c/c++ validation libraries?

[Graham Bennett <graham-xml@simulcra.org>]

Hi all,

In my application I get an incoming stream of XML data which I would
like to validate.  The API I am dealing with provides no validation
functionality itself, so I would like to find some way of wrapping it
with my own layer of validation.  

Naturally I don't want to write my own w3c schema or relaxng validator,
so I was wondering if there were any libraries that expose the ability
to do validation but are not tied to a particular parser.  Obvious
options are to create a DOM and use something like Xerces to validate
that, or even to serialise to text and parse that with a validating
parser, but both of these are very inefficient.  Ideally I would like to
be able to hook in at the SAX level and generate the SAX events for the
library to validate.  It may be possible to hook into something like
Xerces to do this.

Has anyone come across any c or c++ projects that would offer such
functionality?  It would also be interesting to know what options are
available on other platforms.

Thanks in advance,

Graham.

-- 
Graham Bennett