al_create_path_for_directory man page
al_create_path_for_directory — Allegro 5 API
#include <allegro5/allegro.h> ALLEGRO_PATH *al_create_path_for_directory(const char *str)
This is the same as al_create_path(3), but interprets the passed string as a directory path. The filename component of the returned path will always be empty.