C++ FileIO problem.

[TomCo]

Hi, Im having difficulty populating a linked list with data from a file.

cout << "Please enter filename: ";
        string filename; 
        getline(cin,filename);
 
        ifstream myfile;
        myfile.open (filename.c_str());
 
        if (myfile.is_open())
        {
            node *temp;
 
            temp = new node;
            while (!myfile.eof())
            {
                getline(myfile,temp->name);
                getline(myfile,temp->info);
 
                if (start_ptr == NULL)
                { 
                    start_ptr = temp;
                    start_ptr->nxt = NULL;
                }
 
                cout << start_ptr->name;
                cout << start_ptr->info;
            }
                myfile.close();
        }
        else
            cout << "Unable to open file";

My input file is

a
a

b
b

c
c


Im just trying to get it to correctly create the start_ptr to being with.
start_ptr has a value of NULL to begin with and as far as I can see this code should only print "aaaaaa" but it prints "aabbcc".

If I put in the rest of my code to create the ordered list the whole thing goes into an infinite loop. It works fine without the file input.

What am I doing wrong?

[Banfa]

You have 2 problems

1. The line
   temp = new node;
   
   is where you create your entries in the linked list. However this appears outside the loop that reads them. This means that although you read 3 items from the file for the list you have only ever created 1 item. Each item you read from the file after the first item overwrites the previous item.
2. You only handle the case of start_ptr == NULL, i.e. adding the first entry to the list, you do not handle the case of start_ptr != NULL, adding subsequent entries to the list.

The reason you see aabbcc when you expected aaaaaa is that you only have 1 object that you are overwriting the contents of and printing out.