while (mtbl_iter_next(it, &key, &len_key, &val, &len_val)) {
string move((char *)(key + prefix_len), len_key - prefix_len);
const Count* c = (Count *)val;
while (mtbl_iter_next(it, &key, &len_key, &val, &len_val)) {
string move((char *)(key + prefix_len), len_key - prefix_len);
const Count* c = (Count *)val;