al_set_event_source_data - Allegro 5 API

       Assign  the  abstract  user  data  to  the  event  source.   Allegro does not use the data internally for
       anything; it is simply meant as a convenient way to associate your own data or objects with events.

       al_set_event_source_data - Allegro 5 API

al_get_event_source_data(3alleg5)

Allegro reference manual                                                       al_set_event_source_data(3alleg5)

              #include <allegro5/allegro.h>

              void al_set_event_source_data(ALLEGRO_EVENT_SOURCE *source, intptr_t data)