queue(3)

NAME

SLIST_EMPTY, SLIST_ENTRY, SLIST_FIRST, SLIST_FOREACH,

SLIST_FOREACH_SAFE

SLIST_HEAD, SLIST_HEAD_INITIALIZER, SLIST_INIT,

SLIST_INSERT_AFTER

SLIST_INSERT_HEAD, SLIST_NEXT, SLIST_REMOVE_HEAD,

SLIST_REMOVE

STAILQ_CONCAT, STAILQ_EMPTY, STAILQ_ENTRY, STAILQ_FIRST,

STAILQ_FOREACH

STAILQ_FOREACH_SAFE, STAILQ_HEAD, STAILQ_HEAD_INITIALIZER,

STAILQ_INIT

STAILQ_INSERT_AFTER, STAILQ_INSERT_HEAD, STAILQ_INSERT_TAIL,

STAILQ_LAST

STAILQ_NEXT, STAILQ_REMOVE_HEAD, STAILQ_REMOVE, LIST_EMPTY,

LIST_ENTRY

LIST_FIRST, LIST_FOREACH, LIST_FOREACH_SAFE, LIST_HEAD, LIST_HEAD_INITIALIZER, LIST_INIT, LIST_INSERT_AFTER,

LIST_INSERT_BEFORE

LIST_INSERT_HEAD, LIST_NEXT, LIST_REMOVE, TAILQ_CONCAT,

TAILQ_EMPTY

TAILQ_ENTRY, TAILQ_FIRST, TAILQ_FOREACH, TAILQ_FOREACH_SAFE, TAILQ_FOREACH_REVERSE, TAILQ_FOREACH_REVERSE_SAFE,

TAILQ_HEAD

TAILQ_HEAD_INITIALIZER, TAILQ_INIT, TAILQ_INSERT_AFTER, TAILQ_INSERT_BEFORE, TAILQ_INSERT_HEAD, TAILQ_INSERT_TAIL,

TAILQ_LAST

TAILQ_NEXT, TAILQ_PREV, TAILQ_REMOVE - implementations of

singly-linked
lists, singly-linked tail queues, lists and tail queues

SYNOPSIS

#include <sys/queue.h>
SLIST_EMPTY(SLIST_HEAD *head);
SLIST_ENTRY(TYPE);
SLIST_FIRST(SLIST_HEAD *head);
SLIST_FOREACH(TYPE   *var,   SLIST_HEAD  *head,  SLIST_ENTRY
NAME);
SLIST_FOREACH_SAFE(TYPE *var, SLIST_HEAD *head,  SLIST_ENTRY
NAME,
        TYPE *temp_var);
SLIST_HEAD(HEADNAME, TYPE);
SLIST_HEAD_INITIALIZER(SLIST_HEAD head);
SLIST_INIT(SLIST_HEAD *head);
SLIST_INSERT_AFTER(TYPE  *listelm,  TYPE  *elm,  SLIST_ENTRY
NAME);
SLIST_INSERT_HEAD(SLIST_HEAD *head, TYPE  *elm,  SLIST_ENTRY
NAME);
SLIST_NEXT(TYPE *elm, SLIST_ENTRY NAME);
SLIST_REMOVE_HEAD(SLIST_HEAD *head, SLIST_ENTRY NAME);
SLIST_REMOVE(SLIST_HEAD  *head, TYPE *elm, TYPE, SLIST_ENTRY
NAME);
STAILQ_CONCAT(STAILQ_HEAD *head1, STAILQ_HEAD *head2);
STAILQ_EMPTY(STAILQ_HEAD *head);
STAILQ_ENTRY(TYPE);
STAILQ_FIRST(STAILQ_HEAD *head);
STAILQ_FOREACH(TYPE *var,  STAILQ_HEAD  *head,  STAILQ_ENTRY
NAME);
STAILQ_FOREACH_SAFE(TYPE     *var,     STAILQ_HEAD    *head,
STAILQ_ENTRY NAME,
        TYPE *temp_var);
STAILQ_HEAD(HEADNAME, TYPE);
STAILQ_HEAD_INITIALIZER(STAILQ_HEAD head);
STAILQ_INIT(STAILQ_HEAD *head);
