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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN"><!-- This collection of hypertext pages is Copyright 1995-2005 by Steve Summit. --><!-- Content from the book "C Programming FAQs: Frequently Asked Questions" --><!-- (Addison-Wesley, 1995, ISBN 0-201-84519-9) is made available here by --><!-- permission of the author and the publisher as a service to the community. --><!-- It is intended to complement the use of the published text --><!-- and is protected by international copyright laws. --><!-- The on-line content may be accessed freely for personal use --><!-- but may not be published or retransmitted without explicit permission. --><!-- --><!-- this page built Sat Dec 24 21:47:46 2005 by faqproc version 2.7 --><!-- from source file stdio.sgml dated Wed Dec 21 13:07:57 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/stdio/datafmts.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:57 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 12.16</title><link href="scanfvwid.html" rev=precedes><link href="scanfhang.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="scanfvwid.html" rev=precedes><img src="../images/buttonleft.gif" alt="prev"></a><a href="index.html" rev=subdocument><img src="../images/buttonup.gif" alt="up"></a><a href="scanfhang.html" rel=precedes><img src="../images/buttonright.gif" alt="next"></a> <a href="../index-2.html"><img src="../images/buttontop.gif" alt="top/contents"></a><a href="../search.html"><img src="../images/buttonsrch.gif" alt="search"></a><hr><p><!-- qbegin --><h1>comp.lang.c FAQ list<font color=blue>·</font><!-- qtag -->Question 12.16</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How can I read data fromdata files with particular formats?<br>How can I read ten floats without having to use a jawbreaker <TT>scanf</TT> format<br>like<TT>"%f %f %f %f %f %f %f %f %f %f"</TT>?<br>How can I read an arbitrary number of fields from a line into an array?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>In general, there are threemain waysof parsing data lines:</p><OL><li>Use<TT>fscanf</TT> or <TT>sscanf</TT>,withan appropriate format string.Despite the limitationsmentioned in this section(see question <a href="scanfprobs.html">12.20</a>),the <TT>scanf</TT> family is quite powerful.Though whitespace-separated fields are always the easiest to deal with,<TT>scanf</TT> format strings can also be usedwith more compact,column oriented, FORTRAN-style data.For instance, the line<pre> 1234ABC5.678</pre>could bereadwith <TT>"%d%3s%f"</TT>.(See also the last example in question <a href="scanfjam.html">12.19</a>.)<li>Break the line intofields separated bywhitespace(or some other delimiter),using <TT>strtok</TT> or the equivalent(see question <a href="../lib/strtok.html">13.6</a>),then deal with each field individually,perhaps with functions like <TT>atoi</TT>and <TT>atof</TT>.(Once the line is broken up,the code for handling the fieldsis much like the traditional code in <TT>main()</TT>for handling the <TT>argv</TT> array;see question <a href="../misc/argv.html">20.3</a>.)This method is particularly usefulfor reading an arbitrary(i.e. not known in advance)numberof fields from a line into an array.<p>Here is a simple examplewhich copies a line ofup to 10floating-point numbers(separated by whitespace)into an array:<pre>#define MAXARGS 10char line[] = "1 2.3 4.5e6 789e10";char *av[MAXARGS];int ac, i;double array[MAXARGS];ac = makeargv(line, av, MAXARGS);for(i = 0; i < ac; i++) array[i] = atof(av[i]);</pre>(See question <a href="../lib/strtok.html">13.6</a>for the definition of <TT>makeargv</TT>.)</p><li>Use whatever pointer manipulationsand library routinesare handyto parse the line in anad-hoc way.(The ANSI <TT>strtol</TT> and <TT>strtod</TT> functionsare particularly useful for this style of parsing,because they can return a pointerindicating where they stopped reading.)Thisis obviously the most general way,but it's also the most difficult and error-prone:thethorniestpartsofmanyC programsarethose which use lots oftrickylittle pointers to pick apart strings.</OL><p>Whenpossible, design data files and input formatsso that they don't require arcane manipulations,butcaninsteadbe parsed with easier techniquessuch as 1 and 2:dealing with the files willthenbemuch more pleasantall around.</p><!-- aend --><p><hr><a href="scanfvwid.html" rev=precedes><img src="../images/buttonleft.gif" alt="prev"></a><a href="index.html" rev=subdocument><img src="../images/buttonup.gif" alt="up"></a><a href="scanfhang.html" rel=precedes><img src="../images/buttonright.gif" alt="next"></a> <a href="../questions.html"><img src="../images/buttontop.gif" alt="contents"></a><a href="../search.html"><img src="../images/buttonsrch.gif" alt="search"></a><br><!-- lastfooter --><a href="../about.html">about this FAQ list</a> <a href="../eskimo.html">about eskimo</a> <a href="../search.html">search</a> <a href="../feedback.html">feedback</a> <a href="copyright.html">copyright</a><p>Hosted by<a href="http://www.eskimo.com/"><img src="../../www.eskimo.com/img/link/eskitiny.gif" alt="Eskimo North"></a></body><!-- Mirrored from c-faq.com/stdio/datafmts.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:57 GMT --></html>⌨️ 快捷键说明
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