Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > sci.electronics.design > #447019
| From | David Brown <david.brown@hesbynett.no> |
|---|---|
| Newsgroups | sci.electronics.design |
| Subject | Re: Arduino / compilers on uC |
| Date | 2017-02-09 16:41 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <o7i2fv$ptm$1@dont-email.me> (permalink) |
| References | (4 earlier) <MPG.3304102aef021e2c98a005@news.eternal-september.org> <o7evvu$fuu$1@dont-email.me> <865e7bc1-f9a3-40a4-b1b5-c48867fa1d74@googlegroups.com> <o7fgmo$e0m$3@dont-email.me> <bf33f3d7-1702-4d37-a030-7d22ae46d7ba@googlegroups.com> |
On 09/02/17 15:51, jack4747@gmail.com wrote:
> Il giorno mercoledì 8 febbraio 2017 17:25:43 UTC+1, David Brown ha scritto:
>> On 08/02/17 16:01, pcdhobbs@gmail.com wrote:
>>>> That is a completely different matter. A conditional statement
>>>> ("if", "while", etc.) compares its argument to 0 (in C) or
>>>> "contextually converts to bool" (in C++) - thus any non-false value
>>>> is considered "true".
>>>
>>> Back in the late '70s (iirc) the Forth standard changed to make TRUE
>>> = -1 instead of 1, causing massive breakage. The rationale was that
>>> on a twos-complement machine that made every bit of the word 1, so
>>> you could use TRUE and FALSE in bitwise operations too.
>>>
>>> Nice idea, if they'd thought of it the first time round. :(
>>>
>>
>> It is not entirely unreasonable to standardise on -1 for "true". But C
>> (and C++) standardised on 1, and that's the way it is. (It's a better
>> choice anyway - it has the same representation in all integer types, no
>> matter what size or signedness.)
>
> nope.
You are wrong - and if you don't believe me, look it up in the C standards.
> C per definition has 0 == FALSE, and TRUE is anything different from FALSE.
>
C has no identifier "FALSE", nor an identifier "TRUE" - and if it did,
the "TRUE" would have to be defined to a particular fixed value.
There are three contexts in which C (and C++, which is the language in
question) have a concept of "true" or "false".
1. The boolean types. In C++, this is "bool" - in C from C99 onwards,
it is "_Bool". In C++, "bool" is the type and "true" and "false" are
keywords. In C, "_Bool" is the type and "true" and "false" are macros
defined to 1 and 0 respectively, with "bool" being a macro defined to
"_Bool" (all this is in <stdbool.h>). Prior to C99, C has no boolean
type and no true or false identifiers.
The type _Bool (or bool) may only store 0 or 1. If you convert from
another type to "bool", then any value that does not compare equal to 0
is converted to 1.
2. The relational operators (==, !=, <, >, <=, >=). These evaluate to 0
for false, 1 for true.
3. Conditional statements and expressions ("if", "while", and the
control clause of "for", as well as the conditional operator and the
logical "not", "and" and "or" operators). In C, given "if (x)" then the
condition is considered "true" if x does not compare equal to 0. In
C++, x is "contextually converted to bool". Unless you are doing
something weird with conversion operators, this usually means much the
same thing.
So in C, false is 0, true is 1. Boolean types cannot legally hold any
other value. Any time the compiler is asked to consider a non-boolean
expression in a boolean context, then an expression that does not
compare equal to 0 is converted to 1.
In pre-C99 C code, there is no "_Bool" type standardised (though
implementations may have one as an extension). It was common to use
either an "int" or an "unsigned char" for holding boolean flags, and to
define "true" and "false" as macros meaning 1 and 0. Occasionally
people used an enumerated type with the same effect. Then there were no
guarantees about these variables being restricted to 0 and 1. And some
people would define their "true" (or "TRUE") macro to be -1 instead of 1
- but that was their personal C code - it has never been part of the C
language.
