MFC Programmer's SourceBook : Thinking in C++
Bruce Eckel's Thinking in C++, 2nd Ed Contents | Prev | Next

Chapters

C++ is a language where new and different features are built on top of an existing syntax. (Because of this it is referred to as a hybrid object-oriented programming language.) As more people have passed through the learning curve, we’ve begun to get a feel for the way C programmers move through the stages of the C++ language features. Because it appears to be the natural progression of the C-trained mind, I decided to understand and follow this same path, and accelerate the process by posing and answering the questions that came to me as I learned the language and that came from audiences as I taught it.

This course was designed with one thing in mind: the way people learn the C++ language. Audience feedback helped me understand which parts were difficult and needed extra illumination. In the areas where I got ambitious and included too many features all at once, I came to know – through the process of presenting the material – that if you include a lot of new features, you have to explain them all, and the student’s confusion is easily compounded. As a result, I’ve taken a great deal of trouble to introduce the features as few at a time as possible; ideally, only one at a time per chapter.

The goal, then, is for each chapter to teach a single feature, or a small group of associated features, in such a way that no additional features are relied upon. That way you can digest each piece in the context of your current knowledge before moving on. To accomplish this, I leave many C features in place much longer than I would prefer. For example, I would like to be using the C++ iostreams IO library right away, instead of using the printf( ) family of functions so familiar to C programmers, but that would require introducing the subject prematurely, and so many of the early chapters carry the C library functions with them. This is also true with many other features in the language. The benefit is that you, the C programmer, will not be confused by seeing all the C++ features used before they are explained, so your introduction to the language will be gentle and will mirror the way you will assimilate the features if left to your own devices.

Here is a brief description of the chapters contained in this book [[ Please note this section will not be updated until all the chapters are in place ]]

(0) The evolution of objects. When projects became too big and too complicated to easily maintain, the “software crisis” was born, saying, “We can’t get projects done, and if we can they’re too expensive!” This precipitated a number of responses, which are discussed in this chapter along with the ideas of object-oriented programming (OOP) and how it attempts to solve the software crisis. You’ll also learn about the benefits and concerns of adopting the language and suggestions for moving into the world of C++.

(1) Data abstraction. Most features in C++ revolve around this key concept: the ability to create new data types. Not only does this provide superior code organization, but it lays the ground for more powerful OOP abilities. You’ll see how this idea is facilitated by the simple act of putting functions inside structures, the details of how to do it, and what kind of code it creates.

(2) Hiding the implementation. You can decide that some of the data and functions in your structure are unavailable to the user of the new type by making them private. This means you can separate the underlying implementation from the interface that the client programmer sees, and thus allow that implementation to be easily changed without affecting client code. The keyword class is also introduced as a fancier way to describe a new data type, and the meaning of the word “object” is demystified (it’s a variable on steroids).

(3) Initialization & cleanup. One of the most common C errors results from uninitialized variables. The constructor in C++ allows you to guarantee that variables of your new data type (“objects of your class”) will always be properly initialized. If your objects also require some sort of cleanup, you can guarantee that this cleanup will always happen with the C++ destructor.

(4) Function overloading & default arguments. C++ is intended to help you build big, complex projects. While doing this, you may bring in multiple libraries that use the same function name, and you may also choose to use the same name with different meanings within a single library. C++ makes this easy with function overloading , which allows you to reuse the same function name as long as the argument lists are different. Default arguments allow you to call the same function in different ways by automatically providing default values for some of your arguments.

(5) Introduction to iostreams. One of the original C++ libraries – the one that provides the essential I/O facility – is called iostreams. Iostreams is intended to replace C’s stdio.h with an I/O library that is easier to use, more flexible, and extensible – you can adapt it to work with your new classes. This chapter teaches you the ins and outs of how to make the best use of the existing iostream library for standard I/O, file I/O, and in-memory formatting.

(6) Constants. This chapter covers the const and volatile keywords that have additional meaning in C++, especially inside classes. It also shows how the meaning of const varies inside and outside classes and how to create compile-time constants in classes.

(7) Inline functions. Preprocessor macros eliminate function call overhead, but the preprocessor also eliminates valuable C++ type checking. The inline function gives you all the benefits of a preprocessor macro plus all the benefits of a real function call.

