Howot use a std::vector as TTree branch

ROOT
1

Dear all,
i would like to use a std::vector as branch for a TTree.
Can you please point me to an example or similar ?

Thanks,
Max

2

i’ve tried successfully with this code

#include
#include “TFile.h”
#include “TRandom.h”
#include “TTree.h”
#if defined (MAKECINT)
#pragma link C++ class vector+;
#endif

void test()
{
TFile f(“tree.root”,“RECREATE”);

std::vector* vec = new std::vector;
TRandom r;
TTree *tree = new TTree(“tree”,“tree”);
tree->Branch(“var”, &vec);

for(int i=0; i<100;i++) (*vec).push_back(r.Rndm()*10);

tree->Fill();

f.Write();
}

and it works both on CINT both compiled.
Now i would like to include it in an (atlas) athena algorithm, but it seems to crash on tree Fill() call. Do you know about some implementation working as example ?

Thanks,
Max

3

[quote]Now i would like to include it in an (atlas) athena algorithm, but it seems to crash on tree Fill() call. Do you know about some implementation working as example ? [/quote]I don’t know the details of the athena framework, however, most likely, the issue is that the dictionary for vector has not been loaded.

Cheers,
Philippe.

4

Dear Philippe,
can you please point me to some info about what it’s meant for dictionary (i guess probably in ROOT user guide?) and how to load it ?

Max

5

Hi,

Yes you will find an explanation of what a dictionary is and how to make them in the User’s Guide.
In short this is a source file which contain a description of your classes. This source file (the dictionary) is generated by rootcint (or by genreflex in some case). Once you compile and load this dictionary into a ROOT session, CINT and ROOT know about your classes. You can then use them in the interpreter or save them into a ROOT file.

Your framework must have its own way of inducing the generation, compilation and linking of the dictionary. In some case, you need to write a ‘linkdef’ file and place it in the right or you may have to write a selection.xml file (Both thoses files are means to tell the dictionary generator (rootcint/genreflex) which classes to generate a dictionary for).

Cheers,
Philippe