Path: utzoo!utgpu!jarvis.csri.toronto.edu!torsqnt!hybrid!robohack!druid!darcy
From: darcy@druid.uucp (D'Arcy J.M. Cain)
Newsgroups: comp.lang.c
Subject: Re: Malloc in Turbo C
Keywords: Turbo C Malloc
Message-ID: <1990Feb28.155343.3670@druid.uucp>
Date: 28 Feb 90 15:53:43 GMT
References: <26316@qfagus.OZ>
Reply-To: darcy@druid.UUCP (D'Arcy J.M. Cain)
Organization: D'Arcy Cain Consulting, West Hill, Ontario
Lines: 40

In article <26316@qfagus.OZ> gordon@qfagus.OZ (Peter Gordon) writes:
>
>Please tell me I'm doing something stupid.
OK.  You're doing something stupid.  :-)

>#include	<stdio.h>
>#ifdef __TURBOC__
>#include	<alloc.h>
>#else
>#include	<malloc.h>
>#endif
>#include	<stdlib.h>
>main()
>{
>	char **head, **cp;
>	int	i;
>	head = (char **)malloc(200 * sizeof(char **));
>	for(cp = head, i = 0; i < 200; ++i, ++cp)
>	{
>		fprintf(stdout,"Freeing %d\n", i);
>		fflush(stdout);
>		free(cp);
>	}
>}
The first call to free(cp) frees up the entire memory allocated by malloc.
The functions malloc and free don't have any idea what the allocated space
is used for and don't know what size the items are.  The value returned by
malloc is a pointer and the argument to free is a previously returned
pointer.  For 199 times in the above code you are freeing pointers that
haven't been allocated.  in malloc(3C) this is stated to produce undefined
results so you got what was promised.

Also, even given what you were trying to do, didn't you mean 'cp++' in
the for loop statement, not '++cp'?

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