Enum inheriting from primitive type

Question

From questions such as this and this, I was under the impression that inheriting from a primitive type would cause a compiler error. However, the following code compiles and produces expected output on Ideone.

#include <iostream>

enum class Test : unsigned short int
{
    TEST, TEST2, TEST3, TEST4
};

int main() {
    // your code goes here
    Test ans = Test::TEST3;

    if(ans == Test::TEST3)
    {
        std::cout << "Here" << std::endl;
    }

    return 0;
}

Does the fact that the class is also an enum change the answers in the first two Q&A's? Is this well-defined behavior by the standard?

Answer 1

This does not mean inheritance, this selects the enum's underlying type. The underlying type is the integral type which is used to represent the enumerator values.

You can see the difference in this example:

#include <iostream>

enum class tiny : bool {
    one, two   
};

enum class bigger : long {
    some, lots   
};

int main(int argc, char *argv[])
{
    std::cout << sizeof(tiny::one) << '\n';    //prints 1
    std::cout << sizeof(bigger::some) << '\n'; //prints 8
}

In C++11 you can specify the underlying type of both scoped (i.e. class) and unscoped enums.