CIRCLEQ_INSERT_AFTER, C語言循環隊列

 

CMakeLists.txt

# CMakeList.txt : CMake project for llist, include source and define
# project specific logic here.
#
cmake_minimum_required (VERSION 3.2)

# Add source to this project's executable.
add_executable (poj2823 "main.c" "queue.h")

if (CMAKE_VERSION VERSION_GREATER 3.2)
    set_property(TARGET poj2823 PROPERTY C_STANDARD 99)
endif()

# TODO: Add tests and install targets if needed.

 

queue.h

/*
 * Copyright (c) 1991, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *    @(#)queue.h    8.5 (Berkeley) 8/20/94
 */

#ifndef    _SYS_QUEUE_H_
#define    _SYS_QUEUE_H_

/*
 * This file defines five types of data structures: singly-linked lists,
 * lists, simple queues, tail queues, and circular queues.
 *
 * A singly-linked list is headed by a single forward pointer. 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 list after an existing element or at the
 * head of the list.  Elements being removed from the head of the list
 * should use the explicit macro for this purpose for optimum
 * efficiency. A singly-linked list may only be traversed in the forward
 * direction.  Singly-linked lists are ideal for applications with large
 * datasets and few or no removals or for implementing a LIFO queue.
 *
 * A list is headed by a single forward pointer (or an array of forward
 * pointers for a hash table header). The elements are doubly linked
 * so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before
 * or after an existing element or at the head of the list. A list
 * may only be traversed in the forward direction.
 *
 * A simple queue is headed by a pair of pointers, one the head of the
 * list and the other to the tail of the list. The elements are singly
 * linked to save space, so elements can only be removed from the
 * head of the list. New elements can be added to the list after
 * an existing element, at the head of the list, or at the end of the
 * list. A simple queue may only be traversed in the forward direction.
 *
 * A tail queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or
 * after an existing element, at the head of the list, or at the end of
 * the list. A tail queue may be traversed in either direction.
 *
 * A circle queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or after
 * an existing element, at the head of the list, or at the end of the list.
 * A circle queue may be traversed in either direction, but has a more
 * complex end of list detection.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 */

/*
 * List definitions.
 */
#define    LIST_HEAD(name, type)                        \
struct name {                                \
    struct type *lh_first;    /* first element */            \
}

#define    LIST_HEAD_INITIALIZER(head)                    \
    { NULL }

#define    LIST_ENTRY(type)                        \
struct {                                \
    struct type *le_next;    /* next element */            \
    struct type **le_prev;    /* address of previous next element */    \
}

/*
 * List functions.
 */
#define    LIST_INIT(head) do {                        \
    (head)->lh_first = NULL;                    \
} while (/*CONSTCOND*/0)

#define    LIST_INSERT_AFTER(listelm, elm, field) do {            \
    if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)    \
        (listelm)->field.le_next->field.le_prev =        \
            &(elm)->field.le_next;                \
    (listelm)->field.le_next = (elm);                \
    (elm)->field.le_prev = &(listelm)->field.le_next;        \
} while (/*CONSTCOND*/0)

#define    LIST_INSERT_BEFORE(listelm, elm, field) do {            \
    (elm)->field.le_prev = (listelm)->field.le_prev;        \
    (elm)->field.le_next = (listelm);                \
    *(listelm)->field.le_prev = (elm);                \
    (listelm)->field.le_prev = &(elm)->field.le_next;        \
} while (/*CONSTCOND*/0)

#define    LIST_INSERT_HEAD(head, elm, field) do {                \
    if (((elm)->field.le_next = (head)->lh_first) != NULL)        \
        (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
    (head)->lh_first = (elm);                    \
    (elm)->field.le_prev = &(head)->lh_first;            \
} while (/*CONSTCOND*/0)

#define    LIST_REMOVE(elm, field) do {                    \
    if ((elm)->field.le_next != NULL)                \
        (elm)->field.le_next->field.le_prev =             \
            (elm)->field.le_prev;                \
    *(elm)->field.le_prev = (elm)->field.le_next;            \
} while (/*CONSTCOND*/0)

