Unhandled exception in c++ program for doubly linked list

I wrote a program for doubly linked list in visual studio 2013, and it threw unhandled exception error at the line marked with comment: -

linked_list_double.h: -

#pragma once
#include<iostream>

template <typename T>
struct Node
{
    T data;
    Node *next, *prev;
};

template <typename T>
class doubleLinkedList
{
private:
    Node<T> *top;
public:
    doubleLinkedList()
    {
        top = nullptr;
    }

    void add(T data)
    {
        Node<T> *temp = new Node<T>;

        temp->prev = nullptr;
        temp->next = top;
        top->prev = temp;     //unhandled exception here
        top = temp;
    }

    void display()
    {
        Node<T> *temp;
        temp = top;
        std::cout<<"nullptr<--->\n";
        while(temp)
        {
            std::cout<<temp->data<<"<--->";
            temp = temp->next;
        }
        std::cout<<"nullptr\n";
    }
};

main.cpp: -

#include "linked_list_double.h"

int main()
{
    doubleLinkedList<int> L;

    L.add(3);
    L.add(4);
    L.display();

    return 0;
}

The error is: -

Unhandled exception at 0x011C4B79 in dataStructures2.exe: 0xC0000005: Access violation writing location 0x00000008.

I have never written a doubly linked list before. I am not sure if there any logical error in the program. Any kind of help would be appreciated.

top is null on first add. So any attempt to deference top while it's null is going to crash.

So insted of this:

    top->prev = temp;     //unhandled exception here

Do this:

if (top != nullptr)
{
   top->prev = temp;
}