void list_files(const char *dirname="/home/work/run_longtest_Y3_oct2019_root_files_3/", const char *ext=".root")
{ 
  TList* fileList = new TList;
  std::cout<<dirname<<std::endl;

  TSystemDirectory dir(dirname, dirname); 
  TList *files = dir.GetListOfFiles(); 
  //printf("3\n");
  if (files) 
  {

    //printf("2\n");
    TSystemFile *file; 
    TString fname; 
    TIter next(files); 
    //printf("1\n");
    while ((file=(TSystemFile*)next())) 
    { 
      fname = file->GetName();
      //printf("0\n");
      if (!file->IsDirectory() && fname.EndsWith(ext)) 
      { 
        fileList->Add(file);
      } 

      /*else if (file->IsDirectory() && !fname.EqualTo(".")
					&& !fname.EqualTo("..")) //Directory - recursive call
			{
				TList *sublist = GetRootFilesInDir(file->GetTitle(), ext);
				fileList->AddAll(sublist);

			}*/

      //file->Print();
    }

    
  }

  TString fname ;
  TString fOldName ;

  int ifl = 0;

  //fileList->Sort();

  fileList->DoSort();

  Int_t listSize = fileList->GetSize();
  
  std::cout << "+++++++++I'm going to analyze:     " << listSize << "       files " << std::endl;

  while (1)
  {

    
    if (ifl >= listSize)
    {
      std::cout<< "===============   All files in the specified dir have been analyzed  ========================"<< std::endl;
	    //isIncrementNeeded = kFALSE;
      break ;
    }

    if (ifl < listSize)
    {
      nfile = (TSystemFile*) fileList->At(ifl);

      TString strFileName = nfile->GetName();
      TString strPath = nfile->GetTitle();

      fname = strPath + "/" + strFileName;
 
    }

    ifl++;


    int isFileChange = 0;

    isFileChange = fname.CompareTo(fOldName, TString::kExact);



    if (isFileChange != 0)
    {
	//TString RecoFile  = "1521780828.root";

	//TFile *event_file = TFile::Open(RecoFile.Data(), "READ");
    //TTree *tracktree = (TTree *) event_file->Get("cbmsim");


    

        
      f = new TFile(fname);


      f->Print();
    }
  }

}