Accessing stats-box from fit: Illegal pointer error

[Triple_S]

The problem is if you fit a TGraph with default settings no stats box is created and therefore it cannot be accessed. After you call gStyle->SetOptFit(x); with a non-zero value for x, the stats box is created and can be accessed with (TPaveText*)fivgraph->FindObject("stats")
Further information on the SetOptFit function can be found here: ROOT: TStyle Class Reference

Maybe this topic is also helpful it is a somehow related topic:

Fit statistics from two fits of the same TGraph

I suggest the following procedure: [code]{ gStyle->SetOptFit(1111); float x[5]={1,2,3,4,5}; float y[5]={1,2,5,4,5}; TGraph *gr = new TGraph(5,x,y); gr->SetMarkerStyle(20); gr->SetMarkerSize(1.3); gr->SetMarkerColor(2); gr->Fit(“pol1”,“Q”); gr->DrawClone(“ap”); gr->Fit(“pol2”,“Q”); gr->Draw(“p”); gPad->Update(); //to force the creation of "stats" TPaveStats st = (TPaveStats)gr->FindObject(“stats”); st->SetX1NDC(0.2); //new x start position st->SetX2NDC(0.5); //new x end position …