al_utf16_width - Allegro 5 API

       Returns  the  number  of bytes that would be occupied by the specified code point when encoded in UTF-16.
       This is either 2 or 4 bytes for legal code point values.  Otherwise returns 0.

       al_utf16_width - Allegro 5 API

al_utf16_encode(3alleg5), al_utf8_width(3alleg5)

Allegro reference manual                                                                 al_utf16_width(3alleg5)

              #include <allegro5/allegro.h>

              size_t al_utf16_width(int c)