C++ How to Program, 10/e

12.6 Abstract Classes and Pure virtual Functions

When we think of a class as a type, we assume that programs will create objects of that type. However, there are cases in which it’s useful to define classes from which you never intend to instantiate any objects. Such classes are called abstract classes. Because these classes normally are used as base classes in inheritance hierarchies, we refer to them as abstract base classes. These classes cannot be used to instantiate objects, because, as we’ll soon see, abstract classes are incomplete—derived classes must define the “missing pieces” before objects of these classes can be instantiated. We build programs with abstract classes in Section 12.7.

An abstract class is a base class from which other ...