如何限制從主函數訪問類函數？

Question

如何限制從主函數訪問類函數？

這是我的代碼。

class Bar
{
public: void doSomething(){}
};

class Foo
{
public: Bar bar;
//Only this scope that bar object was declared(In this case only Foo class)
//Can access doSomething() by bar object.
};

int main()
{
    Foo foo;
    foo.bar.doSomething(); //doSomething() should be limited(can't access)
    return 0;
}

PS。對不起，我英語不好。

---

編輯 ：我沒有刪除舊代碼，但我擴展了新代碼。 我認為這種情況不能使用好友類。 因為我計划將其用於所有課程。 謝謝

class Bar
{
public:
    void A() {} //Can access in scope that object of Bar was declared only
    void B() {}
    void C() {}
};

class Foo
{
public:
    Bar bar;
    //Only this scope that bar object was declared(In this case is a Foo class)
    //Foo class can access A function by bar object

    //main function need to access bar object with B, C function
    //but main function don't need to access A function
    void CallA()
    {
        bar.A(); //Correct
    }
};

int main()
{
    Foo foo;
    foo.bar.A(); //Incorrect: A function should be limited(can't access)    
    foo.bar.B(); //Correct
    foo.bar.C(); //Correct
    foo.CallA(); //Correct
    return 0;
}

Answer 1

讓Foo成為Bar的朋友

class Bar
{
    friend class Foo;
private:
    void doSomething(){}
};

並且避免public成員變量。 使用setters/getters代替

Answer 2

您可以將Foo定義為Bar的朋友類，並將doSomething（）設為私有。

Answer 3

在Foo內部將Bar bar Foo私有可以解決問題，不是嗎？ 然后只有Foo類可以使用bar 。