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Please consider...

class B
{
virtual ~B() { ... }
}

class D : B
{
virtual ~D() { ... }
}

void f()
{
void* p = malloc(sizeof(D));
new (p) D; // ...placement new
B* b = (B*) p;
b->~B(); // ...is virtual destructor in effect?
free(p);
}

When f() is executed will D::~D() be called?

Thanks,
Andrew.

Andrew Tomazos wrote:
> Please consider...
>
> class B
> {

public:

> virtual ~B() { ... }
> }
;
>
> class D : B

Need public inheritance to convert:
class D : public B

> {
> virtual ~D() { ... }
> }
;
>
> void f()
> {
> void* p = malloc(sizeof(D));
> new (p) D; // ...placement new
> B* b = (B*) p;

That's *not* a good idea. You should do

D* pd = new (p) D; // ...placement new
B* b = pd;

instead.

> b->~B(); // ...is virtual destructor in effect?
> free(p);
> }
>
> When f() is executed will D::~D() be called?

With your current cast from 'p' to a B*, the behaviour is undefined I'm
afraid.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

On May 7, 11:32*pm, Victor Bazarov <v.Abaza...@comAcast.net> wrote:
> > * * void f()
> > * * {
> > * * * * void* p = malloc(sizeof(D));
> > * * * * new (p) D; // ...placement new
> > * * * * B* b = (B*) p;
>
> That's *not* a good idea. *You should do
>
> * * * D* pd = new (p) D; // ...placement new
> * * * B* b = pd;
>
> instead.
>
> > * * * * b->~B(); // ...is virtual destructor in effect?
> > * * * * free(p);
> > * * }
>
> > When f() is executed will D::~D() be called?
>
> With your current cast from 'p' to a B*, the behaviour is undefined I'm
> afraid.

(1) Can you tell me what the difference is between:

new (p) D;
B* b = (B*) p;

and

D* pd = new (p) D;
B* b = pd;

I would have thought they were equivalent? Why aren't they?

(2) If I use your recommended form, will the virtual destructor of
D::~D be called if I call b->~B() ?

Thanks,
Andrew.