I'm still a bit confused about the behaviour of TBranchObject. The main
description of it seems to be in HowtoWriteTree.html:
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If a data member is pointer to an object, a special branch of type
TBranchObject is created. This is the case in our example for the data
member fH, a pointer to an histogram. The fH branch will be filled by
calling the class Streamer function to serialize this object into the
branch buffer.
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This should set up the pointers of the objects read from a file correctly.
What happens, if the object pointed to belongs to another branch? A small
test showed that also these objects are read, but not the entire
TClonesArray they belong to (judging by the speed).
A part of my current test looks like this:
class ReconstructedTrack:
some parameters
(not done yet:) list of pointers to detector hits
class Event:
two pointers to trigger particles
pointer to TClonesArray of ReconstructedTracks
pointer to TClonesArray of detector hits
The result looks quite promising: it is possible to access the different
branch levels of Event (like in the famous Event example) and the reading
of the trigger particle pointers reads the correct parts of the clones
array.
Is this observation correct? It still seems like magic. If yes, does it
mean that all chains of pointers are restored even if only a very small
branch is read? And: how can I avoid to read large unimportant fractions
of an event, which are pointed to?
Another question: can I find somewhere an example of pointers to
calibration constants, which have different cycles than the events?
Best regards
Christoph
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Christoph Borgmeier | Mail: DESY -F15-, Notkestr. 85, 22607 Hamburg
Humboldt Univ Berlin | Phone: +49 40 8998 2844
Email: borg@ifh.de |
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