使用链表实现错误队列

Question

我正在尝试使用链表实现队列，但它意外停止。找不到原因？

#include <iostream>
#include <string>

using namespace std;

Class 节点创建节点。

class Node
    {
    public:
        int data;
        Node *next;
    };

队列 Class 包含队列的操作。

class Queue{
private:
    Node* front = NULL;
    Node* rear = NULL;
public:
    void enQueue(int x){
    Node* temp = NULL;
    temp->data = x;
    temp->next = NULL;
    if(front == NULL && rear == NULL){
        front = rear = NULL;
        return;
    }
    rear->next = temp;
    rear = temp;
    }
    void dequeue()
    {
        Node* temp = front;
        if(front == NULL)
        {
            cout << "No list found." << endl;
            return;
        }
        if(front == rear){
            front = rear = NULL;
        }
        else{
            front = front->next;
        }
        delete temp;
    }
};

这里是主要函数

int main(){
    Queue a;
    a.enQueue(45);
    a.dequeue();
    a.dequeue();
}

Answer 1

第一次将一个节点加入队列时，您将取消引用一个空指针

void enQueue(int x){
    Node* temp = NULL;
    temp->data = x; // Wrong

取消引用空指针会产生 undefined behavior。

Answer 2

void enQueue(int x){
  Node* temp = NULL;   //Node* temp = new Node;
  temp->data = x;      //BOOM
  temp->next = NULL;
  if(front == NULL && rear == NULL){
    front = rear = NULL;  //What?
    return;
  }
  rear->next = temp;
  rear = temp;
}

您分配的地址无效。

这只会停止来自 "stopping unexpectidly" 的程序。不过还是有bug。

Answer 3

您的入队函数有错误。进行以下更改：

void enQueue(int x){
    Node* temp = new Node();//you need to create this variable and not set it to NULL
    temp->data = x;
    temp->next = NULL;
    if(front == NULL && rear == NULL){
        front = rear = temp;
        return;
    }
    rear->next = temp;
    rear = temp;
    }

现在您的程序将按预期运行

使用链表实现错误队列

Error Queue implementation using Linked List

c++

queue

linked-list

data-structures