尝试以递归方式在 C++ 中打印链表

Question

I've been trying to create an ordered double linked list and then print it out forwards and backwards using recursion. I don't know if I'm adding nodes to the linked list incorrectly or if my problem is in my print functions.

Main

int main() {
    ifstream addData;
    addData.open("proj1adds.data");
    LinkedList<int> List;
    Node<int> *head = NULL:
    int add;
    int i = 0;
    while (!addData.eof()){
        addData >> add;
        List.add(i, add);
        i++;
    }
}

this is my add function

template < typename T >
void LinkedList < T >::add(int index, T element)
{
  if (index == 0){
    addFirst(element);
  }
  else if (index >= size){
    addLast(element);
  }
  else
  {
    Node < T > * current = head;
    for (int i = 1; i < index; i++)
      current = current->next;
    Node < T > * temp = current->next;
    current->next = new Node < T > (element);
    (current->next)->prev = current;
    (current->next)->next = temp;
    size++;
  }
}    

And these are my print functions

template<typename T>
void LinkedList<T>::printForward(Node<T> *head){
    if(head==NULL){
        return;
    }
    cout << head->element << endl;
    printForward(head->next);
}

template<typename T>
void LinkedList<T>::printBackward(Node<T> *head){
    if(head==NULL){
        return;
    }
    printBackward(head->next);
    cout << head->element << endl;
}

I think that I've loaded the data into the nodes, but I'm not sure if its ordered because I cant print it.

Answer 1

In a comment (but not in your question) you say that you're calling printFowards(head) and printBackwards(head) in main() . But in main() , the variable head is a local variable that is set to NULL . So the functions abort, and when you comment out the exit condition [ shudder ] you dereference a null pointer and get Undefined Behavior.

Maybe the list is being constructed correctly; it doesn't matter because your calls to the printing functions have no connection to the list.