c++ - C++模板泛型(模板参数列表)

Question

我正在尝试实现循环双重链接列表，但与链接列表实现本身无关。我遇到的问题是允许它使用模板使用通用参数。我已经查看了一些有关模板的教程，但是还没有找到我想要做的事情。

我相信我已经解决了大多数错误，但是仍然出现错误:

linkedlist.h(37): error C2955: 'Node' : use of class template requires template argument list
linkedlist.h(9) : see declaration of 'Node'
main.cpp(6) : see reference to class template instantiation 'LinkedList<T>' being compiled
      with
      [
          T=int
      ]

这是我的代码:

LinkedList.h:

#ifndef LINKEDLIST_H
#define LINKEDLIST_H

#include <iostream>

//node
template <class T>
class Node
{
private:

public:
    bool first;             //boolean tag 
    Node * next;            //pointer to the next node
    Node * prev;            //pointer to the prev node
    T data;                 //placeholder for generic data

    Node(T d);          //constructor
};

template <class T>
Node<T>::Node(T d)
{
    next = NULL;
    prev = NULL;
    data = d;
    first = false;
}

//a circular doubly-linked list
template <class T>
class LinkedList
{
private:

public:
    Node * p;                   //reference to the current node

    LinkedList();               //constructor

    bool empty();               //returns true if the list is empty, false otherwise
    int size();                 //returns the number of elements in the list    
    void insertBefore(T d); //inserts a node before the current node
    void insertAfter(T d);  //inserts a node after the current node
    void remove();              //removes the current node
    void moveAhead();           //moves to the next node
    void moveBack();            //moves to the previous node
    T access();             //returns the data of the current node
    void listContents();        //displays the data of every element in the list starting with the current
};

template <class T>
LinkedList<T>::LinkedList()
{
    p = NULL;
}

template <class T>
bool LinkedList<T>::empty()
{
    if (p == NULL)
    {
        std::cout << "List is Empty.\n";
        return true;
    }
    else
        return false;
}

template <class T>
int LinkedList<T>::size()
{
    if (p == NULL)
    {
        return 0;
    }
    if (p->next == p)
    {
        return 1;
    }
    else
        return 2; //placeholder
}

template <class T>
void LinkedList<T>::insertBefore(T d)
{
    Node *q, *t;
    if (p == NULL)
    {
        p = new Node<T>(d);
        p->next = p;
        p->prev = p;
        //std::cout << d << " inserted.\n";
    }
    else
    {
        if (p-> next == p)
        {
            q = new Node<T>(d);
            q->next = p;
            q->prev = p;
            p->next = q;
            p->prev = q;
            //std::cout << d << " inserted.\n";
        }
        else
        {
            q = p->prev;
            t = new Node<T>(d);
            p->prev = t;
            q->next = t;
            t->next = p;
            t->prev = q;
            //std::cout << d << " inserted.\n";
        }
    }
}

template <class T>
void LinkedList<T>::insertAfter(T d)
{
    Node *q, *t;
    if (p == NULL)
    {
        p = new Node<T>(d);
        p->next = p;
        p->prev = p;
        //std::cout << d << " inserted.\n";
    }
    else
    {
        if (p-> next == p)
        {
            q = new Node<T>(d);
            q->next = p;
            q->prev = p;
            p->next = q;
            p->prev = q;
            //std::cout << d << " inserted.\n";
        }
        else
        {
            q = p->next;
            t = new Node<T>(d);
            p->next = t;
            q->prev = t;
            t->next = q;
            t->prev = p;
            //std::cout << d << " inserted.\n";
        }
    }
}

template <class T>
T LinkedList<T>::access()
{
    if (p == NULL)
    {
        std::cout << "The list is empty. No data to be accessed.\n";
        return NULL;
    }
    else
        return p->data;
}

template <class T>
void LinkedList<T>::remove()
{
    if (p == NULL)
        std::cout << "The list is empty. No node exists to be removed.\n";
}

template <class T>
void LinkedList<T>::moveAhead()
{
    p = p->next;
}

template <class T>
void LinkedList<T>::moveBack()
{
    p = p->prev;
}

template <class T>
void LinkedList<T>::listContents()
{
    if (p == NULL)
    {
        std::cout << "This list is empty, there are no elements to be displayed.";
    }
    else
    {
        Node *q;
        p->first = true;;
        q = p;
        while (!q->next->first)
        {
            //std::cout << q->data << ", ";
            q = q->next;
        }
        //std::cout << q->data << ".\n";
        p->first = false;
    }
}

#endif

main.cpp:

#include <iostream>
#include "LinkedList.h"

int main()
{
    LinkedList<int> list;

    list.empty();
    std::cout << "p list size is: " << list.size() << std::endl;
    list.remove();
    list.access();
    list.insertBefore(3);
    list.insertBefore(2);
    list.moveBack();
    list.insertBefore(1);
    list.moveBack();
    list.moveAhead();
    list.moveAhead();
    list.insertAfter(5);
    list.insertAfter(4);
    list.moveBack();
    list.moveBack();
    list.listContents();

    system("PAUSE");
    return 0;
}

据我所知，我并没有做错太多，我只需要更正那些错误即可。如果我能做的主要是错误的事情，请您向我指出，或将我引导到适当的资源，我们将不胜感激。

提前致谢。

Answer 1

错误非常明显。您正在Node内的多个位置使用LinkedList，而未将其与模板参数一起使用。

例如:

template <class T>
void LinkedList<T>::insertBefore(T d)
{
    Node *q, *t;

应该

template <class T>
void LinkedList<T>::insertBefore(T d)
{
    Node<T> *q, *t;

其他地方也一样，除了 Node类声明和 Node函数定义内部(在函数定义中，第一个必须具有它)。