Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.c > #120490
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Set the result of void function |
| Date | 2017-09-28 13:31 -0700 |
| Organization | None to speak of |
| Message-ID | <ln7ewiwon8.fsf@kst-u.example.com> (permalink) |
| References | (16 earlier) <oqi94p$jl4$1@dont-email.me> <ej6zB.1196081$ik4.742321@fx38.am4> <oqj43k$g9l$1@dont-email.me> <uB9zB.1550017$WI6.973316@fx30.am4> <oqjk7g$h3p$1@dont-email.me> |
David Brown <david.brown@hesbynett.no> writes:
> On 28/09/17 18:39, bartc wrote:
[...]
>> OK, I understand. If I write this:
>>
>> int main(void) {
>> int a;
>> void fn();
>>
>> fn(100);
>> fn(200.0);
>> fn("Hello, World!");
>> fn(&a);
>> }
>>
>> which is clearly not right, compile it using:
>>
>> gcc -std=c11 -Wextra -Wall -Wpedantic -Werror -c c.c
>>
>> without a peep out of the compiler, the fault is not with the Language,
>> not with the Compiler, and not even with the user. The fault is with
>> Bart for not knowing what options to feed it. Clearly that lot isn't
>> quite enough! (Which ones would be? Serious question.)
>
> You have told the compiler you have a function that can take arguments
> of any type - and then you call that function with a variety of
> arguments. Is the compiler supposed to guess that you don't know what
> you are doing? To me, it is /not/ clear that the code you wrote is not
> right - nor what the correct version might be. It is only clear that
> you have a poor coding style and that if you had used a sensible
> header/source style then mistakes with incorrect function declarations
> are very difficult to make.
It is 100% clear that the program of which the above main function is a
part has undefined behavior. If a function is declared with (), then
it's the caller's responsibility to call it with the correct number and
type(s) of arguments. If the call is inconsistent with the definition
(which in this case is probably in some other source file), then the
behavior is undefined.
There is no possible definition of the fn function that could be
consistent with all 4 calls shown above. In fact, any definition could
be consistent with at most one of them.
Problem: Non-prototyped functions are error-prone. Solution: Don't use
them.
[...]
>> Under what circumstances would a declaration like:
>>
>> void fn();
>>
>> without listing parameter types be used anyway?
>
> I don't think you can legally define a matching function fn() in
> standard C.
In fact you can. For example, you could have:
void fn(const char *s) { puts(s); }
in another translation unit; that would make the fn("Hello, World!")
legal and well behaved.
> I am not an expert on variable argument functions. But it
> is certainly easy to imagine how such a function could be written to
> work (even if it cannot be done in C). You could have a function that
> has a static "stepNo" variable starting at 0 and incrementing for each
> call. On the first call, it interprets the parameter as an integer, and
> prints it out. On the second call, it interprets the parameter as a
> double and prints it out. And so on.
Calling a variadic function without a visible prototype has undefined
behavior. (It might happen to "work", and is likely to in many cases
because compiler writers usually try to make pre-ANSI code works as
expected. Pre-ANSI code didn't have prototypes, nor did it have
variadic functions in their current form.)
The prototype for a variadic function has ", ..." at the end of its
parameter list.
[...]
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Set the result of void function Thiago Adams <thiago.adams@gmail.com> - 2017-09-19 14:23 -0700
Re: Set the result of void function Thiago Adams <thiago.adams@gmail.com> - 2017-09-19 14:38 -0700
Re: Set the result of void function gordonb.tfand@burditt.org (Gordon Burditt) - 2017-09-19 17:16 -0500
Re: Set the result of void function "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-09-20 00:39 +0200
Re: Set the result of void function James Kuyper <jameskuyper@verizon.net> - 2017-09-19 22:06 -0400
Re: Set the result of void function "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-09-20 06:51 +0200
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-20 10:55 +0100
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-20 12:11 +0100
Re: Set the result of void function fir <profesor.fir@gmail.com> - 2017-09-20 07:17 -0700
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-20 11:28 +0100
Re: Set the result of void function mark.bluemel@gmail.com - 2017-09-20 03:30 -0700
Re: Set the result of void function fir <profesor.fir@gmail.com> - 2017-09-20 06:53 -0700
Re: Set the result of void function Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-09-21 03:50 -0500
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-21 11:00 +0100
Re: Set the result of void function scott@slp53.sl.home (Scott Lurndal) - 2017-09-21 12:39 +0000
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-21 14:12 +0100
Re: Set the result of void function scott@slp53.sl.home (Scott Lurndal) - 2017-09-21 13:51 +0000
Re: Set the result of void function Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2017-09-21 08:36 -0600
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-21 17:51 +0100
Re: Set the result of void function supercat@casperkitty.com - 2017-09-21 10:06 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-22 08:51 +0200
Plunging innocent people into poverty (Was: Set the result of void function) gazelle@shell.xmission.com (Kenny McCormack) - 2017-09-23 09:31 +0000
Re: Plunging innocent people into poverty (Was: Set the result of void function) David Brown <david.brown@hesbynett.no> - 2017-09-23 12:09 +0200
Re: Plunging innocent people into poverty (Was: Set the result of void function) gazelle@shell.xmission.com (Kenny McCormack) - 2017-09-23 10:25 +0000
Re: Plunging innocent people into poverty Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2017-09-23 10:43 -0600
Re: Plunging innocent people into poverty supercat@casperkitty.com - 2017-09-23 10:41 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-22 09:37 +0200
