slist

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
       This page is part of release 5.10 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)