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Neal Chen · Guest

Hi All,

I am implementing a framework. In my framework, I want to define a set of
handler classes,
deriving from a common base class. Then in the handler classes, I would like
to define a
set of handler functions, all have the same signature, to say, all have the
signature like:
void f(void *)

Then in another loop, I would instantiates those handlers and dynamically
choose a handler
function in a handler class to fulfill a task. Since the concrete handler
and the name of the
handler functions cannot be pre-determinated, I would like to pass in a
pointer to the object
of a handler class and a pointer to member function to the caller, thus in
the caller, I could
compose those two pointers up to call the desired handler function.

The problem, is then, how could I achieve this under a unified interface? I
defined a pointer
to member function type in the Base class scope and try to assign pointer to
derived class's
member functions to variable of this type. Although I have tried this in
both G++ 3.2 and VC7,
I still doubt if such trick is safe, anybody could give me some suggestions
and hints? And
I would appreciate all of your helps.

Following is a sample code I have used for test under G++ and VC7. Thanks in
advance.

#include <iostream>
using namespace std;

class Base{
public:
Base(){}
virtual ~Base(){}

virtual void v() = 0;
};

typedef void (Base::*MemberFunc)(void);

class Derived1 : public Base{
public:
void f(){
cout << "This is in f." << endl;
}

void g(){
cout << "This is in g." << endl;
}

void v(){
cout << "This is in Derived1: v." << endl;
}
};

class Derived2 : public Base{
public:
void h(){
cout << "This is in h." << endl;
}

void m(){
cout << "This is in m." << endl;
}

void v(){
cout << "This is in Derived2: v." << endl;
}
};

class Leaf : public Derived2{
public:
void n(){
cout << "Hello, world, in n." << endl;
}

using Derived2::v;
};

int main(){
MemberFunc fp;
Base *pBase;

Derived1 d1;
Derived2 d2;
Leaf l;

cout << "Test Derived1 ..." << endl;
pBase = &d1;
fp = static_cast cout << "fp to Derived1::f is: " << fp << endl;
(pBase->*fp)();

fp = static_cast<MemberFunc>(&Derived1::g);
cout << "fp to Derived1::g is: " << fp << endl;
(pBase->*fp)();

fp = static_cast<MemberFunc>(&Derived1::v);
cout << "fp to Derived1::v is: " << fp << endl;
(pBase->*fp)();

cout << "Test Derived2 ..." << endl;
pBase = &d2;
fp = static_cast cout << "fp to Derived2::h is: " << fp << endl;
(pBase->*fp)();

fp = static_cast<MemberFunc>(&Derived2::m);
cout << "fp to Derived2::m is: " << fp << endl;
(pBase->*fp)();

fp = static_cast<MemberFunc>(&Derived2::v);
cout << "fp to Derived2::v is: " << fp << endl;
(pBase->*fp)();

cout <<"Test Leaf ..." << endl;
pBase = &l;
fp = static_cast cout << "fp to Leaf::m is: " << fp << endl;
(pBase->*fp)();

fp = static_cast<MemberFunc>(&Leaf::v);
cout << "fp to Leaf::v is: " << fp << endl;
(pBase->*fp)();

return 0;
}

=============================
output:
=============================
Test Derived1 ...
fp to Derived1::f is: 1
This is in f.
fp to Derived1::g is: 1
This is in g.
fp to Derived1::v is: 1
This is in Derived1: v.
Test Derived2 ...
fp to Derived2::h is: 1
This is in h.
fp to Derived2::m is: 1
This is in m.
fp to Derived2::v is: 1
This is in Derived2: v.
Test Leaf ...
fp to Leaf::m is: 1
Hello, world, in n.
fp to Leaf::v is: 1
This is in Derived2: v.

========================================
BTW: it's queer that the output of "fp to XXXX is:" lines are always 1,
both in output of G++ and VC. Anybody could explain this to me?

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syro555 · Guest

Neal Chen wrote:

Branimir Maksimovic · Guest

"Neal Chen" <zeusnchen (AT) msn (DOT) com> wrote