From: Paul Schlie <schlie@comcast.net>
To: Geoffrey Keating <geoffk@geoffk.org>
Cc: <mrc.lrn@inwind.it>, <gcc@gcc.gnu.org>
Subject: Re: Pointers in comparison expressions
Date: Sun, 24 Jul 2005 01:13:00 -0000 [thread overview]
Message-ID: <BF086354.AF43%schlie@comcast.net> (raw)
> Geoffrey Keating wrote:
>> Mirco Lorenzon wrote:
>>
>> .., are comparisons in the following program legal code?
>
> No.
>
>> ...
>> void *a, *b;
>> ...
>> if (a < b)
>
> Because 'a' and 'b' are not part of the same array,
> the behaviour is undefined.
Although I don't mean to contest the conclusion, I do find it curious that
as all pointer values referencing unique objects must be correspondingly
unique, it would follow that they will be correspondingly ordered with
respect to each other. Therefore although technically undefined, it seems
quite reasonable to expect an implementation to support ordered inequality
comparisons between arbitrary pointers to equivalent effective types?
As it would seem otherwise impossible for an implementation to support the
ability to write code which enables the relative comparison of generalized
memory pointers unless one were to explicitly declare a union of an array
of all potentially allocateable memory, and all explicitly and implicitly
declared objects; which doesn't seem reasonable?
next reply other threads:[~2005-07-24 1:13 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-07-24 1:13 Paul Schlie [this message]
2005-07-26 4:43 ` Geoff Keating
-- strict thread matches above, loose matches on Subject: below --
2005-07-13 13:53 Morten Welinder
2005-07-12 16:24 Mirco Lorenzoni
2005-07-12 16:32 ` Daniel Berlin
2005-07-12 16:53 ` Dave Korn
2005-07-12 21:00 ` Andreas Schwab
2005-07-12 21:42 ` Erik Trulsson
2005-07-12 22:09 ` Joe Buck
2005-07-12 22:28 ` Erik Trulsson
2005-07-12 22:38 ` Falk Hueffner
2005-07-12 23:17 ` Joe Buck
2005-07-12 23:28 ` Falk Hueffner
2005-07-13 2:02 ` Joe Buck
2005-07-13 21:42 ` Olivier Galibert
2005-07-12 23:27 ` Michael Meissner
2005-07-12 22:46 ` Joe Buck
2005-07-16 11:49 ` Vincent Lefevre
2005-07-17 16:55 ` Paul Koning
2005-07-18 1:49 ` Vincent Lefevre
2005-07-18 3:13 ` D. Hugh Redelmeier
2005-07-18 13:13 ` Paul Koning
2005-07-18 13:09 ` Paul Koning
2005-07-12 17:03 ` chris jefferson
2005-07-12 23:18 ` Michael Meissner
2005-07-22 23:20 ` Geoffrey Keating
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