gistfile1.c

#include <string.h>
#include <libxml/tree.h>
#include <libxml/xpath.h>

void
main()
{
	xmlDocPtr doc;
	xmlNodePtr cur;
	xmlXPathContextPtr ctx;
	xmlXPathObjectPtr xpath;
	xmlNodeSetPtr set;
	xmlChar *xml = "<foo></foo>";
	xmlChar *query = "//namespace::*";
	int i;

	xmlInitParser();
	xmlXPathInit();

	doc = xmlReadMemory(xml, strlen(xml), NULL, NULL, XML_PARSE_RECOVER | XML_PARSE_NOERROR);
	ctx = xmlXPathNewContext(doc);
	ctx->node = doc->children;

	xpath = xmlXPathEvalExpression(query, ctx);

	set = xpath->nodesetval;

	/* libxml expects the following to happen:
	 * xmlXPathFreeNodeSet(set);
	 * xmlFreeDoc(doc);
	 */

	/* We cannot guarantee the order of the above and the following can
	 * cause a segfault:
	 * xmlFreeDoc(doc);
	 * xmlXPathFreeNodeSet(set);
	 */

	/* Nokogiri currently does the following, but valgrind complains:
	 */

	xmlFreeDoc(doc);

	for (i = 0; i < set->nodeNr; i++) {
		cur = set->nodeTab[i];
		if (cur && cur->type == XML_NAMESPACE_DECL)
			xmlXPathNodeSetFreeNs(cur);
	}

        xmlXPathFreeNodeSetList(xpath);
        xmlXPathFreeContext(ctx);
	xmlFree(set->nodeTab);
	xmlFree(set);
}