Change tag value on file XML Xerces C++ Parser

I created an XML file and I don't know how can i change the tag text value on this file. also i can get the node text value and I can change it, but how can i write this modification on a file?

    xercesc_3_2::XMLPlatformUtils::Initialize();

    parser = new xercesc_3_2::XercesDOMParser();

    parser->parse(xmlFile);

    xercesc_3_2::DOMDocument* doc = parser->getDocument();

    xercesc_3_2::DOMNodeList* child = doc-getElementsByTagName(xercesc_3_2::XMLString::transcode("A")); 

   xercesc_3_2::DOMNode* currentNode = child->item(i);
   if (currentNode->getNodeType() && currentNode->getNodeType() == xercesc_3_2::DOMNode::ELEMENT_NODE) {
                currentNode->setTextContent(xercesc_3_2::XMLString::transcode("3000"));

void changeXMLNodevalue(std::string fileName, std::string node, std::string value) {

xercesc_3_2::XMLPlatformUtils::Initialize();

// create the DOM parser
xercesc_3_2::XercesDOMParser* parser = new xercesc_3_2::XercesDOMParser;

parser->setValidationScheme(xercesc_3_2::XercesDOMParser::Val_Never);
parser->parse(fileName.c_str());

// get the DOM representation
xercesc_3_2::DOMDocument* doc = parser->getDocument();

// get the root element
xercesc_3_2::DOMElement* root = doc->getDocumentElement();

// evaluate the xpath
xercesc_3_2::DOMXPathResult* result = doc->evaluate(
    xercesc_3_2::XMLString::transcode(node.c_str()),//"/dgml/document/head/zoom/maximum"),
    root,
    NULL,
    xercesc_3_2::DOMXPathResult::ORDERED_NODE_SNAPSHOT_TYPE,
    NULL);

if (result->getNodeValue() == NULL)
{
    cout << "There is no result for the provided XPath " << endl;
}
else
{
        result->getNodeValue()->getFirstChild()->setNodeValue(xercesc_3_2::XMLString::transcode(value.c_str()));// "3000"));
        const XMLCh* a = result->getNodeValue()->getFirstChild()->getNodeValue();
        char* tttt = (char*)a;
        cout << "Node value: " << tttt << endl;
    
}

xercesc_3_2::XMLPlatformUtils::Terminate();
return;
}