Problem with C++ traits under OSX

Hi

I have a problem with C++ traits. The following lil program provides a
Wrapper class which contains 3 static methods. (1 normal, 2 as a
template)
================================================== ====
#include <iostream>
using namespace std;

enum colour_t { White, Black };


static void f(void);
template <colour_t c> static void f(void);


static void f(void)
{
cout << "Hello from colourless f" << endl;
}


template <colour_t c>
void f(void)
{
if(c == White) cout << "Hello from white f" << endl;
else cout << "Hello from black f" << endl;
}


int main(void)
{
f();
f<White>();
f<Black>();

return 0;
}
================================================== ====

The thing compiles w/o problems under Linux (gcc 3.3.3 under gentoo)
and Cygwin (gcc 3.3.1 under WinNT) and produces the expected output:

Hello from colourless f
Hello from white f
Hello from black f


Under MacOSX however (gcc 3.3 20030304) gives the following compile
error:

test.cxx:23: error: redefinition of `static void Wrapper::f()'
test.cxx:16: error: `static void Wrapper::f()' previously declared
here
test.cxx:23: error: no `static void Wrapper::f()' member function
declared in


If the static functions are defined outside the wrapper class, it
compiles fine.

Any idea what's wrong? I'm asking in a non-OSX newsgroup because I'd
like to know whether the program above is really standard-compliant or
not.

Regards,

Sargon

re: Problem with C++ traits under OSX

Sargon wrote:
[color=blue]
> Hi
>
> I have a problem with C++ traits. The following lil program provides a
> Wrapper class which contains 3 static methods. (1 normal, 2 as a
> template)
> ================================================== ====
> #include <iostream>
> using namespace std;
>
> enum colour_t { White, Black };
>
>
> static void f(void);
> template <colour_t c> static void f(void);
>
>
> static void f(void)
> {
> cout << "Hello from colourless f" << endl;
> }
>
>
> template <colour_t c>
> void f(void)
> {
> if(c == White) cout << "Hello from white f" << endl;
> else cout << "Hello from black f" << endl;
> }
>
>
> int main(void)
> {
> f();
> f<White>();
> f<Black>();
>
> return 0;
> }
> ================================================== ====
>
> The thing compiles w/o problems under Linux (gcc 3.3.3 under gentoo)
> and Cygwin (gcc 3.3.1 under WinNT) and produces the expected output:
>
> Hello from colourless f
> Hello from white f
> Hello from black f
>
>
> Under MacOSX however (gcc 3.3 20030304) gives the following compile
> error:
>
> test.cxx:23: error: redefinition of `static void Wrapper::f()'
> test.cxx:16: error: `static void Wrapper::f()' previously declared
> here
> test.cxx:23: error: no `static void Wrapper::f()' member function
> declared in
>
>
> If the static functions are defined outside the wrapper class, it
> compiles fine.
>
> Any idea what's wrong? I'm asking in a non-OSX newsgroup because I'd
> like to know whether the program above is really standard-compliant or
> not.
>
> Regards,
>
> Sargon[/color]
Hi Sargon,
I don't know what the C++ 'law' on this is, but I have come across your
problem in my own C++ code. The 'normal' static method you have must
only be declared in the header of Wrapper, and not defined. So you
should define it in Wrapper.cpp. I actually think this is probably how
it is supposed to be in C++, but couldn't say what the standard says.

Drew McCormack

re: Problem with C++ traits under OSX

On 22 Jul 2004 00:38:34 -0700, sargon@gmail.com (Sargon) wrote:
[color=blue]
>Hi
>
>I have a problem with C++ traits. The following lil program provides a
>Wrapper class which contains 3 static methods. (1 normal, 2 as a
>template)[/color]

No it doesn't, your code contains no "Wrapper" class at all!
[color=blue]
>Under MacOSX however (gcc 3.3 20030304) gives the following compile
>error:
>
>test.cxx:23: error: redefinition of `static void Wrapper::f()'
>test.cxx:16: error: `static void Wrapper::f()' previously declared
>here
>test.cxx:23: error: no `static void Wrapper::f()' member function
>declared in
>
>
>If the static functions are defined outside the wrapper class, it
>compiles fine.
>
>Any idea what's wrong? I'm asking in a non-OSX newsgroup because I'd
>like to know whether the program above is really standard-compliant or
>not.[/color]

Without seeing the real code, it's hard to say what the problem is.
Note that you can't separately declare and define a method inside a
class definition. e.g.

class C
{
void f();
void f()
{
}
};

is not legal, but we can't tell whether that's what you're doing,
since you haven't posted the code.

