1 #if defined foo 2 failure_1 3 #else 4 success_1 5 #endif 6 #define foo 7 #if defined foo 8 success_2 9 #else 10 failure_2 11 #endif 12 #undef foo 13 #if defined foo 14 failure_3 15 #else 16 success_3 17 #endif 18