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Re: Forward declarations

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On 16/11/2015 00:47, Ben Bacarisse wrote:
> "Rick C. Hodgin" <rick.c.hodgin@gmail.com> writes:

>>
>> I believe I am humble.  But also, in this particular case, I happen
>> to be right.
>
> And yet you still haven't answered by question about which function is
> declared twice.  The example included only two and you agreed that at
> least one much be declared twice so there are only two answers: foo or
> bar.  I'd like to be charitable and assume that you are a bit confused
> about what constitutes the declaration of a function, but your not
> answering this question suggests otherwise.  It suggests to me that you
> don't want to say because it would be so obviously false.
>
>> Every person could figure this out for themselves.
>
> That's the good part.  I don't think many people reading this will come
> away thinking that the pointer parameter declaration is a second
> declaration for either "foo" or "bar".  After all there were two
> functions and only two function declarations in the whole code example.

Well I think this solution is unacceptable.

For foo() to call bas() later in the module, the compiler needs certain 
information about how to call it.

If a function pointer is used as here, then that would normally provide 
most of that information. But in Tim's example, that is incomplete, so 
some of that information has to be gleaned from the nature of the call: 
the type and number of the arguments. These have to be provided /before/ 
the definition of the bas.

The only thing not known is the function address, so only an indirect 
call can be made. A direct call would need a forward declaration (unless 
you create some hairy self-modifying code).

The other unsatisfactory thing is that with the incomplete function 
pointer, you can pass anything you like to the function pointer, and the 
compiler doesn't care. But you can also do this:

  struct (int x,y,z;} pt;

   ferrah(s,n);
   ferrah(pt,pt,pt,pt,pt,pt,pt,pt,pt,pt,pt);

and it's perfectly fine! (Another crazy quirk of the language I guess.)

The same technique can be used like this:

int (*fooptr)();
int (*basptr)();

..... foo/bas define here

  fooptr=foo;
  basptr=bas;

Then foo and bas call each other via the pointers; that keeps the 
parameter passing cleaner. Notice however, that to make this work, it is 
those function pointers that now become the forward declarations. foo 
will always need to know something about bas.

(I can appreciate now the advantage of not bothering with parameter 
types for int (*fooptr)() if you can't remember the syntax! But why 
doesn't 'int ferrah()' need the "*" pointer thingy; another quirk?)

-- 
Bartc









-- 
Bartc

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Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-10 14:20 -0800
  Re: Forward declarations jacobnavia <jacob@jacob.remcomp.fr> - 2015-11-10 23:38 +0100
    Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-10 15:00 -0800
      Re: Forward declarations Ian Collins <ian-news@hotmail.com> - 2015-11-11 12:24 +1300
        Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-10 15:53 -0800
          Re: Forward declarations gazelle@shell.xmission.com (Kenny McCormack) - 2015-11-11 00:01 +0000
          Re: Forward declarations Ian Collins <ian-news@hotmail.com> - 2015-11-11 13:46 +1300
            Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-10 21:05 -0800
    Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-11 00:21 +0000
  Re: Forward declarations Lőrinczy Zsigmond <zsiga@nospam.for.me> - 2015-11-11 10:16 +0100
    Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-11 07:19 -0800
  Re: Forward declarations David Brown <david.brown@hesbynett.no> - 2015-11-11 15:40 +0100
    Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-11 07:21 -0800
      Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-11 07:23 -0800
      Re: Forward declarations David Brown <david.brown@hesbynett.no> - 2015-11-11 16:29 +0100
        Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-11 07:31 -0800
        Re: Forward declarations Nick Bowler <nbowler@draconx.ca> - 2015-11-13 18:20 +0000
          Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-13 10:39 -0800
            Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-13 19:40 +0000
          Re: Forward declarations Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-14 11:42 -0800
            Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-14 12:32 -0800
              Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 00:15 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-14 16:34 -0800
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 01:54 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-14 18:00 -0800
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 02:13 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-14 18:26 -0800
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 02:34 +0000
                Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-15 11:11 +0000
              Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 02:36 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-14 19:25 -0800
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-14 19:37 -0800
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-14 20:11 -0800
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 10:36 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 06:16 -0800
                Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-15 14:44 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 09:41 -0800
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 18:26 +0000
                Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-15 18:42 +0000
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 18:53 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 12:58 -0800
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 12:49 -0800
                Re: Forward declarations Ian Collins <ian-news@hotmail.com> - 2015-11-16 10:01 +1300
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 14:54 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 09:53 -0800
                Re: Forward declarations Keith Thompson <kst-u@mib.org> - 2015-11-15 10:36 -0800
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 12:56 -0800
                Re: Forward declarations Ian Collins <ian-news@hotmail.com> - 2015-11-16 10:04 +1300
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 13:11 -0800
                Re: Forward declarations Ian Collins <ian-news@hotmail.com> - 2015-11-16 10:25 +1300
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 13:37 -0800
              Re: Forward declarations Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-15 13:13 -0800
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 13:16 -0800
                Re: Forward declarations David Brown <david.brown@hesbynett.no> - 2015-11-16 00:23 +0100
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 16:20 -0800
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 00:47 +0000
                Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-16 01:28 +0000
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 01:57 +0000
                Re: Forward declarations Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-15 21:15 -0500
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 11:05 +0000
                Re: Forward declarations Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-11-16 10:18 -0500
                Re: Forward declarations Richard Heathfield <rjh@cpax.org.uk> - 2015-11-16 06:44 +0000
                Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-16 11:26 +0000
                Re: Forward declarations David Brown <david.brown@hesbynett.no> - 2015-11-16 12:43 +0100
                Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-16 12:20 +0000
                Re: Forward declarations David Brown <david.brown@hesbynett.no> - 2015-11-16 14:38 +0100
                Re: Forward declarations Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 13:26 +0000
                Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-16 13:53 +0000
                Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-15 18:12 -0800
      Re: Forward declarations pa@see.signature.invalid (Pierre Asselin) - 2015-11-12 01:54 +0000
        Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-12 02:08 -0800
    Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-12 09:58 +0000
  Re: Forward declarations John Bode <jfbode1029@gmail.com> - 2015-11-17 14:46 -0800
    Re: Forward declarations "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-17 14:59 -0800
    Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-17 23:35 +0000
      Re: Forward declarations BartC <bc@freeuk.com> - 2015-11-17 23:40 +0000
        Re: Forward declarations Keith Thompson <kst-u@mib.org> - 2015-11-17 19:48 -0800
      Re: Forward declarations glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-18 01:04 +0000

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