Re: Two dimensional array Question

On Thu, 8 May 2008 08:16:13 -0700 (PDT), mdh <mdeh@[EMAIL PROTECTED]
> wrote:

>I am still having a problem understanding K&RII on p 112. I have
>looked at the FAQs --which I am sure answer it in a way that I have
>missed, so here goes.
>A 2-dim array, (per K&R) is really a 1-dim array, each of whose
>elements is an array.

The C99 standard uses the term "multidinensional array" so K&R is
slightly out of date in this regard.

>Looking at the debugger I use, arr[2][13] is shown as an initial value
>of "2", but when expanded, there are 2 consecutive arrays of 13
>elements.

What do you mean by "2".  Is it an array of char arrays and the first
of such holds the string '2' '\0'?

>So, may I ask this?
>Is there anything special that marks the end of the first 13 elements
>from the beginning of the 2nd 13 elements? In other words, it seems to

No.  It is prohibited.  arr[1] must immediately follow arr[0] in
memory.

>me that this is nothing more than a 1-dim array, with the information
>about the structure of the array provided by the declaration?
>Hopefully this makes sense.

It is true that the 26 "basic elements" of arr will appear in memory
"linearly".  This has prompted many debates about whether a pointer to
arr[0][0] can be used with subscripts ranging from 0 to 25 to access
all 26.  What is not in dispute is that in a 1d array T x[N], x[0]
evaluates to an element of type T.  In your case, arr[0] evaluates to
an array of T.  To my mind, this is sufficient to say arr cannot be
considered a 1d array.

>
>The exercise associated with this, used the construct
>
> *p = arr[1 or 0 ] to point to either the "first" or "second" row of
>the array. Does the compiler "know" where to point to because it has
>been given this information by the declaration of "13" in arr[2][13].
>Hopefully this makes sense too!

Yes and yes.

>
>
>And lastly, K&R's description of "each of whose elements is an array"
>has never made sense to me. It may be that the answer to the above may
>clarify it.

arr[0] is an array 13 T.  arr[1] is an array of 13 T.  arr[2] does not
exist.  arr[i][j] is an object of type T as long as 0<=i<=1 and
0<=j<=12.  arr[i][j] is an element of arr[i] but not element of arr.
arr[i] is an element of arr and it is an array.


Remove del for email