Canvas without histogram from ROOT Guide For Beginners

Hello all,
I took this guide and tried 7.1 Storing ROOT Objects.

When try this macros using .x read_from_file.C:

void read_from_file(){

    // Let's open the TFile
    TFile in_file("my_rootfile.root");

    // Get the Histogram out
    TH1F* h;

    // Draw it
    auto myCanvas = new TCanvas();

it gives canvas without histogram.

If use “online” method

>  root my_rootfile.root
root [0]
Attaching file my_rootfile.root as _file0...
root [1] _file0->ls()
TFile**     my_rootfile.root
 TFile*     my_rootfile.root
  KEY: TH1F my_histogram;1 My Title
root [2] my_histogram->Draw()

everything is fine.

What I do wrong? I use Ubuntu 18.04.1 LTS with ROOT 6.10.04

Instead of h->DrawClone();, use: h->SetDirectory(gROOT); h->Draw();

Works! Thank! How did you understand that you need to write exactly this?