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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