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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!-- but may not be published or retransmitted without explicit permission.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 21:47:45 2005 by faqproc version 2.7 --><!-- from source file decl.sgml dated Wed Dec 21 12:56:18 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/decl/implfdecl.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:45 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 1.25</title><link href="extarraysize.html" rev=precedes><link href="main.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="extarraysize.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="main.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 1.25</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>My compiler is complainingabout an invalid redeclaration of a function,but I only define it onceand call it once.</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Functions which are called without a declaration in scope,perhaps because the first call precedes the function's definition,are assumedto be declared asif by:<pre> extern int f();</pre>That is,an undeclared function is assumed to return <TT>int</TT>,and to accept an unspecified number of arguments(though there must be a fixed number of themand none may be ``narrow'').If the function is later defined otherwise,the compiler complains about the discrepancy.Functions returning other than <TT>int</TT>,or accepting any ``narrow'' arguments,or accepting a variable number of arguments,must all be declared before they are called.(And it's by all meanssafest to declare all functions,so that function prototypes cancheck that arguments are passed correctly.)</p><p>Another possible source of this problem is that the function has the samename asanotherone declared insome header file.</p><p>See also questions<a href="../ansi/argpromos.html">11.3</a>and <a href="../varargs/protos.html">15.1</a>.</p><p>References:K&R1 Sec. 4.2 p. 70<br>K&R2 Sec. 4.2 p. 72<br>ISO Sec. 6.3.2.2<br>H&S Sec. 4.7 p. 101<br></p><!-- aend --><p><hr><a href="extarraysize.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="main.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/decl/implfdecl.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:45 GMT --></html>⌨️ 快捷键说明
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