Re: Reading strings from a tree?

Pasha Murat (murat@cdfsga.fnal.gov)
Mon, 27 Jul 1998 23:31:48 -0500 (CDT)

stefan kluth writes:
>
> Hello,
>
> I try to write strings into a tree (and to read them back of course!). I
> seem to be able to write strings ok, but I can't read them back. Here is
> what I do:
>
> ...
>
> TFile myfile( "treetest.root", "RECREATE" );
> TTree* tree = new TTree( "tree", "ROOT test tree" );
> char* ach;
> TBranch* brach= tree->Branch( "ach", (void*)ach, "ach/C", 8000 );
>
> ... now loop and fill ach with different strings, works ok.
>
> Then I do in root (2.00/08):
>
> root [0] #include <iostream.h>
> root [1] TFile myfile( "treetest.root");
> root [2] myfile.ls();
> TFile** treetest.root
> TFile* treetest.root
> KEY: TTree tree;1 ROOT test tree
> root [3] TBranch *brach = tree.GetBranch("ach");
> root [4] char* ach;
> root [5] brach->SetAddress(ach);
> root [6] tree.GetEvent(3);
> root [7] cout << ach << endl;
>
> root [8]
>
>
> So, somehow the strings stored in the tree branch "ach" don't get assigned
> to the char* ach.
>
> Any ideas as what am I doing wrong here?
>

You may try to define the tree variable when you're reading the data back.
Find below the example of macro which does what (I believe) you need.

regards, pasha.

-------------------------------------------- test.C
int test(int mode) {
char* ach = new char[100];
if (mode == 0) {
// writing

TFile* myfile = new TFile ("test.root", "RECREATE" );
TTree* tree = new TTree ("Tree", "ROOT test tree" );
TBranch* brach = tree->Branch("ach", (void*)ach, "ach/C", 8000 );

for (int i=0; i<99; i++) {
for (int j=0; j<i; j++) ach[j] = 48+i;
ach[i] = 0;
tree->Fill();
}
delete [] ach;
tree->Write();
delete myfile;
}
else {
// reading

TFile* myfile = new TFile( "test.root");
TTree* tree = (TTree* ) myfile->Get("Tree");
TBranch *brach = tree->GetBranch("ach");
brach->SetAddress((void*)ach);

for (int i=1; i<10; i++) {
ach[0] = 0C;
tree->GetEvent(i);
cout << ach << endl;
}
delete myfile;
}
return 0;
}
--------------------------------------------------
root [14] .L test.C
root [15] int rc;
root [16] rc = test(0)
(int)0
root [17] rc = test(1);
1
22
333
4444
55555
666666
7777777
88888888
999999999
root [18]