Formating the numbers in TLegend

Newbie
1

Dear experts,
I have a plot and I create a legend for it including some numbers (yields). the numbers are shown with 6 digits after the decimal point. I would like to format the numbers shown in my Legend to show one digit after decimal point.
example: 152.600000 → 152.6

Thank you for the help

test
test1918×987 29.4 KB

2

Can you post the code creating the legend ?

3

Hi @couet
Thanks for the quick response. Here is the code:

std::string BMassCTitle = "B-Mass Corresponding to Different B-Vertex Probabilities";
	TCanvas* BMass_canv = new TCanvas("BVertexProbability_BMass",BMassCTitle.c_str());
		BMass_canv->SetWindowSize(WW, WH);
		BMass_canv->SetGridx();
		BMass_canv->SetGridy();
		gStyle->SetOptStat(0);
		Functions[0]->SetTitle("B-Vertex Probabilities");
		Functions[0]->GetXaxis()->SetTitle("M_{B}(GeV)");
		Functions[0]->GetXaxis()->SetRangeUser(5.08, 5.48);
		Functions[0]->GetXaxis()->SetNdivisions(8);
		Functions[0]->GetYaxis()->SetRangeUser(0,(Functions[0]->GetMaximum()+0.1*(Functions[0]->GetMaximum())));
		Functions[0]->SetLineColor(1);
		Functions[0]->SetFillColor(1);
		Functions[0]->SetFillStyle(3001);
		Functions[0]->Draw("LF2");
		for (int i=1; i<(int)Functions.size(); i++) {
			int Color = i+1;
			if (Color==10)
				Color = 46;
			Functions[i]->SetLineColor(Color);
			Functions[i]->SetFillColor(Color);
			Functions[i]->SetFillStyle(3001);
			Functions[i]->Draw("LF2,SAME");
		}
	TLegend* BMass_l = new TLegend(0.75,0.60,0.95,0.85);
		BMass_l->SetTextSize(0.015);
		BMass_l->SetNColumns(3);
		BMass_l->SetHeader(BMassCTitle.c_str(),"C");
		for (int j=0; j<(int)Functions.size(); j++) {
			BMass_l->AddEntry(Functions[j],("VtxProb_{B} > "+to_string(BVtxStart+(j*BVtxStep))).c_str(),"l");
			BMass_l->AddEntry((TObject*)0,("SY = "+to_string(Yields[j].first.first)+" +/- "+to_string(Yields[j].first.second)).c_str(),"");
			BMass_l->AddEntry((TObject*)0,("BY = "+to_string(Yields[j].second.first)+" +/- "+to_string(Yields[j].second.second)).c_str(),"");
		}
		BMass_l->Draw();
	BMass_canv->Update();

In the above code, Functions is an array that contains TF1* objects.

4

in your example to_string does the conversion to string. I am not sure you can specify the formatting for to_string

5

Use: c++ - Set precision of std::to_string when converting floating point values - Stack Overflow
or: std::format in C++20 – MC++ BLOG if you can use C++20

6

The reason I used to_string() is because I thought I can only use strings in the AddEntry method.
Is it possible to format before turning into string? or just not use strings?

7

Try what ferhue suggested, or you can also use Form; e.g. if val is a double and you want 1 decimal:

BMass_l->AddEntry(mygraph,Form("%.1f",val),"l");
8

Hi @dastudillo,
That worked perfectly!
Thank you all for your help.