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-22 11:27 +0100
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-22 14:42 +0200
Re: Set the result of void function Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-09-24 12:09 +0000
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-25 08:31 +0200
Re: Set the result of void function Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-09-25 03:52 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-25 13:25 +0200
Re: Set the result of void function Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-09-25 04:58 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-25 14:20 +0200
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-25 13:44 +0100
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-25 15:09 +0200
Re: Set the result of void function Thiago Adams <thiago.adams@gmail.com> - 2017-09-25 05:44 -0700
Re: Set the result of void function Thiago Adams <thiago.adams@gmail.com> - 2017-09-25 05:58 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-25 15:15 +0200
Re: Set the result of void function Thiago Adams <thiago.adams@gmail.com> - 2017-09-25 06:46 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-25 16:01 +0200
Re: Set the result of void function Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-09-25 07:18 -0700
Re: Set the result of void function Thiago Adams <thiago.adams@gmail.com> - 2017-09-25 07:55 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-25 08:49 -0700
Re: Set the result of void function Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-09-25 09:21 -0700
Re: Set the result of void function supercat@casperkitty.com - 2017-09-25 09:51 -0700
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-25 21:57 +0100
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-25 15:03 -0700
Re: Set the result of void function Öö Tiib <ootiib@hot.ee> - 2017-09-25 21:34 -0700
Re: Set the result of void function Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-09-26 04:28 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-27 08:26 +0200
Re: Set the result of void function "James R. Kuyper" <jameskuyper@verizon.net> - 2017-09-27 11:48 -0400
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 08:54 +0200
Re: Set the result of void function gordonb.iddsu@burditt.org (Gordon Burditt) - 2017-09-28 23:33 -0500
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-27 09:15 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-27 17:50 +0100
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-27 10:35 -0700
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-27 18:47 +0100
Re: Set the result of void function supercat@casperkitty.com - 2017-09-27 10:52 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-27 11:10 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 09:10 +0200
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-27 11:06 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-27 20:01 +0100
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-27 12:26 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-27 20:38 +0100
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-27 13:00 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-27 21:54 +0100
Re: Set the result of void function supercat@casperkitty.com - 2017-09-27 14:12 -0700
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-27 14:34 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-27 23:16 +0100
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-27 16:09 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-28 01:12 +0100
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-28 02:03 +0100
Re: Set the result of void function Ian Collins <ian-news@hotmail.com> - 2017-09-28 17:31 +1300
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 09:55 +0200
Re: Set the result of void function Ian Collins <ian-news@hotmail.com> - 2017-09-28 21:00 +1300
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-28 10:48 +0100
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 13:20 +0200
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-28 11:29 +0100
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-27 20:27 -0700
Re: Set the result of void function Gareth Owen <gwowen@gmail.com> - 2017-09-29 19:30 +0100
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-29 19:45 +0100
Re: Set the result of void function Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-29 14:49 -0400
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-27 15:07 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 09:42 +0200
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-28 13:55 +0100
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 17:22 +0200
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 09:14 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 20:13 +0200
Re: Set the result of void function Gareth Owen <gwowen@gmail.com> - 2017-09-29 19:42 +0100
Re: Set the result of void function Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-09-28 09:14 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 09:25 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 20:17 +0200
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-28 17:39 +0100
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-28 10:10 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-28 19:05 +0100
Re: Set the result of void function "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-09-28 14:20 -0400
Re: Set the result of void function Ian Collins <ian-news@hotmail.com> - 2017-09-29 07:52 +1300
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-28 11:59 -0700
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-28 18:50 +0100
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-28 19:47 +0100
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 21:57 +0200
Re: Set the result of void function "James R. Kuyper" <jameskuyper@verizon.net> - 2017-09-28 16:14 -0400
Re: Set the result of void function supercat@casperkitty.com - 2017-09-28 13:17 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-28 21:23 +0100