STAILQ_INSERT_AFTER(STAILQ_HEAD *head, TYPE  *listelm,  TYPE
*elm,
        STAILQ_ENTRY NAME);
STAILQ_INSERT_HEAD(STAILQ_HEAD     *head,     TYPE     *elm,
STAILQ_ENTRY NAME);
STAILQ_INSERT_TAIL(STAILQ_HEAD     *head,     TYPE     *elm,
STAILQ_ENTRY NAME);
STAILQ_LAST(STAILQ_HEAD *head, TYPE, STAILQ_ENTRY NAME);
STAILQ_NEXT(TYPE *elm, STAILQ_ENTRY NAME);
STAILQ_REMOVE_HEAD(STAILQ_HEAD *head, STAILQ_ENTRY NAME);
STAILQ_REMOVE(STAILQ_HEAD    *head,    TYPE    *elm,   TYPE,
STAILQ_ENTRY NAME);
LIST_EMPTY(LIST_HEAD *head);
LIST_ENTRY(TYPE);
LIST_FIRST(LIST_HEAD *head);
LIST_FOREACH(TYPE *var, LIST_HEAD *head, LIST_ENTRY NAME);
LIST_FOREACH_SAFE(TYPE  *var,  LIST_HEAD  *head,  LIST_ENTRY
NAME,
        TYPE *temp_var);
LIST_HEAD(HEADNAME, TYPE);
LIST_HEAD_INITIALIZER(LIST_HEAD head);
LIST_INIT(LIST_HEAD *head);
LIST_INSERT_AFTER(TYPE   *listelm,   TYPE  *elm,  LIST_ENTRY
NAME);
LIST_INSERT_BEFORE(TYPE  *listelm,  TYPE  *elm,   LIST_ENTRY
NAME);
LIST_INSERT_HEAD(LIST_HEAD   *head,  TYPE  *elm,  LIST_ENTRY
NAME);
LIST_NEXT(TYPE *elm, LIST_ENTRY NAME);
LIST_REMOVE(TYPE *elm, LIST_ENTRY NAME);
TAILQ_CONCAT(TAILQ_HEAD    *head1,    TAILQ_HEAD     *head2,
TAILQ_ENTRY NAME);
TAILQ_EMPTY(TAILQ_HEAD *head);
TAILQ_ENTRY(TYPE);
TAILQ_FIRST(TAILQ_HEAD *head);
TAILQ_FOREACH(TYPE   *var,   TAILQ_HEAD  *head,  TAILQ_ENTRY
NAME);
TAILQ_FOREACH_SAFE(TYPE *var, TAILQ_HEAD *head,  TAILQ_ENTRY
NAME,
        TYPE *temp_var);
TAILQ_FOREACH_REVERSE(TYPE *var, TAILQ_HEAD *head, HEADNAME,
        TAILQ_ENTRY NAME);
TAILQ_FOREACH_REVERSE_SAFE(TYPE  *var,   TAILQ_HEAD   *head,
HEADNAME,
        TAILQ_ENTRY NAME, TYPE *temp_var);
TAILQ_HEAD(HEADNAME, TYPE);
TAILQ_HEAD_INITIALIZER(TAILQ_HEAD head);
TAILQ_INIT(TAILQ_HEAD *head);
TAILQ_INSERT_AFTER(TAILQ_HEAD  *head,  TYPE  *listelm,  TYPE
*elm,
        TAILQ_ENTRY NAME);
TAILQ_INSERT_BEFORE(TYPE *listelm,  TYPE  *elm,  TAILQ_ENTRY
NAME);
TAILQ_INSERT_HEAD(TAILQ_HEAD  *head,  TYPE *elm, TAILQ_ENTRY
NAME);
TAILQ_INSERT_TAIL(TAILQ_HEAD *head, TYPE  *elm,  TAILQ_ENTRY
NAME);
TAILQ_LAST(TAILQ_HEAD *head, HEADNAME);
TAILQ_NEXT(TYPE *elm, TAILQ_ENTRY NAME);
TAILQ_PREV(TYPE *elm, HEADNAME, TAILQ_ENTRY NAME);
TAILQ_REMOVE(TAILQ_HEAD *head, TYPE *elm, TAILQ_ENTRY NAME);

