革新C语言：21世纪实战指南

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《21st Century C》是一本专为适应新时代编程需求而编写的C语言指南。作者Ben Klemens邀请读者抛弃对C语言的传统观念，以全新的视角重新学习这门基础且强大的现代编程语言。书中强调了C语言在编写高效和先进应用方面的实用性，并提倡与时代同步，摆脱大型主机时代的遗留习惯。该书首先指导读者如何设置现代化的C语言开发环境，包括利用shell工具、makefile、文本编辑器、调试程序以及内存检查工具。Autotools，作为C语言跨平台套件管理的标准实践，也被深入介绍，帮助开发者实现更有效的项目管理。对于C语言中的过时观念，作者提出了识别并逐渐摒弃的建议，同时深入探讨那些虽然实用但存在问题的概念，如字串处理问题的解决方案。书中特别关注标准库的使用，特别是C语言标准和POSIX标准函数，以便于处理字符串操作。作者还倡导采用现代语法结构，如在函数中引入结构化输入，以提升代码的可读性和易维护性。针对面向对象编程的需求，书中探讨了如何基于高阶对象构建函数库和程序，使代码设计更具灵活性。在数学运算、网络连接和数据库操作等方面，书中推荐利用现有的C语言函数库进行高级操作，确保技术的实用性和兼容性。此外，书末的修订历史和在线资源链接（如www.it-ebooks.info）为读者提供了持续学习和获取最新资讯的途径。《21st Century C》是一本既适合C语言初学者，也适合已有经验程序员升级技能的实用手册，旨在帮助读者充分利用C语言的强大功能，迎接21世纪的编程挑战。

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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