Set bin width defined by user in TH1

[p73]

I have data which I want to represent by a histogram.

Two notes before question:

1. I do not know the range in that data in advance. So I would like to not specify ranges of a histogram.
2. In order to further analysis, for example, to compare this data with other which is also represented by a similar histogram, I want histograms to have the same bin width. And I know this value of desired width in advance.
3. All histograms are TH1I integer type.

Taking into account the first note I create a histogram as follows:

TH1I hist = new TH1I( name, title, Nbins, 0, 0);

On the other hand it fixes bin width implicitly (by specifying number of bins) which is not desired.

Question: How to set fixed bin width without knowing range of a histogram in advance? If possible.

[atha.stam]

Do you have your data stored in an array?

[p73]

It is in separate files. Actually it is .dat files from CAEN ADC. Few lines of such a file are (in this case 2nd column is ADC channel, 3rd - base line):

0 1115 1100
1 1116 1100
2 1116 1100
...

I.e. I read these files line by line in a loop and fill histograms each iteration.

[p73]

What if it would be in an array? What solution would you provide in that case?

[Wile_E_Coyote]

{
  TTree *t = new TTree("t", "a temporary tree");
  t->ReadFile("CAEN_ADC.dat", "i/I:a:b");
  Double_t xmin = t->GetMinimum("i");
  Double_t xmax = t->GetMaximum("i") + 1.;
  Int_t n = Int_t(xmax - xmin + 0.5);
  TH1D *h = new TH1D("h", "CAEN ADC", n, xmin, xmax);
#if 0 /* 0 or 1 */
  t->Project("h", "i + 0.5", "a"); // "raw" ADC
#else /* 0 or 1 */
  t->Project("h", "i + 0.5", "a - b"); // ADC - base_line
#endif /* 0 or 1 */
  delete t; // no longer needed
  h->Draw("");
}