Chapter 15. Object-Oriented Programming

CONTENTS

Section 15.1 OOP: An Overview	558
Section 15.2 Defining Base and Derived Classes	560
Section 15.3 Conversions and Inheritance	577
Section 15.4 Constructors and Copy Control	580
Section 15.5 Class Scope under Inheritance	590
Section 15.6 Pure Virtual Functions	595
Section 15.7 Containers and Inheritance	597
Section 15.8 Handle Classes and Inheritance	598
Section 15.9 Text Queries Revisited	607
Chapter Summary	621
Defined Terms	621

Object-oriented programming is based on three fundamental concepts: data abstraction, inheritance, and dynamic binding. In C++ we use classes for data abstraction and class derivation to inherit one class from another: A derived class inherits the members of its base class(es). Dynamic binding lets the compiler determine at run time whether to use a function defined in the base or derived class.

Inheritance and dynamic binding streamline our programs in two ways: They make it easier to define new classes that are similar, but not identical, to other classes, and they make it easier for us to write programs that can ignore the details of how those similar types differ.

Many applications are characterized by concepts that are related but slightly different. For example, our bookstore might offer different pricing strategies for different books. Some books might be sold only at a given price. Others might be sold subject to some kind of discount strategy. We might give a discount to purchasers who buy a specified number of copies of the book. Or we might give a discount for only the first few copies purchased but charge full price for any bought beyond a given limit.

Object-oriented programming (OOP) is a good match to this kind of application. Through inheritance we can define types that model the different kinds of books. Through dynamic binding we can write applications that use these types but that can ignore the type-dependent differences.

The ideas of inheritance and dynamic binding are conceptually simple but have profound implications for how we build our applications and for the features that programming languages must support. Before covering how C++ supports OOP, we'll look at the concepts that are fundamental to this style of programming.