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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Program to cipher a text, new thread, fresh one |
| Date | 2015-10-31 13:29 -0700 |
| Organization | None to speak of |
| Message-ID | <lnfv0q93z2.fsf@kst-u.example.com> (permalink) |
| References | (1 earlier) <1e1a0897-ba67-47b3-b778-0bc03f8b098b@googlegroups.com> <87oaffb4z9.fsf@bsb.me.uk> <n12oak$mom$1@dont-email.me> <8737wraqhw.fsf@bsb.me.uk> <n130a5$ob3$1@dont-email.me> |
Bartc <bc@freeuk.com> writes:
> On 31/10/2015 17:37, Ben Bacarisse wrote:
>> Bartc <bc@freeuk.com> writes:
>>
>>> On 31/10/2015 12:24, Ben Bacarisse wrote:
>
>>> I tried to make it do the same encoding as yours, but there is a
>>> difference which might be a bug in your code, or a lack of
>>> understanding on my part: lower case strings are encoded differently
>>> from the same upper case input.
>>>
>>> So with key "ABC", then your program encodes "AAA" to "ABC", but "aaa"
>>> to "acb" (after restarting). (I assume that key "AAA..." having no
>>> effect is intentional.)
>>
>> That would be a bug, but I can't reproduce it. I've checked with the
>> code I posted (in case I posted something other that the last version),
>> and it seems to work as expected:
>
> OK, it's to do with the isalpha() function; some libraries in Windows
> return 1 or 2 for an alpha character (for upper or lower case
> presumably), and you use that to step along the key string. (So in
> Windows, it steps twice along the keystring for a lower case input. In
> Linux it stepped just once.)
Do they really? The MSDN documentation for isalpha():
https://msdn.microsoft.com/en-us/library/xt82b8z8.aspx
doesn't mention this; it merely says that isalpha() returns zero or
non-zero.
Even if it were documented, I wouldn't write code that depends on it.
Unless you're referring to some function other than isalpha()?
(There's also a C++specific isalpha() function declared in the <locale>
header, but it returns a bool, and it's not being used here.)
> The specs for isalpha() just say it returns non-zero if test is true.
That's all I'd consider depending on. And in fact I don't think I've
seen any code in this thread that makes any assumptions about which
non-zero value isalpha() returns.
>>> Anyway, in mine other differences are:
>>>
>>> * Requires ASCII (this is checked for)
>>
>> It's not entirely clear what ASCII means. You assume some things about
>> the letters (they they are contiguous) and you assume that no char
>> values are negative. Is that what you mean? Some encodings that some
>> people would call ASCII have negative characters.
>
> ASCII codes go up to 127. But the values of interest are 65 to 90, and
> 97 to 122, which are always going to be positive.
Regardless of the character set, the values of the 52 letters are
guaranteed to be positive. But the characters that aren't letters are
also "of interest", since you're handling user input. If the input
contains, for example, an accented letter in a Latin-1 locale, it's
going to have a negative value as a plain char (assuming CHAR_BIT==8 and
CHAR_MIN<0), which means that passing it to isalpha(), isupper(), or
islower() has undefined behavior (both ISO C and MSDN say so).
[...]
--
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
Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 08:23 -0700
Re: Program to cipher a text, new thread, fresh one Bartc <bc@freeuk.com> - 2015-10-30 15:39 +0000
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 09:33 -0700
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-01 09:33 +0000
Re: Program to cipher a text, new thread, fresh one Mark Storkamp <mstorkamp@yahoo.com> - 2015-10-30 11:17 -0500
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 09:32 -0700
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-01 09:38 +0000
Re: Program to cipher a text, new thread, fresh one "Osmium" <r124c4u102@comcast.net> - 2015-10-30 10:55 -0600
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-01 10:07 +0000
Re: Program to cipher a text, new thread, fresh one Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-01 10:42 +0000
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-01 11:35 +0000
Re: Program to cipher a text, new thread, fresh one James Kuyper <jameskuyper@verizon.net> - 2015-11-01 08:33 -0500
Re: Program to cipher a text, new thread, fresh one Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-01 16:09 +0000
Re: Program to cipher a text, new thread, fresh one Bartc <bc@freeuk.com> - 2015-11-02 12:43 +0000
Re: Program to cipher a text, new thread, fresh one Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-02 13:25 +0000
Re: Program to cipher a text, new thread, fresh one Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-02 06:13 -0800
Re: Program to cipher a text, new thread, fresh one Keith Thompson <kst-u@mib.org> - 2015-11-01 12:26 -0800
