C++ Doubly Linked List Template Error Help

[rgpii]

I am attempting to program a doubly linked list template. My program is setup with the class node defined in a header file,the list itself in a header file and finally the main in a separate cpp file which calls the list header. The list header calls the node header. The error I am receiving is
"dbList<int>::dbList(int, Node<int>*, Node<int>*)", referenced from:
_main in dbList.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

Here is the code below:

template<class dtype>
class Node
{
public:
int position;
dtype data;
Node<dtype>* next;
Node<dtype>* prev;
Node( dtype data, Node<dtype>* next=0, Node<dtype>* prev=0);
};

#include "dbNode.h"
#include<iostream>
using namespace std;

template <typename Type> 
class dbList
{
private:
	int size;
	Node<Type>* head;
	Node<Type>* tail;
	
public:
	dbList(int size=0,Node<Type>* head=0,Node<Type>* tail=0); 
	void insertNode(Type v);
	void insertNode(Type v, int pos);
	void displayList();
	void tester();
};

template <typename Type>
void dbList<Type>::insertNode(Type v)
{
	Node<Type>* tempa;
	Node<Type>* tempb;
	Node<Type>* tempc;
	tempa->data=v;
	
	if(this->head==0)
	{
		this ->head = tempa;
		this ->head ->next = 0;
		this ->head ->prev = 0;
		this ->size++;
		this ->head->position=size;
	}
	
	else  
	{
		tempb = this ->head;
	if(tempb ->next == 0)
	{	
		tempa->next = tempb->next;
		tempa ->prev = tempb;
		tempb ->next = tempa;
		this ->tail = tempa;
		this ->size++;
		this ->tail->position=size;
	}
	
	else
	{
		tempc = this ->tail;
		tempa ->next = tempc ->next;
		tempa ->prev = tempc;
		tempc ->next = tempa;
		this ->tail = tempa;
		this ->size++;
		tempc->position=size;
	}
	
	}
}
template<typename Type>
void dbList<Type>::displayList()
{
	Node<Type> *tempa;
	tempa = this ->head;
	if(tempa == 0)
	{
		cout<<"This list is empty";
	}
	else
	{
		cout<<"List- ";
		while(tempa != 0)
		{
			cout<< tempa -> data;
			cout<< " ";
			tempa = tempa -> next;
		}
		cout<< "\n";
	}
}
template<typename Type>
void dbList<Type>::tester()
{
int selection;
Type tempa;
cout << "What would you like to do\n";
cout << "1. Insert Item\n"<<"2.Print List\n"; 
cin>>selection;
cout<<"\n";
switch(selection)
{
	case 1:cout<<"What value would you like to add?";
		cin>>tempa;
		cout<<"\n";
		insertNode(tempa);
		break;
		
	case 2:dbList<Type>::displayList();
		break;
}
}

#include"dbList.h"
#include <iostream>
using namespace std;



int main () 
{
	dbList<int> intlist;
	intlist.tester();

}

This is my first time using templates. Please point out anything that does not make sense at all. I've been going through "C++ Templates the complete guide" , but it really is not very clear to me in some spots. So any help would be greatly appreciated. Thank you for your time.

[NicAx64]

dbList(int size=0,Node<Type>* head=0,Node<Type>* tail=0);

it seems that you only declare that method. you have to implement it.

[rgpii]

That was supposed to be the constructor. It was the syntax I saw other templates using. Is that incorrect?

I just changed

dbList(int size=0,Node<Type>* head=0,Node<Type>* tail=0);

to

dbList()
{
int size=0;
Node<Type>* head=0;
Node<Type>* tail=0;
}

It compiled but those variables were unused and the tester method sayd Bus Error when I try to input values. Any thoughts? I mean obviously the constructor is not working in the traditional form like I just used because the variables arent being implemented at all

