al_ustr_prev_get - Allegro 5 API

       Find  the  beginning  of  a  code  point  before  byte offset *pos, then return it.  Note this performs a
       pre-increment.

       On success returns the code point value.  If pos was out of bounds (e.g. past the  end  of  the  string),
       return  -1.   On  an  error, such as an invalid byte sequence, return -2.  As with al_ustr_prev(3alleg5),
       invalid byte sequences may be skipped while advancing.

       al_ustr_prev_get - Allegro 5 API

al_ustr_get_next(3alleg5)

Allegro reference manual                                                               al_ustr_prev_get(3alleg5)

              #include <allegro5/allegro.h>

              int32_t al_ustr_prev_get(const ALLEGRO_USTR *us, int *pos)