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Re: Dumb linker/loader question

From: Max Okumoto <okumoto@xxxxxxxx>
Date: Sat, 15 Jan 2005 13:31:15 -0800

Simon 'corecode' Schubert wrote:
On 15.01.2005, at 20:52, Chris Pressey wrote:

I'm clearly lacking some basic understanding of how this whole
thing works.  How can code that uses the header files from a
library compile *and* link successfully without that library?

In brief: because linking to shared objects (.so's) happens only when the program is loaded, i.e. at runtime. It doesn't even try to link in .so's at compile-time - it just takes it on faith that the functions that you've said will be there (by including a header file) will in fact be there - so it doesn't know there are unresolved symbols (missing dependencies) until later, so everything builds without a hitch.

I think that's not 100% true. It won't work with executables because the linker indeed looks for the functions, if they exist in the shared object you're linking to. But it can't do so if you build a shared objects yourself. Then it just takes it for granted that the functions you are referring to will be present at load time.


The linker (/usr/bin/ld) need either a foo.a or a foo.so file. The header is not sufficent. There must be a library laying around in your
link path. Try and run ldd on the binary and see what it thinks it is


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