Skip site navigation (1)Skip section navigation (2) 
Date:      Fri, 07 Nov 2008 22:07:17 +0300
From:      Sergey Matveychuk <sem@FreeBSD.org>
To:        freebsd-hackers@freebsd.org
Subject:   LIST_REMOVE problem
Message-ID:  <491491E5.8090805@FreeBSD.org>
next in thread | raw e-mail | index | archive | help 
Hi!

I wonder how this example from queue(3) works:

      while (!LIST_EMPTY(&head)) {            /* List Deletion. */
              n1 = LIST_FIRST(&head);
              LIST_REMOVE(n1, entries);
              free(n1);
      }

If we'll take a look at code, LIST_REMOVE don't change a head pointer if 
you remove the first element:

#define LIST_FIRST(head)        ((head)->lh_first)
...
#define LIST_REMOVE(elm, field) do {                        \
         if (LIST_NEXT((elm), field) != NULL)                \
                 LIST_NEXT((elm), field)->field.le_prev =    \
                     (elm)->field.le_prev;                   \
         *(elm)->field.le_prev = LIST_NEXT((elm), field);    \
} while (0)

So n1 in the example above will point to removed (and freed) element.

-- 
Dixi.
Sem.

Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?491491E5.8090805>