How to write a tree in the file

ROOT
1

Hello,

I have a program that creates a tree first, than fills the tree, opens a file with the name of the current date, writes the tree and closes the file. In a minute procedure repeats. If the date has changed tree->Reset() is called and file is created with the new name.

I create tree before opening a file and do not use SetDirectory method. It seems not to be right thefore I thought to use the following code

tree=new tree();
today=current_date;
while(1){
       tree->Fill();
       if(today!=current_date){
               tree->Reset();
               today=current_date
       }
       file=new TFile("today.root",);
       tree->SetDirectory(file,"RECREATE");
       tree->Write("","TObject::kOverwrite");
       tree->SetDirectory(0); //I do not want tree to disappear after file is closed
       file->Close();
       usleep(1000000);               //sleep for a minute
}

But is it right? Should I use AutoSave(“current date”) or is there more correct way?
This program is memory resident. There is another program-- viewer that reads the file and does some plotting therefore the file needs to be closed.

With respect,
Anton

2

Anton,

The logic in your example is badly wrong. You should change it
with something like shown below. However, in case you do not know,
ROOT supports reading of a Tree while the Tree is filled by
another process. I give an example in the two short files
in the attachements.

Rene

tree=new tree();
today=current_date;
while(1){
tree->Fill();
if(today!=current_date){
file=new TFile(“today.root”,“RECREATE”);
tree->Write("",“TObject::kOverwrite”);
delete file;
tree->Reset();
today=current_date
}
usleep(1000000); //sleep for a minute
}
treer.C (417 Bytes)
treew.C (370 Bytes)

3

Thank you Rene for reply,

I do not understand why it is ok not to use SetDirectory method.
It is written in manual that tree belongs to current directory, if I created a tree before creating TFile than tree should belong to the global directory, the open file becomes the current directory and I need to call tree->SetDirectory(TFile) in order to write the tree in this file.

I do not understand the logic of it.

Anton

4

Calling setDirectory is perfectly OK. Your code snippet was totally wrong.
When sending mails to roottalk or this Forum, we always ask for a concrete running short piece of code, NOT A KIND OF METALANGUAGE
like your code above.

Rene