xpath - 如何使用libxml依次应用两个xpath表达式？

Question

综上所述，我是libxml的初学者，我必须使用现有的源代码。主要思想是应用第一个xpath表达式从xml文件中提取一组节点。然后，对于每个节点，应使用第二个xpath表达式提取一些值。

现有的源代码是：

int xt_parseXmlResult(xmlDocPtr doc, const char *xpath, assoc_arrayc_t expr, arrayc_t *result)
{
    xmlXPathContextPtr xpathCtx = xmlXPathNewContext(doc);

    // Register namespaces ...

    /*
     * Evaluate main xpath expression
     */
    xmlXPathObjectPtr xpathNodes = xmlXPathEvalExpression((xmlChar *)xpath, xpathCtx);

    /*
     * Now we apply the xpath expressions on each node returned by the first xpath request
     */
    // First loop is on the XML document as we have to create a new context each
    // time we change the document
    int nbDocs = xpathNodes->nodesetval->nodeNr;

    for (row = 0; row < nbDocs; row++)
    {
        xmlXPathContextPtr  subCtx = xmlXPathNewContext(doc);

        // Register namespaces ...

        // Update context to use the nodeset related to this row
        subCtx->node = xpathNodes->nodesetval->nodeTab[row];

        for (col = 0; col < expr.nbItems; col++)
        {
            // Evaluate expression
            xpathRows = xmlXPathEvalExpression((xmlChar *)expr.itemList[col].val, subCtx);

            result->data[(row + 1) * result->nbCols + col] = strdup((char *)xmlXPathCastToString(xpathRows)); 
            xmlXPathFreeObject(xpathRows);
        }
        xmlXPathFreeContext(subCtx);
        subCtx = NULL;
    }

    xmlFreeDoc(doc); 
    xmlXPathFreeContext(xpathCtx);
    xmlXPathFreeObject(xpathNodes);
    return 0;
}

我认为问题出在这条线

    // Update context to use the nodeset related to this row
subCtx->node = xpathNodes->nodesetval->nodeTab[row];

因为第二个xpath表达式是从xml文件的根目录而不是每个节点的根目录应用的。

关于如何做这种事情的任何想法？

Answer 1

一些示例代码。进行修改以适合您的需求和语言。这是C＃，但应该大致相同。请注意，第二个xpath不是以“ /”开头，而是使用从第一个返回的节点的实例。两个xpath都不以“ /”结尾。

XmlDocument doc = new XmlDocument();
doc.Load(docfile);
XmlNodeList items = doc.SelectNodes("/part1/part2");
foreach (item in items)
{
    XMLNode x = item.SelectNodes("part3");
    //Dostuff
}