c++ xml parsing problem

[snakec]

hi every body
i'm new to c++ and xerces. i'm triying to make change in an xml file using xerces dom parser. my xml file which i want to change is following : its name is sel.xml

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
 
<!-- Put site-specific property overrides in this file. -->
 
<configuration>
<property>
  <name>fs.default.name</name>
  <value> name</value>
  </property>
 
</configuration>
 
i want to change <value>name</value> to <value>next</next>
 
my cpp file code is following:
 
#include<string.h>
#include<iostream>
#include<sstream>
#include<sys/types.h>
#include<unistd.h>
#include<errno.h>
#include<sys/stat.h>
#include "parser1.hpp"
#include <typeinfo>
using namespace xercesc ;
using namespace std;
 
GetConfig::GetConfig()
{
XMLPlatformUtils::Initialize();
 TAG_configuration =XMLString::transcode("configuration");
 TAG_property = XMLString::transcode("property");
TAG_name=XMLString::transcode("name");
TAG_value=XMLString::transcode("value");
m_ConfigFileParser=new XercesDOMParser;
}
GetConfig::~GetConfig()
{
 delete m_ConfigFileParser;
 
XMLString::release( &TAG_configuration );
XMLString::release( &TAG_property );
//XMLString::release( &TAG_value );
//XMLString::release( &TAG_name );
XMLPlatformUtils::Terminate();
}
void GetConfig :: readConfigFile(string& configFile)
throw( std::runtime_error )
{
 /*struct stat fileStatus;     
int iretStat = stat(configFile.c_str(), &fileStatus);
   if( iretStat == ENOENT )
          throw ( std::runtime_error("Path file_name does not exist, or path is an empty string.") );
       else if( iretStat == ENOTDIR )
          throw ( std::runtime_error("A component of the path is not a directory."));
       else if( iretStat == ELOOP )
          throw ( std::runtime_error("Too many symbolic links encountered while traversing the path."));
   else if( iretStat == EACCES )
          throw ( std::runtime_error("Permission denied."));
       else if( iretStat == ENAMETOOLONG )
          throw ( std::runtime_error("File can not be read\n"));
*/
       // Configure DOM parser.
 
       m_ConfigFileParser->setValidationScheme( XercesDOMParser::Val_Never );
       m_ConfigFileParser->setDoNamespaces( false );
       m_ConfigFileParser->setDoSchema( false );
       m_ConfigFileParser->setLoadExternalDTD( false );
 
    m_ConfigFileParser->parse( configFile.c_str() );
 
DOMDocument* doc = m_ConfigFileParser->getDocument();
DOMElement *root = doc->getDocumentElement();
const XMLCh* tag = xercesc::XMLString::transcode("property");
const XMLCh* tag1 = xercesc::XMLString::transcode("value");
const XMLCh* tag2 = xercesc::XMLString::transcode("name");
//DOMNodeList * list= doc->getElementbyTagName("tag");
//cout<<moot;
 
//DOMNode * rootElem = doc->getDocumentElement();
 
 
cout << "\nfirst";
 
 
 //DOMNode *root =  doc->getFirstChild() ;
 
cout << "\nsecond\n";
cout<< root<<"\n" ;
 
if ( root )
 {
cout<<"hi\n";
  DOMElement* property = dynamic_cast<DOMElement*>( root->getElementsByTagName( tag )->item( 0) );
 
  if ( property )
 {
    cout<<"hello";
 DOMElement* name = dynamic_cast<DOMElement*>( property->getElementsByTagName( tag2 )->item( 0 ) );
 
if ( name )
{
  cout<<"\nmanish\n";
 
    DOMElement* value = dynamic_cast<DOMElement*>( property->getElementsByTagName( tag1 )->item( 0 ) );
 
    if ( value ) 
{     
      cout<<XMLString::transcode(value->getTextContent()); 
       cout<<"\n";
      value->setTextContent( XMLString::transcode(" next") ); // this will update the element named "value"
    }
  }
}
}
 
int main()
    {
       string configFile="/home/manish.yadav/Desktop/sel.xml"; 
 
       GetConfig appConfig;
 
   appConfig.readConfigFile(configFile);
 
 
       return 0;
    }

i compiled the program successfully and the program is running correctly it shows the out put like that

first
second
0x1314e50
hi
hello
manish
name
the extra output are becoz i want to check the flow control of program

now my problem is that i used the method value->setTextContent( XMLString::transcode(" next") );
it is not working ;
in my xml file i saw the old value. the value is not changing there what should i do so that the value change in sel.xml file too?
what should i do to change the value in xml file ?
what i 'm doing wrong?
i goggled the matter lot but someone saying i cant make change in xml file .
to change xml file i have to read the content of file and create a new file .
can anybody explain what should i do?
i read the dom Programming guide, api Documentation but nothing substantial.
what is the method or way to read from old xml file and write it to a new file ?
can any body explain with code ?
how to make new xml file using dom c++ parser?