str_next
k = str_next(str, n, &sinc);
if ((k = str_next(s, endstr-s, &sinc)) <= 0) {
k = str_next(s, endstr-s, &sinc);
k = str_next(str, endstr-str, &sinc);
else for (str++; str_next(str, endstr-str, &sinc)<0; str++);