Hi Valery,
unfortunately, this does not fix the problem (I had it right
in my real program; I apologize for not being careful in setting
up a test case).
I forgot to mention that this macro behaves the same way in root
v2_21_08 with KCC_3_3 on IRIX64 (cdfsga 6.2 03131016 IP25),
as well as v2_00_13b (also KCC_3_3) on Linux RH 5.0 (5.0.2, at Fermilab)
Thanks,
Petar
>
> At least when I changed your text and it works as expected.
> The result you got os expected as well, since you told Ntuple
> the address to keep the x values is "0" (very likey ZERO it could any
> value, since you didn't initiated Float_t x at all.
>
> Hope this helps,
> Valery
>
> > I'm trying to simultaneously fill an ntuple and read from it (in
> > another section of the code). One can argue that is perfectly
> > reasonable to collect a bunch of events, pause the run, analyze them,
> > and then keep on filling the ntuple.
> >
> > However, it seams that SetBranchAddress() interferes with the Fill()
> > method for the variables for which SetBranchAddress() was issued.
> > These variables end up being 0.
> >
> > The example below (which is a slightly modified root tutorial)
> > illustrates the point:
> >
> > {
> > FILE *fp = fopen("foo.txt","r");
> >
> > Float_t x,y,z;
> > Float_t x1;
> >
> > Int_t ncols;
> > Int_t nlines = 0;
> >
> > TNtuple *ntuple = new TNtuple("ntuple","data from ascii file","x:y:z");
> >
> > // ******************************************************************
> > ntuple->SetBranchAddress("x",x1); // <----- why is this dangerous???
> > // ******************************************************************
> >
> > while (1) {
> > ncols = fscanf(fp,"%f %f %f",&x, &y, &z);
> > if (ncols < 0) break;
> > if (nlines < 5) printf("x=%8f, y=%8f, z=%8f\n",x,y,z);
> > ntuple->Fill(x,y,z);
> > nlines++;
> > }
> > fclose(fp);
> > }
> >
> > Where the ntuple is read from the file
> > % cat foo.txt
> > 1 2 3
> > 1.1 2.2 3.3
> > -1.1 -2.2 -3.3
> > -1 -2 -3
> > 1.5 1.5 1.5
> >
> >
> > Here, if the SetBranchAddress() is commented out, everything is fine.
> > But once it's uncommented, all "x" entries are 0.0.
> >
> > My questions:
> >
> > 1. It's obvious that I'm doing something silly, but for a non-expert
> > like me it's hard to pin down the location of this silliness.
> >
> > 2. If this behavior of TTree is a feature (which it may well be), then
> what
> > is the correct way of doing this?
> >
> > Many thanks!
> >
> > Petar
> >