1 extern void abort (); 2 3 #define _ 2 4 #pragma push_macro("_") 5 #undef _ 6 #define _ 1 7 #pragma pop_macro("_") 8 main()9 int main () 10 { 11 if (_ != 2) 12 abort (); 13 return 0; 14 } 15 16