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Groups > comp.lang.c > #102249
| From | David Brown <david.brown@hesbynett.no> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: while loop condition doesn't work |
| Date | 2017-01-20 19:08 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <o5tjj4$6pg$1@dont-email.me> (permalink) |
| References | (3 earlier) <87pojhbw2h.fsf@bsb.me.uk> <d4616907-128c-442d-b29e-82bf47b4e83d@googlegroups.com> <o5tcfb$ap3$1@dont-email.me> <o5tf8a$lpn$1@dont-email.me> <o5tfrf$o7q$1@dont-email.me> |
On 20/01/17 18:04, Richard Heathfield wrote:
> On 20/01/17 16:54, David Brown wrote:
>> On 20/01/17 17:06, Richard Heathfield wrote:
>>>
>>> /* if we're just at a field boundary, we
>>> want to move to just past that boundary.
>>> If we're at the end of the string,
>>> then two things happen: (1) we can't be
>>> sure that it's legal to move past the '\0'
>>> AND (2) there is in any case nothing more
>>> to convert.
>>>
>>> So if we're not at '\0', we want ptr to
>>> point to not_converted + 1. Otherwise, we
>>> want ptr to point to not_converted (which will
>>> terminate the loop).
>>>
>>> In C, the result of a condition is either 0
>>> (false), or 1 (true), and this happens to map
>>> precisely onto what we want. So we can do this:
>>> */
>>>
>>> ptr = not_converted + (*not_converted != '\0');
>>>
>>
>> And how is that better than:
>>
>> if (*not_converted != '\0') {
>> ptr = not_converted + 1;
>> } else {
>> ptr = not_converted;
>> }
>
> That was in fact my first version (apart from the cuddled 'else'). But
> the duplication of code offended my sense of elegance, so I changed it
> and added the comment to explain exactly how I'd arrived at it.
>
I'm okay with a bit of code duplication, as long as it is short and
clear. If it were more than a simple assignment that were duplicated,
I'd probably hoist the common part to before the conditional.
> Normally, I wouldn't bother with the comment, because to me the code is
> obvious. But I (correctly) guessed that Alla wouldn't be familiar with
> that idiom, so I took the time to explain it.
>
I guess this has the benefit of teaching a new idiom. While I would not
use it in this piece of code, I might use it elsewhere - it's a useful
idea to know.
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while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 01:24 -0800
Re: while loop condition doesn't work mark.bluemel@gmail.com - 2017-01-20 03:29 -0800
Re: while loop condition doesn't work Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-20 12:19 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 05:12 -0800
Re: while loop condition doesn't work Richard Heathfield <rjh@cpax.org.uk> - 2017-01-20 13:17 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 05:20 -0800
Re: while loop condition doesn't work Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-20 15:07 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 05:31 -0800
Re: while loop condition doesn't work Manfred <noname@invalid.add> - 2017-01-20 15:23 +0100
Re: while loop condition doesn't work Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-20 15:16 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 07:45 -0800
Re: while loop condition doesn't work Richard Heathfield <rjh@cpax.org.uk> - 2017-01-20 16:06 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 08:37 -0800
Re: while loop condition doesn't work David Brown <david.brown@hesbynett.no> - 2017-01-20 17:54 +0100
Re: while loop condition doesn't work Richard Heathfield <rjh@cpax.org.uk> - 2017-01-20 17:04 +0000
Re: while loop condition doesn't work David Brown <david.brown@hesbynett.no> - 2017-01-20 19:08 +0100
Re: while loop condition doesn't work Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-30 12:51 -0800
Re: while loop condition doesn't work Keith Thompson <kst-u@mib.org> - 2017-01-30 14:09 -0800
Re: while loop condition doesn't work supercat@casperkitty.com - 2017-01-30 14:57 -0800
Re: while loop condition doesn't work Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-01 21:31 -0800
Re: while loop condition doesn't work Keith Thompson <kst-u@mib.org> - 2017-02-02 10:01 -0800
Re: while loop condition doesn't work Tim Rentsch <txr@alumni.caltech.edu> - 2017-02-04 00:22 -0800
Re: while loop condition doesn't work Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-20 19:12 +0000
Re: while loop condition doesn't work Richard Heathfield <rjh@cpax.org.uk> - 2017-01-23 10:54 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 23:22 -0800
Re: while loop condition doesn't work Richard Heathfield <rjh@cpax.org.uk> - 2017-01-23 11:02 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-21 01:22 -0800
Re: while loop condition doesn't work Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-21 11:00 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-21 08:35 -0800
Re: while loop condition doesn't work Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-21 17:17 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-21 09:32 -0800
Re: while loop condition doesn't work Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-20 19:16 +0000
Re: while loop condition doesn't work Richard Heathfield <rjh@cpax.org.uk> - 2017-01-23 11:03 +0000
Re: while loop condition doesn't work David Brown <david.brown@hesbynett.no> - 2017-01-20 14:34 +0100
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 07:40 -0800
Re: while loop condition doesn't work Richard Heathfield <rjh@cpax.org.uk> - 2017-01-20 15:47 +0000
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 08:26 -0800
Re: while loop condition doesn't work David Brown <david.brown@hesbynett.no> - 2017-01-20 18:01 +0100
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 09:26 -0800
Re: while loop condition doesn't work David Brown <david.brown@hesbynett.no> - 2017-01-20 19:02 +0100
Re: while loop condition doesn't work Alla _ <modelling.data@gmail.com> - 2017-01-20 10:13 -0800
Re: while loop condition doesn't work Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-21 05:36 -0800
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