On Sat, Jul 22, 2023 at 2:40 PM Lénárd Szolnoki via Std-Discussion <
std-discussion_at_[hidden]> wrote:

> Hi,
>
> Given these two arrays, each being a complete object:
>
> int a[2];
> int b[2];
>
> The partial ordering of the addresses (defined by the operator <) of
> the int objects within is:
>
> 1. &a[0] < &a[1]
> 2. &b[0] < &b[1]
>
> A hostile strict total order that is consistent with this is
> &a[0] < &b[0] < &a[1] < &b[1].
>
> Is there wording that prevents the implementation defined strict total
> order to manifest like this?
>

Not as far as I can tell.


>
> One problem with this is that std::less is commonly used to check if a
> given pointer points within a range. If such a manifestation is
> possible then such usages are incorrect (or at least theoretically not
> portable).
>

I agree that this is something that should be banned. To be specific,
`&a[0] < &b[0] < &a[1] < &b[1]` is probably the sort of thing that is
supposed to be allowed, because the idea behind `<` not being a total order
is to support segmented architectures where e.g. it might only compare the
offset part of the address. But `std::less` always has to take into account
both the segment and offset, so I can't see any reason why it should be
allowed to give this "hostile" order.


>
> Cheers,
> Lénárd
>
> P.S. Someone pointed this out to me on the #include <C++> discord.
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-- 
*Brian Bi*