Re: Does ANSI C allow free() to always be empty?

From	glen herrmannsfeldt <gah@ugcs.caltech.edu>
Newsgroups	comp.lang.c
Subject	Re: Does ANSI C allow free() to always be empty?
Date	2014-03-09 09:14 +0000
Organization	Aioe.org NNTP Server
Message-ID	<lfhbdu$jnc$1@speranza.aioe.org> (permalink)
References	<401aa474-05e6-4cf4-a3c2-5e2c2343157e@googlegroups.com>

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partremmaps@gmail.com wrote:
> According to the ANSI C Standard, may free() be an empty function?

> I am not talking about implementations which do not support 
> dynamic memory allocation.

(snip)

> I am talking about implementations and architecture which fully 
> support malloc, calloc, and realloc, and the situation where 
> free() has been passed a valid and current pointer to currently 
> allocated space, having been allocated earlier by a successful 
> call by malloc().

> A couple of people who are in the daily habit of giving C advice 
> on IRC told me that even in these implementations and situations, 
> free() may be an empty function and do nothing and still be 
> standards compliant.

That would be most obvious for a system with garbage collection.

As well as I know it, the standard leaves actual limits on memory
usage system dependent, and if not done carefully might be 
considered a low "quality of implemenation". 

If one isn't careful with garbage collection, for example with
a circular linked list, one might expect it to be released, but
the GC doesn't release it. 

I don't know if there is a C compiler for IBM System/38, but as
I understand it virtual addresses aren't reused. With 64 bit
virtual addresses (and in years past) that was reasonable.
(It might still be that 64 bit virtual is enough.) 

-- glen

Thread

Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-08 22:08 -0800
  Re: Does ANSI C allow free() to always be empty? Kaz Kylheku <kaz@kylheku.com> - 2014-03-09 06:55 +0000
    Re: Does ANSI C allow free() to always be empty? David Brown <david.brown@hesbynett.no> - 2014-03-10 00:47 +0100
      Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-09 22:37 -0700
        Re: Does ANSI C allow free() to always be empty? David Brown <david.brown@hesbynett.no> - 2014-03-10 10:20 +0100
          Re: Does ANSI C allow free() to always be empty? Keith Thompson <kst-u@mib.org> - 2014-03-10 08:52 -0700
          Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-10 20:51 -0700
            Re: Does ANSI C allow free() to always be empty? Robert Wessel <robertwessel2@yahoo.com> - 2014-03-11 01:08 -0500
            Re: Does ANSI C allow free() to always be empty? David Brown <david.brown@hesbynett.no> - 2014-03-11 12:52 +0100
              Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-12 00:09 -0700
                Re: Does ANSI C allow free() to always be empty? David Brown <david.brown@hesbynett.no> - 2014-03-12 12:59 +0100
      Re: Does ANSI C allow free() to always be empty? Kaz Kylheku <kaz@kylheku.com> - 2014-03-10 09:01 +0000
    Re: Does ANSI C allow free() to always be empty? Nick Bowler <nbowler@draconx.ca> - 2014-03-10 15:56 +0000
  Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-09 01:11 -0800
    Re: Does ANSI C allow free() to always be empty? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-09 12:39 +0000
      Re: Does ANSI C allow free() to always be empty? gazelle@shell.xmission.com (Kenny McCormack) - 2014-03-09 13:05 +0000
      Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-09 22:28 -0700
        Re: Does ANSI C allow free() to always be empty? Martin Shobe <martin.shobe@yahoo.com> - 2014-03-10 07:27 -0500
          Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-10 20:55 -0700
            Re: Does ANSI C allow free() to always be empty? Martin Shobe <martin.shobe@yahoo.com> - 2014-03-11 08:19 -0500
              Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-11 23:22 -0700
                Re: Does ANSI C allow free() to always be empty? Martin Shobe <martin.shobe@yahoo.com> - 2014-03-12 08:09 -0500
                Re: Does ANSI C allow free() to always be empty? James Kuyper <jameskuyper@verizon.net> - 2014-03-12 11:29 -0400
      Re: Does ANSI C allow free() to always be empty? Martin Shobe <martin.shobe@yahoo.com> - 2014-03-10 07:29 -0500
  Re: Does ANSI C allow free() to always be empty? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-09 09:14 +0000
    Re: Does ANSI C allow free() to always be empty? Robert Wessel <robertwessel2@yahoo.com> - 2014-03-10 15:33 -0500
  Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-09 23:05 -0700
    Re: Does ANSI C allow free() to always be empty? Martin Shobe <martin.shobe@yahoo.com> - 2014-03-10 07:43 -0500
      Re: Does ANSI C allow free() to always be empty? gordonb.3qcze@burditt.org (Gordon Burditt) - 2014-03-10 12:05 -0500
        Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-10 20:16 -0700
        Re: Does ANSI C allow free() to always be empty? Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 16:27 -0700
      Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-10 21:48 -0700
        Re: Does ANSI C allow free() to always be empty? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-11 05:52 +0000
  Re: Does ANSI C allow free() to always be empty? partremmaps@gmail.com - 2014-03-20 19:14 -0700
    Re: Does ANSI C allow free() to always be empty? Kaz Kylheku <kaz@kylheku.com> - 2014-03-21 03:25 +0000
      Re: Does ANSI C allow free() to always be empty? Richard Damon <Richard@Damon-Family.org> - 2014-03-21 20:58 -0400
        Re: Does ANSI C allow free() to always be empty? Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 16:11 -0700
          Re: Does ANSI C allow free() to always be empty? Richard Damon <Richard@Damon-Family.org> - 2014-03-29 22:27 -0400
            Re: Does ANSI C allow free() to always be empty? Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-30 13:18 -0700
              Re: Does ANSI C allow free() to always be empty? Richard Damon <Richard@Damon-Family.org> - 2014-03-30 20:49 -0400
                Re: Does ANSI C allow free() to always be empty? Tim Rentsch <txr@alumni.caltech.edu> - 2014-04-17 10:52 -0700
            Re: Does ANSI C allow free() to always be empty? James Kuyper <jameskuyper@verizon.net> - 2014-03-31 11:18 -0400
    Re: Does ANSI C allow free() to always be empty? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-21 03:31 +0000
    Re: Does ANSI C allow free() to always be empty? Tim Rentsch <txr@alumni.caltech.edu> - 2014-03-29 15:39 -0700
      Re: Does ANSI C allow free() to always be empty? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-03-30 04:22 +0000

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