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From: phil@ux1.cso.uiuc.edu (Phil Howard KA9WGN)
Newsgroups: comp.lang.c
Subject: Re: Deleting linked lists.
Keywords: C,  C++.
Message-ID: <1991Mar27.025307.20808@ux1.cso.uiuc.edu>
Date: 27 Mar 91 02:53:07 GMT
Article-I.D.: ux1.1991Mar27.025307.20808
References: <2636@borg.cs.unc.edu>
Distribution: na
Organization: University of Illinois at Urbana
Lines: 35

warner@weiss.cs.unc.edu (Byron Warner) writes:

>I was wondering, is it safe to unallocate a singly linked list like this:
>
>struct list *head; /* top of list */
>struct list *ptr = head;
>while (ptr){
>	free(ptr);
>	ptr = ptr->next;
>}
>
>I am not sure if I can assume that
>the value of ptr will not be corrupted
>after it is freed.

The value of "ptr" won't be corrupted, but that value is useless after you
have done the "free(ptr)".  What can be corrupted is "ptr->next" since that
memory is now deallocated.  It might appear to work on your system, but it
cannot be trusted and is certainly wrong.

Try this:

struct list *head; /* top of list */
struct list *ptr = head;
while (ptr){
	register struct list *temp_ptr;
	temp_ptr = ptr->next;
	free(ptr);
	ptr = temp_ptr;
}
-- 
 /***************************************************************************\
/ Phil Howard -- KA9WGN -- phil@ux1.cso.uiuc.edu                              \
\ Lietuva laisva -- Brivu Latviju -- Eesti vabaks                             /
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