DESCRIPTION

These macros define and operate on four types of data struc

tures: singlylinked lists, singly-linked tail queues, lists, and tail

queues. All
four 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. O(1) removal of an entry from the head of the

list.
4. O(n) removal of any entry in the list.
5. Forward traversal through the list.

Singly-linked lists are the simplest of the four data struc

tures 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.

Singly-linked tail queues add the following functionality:
1. Entries can be added at the end of a list.
2. They may be concatenated.

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.

Singly-linked tailqs 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 and tail

queues) additionally allow:
1. Insertion of a new entry before any element in

the list.
2. O(1) removal of any entry in the list.

However:
1. Each elements requires two pointers rather than

one.
2. Code size and execution time of operations (ex

cept for
removal) is about twice that of the singly-linked

data-structures.

Linked 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, from tail to

head.
3. They may be concatenated.

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.

In the macro definitions, TYPE is the name of a user defined

structure,
that must contain a field of type SLIST_ENTRY, STAILQ_ENTRY,

LIST_ENTRY,
or TAILQ_ENTRY, named NAME. The argument HEADNAME is the

name of a user
defined structure that must be declared using the macros

SLIST_HEAD,
STAILQ_HEAD, LIST_HEAD, or TAILQ_HEAD. See the examples be

low for further explanation of how these macros are used.

SINGLY-LINKED LISTS

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 ar

bitrary elements. New elements can be added to the list after an ex

isting element
or at the head of the list. An SLIST_HEAD structure is de

clared as follows:

SLIST_HEAD(HEADNAME, TYPE) head;

where HEADNAME is the name of the structure to be defined,

and 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 macro SLIST_HEAD_INITIALIZER evaluates to an initializer

for the list
head.

The macro SLIST_EMPTY evaluates to true if there are no ele

ments in the
list.

The macro SLIST_ENTRY declares a structure that connects the

elements in
the list.

The macro SLIST_FIRST returns the first element in the list

or NULL if
the list is empty.

The macro SLIST_FOREACH traverses the list referenced by

head in the forward direction, assigning each element in turn to var.

The macro SLIST_FOREACH_SAFE traverses the list referenced

by head in the
forward direction, assigning each element in turn to var.

However,
unlike SLIST_FOREACH() here it is permitted to both remove

var as well as
free it from within the loop safely without interfering with

the traversal.

The macro SLIST_INIT initializes the list referenced by

head.

The macro SLIST_INSERT_HEAD inserts the new element elm at

the head of
the list.

The macro SLIST_INSERT_AFTER inserts the new element elm af

ter the element listelm.

The macro SLIST_NEXT returns the next element in the list.

The macro SLIST_REMOVE_HEAD removes the element elm from the

head of the
list. For optimum efficiency, elements being removed from

the head of
the list should explicitly use this macro instead of the

generic
SLIST_REMOVE macro.

The macro SLIST_REMOVE removes the element elm from the

list.

SINGLY-LINKED LIST EXAMPLE

SLIST_HEAD(slisthead, entry) head =

SLIST_HEAD_INITIALIZER(head);

struct slisthead *headp; /* Singly-linked

List head. */
struct entry {
...
SLIST_ENTRY(entry) entries; /* Singly-linked

List. */
...

