RE: [boost] [serialization] shared_ptr and binary archives

From: David Tonge (david.tonge_at_[hidden])
Date: 2004-03-09 05:55:40

I've been corresponding privately with Robert for a while about the
serialization library and he's encouraged me to start contributing to
this forum.  Recently I've been looking at using shared_ptr with the
serialization tools as this is core to how I plan to use the library.

We found that it was fine to serialize a shared_ptr<A> which held an A*.
However, if there were a derived class B which was a public A then it
wasn't possible to serialize a shared_ptr<A> which held a B* into an
archive.  The workaround for this, was to do this...

     BOOST_CLASS_EXPORT(boost::detail::sp_counted_base_impl<
                             B*, 
                             boost::checked_deleter<B>
                             >)

That seems to give the library enough information to be able to
serialize a shared_ptr<A> that holds a B*.  To save typing I now use a
macro HACK_SERIALIZATION_EXPORT_SHARED_POINTER(T) which is included in
the attached file.

Now let me introduce a new problem.  I seem to have uncovered another
bug.  Using the workaround above I can demonstrate expected behaviour
with text archives.  However, if I try to serialize a shared_ptr<A>
containing a B* to a BINARY archive then I get an assertion failure
(puzzlingly in basic_text_oarchive.hpp - line 133).  I don't have any
problems serializing shared_ptr<A>s containing A*s to binary archives,
and I don't have any problems at all with text archives.

The file I've attached is a heavily modified version of
demo_shared_ptr.cpp which performs four tests:

  1. Serialize shared_ptr<A>s containing A*s to and from text archives.
  2. Serialize shared_ptr<A>s containing B*s to and from text archives.
  3. Serialize shared_ptr<A>s containing A*s to and from binary
archives.
  4. Serialize shared_ptr<A>s containing B*s to and from binary
archives.

Tests 1-3 all work fine. Test 4 fails as described.

I'd appreciate it if others with an interest in the serialization
library could take a look.  I can quite believe that it's an error on my
part but I haven't been able to spot it yet. 

DT