Re: C2248: cannot access protected member

From:
"Alex Blekhman" <tkfx.REMOVE@yahoo.com>
Newsgroups:
microsoft.public.vc.language
Date:
Fri, 1 Feb 2008 19:35:28 +0200
Message-ID:
<#5mUVkPZIHA.5980@TK2MSFTNGP04.phx.gbl>
"Igor Tandetnik" wrote:

Interesting. So &X::foo and &Y::foo have the exact same value
and the same type (pointer-to-member-of-X), but access check
fails for the former and passes for the latter on purely
syntactical grounds.


I think, there is more to it than just syntax. If `Y' actually
contains `foo' member, then "&Y::foo" yields
"pointer-to-member-of-Y" and compilation rightfully fails. So, it
seems that compiler searches starting from `Y' namespace upward
for the `foo' name. The scope where `foo' is found determines
resulting type.

But that does seem to mean I can call a protected method on an
unrelated class:

class X {
protected:
   void foo();
};

class Z : public X {};

class Y : public X {
public:
   void bar() {
       Z z;
       // z.foo(); // doesn't compile
       void (X::*pf)() = &Y::foo;
       (z.*pf)(); // compiles; calls z.foo()
   }
};

Looks to me like a hole in the standard.


Moreover, suppose "void (X::*pf)() = &Y::foo;" statement won't
compile. Then you could legally circumvent it with `static_cast'
(5.2.9/9):

Z z;
// z.foo(); // doesn't compile
void (Y::*pf)() = &Y::foo;
void (X::*pf2)() = static_cast<void (X::*)()>(pf);
(z.*pf2)(); // compiles; calls z.foo()

Alex

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