CODEWITHSUNDEEP
c++classnested
user974967
user974967

Reputation: 2946

accessing nested inner class struct from outer class

class A
{
 class B;
 B::data myData; //Error: incomplete type not allowed.

    class B
    {
    public:
        struct data
        {
        int number;
        };
    };
};

In the code above, how could I declare a member variable of type data in class A?

Upvotes: 2

Views: 1057

Answers (3)

John Humphreys
John Humphreys

Reputation: 39354

Use scope specifiers and make sure you don't use the type until after its defined in the file:

class A
{   
    class B
    {
    public:
        struct data
        {
        int number;
        };
    };

    B::data myData;
};

Also, note that forward-declaration doesn't work unless you're just using a pointer to the class. When you create an instance of the class like you have, it needs the definition to that class available to it immediately.

Upvotes: 0

James McNellis
James McNellis

Reputation: 355367

B must be defined before you use it in the declaration of A::myData:

class A
{
    class B
    {
    public:
        struct data
        {
            int number;
        };
    };

     B::data myData;
};

Upvotes: 3

Dan F
Dan F

Reputation: 17732

I think all you need to do is put the class definition in front of the declaration of the variable. The compiler has no idea what is inside class B, only that it exists, until it encounters the actual definition of the class

Upvotes: 3

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