Re: [Q] about free(ptr)

From: kj (socyl_at_987jk.com.invalid)
Date: 12/06/04 

Date: Mon, 6 Dec 2004 14:11:10 +0000 (UTC)

In <covorf02cgi@news1.newsguy.com> Chris Torek <nospam@torek.net> writes:
>That dinky little my_free() function was worse than useless...

Too bad! I kinda liked that dinky little my_free(). The reason
is this. Suppose I have defined the following struct as the basic
node in a linked list:

  struct elem {
    void *payload;
    struct elem *next_one;
  };

...and I also have

  struct linked_list {
    struct elem *first;
    struct elem *last;
    struct elem *next;
    int length;
  };

Now I want to define a generic destroy_linked_list function, like this:

  void destroy_linked_list(struct linked_list **ll,
                           void (*destroyer_of_payload)(void **)) {
    (*ll)->next = (*ll)->first;
    while ((*ll)->next) {
      struct elem *hold;

      hold = (*ll)->next;
      (*ll)->next = (*ll)->next->next_one;
      _destroy_element(&hold, destroyer_of_payload);
    }
    free(*ll);
    *ll = NULL;
    return;
  }

  void _destroy_element(struct elem **e,
                        void (*destroyer_of_payload)(void **)) {
    if (destroyer_of_payload)
      (*destroyer_of_payload)(&((*e)->payload));
    free(*e);
    *e = NULL;
    return;
  }

OK, I'm beyond my depth here (which is probably pretty obvious by
now), so I imagine there are already quite a few problems with the
code I've written so far, but what *I* can see as the first problem
with this scheme, in light of Chris's post, is in defining specific
destroyer_of_payload functions, since they must have a void **
argument, but free memory associated with a specific type.

Is there any way to get something like this to work (without
switching to C++ that is)?

TIA,

kj 

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