al_set_path_extension - Man Page

#include <allegro5/allegro.h>

bool al_set_path_extension(ALLEGRO_PATH *path, char const *extension)

Replaces the extension of the path with the given one, i.e. replaces everything from the final dot (`.') character onwards, including the dot. If the filename of the path has no extension, the given one is appended. Usually the new extension you supply should include a leading dot.

Returns false if the path contains no filename part, i.e. the filename part is the empty string.

al_set_path_filename(3), al_get_path_extension(3)

al_set_path_filename(3).