Question

Possible Duplicate:
Why should the copy constructor accept its parameter by reference in C++?
Can a object be passed as value to the copy constructor

Consider this piece of code:

class complex{
        private:
                double re, im;
        public:
                complex(double _re, double _im):re(_re),im(_im){}
                complex(complex c):re(c.re),im(c.im){}
};

When compiled, I got an error message: invalid constructor; you probably meant ‘complex (const complex&)’

In the book C++ Programming Language, it is written that:

The copy constructor defines what copying means – including what
copying an argument means – so writing

complex : complex(complex c) :re(c.re) , im(c.im) { } // error

is an error because any call would have involved an infinite recursion.

Why does this cause infinite recursion? It doesn’t make sense.

Answer 1

Passing by value means that the parameter is copied into the function. That calls the copy constructor.

If your copy constructor parameter is pass-by-value… It would call itself… over and over again…