#define    LIST_FOREACH(var, head, field)                    \
    for ((var) = ((head)->lh_first);                \
        (var);                            \
        (var) = ((var)->field.le_next))

/*
 * List access methods.
 */
#define    LIST_EMPTY(head)        ((head)->lh_first == NULL)
#define    LIST_FIRST(head)        ((head)->lh_first)
#define    LIST_NEXT(elm, field)        ((elm)->field.le_next)


/*
 * Singly-linked List definitions.
 */
#define    SLIST_HEAD(name, type)                        \
struct name {                                \
    struct type *slh_first;    /* first element */            \
}

#define    SLIST_HEAD_INITIALIZER(head)                    \
    { NULL }

#define    SLIST_ENTRY(type)                        \
struct {                                \
    struct type *sle_next;    /* next element */            \
}

/*
 * Singly-linked List functions.
 */
#define    SLIST_INIT(head) do {                        \
    (head)->slh_first = NULL;                    \
} while (/*CONSTCOND*/0)

#define    SLIST_INSERT_AFTER(slistelm, elm, field) do {            \
    (elm)->field.sle_next = (slistelm)->field.sle_next;        \
    (slistelm)->field.sle_next = (elm);                \
} while (/*CONSTCOND*/0)

#define    SLIST_INSERT_HEAD(head, elm, field) do {            \
    (elm)->field.sle_next = (head)->slh_first;            \
    (head)->slh_first = (elm);                    \
} while (/*CONSTCOND*/0)

#define    SLIST_REMOVE_HEAD(head, field) do {                \
    (head)->slh_first = (head)->slh_first->field.sle_next;        \
} while (/*CONSTCOND*/0)

#define    SLIST_REMOVE(head, elm, type, field) do {            \
    if ((head)->slh_first == (elm)) {                \
        SLIST_REMOVE_HEAD((head), field);            \
    }                                \
    else {                                \
        struct type *curelm = (head)->slh_first;        \
        while(curelm->field.sle_next != (elm))            \
            curelm = curelm->field.sle_next;        \
        curelm->field.sle_next =                \
            curelm->field.sle_next->field.sle_next;        \
    }                                \
} while (/*CONSTCOND*/0)

#define    SLIST_FOREACH(var, head, field)                    \
    for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)

/*
 * Singly-linked List access methods.
 */
#define    SLIST_EMPTY(head)    ((head)->slh_first == NULL)
#define    SLIST_FIRST(head)    ((head)->slh_first)
#define    SLIST_NEXT(elm, field)    ((elm)->field.sle_next)


/*
 * Singly-linked Tail queue declarations.
 */
#define    STAILQ_HEAD(name, type)                    \
struct name {                                \
    struct type *stqh_first;    /* first element */            \
    struct type **stqh_last;    /* addr of last next element */        \
}

#define    STAILQ_HEAD_INITIALIZER(head)                    \
    { NULL, &(head).stqh_first }

#define    STAILQ_ENTRY(type)                        \
struct {                                \
    struct type *stqe_next;    /* next element */            \
}

/*
 * Singly-linked Tail queue functions.
 */
#define    STAILQ_INIT(head) do {                        \
    (head)->stqh_first = NULL;                    \
    (head)->stqh_last = &(head)->stqh_first;                \
} while (/*CONSTCOND*/0)

#define    STAILQ_INSERT_HEAD(head, elm, field) do {            \
    if (((elm)->field.stqe_next = (head)->stqh_first) == NULL)    \
        (head)->stqh_last = &(elm)->field.stqe_next;        \
    (head)->stqh_first = (elm);                    \
} while (/*CONSTCOND*/0)

#define    STAILQ_INSERT_TAIL(head, elm, field) do {            \
    (elm)->field.stqe_next = NULL;                    \
    *(head)->stqh_last = (elm);                    \
    (head)->stqh_last = &(elm)->field.stqe_next;            \
} while (/*CONSTCOND*/0)

