Thanks for your response on this. I have tried moving the void_cast_register to the derived class constructor (without success) and I have looked further in to my use case. This was probably brought about by me removing the archive and serialization headers from the precompiled header file that Borland uses because there were other compilation problems in keeping them in. The use case is as follows: Classes A and B are derived from class Z. Class M has a pointer to class Z as member data. This member data is set to a pointer to an instance of A or B as appropriate. Class S serializes M. Class S includes the Archive headers as it creates the archive class instance. S includes the headers for M that includes the headers for Z. However S does not include the headers for A or B, because it does not need to, and in fact does not need to know of the existence of A or B as they are used polymorphically. In our case S does not use A/B/Z but others use them via M. I have a free function called RegisterTypes in a module that has BOOST_CLASS_EXPORT(A) and void_cast_register(0,0) in it. It's run once at application start. Which means that A.hpp is never included in a compilation unit with any archive header and therefore the void_cast_register function is not generated (as I understand it). I realise that serializing classes via a pointer to the base class and void_cast_register<T> is a seldom used corner of serialization. I can fix the problem by including archive headers where RegisterTypes is defined even though they may not be needed, and then the application links ok. I'm not sure if there is a need for a change, you are best to judge. I hope this explains my use-case. Richard -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Robert Ramey Sent: 04 August 2005 17:57 To: boost-users@lists.boost.org Subject: Re: [Boost-users] [Serialization] 1.33 RC1 Problemlinkingvoid_cast_register I believe this is a side effect of our efforts to be sure that the mere inclusion of a class that includes serialization headers doesn't trigger (through auto-linking) the requirement for inlcuding a library module. The idea is that one would never need "void_cast_register<T>" to be generated unless there is an archive somewhere involved. So that raises the question of what the context is here. Your test illustrates the link error but it doesn't illustrate the use case. That is, what is the context of explicitly invoking void_cast_register without an archive header present? I'm not saying its wrong. Its just that I don't see how this comes up. When we implemented changes which resulted in this symptom - we enivisioned a pattern of usage like that shown below. In this way, the *.hpp files could be included in other programs without triggering auto-link and requiring linking with the boost library to include code that in fact will never be used. Were we missing something here? What is it? Robert Ramey Z.hpp ==== #include #include #include class Z ... }; BOOST_IS_ABSTRACT(Z) A.hpp ==== #include ... // other serialization headers #include "Z.hpp" class A : public Z { A(){ boost::serialization::void_cast_register(0,0); } }; BOOST_CLASS_EXPORT(A) B.hpp ==== #include ... // other serialization headers #include "Z.hpp" class B : public Z { ... B(){ boost::serialization::void_cast_register(0,0); } }; BOOST_CLASS_EXPORT(B) main.cpp ====== #include #include #include "Z.hpp" #include "A.hpp" #include "B.hpp" int main(int argc, char* argv[]){ return 0; } _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users