[英]Segmentation fault on pointer to pointer assignment
我正在实现霍夫曼压缩,并且正在从包含节点的链接列表中构建霍夫树。 多次迭代后,我在指向分配指针的指针上遇到分段错误。 根据我的经验和研究,我相信分段错误是由于错误而不是程序中断引起的。 任何帮助或建议,将不胜感激。
PS-我是堆栈溢出的新手,从没问过任何问题,所以请告诉我您是否需要更多信息以帮助我解决此问题或其他问题。
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;
}
我的猜测是在语句“ while(head-> weight> temphead-> weight){}”上。 当您遍历列表时,尚未检查磁头是否已变为NULL。
在您的“ huffTree()”函数中,外部while循环(while(count> 2))运行127次迭代,因为count是用129初始化的。
因此,当调用方调用huffTree()时,输入列表(LinkList * head)必须具有129个可用节点。
无论如何,如果列表中的节点少于129个,则应添加以下NULL条件处理。
temphead = head->next->next;
if (NULL == temphead)
{
/* NULL condition handling */
}
当temphead == NULL时,temphead-> weight解引用将导致以下代码行中的分段错误
while(head->weight>temphead->weight)
如果确保malloc()在mergeTree()函数中不会失败,则head-> weight很好。
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