C++ 类A的成员函数作类B的友元函数，怎么访问不了类B的私有成员？

#include<iostream>
#include<string>
using namespace std;
class Bulding
{
    friend void Goodgay::visit();
public:
    Bulding()
    {
        m_room = "正在访问客厅";
        b_room = "正在访问卧室";
    }
    
    string m_room;
private:

    string b_room;
};
class Goodgay
{
public:
    Goodgay();
    void visit();

    Bulding* bulding;
};
 Goodgay::Goodgay()
{
    bulding = new Bulding;
}
void Goodgay::visit()
{
    cout << bulding->m_room << endl;
    cout << bulding->b_room << endl;//显示不可访问
}
void test()
{
    Goodgay b;
    b.visit();
}

int main()
{
    test();

    return 0;
}

在friend void Goodgay::visit();这里的时候，编译器不识别Goodgay，所以报错，代码修改如下：
如有帮助，请采纳一下，谢谢。

#include<iostream>
#include<string>
using namespace std;

class Bulding;
class Goodgay
{
public:
    Goodgay();
    void visit();
    Bulding* bulding;
};


class Bulding
{
    friend void Goodgay::visit();
public:
    Bulding()
    {
        m_room = "正在访问客厅";
        b_room = "正在访问卧室";
    }
    string m_room;
private:
    string b_room;
};

Goodgay::Goodgay()
{
    bulding = new Bulding;
}
void Goodgay::visit()
{
    cout << bulding->m_room << endl;
    cout << bulding->b_room << endl;//显示不可访问
}
void test()
{
    Goodgay b;
    b.visit();
}
int main()
{
    test();
    return 0;
}