Function utflen

depends/lua/src/lutf8lib.c:71–93

** utf8len(s [, i [, j]]) --> number of characters that start in the ** range [i,j], or nil + current position if 's' is not well formed in ** that interval */

** that interval
*/
static int utflen (lua_State *L) {
  int n = 0;
  size_t len;
  const char *s = luaL_checklstring(L, 1, &len);
  lua_Integer posi = u_posrelat(luaL_optinteger(L, 2, 1), len);
  lua_Integer posj = u_posrelat(luaL_optinteger(L, 3, -1), len);
  luaL_argcheck(L, 1 <= posi && --posi <= (lua_Integer)len, 2,
                   "initial position out of string");
  luaL_argcheck(L, --posj < (lua_Integer)len, 3,
                   "final position out of string");
  while (posi <= posj) {
    const char *s1 = utf8_decode(s + posi, NULL);
    if (s1 == NULL) {  /* conversion error? */
      lua_pushnil(L);  /* return nil ... */
      lua_pushinteger(L, posi + 1);  /* ... and current position */
      return 2;
    }
    posi = s1 - s;
    n++;
  }
  lua_pushinteger(L, n);
  return 1;
}


/*