21世纪的C语言编程探索

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"21世纪C语言" 是一本关于C编程语言的书籍，作者是Ben Klemens。这本书由O'Reilly Media, Inc.出版，旨在教育、商业或销售推广使用，并提供了在线版本。书中涵盖了C语言的基础知识、进阶技巧以及可能涉及到的现代编程实践。在21世纪，C语言仍然是一种重要的编程语言，被广泛应用于操作系统开发、嵌入式系统、游戏编程、系统软件和各种应用软件中。这本书可能会讨论C语言的最新发展，包括标准C11的更新，以及如何将C语言与现代编程实践相结合，如错误处理、内存管理、性能优化和代码安全。书中的内容可能包括以下几个方面： 1. **基础语法**：讲解C语言的基本语法结构，如变量、数据类型、运算符、控制流（条件语句、循环语句）、函数等。 2. **指针和内存管理**：深入解析C语言的核心特性——指针，以及动态内存分配和释放，这是理解和使用C的关键。 3. **预处理器和宏**：讨论C语言的预处理器，以及如何使用宏进行代码替换和条件编译，同时强调宏使用时的潜在问题和最佳实践。 4. **结构体和联合体**：介绍如何使用结构体和联合体来组织复杂的数据结构，以及它们在处理记录和对象时的作用。 5. **错误处理**：探讨在C语言中如何有效地处理错误，可能包括自定义错误处理机制，以及对传统错误处理方法的改进。 6. **高级主题**：可能涉及多线程编程、文件I/O、网络编程、位操作等，这些都是C语言在实际项目中常见的应用场景。 7. **C11标准**：介绍C语言的最新标准C11引入的新特性，如线程支持库、原子操作、可选静态类型检查等。 8. **编码风格和最佳实践**：强调编写清晰、可读性强的代码的重要性，以及遵循一定的编码规范和最佳实践。 9. **安全编程**：讨论如何避免常见的C语言编程陷阱，如缓冲区溢出、未初始化的变量、内存泄漏等问题，以提高代码的安全性。 10. **性能优化**：讲解如何通过C语言特性来优化程序性能，包括内存访问模式、算法选择、编译器优化选项等。此外，书籍的制作团队包括编辑Nathan Jepson、生产编辑Rachel Steely、校对员Teresa Horton等人，他们共同确保了内容的质量和可读性。封面设计和内页设计也由专业团队完成，使得书籍不仅在内容上严谨，视觉呈现上也符合阅读者的审美需求。 “21世纪C语言”是一本面向现代编程环境的C语言指南，旨在帮助读者掌握C语言的核心概念，并将其应用于不断发展的技术领域。无论你是初学者还是经验丰富的开发者，都能从中找到提升技能和理解C语言新趋势的宝贵资料。

would be reviled. And indeed, this standard was controversial. There are two com-

mon ways to express a complex variable (rectangular and polar coordinates)—so

where does the ISO get off picking one? Why do we need a mechanism for variable-

length macro inputs when all the good code got written without it? In other words,

the purists accused the ISO of selling out to the pressure for more features.

As of this writing, most compilers support C99 plus or minus a few caveats; the

long double type seems to cause a lot of trouble, for example. However, there is

one notable exception to this broad consensus: Microsoft currently refuses to add

C99 support to its Visual Studio C++ compiler. The section “Compiling C with

Windows” on page 6 covers some of the many ways to compile C code for

Windows, so not using Visual Studio is at most an inconvenience, and having a

major establishment player tell us that we can’t use ISO-standard C only bolsters

the punk rock of it all.

C11

Self-conscious about the accusations of selling out, the ISO made few serious

changes in the third edition of the standard. We got a means of writing type-generic

functions, and things were modernized to further acknowledge that security mat-

ters and that not everybody speaks English.

I’m writing this in 2012, shortly after the C11 standard came out in December of

2011, and there’s already some support from compilers and libraries.

The POSIX Standard

That’s the state of things as far as C itself goes, but the language coevolved with the

Unix operating system, and you will see throughout the book that the interrelationship

matters for day-to-day work. If something is easy on the Unix command line, then it is

probably because it is easy in C; Unix tools are often written to facilitate writing C code.

Unix

C and Unix were designed at Bell Labs in the early 1970s. During most of the 20th

century, Bell was being investigated for monopolistic practices, and one of its

agreements with the US federal government included promises that Bell would not

expand its reach into software. So Unix was given away for free for researchers to

dissect and rebuild. The name Unix is a trademark, originally owned by Bell Labs

and subsequently traded off like a baseball card among a number of companies.

