c++ - C++中的链表

Question

我使用类创建了一个简单的链表。在我的类中，我有 3 个方法:push_back()、push_front() 和 print() 来打印list.push_front() 中的指针 p 有一些问题。用vs 2013调试时，p的value和next是“unable to read memory”，我无法理解，所以请为我解释。

#include <stdio.h>
#include <iostream>
using namespace std;
class Note
{
public :
    int value;
    Note *next;
public :
    Note(int value)
    {
        this->value = value;
        this->next = NULL;
    }
    Note(int value,Note *next)
    {
        this->value = value;
        this->next = next;
    }
};

class LinkList
{
public :
    Note *head;
public :
    LinkList()
    {
        head = NULL;
    }

    void Push_back(int value)
    {
        Note *p = NULL;
        if (head == NULL)
        {
            head = new Note(value, NULL);
        }
        else
        {
            p = head;
            while (p->next != NULL)
                p = p->next;
            p->next = new Note(value, NULL);
        }
    }

    void Push_front(int value)
    {
        Note *p = NULL;

        p->value = 3;
        p->next = this->head;
    }

    void print()
    {
        Note *p = NULL; 
        p = head;
        while (p != NULL)
        {
            cout << p->value<<endl;
            p = p->next;
        }
    }

int main()
{
    LinkList test;
    test.Push_back(6);
    test.Push_back(5);
    test.Push_back(12);
    test.Push_front(13);
    test.print();


}

Answer 1

您还没有为 p 分配任何内存以指向:

void Push_front(int value)
{
    Note *p = NULL;
          ^^^^^^^^

    // you are missing an allocation of a Note object:
    // p = new Note;

    p->value = 3;
    p->next = this->head;
}