Thread: Getting "undeclared member" error with derived class

Basically I have a base class that has its members in a protected block and when I try to access those items in the base class I get the error

error: `child' undeclared (first use this function)

Code:

template <typename T>
class Node
{

protected:
    T** child;   //dynamically allocated T array.
    T data;
    size_t size;

public:
    Node(size_t capacity) : size(capacity)
    {
        child = new T*[capacity];

        for (size_t i = 0; i < capacity; ++i)
            child[i] = NULL;
    }

    Node(size_t capacity, T x) : data(x), size(capacity)
    {
        child = new T*[capacity];

        for (size_t i = 0; i < capacity; ++i)
            child[i] = NULL;
    }

    virtual ~Node()
    {
        for(size_t i = 0; i < size; ++i)
            delete child[i];
    }
};


template <typename T>
class BinaryTreeNode : public Node<T>
{
public:
    BinaryTreeNode() : Node<T>(2) { }

    BinaryTreeNode(T x) : Node<T>(2, x) { }

    ~BinaryTreeNode()
    {
        delete child[0];
        delete child[1];
    }

};

With extraneous code removed, your problem simplifies to

Code:

template <typename T>
class Node
{
protected:
    size_t size;
};

template <typename T>
class BinaryTreeNode : public Node<T>
{
public:
    BinaryTreeNode()
    {
        size = 0;
    }
};

When you remove the templates, the code compiles.

Code:

//template <typename T>
class Node
{
protected:
    size_t size;
};

//template <typename T>
class BinaryTreeNode : public Node//<T>
{
public:
    BinaryTreeNode()
    {
        size = 0;
    }
};

On a hunch, using

Code:

Node<T>::size = 0;

in the original version works. Don't ask me why, I'm a C programmer.

In short, for some reason, you want

Code:

template <typename T>
class BinaryTreeNode : public Node<T>
{
public:
    BinaryTreeNode() : Node<T>(2) { }

    BinaryTreeNode(T x) : Node<T>(2, x) { }

    ~BinaryTreeNode()
    {
        delete Node<T>::child[0];
        delete Node<T>::child[1];
    }

};

By the way, aren't you going to delete the same childs multiple times in BinaryTreeNode because both derived and base class destructor will do that?