The following is a dead simple example of using Boost.Serialization using an XML output archive which follows the patterns laid down in examples: /* \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/ */ #include <iostream> #include <boost/archive/xml_oarchive.hpp> #include <boost/serialization/nvp.hpp> // Warning level 4. #pragma warning(push, 4) #pragma message("********") struct MyData { MyData(int val) : m_Value(val) {} template<typename Archive> void serialize(Archive & ar, const unsigned int) { ar & BOOST_SERIALIZATION_NVP(m_Value); // <-- Warning here. } int m_Value; }; void main() { using namespace std; MyData d(3); boost::archive::xml_oarchive oa(cout); oa << BOOST_SERIALIZATION_NVP(d); <-- Warning here. } // Warning level back to normal. #pragma warning(pop) /* \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/ */ When compiling this code I get the following error: "warning C4239: nonstandard extension used : 'argument' : conversion from 'struct boost::serialization::nvp<struct MyData>' to 'struct boost::serialization::nvp<struct MyData> &' A reference that is not to 'const' cannot be bound to a non-lvalue" I tried MSVC 6 and "Visual C++ 2005" which can be downloaded from here: http://msdn.microsoft.com/vstudio/express/visualC/default.aspx Interestingly I could not get it to happen with "Microsoft Visual C++ Toolkit 2003". The warning seems valid to me. The "BOOST_SERIALIZATION_NVP" looks like this: -------------------------------------------------------------------------------------------------------------------------- #define BOOST_SERIALIZATION_NVP(name) \ boost::serialization::make_nvp(BOOST_PP_STRINGIZE(name), name) -------------------------------------------------------------------------------------------------------------------------- The "make_nvp" function looks like as follows: ------------------------------------------------------- nvp<T> make_nvp(const char * name, T & t){ return nvp<T>(name, t); } ------------------------------------------------------- "Operator<<", which is used in "main" is reproduced below: -------------------------------------------------------------------------------------- template<class Archive> class interface_oarchive { // ... Code removed ... // template<class T> Archive & operator<<(T & t){ this->This()->save_override(t, 0); return * this->This(); } // ... Code removed ... // }; -------------------------------------------------------------------------------------- So, to cut to the chase, "BOOST_SERIALIZATION_NVP" expands to a call to make_nvp" which returns a temporary which is bound to a non-const reference in "interface_oarchive::operator<<": this is not legal in standard C++ (unless I'm mistaken). It seems that if you follow to documentation and examples the resulting code isn't standard C++!?!