Bug: C++ access checking

Bug: C++ access checking

[Nathan Sidwell]

Hi,
I believe this to be a bug, but it's possibly my misunderstanding of 11.2/4.

struct A
{
  protected:
  int m;
};
  
struct C : A
{
  void foo(A *);
  void baz(C *);
};
  
void C::foo(A *ptr)
{
  ptr->m;
}
 
void C::baz(C *ptr)
{
  ptr->m;
}

the 19990405 snapshot says,

nathan@manao:161>ss-g++ -c access.C 
access.C: In method `void C::foo(A *)':
access.C:4: `int A::m' is protected
access.C:15: within this context

I think A::m is accessible in C::foo, even though we're not accessing this's
A::m, but some random A *'s. The third case given in 11.2/4 says,
 "m as a member of N if protected, and the reference occurs ... in a member of
friend of a class P derived from N, where m as a member of P is private or
protected."

In this case N is A, and P is C. m is protected in C and we're in a member of
C. It doesn't mention that the object we're fetching m from has to be a P.

Or am I missing something?

nathan
-- 
Dr Nathan Sidwell :: Computer Science Department :: Bristol University
      You can up the bandwidth, but you can't up the speed of light      
nathan@acm.org  http://www.cs.bris.ac.uk/~nathan/  nathan@cs.bris.ac.uk

Re: Bug: C++ access checking

[Mark Mitchell]

>>>>> "Nathan" == Nathan Sidwell <nathan@acm.org> writes:

    Nathan> In this case N is A, and P is C. m is protected in C and
    Nathan> we're in a member of C. It doesn't mention that the object
    Nathan> we're fetching m from has to be a P.

    Nathan> Or am I missing something?

  [class.protected]

  When  a  friend  or  a member function of a derived class references a
  protected nonstatic member of a base class, an access check applies in
  addition to those described earlier in clause _class.access_.4) Except
  when forming a pointer to member (_expr.unary.op_), the access must be
  through a pointer to, reference to, or object  of  the  derived  class
  itself  (or  any  class derived from that class) (_expr.ref_).  If the
  access is to form a pointer to member, the nested-name-specifier shall
  name the derived class (or any class derived from that class).

--
Mark Mitchell                   mark@codesourcery.com
CodeSourcery, LLC               http://www.codesourcery.com