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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | STANDARDS | HISTORY | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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SLIST(3) Library Functions Manual SLIST(3)
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
Standard C library (libc, -lc)
#include <sys/queue.h>
SLIST_ENTRY(TYPE);
SLIST_HEAD(HEADNAME, TYPE);
SLIST_HEAD SLIST_HEAD_INITIALIZER(SLIST_HEAD head);
void SLIST_INIT(SLIST_HEAD *head);
int SLIST_EMPTY(SLIST_HEAD *head);
void SLIST_INSERT_HEAD(SLIST_HEAD *head,
struct TYPE *elm, SLIST_ENTRY NAME);
void SLIST_INSERT_AFTER(struct TYPE *listelm,
struct TYPE *elm, SLIST_ENTRY NAME);
struct TYPE *SLIST_FIRST(SLIST_HEAD *head);
struct TYPE *SLIST_NEXT(struct TYPE *elm, SLIST_ENTRY NAME);
SLIST_FOREACH(struct TYPE *var, SLIST_HEAD *head, SLIST_ENTRY NAME);
void SLIST_REMOVE(SLIST_HEAD *head, struct TYPE *elm, TYPE,
SLIST_ENTRY NAME);
void SLIST_REMOVE_HEAD(SLIST_HEAD *head,
SLIST_ENTRY NAME);
These macros define and operate on 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, named
NAME. The argument HEADNAME is the name of a user-defined
structure that must be declared using the macro SLIST_HEAD().
Creation
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.)
SLIST_ENTRY() declares a structure that connects the elements in
the list.
SLIST_HEAD_INITIALIZER() evaluates to an initializer for the list
head.
SLIST_INIT() initializes the list referenced by head.
SLIST_EMPTY() evaluates to true if there are no elements in the
list.
Insertion
SLIST_INSERT_HEAD() inserts the new element elm at the head of the
list.
SLIST_INSERT_AFTER() inserts the new element elm after the element
listelm.
Traversal
SLIST_FIRST() returns the first element in the list, or NULL if
the list is empty.
SLIST_NEXT() returns the next element in the list.
SLIST_FOREACH() traverses the list referenced by head in the
forward direction, assigning each element in turn to var.
Removal
SLIST_REMOVE() removes the element elm from the list.
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().
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.
BSD.
4.4BSD.
SLIST_FOREACH() doesn't allow var to be removed or freed within
the loop, as it would interfere with the traversal.
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.
#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 (unsigned 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);
}
insque(3), queue(7)
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user-space interface documentation) project. Information about
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⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 SLIST(3)
Pages that refer to this page: queue(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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