SLIST_ENTRY, SLIST_HEAD, SLIST_HEAD_INITIALIZER,
SLIST_FIRST, SLIST_NEXT,
SLIST_END, SLIST_EMPTY, SLIST_FOREACH,
SLIST_FOREACH_PREVPTR, SLIST_INIT,
SLIST_INSERT_AFTER, SLIST_INSERT_HEAD, SLIST_REMOVE_HEAD,
SLIST_REMOVE_NEXT, SLIST_REMOVE, LIST_ENTRY, LIST_HEAD,
LIST_HEAD_INITIALIZER, LIST_FIRST, LIST_NEXT, LIST_END,
LIST_EMPTY,
LIST_FOREACH, LIST_INIT, LIST_INSERT_AFTER,
LIST_INSERT_BEFORE,
LIST_INSERT_HEAD, LIST_REMOVE, LIST_REPLACE, SIMPLEQ_ENTRY,
SIMPLEQ_HEAD,
SIMPLEQ_HEAD_INITIALIZER, SIMPLEQ_FIRST, SIMPLEQ_NEXT,
SIMPLEQ_END,
SIMPLEQ_EMPTY, SIMPLEQ_FOREACH, SIMPLEQ_INIT,
SIMPLEQ_INSERT_HEAD,
SIMPLEQ_INSERT_TAIL, SIMPLEQ_INSERT_AFTER,
SIMPLEQ_REMOVE_HEAD,
TAILQ_ENTRY, TAILQ_HEAD, TAILQ_HEAD_INITIALIZER,
TAILQ_FIRST, TAILQ_NEXT,
TAILQ_END, TAILQ_LAST, TAILQ_PREV, TAILQ_EMPTY,
TAILQ_FOREACH,
TAILQ_FOREACH_REVERSE, TAILQ_INIT, TAILQ_INSERT_AFTER,
TAILQ_INSERT_BEFORE, TAILQ_INSERT_HEAD, TAILQ_INSERT_TAIL,
TAILQ_REMOVE,
CIRCLEQ_ENTRY, CIRCLEQ_HEAD, CIRCLEQ_HEAD_INITIALIZER,
CIRCLEQ_FIRST,
CIRCLEQ_LAST, CIRCLEQ_END, CIRCLEQ_NEXT, CIRCLEQ_PREV,
CIRCLEQ_EMPTY,
CIRCLEQ_FOREACH, CIRCLEQ_FOREACH_REVERSE, CIRCLEQ_INIT,
CIRCLEQ_INSERT_AFTER, CIRCLEQ_INSERT_BEFORE,
CIRCLEQ_INSERT_HEAD,
CIRCLEQ_INSERT_TAIL, CIRCLEQ_REMOVE - implementations of
singly-linked
lists, doubly-linked lists, simple queues, tail queues, and
circular
queues
#include <sys/queue.h>
SLIST_ENTRY(TYPE);
SLIST_HEAD(HEADNAME, TYPE);
SLIST_HEAD_INITIALIZER(SLIST_HEAD head);
struct TYPE *
SLIST_FIRST(SLIST_HEAD *head);
struct TYPE *
SLIST_NEXT(struct TYPE *listelm, SLIST_ENTRY NAME);
struct TYPE *
SLIST_END(SLIST_HEAD *head);
bool
SLIST_EMPTY(SLIST_HEAD *head);
SLIST_FOREACH(VARNAME, SLIST_HEAD *head, SLIST_ENTRY NAME);
SLIST_FOREACH_PREVPTR(VARNAME, VARNAMEP, SLIST_HEAD *head,
SLIST_ENTRY NAME);
void
SLIST_INIT(SLIST_HEAD *head);
void
SLIST_INSERT_AFTER(struct TYPE *listelm, struct TYPE *elm,
SLIST_ENTRY NAME);
void
SLIST_INSERT_HEAD(SLIST_HEAD *head, struct TYPE *elm,
SLIST_ENTRY NAME);
void
SLIST_REMOVE_HEAD(SLIST_HEAD *head, SLIST_ENTRY NAME);
void
SLIST_REMOVE_NEXT(SLIST_HEAD *head, struct TYPE *elm,
SLIST_ENTRY NAME);
void
SLIST_REMOVE(SLIST_HEAD *head, struct TYPE *elm, TYPE,
SLIST_ENTRY NAME);
LIST_ENTRY(TYPE);
LIST_HEAD(HEADNAME, TYPE);
LIST_HEAD_INITIALIZER(LIST_HEAD head);
struct TYPE *
LIST_FIRST(LIST_HEAD *head);
struct TYPE *
LIST_NEXT(struct TYPE *listelm, LIST_ENTRY NAME);
struct TYPE *
LIST_END(LIST_HEAD *head);
bool
LIST_EMPTY(LIST_HEAD *head);
LIST_FOREACH(VARNAME, LIST_HEAD *head, LIST_ENTRY NAME);
void
LIST_INIT(LIST_HEAD *head);
void
LIST_INSERT_AFTER(struct TYPE *listelm, struct TYPE *elm,
LIST_ENTRY NAME);
void
LIST_INSERT_BEFORE(struct TYPE *listelm, struct TYPE *elm,
LIST_ENTRY NAME);
void
LIST_INSERT_HEAD(LIST_HEAD *head, struct TYPE *elm,
LIST_ENTRY NAME);
void
LIST_REMOVE(struct TYPE *elm, LIST_ENTRY NAME);
void
LIST_REPLACE(struct TYPE *elm, struct TYPE *elm2, LIST_ENTRY