[Agni]

template <typename Type>
void dbList<Type>::insertNode(Type v)
{
	Node<Type>* tempa;
	Node<Type>* tempb;
	Node<Type>* tempc;
	tempa->data=v;
	
	if(this->head==0)
	{
		this ->head = tempa;
		this ->head ->next = 0;
		this ->head ->prev = 0;
		this ->size++;
		this ->head->position=size;
	}
	
	else  
	{
		tempb = this ->head;
	if(tempb ->next == 0)
	{	
		tempa->next = tempb->next;
		tempa ->prev = tempb;
		tempb ->next = tempa;
		this ->tail = tempa;
		this ->size++;
		this ->tail->position=size;
	}
	
	else
	{
		tempc = this ->tail;
		tempa ->next = tempc ->next;
		tempa ->prev = tempc;
		tempc ->next = tempa;
		this ->tail = tempa;
		this ->size++;
		tempc->position=size;
	}
	
	}
}

line 7: should be the first segmentation fault since 'tempa' is not pointing to anything and you try to deference it and assign value to 'data'

line11: this->head = tempa is also wrong, tempa is nothing, and you are assigning this->head to nothing, when you call display it'll probably crash again.

Probable solution:
Remove line 7.
Before you assign 'tempa' to this->head, create a new node and point tempa to it and then assign value to 'data'

something like

temp = new Node<int>();

[rgpii]

First, thank you for all of the replies. Those combined with the generic doubly linked list code snippet has actually allowed my code to compile. I am now receiving a bus error and I am at a complete loss as to why this is happening. Here is my new code.

#include<iostream>
using namespace std;

template <typename Type> 
class dbList
{
public:
	struct Node
	{
		Type data;
		Type position;
		Node* prev;
		Node* next;
		Node(Type t, Node* p, Node* n) : data(t), prev(p), next(n) {}//Could you please explain the purpose this line here? Why am I initializing prev and next to p and n
	};
	
	dbList(): size(0), head(0), tail (0) {} 
	void insertNode(Type v);
	void insertNode(Type v, int pos);
	void displayList();
	void tester();

private:

	int  size;
	Node* head;
	Node* tail;
	
};

template <typename Type>
void dbList<Type>::insertNode(Type v)
{
	Node* tempa;
	Node* tempb;
	Node* tempc;
	tempa->data=v;
	
	if(this->head==0)
	{
		this ->head = tempa;
		this ->head ->next = 0;
		this ->head ->prev = 0;
		this ->size++;
		this ->head->position=size;
	}
	
	else  
	{
		tempb = this ->head;
	if(tempb ->next == 0)
	{	
		tempa->next = tempb->next;
		tempa ->prev = tempb;
		tempb ->next = tempa;
		this ->tail = tempa;
		this ->size++;
		this ->tail->position=size;
	}
	
	else
	{
		tempc = this ->tail;
		tempa ->next = tempc ->next;
		tempa ->prev = tempc;
		tempc ->next = tempa;
		this ->tail = tempa;
		this ->size++;
		tempc->position=size;
	}
	
	}
}
template<typename Type>
void dbList<Type>::displayList()
{
	Node *tempa;
	tempa = this ->head;
	if(tempa == 0)
	{
		cout<<"This list is empty";
	}
	else
	{
		cout<<"List- ";
		while(tempa != 0)
		{
			cout<< tempa -> data;
			cout<< " ";
			tempa = tempa -> next;
		}
		cout<< "\n";
	}
}
template<typename Type>
void dbList<Type>::tester()
{
int tester=0;
int selection;
Type tempa;
while(tester==0)
{
	
cout << "What would you like to do\n";
cout << "9. Exit\n" << "1. Insert Item\n"<<"2.Print List\n"; 
cin>>selection;
cout<<"\n";


switch(selection)
{
	case 1:cout<<"What value would you like to add?";
		cout<< "\n";
		cin>>tempa;
		cout<<"\n";
		insertNode(tempa);
		break;
		
	case 2:dbList<Type>::displayList();
		break;
	case 3:tester=1;
		break;
}
}
}

#include"dbList.h"
#include <iostream>
using namespace std;



int main () 
{
	dbList<int> intlist;
	intlist.tester();

}

I am recieving a bus error after I try to input a second value into a new node.

[Dave Sinkula]

template <typename Type>
void dbList<Type>::insertNode(Type v)
{
   Node* tempa;
   Node* tempb;
   Node* tempc;
   tempa->data=v;

Where does tempa point?

[Agni]

rgpii i don't think you are reading any of the anwers carefully. I see the same mistakes in your code again, which I pointed out in my post earlier. If you don't read and apply what' been suggested then there's really no point.