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, SLIST_REMOVE_HEAD - implementation of a singly linked list
#include <sys/queue.h>
int SLIST_EMPTY(SLIST_HEAD *head);
SLIST_ENTRY(TYPE);
struct TYPE *SLIST_FIRST(SLIST_HEAD *head);
SLIST_FOREACH(struct TYPE *var, SLIST_HEAD *head, SLIST_ENTRY NAME);
SLIST_HEAD(HEADNAME, TYPE);
SLIST_HEAD SLIST_HEAD_INITIALIZER(SLIST_HEAD head);
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);
struct TYPE *SLIST_NEXT(struct TYPE *elm, SLIST_ENTRY NAME);
void SLIST_REMOVE(SLIST_HEAD *head, struct TYPE *elm, SLIST_ENTRY NAME);
void SLIST_REMOVE_HEAD(SLIST_HEAD *head, SLIST_ENTRY NAME);
These macros define and operate on doubly linked lists.
In the macro definitions, TYPE
is the name of a user-defined
structure, that must contain a field of type SLIST_ENTRY
, named
NAME
. The argument HEADNAME
is the name of a
user-defined structure that must be declared using the macro
SLIST_HEAD().
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 struct HEADNAME
is 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 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_EMPTY() returns nonzero if the list is empty, and zero if the list contains at least one entry.
SLIST_FIRST(), and SLIST_NEXT()
return a pointer to the first or next TYPE
structure,
respectively.
SLIST_HEAD_INITIALIZER() returns an initializer that
can be assigned to the list head
.
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/queue.h>
struct entry {
int data;
SLIST_ENTRY(entry) entries; /* Singly linked List. */
};
SLIST_HEAD(slisthead, entry);
int
main(void)
{
struct entry *n1, *n2, *n3, *np;
struct slisthead head; /* Singly linked List
head. */
SLIST_INIT(&head); /* Initialize the queue. */
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);
for (int i = 0; i < 5; i++) {
n1 = malloc(sizeof(struct entry));
SLIST_INSERT_HEAD(&head, n1, entries);
n1->data = i;
}
/* Forward traversal. */
SLIST_FOREACH(np, &head, entries)
printf("%i\n", np->data);
while (!SLIST_EMPTY(&head)) { /* List Deletion. */
n1 = SLIST_FIRST(&head);
SLIST_REMOVE_HEAD(&head, entries);
free(n1);
}
SLIST_INIT(&head);
exit(EXIT_SUCCESS);
}
Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008. Present on the BSDs (SLIST macros first appeared in 4.4BSD).
The macro SLIST_FOREACH() doesn't allow var
to be removed or freed within the loop, as it would interfere with the
traversal. The macro SLIST_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.
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