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From: resnicks@netcom.UUCP (Steve Resnick)
Newsgroups: comp.os.msdos.programmer
Subject: Re: free() question
Message-ID: <21715@netcom.UUCP>
Date: 23 Jan 91 07:16:53 GMT
References: <8822@star.cs.vu.nl>
Organization: Netcom- The Bay Area's Public Access Unix System {408 241-9760 guest}
Lines: 31

In article <8822@star.cs.vu.nl> tamboer@cs.vu.nl (Tamboer Erik) writes:
>A question about the free() function in C. I'm posting it here because I
>thought I might reach a few C programmers here ;-)
>
>Is it safe to free() a block of memory that has already been free()d?
>I have a program that malloc()s trees of structs that may or may not be
>free()d at some later point. Upon termination, it is important that they
>are all released from memory. Is it safe to just free all trees, including
>those that have already been freed, or do I have to resort to something
>like changing every occurence of free() in the program by { free(tree);
>tree = NULL } ? (as free(NULL) is supposed to be harmless).
>
>This is to be a portable program, so it must work with most implementations
>of free(), compiler-independent.

This is a frequently asked question in comp.lang.c, and really belongs there.

No, it's not adviseable to free a block of memory which hasn't been
malloced. If it's been free()'d, then it's not longer malloced.


Hope this helps...
Steve

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