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From: Robert Ramey (ramey_at_[hidden])
Date: 2004-01-21 12:42:40

Vladimir Prus wrote:

>I've just spend about an hour with a colleague looking for a very subtle
>problem with serialization and BOOST_CLASS_EXPORT.

>What we were trying to do is to have some code which reads pointers to base
>class and does something with it. On the saving side, we've got several
>functions which store various derived classes.

>Now the example:

> class B { ... } ;
> class D { ... } ;

> D* d = new D;
> oa << d;

>Looks innocent, but it does not store the name of derived class that is
>stored. So, after loading with

> B* b;
> is >> b;

>you get object of type B, not D. I attach the program which reproduces this

>The gotcha is that if you write

> B* d = new D;
> oa << d;

>everything works. But it's nonintuitive, and the mistake is very easy to make
>and very hard to notice! In my case, one function was intended for saving
>specific derived type, so it naturally declared a pointer of that type, and
>it took an hour to debug the problem.

Only an hour?

>Is it possible to always save proper identification when saving a pointer to
>polymorphic objects?

This looks like an error to me. The intention is that it work as you expected.
I'll look into it.

Robert Ramey

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