how to get the time stamp of a file or folder?

man stat
 or
man fstat

What OS?

For Windows, you can use the following C Run Time library functions.

_fstat, _fstati64
_stat, _wstat, _stati64, _wstati64

Or, the following API functions.

GetFileTime
GetFileInformationByHandle

If you are using MFC...

      CString sTifFileDateTime;
      CFileStatus status;

      try
      {
            CFile cfile( sFile, CFile::modeRead );  //PUT YOUR FILE NAME HERE
            if( cfile.GetStatus( status ) )    
            {

                  //get the file's date/time and format it
                  CString sFileDateTime;
                  CTime fileTime = status.m_mtime;
                  sFileDateTime = fileTime.Format( "%Y%m%d%H%M%S0000" );
            }
            else
            {
                  sError = "Could not get file statistics on file " + sFile;
                  cout << sError << endl;
                  return -1;
            }
            cfile.Close();
      }
      catch (CFileException *ex )
      {
            CString sCause;
            switch ( ex->m_cause )
            {
                  case CFileException::generic:
                        sCause = "An unspecified error occurred.";
                        break;
                  case CFileException::fileNotFound:
                        sCause = "The file could not be located.";
                        break;
                 ....
                                }
                 }