Tom

re: Problem with C++ traits under OSX

tom_usenet <tom_usenet@hotmail.com> wrote in message news:<q45vf0pr406iqt9hrafnpmi9i554pf5cjt@4ax.com>. ..[color=blue]
> On 22 Jul 2004 00:38:34 -0700, sargon@gmail.com (Sargon) wrote:
>[color=green]
> >Hi
> >
> >I have a problem with C++ traits. The following lil program provides a
> >Wrapper class which contains 3 static methods. (1 normal, 2 as a
> >template)[/color]
>
> No it doesn't, your code contains no "Wrapper" class at all![/color]

Oh my... I mistakenly posted the modified code... here's the
correct one:

==================================================
#include <iostream>
using namespace std;

enum colour_t { White, Black };


class Wrapper
{
public:
static void f(void);
template <colour_t c> static void f(void);
};


void Wrapper::f(void)
{
cout << "Hello from colourless f" << endl;
}


template <colour_t c>
void Wrapper::f(void)
{
if(c == White) cout << "Hello from white f" << endl;
else cout << "Hello from black f" << endl;
}


int main(void)
{
Wrapper::f();
Wrapper::f<White>();
Wrapper::f<Black>();

return 0;
}
==================================================

[color=blue][color=green]
> >Under MacOSX however (gcc 3.3 20030304) gives the following compile
> >error:
> >
> >test.cxx:23: error: redefinition of `static void Wrapper::f()'
> >test.cxx:16: error: `static void Wrapper::f()' previously declared
> >here
> >test.cxx:23: error: no `static void Wrapper::f()' member function
> >declared in
> >
> >
> >If the static functions are defined outside the wrapper class, it
> >compiles fine.
> >
> >Any idea what's wrong? I'm asking in a non-OSX newsgroup because I'd
> >like to know whether the program above is really standard-compliant or
> >not.[/color][/color]

re: Problem with C++ traits under OSX

On 22 Jul 2004 06:19:55 -0700, sargon@gmail.com (Sargon) wrote:
[color=blue]
>tom_usenet <tom_usenet@hotmail.com> wrote in message news:<q45vf0pr406iqt9hrafnpmi9i554pf5cjt@4ax.com>. ..[color=green]
>> On 22 Jul 2004 00:38:34 -0700, sargon@gmail.com (Sargon) wrote:
>>[color=darkred]
>> >Hi
>> >
>> >I have a problem with C++ traits. The following lil program provides a
>> >Wrapper class which contains 3 static methods. (1 normal, 2 as a
>> >template)[/color]
>>
>> No it doesn't, your code contains no "Wrapper" class at all![/color]
>
>Oh my... I mistakenly posted the modified code... here's the
>correct one:
>
>================================================= =
>#include <iostream>
>using namespace std;
>
>enum colour_t { White, Black };
>
>
>class Wrapper
>{
> public:
> static void f(void);
> template <colour_t c> static void f(void);
>};
>
>
>void Wrapper::f(void)
>{
> cout << "Hello from colourless f" << endl;
>}
>
>
>template <colour_t c>
>void Wrapper::f(void)
>{
> if(c == White) cout << "Hello from white f" << endl;
> else cout << "Hello from black f" << endl;
>}
>
>
>int main(void)
>{
> Wrapper::f();
> Wrapper::f<White>();
> Wrapper::f<Black>();
>
> return 0;
>}[/color]

The code is fine so the problem is the compiler. I'd suggest working
round the problem by defining the template member inside Wrapper. e.g.

class Wrapper
{
public:
static void f(void);
template <colour_t c> static void f(void)
{
if(c == White) cout << "Hello from white f" << endl;
else cout << "Hello from black f" << endl;
}
};

You don't get any semantic benefit from defining template members
outside the class definition anyway.

Tom