Re: Program to cipher a text, new thread, fresh one supercat@casperkitty.com - 2015-11-01 07:59 -0800
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-02 13:48 +0000
Re: Program to cipher a text, new thread, fresh one Bartc <bc@freeuk.com> - 2015-11-02 14:06 +0000
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-02 14:51 +0000
Re: Program to cipher a text, new thread, fresh one Bartc <bc@freeuk.com> - 2015-11-02 15:48 +0000
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-02 16:00 +0000
Re: Program to cipher a text, new thread, fresh one asetofsymbols@gmail.com - 2015-11-03 01:40 -0800
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-03 11:16 +0000
Re: Program to cipher a text, new thread, fresh one "Osmium" <r124c4u102@comcast.net> - 2015-11-03 05:21 -0600
Re: Program to cipher a text, new thread, fresh one asetofsymbols@gmail.com - 2015-11-03 03:41 -0800
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-03 11:53 +0000
Re: Program to cipher a text, new thread, fresh one "Osmium" <r124c4u102@comcast.net> - 2015-11-03 05:57 -0600
Re: Program to cipher a text, new thread, fresh one Richard Heathfield <rjh@cpax.org.uk> - 2015-11-03 12:48 +0000
Re: Program to cipher a text, new thread, fresh one Rosario19 <Ros@invalid.invalid> - 2015-11-04 09:09 +0100
Re: Program to cipher a text, new thread, fresh one Rosario19 <Ros@invalid.invalid> - 2015-11-04 09:37 +0100
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-11-04 07:09 -0800
Re: Program to cipher a text, new thread, fresh one "Osmium" <r124c4u102@comcast.net> - 2015-11-03 05:53 -0600
Re: Program to cipher a text, new thread, fresh one asetofsymbols@gmail.com - 2015-11-03 04:29 -0800
Re: Program to cipher a text, new thread, fresh one "Osmium" <r124c4u102@comcast.net> - 2015-11-03 06:42 -0600
Re: Program to cipher a text, new thread, fresh one Geoff <geoff@invalid.invalid> - 2015-11-01 08:07 -0800
Re: Program to cipher a text, new thread, fresh one Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-02 02:26 -0800
Re: Program to cipher a text, new thread, fresh one Rosario19 <Ros@invalid.invalid> - 2015-11-06 07:53 +0100
Re: Program to cipher a text, new thread, fresh one Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-07 10:01 -0800
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 10:50 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 10:53 -0700
Re: Program to cipher a text, new thread, fresh one Barry Schwarz <schwarzb@dqel.com> - 2015-10-30 11:52 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 12:12 -0700
Re: Program to cipher a text, new thread, fresh one Barry Schwarz <schwarzb@dqel.com> - 2015-10-30 21:05 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 23:58 -0700
Re: Program to cipher a text, new thread, fresh one Barry Schwarz <schwarzb@dqel.com> - 2015-10-31 03:09 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-31 03:47 -0700
Re: Program to cipher a text, new thread, fresh one Barry Schwarz <schwarzb@dqel.com> - 2015-10-31 11:42 -0700
Re: Program to cipher a text, new thread, fresh one Barry Schwarz <schwarzb@dqel.com> - 2015-10-30 12:04 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 12:10 -0700
Re: Program to cipher a text, new thread, fresh one "Osmium" <r124c4u102@comcast.net> - 2015-10-30 13:17 -0600
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-31 00:04 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-31 00:25 -0700
Re: Program to cipher a text, new thread, fresh one Keith Thompson <kst-u@mib.org> - 2015-10-30 12:34 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-30 21:49 -0700
Re: Program to cipher a text, new thread, fresh one Keith Thompson <kst-u@mib.org> - 2015-10-31 13:18 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-31 00:29 -0700
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-31 01:12 -0700
Re: Program to cipher a text, new thread, fresh one Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-31 12:24 +0000
Re: Program to cipher a text, new thread, fresh one Alla _ <modelling.data@gmail.com> - 2015-10-31 06:11 -0700
Re: Program to cipher a text, new thread, fresh one Bartc <bc@freeuk.com> - 2015-10-31 15:58 +0000
Re: Program to cipher a text, new thread, fresh one Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-31 17:37 +0000
Re: Program to cipher a text, new thread, fresh one Bartc <bc@freeuk.com> - 2015-10-31 18:14 +0000
Re: Program to cipher a text, new thread, fresh one Keith Thompson <kst-u@mib.org> - 2015-10-31 13:29 -0700
Re: Program to cipher a text, new thread, fresh one Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-31 20:35 +0000
Re: Program to cipher a text, new thread, fresh one Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-31 20:32 +0000
Re: Program to cipher a text, new thread, fresh one Rosario19 <Ros@invalid.invalid> - 2015-11-04 09:50 +0100
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