Name
SIMPLEQ_EMPTY, SIMPLEQ_ENTRY, SIMPLEQ_FIRST, SIMPLEQ_FOREACH, SIMPLEQ_HEAD, SIMPLEQ_HEAD_INITIALIZER, SIMPLEQ_INIT, SIMPLEQ_INSERT_AFTER, SIMPLEQ_INSERT_HEAD, SIMPLEQ_INSERT_TAIL, SIMPLEQ_NEXT, SIMPLEQ_REMOVE, SIMPLEQ_REMOVE_HEAD, 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, STAILQ_REMOVE_HEAD — implementation of a singly linked tail queue
Synopsis
#include <sys/queue.h>
STAILQ_ENTRY( |
TYPE); |
STAILQ_HEAD( |
HEADNAME, |
TYPE); |
STAILQ_HEAD
STAILQ_HEAD_INITIALIZER( |
STAILQ_HEAD head); |
void
STAILQ_INIT( |
STAILQ_HEAD *head); |
int
STAILQ_EMPTY( |
STAILQ_HEAD *head); |
void
STAILQ_INSERT_HEAD( |
STAILQ_HEAD *head, |
| struct TYPE *elm, | |
STAILQ_ENTRY NAME); |
void
STAILQ_INSERT_TAIL( |
STAILQ_HEAD *head, |
| struct TYPE *elm, | |
STAILQ_ENTRY NAME); |
void
STAILQ_INSERT_AFTER( |
STAILQ_HEAD *head, |
| struct TYPE *listelm, | |
| struct TYPE *elm, | |
STAILQ_ENTRY NAME); |
struct TYPE
*STAILQ_FIRST( |
STAILQ_HEAD *head); |
struct TYPE
*STAILQ_NEXT( |
struct TYPE *elm, |
STAILQ_ENTRY NAME); |
STAILQ_FOREACH( |
struct TYPE *var, |
| STAILQ_HEAD *head, | |
STAILQ_ENTRY NAME); |
void
STAILQ_REMOVE( |
STAILQ_HEAD *head, |
| struct TYPE *elm, | |
| TYPE, | |
STAILQ_ENTRY NAME); |
void
STAILQ_REMOVE_HEAD( |
STAILQ_HEAD *head, |
STAILQ_ENTRY NAME); |
void
STAILQ_CONCAT( |
STAILQ_HEAD *head1, |
STAILQ_HEAD *head2); |
![[Note]](../stylesheet/note.png) |
Note |
|---|---|
| Identical macros prefixed with SIMPLEQ instead of STAILQ exist; see NOTES. |
DESCRIPTION
These macros define and operate on singly linked tail queues.
In the macro definitions, TYPE is the name of a
user-defined structure, that must contain a field of type
STAILQ_ENTRY, named NAME. The argument HEADNAME is the name of a
user-defined structure that must be declared using the macro
STAILQ_HEAD().
Creation
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 struct HEADNAME is 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.)
STAILQ_ENTRY() declares a
structure that connects the elements in the tail queue.
STAILQ_HEAD_INITIALIZER()
evaluates to an initializer for the tail queue head.
STAILQ_INIT() initializes
the tail queue referenced by head.
STAILQ_EMPTY() evaluates
to true if there are no items on the tail queue.
Insertion
STAILQ_INSERT_HEAD()
inserts the new element elm at the head of the tail
queue.
STAILQ_INSERT_TAIL()
inserts the new element elm at the end of the tail
queue.
STAILQ_INSERT_AFTER()
inserts the new element elm after the element
listelm.
Traversal
STAILQ_FIRST() returns the
first item on the tail queue or NULL if the tail queue is
empty.
STAILQ_NEXT() returns the
next item on the tail queue, or NULL this item is the
last.
STAILQ_FOREACH() traverses
the tail queue referenced by head in the forward
direction, assigning each element in turn to var.
RETURN VALUE
STAILQ_EMPTY() returns
nonzero if the queue is empty, and zero if the queue contains
at least one entry.
STAILQ_FIRST(), and
STAILQ_NEXT() return a pointer
to the first or next TYPE structure,
respectively.
STAILQ_HEAD_INITIALIZER()
returns an initializer that can be assigned to the queue
head.
CONFORMING TO
Not in POSIX.1, POSIX.1-2001, or POSIX.1-2008. Present on the BSDs (STAILQ macros first appeared in 4.4BSD).
BUGS
STAILQ_FOREACH() doesn't
allow var to be
removed or freed within the loop, as it would interfere with
the traversal. STAILQ_FOREACH_SAFE(), which is present on
the BSDs but is not present in glibc, fixes this limitation
by allowing var to
safely be removed from the list and freed from within the
loop without interfering with the traversal.
NOTES
Some BSDs provide SIMPLEQ instead of STAILQ. They are
identical, but for historical reasons they were named
differently on different BSDs. STAILQ originated on FreeBSD,
and SIMPLEQ originated on NetBSD. For compatibility reasons,
some systems provide both sets of macros. Glibc provides both
STAILQ and SIMPLEQ, which are identical except for a missing
SIMPLEQ equivalent to STAILQ_CONCAT().
EXAMPLES
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/queue.h>
struct entry {
int data;
STAILQ_ENTRY(entry) entries; /* Singly linked tail queue */
};
STAILQ_HEAD(stailhead, entry);
int
main(void)
{
struct entry *n1, *n2, *n3, *np;
struct stailhead head; /* Singly linked tail queue
head */
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);
STAILQ_REMOVE(&head, n2, entry, entries); /* Deletion */
free(n2);
n3 = STAILQ_FIRST(&head);
STAILQ_REMOVE_HEAD(&head, entries); /* Deletion from the head */
free(n3);
n1 = STAILQ_FIRST(&head);
n1−>data = 0;
for (int i = 1; i < 5; i++) {
n1 = malloc(sizeof(struct entry));
STAILQ_INSERT_HEAD(&head, n1, entries);
n1−>data = i;
}
/* Forward traversal */
STAILQ_FOREACH(np, &head, entries)
printf("%i\n", np−>data);
/* TailQ deletion */
n1 = STAILQ_FIRST(&head);
while (n1 != NULL) {
n2 = STAILQ_NEXT(n1, entries);
free(n1);
n1 = n2;
}
STAILQ_INIT(&head);
exit(EXIT_SUCCESS);
}