I came up with this great macro called IS_UNSIGNED_CHAR() such that IS_UNSIGNED_CHAR(unsigned char) expands to 1 and IS_UNSIGNED_CHAR(hello world) or any other input, expands to 0. It almost works, but it gets confused by IS_UNSIGNED_CHAR(unsigned world) which expands to garbage: BOOST_PP_IIF_I, EQUALS_42_57, RETURN_0)((42) world_U_I_O_P)); Any suggestions? Here is the code: #include <boost/preprocessor.hpp> #define Q_W_E_R_T_Y_unsigned 42) #define char_U_I_O_P (57 // Transmogrify t #define MOG(t) Q_W_E_R_T_Y_ ## t ## _U_I_O_P // Check if t is (42)(57) #define EQUALS_42_57(t) BOOST_PP_AND(BOOST_PP_EQUAL(42,BOOST_PP_SEQ_ELEM(0, t)), \ BOOST_PP_EQUAL(57,BOOST_PP_SEQ_ELEM(1, t)) ) // return 0 #define RETURN_0(t) 0 #define IS_UNSIGNED_CHAR(t) BOOST_PP_IIF(BOOST_PP_EQUAL(2,BOOST_PP_SEQ_SIZE((MOG(t)))), \ EQUALS_42_57, RETURN_0)((MOG(t))) // Here is some test data: IS_UNSIGNED_CHAR(unsigned char); // should expand to 1 IS_UNSIGNED_CHAR(hello world); // should expand to 0 IS_UNSIGNED_CHAR(unsigned world); // should expand to 0