POinter to member function

Say hello to Function-Pointer.org. It's a great site and has all the information you'll ever need on... uhm, function pointers.

Good ol' reliable:

http://www.codeproject.com/cpp/FastDelegate.asp

Learn it, use it, love it.

But in a word, no. Normal function pointers are generally always 4 bytes in size. Member function pointers can get much bigger. For example, on MSVC they can be up to 16 bytes in size, which means that the member function pointer contains information that a normal function pointer doesn't have to deal with.

Ok, one more thing. Is it possible to cast pointer to member function of one class to ptr to member func of its base class?

Edit: I've briefly looked at suggested article at codeguru and found answer to my question - no. I'll try to redesign my code to get it workin'. Thx anyway

[Edited by - osh on November 8, 2004 11:47:19 AM]

Quote:

Original post by osh Ok, one more thing. Is it possible to cast pointer to member function of one class to ptr to member func of its base class?

No, but it is possible to cast a pointer to member function of a base class to a pointer to member function of a derived class.

osh--
Yeah, the answer is no. But I posted the link because the author, because he was in the same situation you are, built a type (FastDelegate<>) that acts as a function pointer that takes both memeber functions and non-member functions (as long as they're compatible in arguments and return type), and evaluates at compile time to the optimal asm code for making the function call. And it works on all platforms/compilers.

Of course, to do this requires some really insane coding... all under-the-covers, of course, so you don't have to worry about it, but here's a snippet that might drop your jaw:

It is possible to convert a member function pointer to a global function pointer. Under the hood, member functions are regular functions that pass a this pointer to the function automatically. Depending on what calling conventions and possibly what platform you're using the following conversion may actually work properly:

Again, this can be very dependant on what calling conventions you use and how your compiler treats function pointers. In your case you probably need to be able to call the function without passing a pointer to the object it should be called on. In that case, do as was mentioned in the above post and create a wrapper function that will call it for you and has the same signature/return type.

Quote:

Original post by SiCrane Quote: Original post by osh Ok, one more thing. Is it possible to cast pointer to member function of one class to ptr to member func of its base class? No, but it is possible to cast a pointer to member function of a base class to a pointer to member function of a derived class.

You probably wouldn't even need to do such a thing, you probably wont an in-direct polymorphic call instead e.g.:

#include <iostream>struct foo {   virtual void do_bar() const { std::cout << "foo\n"; }   virtual ~foo() {}};struct bar : foo {   void do_bar() const {      foo::do_bar();      std::cout << "bar\n\n";   }};int main() {   typedef void (foo::*foo_mem_func)() const;   typedef void (bar::*bar_mem_func)() const;   foo_mem_func f_func(&foo::do_bar);   bar_mem_func b_func(&bar::do_bar);   bar b;   const foo& f_ref(b);   b.do_bar(); //direct non polymorphic call.   f_ref.do_bar(); //direct polymorphic call.   (b.*b_func)();   //in-direct non polymorphic call.   (b.*f_func)();   //in-direct non polymorphic call (if i remember correctly).   (f_ref.*f_func)(); //in-direct polymorphic call.   }