al_ref_ustr - Allegro 5 API

       Create  a  read-only  string  that  references  the storage of another ALLEGRO_USTR(3alleg5) string.  The
       information about the string (e.g. its size) is stored in the structure pointed to by the info parameter.
       The new string will not have any other storage allocated  of  its  own,  so  if  you  allocate  the  info
       structure on the stack then no explicit “free” operation is required.

       The referenced interval is [start_pos, end_pos).  Both are byte offsets.

       The string is valid until the underlying string is modified or destroyed.

       If  you  need  a  range  of  code-points  instead  of bytes, use al_ustr_offset(3alleg5) to find the byte
       offsets.

       al_ref_ustr - Allegro 5 API

al_ref_cstr(3alleg5), al_ref_buffer(3alleg5)

Allegro reference manual                                                                    al_ref_ustr(3alleg5)

              #include <allegro5/allegro.h>

              const ALLEGRO_USTR *al_ref_ustr(ALLEGRO_USTR_INFO *info, const ALLEGRO_USTR *us,
                 int start_pos, int end_pos)