#define    STAILQ_INSERT_AFTER(head, listelm, elm, field) do {        \
    if (((elm)->field.stqe_next = (listelm)->field.stqe_next) == NULL)\
        (head)->stqh_last = &(elm)->field.stqe_next;        \
    (listelm)->field.stqe_next = (elm);                \
} while (/*CONSTCOND*/0)

#define    STAILQ_REMOVE_HEAD(head, field) do {                \
    if (((head)->stqh_first = (head)->stqh_first->field.stqe_next) == NULL) \
        (head)->stqh_last = &(head)->stqh_first;            \
} while (/*CONSTCOND*/0)

#define    STAILQ_REMOVE(head, elm, type, field) do {            \
    if ((head)->stqh_first == (elm)) {                \
        STAILQ_REMOVE_HEAD((head), field);            \
    } else {                            \
        struct type *curelm = (head)->stqh_first;        \
        while (curelm->field.stqe_next != (elm))            \
            curelm = curelm->field.stqe_next;        \
        if ((curelm->field.stqe_next =                \
            curelm->field.stqe_next->field.stqe_next) == NULL) \
                (head)->stqh_last = &(curelm)->field.stqe_next; \
    }                                \
} while (/*CONSTCOND*/0)

#define    STAILQ_FOREACH(var, head, field)                \
    for ((var) = ((head)->stqh_first);                \
        (var);                            \
        (var) = ((var)->field.stqe_next))

#define    STAILQ_CONCAT(head1, head2) do {                \
    if (!STAILQ_EMPTY((head2))) {                    \
        *(head1)->stqh_last = (head2)->stqh_first;        \
        (head1)->stqh_last = (head2)->stqh_last;        \
        STAILQ_INIT((head2));                    \
    }                                \
} while (/*CONSTCOND*/0)

/*
 * Singly-linked Tail queue access methods.
 */
#define    STAILQ_EMPTY(head)    ((head)->stqh_first == NULL)
#define    STAILQ_FIRST(head)    ((head)->stqh_first)
#define    STAILQ_NEXT(elm, field)    ((elm)->field.stqe_next)


/*
 * Simple queue definitions.
 */
#define    SIMPLEQ_HEAD(name, type)                    \
struct name {                                \
    struct type *sqh_first;    /* first element */            \
    struct type **sqh_last;    /* addr of last next element */        \
}

#define    SIMPLEQ_HEAD_INITIALIZER(head)                    \
    { NULL, &(head).sqh_first }

#define    SIMPLEQ_ENTRY(type)                        \
struct {                                \
    struct type *sqe_next;    /* next element */            \
}

/*
 * Simple queue functions.
 */
#define    SIMPLEQ_INIT(head) do {                        \
    (head)->sqh_first = NULL;                    \
    (head)->sqh_last = &(head)->sqh_first;                \
} while (/*CONSTCOND*/0)

#define    SIMPLEQ_INSERT_HEAD(head, elm, field) do {            \
    if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)    \
        (head)->sqh_last = &(elm)->field.sqe_next;        \
    (head)->sqh_first = (elm);                    \
} while (/*CONSTCOND*/0)

#define    SIMPLEQ_INSERT_TAIL(head, elm, field) do {            \
    (elm)->field.sqe_next = NULL;                    \
    *(head)->sqh_last = (elm);                    \
    (head)->sqh_last = &(elm)->field.sqe_next;            \
} while (/*CONSTCOND*/0)

#define    SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {        \
    if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\
        (head)->sqh_last = &(elm)->field.sqe_next;        \
    (listelm)->field.sqe_next = (elm);                \
} while (/*CONSTCOND*/0)

#define    SIMPLEQ_REMOVE_HEAD(head, field) do {                \
    if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \
        (head)->sqh_last = &(head)->sqh_first;            \
} while (/*CONSTCOND*/0)

