Three methods are used to process "self-assignment" in operator ="

Suppose you create a class to save a pointer pointing to a dynamically allocated bitmap.

1 class Bitmap {......};2 class Widget{3    ...4    private:5       Bitmap* pb ;6 };

1 Widget&  Widget::operator= (const Widget& rhs)2 {3    delete pb;4    pb = new Bitmap(*rhs.pb);5    return *this;6 }

The above is an insecure operator = implementation version, because operator = * This and RHS in the function may be the same object. There are three methods to prevent such errors.

Method 1: Traditional Methods

1 Widget&  Widget::operator= (const Widget& rhs)2  {3    if( this == rhs ) return *this;4     delete pb;5     pb = new Bitmap(*rhs.pb);6     return *this;7  }

Method 2:

1 Widget&  Widget::operator= (const Widget& rhs)2  {3      Bitmap* pOrig = pb ;4    5      pb = new Bitmap(*rhs.pb);6      delete pOrig ;7      return *this;8  }

Method 3: the so-called copy and swap Technology

1 Widget&  Widget::operator= (const Widget& rhs)2  {3       Widget temp( rhs ) ;4       swap(temp);5  6       return *this;7  }