Re: How to reference an object in a TFile?

Hi Tom,

Tom Roberts wrote:
> Thank you. My problem turned out to be an issue with
> std::vector<TNtuple*>. I got it working with TList. Object ownership
> and removal from memory had nothing to do with it. Cint being willing
> to pun between object* and object made this more difficult to debug.
>
> Still one question: what is the difference between directories and
> folders, and why are there both?

TFolder manages objects in memory only while TDirectory can do it with objects in a file too.

Rene Brun
>
>
> Tom Roberts
>
>
> Fine, Valeri wrote:
>> May I advice you to read first the "Object Ownership"
>> ftp://root.cern.ch/root/doc/chapter8.pdf
>> <ftp://root.cern.ch/root/doc/chapter8.pdf> from User's Guide v5.14
>> http://root.cern.ch/root/doc/RootDoc.html
>> <http://root.cern.ch/root/doc/RootDoc.html> ?
>> It is to answer the very basic things your code is facing.
>> Hope this helps, Valeri
>> ________________________________
>>
>> From: owner-roottalk_at_pcroot.cern.ch on behalf of Tom Roberts
>> Sent: Sun 1/7/2007 4:44 PM
>> To: 'ROOT Talk'
>> Subject: [ROOT] How to reference an object in a TFile?
>>
>>
>>
>> I am an experienced C++ developer new to root.
>>
>> I am implementing a graphical user interface for my users, and I want
>> them to be able to select any single TNtuple out of any open Root file.
>>
>> So I loop over gROOT->GetListOfFiles() and descend each file's directory
>> tree, putting the TNtuple pointers into a std::vector<TNtuple*> (and
>> also their names into a TGListBox from which the user will select).
>> Inside that loop I can call p->GetName() and p->GetEntries(), for p the
>> current pointer to a TNtuple. But later, after all NTuples have been
>> found and the loop over files is complete, I cannot call any TNtuple
>> function using those pointers -- an interpreter segfault happens. I
>> guess those objects no longer remain in memory (??).
>>
>> Is there a better way to do this? I do not expect my users to understand
>> TBrowser and then know enough to open the TreeViewer -- I am basically
>> re-implementing HistoScope for Root files....
>>
>> I tried keeping a std::vector<TString> with each entry the full name of
>> the TNtuple (i.e. /path/file.root:/path/name ). How can I turn that name
>> into a TNtuple pointer I can use? -- do I need to laboriously descend
>> into the file as before? (a pain, as TDirectory::GetPath() does not
>> return the actual root path when inside a TFile)
>>
>> What is the difference between folders and directories? -- there seem to
>> be parallel but different functions and objects...(??)
>>
>> How does it decide which objects to remove from memory? -- after all, I
>> had recently referenced each and every NTuple....
>>
>> [If it matters, my loop just uses pointers to TDirectory-s,
>> never opening any TFile nor calling any cd() function.]
>>
>>
>> Tom Roberts
>>
>>
>>
Received on Mon Jan 08 2007 - 11:41:36 CET