#define    SIMPLEQ_REMOVE(head, elm, type, field) do {            \
    if ((head)->sqh_first == (elm)) {                \
        SIMPLEQ_REMOVE_HEAD((head), field);            \
    } else {                            \
        struct type *curelm = (head)->sqh_first;        \
        while (curelm->field.sqe_next != (elm))            \
            curelm = curelm->field.sqe_next;        \
        if ((curelm->field.sqe_next =                \
            curelm->field.sqe_next->field.sqe_next) == NULL) \
                (head)->sqh_last = &(curelm)->field.sqe_next; \
    }                                \
} while (/*CONSTCOND*/0)

#define    SIMPLEQ_FOREACH(var, head, field)                \
    for ((var) = ((head)->sqh_first);                \
        (var);                            \
        (var) = ((var)->field.sqe_next))

/*
 * Simple queue access methods.
 */
#define    SIMPLEQ_EMPTY(head)        ((head)->sqh_first == NULL)
#define    SIMPLEQ_FIRST(head)        ((head)->sqh_first)
#define    SIMPLEQ_NEXT(elm, field)    ((elm)->field.sqe_next)


/*
 * Tail queue definitions.
 */
#define    _TAILQ_HEAD(name, type, qual)                    \
struct name {                                \
    qual type *tqh_first;        /* first element */        \
    qual type *qual *tqh_last;    /* addr of last next element */    \
}
#define TAILQ_HEAD(name, type)    _TAILQ_HEAD(name, struct type,)

#define    TAILQ_HEAD_INITIALIZER(head)                    \
    { NULL, &(head).tqh_first }

#define    _TAILQ_ENTRY(type, qual)                    \
struct {                                \
    qual type *tqe_next;        /* next element */        \
    qual type *qual *tqe_prev;    /* address of previous next element */\
}
#define TAILQ_ENTRY(type)    _TAILQ_ENTRY(struct type,)

/*
 * Tail queue functions.
 */
#define    TAILQ_INIT(head) do {                        \
    (head)->tqh_first = NULL;                    \
    (head)->tqh_last = &(head)->tqh_first;                \
} while (/*CONSTCOND*/0)

#define    TAILQ_INSERT_HEAD(head, elm, field) do {            \
    if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)    \
        (head)->tqh_first->field.tqe_prev =            \
            &(elm)->field.tqe_next;                \
    else                                \
        (head)->tqh_last = &(elm)->field.tqe_next;        \
    (head)->tqh_first = (elm);                    \
    (elm)->field.tqe_prev = &(head)->tqh_first;            \
} while (/*CONSTCOND*/0)

#define    TAILQ_INSERT_TAIL(head, elm, field) do {            \
    (elm)->field.tqe_next = NULL;                    \
    (elm)->field.tqe_prev = (head)->tqh_last;            \
    *(head)->tqh_last = (elm);                    \
    (head)->tqh_last = &(elm)->field.tqe_next;            \
} while (/*CONSTCOND*/0)

#define    TAILQ_INSERT_AFTER(head, listelm, elm, field) do {        \
    if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
        (elm)->field.tqe_next->field.tqe_prev =         \
            &(elm)->field.tqe_next;                \
    else                                \
        (head)->tqh_last = &(elm)->field.tqe_next;        \
    (listelm)->field.tqe_next = (elm);                \
    (elm)->field.tqe_prev = &(listelm)->field.tqe_next;        \
} while (/*CONSTCOND*/0)

#define    TAILQ_INSERT_BEFORE(listelm, elm, field) do {            \
    (elm)->field.tqe_prev = (listelm)->field.tqe_prev;        \
    (elm)->field.tqe_next = (listelm);                \
    *(listelm)->field.tqe_prev = (elm);                \
    (listelm)->field.tqe_prev = &(elm)->field.tqe_next;        \
} while (/*CONSTCOND*/0)

