C++ Primer, Fifth Edition

18.3.5. Constructors and Virtual Inheritance

In a virtual derivation, the virtual base is initialized by the most derived constructor. In our example, when we create a Panda object, the Panda constructor alone controls how the ZooAnimal base class is initialized.

To understand this rule, consider what would happen if normal initialization rules applied. In that case, a virtual base class might be initialized more than once. It would be initialized along each inheritance path that contains that virtual base. In our ZooAnimal example, if normal initialization rules applied, both Bear and Raccoon would initialize the ZooAnimal part of a Panda object.

Of course, each class in the hierarchy might at some point be the “most derived” object. As long ...