Return correct error messages on octave-streams when scanf fails (bug #56396) * file-io.cc (Fsscanf): Add BIST test for bug #56396. * oct-stream.cc (base_stream::do_scanf): Perform end-of-scan processing if EOF has been detected, not just when FAILBIT has been set. If FAILBIT has been set, call error() to set an error message on the octave-stream. At end of function, assign any partial results obtained to output. Don't require that all conversions were successful. * io.tst: Update BIST tests to reflect new Matlab-compatible behavior for error message output.

--- a/libinterp/corefcn/file-io.cc	Sat Jun 01 21:01:45 2019 -0700
+++ b/libinterp/corefcn/file-io.cc	Mon Jun 03 09:04:41 2019 -0700
@@ -1166,6 +1166,15 @@
   return retval;
 }
 
+/*
+%!test <*56396>
+%! [val, count, errmsg, nextpos] = sscanf ('1234a6', '%2d', 3);
+%! assert (val, [12; 34]);
+%! assert (count, 2);
+%! assert (errmsg, "sscanf: format failed to match");
+%! assert (nextpos, 5);
+*/
+
 DEFMETHOD (scanf, interp, args, ,
            doc: /* -*- texinfo -*-
 @deftypefn  {} {[@var{val}, @var{count}, @var{errmsg}] =} scanf (@var{template}, @var{size})