CODEWITHSUNDEEP
xmlxpath
FaceBro
FaceBro

Reputation: 859

What does it require for xmlXPathEval to select some nodes successfully?

I use xmlXPathEval to select some nodes from a ovf file(xml format), but failed.

The xml to parse is as below:

<?xml version="1.0" encoding="UTF-8"?>
 <!--Generated by VMware ovftool 3.0.2 (build-931074), UTC time: 2013-07-15T06:41:49.67628Z-->
  <Envelope vmw:buildId="build-931074" xmlns="http://schemas.dmtf.org/ovf/envelope/1">
  //children elements
  </Envelope>

The selecting code is as below:

xmlXPathContextPtr context;
    xmlXPathObjectPtr obj; 
    xmlNodeSetPtr nodeset=NULL;
    int32 count=0;
    //valid doc input
    assert(doc != NULL);
    //valid xpath
    assert(xpath != NULL);
    assert(nodeset_po != NULL);

    context = xmlXPathNewContext(doc);·
    assert (NULL != context);
    obj = xmlXPathEval((xmlChar *)xpath, context);
    assert (NULL != obj);

    if (xmlXPathNodeSetIsEmpty(obj->nodesetval)) {
        //The select nodes is always empty, even when I use "/Envelope" to select the root element
        ;;
    } else {
        nodeset = obj->nodesetval;
        count = nodeset->nodeNr;
        ;;
    }

The comments in the code details the failuer.

And to make it stranger, when I use another xml as the target file to parse, I can select all the nodes as expected.

So I am wondering if there is any requirements for xmlXPathEval to work properly?

Or am I missing something to get such confusing result?

Upvotes: 0

Views: 1004

Answers (1)

JLRishe
JLRishe

Reputation: 101728

Looks like this is the old default namespace problem. The XPath /Envelope will only select elements in the null namespace, but your element is in the namespace http://schemas.dmtf.org/ovf/envelope/1.

I am not familiar with this particular library, but it looks like you need to declare the namespace and assign it a prefix in an xmlXPathContext, then use that prefix in your XPath:

/p:Envelope

Upvotes: 1

Related Questions