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From: abowers@gate.net (Al Bowers)
Subject: Re: HELP ! need to insert value in array !!
Date: 1997/07/01
Message-ID: <33b7e507.23664154@news.gate.net>#1/1
X-Deja-AN: 253821648
References: <33A9C27C.22F7@post4.tele.dk> <5oci49$97g@crl.crl.com>
 <866920621snz@genesis.demon.co.uk> <5p0v7l$9uc@nntp.seflin.org>
 <dewar.867554609@merv> <33b64c2f.43589878@nntp.ix.netcom.com>
 <dewar.867589873@merv> <33b67602.54296884@nntp.ix.netcom.com>
Organization: CyberGate, Inc.
Newsgroups: 
 comp.lang.c,comp.lang.c++,comp.os.msdos.programmer,comp.lang.asm.x86,comp.lang.ada
Date: 1997-07-01T00:00:00+00:00
List-Id: <comp.lang.ada>


On Sun, 29 Jun 1997 15:05:28 GMT, miker3@ix.netcom.com (Mike
Rubenstein) wrote:
Referring to C language , I agree with your arguments. However,
the C code you use to reinforce your argument is faulty.

>It's quite easy to detect the difference.  For example,
>
>	#include <stdio.h>
>
>	int main(void)
>	{
>	  int a[2];
>	  unsigned long d = (char*) a[1] - (char*) a[0];
should be:
               unsigned long d = (char *)&a[1] - (char *)&a[0];
or 
               unsigned long d = (char *)(a+1) - (char *)a;
>	  printf ("%lu %lu\n", d, sizeof(int));
               printf("%lu %lu\n",d,(unsigned long)sizeof(int));
>	  return 0;
>	}
>
>This must print the same number twice.
>
>Note also that without this rule there would be no guarantee that code
>like
>
>	#include <stdlib.h>
#include <string.h> /* for memcpy() */
>
>	int a[5] = { 1, 2, 3, 4, 5 };;
                                                  ^^
>	int *b = malloc(5 * sizeof *b);
>	if (b != NULL)
>	  memcpy(b, a, sizeof a);
>
>would work.  It would be extremely difficult for an implementation to
>fake this with non-contiguous arrays since the ultimate type of the
>allocated memory may not be known at the time the malloc() is done.
>
>>From ISO 6.1.2.5:
>
>	An array type describes a contiguously allocated nonempty set 
>	of objects ...

Al Bowers                                
Tampa, FL
mailto:abowers@combase.com
http://www.gate.net/~abowers/index.html