单向链表: slist

mill_slist，它实现的是一个单链表，它也实现了pop、push、push_back操作，这意味着也可以把它当做stack、queue来使用。

如何当做stack来使用？push、pop！ 如何当做queue来使用？push_back、pop！

对于当做单链表来使用，其使用方式与list类似，前面也分析了mill_list的相关实现，这里mill_slist的实现思路与也之类似。

slist.h

struct mill_slist_item {
    struct mill_slist_item *next;
};

struct mill_slist {
    struct mill_slist_item *first;
    struct mill_slist_item *last;
};

/* Initialise the list. To statically initialise the list use = {0}. */
void mill_slist_init(struct mill_slist *self);

/* True is the list has no items. */
#define mill_slist_empty(self) (!((self)->first))

/* Returns iterator to the first item in the list or NULL if the list is empty. */
#define mill_slist_begin(self) ((self)->first)

/* Returns iterator to one past the item pointed to by 'it'. If there are no more items returns NULL. */
#define mill_slist_next(it) ((it)->next)

/* Push the item to the beginning of the list. */
void mill_slist_push(struct mill_slist *self, struct mill_slist_item *item);

/* Push the item to the end of the list. */
void mill_slist_push_back(struct mill_slist *self, struct mill_slist_item *item);

/* Pop an item from the beginning of the list. */
struct mill_slist_item *mill_slist_pop(struct mill_slist *self);

slist.c

// slist初始化
void mill_slist_init(struct mill_slist *self) {
    self->first = NULL;
    self->last = NULL;
}

// slist push操作（插到链表头部）
void mill_slist_push(struct mill_slist *self, struct mill_slist_item *item) {
    item->next = self->first;
    self->first = item;
    if(!self->last)
        self->last = item;
}

// slist push_back（插到链表尾部）
void mill_slist_push_back(struct mill_slist *self,
      struct mill_slist_item *item) {
    item->next = NULL;
    if(!self->last)
        self->first = item;
    else
        self->last->next = item;
    self->last = item;
}

// slist pop（从链表头部pop）
struct mill_slist_item *mill_slist_pop(struct mill_slist *self) {
    if(!self->first)
        return NULL;
    struct mill_slist_item *it = self->first;
    self->first = self->first->next;
    if(!self->first)
        self->last = NULL;
    return it;
}