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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | STANDARDS | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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CIRCLEQ(3) Library Functions Manual CIRCLEQ(3)
CIRCLEQ_EMPTY, CIRCLEQ_ENTRY, CIRCLEQ_FIRST, CIRCLEQ_FOREACH,
CIRCLEQ_FOREACH_REVERSE, CIRCLEQ_HEAD, CIRCLEQ_HEAD_INITIALIZER,
CIRCLEQ_INIT, CIRCLEQ_INSERT_AFTER, CIRCLEQ_INSERT_BEFORE,
CIRCLEQ_INSERT_HEAD, CIRCLEQ_INSERT_TAIL, CIRCLEQ_LAST,
CIRCLEQ_LOOP_NEXT, CIRCLEQ_LOOP_PREV, CIRCLEQ_NEXT, CIRCLEQ_PREV,
CIRCLEQ_REMOVE - implementation of a doubly linked circular queue
Standard C library (libc, -lc)
#include <sys/queue.h>
CIRCLEQ_ENTRY(TYPE);
CIRCLEQ_HEAD(HEADNAME, TYPE);
CIRCLEQ_HEAD CIRCLEQ_HEAD_INITIALIZER(CIRCLEQ_HEAD head);
void CIRCLEQ_INIT(CIRCLEQ_HEAD *head);
int CIRCLEQ_EMPTY(CIRCLEQ_HEAD *head);
void CIRCLEQ_INSERT_HEAD(CIRCLEQ_HEAD *head,
struct TYPE *elm, CIRCLEQ_ENTRY NAME);
void CIRCLEQ_INSERT_TAIL(CIRCLEQ_HEAD *head,
struct TYPE *elm, CIRCLEQ_ENTRY NAME);
void CIRCLEQ_INSERT_BEFORE(CIRCLEQ_HEAD *head, struct TYPE *listelm,
struct TYPE *elm, CIRCLEQ_ENTRY NAME);
void CIRCLEQ_INSERT_AFTER(CIRCLEQ_HEAD *head, struct TYPE *listelm,
struct TYPE *elm, CIRCLEQ_ENTRY NAME);
struct TYPE *CIRCLEQ_FIRST(CIRCLEQ_HEAD *head);
struct TYPE *CIRCLEQ_LAST(CIRCLEQ_HEAD *head);
struct TYPE *CIRCLEQ_PREV(struct TYPE *elm, CIRCLEQ_ENTRY NAME);
struct TYPE *CIRCLEQ_NEXT(struct TYPE *elm, CIRCLEQ_ENTRY NAME);
struct TYPE *CIRCLEQ_LOOP_PREV(CIRCLEQ_HEAD *head,
struct TYPE *elm, CIRCLEQ_ENTRY NAME);
struct TYPE *CIRCLEQ_LOOP_NEXT(CIRCLEQ_HEAD *head,
struct TYPE *elm, CIRCLEQ_ENTRY NAME);
CIRCLEQ_FOREACH(struct TYPE *var, CIRCLEQ_HEAD *head,
CIRCLEQ_ENTRY NAME);
CIRCLEQ_FOREACH_REVERSE(struct TYPE *var, CIRCLEQ_HEAD *head,
CIRCLEQ_ENTRY NAME);
void CIRCLEQ_REMOVE(CIRCLEQ_HEAD *head, struct TYPE *elm,
CIRCLEQ_ENTRY NAME);
These macros define and operate on doubly linked circular queues.
In the macro definitions, TYPE is the name of a user-defined
structure, that must contain a field of type CIRCLEQ_ENTRY, named
NAME. The argument HEADNAME is the name of a user-defined
structure that must be declared using the macro CIRCLEQ_HEAD().
Creation
A circular queue is headed by a structure defined by the
CIRCLEQ_HEAD() macro. This structure contains a pair of
pointers, one to the first element in the queue and the other to
the last element in the queue. The elements are doubly linked so
that an arbitrary element can be removed without traversing the
queue. New elements can be added to the queue after an existing
element, before an existing element, at the head of the queue, or
at the end of the queue. A CIRCLEQ_HEAD structure is declared as
follows:
CIRCLEQ_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 queue. A
pointer to the head of the queue can later be declared as:
struct HEADNAME *headp;
(The names head and headp are user selectable.)
CIRCLEQ_ENTRY() declares a structure that connects the elements
in the queue.
CIRCLEQ_HEAD_INITIALIZER() evaluates to an initializer for the
queue head.
