Re: sizeof(arr[0])

From	Richard Heathfield <rjh@cpax.org.uk>
Newsgroups	comp.lang.c
Subject	Re: sizeof(arr[0])
Date	2015-06-16 20:03 +0100
Organization	go, ion artisan!
Message-ID	<mlprsf$1or$1@dont-email.me> (permalink)
References	(9 earlier) <mln8jp$fof$1@dont-email.me> <ea304b74-27ce-4371-a754-80eac3c02d4d@googlegroups.com> <d880c856-c620-47d3-b70f-c2fbe753c5a3@googlegroups.com> <mlpp02$lgu$1@dont-email.me> <b9739cac-6574-4454-a0a0-012899cbbca9@googlegroups.com>

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On 16/06/15 19:43, Rick C. Hodgin wrote:

<snip>

> The example above explains it all:
>
>      sizeof(*p)->x
>
> A person reading that would cringe (at least they should).

I don't see why. It seems pretty clear to me. p is a pointer to a 
pointer to struct. We want to deref the "outer" pointer to get at the 
inner pointer, deref that using -> to get an object x, and find that 
object's size. That C can say such a complicated thing so easily is a 
good thing. I am not convinced that sizeof((*p)->x) is clearer!

> It's one of
> those C quirks along the lines of *tnX++; where tnX is an int*. :-)

Well, it's certainly true that it is legal, in C, to produce a result 
that you then don't use. This is sometimes useful for the side effects 
(for example, when calling printf, we rarely bother to use the value it 
returns). But in *tnX++; the * is of course without merit.

>
>> The only very minor peculiarity of sizeof is that it
>> accepts a parenthesised type as an operand. But the parentheses /are/
>> the oddity. If you take the size of objects rather than types, the
>> peculiarity almost never appears.
>
> In my code they are not an oddity.  They are the norm.

Since I don't anticipate that either of us is likely to be maintaining 
the other's code any time soon, I don't suppose that's a problem. :-)

> If I ever came
> across a sizeof() without parenthesis, I would quickly fix the bug

And if I ever came across a sizeof /with/ parentheses, I would pause to 
make sure I could safely remove them (which, in almost all cases in my 
own code, I could), and /then/ fix what you would refuse to envisage as 
a bug.

>> There is a case for using parentheses to make the intended
>> operand-operator groupings clearer to the reader where the precedence
>> isn't necessarily one that is widely memorised:
>>
>> w = x << y | z; /* clear */
>> w = (x << y) | z; /* clearER, if the reader's in a hurry */
>
> I disagree that the first one is clear. It requires that someone know
> the order of operations.

That's why the second one is clearER.

> In the second example, a person does not need
> to know the order of operations and will still be able to realize that
> the (x << y) must be computed first, even if they still don't know what
> the << is.

If they don't know what << is, they've got no business editing 
production code. But they can be forgiven for not memorising the 
relative precedence of << and |.

>> But parenthesising operands for the sake of it:
>> ++(i);
>> is just silly.
>
> Agreed.  However, this is always much clearer:
>
>      ((a) ? b : c)

I'd /almost/ agree with you there. I just wouldn't go quite so far as to 
say "always".

