c++ - 被包含类的函数怎么访问包含类的成员或函数

Question

class A
{
    A();
    void func();
};

class B
{
    A a;
    int getX() {return x;}
private:
    int x;
};

请问怎么做才能让A的func()访问到x?
因为我想让a变量的func()访问x成员。

Answer 1

Originally I wanted to access B’s x in A’s func(), but later I found out that I could add a function to B to access A’s.
Including can access the included, and the included cannot access the included. This should generally be the case.

Answer 2

I am also a beginner in C++. Is there any other use for declaring A as a member of B? If B is not directly declared as a friend function of A, the members of B can be accessed through A, including private members.

Answer 3

How can I make func() of A access x? Because I want func() of variable a to access the x member.

Please see Section 7.2.1 and Section 7.3.4 of "C++ Primer" for an explanation of Friendship.

class B
{
    friend void A::func();
    // . . .
};