Error in Extracting Histogram from Root file

[HIMANSHU_SHARMA]

I want extract an histogram from a root file. I am using the following macro.

{ 
  TFile *f = new TFile("252.root"); 
  f->ls(); 
 TH1F * Px = (TH1F*)f->Get("Px"); 
  Px->Draw(); 
}

It is returning some error.

> error: redefinition of 'f'
TFile *f = new TFile("252.root"); 

Should I have to use the same name of the histogram here “Px” as declared in the root file.

Thank You

[couet]

Some variable are define by some external include files parsed by cling. of many be you already define “f” in your rootlogon.C. Try to use an other variable name.

[HIMANSHU_SHARMA]

I tried using *myfile insted of *f. The following trace appeared.

TFile** 252.root
TFile* 252.root
KEY: TTree AMPT;1 AMPT DST Tree#0 0x00007fb68751207a in __GI___waitpid (pid=7957, stat_loc=stat_loc
entry=0x7ffe719d9b20, options=options
entry=0) at …/sysdeps/unix/sysv/linux/waitpid.c:29
1 0x00007fb68748afbb in do_system (line=) at …/sysdeps/posix/system.c:148
2 0x00007fb68808e1cd in TUnixSystem::StackTrace() () from /home/himanshu/root/lib/libCore.so
3 0x00007fb6837254c5 in cling::MultiplexInterpreterCallbacks::PrintStackTrace() () from /home/himanshu/root/lib/libCling.so
4 0x00007fb683724f88 in cling_runtime_internal_throwIfInvalidPointer () from /home/himanshu/root/lib/libCling.so
5 0x00007fb6888261de in ?? ()
6 0x00007ffe719dbf50 in ?? ()#7 0x00007fb683725a87 in cling::Interpreter::RunFunction(clang::FunctionDecl const*, cling::Value*) [clone .part.253] [clone .constprop.361] () from /home/himanshu/root/lib/libCling.so
8 0x00007fb6837291bd in cling::Interpreter::EvaluateInternal(std::__cxx11::basic_string<char, std::char_traits, std::allocator > const&, cling::CompilationOptions, cling::Value*, cling::Transaction**, unsigned long) () from /home/himanshu/root/lib/libCling.so
9 0x00007fb6837293c6 in cling::Interpreter::process(std::__cxx11::basic_string<char, std::char_traits, std::allocator > const&, cling::Value*, cling::Transaction**, bool) () from /home/himanshu/root/lib/libCling.so
10 0x00007fb6837ace2e in cling::MetaProcessor::readInputFromFile(llvm::StringRef, cling::Value*, unsigned long, bool) () from /home/himanshu/root/lib/libCling.so
11 0x00007fb6836ea3da in TCling::ProcessLine(char const*, TInterpreter::EErrorCode*) () from /home/himanshu/root/lib/libCling.so
12 0x00007fb6836dcb1d in TCling::ProcessLineSynch(char const*, TInterpreter::EErrorCode*) () from /home/himanshu/root/lib/libCling.so
13 0x00007fb687fb80fa in TApplication::ExecuteFile(char const*, int*, bool) () from /home/himanshu/root/lib/libCore.so
14 0x00007fb687fb9646 in TApplication::ProcessLine(char const*, bool, int*) () from /home/himanshu/root/lib/libCore.so
15 0x00007fb6883fb724 in TRint::ProcessLineNr(char const*, char const*, int*) () from /home/himanshu/root/lib/libRint.so
16 0x00007fb6883fba05 in TRint::HandleTermInput() () from /home/himanshu/root/lib/libRint.so
17 0x00007fb68808fcac in TUnixSystem::CheckDescriptors() () from /home/himanshu/root/lib/libCore.so
18 0x00007fb6880910ea in TUnixSystem::DispatchOneEvent(bool) () from /home/himanshu/root/lib/libCore.so
19 0x00007fb687f8e814 in TSystem::InnerLoop() () from /home/himanshu/root/lib/libCore.so
20 0x00007fb687f8d34f in TSystem::Run() () from /home/himanshu/root/lib/libCore.so
21 0x00007fb687fb5f4f in TApplication::Run(bool) () from /home/himanshu/root/lib/libCore.so
22 0x00007fb6883fcff7 in TRint::Run(bool) () from /home/himanshu/root/lib/libRint.so
23 0x0000000000400c1c in main ()
Error in TRint::HandleTermInput(): cling::InvalidDerefException caught: Trying to dereference null pointer or trying to call routine taking non-null arguments

Thank you

[couet]

Is it possible to access this file ?