NAME);
SIMPLEQ_ENTRY(TYPE);
SIMPLEQ_HEAD(HEADNAME, TYPE);
SIMPLEQ_HEAD_INITIALIZER(SIMPLEQ_HEAD head);
struct TYPE *
SIMPLEQ_FIRST(SIMPLEQ_HEAD *head);
struct TYPE *
SIMPLEQ_NEXT(struct TYPE *listelm, SIMPLEQ_ENTRY NAME);
struct TYPE *
SIMPLEQ_END(SIMPLEQ_HEAD *head);
void
SIMPLEQ_INIT(SIMPLEQ_HEAD *head);
void
SIMPLEQ_INSERT_HEAD(SIMPLEQ_HEAD *head, struct TYPE *elm,
SIMPLEQ_ENTRY NAME);
void
SIMPLEQ_INSERT_TAIL(SIMPLEQ_HEAD *head, struct TYPE *elm,
SIMPLEQ_ENTRY NAME);
void
SIMPLEQ_INSERT_AFTER(SIMPLEQ_HEAD *head, struct TYPE
*listelm,
struct TYPE *elm, SIMPLEQ_ENTRY NAME);
void
SIMPLEQ_REMOVE_HEAD(SIMPLEQ_HEAD *head, SIMPLEQ_ENTRY NAME);
TAILQ_ENTRY(TYPE);
TAILQ_HEAD(HEADNAME, TYPE);
TAILQ_HEAD_INITIALIZER(TAILQ_HEAD head);
struct TYPE *
TAILQ_FIRST(TAILQ_HEAD *head);
struct TYPE *
TAILQ_NEXT(struct TYPE *listelm, TAILQ_ENTRY NAME);
struct TYPE *
TAILQ_END(TAILQ_HEAD *head);
struct TYPE *
TAILQ_LAST(TAILQ_HEAD *head, HEADNAME NAME);
TAILQ_PREV(struct TYPE *listelm, HEADNAME NAME, TAILQ_ENTRY
NAME);
bool
TAILQ_EMPTY(TAILQ_HEAD *head);
TAILQ_FOREACH(VARNAME, TAILQ_HEAD *head, TAILQ_ENTRY NAME);
TAILQ_FOREACH_REVERSE(VARNAME, TAILQ_HEAD *head, HEADNAME,
TAILQ_ENTRY NAME);
void
TAILQ_INIT(TAILQ_HEAD *head);
void
TAILQ_INSERT_AFTER(TAILQ_HEAD *head, struct TYPE *listelm,
struct TYPE *elm, TAILQ_ENTRY NAME);
void
TAILQ_INSERT_BEFORE(struct TYPE *listelm, struct TYPE *elm,
TAILQ_ENTRY NAME);
void
TAILQ_INSERT_HEAD(TAILQ_HEAD *head, struct TYPE *elm,
TAILQ_ENTRY NAME);
void
TAILQ_INSERT_TAIL(TAILQ_HEAD *head, struct TYPE *elm,
TAILQ_ENTRY NAME);
void
TAILQ_REMOVE(TAILQ_HEAD *head, struct TYPE *elm, TAILQ_ENTRY
NAME);
CIRCLEQ_ENTRY(TYPE);
CIRCLEQ_HEAD(HEADNAME, TYPE);
CIRCLEQ_HEAD_INITIALIZER(CIRCLEQ_HEAD head);
struct TYPE *
CIRCLEQ_FIRST(CIRCLEQ_HEAD *head);
struct TYPE *
CIRCLEQ_LAST(CIRCLEQ_HEAD *head);
struct TYPE *
CIRCLEQ_END(CIRCLEQ_HEAD *head);
struct TYPE *
CIRCLEQ_NEXT(struct TYPE *listelm, CIRCLEQ_ENTRY NAME);
struct TYPE *
CIRCLEQ_PREV(struct TYPE *listelm, CIRCLEQ_ENTRY NAME);
bool
CIRCLEQ_EMPTY(CIRCLEQ_HEAD *head);
CIRCLEQ_FOREACH(VARNAME, CIRCLEQ_HEAD *head, CIRCLEQ_ENTRY
NAME);
CIRCLEQ_FOREACH_REVERSE(VARNAME, CIRCLEQ_HEAD *head,
CIRCLEQ_ENTRY NAME);
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);
void
CIRCLEQ_REMOVE(CIRCLEQ_HEAD *head, struct TYPE *elm,
CIRCLEQ_ENTRY NAME);
These macros define and operate on five types of data structures: singlylinked
lists, simple queues, lists, tail queues, and circular queues.
All five structures support the following functionality:
1. Insertion of a new entry at the head of the list.
2. Insertion of a new entry after any element in the
list.
3. Removal of an entry from the head of the list.
4. Forward traversal through the list.
Singly-linked lists are the simplest of the five data structures and support
only the above functionality. Singly-linked lists are
