Making histogram from multiple text files

Can someone please let me know how can I make a histogram from multiple data files?
For one data file with one column only I am doing this:

void Only_one_file(){

TH1F *h = new TH1F(“h”, “histogram”,1000,5.,9.);
ifstream inp; double x;“data.dat”);

for (int i=1; i<=1000; i++) {

  inp >> x;



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Uncle Google → C++ read multiple files