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Groups > comp.lang.c > #101648
| From | BartC <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Correct way of doing string manipulation functions |
| Date | 2017-01-13 18:49 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <o5b7da$611$1@dont-email.me> (permalink) |
| References | (4 earlier) <fe768196-91cb-4db1-a094-c548a709b64d@googlegroups.com> <d16bb2a3-d00e-4f02-b1ea-4f5faa11197e@googlegroups.com> <o598nh$3ue$1@dont-email.me> <58789578.2159625@news.xs4all.nl> <ln4m12n83v.fsf@kst-u.example.com> |
On 13/01/2017 18:11, Keith Thompson wrote:
> raltbos@xs4all.nl (Richard Bos) writes:
>> Richard Heathfield <rjh@cpax.org.uk> wrote:
>>> On 13/01/17 00:50, Malcolm McLean wrote:
> [...]
>>>> The reasons are firstly to avoid creating unaligned pointers,
>>>
>>> Huh? Consider:
>>>
>>> #include <stdio.h>
>>>
>>> int main(void)
>>> {
>>> const char hw[] = "Hello, World.";
>>> const char *s = hw + 7;
>>> printf("%s\n", s);
>>> return 0;
>>> }
>>>
>>> Would you say that s is "unaligned"? If so, what do you mean by that?
>>
>> I would say the word "unaligned" is badly chosen, but I agree with
>> Malcolm that if you do these things without needing to, you may well
>> start changing s and wondering what happened to hw, or vice versa.
>
> If you do *anything* without needing to, you may run into problems.
>
> Since hw is defined as const, and s is a pointer to const char, there's
> no need to be concerned about accidentally modifying anything.
>
> I think Malcolms's concern is that the base address of the array object
> hw is likely to be on a 4-byte or 8-byte boundary, and the address of
> the character pointed to by s is not. But since s is a byte pointer, it
> is as aligned as it needs to be. Malcolm's concern about "unaligned
> pointers" is unfounded.
I have a library that usually allocates strings starting at a 16-byte
boundary, and usually over-allocates so that the whole string resides in
a block size which is a multiple of 16.
Then many things can be done very efficiently (especially if you also
arrange for spare data past the end of the string is always zeros).
However, that doesn't apply to substrings, which can start at any
byte-offset, and end abruptly at any odd address, so have to be treated
differently, and less efficiently.
I don't think concern about such matters is unfounded.
--
Bartc
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Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-10 15:43 -0800
Re: Correct way of doing string manipulation functions "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-10 19:36 -0500
Re: Correct way of doing string manipulation functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-11 03:41 +0000
Re: Correct way of doing string manipulation functions James Kuyper <jameskuyper@verizon.net> - 2017-01-11 07:19 -0500
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:36 -0800
Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 16:41 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 16:54 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:38 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-11 18:24 -0800
Re: Correct way of doing string manipulation functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-11 03:38 +0000
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 20:02 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 20:28 -0800
Re: Correct way of doing string manipulation functions Ian Collins <ian-news@hotmail.com> - 2017-01-11 18:19 +1300
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-11 02:40 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 20:18 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:37 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-11 18:23 -0800
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-11 01:12 +0000
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-11 11:59 +0000
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:39 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-10 17:55 -0800
Re: Correct way of doing string manipulation functions "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-01-10 18:21 -0800
Re: Correct way of doing string manipulation functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-11 03:21 +0000
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-11 07:33 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-11 07:43 -0800
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-11 15:50 +0000
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-11 08:07 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:46 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 03:04 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 03:37 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 05:47 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 06:14 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 06:34 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 07:38 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-12 07:59 -0800
Re: Correct way of doing string manipulation functions Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-14 22:24 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-15 03:30 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-15 03:52 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-15 04:23 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:42 -0800
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-10 19:19 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:40 -0800
Re: Correct way of doing string manipulation functions Barry Schwarz <schwarzb@dqel.com> - 2017-01-10 20:31 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:45 -0800
Re: Correct way of doing string manipulation functions Gareth Owen <gwowen@gmail.com> - 2017-01-11 17:20 +0000
Re: Correct way of doing string manipulation functions "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-11 12:38 -0500
Strings as first class citizens (Was: Correct way of doing string manipulation functions) gazelle@shell.xmission.com (Kenny McCormack) - 2017-01-11 17:53 +0000
Re: Strings as first class citizens (Was: Correct way of doing string manipulation functions) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-11 12:46 -0800
Re: Strings as first class citizens (Was: Correct way of doing string manipulation functions) fir <profesor.fir@gmail.com> - 2017-01-11 14:40 -0800
Re: Strings as first class citizens (Was: Correct way of doing string manipulation functions) Robert Wessel <robertwessel2@yahoo.com> - 2017-01-11 18:12 -0600
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-11 09:56 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 14:48 -0800
Re: Correct way of doing string manipulation functions Thiago Adams <thiago.adams@gmail.com> - 2017-01-11 12:09 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 15:00 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-11 15:11 -0800
Re: Correct way of doing string manipulation functions "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-11 19:03 -0500
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 02:46 -0800
Re: Correct way of doing string manipulation functions Barry Schwarz <schwarzb@dqel.com> - 2017-01-12 00:08 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 03:02 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 11:38 +0000
Re: Correct way of doing string manipulation functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-12 13:51 +0000
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 14:41 +0000
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 09:32 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-12 18:15 +0000
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-12 11:46 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 13:52 -0800
Re: Correct way of doing string manipulation functions Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-12 16:50 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 00:59 +0000
Re: Correct way of doing string manipulation functions raltbos@xs4all.nl (Richard Bos) - 2017-01-13 08:59 +0000
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 13:07 +0000
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-13 10:11 -0800
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-13 18:49 +0000
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 08:43 -0800
Re: Correct way of doing string manipulation functions Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-13 09:45 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 18:17 +0000
Re: Correct way of doing string manipulation functions Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-13 10:30 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 18:48 +0000
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 11:02 -0800
Re: Correct way of doing string manipulation functions Richard Heathfield <rjh@cpax.org.uk> - 2017-01-13 19:15 +0000
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 12:18 -0800
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-13 12:14 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 12:49 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 13:19 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 10:46 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 11:55 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 10:41 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 10:51 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 12:28 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 13:07 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 13:29 -0800
Re: Correct way of doing string manipulation functions BartC <bc@freeuk.com> - 2017-01-13 21:45 +0000
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 13:59 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 15:08 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-13 14:13 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 13:47 -0800
Re: Correct way of doing string manipulation functions fir <profesor.fir@gmail.com> - 2017-01-13 08:02 -0800
Re: Correct way of doing string manipulation functions supercat@casperkitty.com - 2017-01-12 07:50 -0800
Re: Correct way of doing string manipulation functions Keith Thompson <kst-u@mib.org> - 2017-01-12 08:37 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-12 09:41 -0800
Re: Correct way of doing string manipulation functions Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-13 17:39 -0800
Re: Correct way of doing string manipulation functions "Fernando D. Bozzo" <fdbozzo@gmail.com> - 2017-01-13 18:02 -0800
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