ideal for applications
with large datasets and few or no removals, or
for implementing
a LIFO queue.
Simple queues add the following functionality:
1. Entries can be added at the end of a list.
However:
1. All list insertions must specify the head of the
list.
2. Each head entry requires two pointers rather than
one.
3. Code size is about 15% greater and operations run
about 20%
slower than singly-linked lists.
Simple queues are ideal for applications with large datasets
and few or
no removals, or for implementing a FIFO queue.
All doubly linked types of data structures (lists, tail
queues, and circle
queues) additionally allow:
1. Insertion of a new entry before any element in
the list.
2. Removal of any entry in the list.
However:
1. Each element requires two pointers rather than
one.
2. Code size and execution time of operations (except for removal)
is about twice that of the singly-linked
data-structures.
Lists are the simplest of the doubly linked data structures
and support
only the above functionality over singly-linked lists.
Tail queues add the following functionality:
1. Entries can be added at the end of a list.
2. They may be traversed backwards, at a cost.
However:
1. All list insertions and removals must specify the
head of the
list.
2. Each head entry requires two pointers rather than
one.
3. Code size is about 15% greater and operations run
about 20%
slower than singly-linked lists.
Circular queues add the following functionality:
1. Entries can be added at the end of a list.
2. They may be traversed backwards, from tail to
head.
However:
1. All list insertions and removals must specify the
head of the
list.
2. Each head entry requires two pointers rather than
one.
3. The termination condition for traversal is more
complex.
4. Code size is about 40% greater and operations run
about 45%
slower than lists.
In the macro definitions, TYPE is the name tag of a user defined structure
that must contain a field of type SLIST_ENTRY, LIST_ENTRY,
SIMPLEQ_ENTRY, TAILQ_ENTRY, or CIRCLEQ_ENTRY, named NAME.
The argument
HEADNAME is the name tag of a user defined structure that
must be declared
using the macros SLIST_HEAD(), LIST_HEAD(),
SIMPLEQ_HEAD(),
TAILQ_HEAD(), or CIRCLEQ_HEAD(). See the examples below for
further explanation
of how these macros are used.
A singly-linked list is headed by a structure defined by the
SLIST_HEAD()
macro. This structure contains a single pointer to the
first element on
the list. 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. A SLIST_HEAD structure is declared as follows:
SLIST_HEAD(HEADNAME, TYPE) head;
where HEADNAME is the name of the structure to be defined,
and struct
TYPE is the type of the elements to be linked into the list.
A pointer
to the head of the list can later be declared as:
struct HEADNAME *headp;
(The names head and headp are user selectable.)
