如何从文本文件加载链表？

Question

Greetings I've been working on a homework in which I must create a linked list program which can save and restore its data from a text file. I have gotten most of it working but I'm having some problems with restoring the linked list using the data from the text file that was created from it. When I restore it the last element is repeated twice. I believe it has something to do with the loop but as I'm not sure I'm including the whole scope of my assignment.

Below is the code I've written so far of the program:

ListNode.h

#pragma once
template<class T> class List;
template<class T>

class ListNode
{
 friend class List<T>;
public:
 ListNode(const T&);
 T getData()const;
private:
 T data;
 ListNode<T>*next;
};//end ListNode class

template<class T>
ListNode<T>::ListNode( const T &info):data(info), next(NULL)
{
}//end default constructor
template<class T>
T ListNode<T>::getData()const
{
 return data;
}//end function getData 

List.h

#pragma once
#include<iostream>
#include <fstream>
using namespace :: std;
#include "ListNode.h"
template<class T> 
class List 
{
private:
 ListNode<T> *head;
 int size;
 ListNode<T> *find(int index) const;
public:
 List();
 List(const List<T> &aList);
 ~List();
 int getLength() const;
 void insert (int index, T tempData);
 void remove(int index);
 void retrieve(int index, T &tempData);
 bool isEmpty() const;
 void print() const;
 void save();
 void restore();
};//end List class 

Broken function:

template <class T>
void List<T>::restore()
 {
     ifstream inFile;
     inFile.open("listFile.txt");

     T value=0;
     int index, check =0;

     cout << "Now reading the data from the text file..." << endl;
         //inFile >> value;
         //cout << "Value is : " << value << endl;


        while (inFile != NULL) 
        {
            inFile >> value;
            index = getLength();
            cout << value << endl;
            insert(index+1, value);

            inFile.close();

        } 


 } // end function restore

The linked list data that was saved to the text file during the test was :

35
45
55
65

When the linked list was restored from the text file this was the content of it:

35
45
55
65
65

How can I solve this problem?

Answer 1

It amazes me that your restore function works at all. But yes, it's repeating the last element. Try this instead:

while(inFile >> value)
  ...

All right, just try this much:

while(inFile >> value)
{
  cout << value << endl;
}

Does it display the values correctly?

Answer 2

I had this problem a while ago with one of my programs. It took me a while to figure out and I am not sure if it is the same problem, but check your input file one more time. If you leave an extra line after the last number, the compiler will return the last number twice.

example:

1

2

3

4

5

(extra line)

Just delete the extra line.

Answer 3

Which one is the head of your list? You can use a while loop or even an if statement to traverse through each node and load them all.