C++中的观察者模式如何实现？

#include <iostream>
#include <vector>
#include <string>

// 观察者接口
class Observer {
public:
    virtual void update(const std::string& message) = 0;
    virtual ~Observer() = default;
};

// 主题类
class Subject {
private:
    std::vector<Observer*> observers;

public:
    void attach(Observer* observer) {
        observers.push_back(observer);
    }

    void detach(Observer* observer) {
        observers.erase(std::remove(observers.begin(), observers.end(), observer), observers.end());
    }

    void notify(const std::string& message) {
        for (auto observer : observers) {
            observer->update(message);
        }
    }
};

// 具体观察者类
class WeatherApp : public Observer {
public:
    void update(const std::string& message) override {
        std::cout << "WeatherApp received update: " << message << std::endl;
    }
};

class NewsApp : public Observer {
public:
    void update(const std::string& message) override {
        std::cout << "NewsApp received update: " << message << std::endl;
    }
};

int main() {
    Subject weatherStation;
    WeatherApp weatherApp;
    NewsApp newsApp;

    weatherStation.attach(&weatherApp);
    weatherStation.attach(&newsApp);

    weatherStation.notify("It's going to rain today!");

    weatherStation.detach(&newsApp);

    weatherStation.notify("The rain has stopped.");

    return 0;
}