Re: Compile Time decision static or member

From:

Maxim Yegorushkin <maxim.yegorushkin@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 1 Jun 2009 05:42:07 -0700 (PDT)

Message-ID:

<c11dcf47-3ced-43e9-ac77-53dcf41d424f@l32g2000vba.googlegroups.com>

On Jun 1, 1:18 pm, Anees <anees.hai...@gmail.com> wrote:

Dear Fellows:

I have following scenario:

class A {
public:
        void me_print () { cout << "A" << endl; }
        static void print() { cout << "static A" << endl; }

};

class B {

};

class C : public A, public B {
public:
        void foo() { PRINT; }

};

class D: public B {
public:
        void foo() { PRINT; }

};

int _tmain(int argc, _TCHAR* argv[])
{
        C c;
                D d;

                c.foo();
                d.foo();

                return 0;

}

I want to define a macro (#define) such that when instance of A's
derived class (i.e. C) call PRINT; it gets A's member method me_print
(), and when instance of NON A's derived class (i.e. D) call PRINT, it
should be resolved to A's static subroutine print().

You don't need a macro for that, you can do that in pure C++ (for
clarity, I changed class to struct and removed all public keywords):

    struct A {
        void me_print () { std::cout << "A\n"; }
        static void print() { std::cout << "static A\n"; }
    };

    void do_print(A* a) { a->me_print(); }
    void do_print(void*) { A::print(); }

    struct B {};

    struct C : A, B {
        void foo() { do_print(this); }
    };

    struct D : B {
        void foo() { do_print(this); }
    };

    int main()
    {
        C c;
        D d;
        c.foo();
        d.foo();
    }

The idea here is that there are two overloads of do_print(). One takes
A*, the other one void*. The first one is chosen when you pass A* or
its publicly derived sub-class pointer. The void* overload is chosen
for all other pointers.

--
Max