CIRCLEQ_INIT() initializes the queue referenced by head.
CIRCLEQ_EMPTY() evaluates to true if there are no items on the
queue.
Insertion
CIRCLEQ_INSERT_HEAD() inserts the new element elm at the head of
the queue.
CIRCLEQ_INSERT_TAIL() inserts the new element elm at the end of
the queue.
CIRCLEQ_INSERT_BEFORE() inserts the new element elm before the
element listelm.
CIRCLEQ_INSERT_AFTER() inserts the new element elm after the
element listelm.
Traversal
CIRCLEQ_FIRST() returns the first item on the queue.
CIRCLEQ_LAST() returns the last item on the queue.
CIRCLEQ_PREV() returns the previous item on the queue, or &head
if this item is the first one.
CIRCLEQ_NEXT() returns the next item on the queue, or &head if
this item is the last one.
CIRCLEQ_LOOP_PREV() returns the previous item on the queue. If
elm is the first element on the queue, the last element is
returned.
CIRCLEQ_LOOP_NEXT() returns the next item on the queue. If elm
is the last element on the queue, the first element is returned.
CIRCLEQ_FOREACH() traverses the queue referenced by head in the
forward direction, assigning each element in turn to var. var is
set to &head if the loop completes normally, or if there were no
elements.
CIRCLEQ_FOREACH_REVERSE() traverses the queue referenced by head
in the reverse direction, assigning each element in turn to var.
Removal
CIRCLEQ_REMOVE() removes the element elm from the queue.
CIRCLEQ_EMPTY() returns nonzero if the queue is empty, and zero
if the queue contains at least one entry.
CIRCLEQ_FIRST(), CIRCLEQ_LAST(), CIRCLEQ_LOOP_PREV(), and
CIRCLEQ_LOOP_NEXT() return a pointer to the first, last,
previous, or next TYPE structure, respectively.
CIRCLEQ_PREV(), and CIRCLEQ_NEXT() are similar to their
CIRCLEQ_LOOP_*() counterparts, except that if the argument is the
first or last element, respectively, they return &head.
CIRCLEQ_HEAD_INITIALIZER() returns an initializer that can be
assigned to the queue head.
BSD.
CIRCLEQ_FOREACH() and CIRCLEQ_FOREACH_REVERSE() don't allow var
to be removed or freed within the loop, as it would interfere
with the traversal. CIRCLEQ_FOREACH_SAFE() and
CIRCLEQ_FOREACH_REVERSE_SAFE(), which are present on the BSDs but
are not present in glibc, fix this limitation by allowing var to
safely be removed from the list and freed from within the loop
without interfering with the traversal.
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/queue.h>
struct entry {
int data;
CIRCLEQ_ENTRY(entry) entries; /* Queue */
};
CIRCLEQ_HEAD(circlehead, entry);
int
main(void)
{
struct entry *n1, *n2, *n3, *np;
struct circlehead head; /* Queue head */
int i;
CIRCLEQ_INIT(&head); /* Initialize the queue */
n1 = malloc(sizeof(struct entry)); /* Insert at the head */
CIRCLEQ_INSERT_HEAD(&head, n1, entries);
n1 = malloc(sizeof(struct entry)); /* Insert at the tail */
CIRCLEQ_INSERT_TAIL(&head, n1, entries);
n2 = malloc(sizeof(struct entry)); /* Insert after */
CIRCLEQ_INSERT_AFTER(&head, n1, n2, entries);
n3 = malloc(sizeof(struct entry)); /* Insert before */
CIRCLEQ_INSERT_BEFORE(&head, n2, n3, entries);
CIRCLEQ_REMOVE(&head, n2, entries); /* Deletion */
free(n2);
/* Forward traversal */
i = 0;
CIRCLEQ_FOREACH(np, &head, entries)
np->data = i++;
/* Reverse traversal */
CIRCLEQ_FOREACH_REVERSE(np, &head, entries)
printf("%i\n", np->data);
/* Queue deletion */
n1 = CIRCLEQ_FIRST(&head);
while (n1 != (void *)&head) {
n2 = CIRCLEQ_NEXT(n1, entries);
free(n1);
n1 = n2;
}
CIRCLEQ_INIT(&head);
exit(EXIT_SUCCESS);
}
insque(3), queue(7)
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Linux man-pages 6.9.1 2024-06-15 CIRCLEQ(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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