C++编程语言特别版：初学者指南

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"C++程序设计语言特别版，一本适合C++初学者的编程教程" 《C++程序设计语言特别版》是由Bjarne Stroustrup编写的，他是C++语言的创始人之一，这本书是C++编程领域的重要参考资料。第三版在原有的基础上进行了更新和扩展，以适应现代编程环境的需求，对于想要学习C++编程语言的初学者来说，是一本不可多得的教材。 C++是一种静态类型的、编译式的、通用的、大小写敏感的、不仅支持过程化编程，也支持面向对象编程的程序设计语言。它在C语言的基础上增加了类、模板、命名空间、异常处理等特性，使得程序设计更加灵活和强大。C++的语法严谨，对程序员的要求较高，但同时也提供了更高的性能和更精细的控制。本书的内容涵盖了C++的基础概念，如变量、运算符、流程控制语句（如if、switch、循环）、函数的定义和调用，以及更高级的主题，如类的设计与实现、继承、多态、模板和STL（标准模板库）。STL包括了容器（如vector、list、map）、迭代器、算法和函数对象，是C++编程中不可或缺的一部分。书中详细讲解了C++的关键特性，如构造函数和析构函数在对象生命周期中的作用，以及如何使用友元来打破封装的限制。异常处理机制使得程序能够优雅地处理错误，而不至于崩溃。此外，作者还深入探讨了C++的模板系统，这是一个强大的工具，可以用于创建泛型代码，提高代码的复用性。此外，书中还介绍了C++的最新标准（可能指的是C++11及其后续版本）引入的新特性，如智能指针、右值引用、lambda表达式、统一初始化等，这些新特性使得C++在保持高效性的同时，编程风格更加简洁和安全。学习C++不仅需要理解语言本身，还需要了解如何编写高质量、可维护的代码。本书将帮助读者建立良好的编程习惯，理解面向对象编程的基本原则，并掌握C++的核心概念和技术。同时，通过阅读本书，读者还将了解到C++与其他编程语言的异同，以及如何在实际项目中应用C++。《C++程序设计语言特别版》是一本全面且深入的C++教程，适合那些希望从零开始学习C++的读者，同时也可供有经验的程序员参考，以深化对C++的理解和应用。无论你是编程新手还是资深开发者，都能从这本书中受益匪浅。

Section 1.1.1 Examples and References 5

1.1.1 Examples and References

This book emphasizes program organization rather than the writing of algorithms. Consequently, I

avoid clever or harder-to-understand algorithms. A trivial algorithm is typically better suited to

illustrate an aspect of the language definition or a point about program structure. For example, I

use a Shell sort where, in real code, a quicksort would be better. Often, reimplementation with a

more suitable algorithm is an exercise. In real code, a call of a library function is typically more

appropriate than the code used here for illustration of language features.

Textbook examples necessarily give a warped view of software development. By clarifying and

simplifying the examples, the complexities that arise from scale disappear. I see no substitute for

writing realistically-sized programs for getting an impression of what programming and a program-

ming language are really like. This book concentrates on the language features, the basic tech-

niques from which every program is composed, and the rules for composition.

The selection of examples reflects my background in compilers, foundation libraries, and simu-

lations. Examples are simplified versions of what is found in real code. The simplification is nec-

essary to keep programming language and design points from getting lost in details. There are no

‘‘cute’’ examples without counterparts in real code. Wherever possible, I relegated to Appendix C

language-technical examples of the sort that use variables named x x and y y, types called A A and B B, and

functions called f f() and g g().

In code examples, a proportional-width font is used for identifiers. For example:

#i in nc cl lu ud de e<i io os st tr re ea am m>

i in nt t m ma ai in n()

{

s st td d: :c co ou ut t << "H He el ll lo o, n ne ew w w wo or rl ld d!\ \n n";

}

At first glance, this presentation style will seem ‘‘unnatural’’ to programmers accustomed to seeing

code in constant-width fonts. However, proportional-width fonts are generally regarded as better

than constant-width fonts for presentation of text. Using a proportional-width font also allows me

to present code with fewer illogical line breaks. Furthermore, my experiments show that most peo-

ple find the new style more readable after a short while.

