use exceptions for better invalid index error reporting (bug #45957) * lo-array-gripes.h, lo-array-gripes.cc (index_exception): New base class for indexing errors. (invalid_index, out_of_range): New classes. (gripe_index_out_of_range): New overloaded function. (gripe_invalid_index): New overloaded functions. Delete version with no arguments. (gripe_invalid_assignment_size, gripe_assignment_dimension_mismatch): Delete. Change uses of gripe functions as needed. * Cell.cc (Cell::index, Cell::assign, Cell::delete_elements): Use exceptions to collect error info about and handle indexing errors. * data.cc (Fnth_element, do_accumarray_sum, F__accumarray_sum__, do_accumarray_minmax, do_accumarray_minmax_fun, F__accumdim_sum__): Likewise. * oct-map.cc (octave_map::index, octave_map::assign, octave_map::delete_elements): Likewise. * sparse.cc (Fsparse): Likewise. * sub2ind.cc (Fsub2ind, Find2sub): Likewise. New tests. * utils.cc (dims_to_numel): Likewise. * ov-base-diag.cc (octave_base_diag<DMT, MT>::do_index_op, octave_base_diag<DMT, MT>::subsasgn): Likewise. * ov-base-mat.cc (octave_base_matrix<MT>::subsref, octave_base_matrix<MT>::assign): Likewise. * ov-base-sparse.cc (octave_base_sparse<T>::do_index_op, octave_base_sparse<T>::assign, octave_base_sparse<MT>::delete_elements): Likewise. * ov-classdef.cc (cdef_object_array::subsref, cdef_object_array::subsasgn): Likewise. * ov-java.cc (make_java_index): Likewise. * ov-perm.cc (octave_perm_matrix::do_index_op): Likewise. * ov-range.cc (octave_range::do_index_op): Likewise. * ov-re-diag.cc (octave_diag_matrix::do_index_op): Likewise. * ov-str-mat.cc (octave_char_matrix_str::do_index_op_internal): Likewise. * pt-assign.cc (tree_simple_assignment::rvalue1): Likewise. * pt-idx.cc (tree_index_expression::rvalue, tree_index_expression::lvalue): Likewise. * Array-util.cc (sub2ind): Likewise. * toplev.cc (main_loop): Also catch unhandled index_exception exceptions. * ov-base.cc (octave_base_value::index_vector): Improve error message. * ov-re-sparse.cc (octave_sparse_matrix::index_vector): Likewise. * ov-complex.cc (complex_index): New class. (gripe_complex_index): New function. (octave_complex::index_vector): Use it. * pt-id.h, pt-id.cc (tree_identifier::is_variable, tree_black_hole::is_variable): Now const. * pt-idx.cc (final_index_error): New static function. (tree_index_expression::rvalue, tree_index_expression::lvalue): Use it. * index.tst: New tests.

--- a/libinterp/octave-value/ov-complex.cc	Fri Oct 02 12:25:39 2015 -0400
+++ b/libinterp/octave-value/ov-complex.cc	Fri Oct 02 15:07:37 2015 -0400
@@ -480,3 +480,39 @@
       return octave_base_value::map (umap);
     }
 }
+
+class complex_index_exception : public index_exception
+{
+public:
+
+  complex_index_exception (const char *value) : index_exception (value) { }
+
+  ~complex_index_exception (void) { }
+
+  const char* explain (void) const
+  {
+    return "subscripts must be real (forgot to initialize i or j?)";
+  }
+
+  // ID of error to throw.
+  const char* id (void) const
+  {
+    return error_id_invalid_index;
+  }
+};
+
+// Complain if a complex value is used as a subscript
+
+void
+gripe_complex_index (Complex idx)
+{
+  // FIXME: don't use a fixed size buffer!
+
+  char buf [100];
+
+  sprintf (buf, "%g%+gi", std::real(idx), std::imag(idx));
+
+  complex_index_exception e (buf);
+
+  throw e;
+}