Re: [Boost-users] Optional XML serialization

Subject: Re: [Boost-users] Optional XML serialization
From: Robert Ramey (ramey_at_[hidden])
Date: 2010-02-22 12:13:07

Paul wrote:
> Hi,
>
> I use xml_woarchive and xml_wiarchive for reading/writing
> configuration files.
>
> It seems work work well for me, but now I'd like to see if I can do
> more with it... is it possible to load an XML serialized file, but
> completely IGNORE a subtree of the XML file if desired?

Anything is possible if you're willing to change the code that's in there.

> eg
> template <class Archive>
> void load( Archive & ar, MyConfig & c, const unsigned int version )
> {
>    ar >> make_nvp("standard",c.standard);
>    if (some_global_flag_or_whatever)
>      ar >> make_nvp("advanced", c.advanced);
>    else
>      ar.skip("advanced");  // key bit
> }

Something like the following might be made to work.

ar >> c.standard
if(flag)
    ar >> c.advanced
else{
    Advanced a; // to be thrown away
    ar >> a
}

But you would have to start thinking about issues such as tracking.  That is
if you throw away something that is tracked and referred to somewhere else
then it would be a problem. In general, I can't predict the consequences
of such code.

> The motivation is that I want to "register modules" (in my app) that
> can read/write their configuration in an XML configuration file.  But
> if the module is not registered, I want to skip that part of the
> configuration file and move on.   I figure since the XML format is
> like a tree, it might/should be possible to ignore an entire segment
> of the tree.
>
> Is it possible?

That's what the above would do.

>
> In a related note, the "class_id" bits in xml archives seems to make
> it difficult for users to hand-edit the XML file... Are these tags
> required?

In general, we don't include anything in the archive unless it has
to be there to recover the data.

>
> thanks,
> Paul
>
>
>
>
>
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users