[Bug] TTree -> Fill() returns error only when put under if()

ROOT
1

Hello all,

I have a TTree with events; the TTree has one branch with the UNIX time of each event and some other branches. I want to select a subset of the events based on a time interval so I can analyse these separately. To make the selection, I create another tree and copy all the entries within the right time interval.

The following code works perfectly fine and copies all the events from tree to subtree:

void tree_time_filter(TTree* tree, TTree** subtree, Int_t time_i, Int_t time_f){
     *subtree = tree->CloneTree(0);
     Int_t t;
     tree->SetBranchAddress("UNIX time", &t);
     for(Long64_t i = 0; i<tree->GetEntries(); i++){
        tree->GetEntry(i);
        if (true)
        {
            (*subtree)->Fill();
        }
     }
     cout<<"Tree filtered. "<<(*subtree)->GetEntries()<< " entries were selected.\n";
     return;
}

The problem occurs when I replace if(true) by an actual condition:

void tree_time_filter(TTree* tree, TTree** subtree, Int_t time_i, Int_t time_f){ *subtree = tree->CloneTree(0); Int_t t; tree->SetBranchAddress("UNIX time", &t); for(Long64_t i = 0; i<tree->GetEntries(); i++){ tree->GetEntry(i); if (t > time_i && t < time_f) { (*subtree)->Fill(); } } cout<<"Tree filtered. "<<(*subtree)->GetEntries()<< " entries were selected.\n"; return; }

I receive the error: “Error: illegal pointer to class object subtree 0x0 3084 c:/… *** Interpreter error recovered ***”

The error line refers to (*subtree) -> Fill(), the same code that worked perfectly fine in the first example. Can anyone explain what goes wrong here?

Thank you!

PS. the problem is in the Int_t t; if I use 1<2 as condition all events are copied. If I actually print t, it prints proper UNIX timestrings.

2

Maybe it is because the subtree object is of type TTree* while (*subtree) is of type TTree so you cannot use (*subtree)->Fill(); but you should use (*subtree).Fill(); or subtree->Fill(); instead. I have no idea why it works on the code above though, but still you can try with this and see if it works.

Cheers
Guido

3

Thanks for the reply Guido! subtree is actually of the type TTree**; this was necessary to be able to access the underlying object in my main loop properly. Here is how I call the function:

TTree* subtree; tree_time_filter(tree,&subtree,time_i,time_f);

So (*subtree)->Fill() should be correct; again, everything works fine without the condition. Any other suggestions? Or maybe an alternative method to achieve a filtering of events? I’m new to root, but this should be a fairly common task I suppose?

Thank you!

4

You’re welcome, I’m new to root also, and didn’t notice the declaration of your function actually… :blush:
But I don’t see your point, you could still pass a TTree* object to your function instead of a TTree** one (properly modifying the code inside, of course) and then in your main loop (where you need it if I understood well) define another TTree** object as a pointer to the other one and use it, like

TTree* subtree;
TTree** psubtree=&subtree;
tree_time_filter(tree,&subtree,time_i,time_f);

If I misunderstood what did you mean by [quote]this was necessary to be able to access the underlying object in my main loop properly[/quote] ?

Guido

5

Hi Guido,

Haha can happen. I actually wrote the code with TTree* subtree at first, but if I then tried to access subtree in my main loop, I got an error. That’s why I made it a second order pointer; and that works. It is really just the condition that gives me trouble. Something about the fact that both t and the subtree are related to TTree* tree (via SetBranchAddress and CloneTree, respectively), seems to produce the error. Any other condition unrelated to t, or any other body of the if unrelated to subtree, works fine.

6

Hey people,

I asked the question on stackoverflow as well (stackoverflow.com/questions/2630 … 5#26340465).

Here is a working version of the function; the original error seems very much like a bug in the interpreter (I have no authorization to report bugs as I am not in CERN)

void tree_time_filter(TTree* tree, TTree** subtree, Int_t time_i, Int_t time_f){ *subtree = tree->CloneTree(0); Int_t t; tree->SetBranchAddress("UNIX time", &t); Long64_t i = 0; while (i < tree->GetEntries()) { for(i; i<tree->GetEntries(); i++){ tree->GetEntry(i); if (t > time_i && t < time_f) break; } for (i; i<tree->GetEntries(); i++){ tree->GetEntry(i); (*subtree)->Fill(); if (!(t > time_i && t < time_f)) break; } } cout<<"Tree filtered. "<<(*subtree)->GetEntries()<< " entries were selected.\n"; return; }