stailq(3) — Linux manual page

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

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

NAME         top

       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

SYNOPSIS         top

       #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         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().

   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         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

       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.

NOTES         top

       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().

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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GNU                            2021-03-22                      STAILQ(3)

Pages that refer to this page: queue(7)