Kindly check the updated code..
QDomNodeList nodeList = docElem.elementsByTagName("folder");
for(int k = 0;k < nodeList.count(); k++)
{
QDomElement el = nodeList.at(k).toElement();
firmFolder += el.attribute("name");
firmFolder += "/";
}

nodeList = docElem.elementsByTagName("file");
for(int l = 0;j < nodeList.count(); l++)
{
QDomElement el = nodeList.at(l).toElement();
firmFiles += el.attribute("name");
firmFiles += " ";
}