(PSET5 cs50) 卸载链表数组时出现段错误

Question

这是 cs50pset 5 的一部分，所以它是一个剧透。函数假设从链表数组中卸载附加字符串，某种散列table（我不知道它是否是正确的定义）。但这似乎会造成段错误。你能说这个功能是否会导致段错误，或者我应该检查问题的其他功能。非常感谢您的宝贵时间。

    // Represents a node in a hash table
typedef struct node
{
    char word[LENGTH + 1];
    struct node *next;
}
node;

// Number of buckets in hash table
const unsigned int N = 1000; // trying to find most optimized N it could be different

// Hash table
node *table[N];

// Unloads dictionary from memory, returning true if successful else false
bool unload(void)
{
    for (int i = 0; i < N; i++)
{
    node* iterf; //forward iteration
    node* iterb; //pointer that stays behind of iterf

    iterf = table[i];
    iterb = iterf;
    while (iterb != NULL)
    {
        iterb = table[i];
        iterf = iterb -> next;
        free(iterb);
        iterb = iterf;
    }
}

    return true;
}

Answer 1

考虑这个循环

node* iterf;
node* iterb;

// ...
iterf = table[i];
iterb = iterf;

while (1)
{
    if (iterf == NULL)
    {
        free(iterf);         // <-- Why are you freeing a NULL pointer?
    }
    iterf = iterf -> next;   // <-- iterf CAN be NULL! 
    free(iterb);             
    iterb = iterf;
}                            // How can this be stopped? When it segfaults?

不清楚为什么外循环应该在第一个NULL指针处停止，返回false，但内循环应该只是一个正常的单链表释放。

node *current = table[i];
while ( current != NULL )
{
    // Now I know that the pointer can be dereferenced
    node *next = current->next;

    // Free it only after saving the next
    free(current);
    current = next;
}

Answer 2

我在删除 //THIS LINE 双迭代消失的那一刻找到了解决方案。因为由于该行指针回到开头并尝试释放已经释放的内存。至少我是这么想的。如果有任何意见或补充，请写下来。感谢所有的帮助，有这样一个乐于助人的社区是一种幸运:)

    iterf = table[i];
    iterb = iterf;
    while (iterb != NULL)
    {
        iterb = table[i]; // THIS LINE
        iterf = iterb -> next;
        free(iterb);
        iterb = iterf;
    }

(PSET5 cs50) 卸载链表数组时出现段错误

(PSET5 cs50) Seg Fault while unloading an array of linked lists

c

linked-list

cs50