The following problem popped when trying to compile Microsoft's
[gdiplus.h] with MingW g++ 3.3.4; sanitized version:

   struct Boo {};
   struct Foo { Boo Boo; };

   int main() {}

In the original code Boo is a typedef for int (I think); anyway, g++
3.4.4 says

   error: declaration of `Boo Foo::Boo'
   error: changes meaning of `Boo' from `struct Boo'

Is the compiler within its rights, according to the standard?

MSVC 7.1 and Comeau online 4.3.3 both accept the code.

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>    error: declaration of `Boo Foo::Boo'
>    error: changes meaning of `Boo' from `struct Boo'

I've gotten that as a warning before... but never understood what it
meant. It gave me the warning for code akin to the following:

template<class T>
class Monkey {
public:

    typedef T T;

};


I was employing the typedef so that I could you T outside of the class,
e.g.:

Monkey<T>::T object;


-Tom   s

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"Alf P. Steinbach" wrote:
> The following problem popped when trying to compile Microsoft's
> [gdiplus.h] with MingW g++ 3.3.4; sanitized version:
>
>   struct Boo {};
>   struct Foo { Boo Boo; };
>
>   int main() {}
>
> In the original code Boo is a typedef for int (I think); anyway, g++
> 3.4.4 says
>
>   error: declaration of `Boo Foo::Boo'
>   error: changes meaning of `Boo' from `struct Boo'
>
> Is the compiler within its rights, according to the standard?
>
> MSVC 7.1 and Comeau online 4.3.3 both accept the code.

AFAIK, if Boo is a typedef for 'int', it's different.  You are allowed
to "hide" a class Boo declaration in any scope with a variable simply
because class Boo is still available through the "elaborated type
specifier" (in this case 'struct Boo').  It would not be the case if
'Boo' is a typedef.

V
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"Alf P. Steinbach" wrote:
> The following problem popped when trying to compile Microsoft's
> [gdiplus.h] with MingW g++ 3.3.4; sanitized version:
>
>    struct Boo {};
>    struct Foo { Boo Boo; };
>
>    int main() {}
>
> In the original code Boo is a typedef for int (I think); anyway, g++
> 3.4.4 says
>
>    error: declaration of `Boo Foo::Boo'
>    error: changes meaning of `Boo' from `struct Boo'
>
> Is the compiler within its rights, according to the standard?

In this example, providing the elaborated type specifier fixes the
problem:

    struct Boo {};
    struct Foo { struct Boo Boo; };

If Boo is a typedef, then a different fix is in order:

    typedef int Boo;
    struct Foo { ::Boo Boo; };

I suspect that neither change should be strictly necessary, since I
believe that inner Boo should simply hide the outer Boo's name within
Foo's class scope.

Greg

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