C-双链表

Question

ConsoleInfo         *CI_new(const char *name, const char *ip, ConsoleInfo *prev, ConsoleInfo *next)
{
    ConsoleInfo *list;
    if ((list = malloc(sizeof(ConsoleInfo))))
    {
        list->name  = strdup(name);
        list->ip    = strdup(ip);
        list->prev  = !prev ? NULL : prev;
        list->next  = !next ? NULL : next;
    }
    return (list);
}

bool                CIL_is_empty(ConsoleInfoList *list)
{
    return (list->count == 0);
}

ConsoleInfoList     *CIL_append(ConsoleInfoList *list, const char *name, const char *ip)
{
    if (CIL_is_empty(list))
    {
        list->head = list->tail = CI_new(name, ip, NULL, NULL);
    }
    else
    {
        ConsoleInfo *new = CI_new(name, ip, list->tail, list->head);
        list->tail = new;
        list->head = new->next;
    }
    list->count++;
    return (list);
}

typedef and co..

    typedef struct ConsoleInfo ConsoleInfo;
    typedef struct ConsoleInfoList ConsoleInfoList;

    struct ConsoleInfoList {
      size_t count;
      ConsoleInfo *head;
      ConsoleInfo *tail;
    };

    struct ConsoleInfo {
      char *name;
      char *ip;
      ConsoleInfo *next;
      ConsoleInfo *prev;
    };

typedef struct ConsoleName
{
   char value[256];
} ConsoleName;

typedef struct ConsoleIp
{
   char value[256];
} ConsoleIp;

Now, why when i'm doing this:

ConsoleInfoList     *CIL_new(void)
{
    ConsoleInfoList *list;

    if ((list = malloc(sizeof(ConsoleInfoList))))
    {
        list->count = 0;
        list->head = NULL;
        list->tail = NULL;
    }
    return (list);
}


ConsoleInfoList *cil = CIL_new();
    if (!cil)
        return (NULL);
    ConsoleName name;
    ConsoleIp ip;
    for (int i = 0; i < GetNumberOfConsoles(); ++i)
    {
        GetConsoleInfo(i, &name, &ip);
        cil = CIL_append(cil, name.value, ip.value);
    }
    for (ConsoleInfo *ci = cil->head; ci; ci = ci->next)
        CI_print(ci);

Only the first element is displayed.
I know this is a very amateur question with what I'm sure is going to be a very simple answer, but I can't resolve the problem.

Answer 1

I'm not a C expert, but this part doesn't make sense for a linked list:

ConsoleInfo *new = CI_new(name, ip, list->tail, list->head);
list->tail = new;
list->head = new->next;

It should be

ConsoleInfo *new = CI_new(name, ip, list->tail, NULL);
list->tail->next = new
list->tail = new;

I counldn't test this, since I'm not sure how to get your code to run.

Answer 2

The image below shows the step by step breakdown of whats happening with your link list append operations.

Basically the first time round head and tail point to the new element which has NULL prev and next pointers.

The second time round the head points to the old item and the tail points to the new item. The new item has both prev and next set to the existing item. Only the prev should point to the old item, next should be NULL. You must also update the old item next pointer to point to the new item which you have not done.

As it stands the old element is still first in the list and the next pointer is still NULL so you only get one output.

Your append code should probably be like this:

ConsoleInfo *new = CI_new(name, ip, list->tail, NULL);
list->tail->next = new;
list->tail = new;

(But I have not tested that.)