21世纪C语言实用指南：Ben Klemens深度解读

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《21st Century C》是由Ben Klemens编写的关于C语言的专业著作，于2013年出版。本书旨在为读者提供21世纪的C语言深入理解和实践指南，适合那些希望在C语言领域进阶或寻求最新技术趋势的开发者。作为一本版权著作，所有权利受到保留，可在美国印刷并由O'Reilly Media发行，地址位于加利福尼亚州塞巴斯托波尔。作者Ben Klemens以其丰富的经验和专业知识，带领读者探索C语言的现代应用，内容覆盖了从基础概念到高级技术的广泛范围。书中可能包括章节如：C语言的历史演变、标准库的革新、内存管理和并发编程技巧、C语言在嵌入式系统、游戏开发和高性能计算中的角色，以及如何利用C语言构建高效的现代软件架构。本书的独特之处在于它紧跟时代的步伐，强调C语言在当今软件开发中的实用性，特别是在云计算、物联网、大数据和移动开发等领域的重要性。它不仅是一本技术手册，也可能是对C语言未来发展的洞察之作。编辑Nathan Jepson和生产编辑Rachel Steely共同确保了内容的质量与准确性，而Copyeditor Linley Dolby、Proofreader Teresa Horton则对文本进行了细致的校对工作。此外，本书还配备了详尽的索引，便于读者快速查找所需信息。封面设计由Karen Montgomery负责，而Interior Designer David Futato则负责整体设计风格，确保阅读体验的舒适性。《21st Century C》的初版于2012年10月12日发布，并且提供在线版本供读者随时随地查阅。对于任何已购买书籍的用户，他们可以通过访问http://oreilly.com/catalog/errata.csp?isbn=9781449327149获取最新修订信息和错误修正详情。《21st Century C》是一本不可或缺的C语言参考书，无论是对专业程序员还是对想要深入了解C语言的人来说，都是一个深入学习和提升技能的重要资源。随着技术的不断进步，它会随着时间和新的C语言特性更新，为读者提供持续的价值。

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

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

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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