Friends and nested classes

Question

Ok I'm totally frazzled on this. Code is begin to swim around the screen...must sleep.

So! Ok, troubled by nested classes and friends.

here is the pseudo-code

   class A{
     public:
          //constructor
          // member functions
     private:
          class B{
          //private
          int a();
          };

          class C{
          //private
          int b();
          };
   };

So once an object of type A has been created, I would like it to access a() and b(). I know that I have to use a friend function for this. So where should I put friend class A. Is that the right expression?.

Do you call `b` and `C` constructors when you are instantiating from `A`? — mrz, May 29 '13 at 05:28

Captain Obvlious · Answer 1 · 2013-05-29T05:59:38.903

2

If you would like to access a() and b() from within class A you need to place the friend declaration inside of class B and class C. However, a() and b() are not members of class A so you cannot access them in the way you are thinking. Instead you also need to add forwarding functions to A.

class A
{
public:
    //constructor
    // member functions
private:
    class B
    {
        //private
        int a();

        friend A;    // <-- make A a friend
    };

    class C
    {
        //private
        int b();

        friend A;    // <-- make A a friend
    };

public:

    // forwarding function for a
    int a()
    {
        return bdata_.a();
    }

    // forwarding function for b
    int b()
    {
        return cdata_.b();
    }

private:
    B bdata_;
    C cdata_;
};

edited May 29 '13 at 05:59

answered May 29 '13 at 05:23

Captain Obvlious

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in my main function I use this code to attempt to access a() and b() objectA->a() however it still does work? Where am I going wrong? – A Big Ball Of Lettuce May 29 '13 at 05:30
1

`a()` and `b()` are _not_ members of class `A`. They are members of the classes they are declared in. – Captain Obvlious May 29 '13 at 05:31
its still not working. I tried using an accessor function to access the private data members in Class A but the program complains of an unlawful conversion. What am I doing wrong? – A Big Ball Of Lettuce May 29 '13 at 05:48
@Josh why don't you just post a minimal code example showing what you are trying to do? – juanchopanza May 29 '13 at 05:50
GOTCHA! many thanks, just had to create a new accessor function and make it a public data member. – A Big Ball Of Lettuce May 29 '13 at 05:52
sorry, public member function. – A Big Ball Of Lettuce May 29 '13 at 05:52
sorry, missed adding public. Answer should be complete now – Captain Obvlious May 29 '13 at 06:00

Friends and nested classes

1 Answers1