size_t new_capacity = MAX (4, old_capacity * 2);
char *old_data = old_data_;
char *new_data = xnmalloc (new_capacity, elem_size);
size_t new_capacity = MAX (4, old_capacity * 2);
char *old_data = old_data_;
char *new_data = xnmalloc (new_capacity, elem_size);