al_utf8_width - Allegro 5 API

       Returns  the  number  of  bytes that would be occupied by the specified code point when encoded in UTF-8.
       This is between 1 and 4 bytes for legal code point values.  Otherwise returns 0.

       al_utf8_width - Allegro 5 API

al_utf8_encode(3alleg5), al_utf16_width(3alleg5)

Allegro reference manual                                                                  al_utf8_width(3alleg5)

              #include <allegro5/allegro.h>

              size_t al_utf8_width(int32_t c)