stailq

STAILQ(3)                  Linux Programmer's Manual                 STAILQ(3)

NAME
       STAILQ_CONCAT,  STAILQ_EMPTY,  STAILQ_ENTRY, STAILQ_FIRST, STAILQ_FORE-
       ACH,  STAILQ_HEAD,  STAILQ_HEAD_INITIALIZER,  STAILQ_INIT,   STAILQ_IN-
       SERT_AFTER,    STAILQ_INSERT_HEAD,   STAILQ_INSERT_TAIL,   STAILQ_NEXT,
       STAILQ_REMOVE, STAILQ_REMOVE_HEAD, - implementation of a singly  linked
       tail queue

SYNOPSIS
       #include <sys/queue.h>

       void STAILQ_CONCAT(STAILQ_HEAD *head1, STAILQ_HEAD *head2);

       int STAILQ_EMPTY(STAILQ_HEAD *head);

       STAILQ_ENTRY(TYPE);

       struct TYPE *STAILQ_FIRST(STAILQ_HEAD *head);

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

       STAILQ_HEAD(HEADNAME, TYPE);

       STAILQ_HEAD STAILQ_HEAD_INITIALIZER(STAILQ_HEAD head);

       void STAILQ_INIT(STAILQ_HEAD *head);

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

       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);

       struct TYPE *STAILQ_NEXT(struct TYPE *elm, 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);

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  argu-
       ment  HEADNAME is the name of a user-defined structure that must be de-
       clared using the macro STAILQ_HEAD().

       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  ele-
       ment  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.)

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

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

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

       The  macro  STAILQ_ENTRY()  declares a structure that connects the ele-
       ments in the tail queue.

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

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

       The macro STAILQ_INIT() initializes the tail queue referenced by head.

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

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

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

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

       The macro 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.

       The macro STAILQ_REMOVE() removes the element elm from the tail queue.

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.

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

BUGS
       The  macro  STAILQ_FOREACH()  doesn't  allow var to be removed or freed
       within the loop, as it would interfere with the traversal.   The  macro
       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 (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)

COLOPHON
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GNU                               2020-10-21                         STAILQ(3)