Is using erase(it) in a loop always safe for all containers and platforms?

Question

i want to remove elements within a container(for now it is unordered_set) by certain condition

for (auto it = windows.begin(); it != windows.end(); ) {
    if ((*it)->closed() == 0)
        it = numbers.erase(it);
    else
        ++it;
}

i know the erase(it) will return the position immediately following the last of the elements erased. but

Is it mandatory by the standard there won't cause the rearrangement for the iteation when invoking erase? Is it always safe for all containers and all platforms? Say there may be some magic implementation for certain type of container within certain platform.

Answer 1

The C++ standard requires that unordered_set::erase preserve the order of remaining elements, and return an iterator immediately following those being erased. Therefore, the loop you show is well-defined.

[unord.req]/14 ... The erase members shall invalidate only iterators and references to the erased elements, and preserve the relative order of the elements that are not erased.

[unord.req]/11, Table 91 a.erase(q) Erases the element pointed to by q. Returns the iterator immediately following q prior to the erasure.