Re: Inheritance machanism

From:
Stuart Golodetz <sgolodetz@NdOiSaPlA.pMiPpLeExA.ScEom>
Newsgroups:
comp.lang.c++
Date:
Mon, 26 Oct 2009 20:01:24 +0000
Message-ID:
<f4Gdne81bd6JnXvXnZ2dnUVZ8tSdnZ2d@pipex.net>
Gert-Jan de Vos wrote:

On Oct 26, 3:39 pm, david <david0002...@yahoo.com> wrote:

Here is the code:

class B {
public:
   virtual ~B() {};

};

class D : public B {
public:
   D() { t = new int; }
   ~D() { delete t; }
private:
   int* t;

};

void do_something()
{
    B* pb = static_cast<D*> (new D());
   // do something ...
   delete pb;

}

My question is whether the D class' destructor is called?


B's destructor is public and virtual. Therefore delete pb calls the
destructor
of the dynamic type of *pb, which is D::~D(). This in turn will call
B::B~() to
destruct the base class B subobject after the body of D::~D() has
completed.

 What happens when I use the static_cast?


Nothing since the static type of (new D) is D* already. Even
static_cast<B*>(new D())
will do the same since you assign the result to a B* and B's
destructor is virtual.


Minor nit: The virtuality of B's destructor is only relevant at the
point where delete is invoked on the B*. What's relevant for the
purposes of the cast is that D publicly inherits from B, so a D* is
(implicitly) convertible to a B*. Doing a static_cast to D* is a no-op
(it's already a D*); doing one to B* just replaces a cast that would
otherwise be done implicitly.

Stu

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