Classes

Introduction

This chapter contains solutions to common problems related to working with C++ classes. The recipes are mostly independent, but they are organized into two parts, which each make up about half the chapter. The first half of the chapter contains solutions to common problems you may experience when constructing objects of a class, such as using a function to create objects (which is often called a Factory pattern) or using constructors and destructors to manage resources. The second half contains solutions to problems post-construction, such as determining an object's type at runtime, and miscellaneous implementation techniques, such as how to create an interface with an abstract base class.

Classes are, of course, the central feature of C++ that supports object-oriented programming, and there are lots of different things you can do with classes. This chapter does not contain recipes that explain the basics of classes: virtual functions (polymorphism), inheritance, and encapsulation. I assume you are already familiar with these general object-oriented design principles, whether it's with C++ or another language such as Java or Smalltalk. Rather, the purpose of this chapter is to provide recipes for some of the mechanical difficulties you may run into when implementing object-oriented designs with C++.

Object-oriented design and the related design patterns is a huge subject, and the literature on the subject is vast and comprehensive. I mention only a few design patterns by name in this chapter, and they are the ones for which C++ facilities provide an elegant or perhaps not-so-obvious solution. If you are unfamiliar with the concept of design patterns, I recommend you read Design Patterns by Gamma, et al (Addison Wesley), because it is a useful thing to know in software engineering; however, it is not a prerequisite for this chapter.