Defining a function in a header class with using its own struct?

Question

class List{
        public:
        List();
        void add(int x);
        void remove();
        void display();
        void findingEvens(Node* n, Node* &h);
        private:
        struct Node{
                Node* next;
                int data;

        };
        Node* head;

    };

I have the above code in my header class, in the member function

void findingEvens(Node* n, Node* &h);

The problem is in the main class it gives an error for the following code besides I've already include the list.h,

    Node *result = 0;
    cout << findingEvens(l, result);
    l.display();

As an error it says that

error: ‘Node’ was not declared in this scope

But to declare it in this scope I've already include the list.h class. Am I wrong?

Alok Save · Answer 1 · 2013-01-01T15:30:21.637

3

However the main problem is in the prototype of the function findingEvents it gives an error for the Node* however it's already defined

You use the type before it seen by the compiler in the same file. So the compiler cannot understand what is Node
Move the function declaration after the structure is declared.

 public:
        List();
        void add(int x);
        void remove();
        void display();
        private:
        struct Node{
                Node* next;
                int data;

        };
        Node* head;
        void findingEvens(List::Node* n, List::Node* &h);

Node is a nested structure. You need to tell the compiler where to find it by using its full qualification:

List::Node *result = 0;
^^^^^^^^^^^^

You need to read about Nested classes.

edited Jan 01 '13 at 15:30

answered Jan 01 '13 at 15:07

Alok Save

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Oh I edited that part and it worked. However in main.cpp the error continues. Besides I include list.h. I'm adding it to the question. – Mert Can Celik Jan 01 '13 at 15:14
@Nawaz: He needs your answer now :) – Alok Save Jan 01 '13 at 15:16
@AlokSave: He needs to learn the basics first. He has got so many problems in his code. I'm not in a mood of clarifying all of them. :P – Nawaz Jan 01 '13 at 15:19
@Nawaz Oh no.. You're so cruel. – Mert Can Celik Jan 01 '13 at 15:21
1

@MertCanCelik: You sure need to pick up a [good book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). – Alok Save Jan 01 '13 at 15:22
@AlokSave I'm so happy for your both help and advices thank you :) – Mert Can Celik Jan 01 '13 at 15:24

score 0 · Answer 2 · answered Jan 01 '13 at 15:10

0

Try moving the prototype of findingEvens to be after the definition of struct Node. You should remove the private: for now.

answered Jan 01 '13 at 15:10

David Grayson

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what's the problem with `private`? – SomeWittyUsername Jan 01 '13 at 15:14
1

It doesn't make much sense to have a public method where one of the parameters has a type that is private. C++ might disallow that, so I was warning him about it. – David Grayson Jan 01 '13 at 15:18
Yep, or alternatively move the `struct Node` to `public`. – SomeWittyUsername Jan 01 '13 at 15:28

benjarobin · Answer 3 · 2013-01-01T15:34:01.087

0

This answer is not really useful anymore, but here the fixed code:

class List{
public:
    List();
    void add(int x);
    void remove();
    void display();

    struct Node {
        struct Node* next;
        int data;
    };

    void findingEvens(Node* n, Node* &h);
private:
    Node* head;
};

edited Jan 01 '13 at 15:34

answered Jan 01 '13 at 15:16

benjarobin

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Well I learn one thing today : http://stackoverflow.com/questions/612328/difference-between-struct-and-typedef-struct-in-c – benjarobin Jan 01 '13 at 15:32

Defining a function in a header class with using its own struct?

3 Answers3