How do I avoid iterator invalidation with std::set?

In C++, iterators can become invalidated when the underlying container is modified, leading to unsafe behavior if an invalid iterator is used. With `std::set`, certain operations, such as insertions and deletions, can invalidate iterators, especially if the element being pointed to is removed. To avoid iterator invalidation when using `std::set`, it is crucial to understand how iterators behave in such scenarios and to utilize strategies that prevent operating on invalidated iterators.

Avoiding Iterator Invalidation in std::set

Here are some common strategies:

  • Use a loop to traverse and manage insertion or deletion, while storing the next iterator position before modifying the set.
  • Use `std::set::find` to get an iterator to a specific element before attempting to delete it.
  • Use the returned iterator from the `erase` method of the set to continue safely iterating.

Example

std::set mySet = {1, 2, 3, 4, 5}; for (auto it = mySet.begin(); it != mySet.end(); ) { if (*it % 2 == 0) { // remove even numbers it = mySet.erase(it); // erase returns next valid iterator } else { ++it; // increment only if not erased } }

iterator invalidation std::set C++ C++ iterators avoiding iterator invalidation

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