slist(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | BUGS | EXAMPLES | SEE ALSO | COLOPHON

SLIST(3)                  Linux Programmer's Manual                 SLIST(3)

NAME         top

       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 - implementa‐
       tion of a singly linked list

SYNOPSIS         top

       #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         top

       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 ele‐
       ments 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         top

       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         top

       Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008.  Present on the BSDs
       (SLIST macros first appeared in 4.4BSD).

BUGS         top

       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         top

       #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         top

       insque(3), queue(7)

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

GNU                              2020-10-21                         SLIST(3)

Pages that refer to this page: queue(3)queue(7)