} *n1, *n2, *n3, *np;

SLIST_INIT(&head); /* Initialize the

list. */

n1 = malloc(sizeof(struct entry)); /* Insert at the

head. */
SLIST_INSERT_HEAD(&head, n1, entries);

n2 = malloc(sizeof(struct entry)); /* Insert after. */
SLIST_INSERT_AFTER(n1, n2, entries);

SLIST_REMOVE(&head, n2, entry, entries);/* Deletion. */
free(n2);

n3 = SLIST_FIRST(&head);
SLIST_REMOVE_HEAD(&head, entries); /* Deletion from the

head. */
free(n3);/* Forward traver

sal. */

SLIST_FOREACH(np, &head, entries)
np-> ...
/* Safe forward

traversal. */

SLIST_FOREACH_SAFE(np, &head, entries, np_temp) {
np->do_stuff();
...
SLIST_REMOVE(&head, np, entry, entries);
free(np);

}

while (!SLIST_EMPTY(&head)) { /* List Deletion. */
n1 = SLIST_FIRST(&head);
SLIST_REMOVE_HEAD(&head, entries);
free(n1);

}

SINGLY-LINKED TAIL QUEUES

A singly-linked tail queue is headed by a structure defined

by the
STAILQ_HEAD macro. This structure contains a pair of point

ers, one to
the first element in the tail queue and the other to the

last element in
the tail queue. 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 tail queue

after an
existing element, at the head of the tail queue, or at the

end of the
tail queue. A STAILQ_HEAD structure is declared as follows:

STAILQ_HEAD(HEADNAME, TYPE) head;

where HEADNAME is the name of the structure to be defined,

and 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 macro STAILQ_HEAD_INITIALIZER evaluates to an initializ

er for the
tail queue head.

The macro STAILQ_CONCAT concatenates the tail queue headed

by head2 onto
the end of the one headed by head1 removing all entries from

the former.

The macro STAILQ_EMPTY evaluates to true if there are no

items on the
tail queue.

The macro STAILQ_ENTRY declares a structure that connects

the elements in
the tail queue.

The macro STAILQ_FIRST returns the first item on the tail

queue or NULL
if the tail queue is empty.

The macro STAILQ_FOREACH traverses the tail queue referenced

by head in
the forward direction, assigning each element in turn to

var.

The macro STAILQ_FOREACH_SAFE traverses the tail queue ref

erenced by head
in the forward direction, assigning each element in turn to

var. However, unlike STAILQ_FOREACH() here it is permitted to both

remove var as
well as free it from within the loop safely without inter

fering with the
traversal.

The macro STAILQ_INIT initializes the tail queue referenced

by head.

The macro STAILQ_INSERT_HEAD inserts the new element elm at

the head of
the tail queue.

The macro STAILQ_INSERT_TAIL inserts the new element elm at

the end of
the tail queue.

The macro STAILQ_INSERT_AFTER inserts the new element elm

after the element listelm.

The macro STAILQ_LAST returns the last item on the tail

queue. If the
tail queue is empty the return value is undefined.

The macro STAILQ_NEXT returns the next item on the tail

queue, or NULL
this item is the last.

The macro STAILQ_REMOVE_HEAD removes the element at the head

of the tail
queue. For optimum efficiency, elements being removed from

the head of
the tail queue should use this macro explicitly rather than

the generic
STAILQ_REMOVE macro.

The macro STAILQ_REMOVE removes the element elm from the

tail queue.

SINGLY-LINKED TAIL QUEUE EXAMPLE

STAILQ_HEAD(stailhead, entry) head =

STAILQ_HEAD_INITIALIZER(head);

struct stailhead *headp; /* Singly-linked

tail queue head. */
struct entry {
...
STAILQ_ENTRY(entry) entries; /* Tail queue. */
...