#define    TAILQ_REMOVE(head, elm, field) do {                \
    if (((elm)->field.tqe_next) != NULL)                \
        (elm)->field.tqe_next->field.tqe_prev =         \
            (elm)->field.tqe_prev;                \
    else                                \
        (head)->tqh_last = (elm)->field.tqe_prev;        \
    *(elm)->field.tqe_prev = (elm)->field.tqe_next;            \
} while (/*CONSTCOND*/0)

#define    TAILQ_FOREACH(var, head, field)                    \
    for ((var) = ((head)->tqh_first);                \
        (var);                            \
        (var) = ((var)->field.tqe_next))

#define    TAILQ_FOREACH_REVERSE(var, head, headname, field)        \
    for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));    \
        (var);                            \
        (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))

#define    TAILQ_CONCAT(head1, head2, field) do {                \
    if (!TAILQ_EMPTY(head2)) {                    \
        *(head1)->tqh_last = (head2)->tqh_first;        \
        (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last;    \
        (head1)->tqh_last = (head2)->tqh_last;            \
        TAILQ_INIT((head2));                    \
    }                                \
} while (/*CONSTCOND*/0)

/*
 * Tail queue access methods.
 */
#define    TAILQ_EMPTY(head)        ((head)->tqh_first == NULL)
#define    TAILQ_FIRST(head)        ((head)->tqh_first)
#define    TAILQ_NEXT(elm, field)        ((elm)->field.tqe_next)

#define    TAILQ_LAST(head, headname) \
    (*(((struct headname *)((head)->tqh_last))->tqh_last))
#define    TAILQ_PREV(elm, headname, field) \
    (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))


/*
 * Circular queue definitions.
 */
#define    CIRCLEQ_HEAD(name, type)                    \
struct name {                                \
    struct type *cqh_first;        /* first element */        \
    struct type *cqh_last;        /* last element */        \
}

#define    CIRCLEQ_HEAD_INITIALIZER(head)                    \
    { (void *)&head, (void *)&head }

#define    CIRCLEQ_ENTRY(type)                        \
struct {                                \
    struct type *cqe_next;        /* next element */        \
    struct type *cqe_prev;        /* previous element */        \
}

/*
 * Circular queue functions.
 */
#define    CIRCLEQ_INIT(head) do {                        \
    (head)->cqh_first = (void *)(head);                \
    (head)->cqh_last = (void *)(head);                \
} while (/*CONSTCOND*/0)

#define    CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {        \
    (elm)->field.cqe_next = (listelm)->field.cqe_next;        \
    (elm)->field.cqe_prev = (listelm);                \
    if ((listelm)->field.cqe_next == (void *)(head))        \
        (head)->cqh_last = (elm);                \
    else                                \
        (listelm)->field.cqe_next->field.cqe_prev = (elm);    \
    (listelm)->field.cqe_next = (elm);                \
} while (/*CONSTCOND*/0)

#define    CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {        \
    (elm)->field.cqe_next = (listelm);                \
    (elm)->field.cqe_prev = (listelm)->field.cqe_prev;        \
    if ((listelm)->field.cqe_prev == (void *)(head))        \
        (head)->cqh_first = (elm);                \
    else                                \
        (listelm)->field.cqe_prev->field.cqe_next = (elm);    \
    (listelm)->field.cqe_prev = (elm);                \
} while (/*CONSTCOND*/0)

#define    CIRCLEQ_INSERT_HEAD(head, elm, field) do {            \
    (elm)->field.cqe_next = (head)->cqh_first;            \
    (elm)->field.cqe_prev = (void *)(head);                \
    if ((head)->cqh_last == (void *)(head))                \
        (head)->cqh_last = (elm);                \
    else                                \
        (head)->cqh_first->field.cqe_prev = (elm);        \
    (head)->cqh_first = (elm);                    \
} while (/*CONSTCOND*/0)

#define    CIRCLEQ_INSERT_TAIL(head, elm, field) do {            \
    (elm)->field.cqe_next = (void *)(head);                \
    (elm)->field.cqe_prev = (head)->cqh_last;            \
    if ((head)->cqh_first == (void *)(head))            \
        (head)->cqh_first = (elm);                \
    else                                \
        (head)->cqh_last->field.cqe_next = (elm);        \
    (head)->cqh_last = (elm);                    \
} while (/*CONSTCOND*/0)

