How to pass the instance itself to an external map at the moment of its creation?

Question

I have a class Object and a typedef:

class Object
{
private:
    long int id;
public:
    Object(void);
    ~Object(void) {};
    long int get_id(void);
};

typedef map<long int, Object> obj_map;

And then I have this class App, which has an obj_map and object_counter:

class App
{
public:
    static ALLEGRO_DISPLAY *display;
    static ALLEGRO_EVENT_QUEUE *event_queue;
    static ALLEGRO_TIMER *timer;
    static ALLEGRO_EVENT e;
    static bool running;
    static bool redraw;
    static key_map key_states;
    static obj_map objects; // << Here.
    static long int object_counter; // << Here.
    const char *window_title;
    int screen_width;
    int screen_height;
    float FPS;
    act event_scenes;
    act visual_scenes;
    ALLEGRO_COLOR background_color;

    static ALLEGRO_EVENT event();
    static ALLEGRO_EVENT_TYPE event_type();
    static void shut_down();

    App(int screen_width, int screen_height, const char *window_title = "Joy++ Application", float FPS = 30);
    ~App() {};

    int init_all();
    void register_all();
    void check_key_states();
    void init_key_states();
    void run();
    void destroy_all();
    void add_event_scene(Scene scene);
    void add_visual_scene(Scene scene);
    void remove_event_scene(Scene scene);
    void remove_visual_scene(Scene scene);

    long int get_object_count();
    unsigned int get_random_int(unsigned int min, unsigned int max);
    void set_key_state(int al_key, string key_name, bool state);
    void set_background_color(int r, int g, int b);
};

As you can see, the idea is to store every object inside the app, under an id, inside a map. But, I want that to happen at the moment of the creation of each object. So here's the constructor definition:

Object::Object()
{
    App::object_counter += 1;
    this->id = App::object_counter;
    App::objects[this->id] = this; // Problem.
}

Error:

G:\Development\Game-Development\CB\Joy-Plus-Plus\app.cpp|26|error: no match for 'operator=' (operand types are 'std::map<long int, Object>::mapped_type {aka Object}' and 'Object* const')|

How can I pass the instance itself of each Object to the external map at the moment of its creation?

Answer 1

If your Object has value semantic then just assign *this (the object) and not this.

On the other hand if identity counts then build a map to Object * (or, better std::shared_ptr) and then the assignment will work as is

Answer 2

Because this is a pointer type --> Try *this

Do you want to store copys in the map or just references to the objects ?