Re: [Boost-users] Serialization of dynamic data

From: Anders Sundman (anders.sundman_at_[hidden])
Date: 2007-02-02 05:05:32

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