When I compile the following simple program on VC6: #include <boost/preprocessor/facilities/empty.hpp> #include <boost/preprocessor/punctuation/comma_if.hpp> #define PARAM(has_param) BOOST_PP_IF(has_param, typename Param, BOOST_PP_EMPTY()) #define MACRO(has_param) \ template< PARAM(has_param) BOOST_PP_COMMA_IF(has_param) typename T> \ struct name { }; \ /**/ MACRO(0) int main() { return 0; } I get the following warnings: warning C4003: not enough actual parameters for macro 'BOOST_PP_IIF' warning C4003: not enough actual parameters for macro 'BOOST_PP_IIF_I' warning C4003: not enough actual parameters for macro 'BOOST_PP_IIF_0' It works fine on other compilers. Am I missusing the preprocessor library, or is this a problem with VC6? If the latter, is there a workaround, or should I just turn off warning 4003? Jonathan