Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!saxony!dgil
From: dgil@pa.reuter.COM (Dave Gillett)
Newsgroups: comp.lang.c
Subject: Re: Deleting linked lists.
Keywords: C,  C++.
Message-ID: <846@saxony.pa.reuter.COM>
Date: 1 Apr 91 22:58:53 GMT
References: <2636@borg.cs.unc.edu>
Distribution: na
Organization: Reuter:file Inc  (A Reuter Company) Palo Alto, CA
Lines: 24

In <2636@borg.cs.unc.edu> warner@weiss.cs.unc.edu (Byron Warner) writes:

>struct list *head; /* top of list */
>struct list *ptr = head;
>while (ptr){
>	free(ptr);
>	ptr = ptr->next;
>}

    Even if the value of ptr is not changed by free(), you have absolutely no
guarantee that the value at ptr->next is still valid.  Some implementations of
free() can corrupt data in the freed block; even if this is not true, in some
environments that block might get allocated to somebody else before your
dereference of ptr.  You need another pointer:

struct list *head, *p1;
struct list *ptr = head;
while (ptr){
       p1 = ptr->next;
       free (ptr);
       ptr = p1;
}

                                                 Dave