C++如何实现一个观察者模式（Observer Pattern）？（代码示例）

class Observer {
public:
    virtual ~Observer() = default;
    virtual void update(const std::string& message) = 0; // 简单消息通知
};

#include 
#include 
#include 

class Subject {
protected:
    std::vector> observers;

public:
    void attach(std::shared_ptr obs) {
        if (obs && std::find(observers.begin(), observers.end(), obs) == observers.end()) {
            observers.push_back(obs);
        }
    }

    void detach(std::shared_ptr obs) {
        observers.erase(
            std::remove(observers.begin(), observers.end(), obs),
            observers.end()
        );
    }

    void notify(const std::string& msg) {
        for (auto& obs : observers) {
            if (obs) obs->update(msg); // 安全调用
        }
    }
};

class WeatherStation : public Subject {
private:
    double temperature = 0.0;

public:
    void setTemperature(double temp) {
        temperature = temp;
        notify("Temperature changed to " + std::to_string(temp) + "°C");
    }
};

class PhoneDisplay : public Observer {
public:
    void update(const std::string& message) override {
        std::cout << "[Phone] " << message << std::endl;
    }
};

class WebDisplay : public Observer {
public:
    void update(const std::string& message) override {
        std::cout << "[Web] " << message << std::endl;
    }
};

int main() {
    auto station = std::make_shared();
    auto phone = std::make_shared();
    auto web = std::make_shared();

    station->attach(phone);
    station->attach(web);

    station->setTemperature(25.5); // 输出两条通知
    station->detach(phone);
    station->setTemperature(27.0); // 只输出 Web 通知

    return 0;
}