c++ - Function Pointer (Within Class) -

i'm trying use function pointer (fnptr) reference class method (fnempty) within class method, (in case constructor).

the setup program main.cpp is

#include <iostream> #include "test.hpp"  int main(int argc, char* argv[]){     test test;     return 0; } 

and test.hpp reads

#ifndef _test_h #define _test_h #include <iostream>  class test {     private:      public:         void (*ptrempty)(void);         void fnempty(){ std::cout << "got here" << std::endl;};         test(){ ptrempty = fnempty; };         ~test(){}; };  #endif 

most of material on net details being able reference class method from outside class (see microsoft page , newty.de), not from inside class (as have done).

using above files gives error

in file included main.cpp:6: ./test.hpp:11:21: error: reference non-static member function must called;

so 1) why error result?

if change fnptr declaration on line 10 static reads

static void fnempty(){ std::cout << "got here" << std::endl;}; 

this seems solve problem. begs question 2) why accept 'static' if error says 'non-static' allowed?

if remove static , instead change line 11 (by adding &) reads

        test(){ ptrempty = &fnempty; }; 

i whole new error reads

./test.hpp:11:21: error: must explicitly qualify name of member function when taking address 

unfortunately replacing with

        test(){ test::ptrempty = test::&fnempty; }; 

or variations not including test:: prefix done in links given above not solve problem.

i under impression far function pointers go, when referencing function (say fn),

ptr = fn; 

is equivalent

ptr = &fn; 

3) why getting 2 different sets of errors when include , exclude '&'

so ultimate question have is::

4) correct way point class method (from within different method of same class)? need include 'classname::' qualifier when within same class?

thanks, jeff

fnempty non-static member function, means takes implicit first argument, pointer test instance it's being invoked on (the this pointer). type of pointer member function is

void (test::*ptrempty)(); 

next, form pointer member function, need use syntax &classname::memfnname so, within constructor

ptrempty = &test::fnempty; 

now example should compile. can invoke function ptrempty points using

test t; (t.*(t.ptrempty))(); 

when change fnempty static no longer receives implicit this pointer argument, it's other pointer function, , code compiles.