👀 Views: 15 💬 Answers: 1 📅 Created: 2025-06-24

c++20 unordered-map rehashing cpp

I'm working on a personal project and I am experiencing an issue with `std::unordered_map` where it doesn't seem to be rehashing when I insert a large number of elements... I am using C++20 and expected that the map would automatically resize when the load factor exceeds the threshold. However, in my case, after inserting around 5000 elements, the size of the map remains at 5000, and the load factor does not change. I have explicitly set the maximum load factor to 0.5, but it seems to be ignored. Here is the code snippet where I initialize my unordered map and insert elements: ```cpp #include <iostream> #include <unordered_map> int main() { std::unordered_map<int, std::string> myMap; myMap.max_load_factor(0.5); for (int i = 0; i < 5000; ++i) { myMap[i] = "Value " + std::to_string(i); } std::cout << "Size: " << myMap.size() << '\n'; std::cout << "Bucket count: " << myMap.bucket_count() << '\n'; std::cout << "Load factor: " << myMap.load_factor() << '\n'; return 0; } ``` When I run this code, I expect to see that the bucket count increases and that the load factor is less than or equal to 0.5. However, the output shows that the load factor is around 1.0, indicating that it is not rehashing as anticipated. I have also checked the documentation, and it states that the rehashing should occur automatically. I tried calling `myMap.rehash(10000);` before the loop, which did trigger a rehash, but I want to rely on automatic resizing. Is there something that I'm missing, or is there a known issue with `std::unordered_map` in this version of C++? Any insights would be greatly appreciated! I'd really appreciate any guidance on this.