STAILQ(3) Library Functions Manual STAILQ(3)
NAME
SIMPLEQ_EMPTY, SIMPLEQ_ENTRY, SIMPLEQ_FIRST, SIMPLEQ_FOREACH, SIM-
PLEQ_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_IN-
SERT_TAIL, STAILQ_NEXT, STAILQ_REMOVE, STAILQ_REMOVE_HEAD, - implementa-
tion 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 VERSIONS.
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().
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 arbi-
trary 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 lis-
telm.
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 for-
ward 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.
VERSIONS
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 miss-
ing 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.
STANDARDS
BSD.
HISTORY
4.4BSD.
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)
Linux man-pages 6.9.1 2024-06-16 STAILQ(3)
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