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From: hp@vmars.tuwien.ac.at (Peter Holzer)
Newsgroups: comp.lang.c
Subject: Re: prototyping (oh no! not again??)
Message-ID: <2182@tuvie.UUCP>
Date: 27 Nov 90 14:32:36 GMT
References: <DAVIS.90Nov26144044@pacific.mps.ohio-state.edu> <1990Nov27.001813.9244@ux1.cso.uiuc.edu>
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gordon@osiris.cso.uiuc.edu (John Gordon) writes:


>	Given that you are passing an n-dimensional array to a function, you
>*MUST* explicitly provide at least n-1 of the dimensions in the argument
>declaration.

>	For example:

>		if my_array is a 4-dimensional array, you *must* explicitly
>provide at least 3 of the dimensions when you pass my_array to a function.

>	main()
>	{
>	  int my_array[6][5][4][3];
>	  .
>	  .
>	  .
>	}


>	function_one(int array[6][5][4][])
>	{
>	  .
>	  .
>	  .
>	}

>	Note: There is a rule that governs which dimension may be left out; I
>think it is one of the end ones, but I am not sure which one.

You may leave out the first dimension.
my_array is an array of six elements of type int [5][4][3], and
is treated in expressions like a pointer to an int [5][4][3]. 
Thus function_one wants a pointer to int [5][4][3]. Thus it
should be declared as function_one (int (* array)[5][4][3]).
The form function_one(int array [][5][4][3]) is equivalent, but
it looks as if array were an array, which it is not, so I
recommend the first form.

To answer the original posters question: The best method
(compromise between speed/portability/readability) is to set up
an array of pointers (to pointers ...) to items. You can then
create arrays of arbitrary shape and size at runtime. E.g.

#define N 20
#define M 30

main ()
{
	int	** p;
	int	i;

	if ((p = malloc (N * sizeof (* p))) == NULL) error ();
	for (i = 0; i < N; i ++) {
		if ((p[i] = malloc (M * sizeof (** p))) == NULL) error ();
	}
	function_one (p);
}

function_one (int ** array)
{
	for (i = 0; i < N; i ++){
		for (j = 0; j < M; j ++) {
			/* do something with */ array [i][j];
		}
	}
}

Isn't that in the FAQ list?????

It should be there, because it is asked very often.
--
|    _  | Peter J. Holzer                       | Think of it   |
| |_|_) | Technical University Vienna           | as evolution  |
| | |   | Dept. for Real-Time Systems           | in action!    |
| __/   | hp@vmars.tuwien.ac.at                 |     Tony Rand |