Problem with friend function Union(), DisplaySet()

[shawnbon11]

I am having trouble with a program where I am given a set A and a set B and I have to find the union of the two sets. I know my program is correct, but I am wondering why I am getting a linking error. Can somebody please help me?

//my OrderedLL.h file

#ifndef OrderedLL_H
#define OrderedLL_H

template<class T>
class OrderedLL
{
private:
	
	struct NODE
	{
		T info;
		NODE *next;
	};
	
	NODE *list;

public:

	friend void Union(OrderedLL<T> a, OrderedLL<T> b, OrderedLL<T> &aUb);
	friend void DisplaySet(OrderedLL<T> set);

	//constructor
	OrderedLL();
	//insert item x
	void Insert(T x);
	//display the linked list
	void Display();
	//delete x from the linked list
	void DeleteNode(T x);
	//display a set
	void DisplaySet();
	//destructor
	~OrderedLL();

};

//constructor
template<class T>
OrderedLL<T>::OrderedLL()
{
	list = NULL;
}

//insert x in linked list
template<class T>
void OrderedLL<T>::Insert(T x)
{
	NODE *p = list, *q = list, *r;
	//create new node using r, then insert value of x and NULL terminate it
	r = new(NODE);
	r->info = x;
	r->next = NULL;
	
	while(p != NULL && p->info < x)
	{
		q = p;
		p = p->next;
	}
	
	if(p == list)//x is the first info
	{
		list = r;
		r->next = p;
	}
	else if(p == NULL)//x is the last info
	{
		q->next = r;
	}
	else//x is neither the first nor the last info
	{
		r->next = p;
		q->next = r;
	}
}

//display the linked list
template<class T>
void OrderedLL<T>::Display()
{
	NODE *p = list;
	
	while(p != NULL)
	{
		cout << p->info << "-->";
		p = p->next;
	}
	cout << "NULL\n";
}

//delete x from the linked list
template<class T>
void OrderedLL<T>::DeleteNode(T x)
{
	NODE *p = list, *r = list;

	while(p->info != x)
	{
		r = p;
		p = p->next;
	}

	if(p == list)
	{
		//delete the first node
		list = p->next;
		delete(p);
	}
	else
	{
		r->next = p->next;
		delete(p);
	}
}

//destructor
template<class T>
OrderedLL<T>::~OrderedLL()
{
	NODE *p = list;
	do
	{
		p = list;
		list = p->next;;
		delete(p);
	}while(list != NULL);
}

template<class T>
void Union(OrderedLL<T> a, OrderedLL<T> b, OrderedLL<T> &aUb)
{
	while(a.list != NULL && b.list != NULL)
	{
		if(a.list->info == b.list->info)
		{
			aUb.Insert(a.list->info);
			a.list = a.list->next;
			b.list = b.list->next;
		}
		else if(a.list->info < b.list->info)
		{
			aUb.Insert(a.list->info);
			a.list = a.list->info;
		}
		else//b.list->info < a.list->info
		{
			aUb.Insert(b.list->info);
			b.list = b.list->info;
		}
	}
	
	while(a.list != NULL)
	{
		aUb.Insert(a.list->info);
		a.list = a.list->next;
	}
	
	while(b.list != NULL)
	{
		aUb.Insert(b.list->info);
		b.list = b.list->next;
	}
}

template<class T>
void DisplaySet(OrderedLL<T> set)
{
	while(set.list != NULL)
	{
		cout << set.list->info << "->";
		set.list = set.list->next;
	}
	cout << "NULL" << endl;
}

#endif 

//my .cpp file

#include <iostream>
#include <ctime>
#include "OrderedLL.h"

//Function Prototypes
void Copy(int Set[], OrderedLL<int> &set, int counter);

using namespace std;

int main()
{
	time_t r;
	time(&r);
	cout << "Today is " << ctime(&r) << endl;

	int a[5] = {7, 5, 9, 2, 8};
	int a_count = 5;
	int b[4] = {2, 5, 11, 4};
	int b_count = 4;

	OrderedLL<int> setA, setB, set_union;

	Copy(a, setA, a_count);
	Copy(b, setB, b_count);

	DisplaySet(setA);
	DisplaySet(setB);

	Union(setA, setB, set_union);

	DisplaySet(set_union);

	return 0;
}

void Copy(int Set[], OrderedLL<int> &set, int counter)
{
	for(int i = 0; i < counter; i++)
	{
		set.Insert(Set[i]);
	}
}

//The error I get when I build

1>------ Build started: Project: Proj_6Part_2, Configuration: Debug Win32 ------
1>  Proj_6Part_2.cpp
1>c:\users\shawn\desktop\cpsc131\project6\proj_6part_2\proj_6part_2.cpp(14): warning C4996: 'ctime': This function or variable may be unsafe. Consider using ctime_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
1>          c:\program files\microsoft visual studio 10.0\vc\include\time.inl(86) : see declaration of 'ctime'
1>Proj_6Part_2.obj : error LNK2019: unresolved external symbol "void __cdecl Union(class OrderedLL<int>,class OrderedLL<int>,class OrderedLL<int> &)" (?Union@@YAXV?$OrderedLL@H@@0AAV1@@Z) referenced in function _main
1>Proj_6Part_2.obj : error LNK2019: unresolved external symbol "void __cdecl DisplaySet(class OrderedLL<int>)" (?DisplaySet@@YAXV?$OrderedLL@H@@@Z) referenced in function _main
1>C:\Users\Shawn\Desktop\CPSC131\Project6\Proj_6Part_2\Debug\Proj_6Part_2.exe : fatal error LNK1120: 2 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

[vlad from moscow]

Your friend functions are not template functions. So you did not define them. Instead of them you defined two template functions with the same names. Try to define non-template functions Union and DisplaySet where type int will be used instead of the template parameter T.