Overloading output stream operator: no operator "<<" matches these operands - c++

Question

I recently asked the question: Is ostream& operator<< better practice in a class than using std::cout? and got an excellent answer.
When I tried to implement the solution I got errors:
no operator "<<" matches these operands
and
binary '<<': no operator found which takes a right-hand operand of type 'LinkedList' (or there is no acceptable conversion)
The simplest solution in this case would be to add a std::ostream parameter to your display() method, eg:
LinkedList.h
#include <iostream>
#pragma once
class LinkedList
{
struct Node {
int data = 0;
Node* prev = nullptr;
Node* next = nullptr;
};
private:
Node* m_head;
public:
// CONSTRUCTOR
LinkedList();
// DESTRUCTOR
~LinkedList();
void display(std::ostream& out) const;
};
LinkedList.cpp
#include <iostream>
#include "LinkedList.h"
LinkedList::LinkedList() {
m_head = nullptr;
}
void LinkedList::display(std::ostream &out) const {
Node* curr = m_head;
while (curr) {
out << curr->data << " -> ";
curr = curr->next;
}
out << std::endl;
}
std::ostream& operator<<(std::ostream &out, const LinkedList &list) {
list.display(out);
return out;
}
Main.cpp (generates error)
#include <iostream>
#include "LinkedList.h"
int main() {
LinkedList list;
std::cout << list;
}

Answer 1

I got some help with this question but it was swiftly deleted...
Essentially the problem is that std::ostream& operator<<(std::ostream &out, const LinkedList &list) is not correctly advertised.
We need to add friend std::ostream& operator<<(std::ostream& output, const SortedList& list); to the LinkedList.h file within the LinkedList class
LinkedList.h
#include <iostream>
#pragma once
class LinkedList
{
struct Node {
int data = 0;
Node* next = nullptr;
};
private:
Node* m_head;
public:
// CONSTRUCTOR
LinkedList();
// DESTRUCTOR
~LinkedList();
void display(std::ostream& out) const;
friend std::ostream& operator<<(std::ostream& output, const LinkedList& list);
};