Re: [Boost-users] serialization: curious un-serializing issue RFI

From: Hugh Hoover (hugh_at_[hidden])
Date: 2007-10-30 12:18:44

On Oct 29, 2007, at 7:16 PM, Robert Ramey wrote:

> the package includs test_derived_class.
>
> How does your example differ from that one?

good question...
trivial differences:
5 element classes (1 abstract base+derived pair, 1 abstract base+2  
derived)
2 collection classes - hash_map in both cases, but my own serializer
        (which eliminates a redundant key serialization in my cases)
my serialization code is defined and instantiated in a .cpp file rather
than in the headers.
I'm using split_member for all classes.
The function that attempts to load the object reference (the one that's
failing) is in a load_construct_data and not a "normal" load function.

most "interesting" difference so far:
the save_construct_data is saving the reference through a const pointer,
like:

boost::smart_ptr<B const> b_ptr = this->m_b;
ar << boost::serialization::make_nvp("b_ptr", b_ptr);

while the load_construct_data unserializes with:

boost::smart_ptr<B> b_ptr;
ar >> boost::serialization::make_nvp("b_ptr", b_ptr);

I'll try changing the save_construct_data to use a non-const pointer...

If that doesn't work, I'll create a stripped down test and see if I can
replicate the problem in some simpler test code.

>>> I have a curious problem that's just sprung up, after changing from
>>> using plain-old-pointers to using boost::shared_ptrs internally in  
>>> my
>>> data structures (stl hash_map and map)
>>> The problem is that while the XML archive works correctly, both text
>>> and binary fail (they all used to work).
>>>
>>> This is using gcc 4.0.1 on darwin and VC8 on windows, boost version
>>> is
>>> 1.34.1
>>>
>>> The failure occurs while unserializing an archive, specifically when
>>> trying to read back a shared_ptr to an already unserialized object.
>>> In the archive, it shows the object (pointer) as an object_reference
>>> (the same reference id in XML and text).  While the XML version  
>>> reads
>>> the pointer back correctly, the text version fails and returns NULL.
>>> I have not determined the exact reason why the text version fails  
>>> (it
>>> doesn't throw, just returns NULL).  The serialization does not  
>>> appear
>>> to have any problems.
>>
>> The proximate cause of the problem is in void_upcast, which does not
>> find a pre-registered pair of types matching the base and derived
>> types passed in from load_pointer_type::invoke.  I'm having a hard
>> time understanding how that could be...  I've called
>> void_cast_register for the type pair, so it SHOULD be registered -
>> and the xml_iarchive was able to reconstruct the object properly.
>>
>> Any suggestions?
>
>
>
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