Hello,
I am trying to write a templated linked list, and I am having some difficulties with the add() function. It seems like different behavior occurs depending on how I add to my list, but my two test cases don't seem that different to me. I'll post the list.h, and main.cpp. I snipped a bunch of code out of list.h that didn't seem relevant. Also, if you need to see the "position" class, just let me know (just trying to keep the code down to a minimum).
//list.h
///////////////////////////////////////////////////
// List Template
template <class Type>
class List {
public:
// Constructor
List(): head(0), size(0) { }
// Add an element to the list
void add( const Type &element );
// Returns the head of the list
ListNode<Type>* getHead() const { return head; }
// Returns the current size of the list
int getListSize() const { return size; }
private:
ListNode<Type> *head;
int size;
};
//////////////////////////////////////////////////
// ListNode Template
template <class Type>
class ListNode {
public:
// Constructor
ListNode( const Type &element ): data(element), next(0) { }
// Get the node's data
const Type getData() const { return data; }
// Get the next node
ListNode<Type>* getNext() const { return next; }
// Set the next node
void setNext( ListNode<Type> *nextNode ) { next = nextNode; }
private:
const Type &data;
ListNode<Type> *next;
};
///////////////////////////////////////////////////
// '<<' Operator for the list
template <class Type>
ostream& operator<<( ostream &os, const List<Type> & aList) {
ListNode<Type> *currNode;
currNode = aList.getHead();
while(currNode != 0){
os << *(currNode->getData()) << endl;
currNode = currNode->getNext();
}
return os;
}
//////////////////////////////////////////////////////////////////////
// Adds an element to a list. New element becomes the head of the list
template <class Type>
void List<Type>::add(const Type &element) {
ListNode<Type> *newNode = new ListNode<Type>(element);
newNode->setNext(head);
head = newNode;
++size;
}//main.cpp
#include <iostream>
#include "list.h"
#include "position.h"
using namespace std;
int main(){
////////////
//Case 1
List<Position *> *posListA = new List<Position *>();
posListA->add(new Position(1,1));
posListA->add(new Position(2,2));
posListA->add(new Position(3,3));
cout << "Printing final list: \n" << *posListA << endl;
///////////
//Case 2
List<Position *> *posListB = new List<Position *>();
for(int i = 1; i < 4; i++){
posListB->add(new Position(i,i));
}
cout << "Printing final list: \n" << *posListB << endl;
return 0;
}And the output I'm getting:
mike@mike-Lenovo-G550:~/School/comp_2404/templateTestTwo$ ./main
Printing final list:
(3,3)
(2,2)
(1,1)
Printing final list:
(3,3)
(3,3)
(3,3)
I tried my best to debug it, but I'm still not sure why it's happening. In the second 'case', I checked the memory locations associated with each node. It seemed that each node had it's own space in memory. However, every time it the program entered the add function inside the list (around the first line), it would change all the data values to refer to the new 'element' (as in the same memory location).
My main concern/worry is that the first and second cases look identical to me with the exception of a 'for' loop, so I really don't understand why they are producing different outputs.
I'd be appreciative of any help or even reference to literature that could guide me in the right direction.
Thank you.
