Hello, Boost.Serialization 1.33.0 breaks serialization of derived classes referenced via base class pointers when using DLLs on Windows and VC 7.1. It might also affect shared objects on Unix, but I'm not sure how the various Unix loaders handle multiple instances of the same template member function in multiple shared objects. In particular what happens is that objects that are serialized via a base class pointer are no longer deserialized correctly when deserialized in an application that uses the DLL (and not within the DLL itself). Instead they are deserialized as NULL pointers. The problem is that the virtual equal_to and not_equal_to member functions were removed from the extended_type_info base class. These functions were previously used by extended_type_info::operator == and extended_type_info::operator !=. Now operator == simply performs an equal check on the address of the extended_type_info object, whereas the previous version that used equal_to actually did a full compare of the stored type info keys. If DLLs are used and the DLLs themselves contain serialization code and BOOST_CLASS_EXPORT macros, this will fail because the extended_type_info objects are always static objects allocated on the stack of a member template function, e.g. in extended_type_info_typeid_1::get_instance. In a DLL situation this will cause multiple DLLs that include the header file with that template function to have multiple (i.e. separate) copies of that extended_type_info object. Thus, comparing them only via their addresses leads to disaster. The fix is easy. Simply put the old code for extended_type_info::operator == and extended_type_info::operator != back in. Note that I haven't looked any further if there were other changes made to the code that also rely on the addresses of equal extended_type_info objects to be the same. This will also break serialization code in DLLs. I can only say that after I put the old code back in, our system could deserialize its data properly again. Best Regards, Martin TAB Austria Haiderstraße 40 4052 Ansfelden Austria Phone: +43 7229 78040-218 Fax: +43 7229 78040-209 E-mail: martin.ecker@tab.at http://www.tab.at