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Linking problem

Posted on 2002-04-12
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Last Modified: 2010-04-22
Hello.

While trying to check why my ./configure script cannot find my libraries,
I found this really confusing problem. I've got a libutil library in /usr/local/lib. When I compile a program

gcc -o test test.cpp -lutil -L/usr/local/lib

it goes just fine. But when instead i export LD_LIBRARY_PATH=/usr/local/lib and remove -L option, it fails (and also fails when ./configure checks for libraries, as I've seen in config.log). I've tried to putj /usr/local/lib in ld.so.conf and run ldconfig with no results.

My system is RH 7.2
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Question by:Robson
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Author Comment

by:Robson
ID: 6936429
I solved it!!! My problems were caused by my library name: libutil, which was exactly the same as one of standard system libraries. After renaming it to libfoo_util all goes fine!

And now: first expert who explains why one should not create librares named as standard libraries and why compilation worked with -L option will get at least B grade (I already know it, but I cannot pass points to myself :-)
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Expert Comment

by:IainHere
ID: 6937076
It worked because the system library libutil is in /usr/lib or similar.  The first directory searched is the one specified by -L (and in order, too).  You shouldn't use standard names for the exact reason you posted this question.

More importantly, post a request in CS to have this question PAQ'd, and refund your points (with a link to this question).  Since you answered it yourself, you don't need pay for it.
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by:ahoffmann
ID: 6938545
ld does not use LD_LIBRARY_PATH for searching libraries (except Sun's bundled /usr/ccs/bin/ld)
So  gcc -o test test.cpp -lutil -L/usr/local/lib
works fine 'cause you specified a path to the libutil with -L.

When you omit -L, the default settings of library search pathes apply, and that contains /lib and /usr/lib where it finds libutil system library (if installed).

Check with gcc -v ...
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ID: 6940320
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Computer101
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by:Robson
ID: 6940321
Thanks IainHere! I'll do that.

To ahoffmann: setting LD_LIBRARY_PATH (after rewriting /etc/ld.so.conf) was my first act of desperation. Second act was tracking linking process with 'strace' :-) That's how I found that ld loads /usr/lib/libutil.so instead of /usr/local/lib/libutil.so

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