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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Using XPath to Retrieve Element Content</title><meta name="generator" content="DocBook XSL Stylesheets V1.61.2"><link rel="home" href="index.html" title="Libxml Tutorial"><link rel="up" href="index.html" title="Libxml Tutorial"><link rel="previous" href="ar01s04.html" title="Retrieving Element Content"><link rel="next" href="ar01s06.html" title="Writing element content"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">Using XPath to Retrieve Element ContentIn addition to walking the document tree to find an element,
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Libxml2 includes support for
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use of XPath expressions to retrieve sets of
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nodes that match a specified criteria. Full documentation of the
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XPath API is here.
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XPath allows searching through a document
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for nodes that match specified criteria. In the example below we search
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through a document for the contents of all <tt class="varname">keyword</tt>
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elements.
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![[Note]](images/note.png) | Note |
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A full discussion of XPath is beyond |
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the scope of this document. For details on its use, see the XPath specification.
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Full code for this example is at Appendix D, Code for XPath Example.
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Using XPath requires setting up an
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xmlXPathContext and then supplying the XPath
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expression and the context to the
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<tt class="function">xmlXPathEvalExpression</tt> function. The function returns
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an xmlXPathObjectPtr, which includes the set of nodes satisfying the
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XPath expression.
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xmlXPathObjectPtr
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getnodeset (xmlDocPtr doc, xmlChar *xpath){
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 xmlXPathContextPtr context;
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xmlXPathObjectPtr result;
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 context = xmlXPathNewContext(doc);
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 result = xmlXPathEvalExpression(xpath, context);
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 if(xmlXPathNodeSetIsEmpty(result->nodesetval)){
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xmlXPathFreeObject(result);
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printf("No result\n");
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return NULL;
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| | First we declare our variables. | | | Initialize the <tt class="varname">context</tt> variable. | | | Apply the XPath expression. | | | Check the result and free the memory allocated to |
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<tt class="varname">result</tt> if no result is found.
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The xmlPathObjectPtr returned by the function contains a set of nodes
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and other information needed to iterate through the set and act on the
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results. For this example, our functions returns the
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<tt class="varname">xmlXPathObjectPtr</tt>. We use it to print the contents of
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<tt class="varname">keyword</tt> nodes in our document. The node set object
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includes the number of elements in the set (<tt class="varname">nodeNr</tt>) and
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an array of nodes (<tt class="varname">nodeTab</tt>):
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for (i=0; i < nodeset->nodeNr; i++) {
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keyword = xmlNodeListGetString(doc, nodeset->nodeTab[i]->xmlChildrenNode, 1);
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printf("keyword: %s\n", keyword);
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xmlFree(keyword);
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}
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| | The value of <tt class="varname">nodeset->Nr</tt> holds the number of |
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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.
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| Note |
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Note that we are printing the child node of the node that is |
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returned, because the contents of the <tt class="varname">keyword</tt>
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element are a child text node.
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</body></html>
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