std::unordered_map iterator invalidation implementing custom hash function in C++17
I've encountered a strange issue with I'm experiencing unexpected behavior with `std::unordered_map` when using a custom hash function in C++17. My setup involves a custom struct as the key, and I'm observing that iterators become invalid after performing certain operations, which shouldn't be happening according to the STL guarantees. Here’s a simplified version of my code: ```cpp #include <iostream> #include <unordered_map> #include <string> struct Key { int id; std::string label; }; struct KeyHasher { std::size_t operator()(const Key& k) const { return std::hash<int>()(k.id) ^ std::hash<std::string>()(k.label); } }; int main() { std::unordered_map<Key, int, KeyHasher> myMap; Key k1 = {1, "test"}; myMap[k1] = 100; auto it = myMap.find(k1); std::cout << "Value: " << it->second << std::endl; // Trying to insert another element Key k2 = {2, "test2"}; myMap[k2] = 200; // Accessing the iterator after insertion std::cout << "Value after insertion: " << it->second << std::endl; // This causes Undefined Behavior } ``` I expected `it` to remain valid after inserting `k2`, but it appears `it->second` leads to an access violation. I’ve ensured that my custom hash function is consistent and does not modify the keys. Is there a specific condition under which iterators can become invalid in this scenario? What best practices should I follow regarding custom hash functions and key types in `unordered_map` to avoid these issues? My development environment is Ubuntu 22.04. My team is using C++ for this REST API. Could someone point me to the right documentation?