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Subject: Re: [ub] C provenance semantics proposal
From: Jens Maurer (Jens.Maurer_at_[hidden])
Date: 2019-04-13 14:00:26


On 13/04/2019 14.50, Uecker, Martin wrote:
> Am Samstag, den 13.04.2019, 13:04 +0200 schrieb Jens Maurer:
>> On 13/04/2019 12.07, Freek Wiedijk wrote:
>>> Hi Jens,
>>>
>>>> So, it seems the opinion of WG14 in C DR 260 is at odds with the current
>>>> normative text.  Maybe WG14 wants to revisit and update C DR 260, at
>>>> least with a marker "obsolete" or so.
>>>
>>> I thought that after the C standard gets a new version,
>>> the DR's before that automatically become "obsolete",
>>> because they are supposed to have been integrated in the
>>> standard after that?
>>
>> Yes.
>>
>> However, C DR 260 is from 2004 and doesn't seem to propose
>> a change in wording; instead, it just interprets the existing
>> normative text.  Yet, I'm failing to reconcile the "committee
>> response" in C DR 260 with the C11 text about pointer equality.
>
> Why? The response talks about indeterminate values and includes
> a vague hint about the generic idea of treating pointers
> differently based on origin. But there is nothing even remotely
> contradicting the rules about pointer equality.

So, are you saying that p1==p2 may be true, yet p1 and p2
might be treated differently, e.g. when dereferenced?

It actually seems C++ has the same rule, because two pointers
compare equal if "both represent the same address" (except for
the one-past-the-end case, where C++ says the equality comparison
is unspecified).

Jens


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