Re: smart pointer clarifications

"Phil Bouchard" <>
Thu, 21 Aug 2008 05:40:30 -0700
"mlimber" <> wrote in message

On Aug 20, 12:57 pm, "Phil Bouchard" <> wrote:


Either we do it this way or we share the allocator across the container
smart pointer so that the smart pointer uses deallocate(void *):

std::vector<shifted_ptr<int>, shifted_allocator<shifted_ptr<int> > > c1;

std::vector<shifted_ptr<int, shifted_allocator<int> >,
shifted_allocator<shifted_ptr<int, shifted_allocator<int> > > > c2;

I don't even think option 2) is implementable.

I may just be dense, but I still don't see what you're getting at.
Can't you just use the deleter parameter to indicate special deletion?
Something like this (untested):

  class C { /*...*/ };

  template<class Alloc>
  class MyDeleter
    Alloc& m_alloc;

    typedef typename Alloc::value_type T;

    MyDeleter( Alloc& alloc ) : m_alloc( alloc ) {}

    // Might want a const T* version also
    void operator()( T* const ptr )
      m_alloc.destroy( ptr );
      m_alloc.deallocate( ptr, sizeof(T) );

  void Foo( MyAllocator<C>& alloc, const C& initVal )
    typedef std::vector< std::tr1::shared_ptr<C> > VSPC;
    VSPC v( 10 );
    for( VSPC::iterator it=v.begin(); it != v.end(); ++it )
      // Could hide these next lines in a factory function
      C* const c = alloc.allocate( sizeof(C) );
      alloc.construct( c, initVal );

      it->reset( c, MyDeleter( m_alloc ) );
    // ...

Now, when the vector "v" goes out of scope, the shared_ptrs use the
"alloc" object to deallocate their pointees.

What you are suggesting is very similar to option 2) I was anteriorly
explaining. In my case I was using the allocator passed in as a template
parameter as a deleter so that there is no need to repeatedly call the
overloaded constructor shared_ptr(T *, D *). I can't imagine calling this
special constructor for each node pointer inside a container in a flexible
way. If I forget calling it for one pointer the compiler will not report
any compilation error.


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