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From: donn@utah-cs.UUCP (Donn Seeley)
Newsgroups: net.lang.c
Subject: Re:  help converting multi-dim arrays
Message-ID: <3286@utah-cs.UUCP>
Date: Sun, 14-Apr-85 02:19:43 EST
Article-I.D.: utah-cs.3286
Posted: Sun Apr 14 02:19:43 1985
Date-Received: Mon, 15-Apr-85 05:51:38 EST
Organization: University of Utah CS Dept
Lines: 34

It's not strictly necessary to have an array of pointers to provide a
multi-dimensional array that varies in size, provided the variation is
limited to one dimension.  The following example shows one way to
dynamically allocate a multi-dimensional array:

------------------------------------------------------------------------
# define	MAXROWS		10000
# define	MAXCOLS		1000

f( nrows )
	int		nrows;
{
	register double	(*dp)[MAXROWS][MAXCOLS];
	char		*malloc();

	dp		= (double (*)[MAXROWS][MAXCOLS])
			  malloc( nrows * MAXCOLS * sizeof (double) );
	if ( dp == NULL )
		bomb( "Out of memory" );
	(*dp)[1][0]	= 1.0;
	...
	free( (char *) dp );
	return;
}
------------------------------------------------------------------------

I believe this is portable code, going on the basis of section 14.3 of
the C reference manual, but I'd be happy to be corrected if wrong.
(Actually, the main reason I like this example is that it provides a
rare instance of a use for one of the more bizarre C type
declarations...)

Donn Seeley    University of Utah CS Dept    donn@utah-cs.arpa
40 46' 6"N 111 50' 34"W    (801) 581-5668    decvax!utah-cs!donn