al_mouse_button_down - Man Page

#include <allegro5/allegro.h>

bool al_mouse_button_down(const ALLEGRO_MOUSE_STATE *state, int button)

Return true if the mouse button specified was held down in the state specified.

Unlike most things, the first mouse button is numbered 1. As a convenience, the constants ALLEGRO_MOUSE_BUTTON_LEFT, ALLEGRO_MOUSE_BUTTON_RIGHT, ALLEGRO_MOUSE_BUTTON_MIDDLE are provided. However, depending on the hardware there may be more or fewer mouse buttons. You can check al_get_mouse_num_buttons(3) if you want to be sure.

ALLEGRO_MOUSE_STATE(3), al_get_mouse_state(3), al_get_mouse_state_axis(3)

al_get_mouse_state(3), al_get_mouse_state_axis(3), ALLEGRO_MOUSE_STATE(3).