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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: Module Access Functions</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: Module Access Functions"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: Module Access Functions"><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; 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The interface consists of four functions. In practice, youreally ought not to use these functions, since you would be locking yourproject into this single API, and the class of machines thatsupports it. This description is over-simplified to serve as acomparison with the fully portable libltdl API described in<A HREF="autobook_164.html#SEC164">18. Using GNU libltdl</A>. The minutiae are not discussed, because thereinlie the implementation peculiarities that spoil the portability of thisAPI. As they stand, these descriptions give a good overview ofhow the functions work at a high level, and are broadly applicable tothe various implementations in use. If you are curious, the details ofyour machines particular dynamic loading API will be available inits system manual pages. </P><P><A NAME="IDX22"></A><DL><DT><U>Function:</U> void * <B>dlopen</B> <I>(const char *<VAR>filename</VAR>, int <VAR>flag</VAR>)</I><DD>This function brings the code from a named module into the address spaceof the running program that calls it, and returns a handle which is usedby the other API functions. If <VAR>filename</VAR> is not an absolutepath, GNU/Linux will search for it in directories named in the<SAMP>`LD_LIBRARY_PATH'</SAMP> environment variable, and then in the standardlibrary directories before giving up.</P><P>The flag argument is made by `OR'ing together various flag bitsdefined in the system headers. On GNU/Linux, these flags aredefined in <TT>`dlfcn.h'</TT>:</P><P><DL COMPACT><DT><SAMP>`RTLD_LAZY'</SAMP><DD>Resolve undefined symbols when they are first used.<P><DT><SAMP>`RTLD_NOW'</SAMP><DD>If all symbols cannot be resolved when the module is loaded,<CODE>dlopen</CODE> will fail and return <SAMP>`NULL'</SAMP>.<P><DT><SAMP>`RTLD_GLOBAL'</SAMP><DD>All of the global symbols in the loaded module will be available toresolve undefined symbols in subsequently loaded modules.</DL></DL><P><A NAME="IDX23"></A><DL><DT><U>Function:</U> void * <B>dlsym</B> <I>(void *<VAR>handle</VAR>, char *<VAR>name</VAR>)</I><DD>Returns the address of the named symbol in the module which returned<VAR>handle</VAR> when it was <CODE>dlopen</CODE>ed. You must cast the returnedaddress to a known type before using it.</DL></P><P><A NAME="IDX24"></A><DL><DT><U>Function:</U> int <B>dlclose</B> <I>(void *<VAR>handle</VAR>)</I><DD>When you are finished with a particular module, it can be removed frommemory using this function.</DL></P><P><A NAME="IDX25"></A><DL><DT><U>Function:</U> const char * <B>dlerror</B> <I>(void)</I><DD>If any of the other three API calls fails, this function returns astring which describes the last error that occurred.</DL></P><P>In order to use these functions on GNU/Linux, you must<CODE>#include <dlfcn.h></CODE> for the function prototypes, and link with<SAMP>`-ldl'</SAMP> to provide the API implementation. Other Unices use<SAMP>`-ldld'</SAMP> or provide the implementation of the API inside thestandard C library.</P><P><A NAME="Finding a Module"></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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