C++ Linked List - Reading data from a file with a sentinel

Question

So I've done quite a bit of research on this and can't get my output to work correctly. I need to read in data from a file and have it stored into a Linked List. The while loop used should stop once it hits the $$$$$ sentinel. Then I am to display the data (by searching by ID Number[user input]) I am not that far yet I just want to properly display the data and get it read in for right now.

My problem is when it displays the data is isn't stopping at the $$$$$ (even if I do "inFile.peek() != EOF and omit the $$$$$) I am still getting an extra garbage record.

I know it has something to do with my while loop and how I am creating a new Node but I can't get it to work any other way.

Any help would be appreciated.

students.txt

Nick J Cooley
324123
60
70
80
90
Jay M Hill
412254
70
80
90
100
$$$$$

assign6.h file

#pragma once
#include <iostream>
#include <string>
using namespace std;
class assign6
{
public:
    assign6(); // constructor
    void displayStudents();


private:
struct Node
{ string firstName; 
  string midIni;    
  string lastName;
  int idNum;
  int sco1; //Test score 1
  int sco2; //Test score 2
  int sco3; //Test score 3
  int sco4; //Test score 4
   Node *next;
};
Node *head;
Node *headPtr;


};

assign6Imp.cpp // Implementation File

#include "assign6.h"
#include <fstream>
#include <iostream>
#include <string>
using namespace std;

assign6::assign6() //constructor
{

ifstream inFile;
inFile.open("students.txt");

head = NULL;
head = new Node;
headPtr = head;
while (inFile.peek() != EOF) //reading in from file and storing in linked list
{

    inFile >> head->firstName >> head->midIni >> head->lastName;
    inFile >> head->idNum;
    inFile >> head->sco1;
    inFile >> head->sco2;
    inFile >> head->sco3;
    inFile >> head->sco4;

    if (inFile != "$$$$$")
    {
    head->next = NULL;
    head->next = new Node;
    head = head->next;
    }
}

head->next = NULL;

inFile.close();
}

void assign6::displayStudents()
{
int average = 0;
for (Node *cur = headPtr; cur != NULL; cur = cur->next)
{
    cout << cur->firstName << " " << cur->midIni << " " << cur->lastName << endl;
    cout << cur->idNum << endl;
    average = (cur->sco1 + cur->sco2 + cur->sco3 + cur->sco4)/4;
    cout << cur->sco1 << " " << cur->sco2 << " " << cur->sco3 << " " << cur->sco4 << " " << "average: " << average << endl;
}
}

The final while iteration adds an extraneous node, that subsequently has its `next` pointer set to null. Apart from this member of `Node`, all members of this instance of `Node` are default initialized by the compiler-generated constructor ie a garbage record. — damienh, Oct 30 '12 at 22:58
So it's because I have it in the Constructor? That definitely makes sense. — Nick, Oct 30 '12 at 23:04
Our professor wants us to use Linked Lists and has not officially taught us std::list and would mark off. — Nick, Oct 30 '12 at 23:23

score 1 · Answer 1 · answered Oct 30 '12 at 23:26

Perhaps you should try to read line by line instead, like so.

const string END_OF_FILE_DELIM = "$$$$$";
ifstream inFile("students.txt");
string line;
while( getline(inFile,line) ){
   cout << "line = " << line << endl;
   if(line == END_OF_FILE_DELIM){
      break;
   }
   else{
       //create new Node with value = line;
   }
}

score 0 · Answer 2 · answered Oct 30 '12 at 23:20

0

This can not work:

if (inFile != "$$$$$")

You can not compare the stream to "$$$$$". You can only read a string from the stream and compare that to "$$$$$".

answered Oct 30 '12 at 23:20

Sebastian

1,839
12
16

C++ Linked List - Reading data from a file with a sentinel

2 Answers2