Back to sci.electronics.design | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 15:43 -0800
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 10:58 +1100
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 19:09 -0500
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 18:30 -0800
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 21:43 -0500
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 19:02 -0800
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 23:26 -0500
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 21:05 -0800
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 13:55 +1100
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 20:00 -0800
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 19:31 +1100
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:29 +0100
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-07 07:39 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-08 12:24 +0100
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 08:36 -0800
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-10 08:15 +1100
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 15:37 +0100
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 15:35 +0100
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-07 08:05 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-08 12:30 +0100
Re: Arduino / compilers on uC mrdarrett@gmail.com - 2017-02-06 15:59 -0800
Re: Arduino / compilers on uC Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-06 16:04 -0800
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 18:41 -0800
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 14:08 +1100
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 20:14 -0800
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 08:00 +0000
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 05:42 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-09 15:07 +0100
Re: Arduino / compilers on uC Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-09 09:54 -0800
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 15:55 +0000
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 08:46 -0800
Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-09 14:42 -0500
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-11 06:54 -0800
Re: Arduino / compilers on uC pcdhobbs@gmail.com - 2017-02-11 07:31 -0800
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-11 07:59 -0800
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-11 17:01 +0000
Re: Arduino / compilers on uC pcdhobbs@gmail.com - 2017-02-11 12:52 -0800
Re: Arduino / compilers on uC krw@notreal.com - 2017-02-11 18:46 -0500
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-12 10:20 +1100
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:07 +0100
Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-09 14:16 -0500
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 22:39 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:06 +0100
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-13 15:29 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:49 +0100
Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-13 10:55 -0500
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-13 17:09 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-14 09:49 +0100
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-13 16:07 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-14 10:01 +0100
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-14 09:49 +0000
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-17 04:21 +1100
Re: Arduino / compilers on uC pcdhobbs@gmail.com - 2017-02-16 14:47 -0800
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-17 00:17 +0000
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 19:49 +1100
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 06:22 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:42 +0100
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 06:57 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-09 16:12 +0100
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-10 08:24 +1100
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 19:08 -0500
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 18:47 -0800
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-06 21:51 -0500
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 20:39 -0800
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 20:55 -0800
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-07 20:05 +1100
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-08 12:26 -0500
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-08 12:32 -0500
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-09 08:31 +1100
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-09 08:21 +1100
Re: Arduino / compilers on uC Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-08 13:33 -0800
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 08:15 +0000
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-09 05:51 -0800
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 16:22 +0000
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-09 16:45 -0500
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-09 16:51 -0500
Re: Arduino / compilers on uC Clifford Heath <no.spam@please.net> - 2017-02-10 09:11 +1100
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 22:45 +0000
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-15 10:11 -0500
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:57 +0100
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 08:07 +0000
Re: Arduino / compilers on uC rickman <gnuarm@gmail.com> - 2017-02-07 04:01 -0500
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 09:40 +0000
Re: Arduino / compilers on uC rickman <gnuarm@gmail.com> - 2017-02-07 05:52 -0500
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-07 11:26 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 12:58 +0100
Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-09 14:52 -0500
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-09 22:47 +0000
Re: Arduino / compilers on uC bitrex <bitrex@de.lete.earthlink.net> - 2017-02-09 14:00 -0500
Re: Arduino / compilers on uC Tim Wescott <seemywebsite@myfooter.really> - 2017-02-09 13:24 -0600
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:52 +0100
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-07 10:50 +0100
Re: Arduino / compilers on uC rickman <gnuarm@gmail.com> - 2017-02-06 19:49 -0500
Re: Arduino / compilers on uC "David Eather" <eather@tpg.com.au> - 2017-02-07 12:45 +1000
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-06 18:51 -0800
Re: Arduino / compilers on uC "David Eather" <eather@tpg.com.au> - 2017-02-08 06:35 +1000
Re: Arduino / compilers on uC "David Eather" <eather@tpg.com.au> - 2017-02-08 06:44 +1000
Re: Arduino / compilers on uC M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-07 17:11 -0500
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-08 12:40 +0100
Re: Arduino / compilers on uC pcdhobbs@gmail.com - 2017-02-08 07:01 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-08 17:25 +0100
Re: Arduino / compilers on uC jack4747@gmail.com - 2017-02-09 06:51 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-09 16:41 +0100
Re: Arduino / compilers on uC M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-09 19:44 -0500
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:14 +0100
Re: Arduino / compilers on uC John Devereux <john@devereux.me.uk> - 2017-02-16 12:57 +0000
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-16 14:11 +0000
Re: Arduino / compilers on uC John Devereux <john@devereux.me.uk> - 2017-02-16 14:40 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-16 15:58 +0100
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-16 15:56 +0000
Re: Arduino / compilers on uC John Devereux <john@devereux.me.uk> - 2017-02-16 16:45 +0000
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-16 17:18 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-17 14:59 +0100
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-17 14:24 +0000
Re: Arduino / compilers on uC Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-02-17 21:07 +0200
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-17 20:16 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-17 23:28 +0100
Re: Arduino / compilers on uC Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-17 10:21 -0500
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-17 16:34 +0100
Re: Arduino / compilers on uC M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-09 19:43 -0500
Re: Arduino / compilers on uC Tim Wescott <tim@seemywebsite.com> - 2017-02-10 10:41 -0600
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-11 07:06 -0800
Re: Arduino / compilers on uC Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-02-11 17:09 +0000
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-13 16:28 +0100
Re: Arduino / compilers on uC Tim Wescott <tim@seemywebsite.com> - 2017-02-14 09:59 -0600
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-14 13:46 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-15 10:04 +0100
Re: Arduino / compilers on uC dagmargoodboat@yahoo.com - 2017-02-15 05:57 -0800
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-15 16:02 +0100
Re: Arduino / compilers on uC David Brown <david.brown@hesbynett.no> - 2017-02-15 17:15 +0100
Re: Arduino / compilers on uC Tim Wescott <tim@seemywebsite.com> - 2017-02-16 14:19 -0600
csiph-web