Re: delete an inherited class

On 27 Apr., 20:39, Free0...@[EMAIL PROTECTED]
 wrote:
> if i make a class that inherit another class, when i delete the
> pointer casted to the inherited class, only the destructor of the
> inherited class fires, the base class does not.
>
> ex:
>
> class shape
> {
>  ~shape()
> }
>
> class square : class shape
> {
>  ~square()
> }
>
> square pSquare = new square();
>
> shape pShape = dynamic_cast<shape *>(pSquare);
>
> delete pShape;  <== only calls  ~shape()

Please ensure that code snippets are valid
C++, otherwise it's hard to distinguish what
your actual problem is. Let's first transform
this into syntactically valid C++ (Your comments
imply that your program compiles):

class shape
{
public:
  ~shape(){}
};

class square : public shape
{
public:
  ~square(){}
};

int main() {
   square* pSquare = new square();

   shape* pShape = dynamic_cast<shape *>(pSquare);

   delete pShape; // <== only calls  ~shape()
}

Anything might happen in the very last statement,
because you are in "Undefined Behavior" land (something
like Alice's Wonderland, but not so funny ;-)

The rule behind this is [expr.delete]/3:

"In the first alternative (delete object), if the static
type of the operand is different from its dynamic type,
the static type shall be a base class of the operand’s
dynamic type and the static type shall have a virtual
destructor or the behavior is undefined.[..]"

In other words: If you want to perform a polymorphic
delete, the base class destructor must be virtual:

class shape
{
public:
  virtual ~shape(){}
};

HTH & Greetings from Bremen,

Daniel Krügler


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