Specifying the Size of an enum

Although each enum defines a unique type, it is represented by one of the built-in integral types. Under the new standard, we may specify that type by following the enum name with a colon and the name of the type we want to use:

enum intValues : unsigned long long {
    charTyp = 255, shortTyp = 65535, intTyp = 65535,
    longTyp = 4294967295UL,
    long_longTyp = 18446744073709551615ULL
};

If we do not specify the underlying type, then by default scoped enums have int as the underlying type. There is no default for unscoped enums; all we know is that the underlying type is large enough to hold the enumerator values. When the underlying type is specified (including implicitly specified for a scoped enum), it is an error for an enumerator to have a value that is too large to fit in that type.

Being able to specify the underlying type of an enum lets us control the type used across different implementations. We can be confident that our program compiled under one implementation will generate the same code when we compile it on another.