Professional C__ - Marc Gregoire [25]
There are several aspects of the C++ language that make designing for C++ different, and more complicated, than designing for other languages.
C++ has an immense feature set. It is almost a complete superset of the C language, plus classes and objects, operator overloading, exceptions, templates, and many other features. The sheer size of the language makes design a daunting task.
C++ is an object-oriented language. This means that your designs should include class hierarchies, class interfaces, and object interactions. This type of design is quite different from “traditional” design in C or other procedural languages. Chapter 3 focuses on object-oriented design in C++.
C++ has numerous facilities for designing generic and reusable code. In addition to basic classes and inheritance, you can use other language facilities such as templates and operator overloading for effective design. Design techniques for reusable code are discussed in more details further in this chapter.
C++ provides a useful standard library, including a string class, I/O facilities, and many common data structures and algorithms. All of these facilitate coding in C++.
C++ is a language that readily accommodates many design patterns, or common ways to solve problems. Design patterns are discussed in Chapter 29.
Because of all of these issues, tackling a design for a C++ program can be overwhelming. One of the authors of this book has spent entire days scribbling design ideas on paper, crossing them out, writing more ideas, crossing those out, and repeating the process. Sometimes this process is helpful, and, at the end of those days (or weeks), leads to a clean, efficient design. Other times it can be frustrating, and leads nowhere. It’s important to remain aware of whether or not you are making real progress. If you find that you are stuck, you can take one of the following actions:
Ask for help. Consult a coworker, mentor, book, newsgroup, or web page.
Work on something else for a while. Come back to this design choice later.
Make a decision and move on. Even if it’s not an ideal solution, decide on something and try to work with it. An incorrect choice will soon become apparent. However, it may turn out to be an acceptable method. Perhaps there is no clean way to accomplish what you want to with this design. Sometimes you have to accept an “ugly” solution if it’s the only realistic strategy to fulfill your requirements. Whatever you decide, make sure you document your decision, so that you and others in the future know why you made it.
Keep in mind that good design is hard, and getting it right takes practice. Don’t expect to become an expert overnight, and don’t be surprised if you find it more difficult to master C++ design than C++ coding.
TWO RULES FOR C++ DESIGN
There are two fundamental design rules in C++: abstraction and reuse. These guidelines are so important that they can be considered themes of this book. They come up repeatedly throughout the text, and throughout effective C++ program designs in all domains.
Abstraction
The principle of abstraction is easiest to understand through a real-world analogy. A television is a simple piece of technology found in most homes. You are probably familiar with its features: You can turn it on and off, change the channel, adjust the volume, and add external components such as speakers, VCRs, and DVD players. However, can you explain how it works inside the black box? That is, do you know how it receives signals over the air or through a cable, translates them, and displays them on the screen? We certainly can’t explain how a television works, yet we are quite capable of using it. That is because the television clearly separates its internal implementation from its external interface. We interact with the television through its interface: the power button, channel changer, and volume control. We don’t know, nor do we care, how the television works; we don’t care whether it uses a cathode ray tube or some sort of alien technology to generate the image on our