} *n1, *n2, *n3, *np;

STAILQ_INIT(&head); /* Initialize the

queue. */

n1 = malloc(sizeof(struct entry)); /* Insert at the

head. */
STAILQ_INSERT_HEAD(&head, n1, entries);

n1 = malloc(sizeof(struct entry)); /* Insert at the

tail. */
STAILQ_INSERT_TAIL(&head, n1, entries);

n2 = malloc(sizeof(struct entry)); /* Insert after. */
STAILQ_INSERT_AFTER(&head, n1, n2, entries);
/* Deletion. */

STAILQ_REMOVE(&head, n2, entry, entries);
free(n2);
/* Deletion from the

head. */

n3 = STAILQ_FIRST(&head);
STAILQ_REMOVE_HEAD(&head, entries);
free(n3);/* Forward traver

sal. */

STAILQ_FOREACH(np, &head, entries)
np-> ...
/* Safe forward

traversal. */

STAILQ_FOREACH_SAFE(np, &head, entries, np_temp) {
np->do_stuff();
...
STAILQ_REMOVE(&head, np, entry, entries);
free(np);

}
/* TailQ Deletion.

*/

while (!STAILQ_EMPTY(&head)) {
n1 = STAILQ_FIRST(&head);
STAILQ_REMOVE_HEAD(&head, entries);
free(n1);

}
/* Faster TailQ

Deletion. */

n1 = STAILQ_FIRST(&head);
while (n1 != NULL) {
n2 = STAILQ_NEXT(n1, entries);
free(n1);
n1 = n2;

}
STAILQ_INIT(&head);

LISTS

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 fol

lows:

LIST_HEAD(HEADNAME, TYPE) head;

where HEADNAME is the name of the structure to be defined,

and 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 macro LIST_HEAD_INITIALIZER evaluates to an initializer

for the list
head.

The macro LIST_EMPTY evaluates to true if there are no ele

ments in the
list.

The macro LIST_ENTRY declares a structure that connects the

elements in
the list.

The macro LIST_FIRST returns the first element in the list

or NULL if the
list is empty.

The macro LIST_FOREACH traverses the list referenced by head

in the forward direction, assigning each element in turn to var.

The macro LIST_FOREACH_SAFE traverses the list referenced by

head in the
forward direction, assigning each element in turn to var.

However,
unlike LIST_FOREACH() here it is permitted to both remove

var as well as
free it from within the loop safely without interfering with

the traversal.

The macro LIST_INIT initializes the list referenced by head.

The macro LIST_INSERT_HEAD inserts the new element elm at

the head of the
list.

The macro LIST_INSERT_AFTER inserts the new element elm af

ter the element
listelm.

The macro LIST_INSERT_BEFORE inserts the new element elm be

fore the element listelm.

The macro LIST_NEXT returns the next element in the list, or

NULL if this
is the last.

The macro LIST_REMOVE removes the element elm from the list.

LIST EXAMPLE

LIST_HEAD(listhead, entry) head =

LIST_HEAD_INITIALIZER(head);

struct listhead *headp; /* List head. */
struct entry {
...
LIST_ENTRY(entry) entries; /* List. */
...

} *n1, *n2, *n3, *np, *np_temp;

LIST_INIT(&head); /* Initialize the

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);

n3 = malloc(sizeof(struct entry)); /* Insert before. */
LIST_INSERT_BEFORE(n2, n3, entries);

LIST_REMOVE(n2, entries); /* Deletion. */
free(n2);/* Forward traver

sal. */

LIST_FOREACH(np, &head, entries)
np-> ...

/* Safe forward

traversal. */

LIST_FOREACH_SAFE(np, &head, entries, np_temp) {
np->do_stuff();
...
LIST_REMOVE(np, entries);
free(np);

}

while (!LIST_EMPTY(&head)) { /* List Deletion. */
n1 = LIST_FIRST(&head);
LIST_REMOVE(n1, entries);
free(n1);

}

n1 = LIST_FIRST(&head); /* Faster List Dele

tion. */
while (n1 != NULL) {
n2 = LIST_NEXT(n1, entries);
free(n1);
n1 = n2;

}
LIST_INIT(&head);

TAIL QUEUES

A tail queue is headed by a structure defined by the

TAILQ_HEAD

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 tail
queue after an existing element, before an existing element,

at the head
of the tail queue, or at the end of the tail 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 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 macro TAILQ_HEAD_INITIALIZER evaluates to an initializer

for the tail
queue head.

