👀 Views: 2 💬 Answers: 1 📅 Created: 2025-06-01

c++11 unordered_map custom_hash

I'm running into an issue with my custom hash function while using `std::unordered_map`. I've defined a struct `MyKey` and created a custom hash function for it, but the map seems to be producing unexpected results when I try to retrieve values. Here’s the relevant code snippet: ```cpp #include <iostream> #include <unordered_map> #include <string> struct MyKey { std::string str; int num; bool operator==(const MyKey& other) const { return str == other.str && num == other.num; } }; struct MyKeyHash { std::size_t operator()(const MyKey& k) const { return std::hash<std::string>()(k.str) ^ std::hash<int>()(k.num); } }; int main() { std::unordered_map<MyKey, int, MyKeyHash> myMap; MyKey key1 = {"example", 1}; myMap[key1] = 42; MyKey key2 = {"example", 2}; myMap[key2] = 43; MyKey searchKey = {"example", 1}; std::cout << "Value: " << myMap[searchKey] << std::endl; return 0; } ``` When I run this code, I expect to retrieve `42` for the key `{"example", 1}`, but I get a default-constructed value instead. There are no exceptions or runtime errors, but it seems like the key isn't being found in the map. I've checked the `operator==` method, and it appears to be implemented correctly. I've also verified that the hash values for both `key1` and `searchKey` are identical. It's as if the `unordered_map` isn't recognizing the keys as equal. Is there something subtle I might be missing regarding how `std::unordered_map` handles equality checks or hashing? Any suggestions would be greatly appreciated!