cannot understand OOP code

[syedshan]

hello every one


please see the code below. I cannot understand the following

    Bitmap ()        : _hBitmap (0)    {}

and following

    void operator = (Bitmap & bmp)
    {
        if (bmp._hBitmap != _hBitmap)
        {
            Free ();
            _hBitmap = bmp.Release ();
        }
    }

The whole code for the class is as below.

class Bitmap
{
public:
    Bitmap ()        : _hBitmap (0)    {}
    // Transfer semantics
    Bitmap (Bitmap & bmp)
        : _hBitmap (bmp.Release ())
    {}
    void operator = (Bitmap & bmp)
    {
        if (bmp._hBitmap != _hBitmap)
        {
            Free ();
            _hBitmap = bmp.Release ();
        }
    }
    HBITMAP Release ()
    {
        HBITMAP h = _hBitmap;
        _hBitmap = 0;
        return h;
    }
    ~Bitmap ()
    {
        Free ();
    }
    // implicit conversion for use with Windows API
    operator HBITMAP () { return _hBitmap; }
protected:
    Bitmap (HBITMAP hBitmap)
        : _hBitmap (hBitmap)
    {}
    void Free ()
    {
        if (_hBitmap) 
            ::DeleteObject (_hBitmap);
    }

    HBITMAP    _hBitmap;
};

thanks in advance

 

[zeyad.kassaby]

this is is a graphic buffer , which contains a bitmap for showing and saving