list_for_each 区别 list_for_each_safe

#define __list_for_each(pos, head) \
    for (pos = (head)->next; pos != (head); pos = pos->next)

#define list_for_each_safe(pos, n, head) \
    for (pos = (head)->next, n = pos->next; pos != (head); \
        pos = n, n = pos->next)

__list_for_each(....){
    list_del(pos);
   free(pos)  ;//这样就用可能有问题
}

__list_for_each_safe(......){
    list_del(pos);
   free(pos)  ;//safe 确保free 没问题
}