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Groups > comp.lang.c++ > #9113
| From | Richard Damon <richard@damon-family.org> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: Length of C++ arrays allocated by operator new[] |
| Date | 2011-08-20 11:39 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <j2okfp$lmp$1@dont-email.me> (permalink) |
| References | <4e4fb013$0$6568$9b4e6d93@newsspool3.arcor-online.net> |
On 8/20/11 9:01 AM, Marcel Müller wrote:
> AFAIK it is impossible to detect the original length of an array from
> the object pointer.
>
> class SomeClass
> { // ...
> };
>
> SomeClass* array = new SomeClass[10];
>
> size_t length = get_length_of_array(array); // Impossible
>
> But the runtime needs to keep track of the number of elements anyway, to
> call the appropriate number of destructors at delete[]. Why does the
> language not allow to access this internal field?
>
>
> Marcel
Because array could also have been set by:
class SomeClass
{ //
};
SomeClass element;
SomeClass* array = &element;
or you could have even changed you example to have been
SomeClass* array = (new SomeClass[10])[4];
In either of these cases there is no "length" to get.
Also, the runtime isn't always required to keep track of how many
elements are in the array, if SomeClass has a trivial destructor (like
all of its members are base types and no explicit destructor is defined)
than by the "as-if" rule, the run time doesn't need to know or store the
number of elements (new probably still needs to somewhere store the
allocation size for delete, but that is a different issue).
Allowing this help minimize the overhead in things like new char[10]
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Length of C++ arrays allocated by operator new[] Marcel Müller <news.5.maazl@spamgourmet.org> - 2011-08-20 15:01 +0200
Re: Length of C++ arrays allocated by operator new[] Richard Damon <richard@damon-family.org> - 2011-08-20 11:39 -0400
Re: Length of C++ arrays allocated by operator new[] Marcel Müller <news.5.maazl@spamgourmet.org> - 2011-08-21 22:15 +0200
Re: Length of C++ arrays allocated by operator new[] Richard Damon <richard@damon-family.org> - 2011-08-22 12:56 -0400
Re: Length of C++ arrays allocated by operator new[] Marcel Müller <news.5.maazl@spamgourmet.com> - 2011-08-22 22:41 +0200
Re: Length of C++ arrays allocated by operator new[] Paul <pchristor@yahoo.co.uk> - 2011-08-20 09:20 -0700
Re: Length of C++ arrays allocated by operator new[] Paul <pchristor@yahoo.co.uk> - 2011-08-20 10:38 -0700
Re: Length of C++ arrays allocated by operator new[] ruben safir <ruben@mrbrklyn.com> - 2011-08-21 22:33 -0400
Re: Length of C++ arrays allocated by operator new[] Paul <pchristor@yahoo.co.uk> - 2011-08-22 03:05 -0700
Re: Length of C++ arrays allocated by operator new[] ruben safir <ruben@mrbrklyn.com> - 2011-08-22 20:05 -0400
Re: Length of C++ arrays allocated by operator new[] Paul <pchristor@yahoo.co.uk> - 2011-08-22 17:20 -0700
Re: Length of C++ arrays allocated by operator new[] Paul Brettschneider <paul.brettschneider@yahoo.fr> - 2011-08-23 08:18 +0200
Re: Length of C++ arrays allocated by operator new[] James Kanze <james.kanze@gmail.com> - 2011-08-26 08:29 -0700
Re: Length of C++ arrays allocated by operator new[] Noah Roberts <roberts.noah@gmail.com> - 2011-08-26 09:06 -0700
Re: Length of C++ arrays allocated by operator new[] Juha Nieminen <nospam@thanks.invalid> - 2011-08-20 17:55 +0000
Re: Length of C++ arrays allocated by operator new[] Paul <pchristor@yahoo.co.uk> - 2011-08-20 10:59 -0700
Re: Length of C++ arrays allocated by operator new[] legalize+jeeves@mail.xmission.com (Richard) - 2011-08-21 03:07 +0000
Re: Length of C++ arrays allocated by operator new[] "A" <a@a.a> - 2011-08-20 18:26 +0200
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-20 17:36 +0100
Re: Length of C++ arrays allocated by operator new[] Marcel Müller <news.5.maazl@spamgourmet.org> - 2011-08-21 22:39 +0200
Re: Length of C++ arrays allocated by operator new[] Ian Collins <ian-news@hotmail.com> - 2011-08-22 09:08 +1200
