Extracting from set/unordered_set while using iterators

Question

I just learned about the extract function added to std::set/std::unordered_set in C++17. I know this is valid:

while (!my_set.empty()) {
  auto node_handle = my_set.extract(my_set.begin());
  auto elem = std::move(node_handle.value());
}

But is the following safe? (From https://stackoverflow.com/a/42519996/3234803)

for (auto it = my_set.begin(); it != my_set.end(); ) {
  auto node_handle = my_set.extract(it++);
  auto elem = std::move(node_handle.value());
}

I know extract invalidates the iterator passed to it, so extract(it++) saves the next iterator into it before it gets invalidated. But is it guaranteeed that extract doesn't invalidated other iterators?

@parktomatomi the link says "All Associative Containers: The extract members invalidate only iterators to the removed element; pointers and references to the removed element remain valid [26.2.6/10]" — Aykhan Hagverdili, Nov 04 '20 at 20:07
Does this answer your question? [Iterator invalidation rules](https://stackoverflow.com/questions/6438086/iterator-invalidation-rules) — Aykhan Hagverdili, Nov 04 '20 at 20:08

score 3 · Accepted Answer · answered Nov 04 '20 at 20:07

3

But is it guaranteeed that extract doesn't invalidated other iterators?

Yes. Extract is guaranteed to not invalidate other iterators. Both loops are safe.

answered Nov 04 '20 at 20:07

eerorika

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Extracting from set/unordered_set while using iterators

1 Answers1