QUEUE(3) | Library Functions Manual | QUEUE(3) |
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
#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);
These macros define and operate on four types of data structures: singly-linked lists, singly-linked tail queues, lists, and tail queues. All four structures support the following functionality:
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.
Singly-linked tail queues add the following functionality:
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:
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:
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 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. An
SLIST_HEAD structure is declared 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 elements 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 after 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.
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 traversal. */ 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); }
A singly-linked tail queue is headed by a structure defined by the
STAILQ_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 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 initializer 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
referenced 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 interfering 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
NULL.
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.
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 traversal. */ 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);
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 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 elements 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 after the element
listelm.
The macro LIST_INSERT_BEFORE
inserts the
new element elm before 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_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 traversal. */ 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 Deletion. */ while (n1 != NULL) { n2 = LIST_NEXT(n1, entries); free(n1); n1 = n2; } LIST_INIT(&head);
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 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 after 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 NULL.
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.
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 traversal. */ 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 traversal. */ 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);
The queue
functions first appeared in
4.4BSD.
January 24, 1994 | macOS 14.6 |