Hi Alex,
CINT has the ability to retrive the ROOT using their "NAME". The name of a
ROOT object is usually the first argument of the constructor. In your case
this name is the same as the symbol for the variable holding the object
(i.e. h1). On the second run of your getH method, CINT noticed that their
is no defined variable named 'h1' at this point, so it interogates ROOT and
finds that it exist an histogram whose name is h1 (it is at this point
stored in h2). As a convenience it automatically declared and set a pointer
variable to this histogram (this is for fast prototyping).
You should note that object name is ROOT are important, especially for
histograms.
In you code, when you do
h2 = getH();
you might want to consider doing in addition
h2.SetName("h2");
(this would remove the symptoms you are seing).
Cheers,
Philippe.
PS. Also you are using the method SetBinContent to enter data in your
histogram,
you probably know that the method Fill is a high level version which also
accumulate statistics (Thus it is the prefered method for filling an
histogram).
-----Original Message-----
From: owner-roottalk@pcroot.cern.ch
[mailto:owner-roottalk@pcroot.cern.ch]On Behalf Of Alexander Dietz
Sent: Thursday, June 27, 2002 8:53 AM
To: root list
Subject: [ROOT] ROOT knows the existence of undefined object
Hello,
in the attachement there is a small program with a function 'getH' that
should return a histogram (as a real histogram, not as a pointer).
When starting the program (using ROOT Version 3.02/07 on g++-Linux) with
'prog()' two histograms 'h2' and 'h3' are created with the function
'getH'.
When trying to create 'h3' the value of 'counter' is 1, so that the adress
of 'h1' in 'getH' is printed out. Ths works but 'h1' is not defined yet!!
'h1' will be defined some lines later ('TH1F h1=...').
But why do ROOT know the existence of 'h1' before its creation?
Does ROOT not delete 'h1' at the end of 'getH' (as it is the standard
procedure for any C++ program)?
Is this a bug? Or is this extra property of ROOT?
Cheers
A. Dietz
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