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From: "josephttilahun at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/92798] -fshort-enums can break iterators of std::map
Date: Thu, 05 Oct 2023 17:43:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D92798

Joseph Tilahun <josephttilahun at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |josephttilahun at gmail do=
t com

--- Comment #4 from Joseph Tilahun <josephttilahun at gmail dot com> ---
I encountered this same bug when using -fshort-enums with std::map iterator=
s.

The fact that -fshort-enums breaks std::map iterators implies that there's =
an
enum somewhere without an explicit underlying type. In
/usr/include/c++/9/bits/stl_tree.h, there's an enum that enumerates the
possible colors of a node of a red-black tree:

  enum _Rb_tree_color { _S_red =3D false, _S_black =3D true };

  struct _Rb_tree_node_base
  {
    typedef _Rb_tree_node_base* _Base_ptr;
    typedef const _Rb_tree_node_base* _Const_Base_ptr;

    _Rb_tree_color      _M_color;
    _Base_ptr           _M_parent;
    _Base_ptr           _M_left;
    _Base_ptr           _M_right;

    // Other code that's not relevant
  }

The _Rb_tree_color enum does not have an explicit underlying type. I tried
modifying this to:

  enum _Rb_tree_color : int { _S_red =3D false, _S_black =3D true };

  struct _Rb_tree_node_base
  {
    typedef _Rb_tree_node_base* _Base_ptr;
    typedef const _Rb_tree_node_base* _Const_Base_ptr;

    _Rb_tree_color      _M_color;
    _Base_ptr           _M_parent;
    _Base_ptr           _M_left;
    _Base_ptr           _M_right;

    // Other code that's not relevant
  }

and -fshort-enums does not break this. I also tried modifying this to:

  enum _Rb_tree_color { _S_red =3D false, _S_black =3D true };

  struct _Rb_tree_node_base
  {
    typedef _Rb_tree_node_base* _Base_ptr;
    typedef const _Rb_tree_node_base* _Const_Base_ptr;

    int                 _M_color;
    _Base_ptr           _M_parent;
    _Base_ptr           _M_left;
    _Base_ptr           _M_right;

    // Other code that's not relevant
  }

and -fshort-enums does not break this.

It seems to me that the _Rb_tree_color enum is the real problem. -fshort-en=
ums
simply exposes the fact that the _Rb_tree_color enum does not have an expli=
cit
underlying type. Is there a reason why the _Rb_tree_color enum does not hav=
e an
explicit underlying type?=