Variants of Unix blossomed, as the code was looked over, reimplemented, and im-

proved in different ways by diverse hackers. It just takes one little incompatibility to

make a program or script unportable, so the need for some standardization quickly

became apparent.

xiv | Preface

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POSIX

This standard, first established by the Institute of Electrical and Electronics Engi-

neers (IEEE) in 1988, provided a common basis for Unix-like operating systems.

It specifies how the shell should work, what to expect from commands like ls and

grep, and a number of C libraries that C authors can expect to have available. For

example, the pipes that command-line users use to string together commands are

specified in detail here, which means C’s popen (pipe open) function is POSIX-

standard, not ISO C standard. The POSIX standard has been revised many times;

the version as of this writing is POSIX:2008, and is what I am referring to when I

say that something is POSIX-standard. A POSIX-standard system must have a C

compiler available, via the command name c99.

This book will make use of the POSIX standard, though I’ll tell you when.

With the exception of many members of a family of OSes from Microsoft, just

about every current operating system you could name is built on a POSIX-com-

pliant base: Linux, Mac OS X, iOS, webOS, Solaris, BSD—even Windows servers

offer a POSIX subsystem. And for the hold-out OSes, “Compiling C with Win-

dows” on page 6 will show you how to install a POSIX subsystem.

Finally, there are two more implementations of POSIX worth noting because of their

prevalence and influence:

BSD

After Unix was sent out from Bell Labs for researchers to dissect, the nice people

at the University of California, Berkeley, made major improvements, eventually

rewriting the entire Unix code base to produce the Berkeley Software Distribution.

If you are using a computer from Apple, Inc., you are using BSD with an attractive

graphical frontend. BSD goes beyond POSIX in several respects, and we’ll see a

function or two that are not part of the POSIX standard but are too useful to pass

up (most notably the lifesaver that is asprintf).

GNU

It stands for GNU’s Not Unix, and is the other big success story in independently

reimplementing and improving on the Unix environment. The great majority of

Linux distributions use GNU tools throughout. There are very good odds that you

have the GNU Compiler Collection (gcc) on your POSIX box—even BSD uses it.

Again, the gcc defines a de facto standard that extends C and POSIX in a few ways,

and I will be explicit when making use of those extensions.

Legally, the BSD license is slightly more permissive than the GNU license. Because some

parties are deeply concerned with the political and business implications of the licenses,

one can typically find both GNU and BSD versions of most tools. For example, both

the GNU Compiler Collection (gcc) and the BSD’s clang are top-notch C compilers.

The authors from both camps closely watch and learn from each other’s work, so we

can expect that the differences that currently exist will tend to even out over time.

Preface | xv

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The Legal Sidebar

US law no longer has a registration system for copyright: with few exceptions, as soon

as anybody writes something down, it is copyrighted.

Of course, distribution of a library depends on copying from hard drive to hard drive,

and there are a number of common mechanisms for granting the right to copy a copy-

righted work with little hassle.

• The GNU Public License allows unlimited copying and use of the source code and

its executable version. There is one major condition: If you distribute a program

or library based on the GPLed source code, then you must distribute the source

code to your program. Note well that if you use your program in-house and don’t

distribute it, this condition doesn’t hold, and you have no obligation to distribute

source. Running a GPLed program, like compiling your code with gcc, does not

in itself obligate you to distribute source code, because the program output (such

as the executable you just compiled) is not considered to be based on or a derivative

of gcc. [Example: the GNU Scientific Library.]

• The Lesser GPL is much like the GPL, but it explicitly stipulates that if you are

linking to an LGPL library as a shared library, then your code doesn’t count as a

derivative work, and you aren’t obligated to distribute source. That is, you can

distribute closed-source code that links to an LGPL library. [Example: GLib.]

• The BSD license requires that you preserve copyrights and disclaimers for BSD-

licensed source code, but doesn’t require that you redistribute source code.

[Example: Libxml2, under the BSD-like MIT license.]

Please note the usual disclaimer: I am not a lawyer, and this is a sidebar summary of

several rather long legal documents. Read the documents themselves or consult a lawyer

if you are unsure about how the details apply to your situation.

Some Logistics

Conventions Used in This Book

The following typographical conventions are used in this book:

Italic

Indicates new terms, filenames and file paths, URLs, and email addresses. Many

new terms are defined in a glossary at the end of this book.

Constant width

Used for program listings, as well as within paragraphs to refer to program elements

such as variable or function names, databases, data types, environment variables,

statements, and keywords.

xvi | Preface

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