#define    CIRCLEQ_REMOVE(head, elm, field) do {                \
    if ((elm)->field.cqe_next == (void *)(head))            \
        (head)->cqh_last = (elm)->field.cqe_prev;        \
    else                                \
        (elm)->field.cqe_next->field.cqe_prev =            \
            (elm)->field.cqe_prev;                \
    if ((elm)->field.cqe_prev == (void *)(head))            \
        (head)->cqh_first = (elm)->field.cqe_next;        \
    else                                \
        (elm)->field.cqe_prev->field.cqe_next =            \
            (elm)->field.cqe_next;                \
} while (/*CONSTCOND*/0)

#define    CIRCLEQ_FOREACH(var, head, field)                \
    for ((var) = ((head)->cqh_first);                \
        (var) != (const void *)(head);                \
        (var) = ((var)->field.cqe_next))

#define    CIRCLEQ_FOREACH_REVERSE(var, head, field)            \
    for ((var) = ((head)->cqh_last);                \
        (var) != (const void *)(head);                \
        (var) = ((var)->field.cqe_prev))

/*
 * Circular queue access methods.
 */
#define    CIRCLEQ_EMPTY(head)        ((head)->cqh_first == (void *)(head))
#define    CIRCLEQ_FIRST(head)        ((head)->cqh_first)
#define    CIRCLEQ_LAST(head)        ((head)->cqh_last)
#define    CIRCLEQ_NEXT(elm, field)    ((elm)->field.cqe_next)
#define    CIRCLEQ_PREV(elm, field)    ((elm)->field.cqe_prev)

#define CIRCLEQ_LOOP_NEXT(head, elm, field)                \
    (((elm)->field.cqe_next == (void *)(head))            \
        ? ((head)->cqh_first)                    \
        : (elm->field.cqe_next))
#define CIRCLEQ_LOOP_PREV(head, elm, field)                \
    (((elm)->field.cqe_prev == (void *)(head))            \
        ? ((head)->cqh_last)                    \
        : (elm->field.cqe_prev))

#endif    /* sys/queue.h */

main.c

#include <stdio.h> /* printf */
#include <stdlib.h> /* malloc */
#include "queue.h" /* sys/queue.h */

struct num_entry {
    int num;
    CIRCLEQ_ENTRY(num_entry) entries;   /* Circular queue. */
};
CIRCLEQ_HEAD(cq_nums, num_entry);

int main() {
    struct cq_nums cqnhead;
    struct num_entry *n1, *n2, *n3, *np;

    CIRCLEQ_INIT(&cqnhead);
    n1 = malloc(sizeof(struct num_entry));  /* Insert at the tail. */
    n1->num = 1;
    CIRCLEQ_INSERT_TAIL(&cqnhead, n1, entries);

    n2 = malloc(sizeof(struct num_entry));
    n2->num = 3;
    CIRCLEQ_INSERT_TAIL(&cqnhead, n2, entries);

    n3 = malloc(sizeof(struct num_entry));
    n3->num = -1;
    CIRCLEQ_INSERT_TAIL(&cqnhead, n3, entries);

    /* Forward traversal. */
    for (np = cqnhead.cqh_first; np != (void *)&cqnhead;
         np = np->entries.cqe_next) {
        printf("%d ", np->num);
    }
    printf("\n");
    /* Reverse traversal. */
    for (np = cqnhead.cqh_last; np != (void *)&cqnhead;
        np = np->entries.cqe_prev) {
        printf("%d ", np->num);
    }
    /* Delete. */
    while (cqnhead.cqh_first != (void *)&cqnhead) {
        CIRCLEQ_REMOVE(&cqnhead, cqnhead.cqh_first, entries);
    }
    printf("\n");
    return 0;
}