Is it allowed for an enum to have an unlisted value? [duplicate]

Answer 1

In C and C++, this can work.

Same code for both:

#include 

enum E
{
  Foo = 0,
  Bar = 1
};

int main()
{
    enum E v = (enum E)2;    // the cast is required for C++, but not for C
    printf("v = %d\n", v);
    switch (v) {
    case Foo:
        printf("got foo\n");
        break;
    case Bar:
        printf("got bar\n");
        break;
    default:
        printf("got \n", v);
        break;
    }
}

Same output for both:

v = 2
got default

In C, an enum is an integral type, so you can assign an integer value to it without casting. In C++, an enum is its own type.