SLIST(3) Library Functions 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
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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,
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().
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 lis-
telm.
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_RE-
MOVE().
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.
STANDARDS
Not in POSIX.1, POSIX.1-2001, or POSIX.1-2008. Present on the BSDs
(SLIST macros first appeared in 4.4BSD).
BUGS
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.
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 (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);
}
SEE ALSO
insque(3), queue(7)
Linux man-pages 6.03 2022-10-30 SLIST(3)
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