The macro TAILQ_CONCAT concatenates the tail queue headed by

head2 onto
the end of the one headed by head1 removing all entries from

the former.

The macro TAILQ_EMPTY evaluates to true if there are no

items on the tail
queue.

The macro TAILQ_ENTRY declares a structure that connects the

elements in
the tail queue.

The macro TAILQ_FIRST returns the first item on the tail

queue or NULL if
the tail queue is empty.

The macro TAILQ_FOREACH traverses the tail queue referenced

by head in
the forward direction, assigning each element in turn to

var. var is set
to NULL if the loop completes normally, or if there were no

elements.

The macro TAILQ_FOREACH_REVERSE traverses the tail queue

referenced by
head in the reverse direction, assigning each element in

turn to var.

The macros TAILQ_FOREACH_SAFE and TAILQ_FOREACH_REVERSE_SAFE

traverse the
list referenced by head in the forward or reverse direction

respectively,
assigning each element in turn to var. However, unlike

their unsafe
counterparts, TAILQ_FOREACH and TAILQ_FOREACH_REVERSE permit

to both
remove var as well as free it from within the loop safely

without interfering with the traversal.

The macro TAILQ_INIT initializes the tail queue referenced

by head.

The macro TAILQ_INSERT_HEAD inserts the new element elm at

the head of
the tail queue.

The macro TAILQ_INSERT_TAIL inserts the new element elm at

the end of the
tail queue.

The macro TAILQ_INSERT_AFTER inserts the new element elm af

ter the element listelm.

The macro TAILQ_INSERT_BEFORE inserts the new element elm

before the element listelm.

The macro TAILQ_LAST returns the last item on the tail

queue. If the
tail queue is empty the return value is undefined.

The macro TAILQ_NEXT returns the next item on the tail

queue, or NULL if
this item is the last.

The macro TAILQ_PREV returns the previous item on the tail

queue, or NULL
if this item is the first.

The macro TAILQ_REMOVE removes the element elm from the tail

queue.

TAIL QUEUE EXAMPLE

TAILQ_HEAD(tailhead, entry) head =

TAILQ_HEAD_INITIALIZER(head);

struct tailhead *headp; /* Tail queue head.

*/
struct entry {
...
TAILQ_ENTRY(entry) entries; /* Tail queue. */
...

} *n1, *n2, *n3, *np;

TAILQ_INIT(&head); /* Initialize the

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);

n3 = malloc(sizeof(struct entry)); /* Insert before. */
TAILQ_INSERT_BEFORE(n2, n3, entries);

TAILQ_REMOVE(&head, n2, entries); /* Deletion. */
free(n2);/* Forward traver

sal. */

TAILQ_FOREACH(np, &head, entries)
np-> ...
/* Safe forward

traversal. */

TAILQ_FOREACH_SAFE(np, &head, entries, np_temp) {
np->do_stuff();
...
TAILQ_REMOVE(&head, np, entries);
free(np);

}/* Reverse traver

sal. */

TAILQ_FOREACH_REVERSE(np, &head, tailhead, entries)
np-> ...
/* TailQ Deletion.

*/

while (!TAILQ_EMPTY(&head)) {
n1 = TAILQ_FIRST(&head);
TAILQ_REMOVE(&head, n1, entries);
free(n1);

}
/* Faster TailQ

Deletion. */

n1 = TAILQ_FIRST(&head);
while (n1 != NULL) {
n2 = TAILQ_NEXT(n1, entries);
free(n1);
n1 = n2;

}
TAILQ_INIT(&head);

HISTORY

The queue functions first appeared in 4.4BSD.

BSD January 24, 1994

BSD