Re: [boost] [Serialization]#3118 basic_binary_oarchive.hpp - save_override possible loss of data warnings

Subject: Re: [boost] [Serialization]#3118 basic_binary_oarchive.hpp - save_override possible loss of data warnings
From: Robert Ramey (ramey_at_[hidden])
Date: 2009-06-01 12:29:20

> there is still a possibility of a silent loss of data.

This would only be an issue in following cases:

a) A class has more than 255 backward compatible versions.
b) An archive has more than 64K different classes in it.

It is currently inconcievable to me that such a program
would ever be written.  Setting the sizes of these
types to larger values would make every single binary
archive bigger and slower.

The only think I might suggest is that one add an
assertion so that if either of the above were to occur,
the program would trap - at least in debug mode. So
maybe one might use

assert(t.t < max_value<unsigned char>
>   const unsigned char x = static_cast<unsigned char>(t.t);

assert(t.t < max_value<int_least16_t >
>   const int_least16_t x = static_cast<int_least16_t>(t.t);

Robert Ramey

Jeff Flinn wrote:
> I've posted the following ticket in light of the current bug sprint.
> -----------
> The following save_override overloads cause possible loss of data
> warnings on MSVC8 and XCode3.1.2/gcc4.0.1
>
>   void save_override(const version_type & t, int)
>   void save_override(const class_id_type & t, int)
>   void save_override(const class_id_reference_type & t, int)
>
> with their respective assignments:
>
>   const unsigned char x = t.t;
>   const int_least16_t x = t.t;
>
> While a possible fix would be:
>
>   const unsigned char x = static_cast<unsigned char>(t.t);
>   const int_least16_t x = static_cast<int_least16_t>(t.t);
>
> there is still a possibility of a silent loss of data.
>
> We could be safer and use numeric_cast, but that would possibly impact
> code size and performance, and would introduce a library dependency.
>
> Why are the xxx_type strong typedef's using int rather than the
> smaller types that are being serialized?
>
> Any thoughts on the best solution?
>
> Thanks, Jeff
>
> _______________________________________________
> Unsubscribe & other changes:
> http://lists.boost.org/mailman/listinfo.cgi/boost