指针对指针赋值时出现分段错误

Question

我正在实现霍夫曼压缩，我正在从包含节点的链接列表中构建一个赫芬顿树。多次迭代后，我在指针到指针的分配上得到分割错误。根据我的经验和研究，我认为分割错误是由于程序中断以外的错误造成的。如有任何帮助或建议，我将不胜感激。

p。S -我是堆栈溢出的新手，以前从未问过问题，所以如果你需要更多的信息来帮助我解决这个问题或其他任何问题，请告诉我。

struct LinkList{
    int weight;
    struct TreeNode * bottom;
    struct LinkList * next;
}; typedef struct LinkList LinkList;
//This function takes in a link list where each node points to the next
 //element in the link list and a huff tree node. It also contains weight 
//which is equal to the weight of the hufftree that it points to.
TreeNode * huffTree(LinkList * head)
{
    LinkList * temphead = head;
    LinkList * ptr;
    LinkList * ptr1;
    int count = 127,i;
    while(count>2)
    {
        temphead = head->next->next;
        head->next->next = NULL;
        head = mergeTree(head);
        ptr = temphead;
        ptr1 = temphead;// This is where I get the segmentation fault
//when the value of count is 14
        while(head->weight>temphead->weight)
        {
            ptr1 = temphead;
            temphead = temphead->next;
        }
        if(ptr1!=temphead)
        {
            head->next = temphead;
            ptr1->next = head;
            head = ptr;
        }
        else
        {
            head->next = temphead;
        }
        count--;
    }
    head = mergeTree(head);
    TreeNode * root;
    root = head->bottom;
    head->bottom = NULL;
    free(head);
    return root;
}
LinkList * mergeTree(LinkList * head)
{
    TreeNode * tree1 = head->bottom;
    TreeNode * tree2 = head->next->bottom;
    head->bottom = NULL;
    head->next->bottom = NULL;
    free(head->next);
    free(head);
    TreeNode * newnode = (TreeNode *) malloc(sizeof(TreeNode));
    newnode->weight = tree1->weight + tree2->weight;
    newnode->c = '~';
    newnode->left = tree1;
    newnode->right = tree2;
    LinkList * ptr = (LinkList *) malloc(sizeof(TreeNode));
    ptr->weight = newnode->weight;
    ptr->bottom = newnode;
    ptr->next = NULL;
    return ptr;
}

Answer 1

我猜是在语句"while(head->weight>temphead->weight){}"。当您遍历列表时，您还没有检查头是否已变为NULL。

Answer 2

在你的"huffTree()"函数中，外部while循环(while (count> 2))运行127次迭代，因为count初始化为129。

因此，当调用者调用huffTree()时，输入列表(LinkList *head)必须有129个节点可用。

无论如何，如果列表的节点少于129个，则应该添加以下NULL条件处理。

temphead = head->next->next;
if (NULL == temphead)
{
    /* NULL condition handling */
}

当temphead == NULL时，则temphead->权值解约束将导致以下代码行中的分段错误

while(head->weight>temphead->weight)

head->weight是可以的，如果malloc()在mergeTree()函数中保证不会失败。