Re: object serialization

From:

=?iso-8859-1?q?Kirit_S=E6lensminde?= <kirit.saelensminde@gmail.com>

Newsgroups:

comp.lang.c++

Date:

19 Apr 2007 21:29:57 -0700

Message-ID:

<1177043397.406212.30270@d57g2000hsg.googlegroups.com>

On Apr 20, 8:24 am, "Ron AF Greve" <ron@localhost> wrote:

void MCursor::MCursorInfo::Serialize( MArchive& Archive )
{
Archive.Serialize ( Event );
Archive.Serialize ( OffsetX );
Archive.Serialize ( OffsetY );
Archive.Serialize ( Animation );

}

There is one extra complication that this approach doesn't address. As
the file format changes you need to be able to read old versions with
newer software.

There are a few ways of doing this. The way I've used in the past is
that each object also writes a schema number which can then be used to
work out which structure to use. You may get something that looks a
little more like this:

void MCursor::MCursorInfo::Serialize( MArchive& Archive )
{
    int version = Archive.Version< MCursorInfo >( 2 );
    if ( version >= 1 ) {
        Archive.Serialize( Event );
        Archive.Serialise( OffsetX );
        Archive.Serialise( OffsetY );
    }
    if ( version >= 2 )
        Archive.Serialise( Animation );
}

You want to arrange for Version to return the version that is to be
used. By passing in the type (I've done it via a template
specialisation, but there are other ways too) it can store a lookup
for overall file version against each schema part so that you can also
save to older file formats.

K