具有多重继承的 C++ 链表模板？

Question

我正在尝试创建一个具有多态性和继承自 Stack 和 Queue 头文件的 LinkedList 类。这是我第一次尝试使用模板，但不断收到诸如“类模板已定义”或“不允许抽象类类型”之类的错误。显然我做错了，如何实现模板？

// LinkedList.h File
#include "Stack.h"
#include "Queue.h"
#include "Node.h"

using namespace std;

template <typename T>
class LinkedList : public Queue<T>, public Stack<T>
{
public:
    LinkedList();
    ~LinkedList(void);

protected:
    Node<T> *first;
    Node<T> *last;
    int numItems;
};

// LinkedList.cpp File
#include "LinkedList.h"

using namespace std;

template <typename T>
class LinkedList
{
    LinkedList()
    {
        first = NULL;
        last = NULL;
        numItems = 0;
    }

    LinkedList::~LinkedList(void)
    {
        while (first != NULL)
        {
            Node* cur = first;
            first = first->next;
            delete cur;
        }
    }

    LinkedList::clear() {}    
    LinkedList::size() {}

    // Stack Functions
    LinkedList::push(T item) {}    
    LinkedList::pop() {}    
    LinkedList::top() {}

    // Queue Functions
    LinkedList::enqueue(T item) {}    
    LinkedList::dequeue() {}    
    LinkedList::peek() {}
}

// Stack.h File (Queue is the same except push/pop/top = enqueue/dequeue/peek)
#pragma once

template <typename T> class Stack
{

public:

  virtual ~Stack() {}

  virtual int size() = 0;
  virtual void clear() = 0;
  virtual void push(T item) = 0;
  virtual T pop() = 0;
  virtual T top() = 0;

};

更新代码

// LinkedList.h File
#pragma once
#include "Stack.h"
#include "Queue.h"
#include "Node.h"

template <typename T>
class LinkedList : public Queue<T>, public Stack<T>
{
public:
    LinkedList();
    ~LinkedList(void);

    void clear();
    int size();

    void push(T item);
    T pop();
    T top();

    void enqueue(T item);
    T dequeue();
    T peek();


protected:
    Node<T> *first;
    Node<T> *last;
    int numItems;
};

// LinkedList.cpp File
#include "LinkedList.h"

class LinkedList
{
    LinkedList::LinkedList()
    {
        first = NULL;
        last = NULL;
        numItems = 0;
    }

    LinkedList::~LinkedList(void)
    {
        while (first != NULL)
        {
            Node* cur = first;
            first = first->next;
            delete cur;
        }
    }

    LinkedList::clear(){}
    LinkedList::size(){}

    // Stack Functions
    void LinkedList::push(T item){}
    T LinkedList::pop(){}
    T LinkedList::top(){}

    // Queue Functions
    void LinkedList::enqueue(T item){}
    T LinkedList::dequeue(){}
    T LinkedList::peek(){}
}


// Stack.h File (Queue is the same except push/pop/top = enqueue/dequeue/peek)
#pragma once

template <typename T> class Stack
{

public:

  virtual ~Stack() {}

  virtual int size() = 0;
  virtual void clear() = 0;
  virtual void push(T item) = 0;
  virtual T pop() = 0;
  virtual T top() = 0;

};

Answer 1

我明白了

// LinkedList.cpp File

模板定义必须在每个翻译单元上可见，您不能将它们的定义放在 cpp 文件中并期望它能够正常工作（就像常规课程一样）。所有模板函数的定义都应该出现在头文件中。

另外，编译器错误是正确的。您正在为两个 LinkedList 类编写定义。我假设您正在寻找：

LinkedList::LinkedList(){ ... }