Re: [Boost-users] Serialization of dynamic data

From: Anders Sundman (anders.sundman_at_[hidden])
Date: 2007-02-03 10:11:14

This turned out to be a const issue easily solved by reading the docs :) 
(see: rationale section).

// Anders

Anders Sundman skrev:
> A new, slightly different question on the same subject: How to treat 
> data with special "allocator" functions?
> 
> Ex:
> 
> In pseudo code, I would like to do something like this:
> 
> // Serialize
> Fu* bar = allocFu();
> boost::archive::text_oarchive oa(stream, flags);
> oa << bar;
> destroyFu(bar);
> 
> // De-serialize
> Fu* foo = 0;
> boost::archive::text_iarchive ia(stream, flags);
> ia >> foo;	
> // Use foo
> destroyFu(foo);
> 
> But how do I create the load/save functions for this:
> 
> template<class Archive>
> void save(Archive & ar, const Fu* & t, unsigned int version) {
> ...
> }
> template<class Archive>
> void load(Archive & ar, Fu* & t, unsigned int version) {
> ... (run t = allocFu(), among other things) ...
> }
> BOOST_SERIALIZATION_SPLIT_FREE(Fu*)
> 
> But the compiler trips on a static assertion with the comment:
> 
> if your program traps here, it indicates taht your doing one of the 
> following:
> a) serializing an object of a type marked "track_never" through a pointer.
> b) saving an non-const object of a type not markd "track_never)
> Either of these conditions may be an indicator of an error usage of the 
> serialization library and should be double checked.  See documentation 
> on object tracking.
> 
> I don't really understand the error message, and I can't seem to figure 
> out whats wrong with the code. Any idéas anyone?
> 
> // Anders Sundman
> 
> Anders Sundman skrev:
>> Hi!
>>
>> About the boost::serialization library, what is the best way to handle 
>> dynamic data in classes? Any idéas, suggestions or caveats? I didn't 
>> manage to find anything about this in the docs.
>>
>> Consider the following sample class:
>>
>> struct Dyn {
>> 	Dyn(int s) : data(0), size(s) {
>> 		data = new char[size];
>> 	}
>>
>> 	~Dyn() { delete data; }
>>
>> 	char* data;
>> 	int size;
>>
>> private:
>> 	friend class boost::serialization::access;
>> 	template< class Archive > void serialize( Archive &ar, unsigned int ver ) {
>> 		// -> ar & data; What to do here?
>> 		ar & size;
>> 	}
>> };
>>
>> What to do with the data pointer?
>>
>> Is there any way to determine (in the serialize function) if a 
>> serialization or "de-serialization" is taking place? And have different 
>> behaviours - either allocating a new char[x] or copying data to the archive?
>>
>> Is there any way to store dynamic data in an archive?
>>
>> Best regards,
>> Anders Sundman