C++中自定义数据结构作为unordered-set以及set中的元素

#include 
#include 
#include 
#include 

class Person {
public:
    std::string name;
    int age;

    Person(std::string name, int age) : name(name), age(age) {}

    friend struct std::hash<Person>;

    size_t operator()(const Person &p) const {
        size_t hash_name = std::hash<std::string>{}(p.name);
        size_t hash_age = std::hash<int>{}(p.age);
        return hash_name ^ hash_age;
    }
    // 作为unordered_set中元素需要使用operator==重载以及hansh函数
    bool operator==(const Person &other) const {
        return name == other.name && age == other.age;
    }
    
    // 作为set中的元素需要使用operator<重载 注意不要忘了两个const
    bool operator<(const Person &other) const {
        if (name == other.name) {
            return age < other.age;
        }
        return name < other.name;
    }
};


// 注意要实现这个
namespace std {
    template<>
    struct hash<Person> {
        size_t operator()(const Person &p) const {
            return p(p);
        }
    };
}

int main() {
    std::unordered_set<Person> people_unordered;
    people_unordered.insert(Person("Alice", 30));
    people_unordered.insert(Person("Bob", 25));
    people_unordered.insert(Person("Alice", 30));

    std::set<Person> people_ordered;
    people_ordered.insert(Person("Alice", 30));
    people_ordered.insert(Person("Bob", 25));
    people_ordered.insert(Person("Alice", 30));


    std::cout << "Unordered Set:" << std::endl;
    for (const auto &person: people_unordered) {
        std::cout << person.name << " - " << person.age << std::endl;
    }


    std::cout << "\nOrdered Set:" << std::endl;
    for (const auto &person: people_ordered) {
        std::cout << person.name << " - " << person.age << std::endl;
    }

    return 0;
}

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上述实现hash有一种写法，下面给出第二种写法

#include 
#include 
#include 

class MyData {
private:
    int id;
    std::string name;

public:
    MyData(int _id, const std::string &_name) : id(_id), name(_name) {}

    friend struct MyDataHash;

    bool operator==(const MyData &other) const {
        return (id == other.id) && (name == other.name);
    }

    friend std::ostream &operator<<(std::ostream &os, const MyData &data) {
        os << "ID: " << data.id << ", Name: " << data.name;
        return os;
    }
};

struct MyDataHash {
    size_t operator()(const MyData &data) const {
        return std::hash<int>()(data.id) ^ std::hash<std::string>()(data.name);
    }
};

int main() {
    std::unordered_set<MyData, MyDataHash> mySet;
    mySet.insert(MyData(1, "Alice"));
    mySet.insert(MyData(2, "Bob"));
    mySet.insert(MyData(1, "Alice"));

    for (const auto &data: mySet) {
        std::cout << data << std::endl;
    }

    return 0;
}

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