Re: Which objects are stored by TFile::Write()?

Rene Brun (Rene.Brun@cern.ch)
Fri, 30 May 1997 17:52:46 +0200

Robert Casties wrote:
>
> Hello!
>
> Is there any scheme explaining which objects are stored by TFile::Write()
> and which have to be written by the object's ->Write()?
>
> I (after quite some time) found that e.g. TH1's are written
> automatically and TText's aren't.
>
> The TFile reference says on Write():
> [...]
> *-* Loop on all objects in memory (including subdirectories)
> *-* A new key is created in the KEYS linked list for each object
> *-* The list of keys is then saved on the file (via WriteKeys)
> *-* as a single data record
> [...]
>
> What is meant by 'all objects' in this case?
>

TFile::Write() writes all the objects entered into the list
of objects in memory associated with this file.
Assume TFile *file:
the file object has a list(TList) of objects that you can find at
TList *list = file->GetList();
By default, TH1 objects and TTree objects are automatically inserted
in this list when these objects are created.
TFile::Write scans all the objects in this list and for each object
executes obj->Write.
You can insert your own objects in this list if you want with a
statement like
file->GetList()->Add(object);
and your object will be automatically saved by TFile::Write.
Note that this is only convenient for objects derived from TNamed,
such as TH1, TTree, TF1.

Rene Brun