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downcasting and dynamic_cast

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Join Date: Jun 2006

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Laiq Ahmed Laiq Ahmed is offline

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downcasting and dynamic_cast

Jul 8th, 2006

I've gone through several books they explain Upcasting as
Base class pointer pointing to Drived class Object

this definition is correct.
Downcasting:

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Drived class pointer pointing to base class object..

i got a bit confused.....not having crystal clear image in my mind.....
if the above definition is correct... whats wrong with the below code

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class Shape {
public:
   virtual ~Shape() {}
};
class Circle: public Shape {
public: 
   ~Circle() {} 
};
 
int main() 
{
      //why this can't work ...........according to definition....
    //  Circle* c = dynamic_cast<Shape*>(new Shape);
 
     //why this
     Shape* s = new Shape;
     Circle* c = dynamic_cast<Circle*>(s);
     return 0;
}
class Shape {
public:
   virtual ~Shape() {}
};
class Circle: public Shape {
public: 
   ~Circle() {} 
};
 
int main() 
{
      //why this can't work ...........according to definition....
    //  Circle* c = dynamic_cast<Shape*>(new Shape);
 
     //why this
     Shape* s = new Shape;
     Circle* c = dynamic_cast<Circle*>(s);
     return 0;
}

I know that downcasting is performed between polymorphic types

. I m bit confused with its definition and implementation... please give me the solid concept

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Dave Sinkula Dave Sinkula is offline

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long time no c

Re: downcasting and dynamic_cast

Jul 8th, 2006

Hmm. Clues here: http://www.gotw.ca/gotw/017.htm ?

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