Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Why _Bool was not defined as enum in C99? |
| Date | 2016-09-14 19:04 -0700 |
| Organization | None to speak of |
| Message-ID | <lna8f95360.fsf@kst-u.example.com> (permalink) |
| References | (3 earlier) <kfnmvjaiwbw.fsf@x-alumni2.alumni.caltech.edu> <02a1a24e-5ead-486c-8397-e68a2a79f8f7@googlegroups.com> <8760pynx50.fsf@bsb.me.uk> <lnd1k65hmr.fsf@kst-u.example.com> <87twdim428.fsf@bsb.me.uk> |
Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> Keith Thompson <kst-u@mib.org> writes:
>
>> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>>> supercat@casperkitty.com writes:
>> [...]
>>>> if the Committee had simply used an enumerated type, the
>>>> semantics of enumerated types would--by definition--have fit
>>>> perfectly.
>>>
>>> You'd have expressions E such that
>>>
>>> if ((_Bool)E)
>>>
>>> and
>>>
>>> if (E)
>>>
>>> behave differently.
>>>
>>> <snip>
>>
>> Not if the hypothetical enumerated _Bool has the same conversion
>> semantics as the built-in _Bool that was actually added in C99.
>> I don't think anyone is suggesting just adding the equivalent of
>> a predefined
>>
>> typedef enum { false, true } _Bool;
>>
>> and leaving it at that.
>
> Actually, I thought that was exactly what the OP was asking about. And
> it sounds like it is what supercat was talking about in the message I
> replied to. That's how I read "if the Committee had simply used an
> enumerated type" and the idea that the semantics would be right by
> definition.
Ok, I might have misinterpreted what others were saying.
> But if it's a special enumeration with its own conversion semantics, how
> do you know that is *not* how _Bool is implemented? Or, to put it
> slightly differently, what would give the game away so you could say
> that it's a special enumerated type with its own semantics?
For the type itself, I can't think of a way to detect the difference.
But you could certainly detect the difference in the way false
and true are defined (assuming that the type name _Bool and the
constants false and true are all predefined by something resembling
an enumerated type definition).
BTW, I've been wondering why bool is defined as a macro rather than
as a typedef. My best guess is that it's to allow for code that
(a) defines its own "bool" somehow, but (b) indirectly, and probably
unintentionally, includes <stdbool.h>. If you have some pre-C99 code
that has, for example:
typedef enum { false, true } bool;
then you can change it to:
#undef bool
#undef false
#undef true
typedef enum { false, true } bool;
and it will still compile correctly even if <stdbool.h> is present.
--
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
Why _Bool was not defined as enum in C99? thiago.adams@gmail.com - 2016-09-12 13:24 -0700
Re: Why _Bool was not defined as enum in C99? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-12 21:56 +0100
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-12 15:59 -0700
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-13 16:05 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-13 18:17 -0700
Re: Why _Bool was not defined as enum in C99? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-14 01:20 +0100
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-14 03:59 -0700
Re: Why _Bool was not defined as enum in C99? Nobody <nobody@nowhere.invalid> - 2016-09-14 17:31 +0100
Re: Why _Bool was not defined as enum in C99? Thiago Adams <thiago.adams@gmail.com> - 2016-09-14 09:49 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 11:45 -0700
Re: Why _Bool was not defined as enum in C99? <william@wilbur.25thandClement.com> - 2016-09-14 14:13 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 16:26 -0700
Re: Why _Bool was not defined as enum in C99? "James R. Kuyper" <jameskuyper@verizon.net> - 2016-09-12 17:11 -0400
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-13 15:55 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-13 18:08 -0700
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-14 03:56 -0700
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-14 07:58 -0700
Re: Why _Bool was not defined as enum in C99? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-14 19:39 +0100
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 13:52 -0700
Re: Why _Bool was not defined as enum in C99? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-15 00:53 +0100
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-14 17:04 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 20:52 -0700
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-14 19:26 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 19:04 -0700
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-14 14:21 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 16:23 -0700
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-14 17:06 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 20:45 -0700
Re: Why _Bool was not defined as enum in C99? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-14 22:12 -0400
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-15 12:37 +0200
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-15 09:35 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 00:47 +0200
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-15 22:02 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 09:56 +0200
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-16 07:34 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 20:31 +0200
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-16 12:32 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-17 23:30 +0200
Re: Why _Bool was not defined as enum in C99? BartC <bc@freeuk.com> - 2016-09-15 18:25 +0100
Re: Why _Bool was not defined as enum in C99? luser droog <luser.droog@gmail.com> - 2016-09-15 12:35 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 00:51 +0200
Re: Why _Bool was not defined as enum in C99? luser droog <luser.droog@gmail.com> - 2016-09-16 17:02 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-16 19:23 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-17 23:35 +0200
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 10:40 -0700
Re: Why _Bool was not defined as enum in C99? Thiago Adams <thiago.adams@gmail.com> - 2016-09-14 10:01 -0700
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-14 11:35 -0700
Re: Why _Bool was not defined as enum in C99? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-14 22:15 -0400
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-14 23:51 -0700
Re: Why _Bool was not defined as enum in C99? Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-15 15:14 -0400
Re: Why _Bool was not defined as enum in C99? Ian Collins <ian-news@hotmail.com> - 2016-09-15 16:08 +1200
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-15 12:46 +0200
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-15 09:37 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 00:53 +0200
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-15 21:45 -0700
Re: Why _Bool was not defined as enum in C99? Richard Heathfield <rjh@cpax.org.uk> - 2016-09-16 06:32 +0100
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 09:59 +0200
Re: Why _Bool was not defined as enum in C99? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-16 11:00 +0100
Re: Why _Bool was not defined as enum in C99? Thiago Adams <thiago.adams@gmail.com> - 2016-09-16 04:46 -0700
Re: Why _Bool was not defined as enum in C99? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-16 12:58 +0100
Re: Why _Bool was not defined as enum in C99? Melzzzzz <Melzzzzz@zzzzz.com> - 2016-09-16 12:06 +0000
Re: Why _Bool was not defined as enum in C99? Thiago Adams <thiago.adams@gmail.com> - 2016-09-16 05:13 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-16 10:47 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-16 10:46 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 10:02 +0200
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-15 11:42 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 10:19 +0200
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-16 08:06 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 20:51 +0200
Re: Why _Bool was not defined as enum in C99? Thiago Adams <thiago.adams@gmail.com> - 2016-09-16 11:56 -0700
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-22 22:38 -0700
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-14 11:42 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-14 14:02 -0700
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-15 10:51 -0700
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-15 11:18 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-15 13:46 -0700
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-15 13:10 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-15 16:01 -0700
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-15 13:40 -0700
Re: Why _Bool was not defined as enum in C99? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-16 07:21 -0700
Re: Why _Bool was not defined as enum in C99? Thiago Adams <thiago.adams@gmail.com> - 2016-09-16 07:37 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-16 20:55 +0200
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-16 14:43 -0700
Re: Why _Bool was not defined as enum in C99? supercat@casperkitty.com - 2016-09-16 15:36 -0700
Re: Why _Bool was not defined as enum in C99? David Brown <david.brown@hesbynett.no> - 2016-09-17 23:45 +0200
Re: Why _Bool was not defined as enum in C99? Keith Thompson <kst-u@mib.org> - 2016-09-17 17:14 -0700
csiph-web