g++ LinkedQueueMain.cpp -o LinkedQueueMain
/tmp/ccqwStpK.o: In function `main':
LinkedQueueMain.cpp:(.text+0x2ee): undefined reference to `LinkedQueue<char>::operator=(LinkedQueue<char> const&)'
collect2: ld returned 1 exit status

// LinkedQueue.h

#ifndef LINKEDQUEUE_H
#define LINKEDQUEUE_H

#include <iostream>
#include "RuntimeException.h"
#include "LinkedList.h"

template<typename T> class LinkedQueue;

template<typename T>
std::ostream& operator<<(std::ostream& out, const LinkedQueue<T>& queue);

template<typename T>
class LinkedQueue {
private:
   LinkedList<T> ll;

public:
   // user-defined exceptions
   class QueueEmptyException : public RuntimeException {
   public:
     QueueEmptyException() : RuntimeException("Access to an empty queue") {}
   };

   LinkedQueue() { } // constructor
   ~LinkedQueue() { } // destructor
   LinkedQueue(const LinkedQueue& queue) { ll = queue.ll; } // copy constructor
   LinkedQueue& operator=(const LinkedQueue& queue); // assignment operator
   
   // I have cut out accessory function declarations
   
   friend std::ostream& operator<< <>(std::ostream& out, const LinkedQueue<T>& queue); // overload <<
};

//-------------------------------------------------------------------------------------------------------------------------

template<typename T>
LinkedQueue<T>& LinkedQueue<T>::operator=(const LinkedQueue& queue) {
	ll = queue.ll;
	return *this;
}

// other functions defined here I just cut them out for space

#endif

#include "LinkedQueue.h"
#include <iostream>
#include <string>
#include <iterator>
using namespace std;

int main()
{
  LinkedQueue<char> queue;
  LinkedQueue<char> queue_copy;

  //===== enqueue() =====
   
  queue.enqueue('1');
  queue.enqueue('2');
  queue.enqueue('3');
  queue.enqueue('4');
  queue.enqueue('5');
  queue.enqueue('6');
   
  queue_copy = queue;  //THIS IS WHERE I BELIEVE THE PROBLEM IS
  cerr << "assigning queue to queue_copy, queue_copy = ";
  cerr << queue_copy << endl;
  cerr << "size of queue_copy = " << queue_copy.size() << endl;
  cerr << "first of queue_copy = " << queue_copy.first() << endl << endl;

return 0;
}

ll = queue.ll;

//operators
//=
Complex& Complex::operator=(Complex const& aCplx){
    if (this != &aCplx){
        mNum.Im = aCplx.getIm();
        mNum.Re = aCplx.getRe();
    }
    return *this;
}