"undefined reference" при инклюде внешних классов/библиотек

#ifndef STACK_H_
#define STACK_H_
 
template<class T>
class ComplexStack {
private:
    T d;
    struct ComplexStack *next;
public:
    void push(ComplexStack* &stack, T d);
    T pop(ComplexStack* &stack);
    void clear(ComplexStack* &stack);
};
 
template<class T>
class Stack: ComplexStack<T> {
private:
    ComplexStack<T> * cs;
public:
    void push(T in);
    T pop();
    void clear();
};
 
#endif /* STACK_H_ */

#include "Stack.h"
 
template<class T>
void ComplexStack<T>::push(ComplexStack* &stack, T d) {
    ComplexStack *pv = new ComplexStack;
    pv->d = d;
    pv->next = stack->next;
    stack = pv;
}
 
template<class T>
T ComplexStack<T>::pop(ComplexStack* &stack) {
    if (!stack)
        return 0;
    T temp = stack->d;
    ComplexStack *pv = stack;
    stack = stack->next;
    delete pv;
    return temp;
}
 
template<class T>
void ComplexStack<T>::clear(ComplexStack* &stack) {
    ComplexStack *temp;
    while (stack) {
        temp = stack;
        stack = stack->next;
        delete temp;
    }
}
 
template<class T>
void Stack<T>::push(T in) {
    cs->push(cs, in);
}
template<class T>
T Stack<T>::pop() {
    if (!cs)
        return 0;
    return cs->pop(cs);
}
template<class T>
void Stack<T>::clear() {
    cs->clear(cs);
}

#include <iostream>
#include "Stack.h"
 
using namespace std;
 
int main() {
    Stack<int> s;
    s.push(10);
    cout << s.pop();
    return 0;
}