utf8_towc
if (utf8_towc(&ud, &wc) == UTF8_DONE)
enum utf8_state utf8_towc (const struct utf8_data *, wchar_t *);
if (utf8_towc(with, &w) != UTF8_DONE)
if (utf8_towc(add, &a) != UTF8_DONE)
if (utf8_towc(ud, &wc) != UTF8_DONE)