Hi Maurik,
The restrictions about the split mode listed at the URL:
http://root.cern.ch/root/HowtoWriteTree.html
concern the automatic split mode. The last section of this URL says:
"Making branches by hand
If you are not happy with the way the automatic split algorithm works,
you can create branches yourself by invoking directly the
TTree::Branch function."
Obviously, we encourage people to create classes such that the automatic
split algorithm can be applied.
When you run in "NON-SPLIT" mode, the Streamer function for the
referenced
object is called.
When you run in SPLIT mode, each data member of the referenced object
is written to a separate branch.
- If Root encounters a basic type, it does not need to invoke a
Streamer
function (which one?). It can directly write this member to the
branch
buffer.
- same for a static array (eg, Int_t array[12])
- If a member is a pointer to TObject* or derived, the corresponding
Streamer
is called to stream this object in its branch buffer.
- If a member is a pointer to a TClonesArray, each member of the class
referenced by the TClonesArray is written to a separate branch. No
need
for a Streamer in this case.
Rene Brun
Maurik Holtrop wrote:
>
> 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)
> };
>
> ------------------------------------------------------------------------
>
> Maurik Holtrop <maurik.holtrop@unh.edu>
> UNH Nuclear Physics
>
> Maurik Holtrop
> UNH Nuclear Physics <maurik.holtrop@unh.edu>
> 9 Library Way Fax: (603) 862-2998
> Lee Home: (603) 659-8765
> NH Work: (603) 862-2019
> 03824 Netscape Conference Address
> USA
> Additional Information:
> Last Name Holtrop
> First Name Maurik
> Version 2.1
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