Writing and reading objects from a file... don't read back the same

Gordon Watts (gwatts@fnal.gov)
Thu, 23 Oct 1997 17:34:46 -0500

Hi,
Ok, I've been careful to isolate the problems I've been having this time.
So, while it is likely something I am doing, I can reproduce the behavior
in a small example program I've included below. Basically, it would seem
that when I write out an object and then read it back in, some of the
values read back in aren't put in the correct spot. This happens only when
split level = 1, not zero. I am using Windows NT 4.0, with MSVC 5.0 (not
4... if this isn't a bug in my code one of my first guesses will be an
incompatibility between 4.0 and 5.0 object layouts...>?).

First, the macro I use to run the test. Right below it is the output it
produces on my windows nt maching. I'm using root 1.03/05, btw:

------------ dump_out_test.cpp ----------------------------------------
{
gROOT -> Reset();

TFile output_file ("output.stuff", "RECREATE", "Junk");

TTree *output_tree = new TTree ("T", "Stuff", 1024);

B *event = new B;

output_tree -> Branch ("event", "B", &event, 2048, 1);

if (!output_tree)
cout << "No output tree!" << endl;

for (int i = 0; i < 10; i++) {
output_tree -> Fill();
}
event->Dump(); // What we think we wrote

output_file.Write();
// output_tree -> Print();
output_file.Close();

gROOT -> Reset();

TFile ("output.stuff");
TBranch *b = T.GetBranch("event");
B *event;
b->SetAddress(&event);
b->GetEvent(1);
event.Dump(); // What we read!
return 0;
}
---------------- Output of this maco on my Windows NT machine.
------------------

Processing dump_out_test.cpp...
_the_a_obj._item[2] 0
_the_a_obj.fUniqueID 0 object unique identifier
_the_a_obj.fBits 50331648 bit field status word
fUniqueID 0 object unique identifier
fBits 50331648 bit field status word
TFile Writing Name=output.stuff Title=Junk
_the_a_obj._item[2] 0
_the_a_obj.fUniqueID 50331648 object unique identifier <<<<<<<<<<
Huh?
_the_a_obj.fBits 0 bit field status word
fUniqueID 50331648 object unique identifier <<<<<<<<<<
<
Huh?
fBits 50331648 bit field status word

If I set splitlevel to be "0" when I write out, then fUniqueID is zero,
just as it is when
it is written out.

I much more complex programs I see this sort of behavior happening to my
data members (floats or integers are overwritten with the 50331648 number).

-------------- The LinkDef.h
-------------------------------------------------
//
// Stuff for CINT
//

#ifdef __CINT__

#pragma link off all globals;
#pragma link off all classes;
#pragma link off all functions;

#pragma link C++ class A;
#pragma link C++ class B;
#endif

-------------- test.h file
---------------------------------------------------------

#include "TObject.h"

class A : public TObject {

private:
float _item[2];

public:
A (void) {_item[0] = 0; _item[1] = 0;};

ClassDef (A,1) // The A Class
};

class B : public TObject {
public:
A _the_a_obj;

B (void) {};
A &get_A (void) {return _the_a_obj;};

ClassDef (B,1) // The B class
};

---------------- test.cpp file
-------------------------------------------------

#include
"test.h"

ClassImp(A)
ClassImp(B)

---------------------------------------------------------------------------------

I have not been able to check this in UNIX, and I do not have access to the
MSVC 4.0 compilers to see if that is the real cause here...

Cheers,
Gordon.