[Bug c++/37112] New: nested inherited class can't access protected members of base class

[Bug c++/37112] New: nested inherited class can't access protected members of base class

[darkwingz at yahoo dot com]

The following code fails to compile:

class A {
protected:
    int i;
};

class B {
    class C : public A {
    public:
        void foo(A a) { 
            a.i = 1;
        }
    };
};

int main()
{

}

nest2.cpp: In member function 'void B::C::foo(A)':
nest2.cpp:3: error: 'int A::i' is protected
nest2.cpp:10: error: within this context

I can't find anything in the standard that says this should be invalid, but
perhaps I missed it. Thanks for your time and efforts.


-- 
           Summary: nested inherited class can't access protected members of
                    base class
           Product: gcc
           Version: 4.2.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: darkwingz at yahoo dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37112

[Bug c++/37112] nested inherited class can't access protected members of base class

[chris dot fairles at gmail dot com]

------- Comment #1 from chris dot fairles at gmail dot com  2008-08-13 15:32 -------
You're simply trying to access a protected member variable which is not
allowed. It doesn't matter if you try to access it from a member function of a
sub-object of A; if you have an object of type A, and it has a protected member
var i, you cannot access it directly. If foo() took a type C, or only tried to
access "i" (the protected member var of A from which C inherits) as opposed to
a.i, then it will compile as expected.

HTH,

Chris


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37112

[Bug c++/37112] nested inherited class can't access protected members of base class

[darkwingz at yahoo dot com]

------- Comment #2 from darkwingz at yahoo dot com  2008-08-13 15:57 -------
Thanks for your reply. I think I would have seen this had I tried testing it
without the nesting. I tried to compile the following code:

class A {
protected:
    int i;
};

class B : public A {
public:
    void foo(A *a) {
        a->i = 1;
    }
};

And it also did not work. However, if I change the parameter of foo() to a B,
then it works. I guess this is to prevent a child class from modifying an
instance of type parent, and not type child. It's ok to modify something
protected if it's your type, but by making the parameter the type of the parent
you can't be sure it's the same child type. (Well, you can with dynamic_cast,
but it wouldn't make sense to allow it.) 

Thanks for the food for thought. I'll cancel the bug.


-- 

darkwingz at yahoo dot com changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37112