Path: utzoo!attcan!uunet!wuarchive!usc!elroy.jpl.nasa.gov!ames!sgi!shinobu!odin!delrey.sgi.com!shap
From: shap@delrey.sgi.com (Jonathan Shapiro)
Newsgroups: comp.lang.c++
Subject: Change to delete is in order
Message-ID: <5136@odin.SGI.COM>
Date: 12 Mar 90 16:22:06 GMT
Sender: news@odin.SGI.COM
Reply-To: shap@delrey.sgi.com (Jonathan Shapiro)
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 29

I believe that a small change to the definition of the delete operator
is worth considering.  The change would have no effect on correct
programs, but would help find incorrect programs in some circumstances.

	delete should be defined to zero the pointer it is handed
	after freeing the associated store.

Reasons:

1. Unlike C, C++ does not guarantee that the object is live until the
   next call to new.

2. In the absence of setting the pointer to zero, accesses to data
   items that erroneously follow the delete cannot be caught even when
   the hardware traps page-zero references, and compilers have not yet
   arrived that understand about this.

3. If the code is correct, dead code elimination in the compiler can
   generally be relied on to eliminate the zero set, so the run-time cost
   should be nil.

4. I can't think of a correct code sequence it would break.

Of course, compilers should be taught to understand about use after
clobber, but that's a bit harder, and I don't see how this tweak to
the language spec can hurt.

Jonathan Shapiro
Silicon Graphics, Inc.