Re: OT: Possible memory leak in an exercise of a C handbook

From	Franco Martelli <martellif67@gmail.com>
Newsgroups	linux.debian.user
Subject	Re: OT: Possible memory leak in an exercise of a C handbook
Date	2024-12-17 20:50 +0100
Message-ID	<JULJT-hN1-3@gated-at.bofh.it> (permalink)
References	<JUkTn-hz8W-9@gated-at.bofh.it> <JUpq2-1DO-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 16/12/24 at 20:49, Jeffrey Walton wrote:
> Here's the problem:
> 
> void dealloc()
> {
>      for ( const DIGIT *p = first; p->next != NULL; p = p->next )
>          if ( p->prev != NULL )
>              free( p->prev );
>      free( last );
> }
> 
> You seem to be checking backwards (p->prev) but walking the list
> forwards (p = p->next) at the same time.
> 
> Try something like this. It allows you to walk the list forward.
> 
>      void dealloc()
>      {
>          for ( const DIGIT *next, *p = head; p->next != NULL; )
>              if ( p != NULL )
>                  next = p->next, free( p ), p = next;
>          free( last );
>      }
> 
> The use of 'next' stashes away the pointer so you can free 'p' and
> still access the next pointer.

Thanks, your code works, Valgrind says 0 errors and: "All heap blocks 
were freed -- no leaks are possible".
GCC gives me a warning, so I've to remove the "const" modifier in the 
"for loop":

$ gcc -Wall e09-01.c
e09-01.c: In function ‘dealloc’:
e09-01.c:57:47: warning: passing argument 1 of ‘free’ discards ‘const’ 
qualifier from pointer target type [-Wdiscarded-qualifiers]
    57 |                         next = p->next, free( p ), p = next;
       |                                               ^
In file included from e09-01.c:5:
/usr/include/stdlib.h:568:25: note: expected ‘void *’ but argument is of 
type ‘const DIGIT *’ {aka ‘const struct digit *’}
   568 | extern void free (void *__ptr) __THROW;

after done this, all works nicely. Thanks again.

-- 
Franco Martelli

Thread

OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-16 16:10 +0100
  Re: OT: Possible memory leak in an exercise of a C handbook Michael Kjörling <c9bc136c6063@ewoof.net> - 2024-12-16 16:50 +0100
    Re: OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-16 17:30 +0100
      Re: OT: Possible memory leak in an exercise of a C handbook Michael Kjörling <c9bc136c6063@ewoof.net> - 2024-12-16 20:50 +0100
        Re: OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-16 22:00 +0100
  Re: OT: Possible memory leak in an exercise of a C handbook Greg Wooledge <greg@wooledge.org> - 2024-12-16 17:00 +0100
    Re: OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-16 17:40 +0100
      Re: OT: Possible memory leak in an exercise of a C handbook Greg Wooledge <greg@wooledge.org> - 2024-12-16 18:00 +0100
        Re: OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-16 21:20 +0100
  Re: OT: Possible memory leak in an exercise of a C handbook Charles Curley <charlescurley@charlescurley.com> - 2024-12-16 19:40 +0100
  Re: OT: Possible memory leak in an exercise of a C handbook Jeffrey Walton <noloader@gmail.com> - 2024-12-16 21:00 +0100
    Re: OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-16 22:40 +0100
      Re: OT: Possible memory leak in an exercise of a C handbook songbird <songbird@anthive.com> - 2024-12-17 05:00 +0100
      Re: OT: Possible memory leak in an exercise of a C handbook Anssi Saari <anssi.saari@debian-user.mail.kapsi.fi> - 2024-12-17 12:30 +0100
        Re: OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-17 15:30 +0100
          Re: OT: Possible memory leak in an exercise of a C handbook Anssi Saari <anssi.saari@debian-user.mail.kapsi.fi> - 2024-12-18 11:20 +0100
        Re: OT: Possible memory leak in an exercise of a C handbook Jean-François Bachelet <jfbachelet@free.fr> - 2024-12-18 05:50 +0100
    Re: OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-17 20:50 +0100
      Re: OT: Possible memory leak in an exercise of a C handbook Greg Wooledge <greg@wooledge.org> - 2024-12-17 22:20 +0100
        Re: OT: Possible memory leak in an exercise of a C handbook <tomas@tuxteam.de> - 2024-12-18 06:10 +0100
          Re: OT: Possible memory leak in an exercise of a C handbook Kevin Chadwick <m8il1ists@gmail.com> - 2024-12-18 11:50 +0100
            Re: OT: Possible memory leak in an exercise of a C handbook <tomas@tuxteam.de> - 2024-12-18 12:00 +0100
      Re: OT: Possible memory leak in an exercise of a C handbook Jeffrey Walton <noloader@gmail.com> - 2024-12-17 22:20 +0100
        Re: OT: Possible memory leak in an exercise of a C handbook Franco Martelli <martellif67@gmail.com> - 2024-12-18 17:00 +0100
          Re: OT: Possible memory leak in an exercise of a C handbook Jeffrey Walton <noloader@gmail.com> - 2024-12-18 17:20 +0100

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