Re: TChain->GetEntry(jentry) - Segmentation Fault

From: Marc Escalier <escalier_at_lal.in2p3.fr>
Date: Tue, 31 Aug 2010 14:54:18 +0200

> Can someone direct as to how to locate/fix the problem? 

Hi,

i would suggest that you try to find the elementary instruction that crashes, using a dichotomical printing for example (or gdb if you know how to use it)

often, it is due to an instruction of something like :

myobject->myparameter
for which myobject is 0, so that it is forbidden to do it (something like an object with no memory allocation before)

the fact that when you remove events, the crash occurs to another place is strange anyway, and would point to an another direction, as for example forgetting to free memory

good luck

---

On Tue, 31 Aug 2010, Alexandros Attikis wrote:

> Hi ROOTers,
>
> I have a used  "makeClass" to access an ntuple and manipulate it using C++ code and ROOT. I compile
> the code with g++ and 
> have run on multiple samples including millions of events.
>
> Now, when trying to run on a specific QCD ntuple, I get a segmentation fault after ~140k events,
> always at the same point if a start from zero.
> I have tried to start 10 events before it and and runs smoothly up to some other event later on where
> it crashes with the same error. Obviously it is not 
> the specific event that is causing the seg. fault. I have also had a look at the ROOT files (2) and
> they seem okay. 
>
> I have used cout to pinpoint the error to right before I access the specific entry of the TChain:
> nb = fChain->GetEntry(jentry);
>
> I have tried to use gdb (beginner using this) but with no success of finding something useful. The
> Crash when running gdb gives:
> Program received signal SIGSEV, Segmentation fault. 
> 0x00000033c627ac4a in memset () from /lib64/libc.so.6
>
> Back-tracing hasn't been very useful, but as I said I am not experienced in using gdb.
>
> Can someone direct as to how to locate/fix the problem? 
> Is it the aforementioned piece of code or is it possible that the problem lies somewhere else?
>
>
> Cheers,
> Alexandros
>
>
Received on Tue Aug 31 2010 - 14:54:23 CEST