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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | BUGS | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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STAILQ(3) Library Functions Manual STAILQ(3)
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
Standard C library (libc, -lc)
#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.
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.
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.
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().
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.
BSD.
4.4BSD.
#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);
}
insque(3), queue(7)
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Linux man-pages 6.9.1 2024-06-16 STAILQ(3)
Pages that refer to this page: queue(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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