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| From | Shao Miller <sha0.miller@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Size of an arraylist in bytes |
| Date | 2012-02-06 00:01 -0500 |
| Organization | A noiseless patient Spider |
| Message-ID | <jgnmqa$8lv$1@dont-email.me> (permalink) |
| References | (13 earlier) <ln8vkv5yiz.fsf@nuthaus.mib.org> <kfnsjivz2sa.fsf@x-alumni2.alumni.caltech.edu> <lnzkd2te2w.fsf@nuthaus.mib.org> <eketv8-fdf.ln1@jones.homeip.net> <20120203135041.829@kylheku.com> |
On 2/3/2012 17:35, Kaz Kylheku wrote:
> On 2012-02-03, lawrence.jones@siemens.com<lawrence.jones@siemens.com> wrote:
>> Keith Thompson<kst-u@mib.org> wrote:
>>>
>>> (An aside: I've complained before that the C90 and C99 standards'
>>> definitions of "lvalue" were flawed, and suggested "expression that
>>> potentially designates an object" to fix the problem. The word
>>> "potentially" is needed to ensure that *ptr is an lvalue even if
>>> ptr==NULL. I just now noticed that N1570 has this updated wording.
>>> Looks like somebody was listening. I am inordinately pleased.)
>>
>> You're welcome. :-)
>
> A very simple, define an lvalue is as an expression which satisfies these three
> conditions:
>
> - [lvalue syntactic form] An lvalue is either a certain kind of primary
> expression, (identifier or string literal) or its operator falls into a
> certain set:
> - struct/union member selection (. operator) applied to an expression which
> itself has lvalue syntactic form).
> - pointer member selection (-> operator)
> - pointer dereference or array indexing
> If E has the syntactic form of an lvalue, then so does (E) and
> denotes the same lvalue as E.
>
Huh?
'.' and '->' and '[]' have two operands. When you say "its operator,"
do you really mean when it's either the left or right operand of these?
The first point appears to be circular: An expression is an lvalue if it
is an operand to the '.' operator and that operator's operand (which
one?) is an lvalue; one operand of the '.' operator we are trying to
figure out right now whether or not it is an lvalue.
> - [lvalue context] An lvalue is the argument of certain operators in certain
> positions (those which require lvalues):
> - destination operand of assignment
> - operand of& address-of
> - operand of increment
> - ... etc
> Expressions not in these contexts are not lvalues even if they have
> lvalue syntactic form.
>
> - [lvalue type] An lvalue has object type.
>
An "lvalue," what the "lvalue" means, and what the type of the "lvalue" is:
http://en.wikipedia.org/wiki/Haddocks%27_Eyes#Naming
> Further, lvalues are then classified as modifiable if they are not array types,
> and not const-qualified, and do not have any member which is const-qualified,
> (if they are struct or unions).
>
> That's it. These rules should cover everything. There is no need to mention
> anything about lvalues anywhere else, except to state that an lvalue (or
> perhaps a modifiable one) is required.
>
What about compound literals?
> And note how it is not necessary to inherit the lvalue attribute semantically.
> According to standard C, f().d cannot be an lvalue because the struct returned
> by f() is not an lvalue, and x.y is only an lvalue if x is. According to the
> above rules, however, f().d is not an lvalue simply because, although it is
> a member selection, the base expression f() lacks lvalue syntactic form.
> (If you can determine an attribute purely from syntax, there is no need
> to compute it inheritance of abstract attributes!)
>
If I understand the syntactic form you've given above, then given:
enum foo { bar };
'foo' is syntactically an lvalue and 'foo.blecch' is syntactically an
lvalue and 'bar' is syntactically an lvalue and 'bar.blecch' is
syntactically an lvalue?
And for the '->' operator, the '42' in '42->blecch' is syntactically an
lvalue? Its operator is '->'. Then I guess '42->blecch' is an lvalue, too.
Then to establish context:
- The 'foo' in '&foo' is contextually and syntactically an lvalue
- The 'foo.blecch' in '&foo.blecch' is contextually and syntactically an
lvalue
- The 'bar' in '&bar' is contextually and syntactically an lvalue
- The 'bar.blecch' in '&bar.blecch' is contextually and syntactically an
lvalue
- The '42->blecch' in '&42->blecch' is contextually and syntactically an
lvalue
But then when it boils down to "type," these identifiers cannot be said
to have an object type, so they are not lvalues, right? Interesting...
So what if we have:
enum foo { bar };
char foo;
Now when we are considering '&foo', it's contextually and syntactically
an lvalue, but for the type consideration, are we considering the 'enum'
type or the 'char' object?
> [...]
