NAME

       SLIST_EMPTY,  SLIST_ENTRY,  SLIST_FIRST,  SLIST_FOREACH,  SLIST_HEAD, SLIST_HEAD_INITIALIZER, SLIST_INIT,
       SLIST_INSERT_AFTER, SLIST_INSERT_HEAD, SLIST_NEXT, SLIST_REMOVE, SLIST_REMOVE_HEAD - implementation of  a
       singly linked list

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/queue.h>

       SLIST_ENTRY(TYPE);

       SLIST_HEAD(HEADNAME, TYPE);
       SLIST_HEAD SLIST_HEAD_INITIALIZER(SLIST_HEAD head);
       void SLIST_INIT(SLIST_HEAD *head);

       int SLIST_EMPTY(SLIST_HEAD *head);

       void SLIST_INSERT_HEAD(SLIST_HEAD *head,
                               struct TYPE *elm, SLIST_ENTRY NAME);
       void SLIST_INSERT_AFTER(struct TYPE *listelm,
                               struct TYPE *elm, SLIST_ENTRY NAME);

       struct TYPE *SLIST_FIRST(SLIST_HEAD *head);
       struct TYPE *SLIST_NEXT(struct TYPE *elm, SLIST_ENTRY NAME);

       SLIST_FOREACH(struct TYPE *var, SLIST_HEAD *head, SLIST_ENTRY NAME);

       void SLIST_REMOVE(SLIST_HEAD *head, struct TYPE *elm,
                               SLIST_ENTRY NAME);
       void SLIST_REMOVE_HEAD(SLIST_HEAD *head,
                               SLIST_ENTRY NAME);

DESCRIPTION

       These macros define and operate on doubly linked lists.

       In the macro definitions, TYPE is the name of a user-defined structure, that must contain a field of type
       SLIST_ENTRY, named NAME.  The argument HEADNAME is the name of a  user-defined  structure  that  must  be
       declared using the macro SLIST_HEAD().

   Creation
       A singly linked list is headed by a structure defined by the SLIST_HEAD() macro.  This structure contains
       a single pointer to the first element on the list.  The elements are singly linked for minimum space  and
       pointer manipulation overhead at the expense of O(n) removal for arbitrary elements.  New elements can be
       added to the list after an existing element or at the head of  the  list.   An  SLIST_HEAD  structure  is
       declared as follows:

           SLIST_HEAD(HEADNAME, TYPE) head;

       where  struct  HEADNAME is the structure to be defined, and struct TYPE is the type of the elements to be
       linked into the list.  A pointer to the head of the list can later be declared as:

           struct HEADNAME *headp;

       (The names head and headp are user selectable.)

       SLIST_ENTRY() declares a structure that connects the elements in the list.

       SLIST_HEAD_INITIALIZER() evaluates to an initializer for the list head.

       SLIST_INIT() initializes the list referenced by head.

       SLIST_EMPTY() evaluates to true if there are no elements in the list.

   Insertion
       SLIST_INSERT_HEAD() inserts the new element elm at the head of the list.

       SLIST_INSERT_AFTER() inserts the new element elm after the element listelm.

   Traversal
       SLIST_FIRST() returns the first element in the list, or NULL if the list is empty.

       SLIST_NEXT() returns the next element in the list.

       SLIST_FOREACH() traverses the list referenced by head in the forward direction, assigning each element in
       turn to var.

   Removal
       SLIST_REMOVE() removes the element elm from the list.

       SLIST_REMOVE_HEAD()  removes the element elm from the head of the list.  For optimum efficiency, elements
       being removed from the head of the  list  should  explicitly  use  this  macro  instead  of  the  generic
       SLIST_REMOVE().

RETURN VALUE

       SLIST_EMPTY() returns nonzero if the list is empty, and zero if the list contains at least one entry.

       SLIST_FIRST(), and SLIST_NEXT() return a pointer to the first or next TYPE structure, respectively.

       SLIST_HEAD_INITIALIZER() returns an initializer that can be assigned to the list head.

STANDARDS

       BSD.

HISTORY

       4.4BSD.

BUGS

       SLIST_FOREACH()  doesn't allow var to be removed or freed within the loop, as it would interfere with the
       traversal.  SLIST_FOREACH_SAFE(), which is present on the BSDs but is not present in  glibc,  fixes  this
       limitation  by  allowing  var  to  safely be removed from the list and freed from within the loop without
       interfering with the traversal.

EXAMPLES

       #include <stddef.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/queue.h>

       struct entry {
           int data;
           SLIST_ENTRY(entry) entries;             /* Singly linked list */
       };

       SLIST_HEAD(slisthead, entry);

       int
       main(void)
       {
           struct entry *n1, *n2, *n3, *np;
           struct slisthead head;                  /* Singly linked list
                                                      head */

           SLIST_INIT(&head);                      /* Initialize the queue */

           n1 = malloc(sizeof(struct entry));      /* Insert at the head */
           SLIST_INSERT_HEAD(&head, n1, entries);

           n2 = malloc(sizeof(struct entry));      /* Insert after */
           SLIST_INSERT_AFTER(n1, n2, entries);

           SLIST_REMOVE(&head, n2, entry, entries);/* Deletion */
           free(n2);

           n3 = SLIST_FIRST(&head);
           SLIST_REMOVE_HEAD(&head, entries);      /* Deletion from the head */
           free(n3);

           for (unsigned int i = 0; i < 5; i++) {
               n1 = malloc(sizeof(struct entry));
               SLIST_INSERT_HEAD(&head, n1, entries);
               n1->data = i;
           }

                                                   /* Forward traversal */
           SLIST_FOREACH(np, &head, entries)
               printf("%i\n", np->data);

           while (!SLIST_EMPTY(&head)) {           /* List deletion */
               n1 = SLIST_FIRST(&head);
               SLIST_REMOVE_HEAD(&head, entries);
               free(n1);
           }
           SLIST_INIT(&head);

           exit(EXIT_SUCCESS);
       }

SEE ALSO

       insque(3), queue(7)