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

When working with std::multimap in C++, iterator invalidation can be a concern, especially when inserting or deleting elements. In general, you want to avoid performing operations that can lead to invalidated iterators. This can be particularly tricky with a std::multimap because duplicate keys allow multiple entries and modifications that might affect iterators. Here are some strategies to avoid iterator invalidation:

Use iterators carefully: Avoid storing iterators to elements that you may modify.
Prefer to use `find` or `equal_range` for access: This will help to get valid iterators even after modifications.
Refrain from erasing elements while iterating through the multimap directly, as this can invalidate iterators. Consider using a copy of the keys to erase after the iteration.

Here's a simple example demonstrating the safe use of iterators with std::multimap:


        #include <iostream>
        #include <map>

        int main() {
            std::multimap myMap;
            myMap.insert({1, "One"});
            myMap.insert({2, "Two"});
            myMap.insert({2, "Deux"});
            myMap.insert({3, "Three"});

            // Using iterator for safe traversal
            for (auto it = myMap.begin(); it != myMap.end(); /* no increment here */) {
                // Example of safe access
                std::cout << it->first << ": " << it->second << std::endl;

                // Example of conditional erase (without invalidating iterator)
                if (it->first == 2) {
                    it = myMap.erase(it); // erase returns next valid iterator
                } else {
                    ++it; // move to next only if not erasing
                }
            }

            return 0;
        }

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

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

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