Question

#include <iostream>


int main(void)
{

class date {
private:
  int day;
  int month;
  int year;
public:
  date( )  { std::cout << "default constructor called" << std::endl; }
  date& operator=(const date& a) { std::cout << "copy constructor called" << std::endl; day=a.day; month=a.month; year=a.year; }
  date(int d ,int m ,int y  ) : day(d),month(m),year(y){ std::cout << "constructor called" << std::endl; }
  void p_date(){ std::cout << "day=" << day << ",month=" << month  << ",year=" << year << std::endl; }
  date& add_day(int d) { day += d; return  *this;}
  date& add_month(int d) { month += d;return  *this; }
  date& add_year(int d) { year += d;return  *this; }

};

class cdate {
  date n;
public:
   cdate(date b) : n(b)  { std::cout << "cdate constructor called" << std::endl;}
   void p_cdate() { n.p_date(); }
};

  cdate ncdate(date(30,1,2012));
  ncdate.p_cdate();
}

When we instantiate ncdate in this code:

1. temporary date object created when we call cdate ncdate(date(30,1,2012));
2. then i expect the call n = b and expect n‘s copy constructor to be called.

n‘s copy constructor is not getting called and i cant figure out why. I know there is something wrong in the 2nd assumption. Note: this is test code only so don’t go over its performance, usability etc.

Answer 1

You have not defined a copy constructor for date, so the implicitly-declared copy constructor is used.

A copy constructor would look like date(date const& other) { }. You have provided a default constructor (date()) and a copy assignment operator (date& operator=(const date& a)). Neither of these is the copy constructor.