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From: cs411s03@uhccux.uhcc.hawaii.edu (Cs411s03)
Newsgroups: comp.lang.c
Subject: dynamically allocating array of struct
Keywords: dynamic array struct
Message-ID: <3658@uhccux.uhcc.hawaii.edu>
Date: 5 Apr 89 08:36:06 GMT
Distribution: usa
Organization: University of Hawaii
Lines: 55


I am having difficulty writing a program which dynamically allocates
an array of structs via malloc() and casting. The program seems to
compile OK, but at run time I am addressing the SAME struct over and
over, I want to step thru them with an index. The program goes like
so:

/* malloc struct test */

#include <stdio.h>
#include <malloc.h>

#define NUMRECS 60

struct ttst {
	int num;
};

struct ttst (*tptr)[];

main()
{
	int i, j;

	if ((tptr = (struct ttst (*)[]) \
	malloc(sizeof(struct ttst) * NUMRECS)) == (struct ttst (*)[]) 0) {
		perror("malloc");
		exit(1);
	}

	printf("sizeof = %d\n", sizeof(struct ttst) * NUMRECS);

	for (i = j = 0; i < NUMRECS; i++) {
		tptr[i]->num = ++j;
		printf("Rec: %x %d %d\n", tptr[i], i, tptr[i]->num);
	}

	printf("---------------\n");

	for (i = 0; i < NUMRECS; i++)
		printf("Rec: %x %d %d\n", tptr[i], i, tptr[i]->num);

	free(tptr);
	exit(0);
}

The program will do much more than this once completed, this program
was just to test the basic concept of dynamically allocating the
structures rather than just declaring a fixed length array ...

The first loop looks as if it is working, but the second loop proves it
is not. It seems that the same structure is being written to over and
over. I must be missing something fundamental here ...

cs411s03!uhccux