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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html> <head> <meta http-equiv="content-type" content="text/html;charset=iso-8859-1"> <link title="David R. Hanson" href="http://drh.home.dyndns.org" rev="made"> <link href="style.css" type="text/css" rel="stylesheet" media="all"> <title>Preface for C Interfaces and Implementations</title> </head> <body> <h1>Preface</h1> <p>Programmers are inundated with information about application programming interfaces, or APIs. Yet, while most programmers use APIs and the libraries that implement them in almost every application they write, relatively few create and disseminate new, widely applicable, APIs. Indeed, programmers seem to prefer to “roll their own” instead of searching for a library that might meet their needs, perhaps because it is easier to write application-specific code than to craft well-designed APIs.</p> <p>I<a href="http://www.cs.princeton.edu/%7ers/">’</a>m as guilty as the next programmer: <a href="http://www.cs.princeton.edu/software/lcc/">lcc</a>, a compiler for ANSI/ISO C written by Chris Fraser and myself, was built from the ground up. (<tt>lcc</tt> is described in C.W. Fraser and D. R. Hanson, <cite>A Retargetable C Compiler: Design and Implementation</cite>, Addison-Wesley, 1995.) A compiler exemplifies the kind of application for which it possible to use standard interfaces and to create interfaces that are useful elsewhere. Examples include interfaces for memory management, string and symbol tables, and list manipulation. But <tt>lcc</tt> uses only a few routines from the standard C library, and almost none of its code can be used directly in other applications.</p> <p>This book advocates a design methodology based on interfaces and their implementations, and it illustrates this methodology by describing 24 interfaces and their implementations in detail. These interfaces span a large part of the computing spectrum and include data structures, arithmetic, string processing, and concurrent programming. The implementations aren<a href="http://www.cs.princeton.edu/%7ers/">’</a>t toys—they’re designed for use in production code. As described below, the source code is freely available.</p> <p>There’s little support in the C programming language for the interface-based design methodology. Object-oriented languages, like C++ and Modula-3, have language features that encourage the separation of an interface from its implementation. Interface-based design is independent of any particular language, but it does require more programmer willpower and vigilance in languages like C, because it’s too easy to pollute an interface with implicit knowledge of its implementation and vice versa.</p> <p>Once mastered, however, interface-based design can speed development time by building upon a foundation of general-purpose interfaces that can serve many applications. The foundation class libraries in some C++ environments are examples of this effect. Increased reuse of existing software—libraries of interface implementations—reduces initial development costs. It also reduces maintenance costs, because more of an application rests on well-tested implementations of general-purpose interfaces.</p> <p>The 24 interfaces come from several sources, and all have been revised for this book. Some of the interfaces for data structures—abstract data types—originated in <code>lcc</code> code, and in implementations of the <a href="http://www.cs.arizona.edu/icon/">Icon programming language</a> done in the late 1970s and early 1980s (see R. E. Griswold and M. T. Griswold, <cite>The Icon Programming Language</cite>, Prentice Hall, 1990). Others come from the published work of other programmers; the “Further Reading” sections at the end of each chapter give the details.</p> <p>Some of the interfaces are for data structures, but this is not a data structures book, per se. The emphasis is more on algorithm engineering—packaging data structures for general use in applications—than on data-structure algorithms. Good interface design does rely on appropriate data structures and efficient algorithms, however, so this book complements traditional data structure and algorithms texts like <a href="http://www.cs.princeton.edu/rs/">Robert Sedgewick’s</a> <a href="http://www.aw-bc.com/catalog/academic/product/0,1144,0805316701,00.html"><cite>Algorithms in C</cite></a> (Addison-Wesley, 1998).</p> <p>Most chapters describe one interface and its implementation; a few describe related interfaces. The "Interface" section in each chapter gives a concise, detailed description of the interface alone. For programmers interested only in the interfaces, these sections form a reference manual. A few chapters include “Example” sections, which illustrate the use of one or more interfaces in simple applications.</p> <p>The “Implementation” section in each chapter is a detailed tour of the code that implements the chapter’s interface. In a few cases, more than one implementation for the same interface is described, which illustrates an advantage of interface-based design. These sections are most useful for those modifying or extending an interface or designing related interfaces. Many of the exercises explore design and implementation alternatives. It should not be necessary to read an “Implementation” section in order to understand how to use an interface.</p> <p>The interfaces, examples, and implementations are presented as <em>literate programs</em>; that is, the source code is interleaved with its explanation in an order that best suits understanding the code. The code is extracted automatically from the text files for this book and assembled into the order dictated by the C programming language. Other book-length examples of literate programming in C include <cite>A Retargetable C Compiler</cite> and <cite>The Stanford GraphBase: A Platform for Combinatorial Computing</cite> by D.E. Knuth (Addison-Wesley, 1993).</p> <h2>Organization</h2> <p>The material in this book falls into the following broad categories:</p> <blockquote> <table cellpadding="12"> <tr align="LEFT" valign="TOP"> <td><i>Foundations</i></td> <td>1. Introduction<br> 2. Interfaces and Implementations<br> 4. Exceptions and Assertions<br> 5. Memory Management<br> 6. More Memory Management</td> </tr> <tr align="LEFT" valign="TOP"> <td><i>Data Structures</i></td> <td>7. Lists<br> 8. Tables<br> 9. Sets<br> 10. Arrays<br> 11. Sequences<br> 12. Rings<br> 13. Bit Vectors</td> </tr> <tr align="LEFT" valign="TOP"> <td><i>Strings</i></td> <td>3. Atoms<br> 14. Formatting<br> 15. Low-Level Strings<br> 16. High-Level Strings</td> </tr> <tr align="LEFT" valign="TOP"> <td><i>Arithmetic</i></td> <td>17. Extended-Precision Arithmetic<br> 18. Arbitrary-Precision Arithmetic<br> 19. Multiple-Precision Arithmetic</td> </tr> <tr align="LEFT" valign="TOP"> <td><i>Threads</i></td> <td>20. Threads</td> </tr> </table> </blockquote> <p>Most readers will benefit from reading all of Chapters 1 through 4, because these chapters form the framework for the rest of the book. The remaining chapters can be read in any order, although some of the later chapters refer to their predecessors.</p> <p>Chapter 1 covers literate programming and issues of programming style and efficiency. Chapter 2 motivates and describes the interface-based design methodology, defines the relevant terminology, and tours two simple interfaces and their implementations. Chapter 3 describes the prototypical <tt>Atom</tt> interface, which is the simplest production-quality interface in this book. [<a href="http://ciibook.webhop.net/pdf/atom.pdf">Download/view Chapter 3</a>, an Adobe Acrobat PDF file (52K).] Chapter 4 introduces exceptions and assertions, which are used in every interface. Chapters 5 and 6 describe the memory management interfaces used by almost all the implementations. The rest of the chapters each describe an interface and its implementation.</p>⌨️ 快捷键说明
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