Path: utzoo!attcan!uunet!lll-winken!sol.ctr.columbia.edu!ira.uka.de!rusux1!jellosub.luftfahrt.uni-stuttgart.de!schmid
From: schmid@jellosub.luftfahrt.uni-stuttgart.de (Georg Schmid)
Newsgroups: comp.lang.c++
Subject: this in Heap-/Stack Objects
Message-ID: <1990Oct9.162831@jellosub.luftfahrt.uni-stuttgart.de>
Date: 9 Oct 90 15:28:31 GMT
Sender: zrf80385@rusux1.rus.uni-stuttgart.de
Reply-To: schmid@jellosub.luftfahrt.uni-stuttgart.de (Georg Schmid)
Organization: Dept. for Statics & Dynamics of Aerospace Structures (ISD)
Lines: 51

Just a simple question:
One of my c++ books (Bruce Eckel, Using C++) states that one
can determine the type (heap- or stack-based) of an instance
at runtime by looking at 'this' in the constructor: 

"... code is secretly generated in a constructor to differ-
entiate between objects created on the stack (the value of
'this' when the constructor is called is non-zero) and objects
created on the free store (the value of 'this' when the con-
structor is called is zero)..."

I tested this with the following little program on an Apollo 
with Apollos (Glockenspiel) C++ 1.2.2:

#include <stdio.h>

class Something
	{
	public:
	Something();
	};

Something::Something()
	{
	printf("This is %lX\n", this);
	}

int main(int, char**)
	{
	Something	a;    
	Something*	b = new Something;
	}

The output is:

This is 3B3C7556
This is 10C00

Am I wrong, is Eckel wrong or is the compiler wrong ?

Any hints appreciated.
 

-- georg

________________________________________________________________________
Georg Schmid, ISD University of Stuttgart, Germany                 
email: schmid@asterix.luftfahrt.uni-stuttgart.de (129.69.110.2)       
voice: +49 711-685-2053                                        
fax:   +49 711-685-3706
________________________________________________________________________