Re: Pointer to a function member.

t the response that they need the instance information. Of course. This is =
a Duh.... But They have it. They have the class deceleration, the function=
 (and therefore the function offset from the class instance), The this poi=
nter. As I see it everything is available tothem.

It has nothing to do with the compiler manufacturers. What you're
wanting to do is just not part of the language. It's as simple as
that. You can possibly go with some compiler extension but then you
you've just locked yourself into a certain vendor by writing non-
portable code.

Anyway, the best way to do this is probably to define a base class
with a virtual function that takes an int parameter, and then subclass
it with a template class that actually stores the member function and
object pointers, overriding the virtual function to call the member
function. The UI class would declare a shared pointer or what have you
to the base class, and when SetCallback is invoked it assigns the
pointer to a new Derived<User>(ptr, &User::function).

An even simpler way (but it is sort of a hack, and I'm not sure it
would be safe for classes using multiple inheritance) would be
something like this:

class UI
{
    public:

    UI( void )
    : user( 0 ), callback( 0 )
    { }

    class User
    {
        public:

        typedef int ( User:: *callback_function )( int );
    };

    template < typename Derived >
    void SetCallback( User* self, int ( Derived:: *function )( int ) )
    {
        user = self;
        callback = User::callback_function( function );
    }

    void check( int value )
    {
        ( user->*callback )( value );
    }

    User* user;
    User::callback_function callback;
};

class FL : public UI::User
{
    public:

    UI ui;

    FL( void )
    {
        ui.SetCallback( this, &FL::MyChecker );
    }

    int MyChecker( int value )
    {
        std::cout << "FL::MyChecker( " << char( value ) << " ) " <<
std::endl;
    }
};

class LI : public UI::User
{
    public:

    UI ui;

    LI( void )
    {
        ui.SetCallback( this, &LI::DoCheck );
    }

    int DoCheck( int value )
    {
        std::cout << "LI::DoCheck( " << char( value ) << " ) " << std::endl;
    }
};

int main( void )
{
    FL fl;
    LI li;
    fl.ui.check( 'S' );
    li.ui.check( 'G' );
}