al_ustr_dup_substr - Allegro 5 API

       Return  a  new  copy of a string, containing its contents in the byte interval [start_pos, end_pos).  The
       new string will be NUL terminated and will need to be freed with al_ustr_free(3alleg5).

       If necessary, use al_ustr_offset(3alleg5) to find the byte offsets for a given code point  that  you  are
       interested in.

       al_ustr_dup_substr - Allegro 5 API

al_ustr_dup(3alleg5), al_ustr_free(3alleg5)

Allegro reference manual                                                             al_ustr_dup_substr(3alleg5)

              #include <allegro5/allegro.h>

              ALLEGRO_USTR *al_ustr_dup_substr(const ALLEGRO_USTR *us, int start_pos,
                 int end_pos)