On Fri, Aug 06, 2010 at 09:02:00PM +0100, Garth N. Wells wrote: > I have trouble following the logic in the DOLFIN XML io code, which I > suspect is because of the pointers to callback functions being passed to > libxml2. Has anyone looked at libxml++ > (http://library.gnome.org/devel/libxml++-tutorial/stable/) which > provides C++ bindings to libxml2?
No, and I'm not sure if it's worth the trouble.
I think the libxml2 interface is not much of a problem, at least not
since we realized how to only set the callbacks we are interested in:
XMLFile::XMLFile(std::ostream& s)
: GenericFile(""), sax(0), outstream(&s)
{
// Set up the sax handler.
sax = new xmlSAXHandler();
// Set up handlers for parser events
sax->startDocument = sax_start_document;
sax->endDocument = sax_end_document;
sax->startElement = sax_start_element;
sax->endElement = sax_end_element;
sax->warning = sax_warning;
sax->error = sax_error;
sax->fatalError = sax_fatal_error;
}
Ola did a very good job at redesigning the parsing to allow reuse of
code. For example, we can reuse the parsing of MeshFunction data
inside the <data> tag inside the <mesh> tag. Previously, every top
level tag had its own implementation which prevented reuse of code for
parsing nested data.
This is what makes the implementation difficult to follow, but it's
essentially a stack of parsers where we push and pop the handler
currently responsible for accepting the callbacks from libxml2 when it
reads data.
I don't think it would be easier if we used the C++ interface. It
would probably be less transparent. Right now, our interaction with
libxml2 is very minimal: setting the callbacks and receiving the data
parsed by libxml2.
--
Anders
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