How to retrieve two objects from two files

I have two TH1S objects in two files, now I want to put them on one canvas to compare. But I couldn’t by openning files one by one. Once I open a new file, the old object will be NULL.
Anyone can give me some hints?
Thanks a lot!

Do something like:

TFile *f1 = new TFile("file1.root"); TH1 *h1 = (TH1*)f1->Get("myFirstHist"); TFile *f2 = new TFile("file2.root"); TH1 *h2 = (TH1*)f2->Get("mySecondHostogram"); h1->Draw(); h2->Draw("same");