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_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         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 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         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

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       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(3)queue(7)