Re: [xml] MacOSX specific problem when using xmlXPathNodeSetIsEmpty()

[Håkon Skjelten <skjelten pvv org>]

On Mon, Jun 28, 2004 at 06:57:21AM +1000, Steve Ball wrote:
> xmlXPathNodeSetIsEmpty is a macro defined in include/libxml/xpath.h:
>
> #define xmlXPathNodeSetIsEmpty(ns)                                      
> \
>     (((ns) == NULL) || ((ns)->nodeNr == 0) || ((ns)->nodeTab == NULL))
>
> so all it is doing is comparing a few data values to zero.  I cannot 
> see what the problem might be;
> there are no compiler errors when I build the code.

Yes - I believe the problem is bigger than just that single function/macro. 
Notice that when I change the line:
if (xmlXPathNodeSetIsEmpty(_query->nodesetval))
to
if (xmlXPathNodeSetGetLength(_query->nodesetval) == 0)
I get the same result, and if I skip the entire test the program segfaults
instantly.


> I notice you're using C++.  How is _query defined?

In xml_parser.h:
 xmlXPathObjectPtr _query;

Full source code can be seen here:
http://cvs.sourceforge.net/viewcvs.py/nidhogg/nidhogg/src/


Regards,
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Håkon Skjelten  (skjelten pvv org)
Student, Engineering Cybernetics
Norwegian University of Science and Technology



> On 18/06/2004, at 7:14 AM, Håkon Skjelten wrote:
>
> > Hi
> >
> > I'm working on a project where we use libxml2 to store level data. The 
> > code
> > works perfectly on GNU/Linux (PPC/i386/AMD64) but it fails on MacOSX.
> >
> > The code that fails is the xmlXPathNodeSetIsEmpty(_query->nodesetval)
> > function call. For some reason it returns TRUE on MacOSX even though 
> > this is
> > not correct (same code & XML file returns FALSE in GNU/Linux). All 
> > other
> > libxml2 functions seems to work fine on the Mac.
> >
> > The method that fails:
> > int XMLParser::query_start(std::string xpath)
> > {
> >  if (_query != NULL)
> >     return -1;
> >
> >  _query_element = 0;
> >  xmlXPathContextPtr context = xmlXPathNewContext(_xmlDocument);
> >  _query = xmlXPathEvalExpression( (xmlChar*)xpath.c_str(), context);
> >  xmlXPathFreeContext(context);
> >
> > /*
> >  This does not work either:
> >     if (xmlXPathNodeSetGetLength(_query->nodesetval) == 0) {
> > */
> >  if (xmlXPathNodeSetIsEmpty(_query->nodesetval)) {
> >     _query_matches = 0;
> >     _query_attr = NULL;
> >  } else {
> >     _query_matches = _query->nodesetval->nodeNr;
> >     _query_attr =  _query->nodesetval->nodeTab[0]->properties;
> >  }
> >
> >  return 0;
> > }
> >
> > _query_matches always equals 0 on MacOSX (and if I skip the entire 
> > test and
> > set _query_matches = _query->nodesetval->nodeNr; I get a segmentation 
> > fault).
> >
> > The same problem occur both on old and new versions of libxml2.
> >
> > Is this a known problem? Are there any known workarounds? Suggestions?
> >
> >
> > Regards,
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > Håkon Skjelten  (skjelten pvv org)
> > Student, Engineering Cybernetics
> > Norwegian University of Science and Technology
> > _______________________________________________
> > xml mailing list, project page  http://xmlsoft.org/
> > xml gnome org
> > http://mail.gnome.org/mailman/listinfo/xml
>
> ---
>
> Steve Ball            |   XSLT Standard Library   | Training & Seminars
> Zveno Pty Ltd         |     Web Tcl Complete      |   XML XSL Schemas
> http://www.zveno.com/ |      TclXML TclDOM        | Tcl, Web Development
> Steve Ball zveno com  +---------------------------+---------------------
> Ph. +61 2 6242 4099   |   Mobile (0413) 594 462   | Fax +61 2 6242 4099