The HEADNAME facility is often not used, leading to the following bizarre
code:
SLIST_HEAD(, TYPE) head, *headp;
The SLIST_ENTRY() macro declares a structure that connects
the elements
in the list.
The SLIST_INIT() macro initializes the list referenced by
head.
The list can also be initialized statically by using the
SLIST_HEAD_INITIALIZER() macro like this:
SLIST_HEAD(HEADNAME, TYPE) head = SLIST_HEAD_INITIALIZER(head);
The SLIST_INSERT_HEAD() macro inserts the new element elm at
the head of
the list.
The SLIST_INSERT_AFTER() macro inserts the new element elm
after the element
listelm.
The SLIST_REMOVE_HEAD() macro removes the first element of
the list
pointed by head.
The SLIST_REMOVE_NEXT() macro removes the list element immediately following
elm.
The SLIST_REMOVE() macro removes the element elm of the list
pointed by
head.
The SLIST_FIRST() and SLIST_NEXT() macros can be used to
traverse the
list:
for (np = SLIST_FIRST(&head); np != NULL; np =
SLIST_NEXT(np, NAME))
Or, for simplicity, one can use the SLIST_FOREACH() macro:
SLIST_FOREACH(np, head, NAME)
The SLIST_FOREACH_PREVPTR() macro is similar to
SLIST_FOREACH() except
that it stores a pointer to the previous element in
VARNAMEP. This provides
access to the previous element while traversing the
list, as one
would have with a doubly-linked list.
The SLIST_EMPTY() macro should be used to check whether a
simple list is
empty.
A list is headed by a structure defined by the LIST_HEAD()
macro. This
structure contains a single pointer to the first element on
the list.
The elements are doubly linked so that an arbitrary element
can be removed
without traversing the list. New elements can be
added to the list
after an existing element, before an existing element, or at
the head of
the list. A LIST_HEAD structure is declared as follows:
LIST_HEAD(HEADNAME, TYPE) head;
where HEADNAME is the name of the structure to be defined,
and struct
TYPE is the type of the elements to be linked into the list.
A pointer
to the head of the list can later be declared as:
struct HEADNAME *headp;
(The names head and headp are user selectable.)
The HEADNAME facility is often not used, leading to the following bizarre
code:
LIST_HEAD(, TYPE) head, *headp;
The LIST_ENTRY() macro declares a structure that connects
the elements in
the list.
The LIST_INIT() macro initializes the list referenced by
head.
The list can also be initialized statically by using the
LIST_HEAD_INITIALIZER() macro like this:
LIST_HEAD(HEADNAME, TYPE) head = LIST_HEAD_INITIALIZER(head);
The LIST_INSERT_HEAD() macro inserts the new element elm at
the head of
the list.
The LIST_INSERT_AFTER() macro inserts the new element elm
after the element
listelm.
The LIST_INSERT_BEFORE() macro inserts the new element elm
before the element
listelm.
The LIST_REMOVE() macro removes the element elm from the
list.
The LIST_REPLACE() macro replaces the list element elm with
the new element
elm2.
The LIST_FIRST() and LIST_NEXT() macros can be used to traverse the list:
for (np = LIST_FIRST(&head); np != NULL; np =
LIST_NEXT(np, NAME))
Or, for simplicity, one can use the LIST_FOREACH() macro:
LIST_FOREACH(np, head, NAME)
The LIST_EMPTY() macro should be used to check whether a
list is empty.
LIST_HEAD(listhead, entry) head;
struct listhead *headp; /* List head. */
struct entry {
...
LIST_ENTRY(entry) entries; /* List. */
...
} *n1, *n2, *np;
LIST_INIT(&head); /* Initialize list.
*/
n1 = malloc(sizeof(struct entry)); /* Insert at the
head. */
LIST_INSERT_HEAD(&head, n1, entries);
n2 = malloc(sizeof(struct entry)); /* Insert after. */
LIST_INSERT_AFTER(n1, n2, entries);
n2 = malloc(sizeof(struct entry)); /* Insert before. */
LIST_INSERT_BEFORE(n1, n2, entries);
/* Forward traversal. */
for (np = head.lh_first; np != NULL; np = np->entries.le_next)
np-> ...
while (head.lh_first != NULL) /* Delete. */
LIST_REMOVE(head.lh_first, entries);
A simple queue is headed by a structure defined by the
SIMPLEQ_HEAD()
macro. This structure contains a pair of pointers, one to
the first element
in the simple queue and the other to the last element
in the simple
queue. The elements are singly linked. New elements can be
added to the
queue after an existing element, at the head of the queue or
at the tail
of the queue. A SIMPLEQ_HEAD structure is declared as follows:
SIMPLEQ_HEAD(HEADNAME, TYPE) head;
where HEADNAME is the name of 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.)
