如何在cpp的xmlXPathRegisterNs (libxml2)中添加多个命名空间

#include <libxml/xpath.h>

xmlXPathContextPtr xpathCtx = xmlXPathNewContext(doc);

const xmlChar* prefix1 = (const xmlChar*)"ns1";
const xmlChar* uri1 = (const xmlChar*)"http://www.example.com/ns1";
const xmlChar* prefix2 = (const xmlChar*)"ns2";
const xmlChar* uri2 = (const xmlChar*)"http://www.example.com/ns2";

xmlXPathRegisterNs(xpathCtx, prefix1, uri1);
xmlXPathRegisterNs(xpathCtx, prefix2, uri2);

const xmlChar* xpathExpr = (const xmlChar*)"/ns1:root/ns2:element";
xmlXPathObjectPtr xpathObj = xmlXPathEvalExpression(xpathExpr, xpathCtx);

if (xpathObj) {
    xmlNodeSetPtr nodes = xpathObj->nodesetval;
    if (nodes) {
        for (int i = 0; i < nodes->nodeNr; i++) {
            // 处理每个节点
            xmlNodePtr node = nodes->nodeTab[i];
            // ...
        }
    }
}