From:	"Tom" <TomHey AT dial DOT pipex DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: 3 questions
Date:	Tue, 27 Apr 1999 21:07:46 +0100
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To:	djgpp AT delorie DOT com
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>> >2) How do I make a pointer to a class function and call it using that
>> >pointer?
>> This is a C++ question, not a DJGPP question, but the answer is that you
>> can't take the pointer of a member function unless it is a static member
>> function.  See the following:
>
>    That is incorrect.  This compiles under DJGPP and shows how to take the
>address of a non-static member function and call it.  Please note that you
must
>explicitly pass the object to the function.  There are some warnings which
can
>be removed with casts, but this runs and prints what you would expect
"static
>\n myMember bb = 42".  And if you feel it is too much to separetly take
care of
>the function pointer and the object pointer, just stick them in a struct,
and
>make a #define which will call it correctly.


Although this works the operators ::*  and ->* allow pointers to member
functions and data. These operators will allow pointers to members to
function correctly with virtual functions. In concept these work like
offsets requiring a base pointer.

Example of member function pointers

#include <stdio.h>

class foo
{
  public:
     int bb;
     void myMember( void );
};

void foo::myMember()
{
printf("myMember: bb = %d", bb);
}

void main( void )
{
  void (*ptr)();

  // NB: ALL the brackets on the following line are required
  void (foo::*member_ptr)() = foo::myMember;

  foo bar = {42};
  foo* pbar = &bar;

  // NB: ALL the brackets on the following line are required
  (pbar->*member_ptr)();
}

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