Question

I am implementing an Ordered List data structure in C++ using class templates.For simplicity, I implemented each constructor and function inline. I made my own Node class for this project.

The compiler error is pasted at the bottom of this question. “undefined reference to `Node::~Node()'”. This is my first time working with templates and I’ve never seen this error before. I have no idea where to begin.
Any help would be appreciated!

Node.h

#ifndef NODE_H
#define NODE_H

#include <iostream>
#include <cstdlib>

template <class E>
class Node {
public:
    Node(const E init_data = NULL, Node<E>* init_link = NULL){data = init_data; link = init_link;}
    Node(const Node<E>& orig){data = orig.getData(); setLink = NULL;}
    virtual ~Node();

    E getData() const{return data;}
    void setData(E newData){data = newData;}

    Node<E>* getLink(){return link;}
    void setLink(Node<E>* nextLink) {link = nextLink;}
private:
    E data;
    Node<E>* link;
};

#endif  /* NODE_H */

MyOrderedList.h

#ifndef MYORDEREDLIST_H
#define MYORDEREDLIST_H

#include <iostream>
#include <cstdlib>
#include "Node.h"

template <class E>
class MyOrderedList;
template <class E>
std::ostream& operator <<(std::ostream& out, const MyOrderedList<E>& list);

template <class E>
class MyOrderedList {
public:
    MyOrderedList()
    {/*IMPLEMENTATION*/}

    MyOrderedList(const MyOrderedList<E>& orig)
    {/*IMPLEMENTATION*/}

    void operator =(const MyOrderedList<E>& orig)
    {/*IMPLEMENTATION*/}

    virtual ~MyOrderedList()
    {/*IMPLEMENTATION*/}

    bool remove(E data)
    {/*IMPLEMENTATION*/}

    MyOrderedList<E> kLargest(int k) const
    {/*IMPLEMENTATION*/}

    E get(int pos) const
    {/*IMPLEMENTATION*/}

    void insert(E data)
    {/*IMPLEMENTATION*/}

    MyOrderedList<E> operator +(const MyOrderedList<E>& list)
    {/*IMPLEMENTATION*/}

    friend std::ostream& operator <<(std::ostream& out, const MyOrderedList<E>& list)
    {/*IMPLEMENTATION*/}

private:
    Node<E>* head;
    int size;
};

#endif  //MYORDEREDLIST_H

main.cpp

#include <cstdlib>
#include <iostream>
#include "MyOrderedList.h"

using namespace std;

int main(int argc, char** argv) 
{
    MyOrderedList<int> list;
    list.insert(5);
    std::cout << list << std::endl;;

    return 0;
}

Compiler Error

g++     -o dist/Debug/Cygwin-Windows/project7_windows build/Debug/Cygwin-Windows/main.o  
build/Debug/Cygwin-Windows/main.o: In function `_ZN4NodeIiE7getLinkEv':
/cygdrive/c/Users/John/Desktop/Dropbox/Data Structures/Project7 Windows/MyOrderedList.h:(.rdata$_ZTV4NodeIiE[vtable for Node<int>]+0x8): undefined reference to `Node<int>::~Node()'
/cygdrive/c/Users/John/Desktop/Dropbox/Data Structures/Project7 Windows/MyOrderedList.h:(.rdata$_ZTV4NodeIiE[vtable for Node<int>]+0xc): undefined reference to `Node<int>::~Node()'
collect2: ld returned 1 exit status
make[2]: *** [dist/Debug/Cygwin-Windows/project7_windows.exe] Error 1

make[1]: * [.build-conf] Error 2
make: * [.build-impl] Error 2

Answer 1

This

class Node {
  virtual ~Node(); 
};

declares (but does not define) a virtual destructor for Node (the templateness does not matter here). You will either need to

1. delete this line (thus going with the compiler provided default implementation) or
2. provide an definition as well:

.

class Node {
  virtual ~Node() { /* put your dtor logic here */ } 
};

Do not be affraid to delete the declaration uless you are planning to inherit from Node as you cannot put much logic in Node’s dtor: it does not know much about its template type. Unless you are planning to delete the pointer to the next node (Node::link), which is probably a dangerous proposition