RE: [xml] Combining two xml files.

On Mon, Aug 09, 2004 at 07:49:12AM -0400, Cory Virok wrote:

So either no one understands my question or it's just been ignored. 
Either way I'd like to try posting it again.
Anyone?

  There is nothing in your report which could explain why that would
fail. XPath work on a tree. You modify the tree, rerun XPath, that 
should just work unless you made a programming error. So my bet is
it's the second and there is no way I can know what happens, how,
nor do I really have time chasing those issues.
  Since I have nothing to report I did not reply to your email.

Daniel

On Mon, Aug 09, 2004 at 07:49:12AM -0400, Cory Virok wrote:

So either no one understands my question or it's just been ignored. 
Either way I'd like to try posting it again.
Anyone?

  There is nothing in your report which could explain why that would
fail. XPath work on a tree. You modify the tree, rerun XPath, that 
should just work unless you made a programming error. So my bet is
it's the second and there is no way I can know what happens, how,
nor do I really have time chasing those issues.
  Since I have nothing to report I did not reply to your email.

Daniel

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Please help!

I have generated an xml file using kxmleditor.  With libxml, I am trying to use the xpath interface to retrieve a node list for the elements in my file.  The document has (currently) a three level hierarchy and I am trying to retrieve data from the inner most tier.  My code snippet:

if(!(xmldoc=xmlParseFile("statics.xml"))) break;

xpath_context=xmlXPathNewContext(xmldoc);

xpath_object=xmlXPathEvalExpression((xmlChar*)"root/main_ui/config_menu/*",xpath_context);

When I run my code, I get the following error messages:

xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL

xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL

xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL

xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL

Apparently, each one of these error messages corresponds to each level of the hierarchy.  I have tried many permutations of the same expression.  In all cases xpath_object is returned invalid.  I suspect my syntax for the expression is wrong, but I cannot figure it out.

Also, I have studied the code example at http://www.xmlsoft.org/tutorial/apd.html and have reviewed the syntax for xpath as describe here http://www.w3.org/TR/xpath#section-Introduction.  Neither has helped.  As far as I can tell, my code is really the same as that provided by the example.  Please help!

Thanks in advance,

Bryan Christ

On Mon, Aug 09, 2004 at 02:39:10PM -0500, Bryan Christ wrote:
> Please help!
> 
> I have generated an xml file using kxmleditor.  With libxml, I am trying
> to use the xpath interface to retrieve a node list for the elements in
> my file.  The document has (currently) a three level hierarchy and I am
> trying to retrieve data from the inner most tier.  My code snippet:
> 
> if(!(xmldoc=xmlParseFile("statics.xml"))) break;
> xpath_context=xmlXPathNewContext(xmldoc);
> xpath_object=xmlXPathEvalExpression((xmlChar*)"root/main_ui/config_menu/*",xpath_context);
> 
> When I run my code, I get the following error messages:
> 
> xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL
> xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL
> xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL
> xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL

  The current node is not defined. Strange but possible, 

> Apparently, each one of these error messages corresponds to each level
> of the hierarchy.  I have tried many permutations of the same
> expression.  In all cases xpath_object is returned invalid.  I suspect
> my syntax for the expression is wrong, but I cannot figure it out.

  Try /root/main_ui/config_menu/* The leading / ask XPath to start
from the root of the document.

> Also, I have studied the code example at
> http://www.xmlsoft.org/tutorial/apd.html and have reviewed the syntax
> for xpath as describe here
> http://www.w3.org/TR/xpath#section-Introduction.  Neither has helped. 
> As far as I can tell, my code is really the same as that provided by the
> example.  Please help!

  Check that example:
    http://xmlsoft.org/examples/index.html#xpath1.c
but it looks really similar. 

Daniel
On Mon, Aug 09, 2004 at 03:44:47PM -0500, Bryan Christ wrote:
> Supplying the leading / is one of the permutations of the expression
> that I have already tried.  When I do this, I *do not* get the error
> messages:
> 
> xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL
> 
> However, xpath_object is still returned as NULL.  According to the
> documentation, even if there are no matches, shouldn't I receive back a
> valid pointer to an empty list?

  No, you may get NULL for an empty Nodeset. It's an optimization 
which made huge difference for XSLT performances (no need to allocate/
deallocate empty lists all the time).

Daniel
Hi Bryan,

do you use namespaces in your xml file. If so, that one needs to be registered
first, before doing queries. In the future it is helpful to add a snipped of the
XML files as well, when asking.

Stefan

Bryan Christ wrote:
> Well that helps a bit, but the problem still remains that the list
> shouldn't return empty.  Any thoughts?
> 
> On Mon, 2004-08-09 at 16:14, Daniel Veillard wrote:
> 
> 
>>On Mon, Aug 09, 2004 at 03:44:47PM -0500, Bryan Christ wrote:
>>
>>>Supplying the leading / is one of the permutations of the expression
>>>that I have already tried.  When I do this, I *do not* get the error
>>>messages:
>>>
>>>xmlXPathNodeCollectAndTest xpath.c:1923 : nodelist and node are NULL
>>>
>>>However, xpath_object is still returned as NULL.  According to the
>>>documentation, even if there are no matches, shouldn't I receive back a
>>>valid pointer to an empty list?
>>
>>  No, you may get NULL for an empty Nodeset. It's an optimization 
>>which made huge difference for XSLT performances (no need to allocate/
>>deallocate empty lists all the time).
>>
>>Daniel
> 
> 
> 
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> 
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