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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!-- but may not be published or retransmitted without explicit permission.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 ansi.sgml dated Wed Aug 11 00:43:45 2004 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/ansi/macstrexp.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:55 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 11.18</title><link href="stringize.html" rev=precedes><link href="ifdefsyntax.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="stringize.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="ifdefsyntax.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 11.18</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>What does the message``warning: macro replacement within a string literal''mean?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>Somepre-ANSI compilers/preprocessorsinterpreted macro definitions like<pre> #define TRACE(var, fmt) printf("TRACE: var = fmt\n", var)</pre>such that invocations like<pre> TRACE(i, %d);</pre>were expanded as<pre> printf("TRACE: i = %d\n", i);</pre>In other words, macro parameters wereexpandedeven insidestring literals and character constants.(This interpretation may even have been an accident of early implementations,but it can prove useful for macros like this.)</p><p>Macro expansion is <em>not</em> defined in this wayby K&R or by Standard C.(It can be dangerous and confusing:see question <a href="../cpp/macstrexp2.html">10.22</a>.)When you do wantto turn macro arguments into strings,you can use the new <TT>#</TT> preprocessing operator,along with string literal concatenation(another new ANSI feature):<pre> #define TRACE(var, fmt) \ printf("TRACE: " #var " = " #fmt "\n", var)</pre>See also question <a href="stringize.html">11.17</a>.</p><p>References:H&S Sec. 3.3.8 p. 51<br></p><!-- aend --><p><hr><a href="stringize.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="ifdefsyntax.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/ansi/macstrexp.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:55 GMT --></html>⌨️ 快捷键说明
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