[Octave-bug-tracker] [bug #49743] Two-input version of `eval` fails for certain inputs

[Luis Mendo]

URL:
  <http://savannah.gnu.org/bugs/?49743>

                 Summary: Two-input version of `eval` fails for certain inputs
                 Project: GNU Octave
            Submitted by: lmendo
            Submitted on: Wed Nov 30 15:12:22 2016
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Luis Mendo
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.0
        Operating System: Any

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Details:

The two-input version of `eval` seems to be buggy. Try for example:


eval("s = ( +2 ( +2 ) +2 ) +2", "disp('Wrong input')")


That string should give an error when eval'ed, which should be caught. But
that's not the case: the above does nothing (no error, no displaying `Wrong
input` as it should). In fact, it seems to do worse than nothing: subsequent
statements are ignored. Try for example


eval("s = ( +2 ( +2 ) +2 ) +2", "disp('Wrong input')"); disp('Next
statement')


The explicit version does work:


try eval("s = ( +2 ( +2 ) +2 ) +2"); catch disp("Wrong input"); end;
disp('Next statement')


correctly displays `Wrong input` and then `Next statement`.

This bug happens in Octave 4.0.0, at least on Windows 7 and on Linux (tested
on https://octave-online.net/). I haven't tried Octave 4.2.

This also affects `str2num` (because it internally uses the two-input version
of `eval`). Try for example


s = str2num('( +2 ( +2 ) +2 ) +2'); whos s; disp("Next statement")


To fix `str2num`, simply replace line


eval (s, "m = []; state = false;");


by


try eval(s); catch m = []; state = false; end





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