Class Linked List Template run time error - c++

Question

I have a linked list class that uses templates for both the Node class and the List class. I've done some debugging and come to the conclusion that in my Node class, the member functions cannot access the member data, but the constructors can. I would like to know how i can fix this!
#include <iostream>
#include <fstream>
#include <string>
#include "List.h"
using namespace std;
int main()
{
ifstream fileIn("data1.txt");
List<int> studentList;
if(fileIn.fail())
cout << "file did not open" << endl;
else
studentList.add(fileIn);
fileIn.close();
cin.get();
cin.ignore();
return 0;
}
//List.h
//ignore the commented methods, have yet to write them.
#ifndef LIST_H
#define LIST_H
#include <cstdlib>
#include <iostream>
#include <fstream>
#include "Node.h"
using namespace std;
template <class NumType>
class List
{
int counter;
bool isEmpty();
const bool print(){
}
public:
Node<NumType> * head;
List()
{
this->head = NULL;
counter = 0;
}
~List()
{
}
//place in an order thart keeps the array in ascending order
void add(ifstream &);
/*
Node* location(Node *){
}
bool remove(const int){
}
bool clear(){
}
const void peek(const Node*){
}
//average of all test scores or just one students test scores?
float average(){
}
char grade(){
}
*/
};
#include "List.cpp"
#endif
//List.cpp
#include "List.h"
using namespace std;
template <class NumType>
bool List<NumType> :: isEmpty()
{
cout << "inside isEmpty" << endl;
return(head == NULL);
}
template <class NumType>
void List<NumType> :: add(ifstream & fin)
{ int dummyID;
NumType tests[3];
string dummyName;
while(fin >> dummyID)
{ fin.ignore();
getline(fin, dummyName);
for(int x = 0; x < 3; x++)
fin >> tests[x];
fin.ignore();
cout << dummyID << endl;
cout <<dummyName << endl;
for(int y = 0; y < 3; y++)
cout << tests[y] << " ";
if(isEmpty())
{
this->head = new Node<NumType>(NULL, tests, dummyID, dummyName);
counter++;cout << "inside" << endl;
}
else
{
Node<NumType> *newNode = new Node<NumType>(NULL, tests, dummyID, dummyName);
Node<NumType> *first = new Node<NumType>(NULL, tests, dummyID, dummyName);
Node<NumType> *second;
first = this->head;
second = this->head->getNext();
//create location() method to handle this!
for(int x = 0; x < counter; x++)
{
if(first->getID() > newNode->getID())
{
head = newNode;
counter++;
break;
}
else if(first->getID() < newNode->getID() && second->getID() > newNode->getID())
{
newNode->setNext(second);
first->setNext(newNode);
counter++;
break;
}
else if(second->getID() < newNode->getID() && second->getNext() == NULL)
{
second->setNext(newNode);
counter++;
break;
}
else
{
first = second;
second = second->getNext();
}
}
}
}
Node<NumType> * temp = head;
for(int x = 0; x <= counter; x++)
{
NumType *arr;
cout << temp->getID() << endl << temp->getName() << endl;
arr = temp->getAllScores();
for(int y = 0; y <3 ; y++)
cout << *(arr+y) << endl;
temp = temp->getNext();
}
}
//Node.h
#ifndef NODE_H
#define NODE_H
#include <cstdlib>
#include <iostream>
using namespace std;
template <class ItemType>
class Node
{
static const int SIZE = 3;
int ID;
ItemType scores[SIZE];
string name;
Node *next;
public:
Node()
{
this->scores[0] = 0;
this->scores[1] = 0;
this->scores[2] = 0;
this->name = "";
this->ID = 0;
this->next = NULL;
}
Node(Node * nPtr, ItemType tests[], int num, string n)
{
this->next = nPtr;
for(int z = 0; z < SIZE; z++)
this->scores[z] = tests[z];
this->ID = num;
this->name = n;
}
~Node(){}
void setNext( Node * );
string getName();
int getID();
ItemType* getAllScores();
Node* getNext();
};
#include "Node.cpp"
#endif
Node.cpp
#include "Node.h"
#include <string>
using namespace std;
template <class ItemType>
void Node<ItemType> :: setNext( Node * nextPtr)
{
cout << "inside setNext()" << endl;
this->next = nextPtr;
cout << "exited setNext()" << endl;
}
template <class ItemType>
string Node<ItemType> :: getName()
{
return (this->name);
}
template <class ItemType>
int Node<ItemType> :: getID()
{
return (this->ID);
}
template <class ItemType>
ItemType* Node<ItemType> :: getAllScores()
{
return (this->scores);
}
template <class ItemType>
Node<ItemType> * Node<ItemType> :: getNext()
{
return (this->next);
}

Answer 1

I think I found the error. The first time you run the add method head is set, but the second time you are trying to set the second value. You have this code
first = this->head;// this is the first element
second = this->head->getNext(); // this is null (hast been assign yet
then you go inside of a for loop, and in the first "else if" statement you have this:
else if(first->getID() < newNode->getID() && second->getID() > newNode->getID())
when you say second->getID() you are saying null->getID() causing you a segmentation fault.
I hope this fixes your problem. Good luck!