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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!-- but may not be published or retransmitted without explicit permission.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 varargs.sgml dated Sun Nov 25 08:09:42 2001 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/varargs/float.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:00 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 15.10</title><link href="onefixedarg.html" rev=precedes><link href="funcptr.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="onefixedarg.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="funcptr.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 15.10</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>I have a varargs function which accepts a <TT>float</TT> parameter.Why isn't<pre>va_arg(argp, float)</pre>working?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>In the variable-length part of variable-length argument lists,theold``default argument promotions''apply:arguments of type <TT>float</TT> are always promoted(widened)to type <TT>double</TT>,and types <TT>char</TT> and <TT>short int</TT> are promoted to <TT>int</TT>.Therefore, it is never correct to invoke<TT>va_arg(argp, float)</TT>;insteadyou shouldalways use<TT>va_arg(argp, double)</TT>.Similarly, use<TT>va_arg(argp, int)</TT>to retrieve arguments which were originally<TT>char</TT>, <TT>short</TT>, or <TT>int</TT>.(For analogous reasons,the last ``fixed'' argument,as handed to <TT>va_start</TT>,should not be widenable,either.)See also questions <a href="../ansi/argpromos.html">11.3</a>and <a href="promos.html">15.2</a>.</p><p>References:ISO Sec. 6.3.2.2<br>Rationale Sec. 4.8.1.2<br>H&S Sec. 11.4 p. 297<br></p><!-- aend --><p><hr><a href="onefixedarg.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="funcptr.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/varargs/float.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:59:00 GMT --></html>⌨️ 快捷键说明
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