C:双向链表中的段错误，在追加和删除函数中

Question

我在用 C 语言创建双向链表时遇到问题，因为它在追加和删除时返回段错误。好像我将其中一个指针指向了错误的位置，但我很难找到它。

我的问题函数如下:

追加:

int list_append(list_t *list, int val) {
    if(!list) { return 1; }

//    create a new node, then assign the value
    struct node_t *new = (node_t *) malloc(sizeof(node_t));
    new->val = val;
    new->prev = NULL;
    new->next = NULL;

//    place the new node (since it is tail, make next null)
    new->next = NULL;

//    if there's no head(null), make the new node the head (and tail)
    if (list->head == NULL)
    {
        list->head = new;
    }

//    if the next value is not null, traverse until it is (=tail)
    struct node_t *node = list->head;

    while (node)
    {
        node = list->tail;
    }
//    place the new node at the next of tail
    list->tail->next = new;

//    set the old tail as the previous of new node
    new->prev = list->tail;

    list->tail->next = NULL;

    CHECK_LIST(list);

    return 0;
}

删除:

int list_delete(list_t *list, int val) {
    if(!list) { return 1; }

    CHECK_LIST(list);

//    make a temporary node to help find the value
    struct node_t *temp = list->head;


//    start traversing the list

    while (temp)
    {

//      if match is found
        if (temp->val == val)
        {
//          if the match is actually the head, make the next node the new head,
//          then make old head null
            if (temp == list->head)
            {
                list->head = list->head->next;
                list->head->prev = NULL;
            }
//          if the match is at the tail, make the previous node the new tail,
//          then make the old tail null
            if (temp == list->tail)
            {
                list->tail = list->tail->prev;
                temp->prev->next = NULL;
            } else
            {
//              set new next of temp as the old next of temp, and vice versa
//              then, free temp from memory
                temp->next = temp->prev->next;
                temp->prev = temp->next->prev;

                temp = NULL;
                free(temp);
            }
        }

//      keep moving
        temp = temp->next;
    }

    CHECK_LIST(list);

    return 0;
}

提前感谢您的帮助。

Answer 1

append() 函数的以下代码块中存在错误

while (node) {
    node = list->tail; /*what is tail here ?? */
}
/* after this loop you are not using node anywhere, what's the use 
    of iterating through loop */
//    place the new node at the next of tail
list->tail->next = new;
//    set the old tail as the previous of new node
new->prev = list->tail;
list->tail->next = NULL;

替换为

struct node_t *node = list->head;

while (node->next) {/* when loop fails node holds  last node address */
     node = list->next;
}
node->next = new; /* replace node->next as new node */
new->prev = node->next; /* new node previous make it as old node next */
new->next = NULL;/* last node next make it as 0*/

最好先运行 gdb 然后执行 bt