Friend function can't access private members

Question

I'm trying to get a friend function of class1 and ships to access the private members of both, but it says that those members are inaccessible.

The code is below, the problem is in ships.cpp. I tried to reproduce this problem in an even more simple manner in a single file but it didn't happen there, so I don't know what's wrong here. Maybe it's a circular declaration problem?

ships.h

#ifndef  _SHIPS_H_
#define _SHIPS_H_

#include "point.h"

class class1;

class Ships{
public:
    friend char* checkpoints();
private:
    Point ship[6]; 
};
#endif // ! _SHIPS_H_

ships.cpp

#include "ships.h"
#include "class1.h"

char* checkpoints(Ships ship, class1 game) {

    ship.ship[0];//cannot access private member declared in class 'Ships'
    game.smallship;//cannot access private member declared in class 'class1'

    return nullptr;
}

class1.h

#ifndef _CLASS1_H_
#define _CLASS1_H_

#include  "ships.h"
class class1 {
public:
    friend char* checkpoints();
private:
    static const int LIVES = 3;
    Ships smallship, bigship;
};

#endif 

Answer 1

Just making my comment an answer. You declared char* checkpoints() as a friend function. Declare the correct prototype char* checkpoints(Ships ship, class1 game) as a friend instead.

You also probably want to use references (maybe const) otherwise the arguments are passed by value (copy): char* checkpoints(Ships& ship, class1& game)