AMDG I've been trying to work out a way to cause an explicit error if configuration macros are defined differently in different translation units. I really wish I could cause a link error, but the best I've been able to come up with so far is a runtime error // test_odr.hpp #ifndef TEST_ODR_HPP_INCLUDED #define TEST_ODR_HPP_INCLUDED #include <iostream> #include <cstdlib> #ifndef SOME_MACRO #define SOME_MACRO true #endif template<bool> struct test_odr { static bool value; }; template<bool b> bool test_odr<b>::value = SOME_MACRO; namespace { struct test_odr_impl_t { test_odr_impl_t() { if(test_odr<true>::value != SOME_MACRO) { std::cerr << "Error: SOME_MACRO defined differently in two translation units.\n"; std::abort(); } } }; test_odr_impl_t test_odr_impl; } #endif // test_odr1.cpp #include "test_odr.hpp" int main() {} // test_odr2.cpp #define SOME_MACRO false #include "test_odr.hpp" Comments? Any better ideas? In Christ, Steven Watanabe