[Boost-users] How to prevent boost serialize from object tracking a pointer

[Frank]

Hi all,

I have a shared_ptr to an object that changes (the underlying object is
non-const, that is, not the shared_ptr), and I'd like to serialize the
object each time it changes (size of the archive is not an issue). The
problem stems, I think, from object tracking: every time after the first
serialization, boost detects that the pointer is the same, and does not
write out the (full, updated) object.

I've tried putting in BOOST_CLASS_TRACKING(T,
boost::serialization::track_never) but it won't compile because there is a
BOOST_STATIC_ASSERT in shared_ptr.hpp that prevents setting class T's
tracking to track_never if it is then serialized via a shared_ptr, with the
comment that "correct shared_ptr serialization depends upon object tracking
being used."

Am I missing something obvious here, or is another a way to accomplish this?
Any help would be greatly appreciated...

Thanks,
Frank

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[Robert Ramey]

Frank wrote:
> Hi all,
>
> I have a shared_ptr to an object that changes (the underlying object
> is non-const, that is, not the shared_ptr), and I'd like to serialize
> the object each time it changes (size of the archive is not an
> issue). The problem stems, I think, from object tracking: every time
> after the first serialization, boost detects that the pointer is the
> same, and does not write out the (full, updated) object.
>
> I've tried putting in BOOST_CLASS_TRACKING(T,
> boost::serialization::track_never) but it won't compile because there
> is a BOOST_STATIC_ASSERT in shared_ptr.hpp that prevents setting
> class T's tracking to track_never if it is then serialized via a
> shared_ptr, with the comment that "correct shared_ptr serialization
> depends upon object tracking being used."
>

> Am I missing something obvious here,..?

It might be obvious now but it will be if you think about it. Suppose
you have one object pointed to by two different points. Now suppose
you don't track this pointer. When you load, you won't have a shared
pointer anymore. That is you'll have two objects instead of the orginal
one.
And each "shared_ptr" won't be shared anymore. So after loading
things will be quite different than they were when you saved.

Robert Ramey

>
> Thanks,
> Frank

[Frank]

Hi Robert,

Thanks for the quick reply (and all your hard work on the library...).

I understand what you are saying, that makes a lot of sense. I don't see any
other way to ensure the integrity of the shared_ptr than to forbid
track_never. However, it still seems strange that when I serialize the
shared_ptr the second time (after the pointed-to object has been changed),
what is serialized does not reflect any change. It's almost like it would be
safer to forbid serialization of shared_ptr to non-const objects,
altogether...

Anyway, thank you for the explanation, it is much appreciated.

Frank

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