From: Jeff Garland (jeff_at_[hidden])
Date: 2007-01-11 09:46:24
Russell Hind wrote:
> Hi, we've been serializing data to binary archives since serialization
> was first released. As such we have collected a lot of data files.
>
> They are serialized using C++Builder 6 and boost-1.32.0.
>
> We're now looking to move to VS 2005 and as such, boost-1.33.1 seems a
> much easier solution than trying to get 1.32.0 to run.
>
> But I've had trouble de-serializing archives created with BCB6 and
> 1.32.0 with VS 2005 and 1.33.1. I've found the problem in time_duration
> serialization.
I see -- I take it this was the change that fixed serialization of special
values: time_serialize.hpp 1.6 to 1.7?
> Its serialization was changed between 1.32.0 and 1.33.1 but no version
> increment occured. As such, 1.33.1 can't read archives created with
> 1.32.0 because of this.
>
> A version could be added to 1.33.1 now to check for this, but I guess
> this would then break all archives currently written with 1.33.1.
>
> For us, we're trying to move to C# so I guess we will mostly be using
> boost for backwards compatibility for the foreseeable future so our
> solution is to add a #define to the 1.33.1 header that makes it behave
> like 1.32.0 did which enables us to load our files.
>
> But I'm not sure how you would solve this for other users or what to do
> before 1.34.0. This situation isn't ideal as can't think of a solution
> without breaking compatibility at some point.
Well, I think at a minimum there needs to be a warning in the documentation.
The only other obvious solution would be to provide a macro to allow the
switchback to the old, broken, behavior. The other possibility I could see is
to provide a macro which allows a program that takes the input the old format
and the output the new format. This allows for creation of an archive
conversion program and hence an upgrade path.
> But as a last thought, please can people be careful when modifying
> serialization functions to keep backwards compatibility. This has taken
> quite a while to track down but that isn't nearly as scary as not
> being able to move forward to another version of boost without loosing
> the ability to load in all our customers data.
Thx for the report -- I clearly didn't understand the potential impact of this
change. At a minimum there will be doc notes in 1.34.
Jeff