Re: delete an inherited class

=?ISO-8859-1?Q?Daniel_Kr=FCgler?= <>
Sun, 27 Apr 2008 15:43:41 CST
On 27 Apr., 20:39, 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.


class shape

class square : class shape

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

class square : public shape

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
  virtual ~shape(){}

HTH & Greetings from Bremen,

Daniel Kr?gler

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