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Re: C standard compliance?

From
Junio C Hamano <gitster@pobox.com>
Date
Jan 29, 2014, 20:42 UTC
Message-ID
<xmqqwqhiikpg.fsf@gitster.dls.corp.google.com>
In-Reply-To
<87iot25y0r.fsf@fencepost.gnu.org>
David Kastrup <dak@gnu.org> writes:
Show 6 quoted lines
> Hi, I am wondering if I may compare pointers with < that have been
> created using different calls of malloc.
>
> The C standard does not allow this (inequalities are only allowed for
> pointers into the same structure) to allow for some cheapskate sort of
> comparison in segmented architectures.

Hmm... if you were to implement a set of pointers in such a way that you can cheaply tell if an unknown pointer belongs to that set, you would use a hashtable, keyed with something that is derived from the value of the pointer casted to uintptr_t, I would think. Is such a use of ((uintptr_t)ptr) unallowed? If it is allowed, comparing two unrelated pointers after casting them to uintptr_t would equally be valid, I would have to think.

Previous: David KastrupNext: David Kastrup
Message 2 of 6 in “C standard compliance?”
  1. David KastrupJan 29, 2014
  2. Junio C HamanoJan 29, 2014
  3. David KastrupJan 29, 2014
  4. Philip OakleyJan 29, 2014
  5. brian m. carlsonJan 29, 2014
  6. David KastrupJan 30, 2014

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