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 13:55 -0700
Re: Set the result of void function Gareth Owen <gwowen@gmail.com> - 2017-09-29 19:50 +0100
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-28 13:57 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-28 23:18 +0200
Re: Set the result of void function "James R. Kuyper" <jameskuyper@verizon.net> - 2017-09-28 17:38 -0400
Re: Set the result of void function supercat@casperkitty.com - 2017-09-28 15:54 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-29 08:59 +0200
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 14:43 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-29 10:43 +0200
Re: Set the result of void function supercat@casperkitty.com - 2017-09-29 07:43 -0700
Re: Set the result of void function Gareth Owen <gwowen@gmail.com> - 2017-09-30 19:21 +0100
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-30 19:45 +0100
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 13:31 -0700
Re: Set the result of void function supercat@casperkitty.com - 2017-09-28 13:41 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 14:07 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-28 16:25 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 18:45 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-28 19:54 -0700
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-28 20:51 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-28 22:39 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-29 09:16 -0700
Re: Set the result of void function gazelle@shell.xmission.com (Kenny McCormack) - 2017-09-29 16:17 +0000
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-29 11:05 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-29 11:23 -0700
Re: Set the result of void function supercat@casperkitty.com - 2017-09-29 12:15 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-29 16:04 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-29 16:44 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-30 10:04 -0700
Re: Set the result of void function supercat@casperkitty.com - 2017-09-30 10:33 -0700
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-29 11:26 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-29 16:03 -0700
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-29 09:44 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-29 11:15 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-29 11:35 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-29 16:11 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-29 16:14 -0700
Re: Set the result of void function supercat@casperkitty.com - 2017-09-30 08:55 -0700
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-29 11:36 -0700
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-29 12:05 +0100
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-29 12:17 +0100
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-29 09:15 -0700
Re: Set the result of void function Ian Collins <ian-news@hotmail.com> - 2017-09-29 09:42 +1300
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-28 21:55 +0100
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 14:12 -0700
Re: Set the result of void function "James R. Kuyper" <jameskuyper@verizon.net> - 2017-09-28 17:22 -0400
Re: Set the result of void function Gareth Owen <gwowen@gmail.com> - 2017-09-29 19:50 +0100
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 09:00 -0700
Re: Set the result of void function supercat@casperkitty.com - 2017-09-28 09:35 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-28 10:57 -0700
Re: Set the result of void function Thiago Adams <thiago.adams@gmail.com> - 2017-09-25 10:35 -0700
Re: Set the result of void function Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-09-25 06:57 -0700
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-25 16:32 +0100
Re: Set the result of void function Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2017-09-25 08:43 -0700
Re: Set the result of void function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-09-25 22:12 +0100
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-25 09:03 -0700
Re: Set the result of void function Jorgen Grahn <grahn+nntp@snipabacken.se> - 2017-09-25 14:17 +0000
Re: Set the result of void function "James R. Kuyper" <jameskuyper@verizon.net> - 2017-09-20 11:32 -0400
Re: Set the result of void function fir <profesor.fir@gmail.com> - 2017-09-20 01:50 -0700
Re: Set the result of void function David Kleinecke <dkleinecke@gmail.com> - 2017-09-20 15:56 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-19 23:01 +0100
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-20 15:40 +0200
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-20 08:50 -0700
Re: Set the result of void function David Brown <david.brown@hesbynett.no> - 2017-09-20 22:52 +0200
Re: Set the result of void function supercat@casperkitty.com - 2017-09-20 15:04 -0700
Re: Set the result of void function supercat@casperkitty.com - 2017-09-20 07:39 -0700
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-19 15:18 -0700
Re: Set the result of void function bartc <bc@freeuk.com> - 2017-09-20 01:21 +0100
Re: Set the result of void function jameskuyper@verizon.net - 2017-09-19 19:40 -0700
Re: Set the result of void function rockbrentwood@gmail.com - 2017-09-19 16:36 -0700
Re: Set the result of void function James Kuyper <jameskuyper@verizon.net> - 2017-09-19 22:13 -0400
Re: Set the result of void function gazelle@shell.xmission.com (Kenny McCormack) - 2017-09-22 01:48 +0000
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-19 19:36 -0700
Re: Set the result of void function mark.bluemel@gmail.com - 2017-09-20 01:00 -0700
Re: Set the result of void function fir <profesor.fir@gmail.com> - 2017-09-20 02:01 -0700
Re: Set the result of void function Keith Thompson <kst-u@mib.org> - 2017-09-20 08:36 -0700
Re: Set the result of void function "James R. Kuyper" <jameskuyper@verizon.net> - 2017-09-20 11:36 -0400
Re: Set the result of void function John Bode <jfbode1029@gmail.com> - 2017-09-20 15:30 -0700
csiph-web