c - 哈夫曼树卡在最后一个非内部节点

Question

因此，我创建了一个函数来构建哈夫曼树，该树按频率升序传递链表(每个节点内分配的值)，但当它下降到最后一个“非内部节点”时，它似乎会卡住'，就像在链表中的节点中一样，该节点被赋予了一个字符作为开头。

void build_tree(pqueue *list)
{

node *temp; 
node* parent_node;
int min_1, min_2, ind = 0, counter = 0, length = 4;
temp = new_node();


    while (length > 2)
    {
        temp = list -> start;            /* 0. point temp at the linked list start (lowest frequency/letter) */
        parent_node = new_node();              /* 1. make new node */
        min_1 = temp -> frequency;    
        parent_node -> left = temp;         /* 2. assign parent to point at left leaf */
        temp = temp -> next;                /* 3. move to next node */
        min_2 = temp -> frequency;      
        parent_node -> right  = temp;        /* 4. assign parent to point at right leaf */
        parent_node -> letter = '$';
        parent_node -> frequency = min_1 + min_2; /* 5.assign internal node frequency */
        list -> start = temp -> next;/* set the list to point at the next node for the next iteration through the loop */

        while (ind == 0 && temp -> next != NULL)
        {
            temp = temp -> next;
            if (temp -> next -> frequency >= parent_node -> frequency && temp != NULL) /* insert parent node */
            {
                parent_node -> next = temp -> next; /* parent points at higher freq node */
                temp -> next = parent_node; /* parent node is temp next */
                ind = 1;
            }
            else if (temp -> next == NULL) /* insert at end of list if parent node is biggest frequency */
            {
                temp -> next = parent_node;
                ind = 1;
            }
        } 
        ind = 0;
        temp =  list -> start; /* temp points at new start (two nodes along)*/
        while (temp -> next != NULL)
        {
            temp = temp -> next;
            counter++;
            printf("%c : %d\n", temp -> letter, temp -> frequency);
        }
        printf("----------------------------------------------\n");
        length = counter;
        counter = 0;
    }
}

当传递一个文本文件时，它将打印构建树的每次迭代，以显示两个节点的添加、这些节点的删除以及新节点的插入(两个先前节点频率加在一起)，但它以当它仅到达内部节点(标记为 $)和一个非内部节点时，会出现段错误。即，经过多次迭代才将其减少到这个节点数:

$:4 美元:4 美元:4 兹:6 段错误(核心转储)

Answer 1

好吧，这里至少有一个错误:

while (ind == 0 && temp -> next != NULL)
{
    temp = temp -> next;
    if (temp -> next -> frequency >= parent_node -> frequency && temp != NULL) /* insert parent node */
    {
        ...

假设 temp->next 不是 NULL，但 temp->next->next 是 NULL 。然后输入循环体，并将 temp 替换为 temp->next。所以现在 temp->next 是 NULL。但是您尝试引用 temp->next->frequencey。这是分段违规。核心已转储。