Null Pointer exception while using Linked List in c++

Question

I have an error of " read access violation " or as well " Segmentation fault ".

Here is my Code:

#include<iostream>

using namespace std;

class Node {
 int data;
 public:
Node* next;
Node(int d) :data(d), next(NULL) {}
int getData() {
    return data;
}
 };

class LinkedList {

Node* head;
Node* tail;

public:
LinkedList() :head(NULL), tail(NULL) {}

void push_front(int data) {
    if (head == NULL) {
        Node* n = new Node(data);
        head = tail = n;
    }
    else {
        Node* n = new Node(data);
        n->next = head;
        head = n;
     }
}

void push_back(int data) {
    if (head == NULL) {
        Node* n = new Node(data);
        tail = head = n;
    }
    else {
        Node* n = new Node(data);
        tail->next =n;
        tail = n;
    }
}

void insert(int data,int pos) {
    if (pos == 0) push_front(data);
    else {
        Node* temp = head;
        for (int i = 0; i < pos; i++) {
            temp = temp->next;
           
        }
        Node* n = new Node(data);
        n->next = temp->next;
        temp->next=n;
    }
}
void print() { 
    while (head != NULL) {
        cout <<  head->getData() << "=>";
        head = head->next;
    }
}
 };

int main() {
LinkedList l;
l.push_front(5);
l.push_back(8);
l.push_front(0);
l.print();
l.insert(9, 2);
cout << "\n";

}

The error is in Insert Function in the LinkedList class.

In actual an exception pops up in this function at line number 52 .

I am using VISUAL STUDIO 2019 as my IDE. I shall be very thankful if anyone helps me to resolve it. I have looked about this error it was about my temp->next is Null but now I do not know how catch this flaw as in initial state I have inititalised the Next with Head but beside of this it is still giving the same error.

Answer 1

When you insert into the last position, handle it as the same way you did in push_back() .

Edit: I didn't notice that you modified the head pointer in your print function..that is the root cause, as pointed out by @retired-ninja