How to declare destructor of a templated class

Question

I get error while trying to compile following class

Stack.cpp:28: error: expected constructor, destructor, or type conversion before ‘::’ token

#include <iostream>
using namespace std;

template <class T>
class Stack
{
public:
    Stack(): head(NULL) {};
    ~Stack();

    void push(T *);
    T* pop();

protected:
    class Element {
    public:
            Element(Element * next_, T * data_):next(next_), data(data_) {}
            Element * getNext() const { return next; }
            T * value() const {return data;}
    private:
            Element * next;
            T * data;
    };

    Element * head;
};

Stack::~Stack()
{
    while(head)
    {
            Element * next = head->getNext();
            delete head;
            head = next;
      }
 }

Answer 1

You are declaring a template class. You can either:

• implement the destructor within the class declaration, like this

  public:
      Stack(): head(NULL) {};
      ~Stack() {
          // ...
      }
  

• define the templated destructor outside the class declaration, like this

  template <class T>
  Stack<T>::~Stack()
  {
      // ...
  }
  

However, if you attempt to define just Stack::~Stack() then the compiler does not know which type T you are implementing the destructor for.

Answer 2

template<typename T>
Stack<T>::~Stack()
{
    //...
}

This is generally valid for every method you define outside of the class' declaration, not just the destructor.