Segmentation fault in linked list code in C++

Question

So, i'm trying to implement this code on C++ which inserts an element at a specific position in a linked list and I keep getting a segmentation fault. I've narrowed it down to it being the l.push(a) statement in the main function but can't rectify it.

n - number of nodes. then the linked list is inserted. data - the data to be inserted in the list. pos - the position in which the data is to be inserted.

Any help on how to rectify this and advice on how to avoid segmentation faults in such code would be much appreciated :)

//INSERTING ELEMENT AT A SPECIFIC POSITION IN A LINKED LIST - HACKERRANK
#include<iostream>
#include<cstdio>
#include<vector>
#include<limits>
#include<algorithm>
#include<cmath>
using namespace std;

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

struct Linkedlist{
    Node* head;
    Linkedlist(){
        head= NULL;
    }
    void push(int data){
        Node* temp = new Node;
        temp->data = data;
        temp->next = NULL;
        Node* curr = head;
        while(curr->next!=NULL)
            curr= curr->next;
        curr->next = temp;
    }
    void pushpos(int data,int pos){
        Node *curr = head;
        int curr_index = 0;
        while((pos-1)!=curr_index){
            curr=curr->next;
            curr_index++;
        }
        Node *temp = new Node;
        temp->data = data;
        temp->next = curr->next;
        curr->next = temp;

    }
    void print(){
        Node *curr = head;
        while(curr!=NULL){
            cout<<curr->data<<endl;
            curr = curr->next;
        }
    }
};
 
int main(){
    int n,i,a,data,pos;
    Linkedlist l;
    cin>>n;
    for(i=0;i<n;i++){
        cin>>a;
        l.push(a);
    }
    cout<<"pushed";
    cin>>data>>pos;
    l.pushpos(data,pos);
    l.print();  
    return 0;
}

Node* curr = head; while(curr->next!=NULL) You never checked if head or curr were NULL. Think about the state of an empty list when you're adding the first node. — Retired Ninja
– Retired Ninja, Commented Aug 25, 2020 at 4:42
When you get a segmentation fault, you can easily open up the core dump in a debugger such as gdb and often reveal the exact line of code that caused the problem. If you learn to use a debugger, you will spend more time being productive at the computer and less time asking questions or making wild guesses. — paddy
– paddy, Commented Aug 25, 2020 at 4:50
Creating a minimal reproducible example makes it easier for both you and us to debug a problem. Some tips for this example: Don't ask the user for input; hardcode a value of n (preferably as small as possible) for which the segfault occurs. Similarly, push pre-determined values (perhaps i) onto your list. Don't bother with code that is never executed because of the segfault (such as the call to l.pushpos() plus the definition of pushpos()). Simplify until the bug has nowhere to hide. Your main function might just end up being int main() { LinkedList l; l.push(0); }. — JaMiT
– JaMiT, Commented Aug 25, 2020 at 5:47

SPB · Accepted Answer · 2020-08-25 04:50:59Z

0

You have made couple of mistakes here.

1.In your Push API you are not checking for Null.

void push(int data) {
        Node* temp = new Node;
        temp->data = data;
        temp->next = NULL;
        if (head == NULL)
            head = temp;
        else {
            Node* curr = head;
            while (curr->next != NULL)
                curr = curr->next;
            curr->next = temp;
        }
    }

Again in pushpos you are not checking for failure conditions like NULL and what if pos being greater than size of linked list itself

answered Aug 25, 2020 at 4:50

SPB

4,20816 gold badges53 silver badges62 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Segmentation fault in linked list code in C++

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related