Where possible, the C

language and library features are presented in the context of their use

rather than in the dry manner of a manual. The language features presented and the detail in which

they are described reflect my view of what is needed for effective use of C

. A companion, The

Annotated C

Language Standard, authored by Andrew Koenig and myself, is the complete defi-

nition of the language together with comments aimed at making it more accessible. Logically,

there ought to be another companion, The Annotated C

Standard Library. However, since both

time and my capacity for writing are limited, I cannot promise to produce that.

References to parts of this book are of the form §2.3.4 (Chapter 2, section 3, subsection 4),

§B.5.6 (Appendix B, subsection 5.6), and §6.6[10] (Chapter 6, exercise 10). Italics are used spar-

ingly for emphasis (e.g., ‘‘a string literal is not acceptable’’), for first occurrences of important con-

cepts (e.g., polymorphism), for nonterminals of the C

grammar (e.g., for-statement), and for com-

ments in code examples. Semi-bold italics are used to refer to identifiers, keywords, and numeric

values from code examples (e.g., c co ou un nt te er r, c cl la as ss s, and 1 17 71 12 2).

The C++ Programming Language, Special Edition by Bjarne Stroustrup. Copyright 2000 by AT&T.

6 Notes to the Reader Chapter 1

1.1.2 Exercises

Exercises are found at the ends of chapters. The exercises are mainly of the write-a-program vari-

ety. Always write enough code for a solution to be compiled and run with at least a few test cases.

The exercises vary considerably in difficulty, so they are marked with an estimate of their diffi-

culty. The scale is exponential so that if a (∗1) exercise takes you ten minutes, a (∗2) might take an

hour, and a (∗3) might take a day. The time needed to write and test a program depends more on

your experience than on the exercise itself. A (∗1) exercise might take a day if you first have to get

acquainted with a new computer system in order to run it. On the other hand, a (∗5) exercise might

be done in an hour by someone who happens to have the right collection of programs handy.

Any book on programming in C can be used as a source of extra exercises for Part I. Any book

on data structures and algorithms can be used as a source of exercises for Parts II and III.

1.1.3 Implementation Note

The language used in this book is ‘‘pure C

’’ as defined in the C

standard [C

,1998]. There-

fore, the examples ought to run on every C

implementation. The major program fragments in

this book were tried using several C

implementations. Examples using features only recently

adopted into C

didn’t compile on every implementation. However, I see no point in mentioning

which implementations failed to compile which examples. Such information would soon be out of

date because implementers are working hard to ensure that their implementations correctly accept

every C

feature. See Appendix B for suggestions on how to cope with older C

compilers and

with code written for C compilers.

1.2 Learning C

The most important thing to do when learning C

is to focus on concepts and not get lost in

language-technical details. The purpose of learning a programming language is to become a better

programmer; that is, to become more effective at designing and implementing new systems and at

maintaining old ones. For this, an appreciation of programming and design techniques is far more

important than an understanding of details; that understanding comes with time and practice.

supports a variety of programming styles. All are based on strong static type checking, and

most aim at achieving a high level of abstraction and a direct representation of the programmer’s

ideas. Each style can achieve its aims effectively while maintaining run-time and space efficiency.

A programmer coming from a different language (say C, Fortran, Smalltalk, Lisp, ML, Ada, Eiffel,

Pascal, or Modula-2) should realize that to gain the benefits of C

, they must spend time learning

and internalizing programming styles and techniques suitable to C

. The same applies to pro-

grammers used to an earlier and less expressive version of C

Thoughtlessly applying techniques effective in one language to another typically leads to awk-

ward, poorly performing, and hard-to-maintain code. Such code is also most frustrating to write

because every line of code and every compiler error message reminds the programmer that the lan-

guage used differs from ‘‘the old language.’’ You can write in the style of Fortran, C, Smalltalk,

etc., in any language, but doing so is neither pleasant nor economical in a language with a different

philosophy. Every language can be a fertile source of ideas of how to write C

programs.

The C++ Programming Language, Special Edition by Bjarne Stroustrup. Copyright 2000 by AT&T.

Section 1.2 Learning C

However, ideas must be transformed into something that fits with the general structure and type

system of C

in order to be effective in the different context. Over the basic type system of a lan-

guage, only Pyrrhic victories are possible.

supports a gradual approach to learning. How you approach learning a new programming

language depends on what you already know and what you aim to learn. There is no one approach

that suits everyone. My assumption is that you are learning C

to become a better programmer

and designer. That is, I assume that your purpose in learning C

is not simply to learn a new syn-

tax for doing things the way you used to, but to learn new and better ways of building systems.

