CODEWITHSUNDEEP
c++pointers
user3280133
user3280133

Reputation: 10699

C++ Setting next node pointer in Linked List

So I'm recreating a LinkedList in C++ and I am trying to change the pointer to the last Node in my list. Here is my overloaded += operator where all the magic and errors happen. I have two different ways of changing the pointer, but both throw Unhandled exception at 0x00ee42f3 in Lab3.exe: 0xC0000005: Access violation writing location 0xccccccec.. What is going on and how can I fix it?

void MyLinkedList::operator+=(const std::string& s)
{
    allocator<Node> a;
    Node* n = a.allocate(1);
    a.construct(n, s);


    if (first == NULL)
        first = n;
    else
    {
        (*last).next = n;    // crashes here
        (*last).SetNext(n);  //also will crash here, if the previous statement is removed
        last = n;
    }
}

To further clarify, it will go through and set the first Node, exit the method, and the next time it is called will run and enter the else statement. At this point there is a second Node, it is allocated in memory and instantiated. What I am trying to do is set the Node* next pointer in the first Node to this new Node, but it throws the exception. Sorry for being very vague initially.

Upvotes: 1

Views: 2532

Answers (2)

PaulMcKenzie
PaulMcKenzie

Reputation: 35440

Your operator += has a lot of issues.

1) The operator+= should return a reference to this, not void. Otherwise a+=b makes no sense.

MyLinkedList& MyLinkedList::operator+=(const std::string& s) 
{
    //...
    return *this;
}

2) Second, your last pointer may not have been initialized if the list is empty.

3) Style issue -- why are you doing this:

(*last).next = n;

when you should just do this:

last->next = n;

?

Upvotes: 1

Charlie
Charlie

Reputation: 438

We do not know the allocate and SetNext specific realization.

If they are no problem, please look here:

if (first == NULL) 
{
    first = n;
    last = first; // You should assign last with the head node pointer.
}
...

Maybe it help.

Upvotes: 2

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