📄 scanfprobs.html
字号:
<!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!-- but may not be published or retransmitted without explicit permission.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/scanfprobs.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:58 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 12.20</title><link href="scanfjam.html" rev=precedes><link href="sprintfsize.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="scanfjam.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="sprintfsize.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 12.20</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>Why does everyone say not to use <TT>scanf</TT>?What should I use instead?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font><TT>scanf</TT>hasa number of problems--see questions<a href="scanfhang.html">12.17</a>,<a href="scanfinterlace.html">12.18a</a>,and<a href="scanfjam.html">12.19</a>.Also, its <TT>%s</TT>format has the same problemthat <TT>gets()</TT> has(see question <a href="getsvsfgets.html">12.23</a>)--it'shard to guarantee thatthe receiving bufferwon't overflow.<a href="overflow.html" rel=subdocument>[footnote]</a></p><p>More generally,<TT>scanf</TT> is designed for relatively structured,formatted input(its name isin factderived from``scanformatted'').If you pay attention,it will tell you whether it succeeded or failed,but it can tell you only approximately where it failed,and not at all how or why.You have very little opportunity to do any error recovery.</p><p>Yet interactive user inputis the least structuredinput there is.A well-designed user interfacewill allow for the possibility of the user typing just about anything--notjust letters or punctuation when digits were expected,but also more or fewer characters than were expected,or no characters at all(i.e. just the RETURN key),or premature EOF,or anything.It's nearlyimpossibleto deal gracefullywith all of these potential problemswhen using <TT>scanf</TT>;it'sfareasierto read entire lines(with <TT>fgets</TT> or the like),then interpret them,either using <TT>sscanf</TT>or some other techniques.(Functions like<TT>strtol</TT>,<TT>strtok</TT>,and<TT>atoi</TT>are often useful;see alsoquestions <a href="datafmts.html">12.16</a> and <a href="../lib/strtok.html">13.6</a>.)If you do useany <TT>scanf</TT> variant,be sureto check the return valueto make sure that the expected number of items werefound.Also,if you use <TT>%s</TT>,be sure to guardagainst buffer overflow.</p><p>Note,by the way,thatcriticisms of<TT>scanf</TT>are not necessarily indictments of<TT>fscanf</TT>and <TT>sscanf</TT>.<TT>scanf</TT> reads from <TT>stdin</TT>,which is usually an interactive keyboardand is therefore the leastconstrained,leading to the most problems.When a data file has a known format,on the other hand,it may be appropriate to read it with <TT>fscanf</TT>.It's perfectly appropriate to parse strings with <TT>sscanf</TT>(as long as the return value is checked),because it's so easy to regain control,restart the scan,discard the input if it didn't match,etc.</p><p>Additional links:<UL><li><a href="gets_flush1.html">longer explanation</a> by Chris Torek<li><a href="gets_flush2.html">longer explanation</a> by yours truly</UL></p><p>References:K&R2 Sec. 7.4 p. 159<br></p><!-- aend --><p><hr><a href="scanfjam.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="sprintfsize.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/scanfprobs.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:58 GMT --></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -