What Compile Do When An Empty Class Is Declared?

• conclusion: when an empty class is declared, the compile will generate some members by default.
  (1) default constructor;
  (2) copy constructor;
  (3) operator=();
  (4) default destructor;
• code

// the mepty class
class Empty{
};

//euqal to following
class Empty{
public:
    Empty(){};
    Empty(const Empty&){};
    Empty& operator=(const Empty&){return *this};
    inline ~Empty(){};
};

if user declares a constructor, the compile will not generate default constructor

• explaination: when a constrcutor is decalred in C++, the compile will not generate default constructor any more. Due to compile regards you do not need a default constructor anymore.
• code

// the mepty class
class Empty{
 public:
    Empty(int val):m_data(val){}
  private:
    int m_data;
};

//equals to following
class Empty{
public:
    Empty(int val):m_data(val){}
    //Empty(){};
    Empty(const Empty&){};
    Empty& operator=(const Empty&){return *this};
    inline ~Empty(){};
};