In addition, static libraries (archives) that you are linking to, should appear _last_ on the command line - or at least, after all .o files and shared libraries. Otherwise, not all symbols from the static library may get picked up properly. Basically, when the linker looks at the static library, it tries to resolve any currently unresolved symbols using the static library. Once it's done with the library, it effectively throws it away and never looks at it again. And it doesn't keep a record of what symbols were defined in the library but that weren't needed. That means that if you have another library or .o file that needs a symbol defined in the static library, but that comes after it on the command line, the linker will not properly resolve the symbol. For example, let's say that you have a program in prog.c and you're using some routines from libroutines.a. If you compile your program like this: gcc -c prog.c gcc -o prog -lroutines prog.o The linker will look at libroutines before looking at prog.o. And when it does, it will say, "there are currently no undefined symbols that are defined in libroutine.a," and throw it away. Then when it looks at prog, it will add new undefined symbols to the symbol table (which are defined in libroutine.a). However, since it already processed libroutine.a, it won't do it again, and it doesn't know that your missing symbols can be found there. So, you need to link it like this, instead: gcc -o prog prog.o -lroutines Make sense? Cheers, Lyle -----Original Message----- From: gcc-help-owner@xxxxxxxxxxx [mailto:gcc-help-owner@xxxxxxxxxxx] On Behalf Of Sisyphus Sent: Sunday, February 01, 2004 3:22 PM To: Frank Cc: GNU GCC help list Subject: Re: Creating/using shared libraries Frank wrote: > Trying to move from archive to shared libraries for an application. I > believe I was able to create the shared library ok by compiling the > .cpp's with -fpic and using g++ -shared with the objects (.o's). But > when I try to compile a program that used that library I get a undefined > reference from the shared library about an archive library object that > it was compiled with (it was included on the link fro both the shared > lib and the executable). Is there some other option/procedure I need to > do to use the shared library? > > Any good reference to understand how to build and use shared libraries. > I'm using GNU gcc/make > http://vergil.chemistry.gatech.edu/resources/programming/c-tutorial/libr aries.html You still need to link to the static library when building the app. Hope I've understood you correctly. Cheers, Rob -- Any emails containing attachments will be deleted from my ISP's mail server before I even get to see them. If you wish to email me an attachment, please provide advance warning so that I can make the necessary arrangements.
