Thread: reading a txt file into a linked list:

Code:

void loadData(fstream& fin, nodePtr head)
{
    if (fin.eof()) {
        return ;
    }
    else
    {
        while (!fin.eof())
        {
        if (!head) {
            head= new node;
            getline(cin, head->name, '\n');
            getline(cin, head->last, '\n');
            fin>>head->age;
            head->next=nullptr;
        }
        else
        {
            nodePtr curr =head;
            while (curr->next)
                curr=curr->next;
            getline(cin, curr->next->name, '\n');
            getline(cin, curr->next->last, '\n');
            fin>>curr->next->age;
            curr->next->next=nullptr;
        }
    }
    }
        
}

This is my function and it is not working. Any advice?

Do you have a link I can read more on how to do this? I think my problem is truly my lack of understanding how to do this. I didn't learn it in my C++ class. However I would really like to figure this out.

Note that void loadData(fstream& fin, nodePtr head) is taking a copy of the pointer value in head, so it doesn't update head. In order to update a head pointer the function should be: loadData(fstream& fin, nodePtr *head), and the function should use *head instead of head.

The function should always allocate a node unless it's reached the end of file. Use a temp nodePtr for this.

As already mentioned, the program is using both fin and cin

I don't know if there is an issue mixing getline() calls with ... >> to a variable. The code could always use getline, and for the numeric fields, use getline() with a temp buffer, then sscanf() to convert the buffer into an integer.

Code:

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <cstdlib>
#include <iomanip>
#include "contacts.h"

#define MYFILE "/Users/peterjocham/Desktop/textoutput.txt"

using namespace std;

void loadData(ifstream& fin, nodePtr &head)
{
    if (fin.eof()) {
        return ;
    }
    else
    {
        while (!fin.eof())
        {
            if (!head) {
                head= new node;
                getline(fin, head->name, '\n');
                getline(fin, head->last, '\n');
                fin>>head->age;
                head->next=nullptr;
            }
            else
            {
                nodePtr curr = head;
                while (curr->next)
                    curr=curr->next;
                curr->next=new node;
                fin.ignore();
                getline(fin, curr->next->name, '\n');
                getline(fin, curr->next->last, '\n');
                fin>>curr->next->age;
                curr->next->next=nullptr;
            }
            
        }
    }
}

int main()
{
    
    addressBook MyaddressBook;
    ofstream outfile;
    ifstream infile(MYFILE,ios::in);

    int userInput=0;
	nodePtr temp=new node;
	string NAME;
    MyaddressBook.userPromptStatement();
    
	nodePtr head=nullptr;
    loadData(infile, head);
    MyaddressBook.sethead(head);
    outfile.open(MYFILE,ios::app);
    
    if (outfile.fail()) {
        cerr<<"File couldn't be opened";
        exit(EXIT_FAILURE);
    }
    while(1)
	{
  cin>>userInput;
        if (!cin || (userInput!=1 && userInput!=2 && userInput!=3 && userInput!=4 &&userInput!=5))
        {
            cin.ignore();
            cout<<"Only enter a 1,2,3,4, or 5"<<endl;
            cout<<"You have entered an incorrect value."<<endl;
            cout<<endl<<endl;
            MyaddressBook.userPromptStatement();
            continue;
        }
        switch (userInput) {
            case 1:
                
                cout<<"NAME: ";
                cin.ignore();
                getline(cin,temp->name,'\n');
                
                cout<<"\nLAST NAME: ";
                getline(cin,temp->last,'\n');
                
                cout<<"\nAGE: ";
                cin>>temp->age;
                
                outfile<<
                setw(2)<<temp->name<<"\n"
                <<setw(2)<<temp->last<<"\n"
                <<setw(2)<<temp->age<<"\n\n";
                
                MyaddressBook.addContact(temp);
                MyaddressBook.userPromptStatement();
                cout<<"\n"<<"\n";
                break;
                
            case 2:
                cout<<"Which contact would you like to delete?\n";
                cin>>NAME;
                
                MyaddressBook.deleteName(NAME);
                MyaddressBook.userPromptStatement();
                cout<<"\n"<<"\n";
                break;
            case 3:
                MyaddressBook.editName(NAME);
                break;
            case 4:
                MyaddressBook.printContactList();
                MyaddressBook.userPromptStatement();
                cout<<"\n"<<"\n";
                break;
            case 5:
                outfile.close();
                exit(EXIT_SUCCESS);
            default:
                break;
        }
    }
    
    return 0;
}

I have nodPtr is a point as I will show below:

Code:

typedef struct node{
    std::string name;
    std::string last;
    int age;
    node *next;
}*nodePtr;

so I am doing *head, however yes I did need to do fin and not cin.

I tried using

Code:

stringstream convert (head->age);

and I had a few problems. So I decided to use fin>>, was I wrong in doing so?

I tired not using eof but I don't think I quite got the concept.

I got the program to work but now I am concern I am using bad programing practice.

Originally Posted by jocdrew21

I have nodPtr is a point as I will show below:

Code:

typedef struct node{
    std::string name;
    std::string last;
    int age;
    node *next;
}*nodePtr;

so I am doing *head

This is equivalent to saying "I received a paper today, therefore there are eight days in a week." (1) The two concepts are not related (that is, the type of nodePtr is irrelevant to the problem), and (2) the conclusion is false (as you are not doing *head).
What you have done to fix it is change your function prototype to accept a reference, instead of a copy of the value, and that is what you needed to do.

Originally Posted by jocdrew21

I tried using

Code:

stringstream convert (head->age);

and I had a few problems.

What does that even mean? Do you mean you tried to write a convert function?

Originally Posted by jocdrew21

So I decided to use fin>>, was I wrong in doing so?

If you try to mix >> with getline, you're going to have sprinkle those "ignore" statements very carefully (get one too many, and you'll ignore some input; get one too few, and you'll get a blank read). Easier to just do it correctly, I would think.

Originally Posted by jocdrew21

I tired not using eof but I don't think I quite got the concept.

Since your loop still says "while (!fin.eof())" I'm skeptical that you tried not using eof. You need something like

Code:

while (READ INTO YOUR VARIABLE HERE)

to check whether your read was successful.

Hook, Hook, jape, upper cut....

I'll work at it more. I just don't want it to work, I want it to be correct.(I am really happy it works though) This is not an assignment, and i have didn't learn this in my pervious C++ class but I know it is very important concept. I am getting the there slowly and I thank you for your advice. I am sure I will be back shortly with new code asking for a critique.