Hi,

I wondered whether the following is legal C++. gcc gives an error while
Borland C++ accepts it. I couldn't find much in the Standard, the examples
usually involved only either namespaces or using declarations within class
definitions.

Here's the code:

class A {
    class B { };
};

using A::B; // valid using declaration?

B b; // valid declarator for b?

TIA,

sm


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In article <94b6qf$pgh$00$2@news.t-online.com>:
> Here's the code:
>
> class A {
>     class B { };
> };
>
> using A::B; // valid using declaration?
>
> B b; // valid declarator for b?

g++ isn't always a good platform to decide whether or not something is
legel. For instance, section 7.3.3 paragraph 3 on page 115 of the standard
has the following example:

struct B {
        void f(char);
        void g(char);
        enum E { e };
        union { int x; };
};

struct D : B {
        using B::f;
        void f(int) { f('c'); }     // calls B::f(char)
        void g(int) { g('c'); }     // recursively calls D::g(int)
};

Which g++ gives the following error message for:

  test.C:13: cannot adjust access to `void B::f(char)' in `struct D'
  test.C:11:   because of local method `void D::f(int)' with same name

Having said that, I think the using directive in your code segment should be
accepted by a conforming compiler. I think g++'s error message indicates a
set of rules for using directives that is more restrictive than the standard:

  test.C:6: A' is not a namespace

Just my $.02

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> I wondered whether the following is legal C++. gcc gives an error while
> Borland C++ accepts it. I couldn't find much in the Standard, the examples
> usually involved only either namespaces or using declarations within class
> definitions.
>
> Here's the code:
>
> class A {
>     class B { };
> };
>
> using A::B; // valid using declaration?
This is not allowed by the Standard, because "A using declaration for a
class member shall be a member-declaration" See 7.3.3/5. Besides, the
name A::B is not accessible in the scope where the using declaration
occurs.

>
> B b; // valid declarator for b?
This is automatically not valid too, as the class name B is not visible
in this scope.

Regards,

Andrei Iltchenko
Brainbench MVP for C++
http://www.brainbench.com




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