继承中的语法错误

Question

我在尝试继承这些节点时遇到了一些问题。我在网上查看了很多示例，但无法弄清楚我做错了什么。

我的编译器给了我这些信息：

error: expected identifier before 'public'
error: expected '{' before 'public'
error: expected unqualified-id before 'public'

任何帮助将不胜感激:)

template <typename T>
class Node
{
    protected:
        Node<T>* next;
        Node<T>* prev;
        T* data;
    public:
        Node();
        ~Node();
        Node* getNext();
        Node* getPrev();
        void setNext(Node<T>*);
        void setPrev(Node<T>*);
        T* getData();
        void setData(T*);
};
template <typename T>
class HeadNode : public Node<T>
{
    public:
        HeadNode();
        ~HeadNode();
};
template <typename T>
class TailNode : public Node<T>
{
    public:
        TailNode(Node<T>*);
        ~TailNode();
};
template <typename T>
class InternalNode : public Node<T>
{
    public:
        InternalNode(Node<T>*, Node<T>*, T*);
        ~InternalNode();
};

template <typename T>
Node<T>::Node()
{
    next = 0;
    prev = 0;
    data = 0;
}
template <typename T>
Node<T>::~Node()
{
    //delete data;
}
template <typename T>
Node<T>* Node<T>::getNext()
{
    return next;
}
template <typename T>
Node<T>* Node<T>::getPrev()
{
    return prev;
}
template <typename T>
void Node<T>::setNext(Node<T>* n)
{
    next = n;
}
template <typename T>
void Node<T>::setPrev(Node<T>* n)
{
    prev = n;
}
template <typename T>
T* Node<T>::getData()
{
    return data;
}
template <typename T>
void Node<T>::setData(T* nData)
{
    delete data;
    data = nData;
}
template <typename T>
HeadNode<T>::HeadNode() : public Node<T>()
{
    next = new TailNode<T>(this);
}
template <typename T>
HeadNode<T>::~HeadNode()
{
}
template <typename T>
TailNode<T>::TailNode(Node<T>* p) : public Node<T>()
{
    prev = p;
}
template <typename T>
TailNode<T>::~TailNode()
{
}
template <typename T>
InternalNode<T>::InternalNode(Node<T>* n, Node<T>* p, T* nData):         public Node<T>()
{
    next = n;
    prev = p;
    data = nData;
}
template <typename T>
InternalNode<T>::~InternalNode()
{
    //delete data;
}

Answer 1

我不太擅长 C++，但这通过了编译器。

• 从构造函数的初始化中移除 public
• 将Node<T>::添加到子类要使用父类成员的位置
• 将virtual添加到Node的析构函数中，这样子类的析构函数就会在删除时被调用

---

template <typename T>
class Node
{
    protected:
        Node<T>* next;
        Node<T>* prev;
        T* data;
    public:
        Node();
        virtual ~Node(); // add virtual
        Node* getNext();
        Node* getPrev();
        void setNext(Node<T>*);
        void setPrev(Node<T>*);
        T* getData();
        void setData(T*);
};
template <typename T>
class HeadNode : public Node<T>
{
    public:
        HeadNode();
        ~HeadNode();
};
template <typename T>
class TailNode : public Node<T>
{
    public:
        TailNode(Node<T>*);
        ~TailNode();
};
template <typename T>
class InternalNode : public Node<T>
{
    public:
        InternalNode(Node<T>*, Node<T>*, T*);
        ~InternalNode();
};

template <typename T>
Node<T>::Node()
{
    next = 0;
    prev = 0;
    data = 0;
}
template <typename T>
Node<T>::~Node()
{
    //delete data;
}
template <typename T>
Node<T>* Node<T>::getNext()
{
    return next;
}
template <typename T>
Node<T>* Node<T>::getPrev()
{
    return prev;
}
template <typename T>
void Node<T>::setNext(Node<T>* n)
{
    next = n;
}
template <typename T>
void Node<T>::setPrev(Node<T>* n)
{
    prev = n;
}
template <typename T>
T* Node<T>::getData()
{
    return data;
}
template <typename T>
void Node<T>::setData(T* nData)
{
    delete data;
    data = nData;
}
template <typename T>
HeadNode<T>::HeadNode() : Node<T>() // remove public
{
    Node<T>::next = new TailNode<T>(this); // add Node<T>::
}
template <typename T>
HeadNode<T>::~HeadNode()
{
}
template <typename T>
TailNode<T>::TailNode(Node<T>* p) :  Node<T>() // remove public
{
    Node<T>::prev = p; // add Node<T>::
}
template <typename T>
TailNode<T>::~TailNode()
{
}
template <typename T>
InternalNode<T>::InternalNode(Node<T>* n, Node<T>* p, T* nData): Node<T>() // remove public
{
    Node<T>::next = n; // add Node<T>::
    Node<T>::prev = p; // add Node<T>::
    Node<T>::data = nData; // add Node<T>::
}
template <typename T>
InternalNode<T>::~InternalNode()
{
    //delete data;
}