I'm having a bit of trouble using boost.serialization with a std::map. It seems like there is something simple I'm not doing correctly. I'm hoping someone can point me in the right direction. Thanks, David K. I'm using VS2005. Here is my test code: #include <map> #include <fstream> #include "boost/serialization/map.hpp" #include "boost/archive/xml_oarchive.hpp" std::map<int, int> map1; int main(int argc, char**argv) { map1[1] = 100; std::ofstream os("out.xml"); boost::archive::xml_oarchive oa(os); oa << BOOST_SERIALIZATION_NVP(map1); } This is the error: ...boost-win32-1_33_1\include\boost\archive\detail\oserializer.hpp(131) : error C2027: use of undefined type 'boost::serialization::extended_type_info_null<T>' with [ T=std::map<int,int> ] ...boost-win32-1_33_1\include\boost\archive\detail\oserializer.hpp(128) : while compiling class template member function 'bool boost::archive::detail::oserializer<Archive,T>::is_polymorphic(void) const' with [ Archive=boost::archive::xml_oarchive, T=std::map<int,int> ] ...boost-win32-1_33_1\include\boost\archive\detail\oserializer.hpp(264) : see reference to class template instantiation 'boost::archive::detail::oserializer<Archive,T>' being compiled with [ Archive=boost::archive::xml_oarchive, T=std::map<int,int> ] ...boost-win32-1_33_1\include\boost\archive\detail\oserializer.hpp(263) : while compiling class template member function 'void boost::archive::detail::save_non_pointer_type<Archive,T>::save_standard::invoke(Archive &,const T &)' with [ Archive=boost::archive::xml_oarchive, T=std::map<int,int> ] ...boost-win32-1_33_1\include\boost\archive\detail\oserializer.hpp(322) : see reference to class template instantiation 'boost::archive::detail::save_non_pointer_type<Archive,T>::save_standard' being compiled with [ Archive=boost::archive::xml_oarchive, T=std::map<int,int> ] ...boost-win32-1_33_1\include\boost\archive\detail\oserializer.hpp(310) : while compiling class template member function 'void boost::archive::detail::save_non_pointer_type<Archive,T>::invoke(Archive &,const T &)' with [ Archive=boost::archive::xml_oarchive, T=std::map<int,int> ] ...boost-win32-1_33_1\include\boost\archive\detail\oserializer.hpp(536) : see reference to class template instantiation 'boost::archive::detail::save_non_pointer_type<Archive,T>' being compiled with [ Archive=boost::archive::xml_oarchive, T=std::map<int,int> ] ...boost-win32-1_33_1\include\boost\archive\basic_xml_oarchive.hpp(99) : see reference to function template instantiation 'void boost::archive::save<Archive,T>(Archive &,const T &)' being compiled with [ Archive=boost::archive::xml_oarchive, T=std::map<int,int> ] ...boost-win32-1_33_1\include\boost\archive\detail\interface_oarchive.hpp(78) : see reference to function template instantiation 'void boost::archive::basic_xml_oarchive<Archive>::save_override<std::map<_Kty,_Ty>>(const boost::serialization::nvp<T> &,int)' being compiled with [ Archive=boost::archive::xml_oarchive, _Kty=int, _Ty=int, T=std::map<int,int> ] ...\source1.cpp(14) : see reference to function template instantiation 'Archive &boost::archive::detail::interface_oarchive<Archive>::operator <<<const boost::serialization::nvp<T>>(const boost::serialization::nvp<T> &)' being compiled with [ Archive=boost::archive::xml_oarchive, T=std::map<int,int> ]