如何实现动态链表的容量?

如果要对链接列表实施容量限制,最好的方法是对每个列表进行限制。以下结构将允许:

// List structure: first/last pointers plus remaining capacity.
typedef struct {
    tNode *first;
    tNode *last;
    size_t freeCount;
} tList;

// Node structure: value pointer and next.
typedef struct sNode {
    void *val;
    struct sNode *next;
} tNode;

然后,您在每个列表中初始化您的限额:

// Creates an empty list.
tList *makeList (size_t limit) {
    tList *list = malloc (sizeof (tList));
    if (list == NULL)
        return NULL;
    list->freeCount = limit;
    list->first = list->last = NULL;
}

// Destroys a list after clearing it if necessary.
void destroyList (tList list) {
    void *val = getNode (list);
    while (val != NULL) {
        free (val);
        val = getNode (list);
    }
    free (list);
}

freeCount 为零,否则将添加一个节点并递减 . 删除节点将增加 自由计数 ,类似于:

// Puts an item on to the list end.
int putNode (tList *list, void *val, size_t sz) {
    // No more capacity.
    if (list->freeCount == 0) return -1;

    // Try to make node, returning error if no memory.
    tNode *node = malloc (sizeof (tNode));
    if (node == NULL) return -1;

    // Try to duplicate payload, clean up and return if no memory.
    node->val = malloc (sz);
    if (node->val == NULL) {
        free (node);
        return -1;
    }

    // Initialise node.
    memcpy (node->val, val, sz)
    node->next = NULL;

    // Adjust remaining capacity and insert into list.
    list->freeCount--;
    if (list->first == NULL) {
        list->first = list->last = node;
    } else {
        list->last->next = node;
        list->last = node;
    }

    return 0;
}

// Gets an item from the list.
void *getNode (tList *list) {
    // If empty, just return NULL.
    if (list->first == NULL)
        return NULL;

    // Get first node and remove it from list.
    tNode node = list->first;
    list->first = list->first->next;

    // Get the payload and free the node.
    void *val = node->val;
    free (node);

    // Adjust remianing capacity and return payload.
    list->freeCount++;
    return val;
}

注意所有正常的错误情况(没有内存,列表为空等等) 以及 当您已经达到最大容量时(当 自由计数 是零)。