error in compiling

[ruchi01]

Hi!
I am a beginner to c++. I tried to compile and link following code


#include "Pythia.h"
#include "TH1.h"
#include "TTree.h"
#include "TFile.h"
using namespace Pythia8;
int ex1() {
// Generator. Process selection. LHC initialization. Histogram.
Pythia pythia;
pythia.readString("HardQCD:all = on");
pythia.readString("PhaseSpace:pTHatMin = 20.");
pythia.init( 2212, 2212, 14000.);
TFile *file = TFile::Open("ex1.root","recreate");
Event *event = &pythia.event;
TTree *T = new TTree("T","ev1 Tree");
T->Branch("event","Event",&event);
TH1F *mult = new TH1F("mult","charged multiplicity", 100, -0.5, 799.5);
// Begin event loop. Generate event. Skip if error. List first one.
for (int iEvent = 0; iEvent < 100; ++iEvent) {
if (!pythia.next()) continue;
//if (iEvent < 1) {pythia.info.list(); pythia.event.list();}
// Find number of all final charged particles and fill histogram.
int nCharged = 0;
for (int i = 0; i < pythia.event.size(); ++i)
if (pythia.event[i].isFinal() && pythia.event[i].isCharged())
++nCharged;
mult->Fill( nCharged );
T->Fill();
// End of event loop. Statistics. Histogram. Done.
}
pythia.statistics();
cout << mult;
T->Print();
T->Write();
delete file;
return 0;
}


I used the command

g++ -o2 -L$ROOTSYS/lib -L$PYTHIA8/lib -I$ROOTSYS/include -I$PYTHIA8/include main01_r.cc

and i got this


/usr/lib/gcc/i386-redhat-linux/3.4.6/../../../crt1.o(.text+0x18): In function `_start':
: undefined reference to `main'
/tmp/cclhLO7b.o(.text+0x148): In function `ex1()':
: undefined reference to `Pythia8::Pythia::Pythia(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
/tmp/cclhLO7b.o(.text+0x213): In function `ex1()':
: undefined reference to `Pythia8::Pythia::readString(std::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool)'
/tmp/cclhLO7b.o(.text+0x2d5): In function `ex1()':
: undefined reference to `Pythia8::Pythia::readString(std::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool)'
/tmp/cclhLO7b.o(.text+0x374): In function `ex1()':
: undefined reference to `Pythia8::Pythia::init(int, int, double)'
/tmp/cclhLO7b.o(.text+0x392): In function `ex1()':
: undefined reference to `TFile::Open(char const*, char const*, char const*, int, int)'
/tmp/cclhLO7b.o(.text+0x3d7): In function `ex1()':
: undefined reference to `TTree::TTree(char const*, char const*, int)'
/tmp/cclhLO7b.o(.text+0x3f6): In function `ex1()':
: undefined reference to `TObject::operator delete(void*)'
/tmp/cclhLO7b.o(.text+0x47e): In function `ex1()':
: undefined reference to `TH1F::TH1F(char const*, char const*, int, double, double)'
/tmp/cclhLO7b.o(.text+0x49d): In function `ex1()':
: undefined reference to `TObject::operator delete(void*)'
/tmp/cclhLO7b.o(.text+0x4dd): In function `ex1()':
: undefined reference to `Pythia8::Pythia::next()'
/tmp/cclhLO7b.o(.text+0x5ec): In function `ex1()':
: undefined reference to `Pythia8::Pythia::statistics(bool, bool)'
/tmp/cclhLO7b.o(.text+0x67a): In function `ex1()':
: undefined reference to `Pythia8::Pythia::~Pythia()'
/tmp/cclhLO7b.o(.text+0x6a4): In function `ex1()':
: undefined reference to `Pythia8::Pythia::~Pythia()'
/tmp/cclhLO7b.o(.text+0x723): In function `__static_initialization_and_destruction_0(int, int)':
: undefined reference to `TVersionCheck::TVersionCheck(int)'
/tmp/cclhLO7b.o(.gnu.linkonce.t._ZN7TObjectnwEj+0xd): In function `TObject::operator new(unsigned int)':
: undefined reference to `TStorage::ObjectAlloc(unsigned int)'
/tmp/cclhLO7b.o(.gnu.linkonce.t._ZN5TTree6BranchIN7Pythia85EventEEEP7TBranchPKcS6_PPT_ii+0x27):In function `TBranch* TTree::Branch<Pythia8::Event>(char const*, char const*, Pythia8::Event**,int, int)':
: undefined reference to `TBuffer::GetClass(std::type_info const&)'
collect2: ld returned 1 exit status



Can anyone please tell where the problem is?

Thanks in advance!

[kbw]

Please use the code formating tag on the right to format your code.

The first error says your program doesn't provide a function main.
The remainder seem to be caused by you not linking to the right libraries.