Hello I agree with you, and currently have the same comprehension of the problem than you. I am currently also including BOOST_EXPORT_CLASS in only one implementation file *per class*. This seems to work. Robert is saying however, that even that can cause problem, but as written on a previous message, I cannot manage to follow his advice on including the archive headers in only one instantiation module (except putting all serialization code into that module, which I did previously: this is a maintenance nightmare, to the point that I ended up trying to break my code into smaller places). I'll chime in, as I'm having exactly the same issue, but on darwin/ gcc-4 with code in multiple dynamically loaded libraries... (I have other issues too, I get to those later) The problem is that although export.hpp is only included once per generated .o file, there are multiple .o files all including the same headers - and each therefore generates the same template instantiations, thereby causing the multiple definitions during linking. Also - the same headers may be included in multiple shared libraries, exacerbating the problem with the same code instantiated into multiple libraries - a serious problem if there are singletons. I may not be understanding this correctly - here's what >I< think needs to happen - please correct me. For any derived class, there is a set of code (templates) that need to be instantiated for each archive type (specifically, the list boost::archive::detail::known_archive_types::type, for the templates guid_initializer<T> and export_instantiate) From what I see, these are NOT declarations required by the other serialization code, but singletons that, during construction, register the serializers to the derived classes with the extended_type_info class registry. Is that incorrect? If the above is correct, then the BOOST_EXPORT_CLASS should only be in exactly one implementation file (.cpp, .C, .cc, whatever). And also, THAT implementation file should ONLY be linked into one shared library. _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users