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Re: calling argumentless function with argument

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Bart <bc@freeuk.com> writes:
> On 04/01/2019 16:34, David Brown wrote:
>> On 04/01/2019 17:04, Jens Thoms Toerring wrote:
>>>     is there anything to worry about if one calls a function
>>> that takes no arguments with an argument like this?
>>>
>>> void foo(void);       // defined somewhere else
>>>
>>> int main(void)
>>> {
>>>      void (*p)() = foo;
>>> 	p(4);
>>> }
>> 
>> It is undefined behaviour.  It is likely to "work" in most cases (the
>> argument would be put onto the stack or into a register, and then
>> ignored by the called function).
>> 
>> However, if the compiler is using a "callee cleanup" calling convention
>> rather than "caller cleanup", you'll be in trouble.  "Caller cleanup" is
>> the traditional for C, especially on *nix systems.  But "callee cleanup"
>> is used with a variety of calling conventions on Windows (like MS
>> fastcall, stdcall, etc.).  If your call requires putting anything on the
>> stack instead of just registers, you'll get in trouble.
>
> If it's C calling C, then I think caller clean-up is always used (from 
> what I've seen on Windows anyway), otherwise it would be harder to 
> implement variadic functions such as printf.
  
It may well be the case that most or all C compilers use caller cleanup,
at least partly for historical reasons.  It makes it possible, for
example, to call printf without a correct declaration in scope.
(Pre-ANSI C didn't have prototypes, so a compiler wouldn't necessarily
even know that printf is variadic.)

But the standard is carefully worded to permit either caller cleanup or
callee cleanup.  Calling a variadic function with no visible prototype
(or with a prototype that doesn't match the definition) has undefined
behavior, which allows a compiler to treat variadic functions specially.

[...]

>> In what circumstances would it be useful?
>
> You have a function pointer intended to call a range of functions some 
> of which have a parameter, and some don't. But you want to use the same, 
> consistent function pointer type and the same call code. Then you want 
> those functions without a parameter to ignore it.

I can imagine that being useful -- but C doesn't support it with
defined behavior.  Just be aware of the risk that some compiler could
break your code.

-- 
Keith Thompson (The_Other_Keith) kst@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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calling argumentless function with argument jt@toerring.de (Jens Thoms Toerring) - 2019-01-04 16:04 +0000
  Re: calling argumentless function with argument David Brown <david.brown@hesbynett.no> - 2019-01-04 17:34 +0100
    Re: calling argumentless function with argument Bart <bc@freeuk.com> - 2019-01-04 17:30 +0000
      Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-04 09:50 -0800
        Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-05 05:58 -0800
          Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-05 07:56 -0800
            Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-05 10:56 -0800
              Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-05 14:55 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 01:29 +0100
                Re: calling argumentless function with argument Bart <bc@freeuk.com> - 2019-01-06 02:20 +0000
                Re: calling argumentless function with argument Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-01-06 02:51 +0000
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 12:12 +0100
                Re: calling argumentless function with argument Bart <bc@freeuk.com> - 2019-01-06 11:53 +0000
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 12:58 +0100
                Re: calling argumentless function with argument Bart <bc@freeuk.com> - 2019-01-06 11:45 +0000
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 12:58 +0100
                Re: calling argumentless function with argument Bart <bc@freeuk.com> - 2019-01-06 12:24 +0000
                Re: calling argumentless function with argument Keith Thompson <kst-u@mib.org> - 2019-01-06 04:34 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 13:41 +0100
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 04:10 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 13:51 +0100
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 13:56 +0100
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 05:20 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 16:08 +0100
                Re: calling argumentless function with argument Keith Thompson <kst-u@mib.org> - 2019-01-06 15:59 -0800
                Re: calling argumentless function with argument Bart <bc@freeuk.com> - 2019-01-06 13:42 +0000
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 06:22 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 16:19 +0100
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 07:42 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 08:05 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 08:30 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 17:44 +0100
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 08:54 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-07 08:02 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-07 08:07 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-07 09:16 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-07 09:40 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-07 09:57 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-09 02:23 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 16:17 +0100
                Re: calling argumentless function with argument Bart <bc@freeuk.com> - 2019-01-06 16:56 +0000
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 09:12 -0800
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 12:39 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 18:26 +0100
                Re: calling argumentless function with argument Bart <bc@freeuk.com> - 2019-01-06 18:52 +0000
                Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-06 02:32 -0800
                Re: calling argumentless function with argument Keith Thompson <kst-u@mib.org> - 2019-01-06 04:38 -0800
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 13:42 +0100
                Re: calling argumentless function with argument Robert Wessel <robertwessel2@yahoo.com> - 2019-01-06 10:27 -0600
                Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-06 17:47 +0100
      Re: calling argumentless function with argument David Brown <david.brown@hesbynett.no> - 2019-01-04 19:30 +0100
      Re: calling argumentless function with argument Keith Thompson <kst-u@mib.org> - 2019-01-04 10:55 -0800
      Re: calling argumentless function with argument Robert Wessel <robertwessel2@yahoo.com> - 2019-01-05 00:16 -0600
    Re: calling argumentless function with argument queequeg@trust.no1 (Queequeg) - 2019-01-07 10:43 +0000
      Re: calling argumentless function with argument Robert Wessel <robertwessel2@yahoo.com> - 2019-01-07 16:25 -0600
  Re: calling argumentless function with argument Barry Schwarz <schwarzb@dqel.com> - 2019-01-04 09:54 -0800
  Re: calling argumentless function with argument Thiago Adams <thiago.adams@gmail.com> - 2019-01-04 10:26 -0800
    Re: calling argumentless function with argument Keith Thompson <kst-u@mib.org> - 2019-01-04 12:07 -0800
  Re: calling argumentless function with argument James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-01-04 15:03 -0500
    Re: calling argumentless function with argument Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-01-05 00:04 +0000
      Re: calling argumentless function with argument James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-01-05 22:36 -0500
  Re: calling argumentless function with argument jt@toerring.de (Jens Thoms Toerring) - 2019-01-05 13:17 +0000
    Re: calling argumentless function with argument fir <profesor.fir@gmail.com> - 2019-01-05 06:06 -0800
    Re: calling argumentless function with argument David Brown <david.brown@hesbynett.no> - 2019-01-05 15:42 +0100
      Re: calling argumentless function with argument Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-01-05 14:58 +0000
    Re: calling argumentless function with argument "Pascal J. Bourguignon" <pjb@informatimago.com> - 2019-01-05 16:11 +0100
    Re: calling argumentless function with argument Richard Damon <Richard@Damon-Family.org> - 2019-01-05 11:23 -0500
      Re: calling argumentless function with argument Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-01-05 16:53 +0000
        Re: calling argumentless function with argument Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-01-06 00:46 +0000

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