我收到STATUS_ACCESS_VIOLATION（C ++）

Question

I'm trying to test out my delete method in the LinkedList.ccp file. When I'm in debug mode it completly deletes all of the 4s from the the list but then I get this message:

  1 [main] trainlinkedlist 9904 exception::handle: Exception: STATUS_ACCESS_VIOLATION
614 [main] trainlinkedlist 9904 open_stackdumpfile: Dumping stack trace to trainlinkedlist.exe.stackdump

Any ideas what I need to do to fix this?

main.ccp

#include "LinkedList.h"
#include <iostream>     //ADDED BECAUSE IT IS NEED FOR PROGRAM TO RUN
#include <cstdlib>
using namespace std;    //ADDED BECAUSE IT IS NEED FOR PROGRAM TO RUN

/*
 * 
 */

int main() {
    LinkedList Train;
    srand(time(0));
        Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
        Train.InsertAtEnd(4);
    Train.InsertAtEnd(5);
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
    for(int i=0;i<5;i++){
        Train.InsertAtEnd((rand()%20));
    }
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
        Train.InsertAtEnd(35);
    Train.InsertAtEnd(2);
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
        Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(5);
    Train.InsertAtEnd(4);
        Train.InsertAtEnd(4);
    Train.InsertAtEnd(6);
    Train.InsertAtEnd(4);
    Train.InsertAtEnd(4);
    Train.Delete(4);
    Train.Display();
    return 0;
}

LinkedList.h

#ifndef LINKEDLIST_H
#define LINKEDLIST_H

typedef int ElementType;
struct Node {
    ElementType data;
    Node * next;
};

class LinkedList
{
 public: 
   LinkedList();//create an empty list
   bool empty(); // return true if the list is empty, otherwise return false
   void InsertAtEnd(ElementType x);//insert a value x at the end of list
   void Delete(ElementType x); //if value x is in the list, remove x
   void Display();// Display the data values in the list
  private:
Node * first;   //The first node in a Linked list
};

#endif  /* LINKEDLIST_H */

LinkedList.ccp

#include "LinkedList.h"
#include <iostream>
using namespace std;

/**
 * LinkedList() sets first as a Dummy Node
 */
LinkedList::LinkedList() {
    first = NULL;
}

bool LinkedList::empty() {
    if (first == NULL) {  //when this is true the list is empty
        return true;
    } else {
        return false;   //when this is false the list is NOT empty
    }
}

void LinkedList::InsertAtEnd(ElementType x) {
    Node *p;
    p = first;
    if(empty()){
        p = new Node;
        p->data = x;
        p->next = NULL;
        first=p;
        return;
    }
    while (p != NULL) { //this while loop looks for the end of the list
        if (p->next == NULL) {  //this is a check for if node p is the last node in the list
            p->next = new Node; //a new node is created at the end of the list with data value of x and the next is NULL
            p->next->data = x;
            p->next->next = NULL;
            break;      //breaks the while loop when a new node is added
        }
        p = p->next;
    }
}

void LinkedList::Delete(ElementType x) {
    Node *p;    //p is used to the find Node that will be deleted
    Node *q;    //q keeps track of the node before the one that is deleted
    p = first;
    q = NULL;
    while(p->data==x){
        first=first->next;
        p->data =0;
        p->next=NULL;
        delete p;
        p=first;
    }
    while(p!=NULL){     //this while loop goes through the list
        if(p->next->data==x){
            q=p->next;
            p->next=p->next->next;
            q->data=0;
            q->next=NULL;
            delete q;
            q=NULL;
        }else{
            p=p->next;
        }
//        if(p->data==x){ //check for the node that needs to be deleted
//            q->next=p->next;    //connects q's next to the p's next
//            delete p;   //deletes the node p points to
//            p->next= NULL;
//        }
//        q=p;
//        p=p->next;
    }
}

void LinkedList::Display() {
    Node *p;
    p = first;
    while (p != NULL) {
        if(p->data==-1){        //check used to skip the dummy node
            p=p->next;
            continue;
        }
        cout << p->data << " "; //prints out all the values in the list
        p = p->next;
    }
}

Answer 1

You aren't making enough checks and likely dereferencing NULL pointers.

while(p->data==x) does not first check whether or not p is 0.

if(p->next->data==x) does not first check whether or not p->next is 0.