A Class to be accessed by another class only

Question

I have a class which declares some static variables:

#include <iostream>
class A
{
private:
static int x;
public:
static int y;
static getX(){ return A::x;}
static setX(int z){ A::x = z;}
};

int A::x = 0;
int A::y = 0;

Now class A can be accessed by anyone/anywhere and its member variables can be manipulate. How can I allow only one another class that will have access to class A static variables / methods?

class B
{
public:
void showX(){A::setX(9) ; std::cout << A::getX() << std::endl;}
void showY(){A::y = 8; std::cout << A::y << std::endl;}
};

int main()
{
B b1;
b1.showX();
b1.showY();
}

Answer 1

Define A inside B as private class.

#include <iostream>

class B
{
    class A
    {
    private:
        static int x;
    public:
        static int y;
        static int getX() {
            return A::x;
        }
        static void setX(int z) {
            A::x = z;
        }
    };

public:
    void showX() {
        A::setX(9) ;
        std::cout << A::getX() << std::endl;
    }
    void showY() {
        A::y = 8;
        std::cout << A::y << std::endl;
    }
};

int B::A::x = 0;
int B::A::y = 0;

int main()
{
    B b1;
    b1.showX();
    b1.showY();
}