al_get_display_adapter - Allegro 5 API

       Returns which adapter the window is currently placed on.  Returns -1 if there was an error in determining
       the adapter.

       al_get_display_adapter - Allegro 5 API

       5.2.10

Allegro reference manual                                                         al_get_display_adapter(3alleg5)

              #include <allegro5/allegro.h>

              int al_get_display_adapter(ALLEGRO_DISPLAY *display)