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From: Biju Thomas <bijuthom@ibm.net>
Subject: Re: A suspect bug in Visual C++
Date: 1998/11/29
Message-ID: <3661A689.4C80EFFE@ibm.net>#1/1
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References: <8767c1s375.fsf@pot.cnuce.cnr.it> <GqF0WmAxWJY2Ewyw@robinton.demon.co.uk>
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Francis Glassborow wrote:
> 
> I find this an interesting question.  To what is f() being granted
> access?
> The private interface of class B.  But this is not the same as the
> private interface of class A.
> 
> I think you have to declare friend void f() in both A and B.  Can anyone
> quote the Standard to justify accepting the code as written?

Quote from 11.4/2:

"Declaring a class to be a friend implies that the names of private and
protected members from the class granting friendship can be accessed in
declarations of members of the befriended class."

There is an example too, which elaborates this point in the case of
nested classes:

class A {
  class B { };
  friend class X;
};

class X {
  A::B mx; // ok: A::B used to declare member of X
};

This talks about befriended classes only. But, I think, it extends to
befriended functions too. May be, the wording of the above clause has to
be changed so that it is made explicit in the case of friend functions
too.

Without such a feature, declaring friends of nested classes becomes a
nightmare, as all the containing classes have to have the same friend
declaration. And, having such a friend declaration in the containing
class is dangerous, as it will expose the containing class the friend
class/function unnecessarily.

> 
> In article <8767c1s375.fsf@pot.cnuce.cnr.it>, Francesco Potorti`
> <F.Potorti@cnuce.cnr.it> writes
> 
> >Hi,  this is  observed  behaviour on  VC++  4.0, 5.0,  6.0.  The  following
> >snippet of  code compiles without  errors under egcs  (as it should,  in my
> >opinion), while it generates an error when compiled by VC++.
> 
> >---------------------------
> >class A {
> >    class B {
> >        struct C {};
> >        friend void f();
> >    };
> >};
> >void f() {
> >    A::B::C *p;
> >}
> >---------------------------
> >--> baco_VC.cpp(9) : error C2248: 'C' :
> >    cannot access private struct declared in class 'A::B'

Regards,
Biju Thomas



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