How can I save references to a file?

Question

Hi,
I just ran into a really tricky problem where I'm trying to write objects to a file. The problem is like :
class A
B b1;
B b2;
The two B objects may be references to the same object, they don't have to be. How can I write this structure to a file? I want to be able to recreate it exactly, with references to objects kept intact. If the two B objects were referencing the same object I still want them to reference the same object after reading in from a file.
Naturally, the above example is an oversimplified one. My problem is actually much more complex involving superclasses, subclasses, bla bla bla, but this is the fundamental thing I can't do.
If anyone has any ideas whatsoever please share them. I'm really desperate, filehandling is key to my project and my teacher couldn't help me.
Thank you to anyone that replies.

Answer 1

Is there a way to do it without Serializable?
Strictly speaking I'm allowed to use Serializable,
I'm supposed to write out the ints and floats myself,
but if all else fails maybe I can plead to the
teacher. =)Then basically the teacher wants you to replicate what serialization already does.
Presumably what you are writing is very simple.
Say you have the following...
           class Data
                 int i;
                 String s;
           class Holder
                 Data d1;
                 Data d2;
The first task is write out a Data. So you figure out how to write an int and how to write a String. This could look something like this in the file(all text, each item on a different line)
          int:i: 47
          string:s: test
  Next you need to identify a reference. Notice that a reference is a type, just as int and String is.
A reference is a pointer. And you need some way to point.
So one way is to add another element to each class which is a unique id. Thus when you write a Data out it would look like the following...
          id::  1
          int:i: 47
          string:s: test
  And then when you write out Holder it would look like this...
          id:: 3
          ref:d1:  1
          ref:d2:  2
  So your entire file for the code sample given would look like this...
          id::  1
          int:i: 47
          string:s: test
          id::  2
          int:i: 53
          string:s: test other
          id:: 3
          ref:d1:  1
          ref:d2:  2
   Keep in mind that you must write the referenced objects first. Thus Holder must always come after Data.