10 Defining Classes

1. 10.1 Structures 544

   1. Structures for Diverse Data 544

   2. Pitfall: Forgetting a Semicolon in a Structure Definition 549

   3. Structures as Function Arguments 550

   4. Programming Tip: Use Hierarchical Structures 551

   5. Initializing Structures 553

2. 10.2 Classes 556

   1. Defining Classes and Member Functions 556

   2. Public and Private Members 561

   3. Programming Tip: Make All Member Variables Private 569

   4. Programming Tip: Define Accessor and Mutator Functions 569

   5. Programming Tip: Use the Assignment Operator with Objects 571

   6. Programming Example: BankAccount Class—Version 1 572

   7. Summary of Some Properties of Classes 576

   8. Constructors for Initialization 578

   9. Programming Tip: Always Include a Default Constructor 586

   10. Pitfall: Constructors with No Arguments 587

   11. Member Initializers and Constructor Delegation in C++11 589

3. 10.3 Abstract Data Types 590

   1. Classes to Produce Abstract Data Types 591

   2. Programming Example: Alternative Implementation of a Class 595

4. 10.4 Introduction to Inheritance 600

   1. Derived Classes 601

   2. Defining Derived Classes 602

1. Chapter Summary 606

2. Answers to Self-Test Exercises 607

3. Practice Programs 613

4. Programming Projects 614

“The time has come,” the Walrus said,

“To talk of many things:

Of shoes—and ships—and sealing wax—

Of cabbages—and kings—”

LEWIS CARROLL, Through the Looking-Glass

Introduction

In Chapter 6 you learned how to use classes and objects, but not how to define classes. In this chapter we will show you how to define your own classes. A class is a data type. You can use the classes you define in the same way you use the predefined data types, such as int, char, and ifstream. However, unless you define your classes the right way, they will not be as well behaved as the predefined data types. Thus, we spend a good deal of time explaining what makes for a good class definition and give you some techniques to help you define your classes in a way that is consistent with modern programming practices.

Before we introduce classes, we will first present structures (also known as structs). When used in the way we present them here, a structure is a kind of simplified class and structures will prove to be a stepping-stone to understanding classes.

Prerequisites

This chapter uses material from Chapters 2 through 6.