Destructor of List cannot delete the last node

问题

Here is my test code:

#include <iostream>
#include <cstdlib>

using namespace std;

class List
{
    private:
        class Node{
            public:
                int data;
                Node* next;
            public:
                virtual ~Node()
                {
                    if (next != NULL)
                    {
                        cout << "Node is out: " << data << endl;
                        delete next;
                    }
                }
                Node()
                {
                    next = NULL;
                }
        };

        Node* head;
    public:
        virtual ~List()
        {
            if (head != NULL)
            {
                delete head;
            }
        }
        List()
        {
            head = NULL;
        }
    public:
        void AddNode(int data);
        void DeleteNode(int data);
        //....  
};

void List::AddNode(int data)
{
    Node* temp = new Node;
    temp -> data = data;

    if (head == NULL)
    {
        head = temp;
    }
    else
    {
        Node* ptr = head;
        while (ptr -> next != NULL)
        {
            ptr = ptr -> next;
        }
        ptr -> next = temp;
    }   

}

int main()
{
    List test_list;
    test_list.AddNode(1);
    test_list.AddNode(2);
    test_list.AddNode(3);
    test_list.AddNode(4);
    test_list.AddNode(5);

    return 0;   
}

The output is like this:

Node is out: 1
Node is out: 2
Node is out: 3
Node is out: 4

It a common list and you can pay attention to the two destructor function for Node and List. I thought this one can work but the out showed that the last node cannot be deleted. I also test for other number of nodes. The result is the same, last node cannot be deleted. Thanks ahead for your advices:-).

回答1:

Change your destructor to print on the outside of the if statement.

The destructor is being called, however, on your last node next is NULL, so the if statement returns false and the cout line is not being called.

virtual ~Node()
{
    cout << "Node is out: " << data << endl;                
    if (next != NULL)
    {        
        delete next;
    }
}

来源：https://stackoverflow.com/questions/22998753/destructor-of-list-cannot-delete-the-last-node

标签

c++

list

nodes

destructor