Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!ecsv38
From: ecsv38@castle.ed.ac.uk (S Manoharan)
Newsgroups: comp.lang.c++
Subject: Re: Design Questions : Help !!!
Keywords: Object Identity
Message-ID: <4925@castle.ed.ac.uk>
Date: 27 Jun 90 11:11:06 GMT
References: <23694@uflorida.cis.ufl.EDU>
Reply-To: ecsv38@castle.ed.ac.uk (S Manoharan)
Organization: Dept of Computer Science, University of Edinburgh
Lines: 48

In article <23694@uflorida.cis.ufl.EDU> sml@beach.cis.ufl.edu (Shein-Fong Law) writes:
>
>      I am trying to implement an object idendity generator for my database
>project. I want to assign an instance i.d (i.i.d) for each object created. The
>format of i.i.d is a concatenation of class i.d (c.i.d) and object i.d (o.i.d).
>All the objects belonging to the same class will have the same c.i.d but 
>different (unique) o.i.d's. Internally, the identifiers can be just unsigned 
>integers.
>
>   Also, I want the creation of such identifiers to be known by the system only
>(in this case, me). Of course, the design should be object-oriented.
>

One possible way could be:

class Root {
private:
   char *cname;
   int oid;
protected:
   void name(char *const s)	{ cname = s; }
public:
   Root(char * = 0);

   int id()		{ return oid; }
   char *name() const	{ return cname; }
   int class_id()	{ return (int)cname; }
};

Root::Root(char *s)		// should not be inline
{
   static int ob = 0;

   oid = ob++;
   cname = s ? s : "Root";
}

class Leaf : public Root {
public:
   Leaf() : ("Leaf")	{ /* */ }
};

All objects, whether they belong to the same class or not,
will have different ids. Class names are to be given whenever
you derive a class from Root. (This will also help in debugging!)
Address of class names can serve as class ids.

Manoharan.