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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) |
| Date | 2012-12-16 14:21 -0800 |
| Organization | None to speak of |
| Message-ID | <lnlicxk590.fsf@nuthaus.mib.org> (permalink) |
| References | (4 earlier) <kaiqj8$3dv$1@dont-email.me> <0.732b2ccaffb639498a0c.20121215221017GMT.87a9tfdl12.fsf@bsb.me.uk> <kaitq5$n2t$1@dont-email.me> <lny5gykhke.fsf@nuthaus.mib.org> <kajsf4$1fn$1@dont-email.me> |
Shao Miller <sha0.miller@gmail.com> writes:
> On 12/15/2012 18:43, Keith Thompson wrote:
>> Shao Miller <sha0.miller@gmail.com> writes:
>>> On 12/15/2012 17:10, Ben Bacarisse wrote:
>>>> Shao Miller <sha0.miller@gmail.com> writes:
[...]
>>>>> It can also be a matter of lifetime (for C >= C99), which could
>>>>> potentially impact memory usage. By using declarations (but not
>>>>> compound literals) in the 'for', such objects needn't've storage for
>>>>> the enclosing block.
>>>>
>>>> That does not match my understanding. Can you provide supporting
>>>> evidence?
>>>>
>>>> Putting a declaration in a for statement (as opposed to just before a
>>>> while) alters the scope the scope of the name but does not, I think,
>>>> have any effect on the lifetime of the declared object.
>>>>
>>>
>>> Sure thing. C99 6.8.5.3p1 with 6.2.4p6.
>>>
>>> Personally, these days I like to declare everything at the top of a
>>> function, so I don't actually take advantage of this, but it might be
>>> worth noting, for C >= C99.
>>
>> 6.8.5.3p1:
>> If *clause-1* is a declaration, the scope of any identifiers
>> it declares is the remainder of the declaration and the entire
>> loop, including the other two expressions
>>
>> 6.2.4p6:
>> For such an object that does not have a variable length array type,
>> its lifetime extends from entry into the block with which it is
>> associated until execution of that block ends in any way.
I was quoting from N1570, the C11 draft; sorry if I didn't make that
clear. The paragraph numbering of section 6.2.4 changed from C99 to
C11. N1570 6.2.4p6 is C99 and N1256 6.2.4p5.
Apart from the renumbering, the paragraph discussing non-VLA objects is
word-for-word identical between C99 and N1256; N1570 adds the phrase "or
compound literal".
The following paragraph, discussing VLA objects (which is *not* what I
was discussing) is word-for-word identical in C99, N1256, and N1570.
> I must _sincerely_ apologize. This must be a circumstance where
> N1256.PDF differs from C99. Please forgive me for referring to the
> wrong point! N1256.PDF's 6.2.4p6:
>
> "For such an object that does have a variable length array type, its
> lifetime extends from the declaration of the object until execution of
> the program leaves the scope of the declaration.27) If the scope is
> entered recursively, a new instance of the object is created each time.
> The initial value of the object is indeterminate."
[...]
> Because VLAs are the predominant feature for C99 from my perspective, I
> realize now that I've actually skipped mentioning them, but they are
> precisely what I'm referring to.
Hmm. I consider VLAs to be just one of a number of features added by
C99, certainly not the predominant one. Until now, I hadn't even
considered them in the context of this discussion.
Perhaps you could briefly restate the point you were making?
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Will write code for food.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Test <test@.nil.invalid.com> - 2012-12-15 15:47 +0200
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-15 14:05 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-15 20:26 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-15 20:47 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Les Cargill <lcargill99@comcast.com> - 2012-12-15 15:34 -0600
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-12-16 03:23 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Shao Miller <sha0.miller@gmail.com> - 2012-12-15 16:37 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-15 22:10 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Shao Miller <sha0.miller@gmail.com> - 2012-12-15 17:32 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Keith Thompson <kst-u@mib.org> - 2012-12-15 15:43 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Shao Miller <sha0.miller@gmail.com> - 2012-12-16 02:15 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Keith Thompson <kst-u@mib.org> - 2012-12-16 14:21 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Shao Miller <sha0.miller@gmail.com> - 2012-12-16 18:34 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-17 01:15 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Keith Thompson <kst-u@mib.org> - 2012-12-17 10:30 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-17 16:07 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-17 08:13 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Keith Thompson <kst-u@mib.org> - 2012-12-17 10:33 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-16 01:24 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Shao Miller <sha0.miller@gmail.com> - 2012-12-16 02:19 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-16 13:11 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Shao Miller <sha0.miller@gmail.com> - 2012-12-16 14:51 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-16 21:16 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-17 00:55 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 15:08 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-20 10:40 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-12-15 22:09 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-12-15 06:11 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Les Cargill <lcargill99@comcast.com> - 2012-12-15 13:26 -0600
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) James Kuyper <jameskuyper@verizon.net> - 2012-12-15 09:24 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Keith Thompson <kst-u@mib.org> - 2012-12-15 12:21 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) James Kuyper <jameskuyper@verizon.net> - 2012-12-15 16:42 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Philip Lantz <prl@canterey.us> - 2012-12-16 00:09 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) James Kuyper <jameskuyper@verizon.net> - 2012-12-16 08:46 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Keith Thompson <kst-u@mib.org> - 2012-12-16 14:29 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-16 10:30 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:42 +0200
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 23:07 +0200
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-17 19:31 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-18 01:32 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-17 20:53 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-18 02:29 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-18 05:48 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-18 11:26 +0000
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-20 16:20 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Keith Thompson <kst-u@mib.org> - 2012-12-18 03:44 -0800
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) James Kuyper <jameskuyper@verizon.net> - 2012-12-17 22:13 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-18 05:40 -0500
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-20 15:14 +0200
Re: comma in a c statement, ie for(i=0,i2=0;i<10;i++,i2) pete <pfiland@mindspring.com> - 2012-12-20 16:31 -0500
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