TMultiGraph anomalies

ROOT
1

Hi guys,
I’m having some problem with TMultiGraph: when I try to change the range of the Xaxis the program crashes.

here a code to reproduce the crash

#include <iostream>

#include <TMultiGraph.h>
#include <TApplication.h>
#include <TCanvas.h>

#include <TGraph.h>
#include <TAxis.h>
#include <TH1.h>


using namespace std;

void graph();

int main(int argc, char* argv[])
{
    TApplication* rootapp = new TApplication("example",&argc, argv);
    graph();
    rootapp->Run();
    return 0;
}

void graph() {
   const Int_t n = 20;
   Double_t x[n], y1[n], y2[n];
   for (Int_t i=0; i<n; i++) {
     x[i] = i*0.1;
     y1[i] = 10*sin(x[i]+0.2);
     y2[i] = y1[i] + 2;
   }
   TGraph* gr1 = new TGraph(n,x,y1);
   TGraph* gr2 = new TGraph(n,x,y2);

   TMultiGraph *mg = new TMultiGraph("mg","a multigraph");
   mg->Add(gr1);
   mg->Add(gr2);
   TCanvas * c3 =new TCanvas("c3","A Multigraph");
   mg->GetXaxis()->SetRangeUser(0.,1.);  //the program property works without this line
   mg->Draw("AL");
}

and this is the crash

*** Break *** segmentation violation



===========================================================
There was a crash (#6 0xb6c4accb in SigHandler(ESignals) () from /usr/local/lib/root/libCore.so.5.34).
This is the entire stack trace of all threads:
===========================================================
#0  0xb77bb424 in __kernel_vsyscall ()
#1  0xb68107c3 in waitpid () from /lib/i386-linux-gnu/libc.so.6
#2  0xb6796ff3 in ?? () from /lib/i386-linux-gnu/libc.so.6
#3  0xb6c4395b in TUnixSystem::Exec(char const*) () from /usr/local/lib/root/libCore.so.5.34
#4  0xb6c48090 in TUnixSystem::StackTrace() () from /usr/local/lib/root/libCore.so.5.34
#5  0xb6c4abb7 in TUnixSystem::DispatchSignals(ESignals) () from /usr/local/lib/root/libCore.so.5.34
#6  0xb6c4accb in SigHandler(ESignals) () from /usr/local/lib/root/libCore.so.5.34
#7  0xb6c41a02 in sighandler(int) () from /usr/local/lib/root/libCore.so.5.34
#8  <signal handler called>
#9  0x080499fe in graph () at main.cpp:47
#10 0x08049824 in main (argc=1, argv=0xbfb0c764) at main.cpp:19
===========================================================


The lines below might hint at the cause of the crash.
If they do not help you then please submit a bug report at
http://root.cern.ch/bugs. Please post the ENTIRE stack trace
from above as an attachment in addition to anything else
that might help us fixing this issue.
===========================================================
#9  0x080499fe in graph () at main.cpp:47
#10 0x08049824 in main (argc=1, argv=0xbfb0c764) at main.cpp:19
===========================================================

can someone help me?
It is a root bug or I’m doing something wrong?
My root version is 5.34_21

Thanks

2

using cint for the same code I get:

root [16] mg->GetXaxis()->SetRangeUser(0.,1.); Error: illegal pointer to class object GetXaxis() 0x0 161 (tmpfile):1: *** Interpreter error recovered ***

3

Replace:

   mg->GetXaxis()->SetRangeUser(0.,1.);
   mg->Draw("AL");

with:

   mg->Draw("AL");
   // gPad->Modified(); gPad->Update(); // make sure it's really (re)drawn
   mg->GetXaxis()->SetRangeUser(0., 1.);
   gPad->Modified(); gPad->Update(); // make sure it's really (re)drawn
4

Hi Wile and thanks for your reply.
I tried your code and in this manner the program doesn’t crash but it doesn’t change the axis range…
some more hints?

thanks

5

Can it be that you left out the final “gPad” related calls?