al_get_num_joysticks man page
al_get_num_joysticks — Allegro 5 API
#include <allegro5/allegro.h> int al_get_num_joysticks(void)
Return the number of joysticks currently on the system (or potentially on the system). This number can change after al_reconfigure_joysticks(3) is called, in order to support hotplugging.
Returns 0 if there is no joystick driver installed.