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From: chase@boulder.Colorado.EDU (Chase Turner)
Newsgroups: comp.lang.c++
Subject: constructors and instantiation
Message-ID: <2575@sigi.Colorado.EDU>
Date: Wed, 14-Oct-87 22:51:20 EDT
Article-I.D.: sigi.2575
Posted: Wed Oct 14 22:51:20 1987
Date-Received: Fri, 16-Oct-87 07:17:07 EDT
Sender: news@sigi.Colorado.EDU
Reply-To: chase@boulder.Colorado.EDU (Chase Turner)
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Organization: University of Colorado, Boulder
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This message was submitted two weeks ago; there have not been any replies yet.
I am re-submitting the question to determine the following:

a) am I violating the sprit of instantiation?

b) I want to instantiate objects in shared memory which is accessable to 
seperate processes (environment : sun workstations, 4.3 unix) --  I do not want
a function call *new* which provides an object space in local memory which
would then have to be copied to a shared memory area.  (and, the local memory 
reference would have to be deleted since I do not want the object there....) 
Is the constructor the appropiate mechanism?

c)  why is the value of *this* not updated in the main body to reflect the
assignment of the object to the malloc space I created?

Any reply would be appreciated.  Thanks in advance.  Chase.

---------old message below------------------------------

I am having difficulty utilizing the Free Store example (8.5.8, pg 280
of The C++ Programming Language).  Specifically,  I need to instantiate
objects within shared memory; for the purposes of this example, I will
utilize a malloc instead of the call shmget ().
Within the constructor, I re-assign the value of "this"
but the update value is ignored.  In fact, I assumed that the constructor
would over-ride the instantiation of the object "ts"  in the main body,
but the c code generated by the CC pre-compilier indicates that a local
structure is created prior to the call to the constructor.

The following is a run-time example.....
 value is 11, address is 142912    // within the constructor
 value is 10, address is 251657776 // after returning from constructor


The following is the program......

#include <stream.h>
#include <libc.h>
#include <syscall.h>

class stamp {
        int val;

        public:
                                   stamp (int);
                void            print_myself ();
        }; 

stamp::stamp (int v) 
        {
                val = v;   //val should not exist since I have not made a call
                           //to new or reserved the space for the object.
                           //obviously it does exist.  Is there an implicit 
                           //call to new? Should I override new with another
                           //function?  How can new be 'intercepted'?   

                this  = (stamp*) malloc (sizeof (stamp));

                val = v+1;
                print_myself ();
        }


void stamp::print_myself ()
        {
        printf(" value is %d, address is %d \n",val,&val);
        }

main()
{
                stamp   ts (10);
                ts.print_myself ();
}