al_join_paths man page
al_join_paths — Allegro 5 API
#include <allegro5/allegro.h> bool al_join_paths(ALLEGRO_PATH *path, const ALLEGRO_PATH *tail)
Concatenate two path structures. The first path structure is modified. If 'tail' is an absolute path, this function does nothing.
If 'tail' is a relative path, all of its directory components will be appended to 'path'. tail's filename will also overwrite path's filename, even if it is just the empty string.
Tail's drive is ignored.
Returns true if 'tail' was a relative path and so concatenated to 'path', otherwise returns false.