This has to be done gradually because acquiring any significant new skill takes time and requires

practice. Consider how long it would take to learn a new natural language well or to learn to play a

new musical instrument well. Becoming a better system designer is easier and faster, but not as

much easier and faster as most people would like it to be.

It follows that you will be using C

– often for building real systems – before understanding

every language feature and technique. By supporting several programming paradigms (Chapter 2),

supports productive programming at several levels of expertise. Each new style of program-

ming adds another tool to your toolbox, but each is effective on its own and each adds to your

effectiveness as a programmer. C

is organized so that you can learn its concepts in a roughly lin-

ear order and gain practical benefits along the way. This is important because it allows you to gain

benefits roughly in proportion to the effort expended.

In the continuing debate on whether one needs to learn C before C

, I am firmly convinced

that it is best to go directly to C

. C

is safer, more expressive, and reduces the need to focus on

low-level techniques. It is easier for you to learn the trickier parts of C that are needed to compen-

sate for its lack of higher-level facilities after you have been exposed to the common subset of C

and C

and to some of the higher-level techniques supported directly in C

. Appendix B is a

guide for programmers going from C

to C, say, to deal with legacy code.

Several independently developed and distributed implementations of C

exist. A wealth of

tools, libraries, and software development environments are also available. A mass of textbooks,

manuals, journals, newsletters, electronic bulletin boards, mailing lists, conferences, and courses

are available to inform you about the latest developments in C

, its use, tools, libraries, implemen-

tations, etc. If you plan to use C

seriously, I strongly suggest that you gain access to such

sources. Each has its own emphasis and bias, so use at least two. For example, see [Barton,1994],

[Booch,1994], [Henricson,1997], [Koenig,1997], [Martin,1995].

1.3 The Design of C

Simplicity was an important design criterion: where there was a choice between simplifying the

language definition and simplifying the compiler, the former was chosen. However, great impor-

tance was attached to retaining a high degree of compatibility with C [Koenig,1989] [Strous-

trup,1994] (Appendix B); this precluded cleaning up the C syntax.

has no built-in high-level data types and no high-level primitive operations. For example,

the C

language does not provide a matrix type with an inversion operator or a string type with a

concatenation operator. If a user wants such a type, it can be defined in the language itself. In fact,

defining a new general-purpose or application-specific type is the most fundamental programming

The C++ Programming Language, Special Edition by Bjarne Stroustrup. Copyright 2000 by AT&T.

8 Notes to the Reader Chapter 1

activity in C

. A well-designed user-defined type differs from a built-in type only in the way it is

defined, not in the way it is used. The C

standard library described in Part III provides many

examples of such types and their uses. From a user’s point of view, there is little difference

between a built-in type and a type provided by the standard library.

Features that would incur run-time or memory overheads even when not used were avoided in

the design of C

. For example, constructs that would make it necessary to store ‘‘housekeeping

information’’ in every object were rejected, so if a user declares a structure consisting of two 16-bit

quantities, that structure will fit into a 32-bit register.

was designed to be used in a traditional compilation and run-time environment, that is, the

C programming environment on the UNIX system. Fortunately, C

was never restricted to UNIX;

it simply used UNIX and C as a model for the relationships between language, libraries, compilers,

linkers, execution environments, etc. That minimal model helped C

to be successful on essen-

tially every computing platform. There are, however, good reasons for using C

in environments

that provide significantly more support. Facilities such as dynamic loading, incremental compila-

tion, and a database of type definitions can be put to good use without affecting the language.

type-checking and data-hiding features rely on compile-time analysis of programs to pre-

vent accidental corruption of data. They do not provide secrecy or protection against someone who

is deliberately breaking the rules. They can, however, be used freely without incurring run-time or

space overheads. The idea is that to be useful, a language feature must not only be elegant; it must

also be affordable in the context of a real program.

For a systematic and detailed description of the design of C

, see [Stroustrup,1994].

