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Groups > comp.lang.c > #163889
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: on understanding & and pointer arithmetic |
| Date | 2021-12-16 22:20 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87fsqsur88.fsf@bsb.me.uk> (permalink) |
| References | <86a6h0eiy9.fsf@levado.to> <spfllt$vkn$1@dont-email.me> <spg7sd$10ue$1@gioia.aioe.org> |
Manfred <noname@add.invalid> writes:
> On 12/16/2021 4:23 PM, David Brown wrote:
>> On 16/12/2021 15:13, Meredith Montgomery wrote:
> [...]
>>
>>> printf("a: %s\n", &a + 3);
>> "a" here is the full array, so "&a" is a pointer to an array of 13 char.
>> Adding 3 gives a new pointer to an array of 13 char, at the address 39
>> bytes higher than address of "a". Basically, you are pretending that
>> there is an array of 4 elements, each of which is itself an array of 13
>> chars - with "a" being the first of those 4 elements. Now you are
>> asking to print the 4th element here, which is just whatever happens to
>> be in the memory at that address.
>>
>
> It might be worth mentioning that accessing memory at that address (&a
> + 3) technically yields undefined behavior, because it is an attempt
> to access a location outside the array (a).
That's a good point to make. It reminds me of a construct that I rather
like:
char buffer[some-complex-size];
char *end_of_buffer = (&buffer)[1];
(&buffer)[1] means *(&buffer + 1). The constructed pointer &buffer + 1
is valid, and the * does not attempt to dereference it as *(&buffer + 1)
is an array-valued expression. It is, instead, converted to a pointer
to the first element of this non-existent array object -- a pointer one
past the end of 'buffer'.
--
Ben.
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on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-16 11:13 -0300
Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-16 14:23 +0000
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-16 11:57 -0300
Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 17:42 +0000
Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-16 18:14 +0000
Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 21:14 +0000
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-16 16:42 -0300
Re: on understanding & and pointer arithmetic Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-16 12:44 -0800
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:06 -0300
Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 21:34 +0000
Re: on understanding & and pointer arithmetic Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-16 14:14 -0800
Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 23:44 +0000
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:09 -0300
Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-16 16:23 +0100
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-16 16:25 -0300
Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-16 21:08 +0100
Re: on understanding & and pointer arithmetic Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-16 12:54 -0800
Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-17 10:53 +0100
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 11:39 -0300
Re: on understanding & and pointer arithmetic scott@slp53.sl.home (Scott Lurndal) - 2021-12-18 16:31 +0000
Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-18 18:56 +0100
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-25 21:29 -0300
Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-18 18:29 +0000
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 11:32 -0300
Re: on understanding & and pointer arithmetic Manfred <noname@add.invalid> - 2021-12-16 21:34 +0100
Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 22:20 +0000
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:02 -0300
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:34 -0300
Re: on understanding & and pointer arithmetic Manfred <noname@add.invalid> - 2021-12-18 18:36 +0100
Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-18 21:17 +0000
Re: on understanding & and pointer arithmetic James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-16 18:59 -0500
Re: on understanding & and pointer arithmetic James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-16 18:38 -0500
Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-16 23:50 +0000
Re: on understanding & and pointer arithmetic "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-12-17 07:34 -0800
Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-17 17:48 +0000
Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 23:56 +0000
Re: on understanding & and pointer arithmetic James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-16 19:06 -0500
Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-17 00:10 +0000
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:32 -0300
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:30 -0300
Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-17 11:08 +0100
Re: on understanding & and pointer arithmetic Manfred <noname@add.invalid> - 2021-12-17 16:24 +0100
Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-17 18:17 +0100
Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:11 -0300
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