Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!netcom!teda!ditka!mcdchg!tellab5!balr!clrcom!rmartin
From: rmartin@clear.com (Bob Martin)
Newsgroups: comp.lang.c++
Subject: Re: Comparison functions for qsort() and bsearch()
Keywords: Sun, C++
Message-ID: <1991Feb6.222244.23132@clear.com>
Date: 6 Feb 91 22:22:44 GMT
References: <1991Jan21.022720.20707@cbnewsk.att.com> <70271@microsoft.UUCP> <1991Feb3.195156.151@cbnewsk.att.com>
Organization: Clear Communications, Inc.
Lines: 37

From: jimad@microsoft.UUCP (Jim ADCOCK)
>< [... some stuff deleted ...]
>< I see nothing in ARM that gives one permission to
>< explicitly cast back from a void* back to the original object* type.
>

If you refer to ARM section 4.6 there is an peculiar statement which reads:

	"in C++ a void* cannot be assigned to an object of any type other than
	a void* without an explicit cast."

If we remove the double negative it becomes:

	"in C++ a void* can be assigned to an object of any type other than
	a void* only with an explicit cast."

This is roundabout, but I think it refutes Jim's statement.

In article <1991Feb3.195156.151@cbnewsk.att.com> hansen@pegasus.att.com 
(Tony L. Hansen) writes:
[ ... lots of stuff about how ANSI C allows conversion of void* to any
other pointer type...  followed by this quote from ANSI C...]
>
>    A pointer to any incomplete or object type may be converted to a pointer
>    to void and back again; the result shall compare equal to the original
>    pointer.
>

Again in ARM 4.6 Stroustrup and Ellis argue against allowing this in C++
without explicit casts on the basis that it opens up a hole in the type
system.  

-- 
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