stailq(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | BUGS | EXAMPLES | SEE ALSO | COLOPHON

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

NAME         top

       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

SYNOPSIS         top

       #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         top

       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().

       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.)

       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
       elements 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         top

       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         top

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

BUGS         top

       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         top

       #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         top

       insque(3), queue(7)

COLOPHON         top

       This page is part of release 5.10 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

GNU                            2020-10-21                      STAILQ(3)

Pages that refer to this page: queue(7)