al_ustr_size_utf16 - Allegro 5 API

       Returns  the  number  of  bytes  required  to  encode the string in UTF-16 (including the terminating 0).
       Usually called before al_ustr_encode_utf16(3alleg5) to determine the size of the buffer to allocate.

       al_ustr_size_utf16 - Allegro 5 API

al_ustr_size(3alleg5)

Allegro reference manual                                                             al_ustr_size_utf16(3alleg5)

              #include <allegro5/allegro.h>

              size_t al_ustr_size_utf16(const ALLEGRO_USTR *us)