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From: "Chris Newton" <chrisnewton@no.junk.please.btinternet.com>
Newsgroups: comp.std.c++,comp.lang.c++
Subject: Re: Inheritance Problems
Date: Sat, 12 May 2001 15:28:04 GMT
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O.Petzold <opetzold@wit.regiocom.net> wrote...
> the follwoing code isn't working (with the gcc-2.95.2).
> If I see the inharritance it should !
>
> class A {
> public:
>   void ModifyAnother(A* a2) {
>     b = 1;              // is working
>     a2->b = 1;          // woking as well
>   }
> protected:
>   int b;
> };
>
>
> class B : public A {
> public:
>   void ModifyAnother(A* a2)  {
>     b = 1;              // is working
>     a2->b = 1;          // not working
>   }
> };
>
> int main() {
>     B b;
> }
>
> `int A::b' is protected
>
> Well but, B is derived from A !!
> What says the standard about ?

Your compiler is correct. You can only access a protected member of A in
B via a pointer or reference to a B object. An A* isn't good enough.
This is from 11.5/1 in the standard if you want to check.

If you replaced B::ModifyAnother's parameter with (B* a2) instead, it
should then work, because member access is controlled on a per-class and
not per-object basis, so this B can access another B's protected
members.

Hope that helps,
Chris


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