c++ - 链表，C++段错误

Question

我一直无法完成作业，因为我似乎无法确定此段错误的来源。

我正在尝试将节点添加到文件的链表中。我已经运行了多个测试并且已经缩小了问题的范围，但是，我不知道到底是什么导致了这个问题，因此当我尝试更改其他细节时我会产生新的问题。

这是我的第二门类(class)，因此，希望我的代码没有糟糕到无可救药的地步。这是添加方法:

    bool OrderedList::add (CustomerNode* newEntry)
{
if (newEntry != 0)
{
    CustomerNode * current;
    CustomerNode * previous = NULL;
    if(!head)
        head = newEntry;
    current = head;
  // initialize "current" & "previous" pointers for list traversal
   while(current && *newEntry < *current) // location not yet found (use short-circuit evaluation)
   {
    // move on to next location to check
    previous = current;
    current = current->getNext();
   }

  // insert node at found location (2 cases: at head or not at head)
  //if previous did not acquire a value, then the newEntry was
  //superior to the first in the list. 
  if(previous = NULL)
    head = newEntry;
  else
  {
    previous->setNext(newEntry); //Previous now needs to point to the newEntry
    newEntry->setNext(current); //and the newEntry points to the value stored in current.
  }
}
    return newEntry != 0;  // success or failure
    }

好的，程序中包含一个重载的运算符<，外部测试并未表明该运算符有问题，但我也会将其包括在内:

    bool CustomerNode::operator< (const CustomerNode& op2) const
    {
       bool result = true;
       //Variable to carry & return result
       //Initialize to true, and then:
       if (strcmp(op2.lastName, lastName))
        result = false;

        return result;
       }

这是来自 gdb 的回溯:

    #0  0x00401647 in CustomerNode::setNext(CustomerNode*) ()
    #1  0x00401860 in OrderedList::add(CustomerNode*) ()
    #2  0x004012b9 in _fu3___ZSt4cout ()
    #3  0x61007535 in _cygwin_exit_return () from /usr/bin/cygwin1.dll
    #4  0x00000001 in ?? ()
    #5  0x800280e8 in ?? ()
    #6  0x00000000 in ?? ()

这是尝试纠正不同段错误的大量工作的结果，而这个更令人惊讶。我不知道我的 setNext 方法是如何导致问题的，这里是:

void CustomerNode::setNext (CustomerNode* newNext)
{
    //set next to newNext being passed
    next = newNext;
    return;
}

在此先感谢，如果有必要确定此问题，我将很乐意发布更多代码。

Answer 1

是

if(previous = NULL)

代替

if(previous == NULL)

这会将previous设置为NULL，然后进入else分支:

previous->setNext(newEntry); //Previous now needs to point to the newEntry
newEntry->setNext(current);

导致未定义的行为。