Re: [Boost-users] boost::serialization throwing "input stream error" on base class ptr XML serialization

Subject: Re: [Boost-users] boost::serialization throwing "input stream error" on base class ptr XML serialization
From: Robert Ramey (ramey_at_[hidden])
Date: 2013-04-26 14:20:12

Jari wrote:
>
> //Why do these need to be wrappers??
> namespace boost
> {
> namespace serialization
> {
> template<> struct is_wrapper<A*> : mpl::true_ {};
> template<> struct is_wrapper<A> : mpl::true_ {};
> template<> struct is_wrapper<const A> : mpl::true_ {};
> }
> }

I don't know why the above is there.  It should be taken out

>
> BOOST_SERIALIZATION_ASSUME_ABSTRACT(A);
> BOOST_CLASS_EXPORT(B)
> BOOST_CLASS_EXPORT(C)
>
> int main(int argc, char** argv)
> {
>     //A* a = new A();
>     A* b = new B();
>     A* c = new C();
>     //A* a1 = nullptr;
>     A* a2 = nullptr;
>     A* a3 = nullptr;
>
>     ostringstream ostream;
>     xml_oarchive oarchive(ostream);
>
>     oarchive /*<< BOOST_SERIALIZATION_NVP(a)*/
>                << BOOST_SERIALIZATION_NVP(b)
>                << BOOST_SERIALIZATION_NVP(c);
>
>     istringstream istream(ostream.str());
>     xml_iarchive iarchive(istream);
>
>     iarchive /*>> BOOST_SERIALIZATION_NVP(a1)*/
>                >> BOOST_SERIALIZATION_NVP(a2)
>                >> BOOST_SERIALIZATION_NVP(a3);
>
>     //delete a;
>     delete b;
>     delete c;
>     //delete a1;
>     delete a2;
>     delete a3;
> }
>

The problem is:

oarchive << BOOST_SERIALIZATION_NVP(a) creates an item <a ...> data </a>
iarchive >> BOOST_SERIALIZATION_NVP(a1) expects an item <a1 ...> data </a1>

The serialization library verifies that the name used to save is the name 
used to load
because that's usually a bug.  If you want the above to work you'l ahve to 
use:

use the following instead so that the tag is always a

oarchive << make_nvp("a", a) creates an item <a ...> data </a>
iarchive >>  make_nvp("a", a1) expects an item <a...> data </a1>