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document [imgName].src = imgOff; } }// --></SCRIPT></HEAD><BODY LANG="EN" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#6688AA" VLINK="#336688" ALINK="#808080"><A NAME="SEC48"></A><TABLE BORDER=0 CELLPADDING=0 CELLSPACING=10><TR VALIGN="TOP"><TD ALIGN="MIDDLE" WIDTH=50 BGCOLOR="#e6e6e6"><TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_47.html#SEC47" onMouseover="img_act('prev')" onMouseout="img_inact('prev')"><IMG SRC="prev.png" BORDER="0" ALT="Back: C Header Files" ALIGN="MIDDLE" NAME="prev"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_49.html#SEC49" onMouseover="img_act('next')" onMouseout="img_inact('next')"><IMG SRC="next.png" BORDER="0" ALT="Forward: Function Definitions" ALIGN="MIDDLE" NAME="next"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"> <TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_49.html#SEC49" onMouseover="img_act('back')" onMouseout="img_inact('back')"><IMG SRC="back.png" BORDER="0" ALT="FastBack: Function Definitions" ALIGN="MIDDLE" NAME="back"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_45.html#SEC45" onMouseover="img_act('up')" onMouseout="img_inact('up')"><IMG SRC="up.png" BORDER="0" ALT="Up: GNU Autotools in Practice" ALIGN="MIDDLE" NAME="up"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_52.html#SEC52" onMouseover="img_act('forward')" onMouseout="img_inact('forward')"><IMG SRC="forward.png" BORDER="0" ALT="FastForward: A Simple Shell Builders Library" ALIGN="MIDDLE" NAME="forward"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook.html#SEC_Top" onMouseover="img_act('home')" onMouseout="img_inact('home')"><IMG SRC="home.png" BORDER="0" ALT="Top: Autoconf, Automake, and Libtool" ALIGN="MIDDLE" NAME="home"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_toc.html#SEC_Contents" onMouseover="img_act('toc')" onMouseout="img_inact('toc')"><IMG SRC="toc.png" BORDER="0" ALT="Contents: Table of Contents" ALIGN="MIDDLE" NAME="toc"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_285.html#SEC285" onMouseover="img_act('index')" onMouseout="img_inact('index')"><IMG SRC="index.png" BORDER="0" ALT="Index: Index" ALIGN="MIDDLE" NAME="index"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_abt.html#SEC_About" onMouseover="img_act('help')" onMouseout="img_inact('help')"><IMG SRC="help.png" BORDER="0" ALT="About: About this document" ALIGN="MIDDLE" NAME="help"></A></TD></TR></TABLE></TD><TD ALIGN="LEFT"><H3> 9.1.3 C++ Compilers </H3><!--docid::SEC48::--><P>In order for a C++ program to use a library compiled with a C compiler,it is necessary for any symbols exported from the C library to bedeclared between <SAMP>`extern "C" {'</SAMP> and <SAMP>`}'</SAMP>. This code isimportant, because a C++ compiler <EM>mangles</EM><A NAME="DOCF7" HREF="autobook_fot.html#FOOT7">(7)</A> all variable and function names, whereas a C compiler does not. On the other hand, a C compiler will notunderstand these lines, so you must be careful to make them invisibleto the C compiler.</P><P>Sometimes you will see this method used, written out in long hand inevery installed header file, like this:</P><P><TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>#ifdef __cplusplusextern "C" {#endif...#ifdef __cplusplus}#endif</FONT></pre></td></tr></table></P><P>But that is a lot of unnecessary typing if you have a few dozen headersin your project. Also the additional braces tend to confuse texteditors, such as emacs, which do automatic source indentation based onbrace characters.</P><P>Far better, then, to declare them as macros in a common header file, anduse the macros in your headers:</P><P><TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>#ifdef __cplusplus# define BEGIN_C_DECLS extern "C" {# define END_C_DECLS }#else /* !__cplusplus */# define BEGIN_C_DECLS# define END_C_DECLS#endif /* __cplusplus */</FONT></pre></td></tr></table></P><P>I have seen several projects that name such macros with a leadingunderscore -- <SAMP>`_BEGIN_C_DECLS'</SAMP>. Any symbol with a leadingunderscore is reserved for use by the compiler implementation, so youshouldn't name <STRONG>any</STRONG> symbols of your own in this way. By way ofexample, I recently ported theSmall<A NAME="DOCF8" HREF="autobook_fot.html#FOOT8">(8)</A> languagecompiler to Unix, and almost all of the work was writing a Perl scriptto rename huge numbers of symbols in the compiler's reserved namespaceto something more sensible so that GCC could even parse thesources. Small was originally developed on Windows, and the author hadused a lot of symbols with a leading underscore. Although his symbolnames didn't clash with his own compiler, in some cases they were thesame as symbols used by GCC.</P><P><A NAME="Function Definitions"></A></TR></TABLE><BR> <FONT SIZE="-1">This document was generatedby <I>Gary V. Vaughan</I> on <I>September, 12 2004</I>using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html"><I>texi2html</I></A></BODY></HTML>⌨️ 快捷键说明
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