CODEWITHSUNDEEP
c++enums
BSD
BSD

Reputation: 339

Syntax accessing Enum from parent class

I am getting an error with a program. Evidently I'm missing something about the syntax. The snippet of C++ code below is the smallest which produces the error.

#include <iostream>
using namespace std;

class Parent
{
    public:
    enum MyEnum {
        Value1,
        Value2,
        Value3
    };

    MyEnum* set;
};

class Child: public Parent
{
    public:
    Child()
    {
      set = new MyEnum[5];
      set[0]=MyEnum.Value1;//<--Something wrong here
      set[1]=MyEnum.Value2;//<--Something wrong here
      set[2]=MyEnum.Value3;//<--Something wrong here
      set[3]=MyEnum.Value2;//<--Something wrong here
      set[4]=MyEnum.Value1;//<--Something wrong here
    }

    void Write()
    {
        for(int i=0;i<5;i++)
        {
            cout<< "This is " << i << ": " << set[i];
        }
    }
};

int main() {
    Child c;
    c.Write();

    return 0;
}

The error has something to do with the indicated syntax. 

 expected primary-expression before ‘.’ token

I have tried Parent.MyEnum.Value1, Parent::MyEnum.Value1, etc. nothing seems to be right. How should I be referring to the specific values in the parent class?

Upvotes: 0

Views: 1091

Answers (2)

Daniel H
Daniel H

Reputation: 7433

An enum, like a class, defines a scope. A regular enum like you use puts its enumerator names both in its own scope and its containing scope. Since this is scope resolution, not member access, you use :: instead of .. Therefore, you can use Parent::Value1, Value1 (because public and protected names of Parent are visible in Child), or Parent::MyEnum::Value1 or MyEnum::Value1.

If you want to disallow the first or two options, you should use enum class instead of just enum.

Upvotes: 1

Daniel Trugman
Daniel Trugman

Reputation: 8501

Enums don't require qualification for their values, meaning you should access them like this:

set[0] = Parent::Value1;

If you would like to enforce qualification, you can use strongly typed enums. It looks like this:

enum struct MyEnum {
    Value1,
    Value2,
    Value3
};

set[0] = Parent::MyEnum::Value1;

But then you should print them using an explicit cast, e.g:

cout << static_cast<int>(set[0]) << endl;

Upvotes: 3

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