(8) Name control. Creating names is a fundamental activity in programming, and when a project gets large, the number of names can be overwhelming. C++ allows you a great deal of control over names: creation, visibility, placement of storage, and linkage. This chapter shows how names are controlled using two techniques. First, the static keyword is used to control visibility and linkage, and its special meaning with classes is explored. A far more useful technique for controlling names at the global scope is C++’s namespace feature, which allows you to break up the global name space into distinct regions.

(9) References & the copy-constructor. C++ pointers work like C pointers with the additional benefit of stronger C++ type checking. There’s a new way to handle addresses; from Algol and Pascal, C++ lifts the reference which lets the compiler handle the address manipulation while you use ordinary notation. You’ll also meet the copy-constructor, which controls the way objects are passed into and out of functions by value. Finally, the C++ pointer-to-member is illuminated.

(10) Operator overloading. This feature is sometimes called “syntactic sugar.” It lets you sweeten the syntax for using your type by allowing operators as well as function calls. In this chapter you’ll learn that operator overloading is just a different type of function call and how to write your own, especially the sometimes-confusing uses of arguments, return types, and making an operator a member or friend.

(11) Dynamic object creation. How many planes will an air-traffic system have to handle? How many shapes will a CAD system need? In the general programming problem, you can’t know the quantity, lifetime or type of the objects needed by your running program. In this chapter, you’ll learn how C++’s new and delete elegantly solve this problem by safely creating objects on the heap.

(12) Inheritance & composition. Data abstraction allows you to create new types from scratch; with composition and inheritance, you can create new types from existing types. With composition you assemble a new type using other types as pieces, and with inheritance you create a more specific version of an existing type. In this chapter you’ll learn the syntax, how to redefine functions, and the importance of construction and destruction for inheritance & composition.

(13) Polymorphism & virtual functions. On your own, you might take nine months to discover and understand this cornerstone of OOP. Through small, simple examples you’ll see how to create a family of types with inheritance and manipulate objects in that family through their common base class. The virtual keyword allows you to treat all objects in this family generically, which means the bulk of your code doesn’t rely on specific type information. This makes your programs extensible, so building programs and code maintenance is easier and cheaper.

(14) Templates & container classes. Inheritance and composition allow you to reuse object code, but that doesn’t solve all your reuse needs. Templates allow you to reuse source code by providing the compiler with a way to substitute type names in the body of a class or function. This supports the use of container class libraries, which are important tools for the rapid, robust development of object-oriented programs. This extensive chapter gives you a thorough grounding in this essential subject.

(15) Multiple inheritance. This sounds simple at first: A new class is inherited from more than one existing class. However, you can end up with ambiguities and multiple copies of base-class objects. That problem is solved with virtual base classes, but the bigger issue remains: When do you use it? Multiple inheritance is only essential when you need to manipulate an object through more than one common base class. This chapter explains the syntax for multiple inheritance, and shows alternative approaches – in particular, how templates solve one common problem. The use of multiple inheritance to repair a “damaged” class interface is demonstrated as a genuinely valuable use of this feature.

(16) Exception handling. Error handling has always been a problem in programming. Even if you dutifully return error information or set a flag, the function caller may simply ignore it. Exception handling is a primary feature in C++ that solves this problem by allowing you to “throw” an object out of your function when a critical error happens. You throw different types of objects for different errors, and the function caller “catches” these objects in separate error handling routines. If you throw an exception, it cannot be ignored, so you can guarantee that something will happen in response to your error.

(17) Run-time type identification. Run-time type identification (RTTI) lets you find the exact type of an object when you only have a pointer or reference to the base type. Normally, you’ll want to intentionally ignore the exact type of an object and let the virtual function mechanism implement the correct behavior for that type. But occasionally it is very helpful to know the exact type of an object for which you only have a base pointer; often this information allows you to perform a special-case operation more efficiently. This chapter explains what RTTI is for and how to use it.

Appendix A: Etcetera. At this writing, the C++ Standard is unfinished. Although virtually all the features that will end up in the language have been added to the standard, some haven’t appeared in all compilers. This appendix briefly mentions some of the other features you should look for in your compiler (or in future releases of your compiler).

Appendix B: Programming guidelines . This appendix is a series of suggestions for C++ programming. They’ve been collected over the course of my teaching and programming experience, and also from the insights of other teachers. Many of these tips are summarized from the pages of this book.

Appendix C: Simulating virtual constructors . The constructor cannot have any virtual qualities, and this sometimes produces awkward code. This appendix demonstrates two approaches to “virtual construction.”

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