Re: TClonesArray

Dear Axel,

On March, 8 you wrote:

> Hi Mario,
> there's no need to copy the particles. Just add them to your TCLonesArray:
> 
> (*fpart)[m]=prt;

Axel, can you explain the statement from comments to the TObject *&TClonesArray::operator[](Int_t idx) method:

http://root.cern.ch/root/htmldoc/src/TClonesArray.cxx.html ...

    // Return pointer to reserved area in which a new object of clones
    // class can be constructed. This operator should not be used for
    // lefthand side assignments, like a[2] = xxx. Only like,
    // new (a[2]) myClass, or xxx = a[2].

By the way, this operator is described as inline function on the page http://root.cern.ch/root/htmldoc/TClonesArray.html I think there is a problem with THtml...

Thank you

-- 
Maxim Nikulin

> You can find a working example attached; running it with .L test.C+
> works for me.
> 
> Axel.
> 
> Mario Kadastik wrote:
> 


>>Hello,

>>

>>I'm trying to filter pythia events before saving them to tree. Currently

>>I get them like this:

>>TClonesArray* particles = (TClonesArray*)pythia->GetListOfParticles();

>>which I then save to tree like this:

>>TTree* part = new TTree("parttree","A tree of particles");

>>part->Branch("particles", &particles);

>>for (Int_t i=0; i<nEvents; i++) {

>>   pythia->GenerateEvent()

>>   part->Fill();

>>}

>>

>>What I'd like to do is to only take some of the particles that mach a

>>specific KF code. What I tried to do:

>>TClonesArray* particles = (TClonesArray*)pythia->GetListOfParticles();

>>TClonesArray *fpart = new TClonesArray("TMCParticle");

>>TClonesArray &fp = *fpart;

>>TMCParticle *prt = new TMCParticle();

>>Int_t fKF = 0, m=0;

>>TFile* f = new TFile(file,"RECREATE"); // open file to write output tree

>>TTree* part = new TTree("parttree","A tree of particles");

>>part->Branch("particles", &fpart);

>>for (Int_t i = 0; i < nEvents; i++) {

>>   fpart->Clear();

>>   pythia->GenerateEvent();

>>   m=0;

>>   for (Int_t j=0; j<particles->GetEntries(); j++) {

>>     prt=(TMCParticle*)particles->At(j);

>>     fKF=abs(prt->GetKF());

>>     if (prt->GetKS() < 20 && (fKF==5 || fKF==6 || fKF==9900041 ||

>>fKF==9900042 || (fKF>10 && fKF<17))) {

>>          new ((*fpart)[m]) *prt;

>>           m++;

>>     }

>>   }

>>   part->Fill();

>> }

>>For some reason this doesn't work. I get segfaults at part->Fill(). If I

>>added a cout << "added particle" << endl; just after new ((*fpart)[m])

>>*prt; then

>>it ran through a number of Fill()-s and then crashed.

>>

>>Mario

>>

>>PS! I did remove some cout << endl; and similiar lines so if it works

>>now then I'd be surprised :)

>>