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.