循环双链表 - 分段故障：11 [英] Circular Doubly Linked List - Segmentation fault: 11

问题描述

我想实现一个循环双向链表，但我不断得到一个分段错误：11错误（我相信这是因为添加和删除功能）。我不知道我的代码是否是接近，但我不能通过这个错误，测试它正确。这是我相信涉及的代码：

（Circular_DLList.cc）

  void Circular_DLList :: add_to_tail（int a）
 {
 if（is_empty（））{
 tail = new DLLNode（a）; 
 tail-> next = tail; 
} 
 else {
 tail-> next = new DLLNode（a，tail-> next）; 
} 
} 
 
 int Circular_DLList :: delete_from_tail（）
 {
 if（！is_empty（））
 {
 int a = tail-> info; 
 tail = tail-> prev; 
 tail-> next = null; 
 return a; 
} 
 else 
 {
 tail = 0; 
} 
 return a; 
} 
  

任何帮助将是太棒了，谢谢。

解决方案

代码中有多个问题，但这里有其中一个问题。

添加第一个元素时，您可以：

  tail = new DLLNode（a）; 
 tail-> next = tail; 
  

，所以你留下 prev 等于 0 （BTW：使用 nullptr 而不是 0 p>

如果您随后删除该元素：

  int a = tail - > info; 
 tail = tail-> prev; // tail become 0 
 tail-> next = null; // Dereference 0 cause seg fault 
 return a; 
  

BTW：您的删除函数也应该删除 DLLNode ！只需更改指针值是不够的。

因此，这会导致3个更改：

新元素一定要始终设置两者 下一页和上一页

2）请记得删除 DLLNode 用新的

创建

你的删除函数你需要一个特殊的情况下检查列表是否只包含一个元素，即 if（tail == tail-> next）{..删除最后一个元素.. set tail equal nullptr}

I'm trying to implement a circular doubly linked list but I keep getting a segmentation fault: 11 error (I believe it's because of the add and delete functions). I have no idea whether my code is even close, but I can't get past this error to test it properly. This is the code I have that I believe is involved:

(Circular_DLList.cc)

void Circular_DLList::add_to_tail(int a)
{
    if (is_empty()) {
        tail = new DLLNode(a);
        tail->next = tail;
    }
    else {
        tail->next = new DLLNode(a, tail->next);
    }
}

int Circular_DLList::delete_from_tail()
{
    if(!is_empty()) 
    {
        int a = tail->info;
        tail = tail->prev;
        tail->next = null;
        return a;
    }
    else
    {
        tail = 0;
    }
    return a;
}

Any help would be fantastic, thanks.

解决方案

There is more than one problem in your code but here is one of them.

When you add the first element, you do:

    tail = new DLLNode(a);
    tail->next = tail;

so you leave prev equal to 0 (BTW: use nullptr instead of 0).

If you then delete the element you do:

    int a = tail->info;
    tail = tail->prev;  // tail becomes 0
    tail->next = null;  // Dereference 0 cause seg fault
    return a;

BTW: Your delete function should also delete the DLLNode ! Just changing pointer values isn't sufficient.

So this leads to 3 changes:

1) When adding new elements make sure to always set both nextand prev

2) Remember to delete the DLLNode created with new

3) In your delete function you need a special case for checking whether the list contains exactly one element, i.e. if (tail == tail->next) { .. delete last element .. set tail equal nullptr}

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