How do I use a custom hash function with unordered_map in C++11?

Can you explain how to use a custom hash function with unordered_map in C++11?

Sure! In C++11, you can define a custom hash function by creating a struct that overloads the operator(). You then pass this struct as a template argument to unordered_map.

Could you provide a code example of that?

Absolutely! Here's a simple example:

#include <iostream>
#include <unordered_map>

struct CustomHash {
    std::size_t operator()(const std::string& key) const {
        return std::hash<std::string>()(key) ^ 0x5bd1e995; // Custom hash logic
    }
};

int main() {
    std::unordered_map<std::string, int, CustomHash> myMap;
    myMap["apple"] = 1;
    myMap["banana"] = 2;
    std::cout << myMap["apple"] << std::endl;
    return 0;
}

What if I want to use a custom equality function as well?

You can also define a custom equality function by creating another struct that overloads the operator==. Then, you can pass both the custom hash and equality functions as template arguments to unordered_map.

Thanks! This is really helpful.