NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/7252

Text File | 1996-08-05 | 3.2 KB | 79 lines

Path: pegasus.montclair.edu!harmon
From: [e-mail] (Derek Harmon)
Newsgroups: comp.lang.c
Subject: Re: Limit on #bytes inside of struct?
Date: 12 Feb 1996 15:31:18 -0500
Organization: Montclair State University
Message-ID: <[e-mail]>
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** Quoting a message by <[e-mail]> dated <12-Feb-1996>:
> No it isn't, see below.

   Yes it is, see below below.  :)

> >    typedef struct {
> >       int the_array[50000];
> >    } struct_type;
>
> This way, you don't put the 50K numbers in the struct, but only
> a pointer to them. Should be at most 4 bytes.

   First of all, we should agree that there are 50,000 continiguous integers
*SOMEPLACE*.  We can rule out having malloc'd them, so they aren't sitting
on the heap, as they haven't been dynamically allocated.  In fact, this is
a static allocation of an array with a fixed number of elements, determined
at compile-time.

   I believe you've confused the degeneration of an array name, when used
without square brackets, into a pointer during execution; and the declaration
of arrays and pointers.

int *p;   /* This is a pointer to an integer, a pointer's declaration will
           * always feature a asterisk (*). */

int n[10];  /* This is an array declaration, it will always feature square
             * brackets ([]). */
int main(void)
{
 ...
 p++;  /* This is a POINTER, whose address is incremented by sizeof(int) */
 n[1] = *p + 2;  /* This is the VALUE at p being added to 2 and placed
                  * into the second spot of array n. */
 n[1] = n[0] + 2; /* This is the VALUE of n's first spot, plus 2, and
                   * placed into the second spot of array n. */
 p = n; /* This sets p, a POINTER, to n, here having degenerated from an
         * ARRAY into a POINTER. */
 ...
}

   So some observations become clear.  In your data declarations, pointers
always have *'s, arrays always have []'s.  In your program, pointers that
are being "dereferenced," or producing a value to which they point, will
always have *'s, and arrays producing a value of which they hold, will
always have []'s.  Only within your function declarations when an array
name is w/o []'s and a pointer is w/o *'s are they rougly equivalent (and
then, they have nothing to do with ints, chars, or other single variables
which NEVER have *'s or []'s associated with them).

> >       int the_array[50000];
                       ^     ^
                       !     !
   Therefore, these square brackets betray this as an Array Declaration,
not a Pointer Declaration, which would have looked like this,

:         int *the_array;
              ^
              !
  (This shouts POINTER!)

                                                     -- Stone
--
# Derek Harmon (aka Stonelight)    [e-mail]
# - Computer Science Undergrad, Montclair State University, NJ
# - My views are my own, nobody else is this creative.  3;)>
... Santa's elves are just a bunch of subordinate Clauses.