SLIST(3) Linux Programmer's Manual SLIST(3)
NAME
SLIST_EMPTY, SLIST_ENTRY, SLIST_FIRST, SLIST_FOREACH, SLIST_HEAD,
SLIST_HEAD_INITIALIZER, SLIST_INIT, SLIST_INSERT_AFTER, SLIST_IN-
SERT_HEAD, SLIST_NEXT, SLIST_REMOVE, SLIST_REMOVE_HEAD - implementation
of a singly linked list
SYNOPSIS
#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);
DESCRIPTION
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 argu-
ment HEADNAME is the name of a user-defined structure that must be de-
clared 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.
RETURN VALUE
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.
CONFORMING TO
Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008. Present on the BSDs
(SLIST macros first appeared in 4.4BSD).
BUGS
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.
EXAMPLES
#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);
}
SEE ALSO
insque(3), queue(7)
COLOPHON
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