TChain and TTreeFormula, segmentation violation

ROOT
1 
#include "TChain.h"
#include "TTreeFormula.h"

void test()
{
	TChain* c=new TChain("T","T");
	c->Add("rootfiles/3924.root");
	c->Add("rootfiles/3925.root");
	TTreeFormula ttf("ttf","abs(L.gold.dp)<0.3",c);
}





root -b -q test.C
root [0] 
Processing test.C...

 *** Break *** segmentation violation
(no debugging symbols found)
Attaching to program: /proc/3453/exe, process 3453
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
[Thread debugging using libthread_db enabled]
[New Thread 0xb6f346c0 (LWP 3453)]
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)...done.
(no debugging symbols found)
0xb7f6c430 in __kernel_vsyscall ()
error detected on stdin
The program is running.  Quit anyway (and detach it)? (y or n) [answered Y; input not from terminal]
Detaching from program: /proc/3453/exe, process 3453
Root > Function test() busy flag cleared

Dear ROOTERs
anyone knows how to fix it?
Thanks

2

I figure it out.
Just add c->LoadTree(0) after Add.