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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: Linking an Executable</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: Linking an Executable"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: Linking an Executable"><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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We tell the compiler which objectsand libraries are required, and it creates an executable for us.</P><P><BLOCKQUOTE>If you want to try this to see what <CODE>libtool</CODE> does on yourmachine, put the following code in a file <TT>`main.c'</TT>, in the samedirectory as <TT>`hello.c'</TT> and <TT>`libhello.la'</TT>, and run the exampleshell commands from there:<P><TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre></FONT></pre></td></tr></table></BLOCKQUOTE><P>To compile an executable which uses the non-Libtool <TT>`libhello.a'</TT>library built previously (see section <A HREF="autobook_70.html#SEC70">10.2 The Libtool Library</A>), I would use thefollowing commands: </P><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>$ gcc -o hello main.c libhello.a$ ./helloHello, World!</pre></td></tr></table></P><P>To create a similar executable on the HP-UX host, using<CODE>libtool</CODE> this time:</P><P><TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>$ libtool gcc -o hello main.c libhello.lalibtool: link: warning: this platform does not like uninstalledlibtool: link: warning: shared libraries.libtool: link: hello will be relinked during installationgcc -o .libs/hello main.c /tmp/hello/.libs/libhello.sl \-Wl,+b -Wl,/tmp/hello/.libs:/usr/local/libcreating hello$ lshello hello.lo libhello.lahello.c hello.o main.c$ ./helloHello, World!</FONT></pre></td></tr></table></P><P>Notice that you linked against the Libtool library, <TT>`libhello.la'</TT>,but otherwise the link command you used was not really very differentfrom non-Libtool static library link command used earlier. Still,<CODE>libtool</CODE> does several things for you: it links with the sharedarchive rather than the static archive; and it sets the compileroptions so that the program can be run in place, even though it islinked against the uninstalled Libtool library. Using a <CODE>make</CODE>rule <EM>without</EM> the benefit of <CODE>libtool</CODE>, it would be almostimpossible to reliably link a program against an uninstalled sharedlibrary in this way, since the particular switches needed wouldbe different between the various platforms you want the project towork with. Also without the extra compiler options <CODE>libtool</CODE>adds for you, the program will search only the standard librarydirectories for a shared <TT>`libhello'</TT>.</P><P>The link warning tells you that <CODE>libtool</CODE> knows that onHP-UX the program will stop working if it is copied directly tothe installation directory; To prevent it breaking, <CODE>libtool</CODE>will relink the program when it is installed, see <A HREF="autobook_80.html#SEC80">10.6 Installing a Library</A>.</P><P>I discussed the creation of static Libtool libraries in <A HREF="autobook_73.html#SEC73">Creating Static Libraries</A>. If youlink an executable against such a library, the library objects, bydefinition, can only be statically linked into your executable. Oftenthis is what you want if the library is not intended for installation,or if you have temporarily disabled building of shared libraries in your development tree to speed up compilation while you are debugging.</P><P>Sometimes, this isn't what you want. You might need to install acomplete Libtool library with shared and static components, but need togenerate a static executable linked against the same library, like this:</P><P><TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>$ libtool gcc -static -o hello main.c libhello.lagcc -o hello main.c ./.libs/libhello.a</FONT></pre></td></tr></table></P><P><A NAME="IDX12"></A>In this case, the <SAMP>`-static'</SAMP> switch instructs <CODE>libtool</CODE>to choose the static component of any uninstalled Libtool library.</P><P><A NAME="IDX13"></A>You could have specified <SAMP>`-all-static'</SAMP> instead, which instructs<CODE>libtool</CODE> to link the executable with only static libraries(wherever possible), for any Libtool or native libraries used.</P><P>Finally, you can also link executables against convenience libraries.This makes sense when the convenience library is being used as an alias(see section <A HREF="autobook_74.html#SEC74">Creating Convenience Libraries</A>). Notice how <TT>`libgraphics.la'</TT> expands toits own dependencies in the link command:</P><P><TABLE><tr><td> </td><td class=smallexample><FONT SIZE=-1><pre>$ libtool gcc -o image loader.o libgraphics.lalibtool: link: warning: this platform does not like uninstalledlibtool: link: warning: shared librarieslibtool: link: image will be relinked during installationgcc -o .libs/image loader.o -lpng -ltiff -ljpeg -lz \-Wl,+b -Wl,/tmp/image/.libs:/usr/local/libcreating image</FONT></pre></td></tr></table></P><P>You can also link against convenience libraries being used as partiallylinked objects, so long as you are careful that each is linked only once.Remember that a partially linked object is just the same as any otherobject, and that if you load it twice (even from different libraries),you will get multiple definition errors when you try to link yourexecutable. This is almost the same as using the <SAMP>`-static'</SAMP>switch on the <CODE>libtool</CODE> link line to link an executable with the static component of a normal Libtool library, except that theconvenience library comprises PIC objects. When statically linkingan executable, PIC objects are best avoided however, see<A HREF="autobook_71.html#SEC71">10.2.1 Position Independent Code</A>.</P><P> <A NAME="Linking a Library"></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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