The SIMPLEQ_ENTRY() macro declares a structure that connects
the elements
in the queue.
The SIMPLEQ_INIT() macro initializes the queue referenced by
head.
The queue can also be initialized statically by using the
SIMPLEQ_HEAD_INITIALIZER() macro like this:
SIMPLEQ_HEAD(HEADNAME, TYPE) head = SIMPLEQ_HEAD_INITIALIZER(head);
The SIMPLEQ_INSERT_HEAD() macro inserts the new element elm
at the head
of the queue.
The SIMPLEQ_INSERT_TAIL() macro inserts the new element elm
at the end of
the queue.
The SIMPLEQ_INSERT_AFTER() macro inserts the new element elm
after the
element listelm.
The SIMPLEQ_REMOVE_HEAD() macro removes the first element
from the queue.
The SIMPLEQ_FIRST() and SIMPLEQ_NEXT() macros can be used to
traverse the
queue. The SIMPLEQ_FOREACH() is used for queue traversal:
SIMPLEQ_FOREACH(np, head, NAME)
The SIMPLEQ_EMPTY() macro should be used to check whether a
list is empty.
SIMPLEQ_HEAD(listhead, entry) head = SIMPLEQ_HEAD_INITIALIZER(head);
struct entry {
...
SIMPLEQ_ENTRY(entry) entries; /* List. */
...
} *n1, *n2, *np;
n1 = malloc(sizeof(struct entry)); /* Insert at the
head. */
SIMPLEQ_INSERT_HEAD(&head, n1, entries);
n2 = malloc(sizeof(struct entry)); /* Insert after. */
SIMPLEQ_INSERT_AFTER(&head, n1, n2, entries);
n2 = malloc(sizeof(struct entry)); /* Insert at the
tail. */
SIMPLEQ_INSERT_TAIL(&head, n2, entries);
/* Forward traversal. */
for (np = SIMPLEQ_FIRST(&head); np != NULL; np = SIMPLEQ_NEXT(np, entries))
np-> ...
/* Delete. */
while ((n1 = SIMPLEQ_FIRST(&head)) != NULL)
SIMPLEQ_REMOVE_HEAD(&head, entries);
A tail queue is headed by a structure defined by the
TAILQ_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 doubly linked so that an arbitrary element can
be removed
without traversing the tail 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 TAILQ_HEAD
structure is declared
as follows:
TAILQ_HEAD(HEADNAME, TYPE) head;
where HEADNAME is the name of 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.)
The TAILQ_ENTRY() macro declares a structure that connects
the elements
in the tail queue.
The TAILQ_INIT() macro initializes the tail queue referenced
by head.
The tail queue can also be initialized statically by using
the
TAILQ_HEAD_INITIALIZER() macro.
The TAILQ_INSERT_HEAD() macro inserts the new element elm at
the head of
the tail queue.
The TAILQ_INSERT_TAIL() macro inserts the new element elm at
the end of
the tail queue.
The TAILQ_INSERT_AFTER() macro inserts the new element elm
after the element
listelm.
The TAILQ_INSERT_BEFORE() macro inserts the new element elm
before the
element listelm.
The TAILQ_REMOVE() macro removes the element elm from the
tail queue.
TAILQ_FOREACH() and TAILQ_FOREACH_REVERSE() are used for
traversing a
tail queue. TAILQ_FOREACH() starts at the first element and
proceeds towards
the last. TAILQ_FOREACH_REVERSE() starts at the last
element and
proceeds towards the first.
TAILQ_FOREACH(np, &head, NAME)
TAILQ_FOREACH_REVERSE(np, &head, HEADNAME, NAME)
The TAILQ_FIRST(), TAILQ_NEXT(), TAILQ_LAST() and
TAILQ_PREV() macros can
be used to manually traverse a tail queue or an arbitrary
part of one.
The TAILQ_EMPTY() macro should be used to check whether a
tail queue is
empty.
TAILQ_HEAD(tailhead, entry) head;
struct tailhead *headp; /* Tail queue head. */
struct entry {
...
