[Bug c++/12265] New: Downcast to class which derives privately rejected

[Bug c++/12265] New: Downcast to class which derives privately rejected

[olau at hardworking dot dk]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12265

           Summary: Downcast to class which derives privately rejected
           Product: gcc
           Version: 3.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: olau at hardworking dot dk
                CC: gcc-bugs at gcc dot gnu dot org

Given the source

  class Base {
  public:
    int x;
    void f();
  };

  class Derived: private Base { };

  void Base::f()
  {
    static_cast<const Derived&>(*this);
  }

GCC says

  $ g++ t1.c++ -o t1 -Wall
  t1.c++: I member function 'void Base::f()':
  t1.c++:11: error: `Base' is an inaccessible base of `Derived'

But as far as I know, that code is legal (I may be wrong). The C++ wrapper of
GTK+, gtkmm, uses such code and now doesn't work. Previous releases of GCC were
 fine. The precise version of GCC is:

  $ gcc-3.3 --version
  gcc-3.3 (GCC) 3.3.2 20030908 (Debian prerelease)

[Bug c++/12265] Downcast to class which derives privately rejected

[nathan at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12265


nathan at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


------- Additional Comments From nathan at gcc dot gnu dot org  2003-09-12 16:46 -------
not a bug. the cast is invalid. [5.2.9]/5 says it is ok if there's a
standard conversion from derived to base.[4.10]/3 says there's a conversion,
but if the base is inaccessible or ambiguous, the program is ill-formed.
[11.2]/4 says a base is accessible if an invented public member of the base
class is accessible. members of Base, such as Base::f have no special
access to the provate bases of Derived, so the base is inaccessible in
Base::f. If the cast were in a member or friend of Derived, it would be ok.

[Bug c++/12265] Downcast to class which derives privately rejected

[olau at hardworking dot dk]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12265



------- Additional Comments From olau at hardworking dot dk  2003-09-13 13:53 -------
OK, I'm sorry. I don't have a copy of the standard so I couldn't check. The
rules seem a little odd.

[Bug c++/12265] Downcast to class which derives privately rejected

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-09-13 14:09 -------
*** Bug 23849 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fang at csl dot cornell dot
                   |                            |edu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12265