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two questions about shared libraries and C++


I had two questions about shared libraries in linux and g++.  One I think
might just be a platform issue - the other might be but I'm not sure.  I'm
using Debian Unstable - linux 2.4.9, g++ 2.95.4 pre-something, g++ 3.0.2
pre-something, and glibc 2.2.4.

The first question is about static data.  Let's say I have static data
defined in a class.  If I compile that class into a shared library, and
then get a handle out of the shared library to an instance of that class,
the static data is different than the data that I access in "main".  I've
got a nice example of this if I'm not clear - I'm not sure about the policy
of attachments on this list.  Is this a platform specific issue with linux
shared libraries, or is this a well defined behavior?

My other question is about multiple virtual inheritence and shared
libraries.  If I define two pure virtual base classes "base1" and "base2",
and then I define a concrete class "concrete" virtually derived from these
base classes.  I write a function that is accessed from a shared library
returning a void * that points at a "concrete".  

In g++ 3.0 if I static cast this to one of the c++ base classes, it works
fine.  If I then dynamic cast it to the other class, I get a null pointer
as if it wasn't derived from that base.  If I static cast this same pointer
to the other base class, it's fine.  Again, I can provide a simple example
of this "problem" in action if it's helpful.

In g++ 2.95.x the dynamic cast works.  Is this a compiler issue, or a
platform issue?  If either of these are platform issues, can someone
suggest who I can address them with?

Thanks,
	Dale
-- 
Dale E. Martin, Clifton Labs, Inc.
Senior Computer Engineer
dmartin@cliftonlabs.com
http://www.cliftonlabs.com
pgp key available


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