[cernRoot] how to get contours from a TH2D

here, i use a TMultiGraph to save the gotten contours, because the contours may be not closed in a TH2D, with the function TMultiGraph * GetContours(const char * fn, const char * th2dname, int nlevel). And in the Test() function, the TGraph objects of the TMultiGraph are extracted.

void Test(){    TMultiGraph * mg = GetContours("res_b64_fit_3id_ddmts_mc.root", "0", 1);    mg->DrawClone("ACP");//    TList * list = mg->GetListOfGraphs();//    TGraph * gr = (TGraph *)list->First();//    gr->DrawClone("ACP");//    cout << list->GetSize() << endl;delete mg;}TMultiGraph * GetContours(const char * fn, const char * th2dname, int nlevel){    TGraph ** gr;    TFile * f = new TFile(fn, "read");    TH2D * h = (TH2D *) f->Get(th2dname);    double chisq = h->GetMinimum();    double contours[2] = {chisq + 2.3, chisq + 6.14};    h->SetContour(2, contours);    TCanvas * cc = new TCanvas(th2dname, th2dname);    cc->Divide(2,2);    cc->cd(1);    h->Draw("CONT1");    cc->cd(2);    h->Draw("CONT Z LIST");    cc->Update();/////////////////////////////    TObjArray * cont = (TObjArray *)(gROOT->GetListOfSpecials()->FindObject("contours"));    TList * list = (TList *)cont->At(nlevel);    int ngr = list->GetSize();    TGraph * grtemp;    if(ngr > 0)    {        gr = new TGraph * [ngr];        grtemp = (TGraph *)list->First();        gr[0] = grtemp->Clone();        for(int igr = 1; igr < ngr; ++ igr)        {            grtemp = (TGraph *)list->After(grtemp);            gr[igr] = grtemp->Clone();        }    }    cc->Close();    delete cc;    f->Close();    delete f;    delete grtemp;    TMultiGraph * mg = new TMultiGraph();    for(int i = 0; i < ngr; ++ i)        mg->Add(gr[i]);    delete [] gr;    return mg;}