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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!-- but may not be published or retransmitted without explicit permission.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 cpp.sgml dated Wed Dec 21 13:52:14 2005 --><!-- corresponding to FAQ list version 4.0 --><html><!-- Mirrored from c-faq.com/cpp/debugmacs.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:54 GMT --><head><meta name=GENERATOR content="faqproc"><title>Question 10.27</title><link href="varargs.html" rev=precedes><link href="../ansi/ansi1.html" rel=precedes><link href="index.html" rev=subdocument></head><body bgcolor="#ffffff"><a href="varargs.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="../ansi/ansi1.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 10.27</h1><p><font face=Helvetica size=8 color=blue><b>Q:</b></font>How can I include expansions of the <TT>__FILE__</TT>and <TT>__LINE__</TT> macrosin a general-purpose debugging macro?</p><p><hr><p><font face=Helvetica size=8 color=blue><b>A:</b></font>This question tends to reduce to question<a href="varargs.html">10.26</a>.One solutioninvolves writing your debug macro in terms ofa varargs function(see questions<a href="../varargs/varargs1.html">15.4</a> and<a href="../varargs/vprintf.html">15.5</a>),and an auxiliary function which stashes the values of<TT>__FILE__</TT> and <TT>__LINE__</TT> away in static variables,as in:<pre>#include <stdio.h>#include <stdarg.h>void debug(const char *, ...);void dbginfo(int, const char *);#define DEBUG dbginfo(__LINE__, __FILE__), debugstatic const char *dbgfile;static int dbgline;void dbginfo(int line, const char *file){ dbgfile = file; dbgline = line;}void debug(const char *fmt, ...){ va_list argp; fprintf(stderr, "DEBUG: \"%s\", line %d: ", dbgfile, dbgline); va_start(argp, fmt); vfprintf(stderr, fmt, argp); va_end(argp); fprintf(stderr, "\n");}</pre>With this machinery in place,a call to<pre> DEBUG("i is %d", i);</pre>expands to<pre> dbginfo(__LINE__, __FILE__), debug("i is %d", i);</pre>and prints something like<pre> DEBUG: "x.c", line 10: i is 42</pre></p><p>A cunning improvementis the idea of havingthe stashing function return apointerto the bona-fide varargs function:<pre>void debug(const char *, ...);void (*dbginfo(int, const char *))(const char *, ...);#define DEBUG (*dbginfo(__LINE__, __FILE__))void (*dbginfo(int line, const char *file))(const char *, ...){ dbgfile = file; dbgline = line; return debug;}</pre>With these definitions,<pre> DEBUG("i is %d", i);</pre>gets expanded to<pre> (*dbginfo(__LINE__, __FILE__))("i is %d", i);</pre></p><p>Another,perhaps easier way might simply be to<pre> #define DEBUG printf("DEBUG: \"%s\", line %d: ", \ __FILE__,__LINE__),printf</pre>Now,<pre> DEBUG("i is %d", i);</pre>simply expands to<pre> printf("DEBUG: \"%s\", line %d: ", __FILE__,__LINE__),printf("i is %d", i);</pre></p><p>Finally, you may be able touse the<pre> #define _ ,</pre>trickfrom question <a href="varargs.html">10.26</a>.</p><p>Additional links:<a href="sd10.html" rel=subdocument>another idea</a></p><!-- aend --><p><hr><a href="varargs.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="../ansi/ansi1.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/cpp/debugmacs.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 07:58:54 GMT --></html>⌨️ 快捷键说明
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