Jeremy, i specially note, that im about case when NO reallocation happens.
Now by standard it is invalidated iterator, but i think it should be just
iterator to last element after push

пн, 8 дек. 2025 г. в 20:03, Jeremy Rifkin via Std-Proposals <
std-proposals_at_[hidden]>:

> > Now "e" points to the newly inserted element.
>
> No, it is an invalidated iterator. Consider the case of a resize.
>
> Cheers,
> Jeremy
>
>
> On Mon, Dec 8, 2025 at 08:52 Nikolay Mihaylov via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
>> std::vector<int> v;
>> v.reserve(10);
>>
>> v.push_back(1);
>>
>> auto b = v.begin();
>> auto e = v.end();
>> v.push_back(1);
>>
>>
>> Hi,
>>
>> isn't this code means following:
>>
>> *auto e = v.end();* - get the end iterator at this moment.
>> *v.push_back(1); * - push new element
>>
>> Now "e" points to the newly inserted element.
>> I believe this is correct.
>> why - because the idea was "e" to be an end() iterator at the moment in
>> which it was invoked.
>>
>>
>>
>> Regards
>> Nikolay
>>
>>
>> On Mon, Dec 8, 2025 at 4:45 PM Nikl Kelbon via Std-Proposals <
>> std-proposals_at_[hidden]> wrote:
>>
>>> The standard needs to better clarify the section on vector iterator
>>> invalidation.
>>>
>>> *Why i think its important:*
>>>
>>> Some implementations added checks like: "oh, we must store all .end()
>>> iterators into global map under mutex and mark them invalid on each
>>> push_back, it will be SO useful for our developers!"
>>> So, minimal example where it breaks completely:
>>>
>>> std::vector<int> v;
>>> v.reserve(10);
>>>
>>> v.push_back(1);
>>>
>>> auto b = v.begin();
>>> auto e = v.end();
>>> v.push_back(1);
>>> ++b;
>>> REQUIRE(b == e); // assertion failure:
>>> // _STL_VERIFY(this->_Getcont() == _Right._Getcont(), "vector iterators incompatible");
>>>
>>>
>>> Its common pattern when using vector to reserve memory and push values,
>>> there are no "better way to do it", thats why it must be valid
>>>
>>>
>>> *Now about standard:*
>>>
>>> here's a quote from the standard regarding append_range and, apparently,
>>> push_back (https://eel.is/c++draft/vector#modifiers-2):
>>>
>>>
>>> If no reallocation happens, then references, pointers, and iterators
>>> before the insertion point remain valid but those at or after the insertion
>>> point, including the past-the-end iterator, are invalidated
>>>
>>>
>>> It explicitly states that despite there are no relocation happen, the
>>> past-the-end iterator is invalidated, although there's no reason for a
>>> vector to be so.
>>> Yes, a* past-the-end iterator will no longer be past-the-end, but that
>>> doesn't make it invalid*. In any implementation, even a foolish one,
>>> it's hard to imagine how, without relocation, this iterator could become
>>> anything other than just an iterator to the last element of the vector.
>>>
>>> I think in this case *standard should separate invalidation and what
>>> happens here - its not invalidation rly.*
>>>
>>>
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>>>
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