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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: sizeof(arr[0]) |
| Date | 2015-06-17 11:16 -0700 |
| Organization | None to speak of |
| Message-ID | <lnoakejj3q.fsf@nuthaus.mib.org> (permalink) |
| References | (8 earlier) <mln7ui$c88$1@dont-email.me> <mln8jp$fof$1@dont-email.me> <ea304b74-27ce-4371-a754-80eac3c02d4d@googlegroups.com> <lnh9q7msum.fsf@nuthaus.mib.org> <c48e8391-87dc-414e-ae42-7a531537951b@googlegroups.com> |
David Kleinecke <dkleinecke@gmail.com> writes:
> On Tuesday, June 16, 2015 at 11:05:49 AM UTC-7, Keith Thompson wrote:
>> David Kleinecke <dkleinecke@gmail.com> writes:
>> [...]
>> > One way to think of it is that "sizeof (int)" is the sizeof operator
>> > acting on a type cast and "sizeof x" is the operator acting on a
>> > variable (like "& x") - and to forget that "sizeof (x)" is possible.
>>
>> That is, in my humble opinion, a misleading way to think about it.
>>
>> A cast operator and the sizeof operator applied to a type name
>> both happen to use a similar syntax, a type name in parentheses,
>> but in very different contexts. (Compound literals also use a
>> type name in parentheses, but it's neither preceded by a `sizeof`
>> operator nor followed by an expression.)
>>
>> In `sizeof (int)`, the `(int)` is not a cast operator, any more than
>> the comma in `func(x, y)` is a comma operator or the `*` in `*ptr`
>> is a multiplication operator. C re-uses punctuation characters in
>> diferent contexts, and their meaning is highly context-specific.
>>
>> As for `sizeof x`, that's a `sizeof` operator applied to an
>> *expression* (specifically, the grammar requires a *unary-expression*
>> in that context). In this case, the expression happens to be the
>> name of an object, but for example `sizeof 42` is equally valid.
>> A parenthesized expression is a unary-expression, so `sizeof (x)`
>> is also valid, but personally I prefer to add parentheses only
>> when they're necessary for grouping or when they improve clarity.
>> I probably wouldn't write `sizeof x ++`, but if I felt the need to
>> do so I might write it as `sizeof (x++)` just to make it obvious
>> what the `sizeof` applies to.
>
> Come on - I didn't say sizeof(int) involved a cast. I said think of
> it as a cast - a gimmick to help one remember the syntax.
I didn't say you said it was a cast. I said that thinking of it as a
cast is misleading.
> And it is useful, if I am writing a compliler, to think of the comma
> in f(a,b) as the comma operator and give the comma operator different
> semantics in free-standing expressions versus function arguments. That
> the standard chose not to do that is irrelevant.
Really? I don't see how that would be useful. Most compilers use some
explicit representation of the C grammar. The use of the comma as an
operator and as a separator between function arguments are in different
clauses of that grammar. Or they use recursive descent, in which case
the handling of the different uses of the comma will be handled in
different parts of the parser. How could it be useful to conflate them?
> There are numerous places in C where details can be handled in the
> syntax or the semantics and which way one goes is more a matter of
> taste than anything else.
--
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"
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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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