How to Safely Remove Elements from a std::map Based on a Condition?

Removing Elements from a std::map Based on a Condition Using STL Algorithms

Question:

How can I remove elements from a std::map that meet a specific condition while ensuring the validity of iterators?

Issue:

remove_if cannot be used to erase elements from a std::map. Additionally, looping through the map and using erase() directly can lead to invalidating iterators.

Solution:

An alternative algorithm that addresses these issues is as follows:

for(; iter != endIter; ) {
     if (Some Condition) {
          iter = aMap.erase(iter);
     } else {
          ++iter;
     }
}

This algorithm iterates through the map and checks each element for the specified condition. If the condition is met, the element is erased using erase(). The iterator is then updated to point to the next valid element in the map. This ensures that iterators remain valid even after an element is erased.

Rationale:

If the element that the iterator currently points to is erased, the iterator is invalidated. By updating the iterator after erasing an element, we skip over the invalidated iterator and prevent any runtime errors.

Note:

It is important to note that only iterators referencing the erased element become invalid. Other iterators in the map remain valid.

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