NAME

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

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#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);

DESCRIPTION

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().

CIRCLEQ_HEAD(HEADNAME, TYPE) head;

struct HEADNAME *headp;

RETURN VALUE

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.

STANDARDS

BSD.

BUGS

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.

EXAMPLES

#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);
}

SEE ALSO

insque(3), queue(7)