Using XPath to Retrieve Element Content

Using XPath to Retrieve Element Content
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In addition to walking the document tree to find an element, + Libxml2 includes support for + use of XPath expressions to retrieve sets of + nodes that match a specified criteria. Full documentation of the + XPath API is here. +

XPath allows searching through a document + for nodes that match specified criteria. In the example below we search + through a document for the contents of all keyword + elements. +

	Note
	A full discussion of XPath is beyond + the scope of this document. For details on its use, see the XPath specification.

+ Full code for this example is at Appendix D, Code for XPath Example. +

Using XPath requires setting up an + xmlXPathContext and then supplying the XPath + expression and the context to the + xmlXPathEvalExpression function. The function returns + an xmlXPathObjectPtr, which includes the set of nodes satisfying the + XPath expression.

+	xmlXPathObjectPtr
+	getnodeset (xmlDocPtr doc, xmlChar *xpath){
+	
+	xmlXPathContextPtr context;
+	xmlXPathObjectPtr result;
+
+	context = xmlXPathNewContext(doc);
+	result = xmlXPathEvalExpression(xpath, context);
+	if(xmlXPathNodeSetIsEmpty(result->nodesetval)){
+		xmlXPathFreeObject(result);
+                printf("No result\n");
+		return NULL;
+

	First we declare our variables.
	Initialize the `context` variable.
	Apply the XPath expression.
	Check the result and free the memory allocated to + `result` if no result is found.

The xmlPathObjectPtr returned by the function contains a set of nodes + and other information needed to iterate through the set and act on the + results. For this example, our functions returns the + xmlXPathObjectPtr. We use it to print the contents of + keyword nodes in our document. The node set object + includes the number of elements in the set (nodeNr) and + an array of nodes (nodeTab): +

+	for (i=0; i < nodeset->nodeNr; i++) {
+	keyword = xmlNodeListGetString(doc, nodeset->nodeTab[i]->xmlChildrenNode, 1);
+		printf("keyword: %s\n", keyword);
+	        xmlFree(keyword);
+	}
+

The value of nodeset->Nr holds the number of + elements in the node set. Here we use it to iterate through the array.

Here we print the contents of each of the nodes returned. +

	Note
	Note that we are printing the child node of the node that is + returned, because the contents of the `keyword` + element are a child text node.

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