Re: [Boost-users] [serialization] Difficulties with shared_ptrandexport.hpp

23 Nov 2006

      The real question here is:
...
What else is supposed to be in this file? Do I need to put in the code
that loads and saves archives in this file?
And here is the answer.

I expect that BOOST_CLASS_EXPORT will be specified in the same
header file as the class declaration to which it corresponds.  That is,
BOOST_CLASS_EXPORT(T) is a "trait" of the class.  This trait
is the "external name" used to identify the class and is needed when
serializing polymorphic types through a base class pointer.

I expect that one's program will generally look like:

#include 
....
#include "my_class.hpp"  // which has BOOST_CLASS_EXPORT inside

In boost 1.35 (aka HEAD) these headers can be in any order.  In 1.34
and earlier, the archive headers have to go before any headers which
contain BOOST_CLASS_EXPORT

This will instantiate any code required to serialize types specified
by BOOST_CLASS_EXPORT for each archive included.  (note that
the code is instantiated regardless of whether or not it is actually
invoked.)

If no archive headers are included - no code should be instantiated.  This
will permit BOOST_CLASS_EXPORT to be a permanent part of the
my_class declaration.  (Right now this provokes an error message.  I'll
rectify that.)

I hope this clarifies things.

Robert Ramey

Deane Yang wrote:
...
Robert Ramey wrote:
...
...
In fact, my implementation file contains *only* BOOST_CLASS_EXPORT
statements.
Then no code will be instantiated - as you have indeed found.

...
...
...
Code like this seems to compile only if I also include archive
headers like: #include 
#include 
correct.
...
If these directives are omitted, then my code does not compile.
Hmmm - the required code to export class x to archive
xml_?archive.hpp will not be instantiated.  I would expect that to
show up as a missing symbol during linking.
No, I get something like:
..\..\..\..\vendor\boost\boost/serialization/type_info_implementation.hpp(48)
...
error C2027: use of undefined type
'boost::serialization::extended_type_info_impl<T>'
        with
        [
            T=Input::Bond
        ]
        ..\..\..\..\vendor\boost\boost/serialization/export.hpp(75) :
see reference to class template instantiation
'boost::serialization::type_info_implementation<T>' being compiled
        with
        [
            T=Input::Bond
        ]
OK - I believe that is misleading. I'm changing my local copy to
#include  so that
this error doesn't appear.