Digital Mars C++ (as in latest version 8.49.1) doesn't insert items from files like <cstdef> into std:: namespace (the headers do not use namespaces at all). BOOST_NO_STDC_NAMESPACE is not defined for the compiler but it should. This will immediatelly help with Serialization and possibly other libraries. Several libraries (e.g. Type Traits) could be updated to handle this problem, e.g. with: #include <cstddef> // std::size_t #include <boost/config.hpp> #if defined(BOOST_NO_STDC_NAMESPACE) #error namespace std{ using ::size_t; } // namespace std #endif or with: #include <boost/config.hpp> #ifdef BOOST_NO_STDC_NAMESPACE # include <boost/compatibility/cpp_c_headers/cstddef> #else # include <cstddef> #endif When such workarounds are applied and the latest STLport (5.10 beta, supporting DMC) are used quite a many libraries get usable under dmc: Optional, Variant, Program Options, etc among others. /Pavel