“cube c2 = c1” is different from “c2 = c1”!

cube c1(1.);

cube c2(2.);

c2 = c1;

cube c1(1.);

cube c2 = c1;

The effect is the same, but what happens is quite different:

=

On the left, we saw that we are calling the operator= member function of object c2.

On the right, we construct the object c2 using c1. We are calling a special constructor, the so-called “copy constructor”, of c2, which gets a reference to the object to be copied (c1 in this case).

class cube : public body {

public:

cube (const float);

cube (const float, const Color *c);

cube (const cube &);

virtual char* identify() const;

virtual float GetVolume() const;

virtual float GetSurface() const;

// the assignment operator

cube& operator= ( const cube & );

protected:

float length;

};

// the copy constructor

cube::cube (const cube& c)

{

length = c.length;

*color = *c.color;

}

Different from the operator member functions, the compiler will automatically generate a copy constructor whether you want it or not, and this is almost never what you really want.

The best is to always supply a copy constructor just to be safe.

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