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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!-- but may not be published or retransmitted without explicit permission.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/printferrno.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 12.24</title><link href="getsvsfgets.html" rev=precedes><link href="fgetpos.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="getsvsfgets.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="fgetpos.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 12.24</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>I thought I'd check <TT>errno</TT>after a long string of <TT>printf</TT> calls,to see if any of them had failed:<pre> errno = 0; printf("This\n"); printf("is\n"); printf("a\n"); printf("test.\n"); if(errno != 0) fprintf(stderr, "printf failed: %s\n", strerror(errno));</pre>Why is it printingsomething strange like``printf failed: Not a typewriter''when I redirect the output to a file?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Many implementations of the stdio package adjust theirbehavior slightly if <TT>stdout</TT> is a terminal.To make the determination,theseimplementations performsomeoperation whichhappens tofail(withENOTTY)if <TT>stdout</TT> is not a terminal.Although the output operation goeson to complete successfully, <TT>errno</TT> still containsENOTTY.This behavior can be mildly confusing, but it is notstrictly incorrect, becauseitis only meaningful for aprogram to inspect the contents of <TT>errno</TT> after an error hasbeen reported.(Moreprecisely,<TT>errno</TT> is only meaningfulafter a library functionthat sets <TT>errno</TT> on errorhas returned an error code.)</p><p>In general,it's best to detect errors by checkinga function'sreturn value.To check for anyaccumulatederror after a long string of stdio calls,you can use <TT>ferror</TT>.See also questions<a href="feof.html">12.2</a>and<a href="../misc/errno.html">20.4</a>.</p><p>References:ISO Sec. 7.1.4, Sec. 7.9.10.3<br>CT&P Sec. 5.4 p. 73<br>PCS Sec. 14 p. 254<br></p><!-- aend --><p><hr><a href="getsvsfgets.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="fgetpos.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/printferrno.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:58 GMT --></html>⌨️ 快捷键说明
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