👀 Views: 12 💬 Answers: 1 📅 Created: 2025-06-10

c++ std-map custom-comparator cpp

I'm sure I'm missing something obvious here, but I'm getting frustrated with Quick question that's been bugging me - I just started working with I'm getting frustrated with I'm working on a project and hit a roadblock....... I'm working with an scenario where my `std::map` does not seem to update existing values when using a custom comparator. I have a custom object as the key, and I expected that if I insert a new value with a key that already exists, the value should get updated. However, it seems that the map retains the old value instead. Here's a simplified version of my code: ```cpp #include <iostream> #include <map> #include <string> struct CustomKey { std::string id; bool operator<(const CustomKey& other) const { return id < other.id; } }; int main() { std::map<CustomKey, int> myMap; CustomKey key1 = {"key1"}; myMap[key1] = 100; std::cout << "Initial value: " << myMap[key1] << std::endl; // Attempting to update the value using the same key CustomKey key2 = {"key1"}; myMap[key2] = 200; std::cout << "Updated value: " << myMap[key1] << std::endl; return 0; } ``` When I run this code, I see the following output: ``` Initial value: 100 Updated value: 100 ``` I expected the updated value to be `200`, but it remains `100`. I've verified that the keys are indeed the same according to my `<` operator, and I've tried using a hash map instead, but that leads to other issues with non-hashable keys. Could someone explain why the value isn't updating, and how I can fix this behavior? Am I missing something in the way I'm using the map or the custom comparator? This is part of a larger service I'm building. Thanks in advance! Any examples would be super helpful. This is part of a larger service I'm building. What's the best practice here? Could this be a known issue? I'd love to hear your thoughts on this. My team is using Cpp for this web app. Any suggestions would be helpful.