al_get_default_menu_event_source - Allegro 5 API

       Returns  the default event source used for menu clicks.  If a menu was not given its own event source via
       al_enable_menu_event_source(3alleg5), then it will use this default source.

       al_get_default_menu_event_source - Allegro 5 API

al_register_event_source(3alleg5),                                  al_enable_menu_event_source(3alleg5),
       al_disable_menu_event_source(3alleg5)

Allegro reference manual                                               al_get_default_menu_event_source(3alleg5)

       5.1.0

              #include <allegro5/allegro_native_dialog.h>

              ALLEGRO_EVENT_SOURCE *al_get_default_menu_event_source(void)