C语言编程基础：英文原版入门指南

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"C编程语言的学习资源，英文原版，适合初学者" 《C Programming Language》是C语言的经典著作，由Bjarne Stroustrup编写，他在书中详细介绍了C语言的基础和高级特性。这本书通常被称为“K&R”（Kernighan & Ritchie）的第二版，因其两位作者的名字首字母而得名，对于学习C语言的初学者来说是不可或缺的参考书。 C语言是一种结构化的编程语言，它以简洁、高效和灵活著称，广泛应用于系统编程、软件开发、驱动编写等领域。通过阅读这本书，读者可以了解到C语言的基本语法，如变量、数据类型、运算符、控制结构（如if语句和循环）、函数、指针等概念。这些基础知识是理解C语言程序设计的关键。在《C Programming Language》中，Stroustrup深入浅出地讲解了指针，这是C语言的一大特色，也是许多初学者遇到的难点。书中详细阐述了指针如何作为地址工作，如何通过指针进行动态内存管理，以及如何使用指针实现高效的数据结构，如链表和树。此外，书中还涵盖了预处理器、结构体与联合、位字段、文件I/O等进阶主题。这些内容帮助读者掌握C语言的完整功能，能够编写复杂的程序，并理解操作系统和其他底层系统的工作原理。书中的例子和练习题设计精巧，鼓励读者动手实践，通过编程加深对概念的理解。这本教材不仅适合自学，也常被大学计算机科学课程用作教材。虽然《C Programming Language》主要关注C语言本身，但阅读本书时，读者也会了解到面向过程编程的思想，这对于后续学习其他编程语言（如C++，它是C语言的一个扩展，引入了类和对象等面向对象的概念）也是大有裨益的。《C Programming Language》是学习C语言的绝佳资料，无论你是编程新手还是有一定经验的程序员，都可以从中获得宝贵的指导和启示。通过本书，你可以系统地学习和掌握C语言，为你的编程生涯打下坚实的基础。

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.

10 Notes to the Reader Chapter 1

1.4 Historical Note

I invented C

, wrote its early definitions, and produced its first implementation. I chose and for-

mulated the design criteria for C

, designed all its major facilities, and was responsible for the

processing of extension proposals in the C

standards committee.

Clearly, C

owes much to C [Kernighan,1978]. Except for closing a few serious loopholes in

the type system (see Appendix B), C is retained as a subset. I also retained C’s emphasis on facili-

ties that are low-level enough to cope with the most demanding systems programming tasks. C in

turn owes much to its predecessor BCPL [Richards,1980]; in fact, BCPL’s / / comment convention

was (re)introduced in C

. The other main source of inspiration for C

was Simula67

[Dahl,1970] [Dahl,1972]; the class concept (with derived classes and virtual functions) was bor-

rowed from it. C

’s facility for overloading operators and the freedom to place a declaration

wherever a statement can occur resembles Algol68 [Woodward,1974].

Since the original edition of this book, the language has been extensively reviewed and refined.

The major areas for revision were overload resolution, linking, and memory management facilities.

In addition, several minor changes were made to increase C compatibility. Several generalizations

and a few major extensions were added: these included multiple inheritance, s st ta at ti ic c member func-

tions, c co on ns st t member functions, p pr ro ot te ec ct te ed d members, templates, exception handling, run-time type

identification, and namespaces. The overall theme of these extensions and revisions was to make

a better language for writing and using libraries. The evolution of C

is described in [Strous-

trup,1994].

The template facility was primarily designed to support statically typed containers (such as lists,

vectors, and maps) and to support elegant and efficient use of such containers (generic program-

ming). A key aim was to reduce the use of macros and casts (explicit type conversion). Templates

were partly inspired by Ada’s generics (both their strengths and their weaknesses) and partly by

Clu’s parameterized modules. Similarly, the C

exception-handling mechanism was inspired

partly by Ada [Ichbiah,1979], Clu [Liskov,1979], and ML [Wikstr

. .

om,1987]. Other developments

in the 1985 to 1995 time span – such as multiple inheritance, pure virtual functions, and name-

spaces – were primarily generalizations driven by experience with the use of C

rather than ideas

imported from other languages.

Earlier versions of the language, collectively known as ‘‘C with Classes’’ [Stroustrup,1994],

have been in use since 1980. The language was originally invented because I wanted to write some

event-driven simulations for which Simula67 would have been ideal, except for efficiency consid-

erations. ‘‘C with Classes’’ was used for major projects in which the facilities for writing programs

that use minimal time and space were severely tested. It lacked operator overloading, references,

virtual functions, templates, exceptions, and many details. The first use of C

outside a research

organization started in July 1983.

The name C

(pronounced ‘‘see plus plus’’) was coined by Rick Mascitti in the summer of

1983. The name signifies the evolutionary nature of the changes from C; ‘‘++’’ is the C increment

operator. The slightly shorter name ‘‘C+’’ is a syntax error; it has also been used as the name of an

unrelated language. Connoisseurs of C semantics find C

inferior to ++C. The language is not

called D, because it is an extension of C, and it does not attempt to remedy problems by removing

features. For yet another interpretation of the name C

, see the appendix of [Orwell,1949].

was designed primarily so that my friends and I would not have to program in assembler,

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

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