是以下C++单例实现？

class Singleton {
private:
    static Singleton* instance;
    Singleton() {} // 私有构造函数，防止外部实例化

public:
    static Singleton* getInstance() {
        if (instance == nullptr) {
            instance = new Singleton();
        }
        return instance;
    }
};

Singleton* Singleton::instance = nullptr;