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| From | Shao Miller <sha0.miller@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Size of an arraylist in bytes |
| Date | 2012-02-02 01:07 -0500 |
| Organization | A noiseless patient Spider |
| Message-ID | <jgd96r$pbr$1@dont-email.me> (permalink) |
| References | <e9dcfb2d-dfef-4ae6-9d9f-979a8f08b962@t36g2000prt.googlegroups.com> <kfnsjivz2sa.fsf@x-alumni2.alumni.caltech.edu> <lnzkd2te2w.fsf@nuthaus.mib.org> <jgct3h$bku$1@dont-email.me> <jgd0s2$mj5$1@reader1.panix.com> |
On 2/1/2012 22:45, Joe keane wrote:
>> Now I have to read it to find out if there've been any changes in
>> regards to bounds-checking.
>>
>> int a[2][2];
>> int * p =&a[0][3];
>>
>
> So far i know
>
> int d(int x)
> {
> int a[4][5];
> int j;
>
> for (j =0< j< 20; j++)
> {
> a[[0][j] = 0;
> }
>
> ..
> }
>
> is legval C, and if it is not please let me know.
Stepping through the critical [corrected] line 'a[0][j] = 0;', we have:
j -> identifier -> primary-expression -> ... -> expression
0 (both instances) -> constant -> primary-expression -> ... -> expression
a -> identifier -> primary-expression -> ... -> expression
a[0] -> postfix-expression -> ... -> expression
a[0][j] -> postfix-expression -> ... -> expression
a[0][j] = 0 -> assignment-expression -> ... -> expression
a[0][j] = 0; -> expression-statement -> statement
#1 'a' is an "lvalue": an expression that designates an object and has
type 'int[4][5]' as per the declaration.
#2 'a' is not the operand of either 'sizeof' nor of '&', so its
evaluation yields an expression with type 'int(*)[5]' and with value
"pointing to the first element of the array."
#3 'E1[E2]' is identical to '(*((E1)+(E2)))', so...
#4 First we add 0 to the pointer we obtained above (#2). That result
will be an expression with the same type and same value as the original
pointer (#2).
#5 Then we apply the unary indirection '*' operator. Since our pointer
(#4) does point to the first element of the array, an object is
designated and the result has type 'int[5]' and is an lvalue designating
that array object.
#6 Meanwhile 'j' has been evaluated and it has yielded a particular
run-time value with type 'int'.
#7 Just before we apply the '[]' operator, the lvalue we obtained (#5)
that has array type is not the operand or either 'sizeof' nor of '&', so
its evaluation yields an expression with type 'int *' and with value
"pointing to the first element of the array."
#8 Then we apply the second '[]' array subscripting operator.
Considering the identity above, again we first have a pointer (#7) and
an 'int' value (#6) being added together. If the
pointed-to/pointed-into array is large enough, the result will point to
an element of the array, or one element past the final element. If the
pointed-to/pointed-into array is not large enough, the behaviour is
undefined. We need to figure out this result before we can proceed with
application of the unary '*' operator (#3).
So is the array large enough for all the values of 'j' you allowed in
your 'for' loop? Your loop body is allowed to have values of 'j' from 0
through 19. How large is the array object? Well, that depends...
Is the array object the 'int[5]'-typed array designated by the lvalue
from #5? If so, then 'j' can run out of bounds.
Is the array object the 'int[4][5]'-typed array designated by the lvalue
from #1? If so, how many 'int'-typed elements are in that array? 0? 20?
Is the array object a region of data storage with contents that can
represent values for 20 contiguous 'int's and so happens to be suitably
aligned for 20 contiguous 'int's?
If the answers for these questions aren't clearly defined, perhaps
implementations will define the answers according to some particular
interpretation, including "bounds-checking" interpretations which define
your 'j' to go out of bounds.
--
"The stationery store has moved. Aaargh!"
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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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