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Re: Size of an arraylist in bytes Joe Wright <joewwright@comcast.net> - 2011-11-21 16:25 -0500
Re: Size of an arraylist in bytes Keith Thompson <kst-u@mib.org> - 2011-11-21 14:03 -0800
Re: Size of an arraylist in bytes pete <pfiland@mindspring.com> - 2011-11-21 17:45 -0500
Re: Size of an arraylist in bytes Ark <akhasin@macroexpressions.com> - 2011-11-21 21:19 -0500
Re: Size of an arraylist in bytes Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-21 22:06 -0500
Re: Size of an arraylist in bytes Ark <akhasin@macroexpressions.com> - 2011-11-22 03:07 -0500
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2011-11-22 06:51 -0500
Re: an instance of an object (was: Size of an arraylist in bytes) Keith Thompson <kst-u@mib.org> - 2011-11-21 21:54 -0800
Re: Size of an arraylist in bytes pete <pfiland@mindspring.com> - 2011-11-22 01:49 -0500
Re: Size of an arraylist in bytes Ark <akhasin@macroexpressions.com> - 2011-11-22 03:17 -0500
Re: Size of an arraylist in bytes Keith Thompson <kst-u@mib.org> - 2011-11-22 00:48 -0800
Re: Size of an arraylist in bytes pete <pfiland@mindspring.com> - 2011-11-23 05:16 -0500
Re: Size of an arraylist in bytes Kaz Kylheku <kaz@kylheku.com> - 2011-11-22 16:49 +0000
Re: Size of an arraylist in bytes pete <pfiland@mindspring.com> - 2011-11-23 09:30 -0500
Re: Size of an arraylist in bytes Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-22 00:07 -0800
Re: Size of an arraylist in bytes Keith Thompson <kst-u@mib.org> - 2011-11-22 00:24 -0800
Re: Size of an arraylist in bytes Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 05:06 -0800
Re: Size of an arraylist in bytes Keith Thompson <kst-u@mib.org> - 2012-01-25 12:15 -0800
Re: Size of an arraylist in bytes Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-31 18:49 -0800
Re: Size of an arraylist in bytes Keith Thompson <kst-u@mib.org> - 2012-02-01 13:53 -0800
Re: Size of an arraylist in bytes lawrence.jones@siemens.com - 2012-02-01 18:53 -0500
Re: Size of an arraylist in bytes Keith Thompson <kst-u@mib.org> - 2012-02-01 20:06 -0800
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-01 21:40 -0500
Re: Size of an arraylist in bytes jgk@panix.com (Joe keane) - 2012-02-02 03:45 +0000
Re: Size of an arraylist in bytes Keith Thompson <kst-u@mib.org> - 2012-02-01 20:14 -0800
Re: Size of an arraylist in bytes Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-01 23:14 -0500
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-02 18:38 -0500
Re: Size of an arraylist in bytes jgk@panix.com (Joe keane) - 2012-02-03 16:32 +0000
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-03 11:57 -0500
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-03 20:07 -0500
Re: Size of an arraylist in bytes jgk@panix.com (Joe keane) - 2012-02-04 22:35 +0000
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-04 18:43 -0500
Re: Size of an arraylist in bytes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-05 01:50 +0000
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-04 21:37 -0500
Re: Size of an arraylist in bytes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-05 14:48 +0000
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-05 10:20 -0500
Re: Size of an arraylist in bytes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-05 16:25 +0000
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-05 12:06 -0500
Re: Size of an arraylist in bytes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-05 19:21 +0000
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-05 15:29 -0500
Re: Size of an arraylist in bytes Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-08 10:46 -0800
Re: Size of an arraylist in bytes Kaz Kylheku <kaz@kylheku.com> - 2012-02-05 02:39 +0000
Re: Size of an arraylist in bytes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-05 15:17 +0000
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-05 12:06 -0500
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-05 15:06 -0500
Re: Size of an arraylist in bytes jgk@panix.com (Joe keane) - 2012-02-07 17:35 +0000
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-07 19:51 -0500
Re: Size of an arraylist in bytes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-08 01:14 +0000
Re: Size of an arraylist in bytes Kaz Kylheku <kaz@kylheku.com> - 2012-02-05 02:31 +0000
Re: Size of an arraylist in bytes Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-03 21:26 -0500
Re: Size of an arraylist in bytes Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-03 21:31 -0500
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-04 06:57 -0500
Re: Size of an arraylist in bytes Kaz Kylheku <kaz@kylheku.com> - 2012-02-04 18:32 +0000
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-05 22:51 -0500
Re: Size of an arraylist in bytes jgk@panix.com (Joe keane) - 2012-02-04 21:25 +0000
Re: Size of an arraylist in bytes Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-04 17:08 -0500
Re: Size of an arraylist in bytes Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-08 10:52 -0800
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-04 17:32 -0500
Re: Size of an arraylist in bytes Kaz Kylheku <kaz@kylheku.com> - 2012-02-05 02:19 +0000
Re: Size of an arraylist in bytes Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-05 09:20 -0500
Re: Size of an arraylist in bytes James Kuyper <jameskuyper@verizon.net> - 2012-02-05 09:42 -0500
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-05 16:17 -0500
Re: Size of an arraylist in bytes Zoltan Kocsi <zoltan@bendor.com.au> - 2012-02-05 17:49 +1100
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-05 16:48 -0500
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-05 16:52 -0500
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-02 01:07 -0500
Re: Size of an arraylist in bytes lawrence.jones@siemens.com - 2012-02-03 11:29 -0500
Re: Size of an arraylist in bytes Keith Thompson <kst-u@mib.org> - 2012-02-03 12:42 -0800
lvalue "potentially" designates an object (was Re: Size of an arraylist in bytes) Kenneth Brody <kenbrody@spamcop.net> - 2012-02-04 12:47 -0500
Re: lvalue "potentially" designates an object (was Re: Size of an arraylist in bytes) Kaz Kylheku <kaz@kylheku.com> - 2012-02-04 18:39 +0000
Re: Size of an arraylist in bytes lawrence.jones@siemens.com - 2012-02-04 14:46 -0500
Re: Size of an arraylist in bytes Kaz Kylheku <kaz@kylheku.com> - 2012-02-03 22:35 +0000
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-06 00:01 -0500
Re: Size of an arraylist in bytes Kaz Kylheku <kaz@kylheku.com> - 2012-02-06 08:46 +0000
Re: Size of an arraylist in bytes Shao Miller <sha0.miller@gmail.com> - 2012-02-06 23:17 -0500
Re: Size of an arraylist in bytes lawrence.jones@siemens.com - 2012-02-01 18:34 -0500
Re: Size of an arraylist in bytes Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-08 10:54 -0800
Re: Size of an arraylist in bytes Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 05:00 -0800
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