Class sharing

If i have three classes A, B and C

Code:

---

class A {
    private:
        B b;
        C c;
};

---

I can create a pointer in class A that can access classes B and C however is it possible for classes B and C to then look back at class A?

and is it possible for classes B and C to access each others variables and functions?

I have got around this problem in the past by just making the class a function in side the class it needs to share information with however this is making class A bigger then it should be and causing other sorts of problems, what I am trying to do maybe bad coding practice so any suggestions on a way around this problem is greatly welcome.

To make let's say class B to have access to members of class C you just do that:

Code:

---

class C{
...
friend class B;
//you can also make just one function to have access to class B:
friend MyFunc(....);
};

---

If you want classes B and C to turn back to A you must declare a pointer to an object of class A like this:

Code:

---

class A;//this is smth like a declaration of a function
class B{
A *myPointer;
//.....
};

---

Sorry if my English is bad.

B and C can never look at the A instance which contains them, because It impossible to know if they're even contained wherelse. The solution would be to add a friend method to B and C which receives a instance of A

They can look at the instance of A, which contains them if they have a poiter of type A and in (for example) the constructor of A somehow we make this pointers to "point" to "this" (which is the object of type A).

Ok can someone post some code to show me what you mean as i cant get any of it to work each class has its own cpp and h file if tat makes a differance thanks

Code:

---

//in B.h

class A;

class B{
A *ContainingObject;
....
      B();
void SetContaingObject(A *a);
void ShowContaingObject();
};

//in B.cpp
....
void B::SetContaingObject(A *a)
{
if(a!=NULL)
    ContainingObject=a;
}

B::B(){
ContaingObject=NULL;//#define NULL 0x0
}

//in A.h
class A{
...
B obj;
};

//in A.cpp

A::A(){
obj.SetContainigObject(this);
........
}

---

So the object ot type B, which is in the object of type A (obj) can perform operation on the containing object:

Code:

---

//in B.cpp
void B::ShowContaingObject()
{
if(ContaingObject)
  cout<<(void*) ContaingObject;
}

---

I have created the example in the editor of replies, so it may contain syntax errors, but I think the may idea is clear.

Wish me luck- Tomorrow I have a test on Complex Analisis. :(

I generally try to avoid this scenario. Instead, I prefer to create a 'Link' object between two objects (of different types), with some mechanisms for querying and sending messages between the two 'ends' of the link.

From my perspective, this makes for a much cleaner relationship between objects.

When two classes have pointers to each other, how do you create objects of the classes?

You create them as normal
Then at some point you set the 2 pointers (before using them of course).

In this scenario you would create object A, then B (most likely within A's constructor). At this point A has a pointer to B (or has the entire instance of B) now A can pass B its this pointer so B can set its pointer to A (this can be done in B's constructor).

In a more general case each object has a method to set the pointer ot the other and they are called after object creation (possibly by a third object that knows about both)

Remember that a pointer is not an instance of a class. A pointer is a varialbe that holds the location to an instance of a class. This mean that a pointer might not "point" to any instance at all. This what makes it possible to create 2 objects that have poitners to each other.

I still cant get classes and B and C to look at each other data does someone have a code example of this using different files for each class?