C语言 访问链表中的链表变量

Question

我有一个链表，其中有另一个链表，我想在其中集成数据，但我不能。

下面是我的代码:

结构声明:

typedef struct BigStructure {
    UINT x;
    UINT y;
    struct SmallStructure* smallStructure;
    struct BigStructure* next;
} BigStructure;
typedef struct SmallStructure {
    UINT x;
    UINT y;
    struct SmallStructure* next;
} SmallStructure;

结构操作函数:

BigStructure* addLinkedListElement(BigStructure* linkedList)
{
    if(linkedList-> next == NULL)
    {
        return NULL;
    }
    BigStructure* newLinkedList = malloc(sizeof(linkedList));
    newLinkedList->next = linkedList;
    return newLinkedList;
}
BigStructure* removeLinkedListElement(BigStructure* linkedList)
{
    //If the list is empty, we return NULL
    if(linkedList == NULL)
        return NULL;
    //If the list contains one element
    if(linkedList->next == NULL)
    {
        free(linkedList);
        return NULL;
    }
    //if the list contains at least 2 elements
    BigStructure* tmp = linkedList;
    BigStructure* ptmp = linkedList;
    /* Tant qu'on n'est pas au dernier élément */
    while(tmp->next != NULL)
    {
        //ptmp stores the address of tmp
        ptmp = tmp;
        //We move tmp (but pmpt keeps the old value of tmp)
        tmp = tmp->next;
    }
    ptmp->next = NULL;
    free(tmp);
    return linkedList;
}
BigStructure* getLinkedListElement(BigStructure* linkedList, int id)
{
    int i = 0;
    for(i=0; i<id && linkedList != NULL; i++)
    {
        linkedList = linkedList->next;
    }
    if(linkedList == NULL)
    {
        return NULL;
    }
    else
    {
        return linkedList;
    }
}

我试着用上面的代码访问一个SmallStructure变量，但是我得到了一个很大的数字(看起来像一个地址):

BigStructure* bigStructure = NULL;
void addBigStructure(UINT x, UINT y) {
        if(bigStructureNb == 1)
        {
            bigStructure->x = x;
            bigStructure->y = y;
        }
        else
        {
            BigStructure* newBigStructure;
            newBigStructure = (BigStructure*)addLinkedListElement((BigStructure*)&bigStructure);
            newBigStructure->x = x;
            newBigStructure->y = y;
        }
}
void addSmallStucture(UINT x, UINT y) {
    if(smallStructuresNb == 1)
    {
        bigStructure->startTrigger = malloc(sizeof(BigStructure*));
        bigStructure->startTrigger->x = x;
        bigStructure->startTrigger->y = y;
    }
    else
    {
        BigStructure* tmpBigStructure = NULL;
        tmpBigStructure = (BigStructure*)getLinkedListElement(&bigStructure, rowID); //Table row ID
        g_print("%d", tmpBigStructure->id); //Here I get a false value !!!!
        //Here I want to set the value of the tmpBigStructure->smallStructure->x/y
}
}

Answer 1

在我看来，问题是与getLinkedListElement()。以下是一些代码建议:

  BigStructure* getLinkedListElement(BigStructure** linkedList, int id)
    {
        int i;
        if( linkedList == NULL || *linkedList == NULL)
        return NULL ; 
     //We cannot update HEAD(linkedList), therfore using local pointer.
        BigStructure* linkWalk = * linkedList;
    /*I am asuming ids are mapped to linked list nodes as below.
     id 0 -> first node
     id 1 -> second node
     ......
     id n -> n-1 node
    */
//starting from second node since linkWalk is already pointing to first above.
        for(i=1; i<id && linkWalk != NULL; i++)  
                linkWalk = linkWalk->next;
   // At this point , either id = 0 OR id = i OR the link has been traversed.
       return linkWalk ;
    }

最后,在调用g_print("%d"， tmpBigStructure->id)之前，请检查tmpBigStructure != NULL.

Answer 2

在我看来，全局:"BigStructure* BigStructure = NULL"是你的头指针，你传递了它的地址。您可以在头部添加节点。因此，您不需要遍历列表来添加链接节点。

建议:你正在传递bigStructure的地址(即双指针)并在结构操作函数中作为单个指针对其进行操作。这需要在你所有的函数中修改。

作为一个例子，添加节点的函数可以像这样(假设linkedList是HEAD):

BigStructure* addLinkedListElement(BigStructure** linkedList)
{
    BigStructure* newLinkedList = malloc(sizeof(BigStructure));
    if (newLinkedList == NULL)
      return NULL ;    // Just to handle malloc failure
    newLinkedList->next = *linkedList;
    *linkedList = newLinkedList;
    return newLinkedList;
}