如何在C++中为增加但记住先前对象删除的对象分配唯一标识符

#include <iostream>
#include <memory>
#include <unordered_map>

class Object {
public:
    Object(int id) : id_(id) {}
    int getId() const { return id_; }
private:
    int id_;
};

class ObjectManager {
public:
    ObjectManager() : nextId_(0) {}

    std::shared_ptr<Object> createObject() {
        int id = nextId_++;
        std::shared_ptr<Object> obj = std::make_shared<Object>(id);
        objects_[id] = obj;
        return obj;
    }

    void deleteObject(std::shared_ptr<Object> obj) {
        int id = obj->getId();
        objects_.erase(id);
    }

    std::shared_ptr<Object> getObjectById(int id) {
        auto it = objects_.find(id);
        if (it != objects_.end()) {
            return it->second;
        }
        return nullptr;
    }

private:
    int nextId_;
    std::unordered_map<int, std::shared_ptr<Object>> objects_;
};

int main() {
    ObjectManager manager;

    // 创建对象并分配唯一标识符
    std::shared_ptr<Object> obj1 = manager.createObject();
    std::shared_ptr<Object> obj2 = manager.createObject();

    // 访问对象的唯一标识符
    std::cout << "Object 1 ID: " << obj1->getId() << std::endl;
    std::cout << "Object 2 ID: " << obj2->getId() << std::endl;

    // 通过唯一标识符获取对象
    std::shared_ptr<Object> obj3 = manager.getObjectById(obj1->getId());
    if (obj3 != nullptr) {
        std::cout << "Object 3 ID: " << obj3->getId() << std::endl;
    }

    // 删除对象
    manager.deleteObject(obj1);

    // 尝试获取已删除的对象
    std::shared_ptr<Object> obj4 = manager.getObjectById(obj1->getId());
    if (obj4 == nullptr) {
        std::cout << "Object 4 has been deleted." << std::endl;
    }

    return 0;
}