Precision on printing variables in interactive session: feature or bug?

bomben · November 3, 2017, 2:50pm

Dear all,
what I want to report is a rather annoying feature (if not a bug):

$ root 
   ------------------------------------------------------------
  | Welcome to ROOT 6.11/01                http://root.cern.ch |
  |                               (c) 1995-2017, The ROOT Team |
  | Built for macosx64                                         |
  | From tag v6-09-02-2657-g9339de9e64, 18 May 2017            |
  | Try '.help', '.demo', '.license', '.credits', '.quit'/'.q' |
   ------------------------------------------------------------


Applying ATLAS style settings...

root [0] double Cdep = 1.65428e-12
(double) 0.000000
root [1] Cdep
(double) 0.000000
root [2] Cdep/1e-12
(double) 1.654280

Is it normal that my variable is presented as consistent with 0?
Luckily the correct value it is still there.

Am I missing something?
Best regards,
Marco Bomben

couet · November 3, 2017, 3:33pm

$ root
   ----------------------------------------------------------------
  | Welcome to ROOT 6.11/03                    http://root.cern.ch |
  |                                   (c) 1995-2017, The ROOT Team |
  | Built for macosx64                                             |
  | From heads/master@v6-11-02-590-g814f647, Nov 03 2017, 15:38:50 |
  | Try '.help', '.demo', '.license', '.credits', '.quit'/'.q'     |
   ----------------------------------------------------------------

root [0] double Cdep = 1.65428e-12;
root [1] printf("%g\n",Cdep);
1.65428e-12
root [2]

bomben · November 3, 2017, 4:04pm

Thanks. Still rather annoying in my opinion.
Regards,
Marco Bomben

couet · November 3, 2017, 4:05pm

ROOT command line is interpreted C++ . You should type C++.

bomben · November 3, 2017, 4:24pm

I see, but few months ago it was different:

$ root 
   ------------------------------------------------------------
  | Welcome to ROOT 6.08/06                http://root.cern.ch |
  |                               (c) 1995-2016, The ROOT Team |
  | Built for linuxx8664gcc                                    |
  | From tag v6-08-06, 2 March 2017                            |
  | Try '.help', '.demo', '.license', '.credits', '.quit'/'.q' |
   ------------------------------------------------------------

root [0] double Cdep = 1.6e-12
(double) 1.60000e-12
root [1] Cdep
(double) 1.60000e-12
root [2]

couet · November 3, 2017, 4:38pm

Ok. I am sure @Axel tell more about it.

tbis · November 3, 2017, 5:07pm

I guess it’s due to this change:

github.com

root-project/root/blob/v6-08-04/interpreter/cling/lib/Interpreter/ValuePrinter.cpp#L555-L559


std::string printValue(const double *val) {
  std::ostringstream strm;
  strm << std::showpoint << *val;
  return strm.str();
}

to:

github.com

root-project/root/blob/v6-11-02/interpreter/cling/lib/Interpreter/ValuePrinter.cpp#L337-L341


std::string printValue(const double *val) {
  cling::smallstream strm;
  strm << llvm::format("%.6f", *val);
  return strm.str();
}

To be honest, it would be great to have something like std::setprecision for the output stream within cling, but the implementation seems to work with normal strings and not streams which seems a bit unfortunate

Axel · November 3, 2017, 8:24pm

I agree that’s bad; I’ll fix it at least for 6.12: https://github.com/root-project/root/pull/1278

If you want setprecision just use it You can always use printf or the iostream manipulators from the prompt. But we should still get the default right and sensible.

bomben · November 4, 2017, 8:12am

Thanks a lot you all for the feedback!
Best regards,
Marco Bomben