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-21 22:32 +0100
Re: Length of C++ arrays allocated by operator new[] Marcel Müller <news.5.maazl@spamgourmet.org> - 2011-08-22 00:01 +0200
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 00:04 +0100
Re: Length of C++ arrays allocated by operator new[] Ian Collins <ian-news@hotmail.com> - 2011-08-22 11:38 +1200
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 01:14 +0100
Re: Length of C++ arrays allocated by operator new[] Ian Collins <ian-news@hotmail.com> - 2011-08-22 12:27 +1200
Re: Length of C++ arrays allocated by operator new[] Paul <pchristor@yahoo.co.uk> - 2011-08-21 17:34 -0700
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 01:39 +0100
Re: Length of C++ arrays allocated by operator new[] Paul <pchristor@yahoo.co.uk> - 2011-08-21 18:13 -0700
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 12:16 +0100
Re: Length of C++ arrays allocated by operator new[] Paul <pchristor@yahoo.co.uk> - 2011-08-22 09:09 -0700
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 17:22 +0100
Re: Length of C++ arrays allocated by operator new[] Oliver Jackson <chexmofo@hotmail.com> - 2011-08-22 22:50 -0700
Re: Length of C++ arrays allocated by operator new[] Juha Nieminen <nospam@thanks.invalid> - 2011-08-22 06:10 +0000
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-22 12:20 +0100
Re: Length of C++ arrays allocated by operator new[] Noah Roberts <roberts.noah@gmail.com> - 2011-08-26 09:03 -0700
Re: Length of C++ arrays allocated by operator new[] Nobody <nobody@nowhere.com> - 2011-08-27 02:05 +0100
Re: Length of C++ arrays allocated by operator new[] Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-08-22 02:06 -0700
Re: Length of C++ arrays allocated by operator new[] Juha Nieminen <nospam@thanks.invalid> - 2011-08-22 06:06 +0000
Re: Length of C++ arrays allocated by operator new[] Marcel Müller <news.5.maazl@spamgourmet.com> - 2011-08-22 09:19 +0200
Re: Length of C++ arrays allocated by operator new[] Goran <goran.pusic@gmail.com> - 2011-08-22 04:50 -0700
Re: Length of C++ arrays allocated by operator new[] Juha Nieminen <nospam@thanks.invalid> - 2011-08-22 13:53 +0000
Re: Length of C++ arrays allocated by operator new[] yatremblay@bel1lin202.(none) (Yannick Tremblay) - 2011-08-23 09:40 +0000
Re: Length of C++ arrays allocated by operator new[] Juha Nieminen <nospam@thanks.invalid> - 2011-08-23 10:03 +0000
Re: Length of C++ arrays allocated by operator new[] yatremblay@bel1lin202.(none) (Yannick Tremblay) - 2011-08-22 11:26 +0000
Re: Length of C++ arrays allocated by operator new[] Marcel Müller <news.5.maazl@spamgourmet.com> - 2011-08-22 22:32 +0200
Re: Length of C++ arrays allocated by operator new[] Noah Roberts <roberts.noah@gmail.com> - 2011-08-27 13:30 -0700
Re: Length of C++ arrays allocated by operator new[] Leigh Johnston <leigh@i42.co.uk> - 2011-08-27 22:23 +0100
Re: Length of C++ arrays allocated by operator new[] Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-08-22 02:14 -0700
Re: Length of C++ arrays allocated by operator new[] Gerald Breuer <Gerald.Breuer@Use-Author-Supplied-Address.invalid> - 2011-08-27 22:35 +0200
Re: Length of C++ arrays allocated by operator new[] Noah Roberts <roberts.noah@gmail.com> - 2011-08-27 15:45 -0700
Re: Length of C++ arrays allocated by operator new[] Paavo Helde <myfirstname@osa.pri.ee> - 2011-08-28 02:00 -0500
Re: Length of C++ arrays allocated by operator new[] "Bo Persson" <bop@gmb.dk> - 2011-08-28 16:38 +0200
Re: Length of C++ arrays allocated by operator new[] Gerald Breuer <Gerald.Breuer@Use-Author-Supplied-Address.invalid> - 2011-08-28 16:49 +0200
Re: Length of C++ arrays allocated by operator new[] "Bo Persson" <bop@gmb.dk> - 2011-08-28 22:44 +0200
Re: Length of C++ arrays allocated by operator new[] Gerald Breuer <Gerald.Breuer@Use-Author-Supplied-Address.invalid> - 2011-08-28 23:03 +0200
Re: Length of C++ arrays allocated by operator new[] James Kanze <james.kanze@gmail.com> - 2011-08-29 04:05 -0700
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