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Folder:   GENERAL
From:     enagy@mard05.in2p3.fr
Subject:  How to use ROOT in the D0 framework
Date:     06-SEP-2001 01:57
Expires:  21-SEP-2001 01:57


This note contains the basics to include ROOT routines
                                 =====================
into C++ and in particular into the D0 framework.
                           ======================

All informations cited here come from 
Philippe Canal: pcanal@fnal.gov 630-840-2545

A realization can be found in my class chprt_reco
in the pmcs_chprt package.

I would like to share with you what I have learned from
Philippe, hoping it will spare considerable time for you.

                                 Elemer Nagy


1. Compilation:
===============

in the classname.hpp file add:
       -------------
// include ROOT header files
#include "TFile.h"
#include "TROOT.h" 
#include "TH3.h"

last line before ending class

ClassDef(name::classname, 1)   

where name is the namespace in which the headerfile
is imbedded

in the classname.cpp file add:
       -------------

namespace name{
ClassImp(name::classname) 
    }

in the most general case if namespace name is used
(this replaces using namespace name)

In addition in the same directory where classname.cpp
can be found add a file  classname_linkdef.h
                         -------------------
which contains in the most general case the following
lines (when namespace name1, name2, ... are used):
#include "pkg_name/classname.hpp"
 
#ifdef __CINT__
 
#pragma link off all globals;
#pragma link off all classes;
#pragma link off all functions;
 
#pragma link C++ namespace name1;
#pragma link C++ namespace name2;
 
#pragma link C++ class name1::classname;
 
#endif
 
2. Link:
========

In the pkgname/LIBDEPS

on has to include all library packages which is used
by ROOT. An example (containing presumably many superfluous
packages) can be found in pmcs_chprt/LIBDEPS.
Most probably the minimum needed are:

HepTuple  
CLHEP 
z            
cern                                                                                            
root
stdhep

                                                                                                                                                                                                                                                                


3. ROOT Files
=============
Opening ROOT input-output files should be done
using HepRootFileManager. It provides means to
open any number of files this way independently
of the order. Initialization of the ROOT system
will be done only once.

In the classname.hpp file a forward declaration:
 
class HepRootFileManager;
 
and in the classname.cpp file:
 
#include "HepTuple/HepRootFileManager.h"
  HepRootFileManager::initialiseRoot();
  HepRootFileManager *_hepMgr;
  _hepMgr = new HepRootFileManager(FileName);
  TFile *file = _hepMgr->file();

Having done this *file can be used in a usual
way to retrieve histograms on it. E.g.:

 TH3F *my3dh = (TH3F*)file->Get("ValAccept");

Note that Filename has to be std character string.

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