Re: Rebirthing an object... just making sure

From:

"Tom1s # hilidhe" <toe@lavabit.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 10 Jan 2008 16:47:04 GMT

Message-ID:

<Xns9A21AABD2DBF2toelavabitcom@194.125.133.14>

James Kanze <james.kanze@gmail.com> wrote in comp.lang.c++:

ListBox *const ptemp = p_list;
delete p_list;

You doubtlessly mean "p_list->~ListBox" here.

Yes thanks for that.

    p_list = 0;
    ::new(ptemp) ListBox();
    p_list = ptemp;

...which would probably be better as:

template<class T>
void RebirthObject(T *&pobj)
{
    T *const ptemp = pobj;
    delete pobj;

Again: "pobj->~T()"

And again thanks.

    pobj = 0;
    ::new(ptemp) T();
    pobj = ptemp;
}

And of course, if the constructor of T throws, you still leak
the memory. You really need something like:

    template< typename T >
    void
    renewObject( T*& obj )
    {
        // Fail if object has a derived type...
        assert( typeid( *obj ) == typeid( T ) ) ;
        obj->~T() ;
        try {
            new( obj ) T ;
        } catch ( ... ) {
            ::operator delete( obj ) ;
            obj = NULL ;
            throw ;
        }
    }

I'm intending for there to be a leak, because the dialog's class code
deletes its controls automatically when the dialog is closed.

--
Tom1s # hilidhe