Re: [Boost-users] boost::serialization - prevent object creation whenloading a pointer

From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-12-11 19:29:00

Darryl Lawson:

>I realise that what I am doing is no doubt an unconventional usage of
> boost::serialization, but I wonder if any one has done a similar thing
> before.
>
> I wish to serialize a derived class through a baseclass pointer, but on
> deserilize I do not want the object to be created (I do not want memory
> allocated) - as the object will have all ready been created.
>
> An example, hopefully showing what I mean, is given at the end.

...

> struct A {
>    A() {
>        _m = new derived;
>        cout << "construct A, _m = " << (unsigned long)_m << endl;
>    }
>
>    template<class Archive>
>    void serialize(Archive& ar, const unsigned int version) {
>        // On deserialize this will create a new object, but I do not
> want it to,
>        // rather I would like it to deserialize into the all ready created
>        // object.
>        ar & _m;
>        cout << "serialise A, _m = " << (unsigned long)_m << endl;
>    }
>
>    base* _m;
> };
>
> void save(const A& a, const char* filename) {
>    std::ofstream ofs(filename);
>    boost::archive::text_oarchive oa(ofs);
>    oa << a;
> }
>
> void load(A& a, const char* filename) {
>    std::ifstream ifs(filename);
>    boost::archive::text_iarchive ia(ifs);
>    ia >> a;
> }

You can add

    virtual void load( boost::archive::text_iarchive& ar, unsigned v ) = 0;
    virtual void save( boost::archive::text_oarchive& ar, unsigned v ) = 0;

to base and call them in A::serialize, but this obviously only works for a 
specific archive type.