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From: jcl@lingua.cltr.uq.OZ.AU (Jean-Claude Lacherez)
Newsgroups: comp.lang.c,comp.os.msdos.programmer
Subject: Problem with TURBO C and pointers
Message-ID: <1991Jan9.012509.22427@lingua.cltr.uq.OZ.AU>
Date: 9 Jan 91 01:25:09 GMT
Organization: Centre for Language Teaching and Research, Uni of Queensland, AUSTRALIA.
Lines: 91

Thanks to all those who replied to my question concerning dynamic
dimensioning of arrays.  Unfortunately the problem is not solved:

1/ First there was a confusing typo in my sample code, as follows:

	int	maxrows, maxcols;
	char	**array;

	maxrows = ...whatever...
	maxcols = ...whatever...

	array = (char **) malloc(maxcols * sizeof(char *));

	for(x=0; x < maxrows; x++)
		     ^^^^^^^
			^
			|
		     <This was meant to be maxcols>

		array[x] = (char *) malloc(maxrows);

Sorry about that.  This is not what I have in my original code and
this is not the source of my problem.


2/ A couple of people pointed out that far pointers wrap at 64k, and
suggested that I use huge pointers (at the cost of efficiency).
However, the test program below which dimensions a really tiny array
should not cause wrapping, and still it does not work.


	#include <stdio.h>

	#define	NB_OF_ROWS	5
	#define	ROW_LENGTH	4

	char	*string[] = {"123", "456", "789", "ABC", "DEF"};


	main()
	{
		char	**array;
		int	x, y;
		

		array = (char **) malloc(NB_OF_ROWS * sizeof(char *));
		if (array == NULL){
			puts("Fail 1");
			exit(0);
		}
		else puts("ok ");

		for(x=0; x < NB_OF_ROWS; x++) {
			printf("Making row No %d\n", x);
			array[x] = (char *) malloc(ROW_LENGTH );
			if (array[x] == NULL) {
				puts("Fail 2");
				exit(0);
			}
			strcpy(array[x], string[x]);
			printf("array[%d] as string:  %s\n", x, array[x]);
			printf("By characters: ");
			for(y=0; y < ROW_LENGTH; y++)
				printf("%c ",array[x][y]);
			putchar('\n');
		}
		strcpy(array[0],"abc");
		strcpy(array[1],"def");
		strcpy(array[2],"hij");
		strcpy(array[3],"klm");
		strcpy(array[4],"nop");

		printf ("\nNew values:\nas strings:");
		for(x=0; x<NB_OF_ROWS; x++)
			printf("%s ",array[x]);
		printf("\nas chars:");
		for(x=0; x<NB_OF_ROWS; x++)
			for(y=0; y < ROW_LENGTH; y++)
				printf("%c ",array[x][y]);
	}

So there it is.  Try it: it works on Unix, it works in Turbo C with
the small memory model, it does not work with the large or with
the huge models.

	Jean-Claude Lacherez
	Department of French
	University of Queensland
	QLD, 4072	AUSTRALIA

	jcl@lingua.cltr.uq.oz.au