1.3.1 Efficiency and Structure

was developed from the C programming language and, with few exceptions, retains C as a

subset. The base language, the C subset of C

, is designed to ensure a very close correspondence

between its types, operators, and statements and the objects that computers deal with directly: num-

bers, characters, and addresses. Except for the n ne ew w, d de el le et te e, t ty yp pe ei id d, d dy yn na am mi ic c_ _c ca as st t, and t th hr ro ow w oper-

ators and the try-block, individual C

expressions and statements need no run-time support.

can use the same function call and return sequences as C – or more efficient ones. When

even such relatively efficient mechanisms are too expensive, a C

function can be substituted

inline, so that we can enjoy the notational convenience of functions without run-time overhead.

One of the original aims for C was to replace assembly coding for the most demanding systems

programming tasks. When C

was designed, care was taken not to compromise the gains in this

area. The difference between C and C

is primarily in the degree of emphasis on types and struc-

ture. C is expressive and permissive. C

is even more expressive. However, to gain that increase

in expressiveness, you must pay more attention to the types of objects. Knowing the types of

objects, the compiler can deal correctly with expressions when you would otherwise have had to

specify operations in painful detail. Knowing the types of objects also enables the compiler to

detect errors that would otherwise persist until testing – or even later. Note that using the type sys-

tem to check function arguments, to protect data from accidental corruption, to provide new types,

to provide new operators, etc., does not increase run-time or space overheads in C

The emphasis on structure in C

reflects the increase in the scale of programs written since C

was designed. You can make a small program (say, 1,000 lines) work through brute force even

The C++ Programming Language, Special Edition by Bjarne Stroustrup. Copyright 2000 by AT&T.

Section 1.3.1 Efficiency and Structure 9

when breaking every rule of good style. For a larger program, this is simply not so. If the structure

of a 100,000-line program is bad, you will find that new errors are introduced as fast as old ones are

removed. C

was designed to enable larger programs to be structured in a rational way so that it

would be reasonable for a single person to cope with far larger amounts of code. In addition, the

aim was to have an average line of C

code express much more than the average line of C or Pas-

cal code. C

has by now been shown to over-fulfill these goals.

Not every piece of code can be well-structured, hardware-independent, easy-to-read, etc. C

possesses features that are intended for manipulating hardware facilities in a direct and efficient

way without regard for safety or ease of comprehension. It also possesses facilities for hiding such

code behind elegant and safe interfaces.

Naturally, the use of C

for larger programs leads to the use of C

by groups of program-

mers. C

’s emphasis on modularity, strongly typed interfaces, and flexibility pays off here. C

has as good a balance of facilities for writing large programs as any language has. However, as

programs get larger, the problems associated with their development and maintenance shift from

being language problems to more global problems of tools and management. Part IV explores

some of these issues.

This book emphasizes techniques for providing general-purpose facilities, generally useful

types, libraries, etc. These techniques will serve programmers of small programs as well as pro-

grammers of large ones. Furthermore, because all nontrivial programs consist of many semi-

independent parts, the techniques for writing such parts serve programmers of all applications.

You might suspect that specifying a program by using a more detailed type structure would lead

to a larger program source text. With C

, this is not so. A C

program declaring function argu-

ment types, using classes, etc., is typically a bit shorter than the equivalent C program not using

these facilities. Where libraries are used, a C

program will appear much shorter than its C equiv-

alent, assuming, of course, that a functioning C equivalent could have been built.

1.3.2 Philosophical Note

A programming language serves two related purposes: it provides a vehicle for the programmer to

specify actions to be executed, and it provides a set of concepts for the programmer to use when

thinking about what can be done. The first purpose ideally requires a language that is ‘‘close to the

machine’’ so that all important aspects of a machine are handled simply and efficiently in a way

that is reasonably obvious to the programmer. The C language was primarily designed with this in

mind. The second purpose ideally requires a language that is ‘‘close to the problem to be solved’’

so that the concepts of a solution can be expressed directly and concisely. The facilities added to C

to create C

were primarily designed with this in mind.

The connection between the language in which we think/program and the problems and solu-

tions we can imagine is very close. For this reason, restricting language features with the intent of

eliminating programmer errors is at best dangerous. As with natural languages, there are great ben-

efits from being at least bilingual. A language provides a programmer with a set of conceptual

tools; if these are inadequate for a task, they will simply be ignored. Good design and the absence

of errors cannot be guaranteed merely by the presence or the absence of specific language features.

The type system should be especially helpful for nontrivial tasks. The C

class concept has, in

fact, proven itself to be a powerful conceptual tool.

The C++ Programming Language, Special Edition by Bjarne Stroustrup. Copyright 2000 by AT&T.

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