Re: C++: Access protected virtual member function via a base class

[Nathan Sidwell <nathan at codesourcery dot com>]

Marco Man-Fai Yu wrote:

> g++ prints the following error when compiling the following code.
> 
> foo.cc: In method `void Derived::Do()':
> foo.cc:8: `void Base::Do()' is protected


> Is this a bug in g++? I think it is legal to access protected member
> functions of my base class, even if it is another instantiation,
> according to Stroustrup and other C++ books.
Not a bug. see [11.2]/4 and [11.5]/1 which is a rather convoluted
bit of the standard. 11.2 would allow you access, but 11.5 denies it.

11.5 says an additional check is made for a
protected member of the base, in that the access has to be through
a pointer, reference of object of the derived class itself. In
your example, going via `q' is ok, but `p' is not.

nathan

-- 
Dr Nathan Sidwell   ::   http://www.codesourcery.com   ::   CodeSourcery LLC
         'But that's a lie.' - 'Yes it is. What's your point?'
nathan@codesourcery.com : http://www.cs.bris.ac.uk/~nathan/ : nathan@acm.org