SLIST_EMPTY
,
SLIST_ENTRY
,
SLIST_FIRST
,
SLIST_FOREACH
,
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_HEAD
,
STAILQ_HEAD_INITIALIZER
,
STAILQ_INIT
,
STAILQ_INSERT_AFTER
,
STAILQ_INSERT_HEAD
,
STAILQ_INSERT_TAIL
,
STAILQ_NEXT
,
STAILQ_REMOVE_HEAD
,
STAILQ_REMOVE
,
LIST_EMPTY
,
LIST_ENTRY
,
LIST_FIRST
,
LIST_FOREACH
,
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_REVERSE
,
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
,
TAILQ_SWAP
—
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_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_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_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_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);
LIST_SWAP
(
LIST_HEAD
*head1,
LIST_HEAD
*head2,
TYPE,
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_REVERSE
(
TYPE
*var,
TAILQ_HEAD
*head,
HEADNAME,
TAILQ_ENTRY
NAME);
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);
TAILQ_SWAP
(
TAILQ_HEAD
*head1,
TAILQ_HEAD
*head2,
TYPE,
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:
- Insertion of a new entry at the head of the list.
- Insertion of a new entry after any element in the list.
- O(1) removal of an entry from the head of the list.
- Forward traversal through the list.
- Swapping the contents of two lists.
Singly-linked lists are the simplest of the four 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 lists add the following functionality:
- O(n) removal of any entry in the list.
Singly-linked tail queues add the following functionality:
- Entries can be added at the end of a list.
- O(n) removal of any entry in the list.
- They may be concatenated.
However:
- All list insertions must specify the head of the list.
- Each head entry requires two pointers rather than one.
- Code size is about 15% greater and operations run about 20% slower than
singly-linked lists.
Singly-linked tail 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 and tail queues) additionally
allow:
- Insertion of a new entry before any element in the list.
- O(1) removal of any entry in the list.
However:
- Each element requires two pointers rather than one.
- Code size and execution time of operations (except for removal) is about
twice that of the singly-linked data-structures.
Linked lists are the simplest of the doubly linked data structures. They add the
following functionality over the above:
- They may be traversed backwards.
However:
- To traverse backwards, an entry to begin the traversal and the list in
which it is contained must be specified.
Tail queues add the following functionality:
- Entries can be added at the end of a list.
- They may be traversed backwards, from tail to head.
- They may be concatenated.
However:
- All list insertions and removals must specify the head of the list.
- Each head entry requires two pointers rather than one.
- 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 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:
(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_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-> ...
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:
(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_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_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-> ...
/* 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:
(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_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-> ...
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:
(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 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.
The macro
TAILQ_SWAP
swaps the contents of
head1 and
head2.
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-> ...
/* 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);
n2 = malloc(sizeof(struct entry)); /* Insert before. */
CIRCLEQ_INSERT_BEFORE(&head, n1, n2, entries);
/* Forward traversal. */
for (np = head.cqh_first; np != (void *)&head;
np = np->entries.cqe_next)
np-> ...
/* Reverse traversal. */
for (np = head.cqh_last; np != (void *)&head; np = np->entries.cqe_prev)
np-> ...
/* Delete. */
while (head.cqh_first != (void *)&head)
CIRCLEQ_REMOVE(&head, head.cqh_first, entries);
Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008. Present on the BSDs.
queue
functions first appeared in
4.4BSD.
insque(3)