Compiler Warn on enum

Question

Is there a way to get the compiler to warn if an integer is outside the 'range' of an enum ? For example, something like this:

enum Brothers {Snee, Snoo, Snum};

int main(void) {

  enum Brothers k;
  k = Snee;
  k = 9; // compiler warning for an int outside [0,2] ?

}

Answer 1

I couldn't find an option on GCC matching exactly what you want. There are some enum-related compiler flags for GCC that will make enums slightly more behaved. For example, -Wenum-compare will give a warning when comparing enums of different types for equality:

enum fruit {                                                                                                            
    APPLE,                                                                                                              
    BANANA                                                                                                              
};                                                                                                                      
                                                                                                                      
enum colors {                                                                                                           
    RED,                                                                                                                
    BLUE                                                                                                                
};                                                                                                                      
                                                                                                                                                                                                                                     
if (APPLE == RED) { // -Wenum-compare gives compiler warning here.
    ...
}

The option you're looking for does seem to exist on clang though as -Wassign-enum .

Answer 2

Not for gcc as of version 10.2. There's a related open enhancement request from 2002 but developers haven't seemed interested in implementing it.

clang will warn about this if given the -Wassign-enum option: https://godbolt.org/z/zv8an5