On Tue, 12 Dec 2023 at 14:14, Daniel Krügler <daniel.kruegler_at_[hidden]> wrote:
>
> Am Di., 12. Dez. 2023 um 05:42 Uhr schrieb Yongwei Wu via
> Std-Discussion <std-discussion_at_[hidden]>:
> >
> > In the case of erase in the following form:
> >
> > constexpr iterator erase(const_iterator);
> >
> > basic_string does not say anything about iterator and reference
> > invalidation, while vector specifically says erase "invalidates
> > iterators and references at or after the point of the erase".
>
> That's not quite right. We have [string.require] p4, which says:
>
> 4 References, pointers, and iterators referring to the elements of a
> basic_string sequence may be invalidated
> by the following uses of that basic_string object:
> (4.1) — Passing as an argument to any standard library function taking
> a reference to non-const basic_string
> as an argument.
> (4.2) — Calling non-const member functions, except operator[], at,
> data, front, back, begin, rbegin, end,
> and rend.
>
> So, bullet (4.2) applies for erase, which is a non-const member
> function that is not excluded by the listed functions.

Thank you.

I would argue this is quite weak and vague. vector::erase specifically
says it "invalidates iterators and references at or after the point of
the erase". That implies iterators pointing to elements before the
point of erase remain valid. That would be stronger than the point you
mention here. It does not make sense to me that string provides a
weaker guarantee than vector.

And the main part of the questions is why (under what circumstance).
Why should an iterator pointing to the point of erase be invalidated
for the contiguous sequence containers? The memory layout is fixed,
after all.

-- 
Yongwei Wu
URL: http://wyw.dcweb.cn/