Question

After studying the member copying and the assignment operator in C++,
and looking at ” member copying of class ” which explains the conditions where default assignment operator cannot be generated. I am not very clear about the concepts as the following example I tried actually works on g++4.5

#include<iostream>
using namespace std;

class Y{
  int& x;
  const int cx;
public:
  Y(int v1,int v2)
    :x(v1),cx(v2)
  {}
  int getx(){return x;}
  int getcx(){return cx;}
};

int main()
{
  int a = 10;
  Y y1(a,a);
  Y y2 = y1;//assignment
  cout<<y1.getx()<<" "<<y1.getcx();
  return 0;
}

So where am I not getting the concepts. Please suggest other examples (if possible) so that I can understand better.

Answer 1

Y y2 = y1; is not an assignment. It’s a copy constructor call. If you declare and initialize a variable on the same line, a one parameter constructor is called with the right hand side of the equals sign as the parameter. There’s nothing about Y that prevents the default copy constructor from being instantiated (and called).

Try the following:

Y y1(10, 10);
Y y2(11, 11);
y2 = y1;

This should fail, although I can’t test it right now.