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From: kaiser@ananke.stgt.sub.org (Andreas Kaiser)
Newsgroups: comp.lang.c++
Subject: Invoking Member Functions Via Pointers
Message-ID: <5.273AE276@ananke.stgt.sub.org>
Date: 9 Nov 90 15:58:52 GMT
Organization: Ananke, Stuttgart, FRG
Lines: 51


In your msg to All, dated <09 Nov 90 08:33>, it said:

 AW> I am having a devil of a time trying to invoke a pointer to member
 AW> function through an object which is a base class object for the
 AW> derived class to which the member function belongs.  The whole thing
 AW> is so compliciated, I have tried to "paraphrase" an example:

You cannot invoke non-static member functions via normal function 
pointers. Member functions have a hidden first argument ("this"). 
For this reason, the C++ language has a special function pointer 
type, the "pointer to member function".

Example:

 class Base_class {
 };

 typedef void (Base_class::*v_fn_ptr)(void);
// This is a pointer to a member function of
// class "Base_class" or it's descendants.

 class Derived_class : public class {
        void new_function();
 };

 class Container_class {
         Base_class *list;
         Container_class (int obj_count, ... );
         void apply (v_fn_ptr);
 };

 Derived_class D1, D2;

 Container_class c (2, &D1, &D2);

Now, if you want to run "apply":

         c.apply (Derived_class::new_function);

and within "apply", this function is called by:

         (list->*function_ptr)();


                Andreas

--  
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:: Andreas Kaiser :: fido: 2:509/5.2512 & 2:507/18.7206
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