C++ Primer Plus, Fourth Edition

Inheritance—An Is-a Relationship

The special relationship between a derived class and base class is based upon an underlying model for C++ inheritance. Actually, C++ has three varieties of inheritance: public, protected, and private. Public inheritance is the most common form, and it models an is-a relationship. This is shorthand for saying that an object of a derived class should also be an object of the base class. Anything you do with a base-class object, you should be able to do with a derived-class object. Suppose, for example, you have a Fruit class. It could store, say, the weight and caloric content of a fruit. Because a banana is a particular kind of fruit, you could derive a Banana class from the Fruit class. The new class would inherit ...