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<HTML><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><!-- Created on September, 12 2004 by texi2html 1.64 --><!-- Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author) Karl Berry <karl@freefriends.org> Olaf Bachmann <obachman@mathematik.uni-kl.de> and many others.Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>Send bugs and suggestions to <texi2html@mathematik.uni-kl.de> --><HEAD><TITLE>Autoconf, Automake, and Libtool: Finding a Module</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: Finding a Module"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: Finding a Module"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><META NAME="Generator" CONTENT="texi2html 1.64"><script language="Javascript"><!-- // Check the browser version. function checkVersion() { if (navigator.appVersion.charAt(0)>=3) return true; if (navigator.appVersion.charAt(0)>=4) return true; else return false; 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If you are worried about portability (which you must be, or youwouldn't be reading this book!), you can't rely on the default searchalgorithm of the vendor <CODE>dlopen</CODE> function, since it varies fromimplementation to implementation. You can't even rely on the name ofthe module, since the module suffix will vary according to theconventions of the target host (though you could insist on a particularsuffix for modules you are willing to load).</P><P>Unfortunately, this means that you will need to implement your ownsearching algorithm and always use an absolute pathname when you call<CODE>dlopen</CODE>. A widely adopted mechanism is to look for each module indirectories listed in an environment variable specific to yourapplication, allowing your users to inform the application of thelocation of any modules they have written. If a suitable module is notyet found, the application would then default to looking in a list ofstandard locations -- say, in a subdirectory of the user's homedirectory, and finally a subdirectory of the application installationtree. For application <SAMP>`foo'</SAMP>, you might use<TT>`/usr/lib/foo/module.so'</TT> -- that is, <SAMP>`$(pkglibdir)/module.so'</SAMP>if you are using Automake.</P><P>This algorithm can be further improved:</P><P><UL><LI>If you try different module suffixes to the named module for everydirectory in the search path, which will avoid locking your code into asubset of machines that use the otherwise hardcoded module suffix. Withthis in place you could ask the module loader for module<TT>`foomodule'</TT>, and if it was not found in the first search directory,the module loader could try <TT>`foomodule.so'</TT>, <TT>`foomodule.sl'</TT> and<TT>`foomodule.dll'</TT> before moving on to the next directory.<P><LI>You might also provide command line options to your application whichwill preload modules before starting the program proper or to modify themodule search path. For example, GNU M4, version 1.5, will havethe following dynamic loading options:</UL><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>$ m4 --helpUsage: m4 [OPTION]... [FILE]......Dynamic loading features: -M, --module-directory=DIRECTORY add DIRECTORY to the search path -m, --load-module=MODULE load dynamic MODULE from M4MODPATH...Report bugs to <bug-m4@gnu.org>.</pre></td></tr></table></P><P><A NAME="A Simple GNU/Linux Module Loader"></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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