一个用模板实现的计数基类

#include <stddef.h>

#include <iostream>

template <typename CountedType>
class ObjectCounter {
  private:
   static size_t count;    // number of existing objects
  
  protected:
   // default constructor
   ObjectCounter() {
    ++ObjectCounter<CountedType>::count;
   }
  
   // copy constructor
   ObjectCounter (ObjectCounter<CountedType> const&) {
    ++ObjectCounter<CountedType>::count;
   }
  
   // destructor
   ~ObjectCounter() {
    --ObjectCounter<CountedType>::count;
   }
  
  public:
   // return number of existing objects:
   static size_t live() {
    return ObjectCounter<CountedType>::count;
   }
};
template <typename CountedType>
size_t ObjectCounter<CountedType>::count = 0;

template <typename CharT>
class MyString : public ObjectCounter<CharT> {
 
};

template < typename CharT>
class MyString2 : public ObjectCounter<CharT >{
 
};
void main()
{
    MyString<char> s1, s2;
 MyString2<char> s3;
    MyString<wchar_t> ws;
    std::cout << "number of MyString<char>: "
  << MyString<char>::live() << std::endl;
 std::cout << "number of MyString2<char>: "
  << MyString2<char>::live() << std::endl;
    std::cout << "number of MyString<wchar_t>: "
  << ws.live() << std::endl;
}

Output:  3 3  1

==========

 
template <typename CharT>
class MyString : public ObjectCounter<MyString<CharT> > {
 
};

template < typename CharT>
class MyString2 : public ObjectCounter<MyString2<CharT> >{
 
};
void main()
{
    MyString<char> s1, s2;
 MyString2<char> s3;
    MyString<wchar_t> ws;
    std::cout << "number of MyString<char>: "
  << MyString<char>::live() << std::endl;
 std::cout << "number of MyString2<char>: "
  << MyString2<char>::live() << std::endl;
    std::cout << "number of MyString<wchar_t>: "
  << ws.live() << std::endl;
}

 

Output : 2 1 1