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Re: Remving an element from Queue

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On 05/15/2012 11:38 PM, Barry Schwarz wrote:
> On Tue, 15 May 2012 23:03:39 -0400, James Kuyper
> <jameskuyper@verizon.net> wrote:
...
>> calloc(a,b) must either return a pointer to enough memory to store 'a'
>> objects, each of size 'b' bytes, or a null pointer. If the mathematical
>> product of a*b is greater than SIZE_MAX, then (size_t)(a*b) bytes will
>> not be sufficient to meet that requirement - but the requirement still
>> holds. Therefore, calloc(a,b) must either return a null pointer, or
>> allocate sufficient memory by some mechanism other than malloc(a*b).

...
> array.  size_t must be able to hold the size in bytes of the largest
> possible object, including aggregates such as arrays.

Citation, please?

"sizeof(type)" must yield the size of the specified type, "sizeof
expression" must yield the size of the type of the specified
expression(6.5.3.4p2), and in either case that value must be have the
type size_t (6.5.3.4p5). This does NOT add up to the requirement you state.

Consider an implementation with the following characteristics:
1. It rejects all code that specifies any type with a size greater than
SIZE_MAX, as exceeding that implementation's limits. If it were not
permissible for a conforming implementation to reject such code, every
implementation would be rendered non-conforming by it's inability to
yield the required results for the expression sizeof(char[SIZE_MAX][2]).
2. calloc(a,b) can, at least for some values of a and b, return a
non-null pointer which points at an array of a objects of size b, even
if such an array requires more than SIZE_MAX bytes.

It follows that on such an implementation, it's not possible to write an
expression of the form sizeof(object) that would be required by the
standard to yield the size of the array pointed at by the value returned
by such a call to calloc(). Any such expression would necessarily
require casting that pointer to point at a type with a size larger than
SIZE_MAX, and as such would be rejected by that compiler.

What requirement of the standard would be violated by such an
implementation?

Let me explain that more specifically. If you can declare a pointer p
such that

	p = calloc(a,b);
	size_t size = sizeof(*p);

would violate the requirements of 6.5.3.4 if calloc() returned a
non-null pointer for a*b>SIZE_MAX, then it would ALSO violate those
requirements if calloc() returned a null pointer. That's because the
value of sizeof(*p) depends only upon the type of 'p', not the value of
p. Therefore, you cannot use 6.5.3.4 to derive a requirement that
calloc() return a null pointer.
-- 
James Kuyper

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Thread

Remving an element from Queue arnuld <sunrise@invalid.address> - 2012-05-08 08:09 +0000
  Re: Remving an element from Queue Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-05-08 08:01 -0400
    Re: Remving an element from Queue arnuld <sunrise@invalid.address> - 2012-05-09 05:43 +0000
      Re: Remving an element from Queue Barry Schwarz <schwarzb@dqel.com> - 2012-05-08 23:21 -0700
        Re: Remving an element from Queue arnuld <sunrise@invalid.address> - 2012-05-09 09:27 +0000
          Re: Remving an element from Queue James Kuyper <jameskuyper@verizon.net> - 2012-05-09 07:54 -0400
        Re: Remving an element from Queue arnuld <sunrise@invalid.address> - 2012-05-09 13:18 +0000
          Re: Remving an element from Queue Barry Schwarz <schwarzb@dqel.com> - 2012-05-09 10:59 -0700
            Re: Remving an element from Queue arnuld <arnuld.mizong@gmail.com> - 2012-05-10 05:26 -0700
              Re: Remving an element from Queue nick_keighley_nospam@hotmail.com - 2012-05-11 00:11 -0700
              Re: Remving an element from Queue Barry Schwarz <schwarzb@dqel.com> - 2012-05-14 15:53 -0700
                Re: Remving an element from Queue lawrence.jones@siemens.com - 2012-05-15 17:42 -0400
                Re: Remving an element from Queue Barry Schwarz <schwarzb@dqel.com> - 2012-05-15 16:40 -0700
                Re: Remving an element from Queue James Kuyper <jameskuyper@verizon.net> - 2012-05-15 23:03 -0400
                Re: Remving an element from Queue Barry Schwarz <schwarzb@dqel.com> - 2012-05-15 20:38 -0700
                Re: Remving an element from Queue Jens Gustedt <jens.gustedt@loria.fr> - 2012-05-16 08:09 +0200
                Re: Remving an element from Queue James Kuyper <jameskuyper@verizon.net> - 2012-05-16 07:18 -0400
                Re: Remving an element from Queue Barry Schwarz <schwarzb@dqel.com> - 2012-05-16 16:30 -0700
                Re: Remving an element from Queue James Kuyper <jameskuyper@verizon.net> - 2012-05-17 09:09 -0400
                Re: Remving an element from Queue Barry Schwarz <schwarzb@dqel.com> - 2012-05-17 11:48 -0700
                Re: Removing an element from Queue James Kuyper <jameskuyper@verizon.net> - 2012-05-17 15:38 -0400
                Re: Removing an element from Queue Barry Schwarz <schwarzb@dqel.com> - 2012-05-17 15:21 -0700
                Re: Removing an element from Queue James Kuyper <jameskuyper@verizon.net> - 2012-05-17 19:08 -0400
                Re: Removing an element from Queue Tim Rentsch <txr@alumni.caltech.edu> - 2012-05-19 09:05 -0700
                Re: Removing an element from Queue lawrence.jones@siemens.com - 2012-05-20 15:10 -0400
                Re: Removing an element from Queue Tim Rentsch <txr@alumni.caltech.edu> - 2012-05-21 09:00 -0700
                Re: Remving an element from Queue Tim Rentsch <txr@alumni.caltech.edu> - 2012-05-19 08:49 -0700
                Re: Remving an element from Queue Tim Rentsch <txr@alumni.caltech.edu> - 2012-05-17 12:36 -0700
  Re: Remving an element from Queue nick_keighley_nospam@hotmail.com - 2012-05-08 05:09 -0700
    Re: Remving an element from Queue "BartC" <bc@freeuk.com> - 2012-05-08 14:03 +0100
      Re: Remving an element from Queue nick_keighley_nospam@hotmail.com - 2012-05-09 00:01 -0700
      Re: Remving an element from Queue nick_keighley_nospam@hotmail.com - 2012-05-09 00:03 -0700
        Re: Remving an element from Queue "BartC" <bc@freeuk.com> - 2012-05-09 10:37 +0100
          Re: Remving an element from Queue nick_keighley_nospam@hotmail.com - 2012-05-09 03:05 -0700
    Re: Remving an element from Queue arnuld <sunrise@invalid.address> - 2012-05-09 09:44 +0000
  Re: Remving an element from Queue Mark Bluemel <mark.bluemel@googlemail.com> - 2012-05-08 06:07 -0700
  Re: Remving an element from Queue Mark Bluemel <mark.bluemel@googlemail.com> - 2012-05-08 06:35 -0700
  Re: Remving an element from Queue Johann Klammer <klammerj@NOSPAM.a1.net> - 2012-05-08 20:50 +0200
  Re: Remving an element from Queue 88888 Dihedral <dihedral88888@googlemail.com> - 2012-05-11 00:39 -0700

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