> I design a class for general purpose. I do not allow a client to read
> or modify interface and implemention. I allow them to write a new non-
> member function outside of class' interface and implmention. The
> problem is that non-member function cannot access private data member.
> The friend keyword is not the solution. I am aware that friend
> keyword allows the non-member function to access private data member.
> If you define more than two non-member functions, you will want one of
> some non-member function to be pointed to the member function pointer
> at run-time. The client can decide to remove first non-member
> function from the member function pointer and add another non-member
> function at run-time. The member function pointer array is not
> necessary according to my design.
> Does it mean that it is the only solution to access public data member
> only?
> Take a look at my example code below.
> #ifndef A_H
> #define A_H
> class A
> {
> public:
> typedef void (*Func_Ptr)(A &);
> A(void);
> ~A(void);
> void Run(void);
> void Set_Func_Ptr(Func_Ptr);
> private:
> friend void Non_Member_Func(A &);
> Func_Ptr Member_Func_Ptr;
> public:
> int W;
> int X;
> private:
> int Y;
> int Z;
> };
> #endif // A_H
> // A_CPP
> #include "A.h"
> A::A(void)
> {
> W = 1;
> X = 2;
> Y = 3;
> Z = 4;
> }
> A::~A(void)
> {
> }
> void A::Run(void)
> {
> Non_Member_Func( *this );
> Member_Func_Ptr( *this );
> }
> void A::Set_Func_Ptr(Func_Ptr Ptr)
> {
> Member_Func_Ptr = Ptr;
> }
> // MAIN_CPP
> #include <stdio.h>
> #include "A.h"
> void Non_Member_Func(A &a)
> {
> a.W *= 2; // Can access public
> a.X *= 2; // can access public
> a.Y *= 2; // can access private
> a.Z *= 2; // can access private
> printf("W: %d\nX: %d\nY: %d\nZ: %d\n", a.W, a.X, a.Y, a.Z);
> }
> void Member_Func(A &a)
> {
> a.W *= 2;
> a.X *= 2;
> // a.Y += 4; // Error can't access private
> // a.Z += 6; // Error can't access private
> printf("W: %d\nX: %d\n", a.W, a.X);
> }
> void Member_Func2(A &a)
> {
> a.W *= 4;
> a.X *= 4;
> // a.Y += 4; // Error can't access private
> // a.Z += 6; // Error can't access private
> printf("W: %d\nX: %d\n", a.W, a.X);
> }
> int main(void)
> {
> A a;
> Non_Member_Func( a );
> a.Set_Func_Ptr( Member_Func );
> a.Run();
> a.Set_Func_Ptr( Member_Func2) ;
> a.Run();
> return 0;
> }
