Alternative to nested class

Question

I have two classes A, B of which I want to create the object of class B from class A only. I do not want other classes to create an object of the class B. Here is the code snippet. Any suggestion how can I achieve without nested class? Can somebody please advice what is the correct approach to solving this problem?

class B
{
public:
    B(int x1, int y1, int x2, int y2);
    ~B();

    updateCoordinates(int x1, int y1, int x2, int y2);

private:
    int x1;
    int y1;
    int x2;
    int y2;
};

class A
{
public:
    A(int mode);
    ~A();

private:
    vector<B> bList;
};

A::A()
{
    // Based on the value of mod, create
    // objects of B and add to bList
}

Put the entire B class in A's source file, without a header that other files can use? — Beta, Mar 23 '18 at 13:52
The [PassKey idiom](https://stackoverflow.com/a/3218920/27678) is ideal for this — AndyG, Mar 23 '18 at 13:52
In Live555 Server code, I have seen that nested classes are used. So, I assume the nested class is also not bad. Wanted to get opinion from the forum. — Venkata Subbarao, Mar 23 '18 at 14:07
I have also seen people using friend class for this kind of problems. Some say it is a hack. Please see https://www.gamedev.net/forums/topic/464433-c-friend-keyword---bad-programming-style/ — Venkata Subbarao, Mar 23 '18 at 14:10
If you need to use class B only in class A declare and define class B in A.cpp. — vahancho, Mar 23 '18 at 14:42
I now feel that it may not be possible for me to use the nested class if I want the object of B to be given to the third class, which just has rights to call updateCoordinates(). — Venkata Subbarao, Mar 23 '18 at 14:43

score 2 · Accepted Answer · answered Mar 23 '18 at 13:55

2

class B
{
    friend class A;
    private:
        B(int x1, int y1, int x2, int y2);
    ...
}

answered Mar 23 '18 at 13:55

1

After creating the object, I would like to give the handle to another object so that it can invoke one public function of B. I assume that is possible with this approach and not bad idea – Venkata Subbarao Mar 23 '18 at 14:12

Alternative to nested class

1 Answers1