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NAME

       SIMPLEQ_EMPTY,     SIMPLEQ_ENTRY,     SIMPLEQ_FIRST,     SIMPLEQ_FOREACH,    SIMPLEQ_HEAD,
       SIMPLEQ_HEAD_INITIALIZER,   SIMPLEQ_INIT,    SIMPLEQ_INSERT_AFTER,    SIMPLEQ_INSERT_HEAD,
       SIMPLEQ_INSERT_TAIL,  SIMPLEQ_NEXT,  SIMPLEQ_REMOVE,  SIMPLEQ_REMOVE_HEAD,  STAILQ_CONCAT,
       STAILQ_EMPTY,      STAILQ_ENTRY,      STAILQ_FIRST,      STAILQ_FOREACH,      STAILQ_HEAD,
       STAILQ_HEAD_INITIALIZER,     STAILQ_INIT,     STAILQ_INSERT_AFTER,     STAILQ_INSERT_HEAD,
       STAILQ_INSERT_TAIL, STAILQ_NEXT, STAILQ_REMOVE, STAILQ_REMOVE_HEAD, - implementation of  a
       singly linked tail queue

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/queue.h>

       STAILQ_ENTRY(TYPE);

       STAILQ_HEAD(HEADNAME, TYPE);
       STAILQ_HEAD STAILQ_HEAD_INITIALIZER(STAILQ_HEAD head);
       void STAILQ_INIT(STAILQ_HEAD *head);

       int STAILQ_EMPTY(STAILQ_HEAD *head);

       void STAILQ_INSERT_HEAD(STAILQ_HEAD *head,
                                struct TYPE *elm, STAILQ_ENTRY NAME);
       void STAILQ_INSERT_TAIL(STAILQ_HEAD *head,
                                struct TYPE *elm, STAILQ_ENTRY NAME);
       void STAILQ_INSERT_AFTER(STAILQ_HEAD *head, struct TYPE *listelm,
                                struct TYPE *elm, STAILQ_ENTRY NAME);

       struct TYPE *STAILQ_FIRST(STAILQ_HEAD *head);
       struct TYPE *STAILQ_NEXT(struct TYPE *elm, STAILQ_ENTRY NAME);

       STAILQ_FOREACH(struct TYPE *var, STAILQ_HEAD *head, STAILQ_ENTRY NAME);

       void STAILQ_REMOVE(STAILQ_HEAD *head, struct TYPE *elm, TYPE,
                                STAILQ_ENTRY NAME);
       void STAILQ_REMOVE_HEAD(STAILQ_HEAD *head,
                                STAILQ_ENTRY NAME);

       void STAILQ_CONCAT(STAILQ_HEAD *head1, STAILQ_HEAD *head2);
       Note: Identical macros prefixed with SIMPLEQ instead of STAILQ exist; see NOTES.

DESCRIPTION

       These macros define and operate on singly linked tail queues.

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

   Creation
       A  singly  linked  tail queue is headed by a structure defined by the STAILQ_HEAD() macro.
       This structure contains a pair of pointers, one to the first element in the tail queue and
       the  other  to  the  last  element  in the tail queue.  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 tail queue after an existing
       element, at the head of the tail queue, or at the end of the tail  queue.   A  STAILQ_HEAD
       structure is declared as follows:

           STAILQ_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 tail queue.  A pointer to the head of the  tail  queue  can
       later be declared as:

           struct HEADNAME *headp;

       (The names head and headp are user selectable.)

       STAILQ_ENTRY() declares a structure that connects the elements in the tail queue.

       STAILQ_HEAD_INITIALIZER() evaluates to an initializer for the tail queue head.

       STAILQ_INIT() initializes the tail queue referenced by head.

       STAILQ_EMPTY() evaluates to true if there are no items on the tail queue.

   Insertion
       STAILQ_INSERT_HEAD() inserts the new element elm at the head of the tail queue.

       STAILQ_INSERT_TAIL() inserts the new element elm at the end of the tail queue.

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

   Traversal
       STAILQ_FIRST()  returns  the  first  item  on  the tail queue or NULL if the tail queue is
       empty.

       STAILQ_NEXT() returns the next item on the tail queue, or NULL this item is the last.

       STAILQ_FOREACH() traverses the tail queue referenced by head  in  the  forward  direction,
       assigning each element in turn to var.

   Removal
       STAILQ_REMOVE() removes the element elm from the tail queue.

       STAILQ_REMOVE_HEAD()  removes  the  element  at  the  head of the tail queue.  For optimum
       efficiency, elements being removed from the head of the tail queue should use  this  macro
       explicitly rather than the generic STAILQ_REMOVE() macro.

   Other features
       STAILQ_CONCAT() concatenates the tail queue headed by head2 onto the end of the one headed
       by head1 removing all entries from the former.

RETURN VALUE

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

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

       STAILQ_HEAD_INITIALIZER() returns an initializer that can be assigned to the queue head.

STANDARDS

       Not in POSIX.1, POSIX.1-2001, or POSIX.1-2008.  Present on the BSDs (STAILQ  macros  first
       appeared in 4.4BSD).

NOTES

       Some  BSDs  provide  SIMPLEQ  instead  of  STAILQ.  They are identical, but for historical
       reasons they were named differently on different BSDs.  STAILQ originated on FreeBSD,  and
       SIMPLEQ  originated  on NetBSD.  For compatibility reasons, some systems provide both sets
       of macros.  glibc provides both STAILQ and SIMPLEQ,  which  are  identical  except  for  a
       missing SIMPLEQ equivalent to STAILQ_CONCAT().

BUGS

       STAILQ_FOREACH()  doesn't  allow  var  to be removed or freed within the loop, as it would
       interfere with the traversal.  STAILQ_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;
           STAILQ_ENTRY(entry) entries;        /* Singly linked tail queue */
       };

       STAILQ_HEAD(stailhead, entry);

       int
       main(void)
       {
           struct entry *n1, *n2, *n3, *np;
           struct stailhead head;                  /* Singly linked tail queue
                                                      head */

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

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

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

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

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

           n3 = STAILQ_FIRST(&head);
           STAILQ_REMOVE_HEAD(&head, entries);     /* Deletion from the head */
           free(n3);

           n1 = STAILQ_FIRST(&head);
           n1->data = 0;
           for (unsigned int i = 1; i < 5; i++) {
               n1 = malloc(sizeof(struct entry));
               STAILQ_INSERT_HEAD(&head, n1, entries);
               n1->data = i;
           }
                                                   /* Forward traversal */
           STAILQ_FOREACH(np, &head, entries)
               printf("%i\n", np->data);
                                                   /* TailQ deletion */
           n1 = STAILQ_FIRST(&head);
           while (n1 != NULL) {
               n2 = STAILQ_NEXT(n1, entries);
               free(n1);
               n1 = n2;
           }
           STAILQ_INIT(&head);

           exit(EXIT_SUCCESS);
       }

SEE ALSO

       insque(3), queue(7)