritance Be Resolved?

C Virtual Inheritance: Resolving Constructor Ambiguity for Multiple Virtual Bases

The given code, featuring virtual base classes A and B inherited by derived class C, encounters a compilation error when attempting to construct an instance of C. Despite C inheriting from Base only indirectly through A and B, GCC raises an issue with finding the correct constructor for the Base class to initialize.

Understanding Virtual Base Class Initialization

Virtual base classes differ in their initialization process. Instead of being handled by intermediate base classes, virtual base initialization is delegated to the most derived class. When constructing a derived class that inherits from multiple virtual bases, like C in this instance, the compiler faces the challenge of selecting the appropriate initializer for the virtual base.

Addressing the Ambiguity

To resolve this ambiguity, the most derived class must explicitly initialize the virtual base class in its member initialization list. In this case, C should include the following in its constructor:

C(C* pParent) : Base(pParent), A(pParent), B(pParent) {}

By explicitly initializing Base in the constructor, you instruct the compiler to use the default constructor for Base, ensuring proper initialization.

Default Constructor Availability

It's important to remember that a virtual base class must have an accessible and implicit default constructor. If no default constructor is available or accessible, the compilation will fail.

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