Undeclared identifier when overloading operator

Question

When trying to attempt to overload operator<< in my shape.cpp, it can't seem to recognize the variables within the class, even though it is a friend of the class.

My .cpp file:

#include "Shape.h"

ostream& operator << (ostream& cout, const Shape& shapes)
{
    for (int i = 0; i < points.size(); i++) //points is undefined
    {
        cout << points[i] << endl; 
    }
}

My .h file:

#include <vector>
#include "Point.h"
#pragma once

using namespace std;

class Shape
{
    friend ostream& operator << (ostream& cout, const Shape& shapes);

    private:
        vector <Point> points; //Ordered list of vertices
};

I already used the same overload for my point class and it worked fine.

Answer 1

A friend function is not a class member. It can be treated as any other non-class function. Except that, because it's a friend, it has access to its private members:

ostream& operator << (ostream& cout, const Shape& shapes)
{
    for (int i = 0; i < shapes.points.size(); i++)
    {
        cout << shapes.points[i] << endl; 
    }
}

It should now be clear that the object gets passed in as the shapes parameter. Well, it's points member must, therefore, be shapes.points.

However, we can do even better than that. How about using range iteration?

ostream& operator << (ostream& cout, const Shape& shapes)
{
    for (auto &v:shapes.points)
    {
        cout << v << endl; 
    }
}