#include <iostream>
#include <stddef.h>
 
template <typename CountedType>
class ObjectCounter 
{
private:
  static size_t count;    // number of existing objects
 
protected:
  // default constructor
  ObjectCounter() 
  {
    ++count;
  }
 
  // copy constructor
  ObjectCounter (ObjectCounter<CountedType> const&) 
  {
    ++count;
  }
 
  // destructor
  ~ObjectCounter() 
  {
    --count;
  }
 
public:
  // return number of existing objects:
  static size_t live() 
  {
    return count;
  }
};
 
 
// initialize counter with zero
template <typename CountedType>
size_t ObjectCounter<CountedType>::count = 0;
 
 
template <typename CharT>
class MyString : public ObjectCounter<MyString<CharT> > 
{
  //...
};
 
 
int main()
{
  MyString<char> s1, s2;
  MyString<wchar_t> ws;
 
  std::cout << "number of MyString<char>:    "
            << MyString<char>::live() << std::endl;
 
  std::cout << "number of MyString<wchar_t>: "
            << ws.live() << std::endl;
}