TAILQ_ENTRY(entry) entries; /* Tail queue. */
...
} *n1, *n2, *np;
TAILQ_INIT(&head); /* Initialize queue.
*/
n1 = malloc(sizeof(struct entry)); /* Insert at the
head. */
TAILQ_INSERT_HEAD(&head, n1, entries);
n1 = malloc(sizeof(struct entry)); /* Insert at the
tail. */
TAILQ_INSERT_TAIL(&head, n1, entries);
n2 = malloc(sizeof(struct entry)); /* Insert after. */
TAILQ_INSERT_AFTER(&head, n1, n2, entries);
n2 = malloc(sizeof(struct entry)); /* Insert before. */
TAILQ_INSERT_BEFORE(n1, n2, entries);
/* Forward traversal. */
TAILQ_FOREACH(np, &head, entries)
np-> ...
/* Manual forward
traversal */
for (np = n2; np != NULL; np = TAILQ_NEXT(np, entries))
np-> ...
/* Delete. */
while (np = TAILQ_FIRST(&head))
TAILQ_REMOVE(&head, np, entries);
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 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 HEADNAME is the name of 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 CIRCLEQ_ENTRY() macro declares a structure that connects
the elements
in the circular queue.
The CIRCLEQ_INIT() macro initializes the circular queue referenced by
head.
The circular queue can also be initialized statically by using the
CIRCLEQ_HEAD_INITIALIZER() macro.
The CIRCLEQ_INSERT_HEAD() macro inserts the new element elm
at the head
of the circular queue.
The CIRCLEQ_INSERT_TAIL() macro inserts the new element elm
at the end of
the circular queue.
The CIRCLEQ_INSERT_AFTER() macro inserts the new element elm
after the
element listelm.
The CIRCLEQ_INSERT_BEFORE() macro inserts the new element
elm before the
element listelm.
The CIRCLEQ_REMOVE() macro removes the element elm from the
circular
queue.
The CIRCLEQ_FIRST(), CIRCLEQ_LAST(), CIRCLEQ_END(),
CIRCLEQ_NEXT() and
CIRCLEQ_PREV() macros can be used to traverse a circular
queue. The
CIRCLEQ_FOREACH() is used for circular queue forward traversal:
CIRCLEQ_FOREACH(np, head, NAME)
The CIRCLEQ_FOREACH_REVERSE() macro acts like
CIRCLEQ_FOREACH() but traverses
the circular queue backwards.
The CIRCLEQ_EMPTY() macro should be used to check whether a
circular
queue is empty.
CIRCULAR QUEUE EXAMPLE [Toc] [Back] CIRCLEQ_HEAD(circleq, entry) head;
struct circleq *headp; /* Circular queue
head. */
struct entry {
...
CIRCLEQ_ENTRY(entry) entries; /* Circular queue.
*/
...
} *n1, *n2, *np;
CIRCLEQ_INIT(&head); /* Initialize circular 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);
n2 = malloc(sizeof(struct entry)); /* Insert before. */
CIRCLEQ_INSERT_BEFORE(&head, n1, n2, entries);
/* Forward traversal. */
for (np = CIRCLEQ_FIRST(&head); np != CIRCLEQ_END(&head);
np = CIRCLEQ_NEXT(np, entries))
np-> ...
/* Reverse traversal. */
for (np = CIRCLEQ_LAST(&head); np != CIRCLEQ_END(&head);
np = CIRCLEQ_PREV(np, entries))
np-> ...
/* Delete. */
while (CIRCLEQ_FIRST(&head) != CIRCLEQ_END(&head))
CIRCLEQ_REMOVE(&head, CIRCLEQ_FIRST(&head), entries);
The SLIST_END(), LIST_END(), SIMPLEQ_END() and TAILQ_END()
macros are
provided for symmetry with CIRCLEQ_END(). They expand to
NULL and don't
serve any useful purpose.
Trying to free a list in the following way is a common error:
LIST_FOREACH(var, head, entry)
free(var);
free(head);
Since var is free'd, the FOREACH() macro refers to a pointer
that may
have been reallocated already. Proper code needs a second
variable.
for (var = LIST_FIRST(head); var != LIST_END(head);
var = nxt) {
nxt = LIST_NEXT(var, entry);
free(var);
}
LIST_INIT(head); /* to put the list back in order */
The queue functions first appeared in 4.4BSD.
OpenBSD 3.6 December 13, 1993
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