Class inheritance 但在 C++ 中遇到重新定义错误

Question

I'm learning C++ Data Structure, about implementing Stack using Array and Linked List. The array is default in C++ but I've constructed a Linked List class. The code below is my Linked List header file

#pragma once
#include "Node.h"
#include "Stack.h"
class LinkedList
{
public:
    LinkedList() {head = NULL;}
    Node* AddNode(int index, float x, bool doubly);
    int FindNodeIndex(float x);
    Node* FindNodeAddress(float x);
    void DeleteNode(float x);
    void DisplayList();
    
private:
    Node* head;
    friend class Stack;
};

which also used the Node header file, but it is not relevant here. Then I would like to implement stack using both array and linked list. Below is my Stack header file:

#pragma once

class Stack
{
public:
    Stack(int size = 10);
    bool IsEmpty() { return top == -1;}
    bool IsFull() { return top == maxTop;}
    double Top();
    void Push(const double x);
    double Pop();
    void DisplayStack();
    void Clear();
private:
    int maxTop;
    int top;
    double* values;
};

class Stack: public LinkedList
{
public:
    Stack(){}
    double Top()
    {
        if (!head)
        {
            std::cout << "The stack is empty." << std::endl;
            return -1;
        }
        else
            return head->data;
    }
    void Push(const double x) {AddNode(0,x);}
    void DisplayStack() { DisplayList();}
}

You can see in the Top() method, which is used to find the top element of the linked list, used the head variable (or explicitly, pointer of Node), where in the implementation of array, I have the same Top() method but it only use indexed array. The compiler give me this error message

Stack.h:20:7: error: redefinition of 'class Stack'
   20 | class Stack: public LinkedList

I knew I've probably made some mistake here, but I think it is necessary to write two Stack classes because they have different purpose, for example the Top() method cannot be used for both. Is it possible to combine both as one Stack class, then notify the compiler whether to use array or linked list?

Answer 1

Hi as @Some_programmer_dude said

Classes can't be "overloaded", they must have different names if they are defined in the same namespace.

I would use polymorphism for this situation. So we define a base class named Stack, then will create two other classes named LinkedListStack and ArrayStack which both derive form Stack.

// abstract class Stack
class Stack
{
public:
    Stack(int size = 10);
    virtual bool IsEmpty() = 0; // pure virtual function
    virtual bool IsFull();
    virtual double Top();
    virtual void Push(const double x);
    virtual double Pop();
    virtual void DisplayStack();
    virtual void Clear();
protected:
    int maxTop;
    int top;
    double* values;
};

As you can see, Stack has a member method virtual bool IsEmpty() = 0; , this is called a pure virtual function which won't have any definition, which will cause our class to be an abstract base class.

Abstract base classes are classes that can only be used as base classes and can't be instantiated. Since we don't want to instantiate a Stack class, we want to instantiate LinkedListStack or ArrayStack.

Then for each derived class(LinkedListStack and ArrayStack), we'll define their base class virtual functions.

class LinkedListStack: public Stack
{
public:
    LinkedListStack();
    bool IsEmpty() { return !head; }
    double Top()
    {
        if (IsEmpty())
        {
            std::cout << "The stack is empty." << std::endl;
            return -1;
        }
        else
            return head->data;
    }
    void Push(const double x) { AddNode(0,x); }
    void DisplayStack() { DisplayList(); }
    /* define remaining base member methods. */
}

class ArrayStack : public Stack
{
public:
    ArrayStack(int size = 10);
    bool IsEmpty() { return top == -1; }
    bool IsFull() { return top == maxTop; }
    /* define remaining base member methods. */
};

Check this amazing C++ tutorial , it teaches virtual functions and polymorphism.