友元函数和友元类

class A{
//友元全局函数
friend void printXY(A & a);
//友元成员函数，是B的成员函数
friend void B::printXY(A & a);
public:
A(int a,int b){}

private:
int m_a;
int m_b;

};

class B{
　public:
void printXY(A & a){
    cout<< a.m_a<<endl;
    cout<< a.m_b<<endl;
    }
}
int main(){
    
void printXY(A & a){
    cout<< a.m_a<<endl;
    cout<< a.m_b<<endl;
}

//声明一下A类
class A;
//定义友元类
class B{
friend A;
public:
  B(int x, int y){}
private:
  int _x;
  int _y;
}；
class A{
public:
  void printXY(){
    cout<<b._x<<b._y<<endl;
}
private:
  B b;
};