Ebook the elements of programming style (second edition)

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THE ELEMENTS

OF

PROGRAMMING

STYLE

SECOND EDITION

Kernighan and Plauger

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THE ELEMENTS

OF

PROGRAMMING

STYLE

Second Edition

Brian W Kernighan

Bell laboratories Murray Hill, New Jersey

P J Plauger

Yourdon, Inc

New York, New York

McGRAW-HILL BOOK COMPANY

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Library of Congress Cataloging in Publication Data

Kernighan, Brian W

The elements of programming style

Bibliography: p

Includes index

I Electronic digital computers-Programming

I Plauger, P.J., date joint author

II Title

QA 76.6.K47 1978 001.6'42 78-3498

ISBN 0-07-034207-5

The Elements of Programming Style

All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopy-ing, recordphotocopy-ing, or otherwise, without the prior written permission of Bell Laboratories Printed in the United States of America

12 13 14 15 DODO 8 9

This book was set in Times Roman and Courier 12 by the authors, using a Graphic Sys-tems phototypesetter driven by a PDP-11/70 running under the UNIX operating system

UNIX is a Trademark of Bell Laboratories

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1973 by R V Andree By permission of Prentice-Hall, Inc

V J Calderbank, A Course on Programming m Fortran IV Copyright © 1969 by Chapman and Hall, Ltd By permission Paul M Chirlian, lntroductt0n to Fortran IV Copyright © 1973 by Academic Press By permission

per-mission

permission

1972 By permission

by permission of the publisher

permission

permis-sion

v

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vi THE ELEMENTS OF PROGRAMMING STYLE

Re-printed by permission of the publisher

Pub-lishing, Inc Reprinted by permission of Van Nostrand Reinhold Company, a division of Litton Educational PubPub-lishing, Inc

1973 by Harper & Row, Publishers, Inc Used by permission of Harper & Row, Publishers

Inc By permission

by permission of Holt, Rinehart and Winston

Win•-ton Reprinted by permission of Holt, Rinehart and WinsWin•-ton

by permission of Holt, Rinehart and Winston

by permission of Holt, Rinehart and Winston, Inc

School Mathematics Study Group, Algortthms, Computa11on and Mathema11cs, Fortran Supplement Studen1 Tex1 (Revised Edt110n)

permis-sion

R C Scott and N E Sondak, Pl// for Programmers Copyright ©Addison-Wesley Publishing Company, 1970 By permission Donald D Spencer, Programming with USA S1andard Fortran and Fortran IV Copyright© 1969 by Xerox Corporation Used by

permission of Ginn and Company (Xerox Corporation)

permission

permis-sion

and Bacon Inc Used by permission

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CONTENTS

vii

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PREFACE to the Second Edition

The practice of computer programming has changed since The Elements of Pro-gramming Style first appeared Programming style has become a legitimate topic of discussion After years of producing "write-only code," students, teachers, and computing professionals now recognize the importance of readable programs There has also been a widespread acceptance of structured programming as a valuable cod-ing discipline, and a growcod-ing recognition that program design is an important phase, too often neglected in the past

We have revised The Elements of Programming Style extensively to reflect these changes The first edition avoided any direct mention of the term "structured pro-gramming," to steer well clear of the religious debates then prevalent Now that the fervor has subsided, we feel comfortable in discussing structured coding techniques that actually work well in practice

The second edition devotes a whole new chapter to program structure, showing how top-down design can lead to better organized programs Design issues are dis-cussed throughout the text We have made considerable use of pseudo-code as a program development tool

We have also rewritten many of the examples presented in the first edition, to reflect (we hope) a greater understanding of how to program well There are new examples as well, including several from the first edition which now serve as models

of how not to do things New exercises have been added Finally, we have extended and generalized our rules of good style

We are once again indebted to the authors and publishers who have graciously given us permission to reprint material from their textbooks Looking back on some

of our own examples makes us realize how demanding an effort good programming

is

We would also like to thrnk friends who read the second edition in draft form

In particular, Al Aho, Jim Blue, Stu Feldman, Paul Kernighan, Doug Mcilroy, Ralph Muha, and Dick Wexelblat provided us with valuable suggestions

Brian W Kernighan

P J Plauger

ix

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PREF ACE to the First Edition

Good programming cannot be taught by preaching generalities The way to learn to program well is by seeing, over and over, how real programs can be improved by the application of a few principles of good practice and a little common sense Practice in critical reading leads to skill in rewriting, which in turn leads to better writing

This book is a study of a large number of "real" programs, each of which pro-vides one or more lessons in style We discuss the shortcomings of each example, rewrite it in a better way, then draw a general rule from the specific case The approach is pragmatic and down-to-earth; we are more interested in improving current programming practice than in setting up an elaborate theory of how pro-gramming should be done Consequently, this book can be used as a supplement in

a programming course at any level, or as a refresher for experienced programmers The examples we give are all in Fortran and PL/I, since these languages are widely used and are sufficiently similar that a reading knowledge of one means that the other can also be read well enough (We avoid complicated constructions in either language and explain unavoidable idioms as we encounter them.) The princi-ples of style, however, are applicable in all languages, including assembly codes

Our aim is to teach the elements of good style in a small space, so we concen-trate on essentials Rules are laid down throughout the text to emphasize the les-sons learned Each chapter ends with a summary and a set of "points to ponder," which provide exercises and a chance to investigate topics not fully covered in the text itself Finally we collect our rules in one place for handy reference

A word on the sources of the examples: all of the programs we use are taken from programming textbooks Thus, we do not set up artificial programs to illus-trate our points - we use finished products, written and published by experienced programmers Since these examples are typically the first code seen by a novice pro-grammer, we would hope that they would be models of good style Unfortunately,

we sometimes find that the opposite is true - textbook examples often demonstrate the state of the art of computer programming all too well (We have done our best

to play fair - we don't think that any of the programs are made to look bad by being quoted out of context.)

Let us state clearly, however, that we intend no criticism of textbook authors, either individually or as a class Shortcomings show only that we are all human, and that under the pressure of a large, intellectually demanding task like writing a pro-gram or a book, it is much too easy to do some things imperfectly We have no

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Tiêu đề	The elements of programming style
Tác giả	Brian W. Kernighan, P. J. Plauger
Chuyên ngành	Programming
Thể loại	Book
Năm xuất bản	1978
Thành phố	New York

Định dạng
Số trang	20
Dung lượng	1,47 MB