Re: [Boost-users] Serialization and const

From: Anders Sundman (anders.sundman_at_[hidden])
Date: 2007-02-02 13:20:40

Oh, now I get it.

Thank you.

// Anders Sundman

Robert Ramey skrev:
> This is explained in the "rationale" section of the documentation.
> 
> The issue is that tracking implements the behavior that only one
> copy of an object is serialized even though it mght be passed
> multiple times to the serialization library (e.g. as a pointer).  The
> library takes the passing of a non-const to signal that the programmer
> might be changing this value while its being serialized and traps
> this with a compile time message.  This avoids accidently creating
> archives which cannot be read in the future.
> 
> Robert Ramey
> 
> Anders Sundman wrote:
>> Hi!
>>
>> I'm having some problems grasping how the serialization library works
>> with respect to const/non-const data.
>>
>> Ex:
>>
>> Consider the following simple class that I would like to serialize:
>>
>> struct Simple {
>> Simple() : member(0) {}
>> Simple(int m) : member(m) {}
>> int member;
>> };
>> BOOST_CLASS_EXPORT(Simple);
>> BOOST_SERIALIZATION_SPLIT_FREE(Simple);
>> //BOOST_CLASS_TRACKING(Simple, boost::serialization::track_never);
>>
>> namespace boost {
>>   namespace serialization {
>>     template<class Archive>
>>     void save(Archive & ar, const Simple & t, unsigned int version)
>>     {
>>       ar << t.member;
>>     }
>>     template<class Archive>
>>     void load(Archive & ar, Simple & t, unsigned int version) {
>>       ar >> t.member;
>>     }
>>   }
>> }
>>
>> But when I do the serialization, strange things happen.
>>
>> Ex:
>>
>> const Simple s1(7);
>> //Simple s1(7);
>> boost::archive::text_oarchive oa(ss, f);
>> oa << s1;
>>
>> The non-const alternative above doesn't work unless I do
>> BOOST_CLASS_TRACKING(Simple, boost::serialization::track_never);
>>
>> And,
>>
>> Simple * const s1 = new Simple(7);
>> //Simple * s1 = new Simple(7);
>> boost::archive::text_oarchive oa(ss, f);
>> oa << s1;
>>
>> The non-const alternative above doesn't work even if I do
>> BOOST_CLASS_TRACKING(Simple, boost::serialization::track_never);
>>
>>
>> I'm obviously missing something here, please help me out.
>>
>> Best regards,
>> Anders Sundman