Re: The splitlevel=1 mechanism.

From: Maurik Holtrop (maurik.holtrop@unh.edu)
Date: Tue Jun 08 1999 - 17:31:46 MEST


Hello Rene,

Thank you for the reply. I re-read the documentation you reccommended, and
still don't understand through what method the classes are serialized when
split_level=1. From my tests I think it is not the Streamer method.

The documentation states:
"In split mode, a data member cannot be a pointer to an array of basic
types."
"In split mode, a data member cannot be a C structure."

So an array of structures is definetely out of the question with the
standard code. But can I write my own?
If I can not, is there a way to make writing a tree of my objects more
efficient than the "create" "write" "delete" cycle that is currently used?

The full code for my classes (the one with the pointer into a big memory
array) can be found at:
http://improv.unh.edu/root_problem.txt. This file is a concat of 4 files:
TBOSBankHeader.h and .cc and TBOSRoot.h and .cc.

Your help is much appreciated,

    Maurik Holtrop

P.S. Here is some example code.

Instead of the full class, I send you an example wich illustrates that the
Streamer function of a class does not get called when writing the clas with
split_level=1. This example however, works perfectly fine. When split level
=1 the variables are written to disk through some other mechanism. However,
for classes (unlike this example) that *need* a highly customized streamer,
this means writing won't work.

The following macro (write.C) will print 10 times "Streamer called" when
split level is 0, but not when split level is 1.

/////////////////////////// write.C:
{
tempa *part=new tempa(1,2.);
TFile hfile("split.root","RECREATE","Demo ROOT file");
TTree *tree = new TTree("T","An example");
tree->Branch("tempa","tempa",&part,10240,0);

for(int i=0; i<10; i++){
  part.i=i;
  part.x=i*i*10.;
  tree->Fill();
}
tree->Print();
hfile.Write();
hfile.Close();
}

////////////////////// test2.cc
#include "test2.h"

ClassImp(tempa)

ostream &operator<<(ostream &os,tempa &b)
{
  os << "  Int: " << b.i;
  os << "  Float: " << b.x;
  os << "  C: " << b.str << endl;
  return(os);
}

void tempa::Streamer(TBuffer &R__b)
{
   // Stream an object of class tempa.
  cerr << "Streamer called\n";

   if (R__b.IsReading()) {
      Version_t R__v = R__b.ReadVersion(); if (R__v) { }
      TObject::Streamer(R__b);
      R__b >> i;
      R__b >> x;
      R__b.ReadStaticArray(str);
   } else {
      R__b.WriteVersion(tempa::IsA());
      TObject::Streamer(R__b);
      R__b << i;
      R__b << x;
      R__b.WriteArray(str, 256);
   }
}

///////////////////// test2.h
#ifndef __CINT__
#include "TObject.h"
#endif

#include <iostream.h>


class tempa : public TObject{

 public:
  int i;
  float x;
  char str[256];
 public:

  tempa(){ cout << "******** tempa constructor called\n";};
  ~tempa(){cout << "######## tempa destructor called\n";};
  tempa(int a,float b){
    i=a;
    x=b;
    strcpy(str,"Initialized with constructor.");
  }

  void Print(){
    cout << (*this) << endl;
  }

  friend ostream &operator<<(ostream &os,tempa &b);

  ClassDef(tempa,1)
};







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