Message-ID: <007f01bdf31d$ffc147e0$ef6195cc@uic>
From: "Andrew Deren" <aderen AT interaccess DOT com>
To: "DJGPP" <djgpp AT delorie DOT com>
Subject: Templates Problem
Date: Thu, 8 Oct 1998 19:44:39 -0500
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Reply-To: djgpp AT delorie DOT com

I have created a simple linked list template.
However, compilation goes fine, but when linking
I get errors:
c:/djgpp/tmp/ccaaaaaa1.o(.text+0x24):test.cpp: undefined reference to
`List<int>::List(void)'
c:/djgpp/tmp/ccaaaaaa1.o(.text+0x34):test.cpp: undefined reference to
`List<int>::add(int *)'

I hope nobody minds posting the source here.
Can anyone help me with that, please.
Thank you.

///////////////////////////////////////////////////////////////
// FILE: list.h
///////////////////////////////////////////////////////////////
#ifndef __LIST_H
#define __LIST_H

// a single node
template <class ListType>
class Node
{
 Node(void):next(NULL), prev(NULL), elem(NULL) {}

 Node<ListType>* next;
 Node<ListType>* prev;
 ListType* elem;
};

template <class ListType>
class List
{
public:
 List(void);
 ~List(void);

 bool add(ListType* new_elem);

 int get_count(void) const { return count;}

 // sets the current to head, call get_next to start getting elements
 void start_loop(void) {current = head;}

 // get current element and advance current to next.
 // if there are no more element null is returned
 ListType* get_next(void);

 // removes all the links and elements that those
 // links refer to
 void delete_elements(void);

 // get a value at index (1 is the first one)
 ListType* get_at(int index);

protected:
 int count;

 Node<ListType> *head;
 Node<ListType> *tail;
 Node<ListType> *current;
};


#endif // __LIST_H

///////////////////////////////////////////////////////////////
// FILE: list.cpp
///////////////////////////////////////////////////////////////
template <class ListType>
List<ListType>::List(void)
:head(NULL), tail(NULL), current(NULL), count(0)
{

}

// remove all links (does not remove instances of
// the classes that are contained in the list.
// Use delete_elements to do that
template <class ListType>
List<ListType>::~List(void)
{
 // delete all links
 while (head) {
  current = head->next;
  delete head;
  head = current;
 }
}

template <class ListType>
bool List<ListType>::add(ListType* new_elem)
{
 tail->next = new Node<ListType>();

 if (!tail->next)
  return false;

 tail = tail->next;
 tail->elem = new_elem;

 count++;

 return true;
}

template <class ListType>
void List<ListType>::delete_elements(void)
{
 // delete all links
 while (head) {
  current = head->next;
  delete head->elem;
  delete head;
  head = current;
 }
 head = tail = current = NULL;
 count = 0;
}

// get current element and advance current to next.
// if there are no more element null is returned
template <class ListType>
ListType* List<ListType>::get_next(void)
{
 ListType* temp = NULL;

 if (current) {
  temp = current->elem;
  current = current->next;
 }

 return temp;
}


// get a value at index (1 is the first one)
template <class ListType>
ListType* List<ListType>::get_at(int index)
{
 int i = 1;

 Node<ListType>* temp = head;

 while (temp) {
  if (i == index)
   return temp->elem;

  i++;
  temp = temp->next;
 }

 // could not find a selection at index (out of range)
 return NULL;
}

///////////////////////////////////////////////////////////////
// FILE: test.cpp (just for testing)
///////////////////////////////////////////////////////////////

#include <stdio.h>
#include "list.h"


int main(int argc, char** argv)
{
 int test1 = 3;
 int test2 = 5;
 int test3 = 7;

 List<int> list;

   list.add(&test1);
   list.add(&test2);
   list.add(&test3);

   list.start_loop();

   int *temp;

   while ((temp = list.get_next()) != NULL) {
    printf("%d ", *temp);
   }

   return 0;
}

///////////////////////////////////////////////////////////////