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within

Thread

sizeof(arr[0]) kuznecov.alexey@gmail.com - 2015-06-10 12:38 -0700
  Re: sizeof(arr[0]) James Kuyper <jameskuyper@verizon.net> - 2015-06-10 16:00 -0400
    Re: sizeof(arr[0]) kuznecov.alexey@gmail.com - 2015-06-10 14:53 -0700
  Re: sizeof(arr[0]) kuznecov.alexey@gmail.com - 2015-06-10 13:11 -0700
  Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-10 21:21 +0100
    Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-10 22:08 +0100
      Re: sizeof(arr[0]) Andrew Cooper <amc96@cam.ac.uk> - 2015-06-11 00:27 +0100
        Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-11 00:34 +0100
          Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-11 00:38 +0100
          Re: writing code for people who don't know the language (was: sizeof(arr[0])) Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2015-06-10 21:16 -0400
          Re: writing code for people who don't know the language Richard Heathfield <rjh@cpax.org.uk> - 2015-06-11 02:35 +0100
            Re: writing code for people who don't know the language Bartc <bc@freeuk.com> - 2015-06-11 11:16 +0100
          Re: writing code for people who don't know the language Bartc <bc@freeuk.com> - 2015-06-11 11:29 +0100
            Re: writing code for people who don't know the language gazelle@shell.xmission.com (Kenny McCormack) - 2015-06-11 11:43 +0000
          Re: sizeof(arr[0]) Paul N <gw7rib@aol.com> - 2015-06-14 13:13 -0700
            Re: sizeof(arr[0]) Philip Lantz <prl@canterey.us> - 2015-06-14 17:52 -0700
          Re: sizeof(arr[0]) "Bill Cunningham" <nospam@nspam.invalid> - 2015-06-15 14:26 -0400
            Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-15 19:34 +0100
              Re: sizeof(arr[0]) "Bill Cunningham" <nospam@nspam.invalid> - 2015-06-15 14:55 -0400
                Re: sizeof(arr[0]) Melzzzzz <melz@zzzzz.com> - 2015-06-15 20:59 +0200
                Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-15 20:11 +0100
                Re: sizeof(arr[0]) "Bill Cunningham" <nospam@nspam.invalid> - 2015-06-15 15:22 -0400
                Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-16 09:51 -0700
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 10:51 -0700
                Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 19:14 +0100
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 11:43 -0700
                Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 20:03 +0100
                Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-16 19:15 +0100
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 11:34 -0700
                Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-16 20:28 +0100
                Re: sizeof(arr[0]) James Kuyper <jameskuyper@verizon.net> - 2015-06-16 15:42 -0400
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 13:35 -0700
                Re: sizeof(arr[0]) James Kuyper <jameskuyper@verizon.net> - 2015-06-16 16:59 -0400
                Re: sizeof(arr[0]) Dr Nick <nospam-4@temporary-address.org.uk> - 2015-06-16 22:05 +0100
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 14:27 -0700
                Re: sizeof(arr[0]) Dr Nick <nospam-4@temporary-address.org.uk> - 2015-06-17 07:07 +0100
                Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-17 01:22 +0100
                Re: sizeof(arr[0]) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-06-16 19:45 +0000
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 13:03 -0700
                Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-17 10:58 +0100
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 05:58 -0700
                Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-17 15:46 +0100
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 08:14 -0700
                Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-17 17:58 +0100
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 10:07 -0700
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 10:09 -0700
                Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-17 10:46 -0700
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-17 11:13 -0700
                Re: sizeof(arr[0]) Nathan Wagner <nw@hydaspes.if.org> - 2015-06-18 07:14 +0000
                Re: sizeof(arr[0]) David Brown <david.brown@hesbynett.no> - 2015-06-18 09:54 +0200
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-18 05:19 -0700
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-17 10:53 -0700
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 11:17 -0700
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 13:59 -0700
                Re: sizeof(arr[0]) Ian Collins <ian-news@hotmail.com> - 2015-06-18 13:41 +1200
                Re: sizeof(arr[0]) David Brown <david.brown@hesbynett.no> - 2015-06-18 10:04 +0200
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 13:18 -0700
                Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 21:30 +0100
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 13:53 -0700
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 13:43 -0700
                Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 21:52 +0100
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 14:01 -0700
                Re: sizeof(arr[0]) David Brown <david.brown@hesbynett.no> - 2015-06-16 23:49 +0200
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 14:58 -0700
                Re: sizeof(arr[0]) David Brown <david.brown@hesbynett.no> - 2015-06-17 14:10 +0200
                Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-17 13:20 +0100
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 14:16 -0700
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 14:39 -0700
                Re: sizeof(arr[0]) gazelle@shell.xmission.com (Kenny McCormack) - 2015-06-16 18:38 +0000
                Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-16 11:45 -0700
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 13:22 -0700
                Re: sizeof(arr[0]) gazelle@shell.xmission.com (Kenny McCormack) - 2015-06-16 21:25 +0000
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-16 11:05 -0700
                Re: sizeof(arr[0]) James Kuyper <jameskuyper@verizon.net> - 2015-06-16 14:15 -0400
                Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-17 10:07 -0700
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-17 11:16 -0700
                Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-18 10:22 -0700
                Re: sizeof(arr[0]) Keith Thompson <kst-u@mib.org> - 2015-06-18 10:42 -0700
                Re: sizeof(arr[0]) David Kleinecke <dkleinecke@gmail.com> - 2015-06-18 11:41 -0700
                Re: sizeof(arr[0]) Philip Lantz <prl@canterey.us> - 2015-06-16 00:12 -0700
                Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 10:12 +0100
                Re: sizeof(arr[0]) Philip Lantz <prl@canterey.us> - 2015-06-16 09:12 -0700
                Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-16 17:32 +0100
    Re: sizeof(arr[0]) kuznecov.alexey@gmail.com - 2015-06-10 14:56 -0700
      Re: sizeof(arr[0]) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-10 23:53 +0100
      Re: sizeof(arr[0]) Bartc <bc@freeuk.com> - 2015-06-11 00:33 +0100
        Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-11 00:37 +0100
  Re: sizeof(arr[0]) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 06:05 -0700
    [OT] The number 42 (was Re: sizeof(arr[0])) David Brown <david.brown@hesbynett.no> - 2015-06-17 16:07 +0200
      Re: [OT] The number 42 (was Re: sizeof(arr[0])) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-06-17 08:23 -0700
        Re: [OT] The number 42 (was Re: sizeof(arr[0])) David Brown <david.brown@hesbynett.no> - 2015-06-18 10:21 +0200
      Re: [OT] The number 42 (was Re: sizeof(arr[0])) David Kleinecke <dkleinecke@gmail.com> - 2015-06-17 10:35 -0700
        Re: [OT] The number 42 (was Re: sizeof(arr[0])) David Brown <david.brown@hesbynett.no> - 2015-06-18 10:18 +0200
          Re: [OT] The number 42 (was Re: sizeof(arr[0])) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-18 10:08 +0100
    Re: sizeof(arr[0]) Richard Heathfield <rjh@cpax.org.uk> - 2015-06-17 15:13 +0100
      Re: sizeof(arr[0]) raltbos@xs4all.nl (Richard Bos) - 2015-06-18 20:38 +0000

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