al_ustr_assign_substr - Allegro 5 API

       Overwrite  the  string  us1  with the contents of us2 in the byte interval [start_pos, end_pos).  The end
       points will be clamped to the bounds of us2.

       Usually you will first have to use al_ustr_offset(3alleg5) to find the byte offsets.

       Returns true on success, false on error.

       al_ustr_assign_substr - Allegro 5 API

al_ustr_assign(3alleg5), al_ustr_assign_cstr(3alleg5)

Allegro reference manual                                                          al_ustr_assign_substr(3alleg5)

              #include <allegro5/allegro.h>

              bool al_ustr_assign_substr(ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2,
                 int start_pos, int end_pos)