How can I use custom types with unordered_map in C++11?

How can I use custom types with unordered_map in C++11?

You can use custom types as keys in an unordered_map by defining a hash function and an equality operator for your type.

Can you show me an example of a custom type and how to implement the hash function?

Sure! Here's a simple example:

struct MyKey {
    int id;
    std::string name;
};

struct MyKeyHash {
    std::size_t operator()(const MyKey& k) const {
        return std::hash<int>()(k.id) ^ std::hash<std::string>()(k.name);
    }
};

struct MyKeyEqual {
    bool operator()(const MyKey& lhs, const MyKey& rhs) const {
        return lhs.id == rhs.id && lhs.name == rhs.name;
    }
};

std::unordered_map<MyKey, int, MyKeyHash, MyKeyEqual> myMap;

What if I want to store more complex data in the unordered_map?

You can store complex data types as values in the unordered_map. Just ensure that those types are copyable and assignable.

Are there any performance considerations when using custom types?

Yes, the performance can be affected by the efficiency of your hash function and equality operator. Make sure they are optimized for your use case.