enum class of type string in C++

Question

- Background Information:

There is a class in C++11 known as enum class which you can store variables inside. However, I have only seen the type of the class to be char:

enum class : char {
   v1 = 'x', v2 = 'y'
};

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- Question:

Is there any way I can express this enum class of type string?

For example,

enum class : string{
  v1 = "x", v2 = "y"
};

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- What I think:

I tried using it, but I got errors, I am not sure if I am doing it right or not. The reason why I want to use strings is that they are capable of holding multiple characters at the same time, so it makes them more useful for my code.

Answer 1

There is no way to do that in C++11 or C++14. However, you should consider having some enum class, then code some explicit functions or operators to convert it from and to std::string-s.

There is a class in C++11 known as enum class which you can store variables inside.

That phrasing is not correct: an enum class does not store variables (but enumerators).

So you might code:

enum class MyEnum : char {
   v1 = 'x', v2 = 'y'
};

(this is possible, as answered by druckermanly, because char is an integral type; of course you cannot use strings instead)

then define some MyEnum string_to_MyEnum(const std::string&); function (it probably would throw some exception if the argument is an unexpected string) and another std::string MyEnum_to_string(MyEnum); one. You might even consider also having some cast operator calling them (but I don't find that readable, in your case). You could also define a class MyEnumValue containing one single data member of MyEnum type and have that class having cast operator, e.g.

 class MyEnumValue {
    const MyEnum en;
 public:
    MyEnumValue(MyEnum e) : en(e) {};
    MyEnumValue(const std::string&s)
     : MyEnumValue(string_to_MyEnum(s)) {};
    operator std::string () const { return MyEnum_to_string(en);};
    operator MyEnum () const { return en };
    //// etc....
 };

With appropriate more things in MyEnumValue (see the rule of five) you might almost always use MyEnumValue instead of MyEnum (which perhaps might even be internal to class MyEnumValue)

Answer 2

No, this is not possible.

http://en.cppreference.com/w/cpp/language/enum states:

The values of the constants are values of an integral type known as the underlying type of the enumeration.

The key point being "integral type" -- a string is not an integral type.

Answer 3

Compiler internally converts your char to its equivalent int representation (ASCII). So it would not be possible to use string instead.