Re: [Boost-users] std::vector< boost::shared_ptr<int> >::pop_back()

From: bringiton bringiton (kneeride_at_[hidden])
Date: 2006-07-10 10:28:09

holy! you learn something every day. you can call the destructor of an
object (before destruction)

this is a trap for me because i dont clean up my variables in destructors.

class A {
public:
  A() {
  counter = 0;
}
~A() {
  counter++;
  std::cout << "~A(): " << counter << std::endl;
}
int counter;
};

int main(int argc, char* argv[])
{
 A a;
 a.~A();
 return 0;
}
NOTE: destructor gets called twice.
(so it's probably a good idea to NULL pointers in destructors)

On 7/11/06, bringiton bringiton <kneeride_at_[hidden]> wrote:
>
>  >>just look at the include files:
>
>  i looked at the header, but got a little confused.
> i don't see how you can call a destruct of a a memory space that still
> exists. ie a C version of a vector.
>
> shared_ptr<int> list[1024];
> int n = 0;
>
> // add an item
> shared_ptr<int> newItem(new int(1));
> list[n++] = newItem;
>
> // remove the tail item
> n--;
> // destructor never called
>
> is it possible to call a destructor of an object that exists?
> what then happens then the object goes out of scope? the destructor will
> be called twice.
>
> (or maybe i am completely missing the point)
>
> BTW: not sure if above code compiles (did it in my head)
>
>
> On 7/10/06, Boris Breidenbach <Boris.Breidenbach_at_[hidden]>
> wrote:
> >
> > On Mon, Jul 10, 2006 at 03:58:19PM +1000, bringiton bringiton wrote:
> > > This question is based on curiosity. How does std::vector::pop_back()
> > call
> > > the destructor of the item getting removed?
> > >
> > > i understood std::vector to be a contigious array of memory, therefore
> > an
> > > item's memory does not go out of scope when being popped. ie the item
> > goes
> > > out of scope when the entire array goes out of scope.
> >
> > just look at the include files:
> >
> > bits/stl_vector.h says:
> > void
> >      pop_back()
> >      {
> >        --this->_M_impl._M_finish;
> >        std::_Destroy(this->_M_impl._M_finish);
> >      }
> >
> > so the destructor is called in std::_Destroy.  Which can be found in
> > bits/stl_construct.h:
> > /**
> >   * @if maint
> >   * Destroy the object pointed to by a pointer type.
> >   * @endif
> >   */
> > template<typename _Tp>
> >    inline void
> >    _Destroy(_Tp* __pointer)
> >    { __pointer->~_Tp(); }
> >
> > It just calls the destructor.
> >
> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
> > http://lists.boost.org/mailman/listinfo.cgi/boost-users
> >
>
>