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