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strict aliasing rules in ISO C, someone understands them ?

 
 
Netocrat
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      10-24-2005
On Mon, 24 Oct 2005 13:40:55 +0000, S.Tobias wrote:
> Netocrat <(E-Mail Removed)> wrote:
>> On Wed, 19 Oct 2005 13:24:27 +0000, S.Tobias wrote:
>>> http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:

>> [...]
>>>> It is not explicitly mentioned in the standard, but if access is
>>>> done through a struct, its type must match the type of the container of
>>>> the object we want to access.
>>> It is mentioned at the member access operators. If it weren't, nobody
>>> whould argure this.

[...]
>>I see no
>> mention of it in N869's "6.5.2.3 Structure and union members" which is the
>> section to which I presume you're referring.
>>

> My bad, sorry. It's not explicitly mentioned, but can be derived.
> Pp. 3 and 4 refer to a "member of a structure or union object"; it means
> the operator (and behaviour) is defined iff the _object_ has the specified
> member.


OK - I was expecting something more explicit - the "iff" is implied - but
this seems to be a correct interpretation of the document's intent.

> (However, I decline to explain what exactly it should be; I
> think the Std means the effective type of the object; it's one of the
> questions on my list to c.s.c.)


What else would it be?[*]

> Anyway, if the Std text is not enough, then at least Example 3 shows the
> intention; if it were allowed (in the example) to access `t1::m' with
> `p2->m' (or vv.), then the second part of the example would be moot, as
> well as the "special guarantee" of p. 5 would.


Sure - that makes the intent plain, even if the prior wording is not.
[*] My reaction to your comment in another thread - that you have your own
idea of what it means to "complete a type" - was similar: how many
alternative interpretations could there be?

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