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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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CIRCLEQ(3) Linux Programmer's 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
#include <sys/queue.h>
int CIRCLEQ_EMPTY(CIRCLEQ_HEAD *head);
CIRCLEQ_ENTRY(TYPE);
struct TYPE *CIRCLEQ_FIRST(CIRCLEQ_HEAD *head);
CIRCLEQ_FOREACH(struct TYPE *var, CIRCLEQ_HEAD *head,
CIRCLEQ_ENTRY NAME);
CIRCLEQ_FOREACH_REVERSE(struct TYPE *var, CIRCLEQ_HEAD *head,
CIRCLEQ_ENTRY NAME);
CIRCLEQ_HEAD(HEADNAME, TYPE);
CIRCLEQ_HEAD CIRCLEQ_HEAD_INITIALIZER(CIRCLEQ_HEAD head);
void CIRCLEQ_INIT(CIRCLEQ_HEAD *head);
void CIRCLEQ_INSERT_AFTER(CIRCLEQ_HEAD *head, struct TYPE *listelm,
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_HEAD(CIRCLEQ_HEAD *head, struct TYPE *elm,
CIRCLEQ_ENTRY NAME);
void CIRCLEQ_INSERT_TAIL(CIRCLEQ_HEAD *head, struct TYPE *elm,
CIRCLEQ_ENTRY NAME);
struct TYPE *CIRCLEQ_LAST(CIRCLEQ_HEAD *head);
void CIRCLEQ_LOOP_NEXT(CIRCLEQ_HEAD *head, struct TYPE *elm,
CIRCLEQ_ENTRY NAME);
void CIRCLEQ_LOOP_PREV(CIRCLEQ_HEAD *head, struct TYPE *elm,
CIRCLEQ_ENTRY NAME);
struct TYPE *CIRCLEQ_NEXT(struct TYPE *elm, CIRCLEQ_ENTRY NAME);
struct TYPE *CIRCLEQ_PREV(struct TYPE *elm, 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().
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 circular queue and the
other to the last element in the circular queue. The elements
are doubly linked so that an arbitrary element can be removed
without traversing the circular queue. New elements can be added
to the circular queue after an existing element, before an
existing element, at the head of the circular queue, or at the
end of the circular 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 circular
queue. A pointer to the head of the circular queue can later be
declared as:
struct HEADNAME *headp;
(The names head and headp are user selectable.)
The macro CIRCLEQ_HEAD_INITIALIZER() evaluates to an initializer
for the circular queue head.
The macro CIRCLEQ_EMPTY() evaluates to true if there are no items
on the circular queue.
The macro CIRCLEQ_ENTRY() declares a structure that connects the
elements in the circular queue.
The macro CIRCLEQ_FIRST() returns the first item on the circular
queue.
The macro CIRCLEQ_FOREACH() traverses the circular 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.
The macro CIRCLEQ_FOREACH_REVERSE() traverses the circular queue
referenced by head in the reverse direction, assigning each
element in turn to var.
The macro CIRCLEQ_INIT() initializes the circular queue
referenced by head.
The macro CIRCLEQ_INSERT_HEAD() inserts the new element elm at
the head of the circular queue.
The macro CIRCLEQ_INSERT_TAIL() inserts the new element elm at
the end of the circular queue.
The macro CIRCLEQ_INSERT_AFTER() inserts the new element elm
after the element listelm.
The macro CIRCLEQ_INSERT_BEFORE() inserts the new element elm
before the element listelm.
The macro CIRCLEQ_LAST() returns the last item on the circular
queue.
The macro CIRCLEQ_NEXT() returns the next item on the circular
queue, or &head if this item is the last one.
The macro CIRCLEQ_PREV() returns the previous item on the
circular queue, or &head if this item is the first one.
The macro CIRCLEQ_LOOP_NEXT() returns the next item on the
circular queue. If elm is the last element on the circular
queue, the first element is returned.
The macro CIRCLEQ_LOOP_PREV() returns the previous item on the
circular queue. If elm is the first element on the circular
queue, the last element is returned.
The macro CIRCLEQ_REMOVE() removes the element elm from the
circular 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_NEXT(), and
CIRCLEQ_PREV() return a pointer to the first, last, next or
previous TYPE structure, respectively.
CIRCLEQ_HEAD_INITIALIZER() returns an initializer that can be
assigned to the queue head.
Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008. Present on the
BSDs (CIRCLEQ macros first appeared in 4.4BSD).
The macros 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. The macros 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)
This page is part of release 5.10 of the Linux man-pages project.
A 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 CIRCLEQ(3)
Pages that refer to this page: queue(7)
Copyright and license for this manual page
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