list(3) — Linux manual page

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

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

NAME         top

       LIST_EMPTY,    LIST_ENTRY,   LIST_FIRST,   LIST_FOREACH,   LIST_HEAD,
       LIST_HEAD_INITIALIZER, LIST_INIT, LIST_INSERT_AFTER,  LIST_INSERT_BE‐
       FORE, LIST_INSERT_HEAD, LIST_NEXT, LIST_PREV, LIST_REMOVE - implemen‐
       tation of a doubly linked list

SYNOPSIS         top

       #include <sys/queue.h>

       int LIST_EMPTY(LIST_HEAD *head);

       LIST_ENTRY(TYPE);

       struct TYPE *LIST_FIRST(LIST_HEAD *head);

       LIST_FOREACH(struct TYPE *var, LIST_HEAD *head, LIST_ENTRY NAME);

       LIST_HEAD(HEADNAME, TYPE);

       LIST_HEAD LIST_HEAD_INITIALIZER(LIST_HEAD head);

       void LIST_INIT(LIST_HEAD *head);

       void LIST_INSERT_AFTER(struct TYPE *listelm, struct TYPE *elm,
                       LIST_ENTRY NAME);

       void LIST_INSERT_BEFORE(struct TYPE *listelm, struct TYPE *elm,
                       LIST_ENTRY NAME);

       void LIST_INSERT_HEAD(LIST_HEAD *head, struct TYPE *elm,
                       LIST_ENTRY NAME);

       struct TYPE *LIST_NEXT(struct TYPE *elm, LIST_ENTRY NAME);

       void LIST_REMOVE(struct TYPE *elm, LIST_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 LIST_ENTRY, named NAME.
       The argument HEADNAME is the name of a user-defined structure that
       must be declared using the macro LIST_HEAD().

       A list is headed by a structure defined by the LIST_HEAD() macro.
       This structure contains a single pointer to the first element on the
       list.  The elements are doubly linked so that an arbitrary element
       can be removed without traversing the list.  New elements can be
       added to the list after an existing element, before an existing
       element, or at the head of the list.  A LIST_HEAD structure is
       declared as follows:

           LIST_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 LIST_HEAD_INITIALIZER() evaluates to an initializer for the
       list head.

       The macro LIST_EMPTY() evaluates to true if there are no elements in
       the list.

       The macro LIST_ENTRY() declares a structure that connects the ele‐
       ments in the list.

       The macro LIST_FIRST() returns the first element in the list or NULL
       if the list is empty.

       The macro LIST_FOREACH() traverses the list referenced by head in the
       forward direction, assigning each element in turn to var.

       The macro LIST_INIT() initializes the list referenced by head.

       The macro LIST_INSERT_HEAD() inserts the new element elm at the head
       of the list.

       The macro LIST_INSERT_AFTER() inserts the new element elm after the
       element listelm.

       The macro LIST_INSERT_BEFORE() inserts the new element elm before the
       element listelm.

       The macro LIST_NEXT() returns the next element in the list, or NULL
       if this is the last.

       The macro LIST_REMOVE() removes the element elm from the list.

RETURN VALUE         top

       LIST_EMPTY() returns nonzero if the list is empty, and zero if the
       list contains at least one entry.

       LIST_FIRST(), and LIST_NEXT() return a pointer to the first or next
       TYPE structure, respectively.

       LIST_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
       (LIST macros first appeared in 4.4BSD).

BUGS         top

       The macro LIST_FOREACH() doesn't allow var to be removed or freed
       within the loop, as it would interfere with the traversal.  The macro
       LIST_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;
           LIST_ENTRY(entry) entries;              /* List. */
       };

       LIST_HEAD(listhead, entry);

       int
       main(void)
       {
           struct entry *n1, *n2, *n3, *np;
           struct listhead head;                   /* List head. */
           int i;

           LIST_INIT(&head);                       /* Initialize the list. */

           n1 = malloc(sizeof(struct entry));      /* Insert at the head. */
           LIST_INSERT_HEAD(&head, n1, entries);

           n2 = malloc(sizeof(struct entry));      /* Insert after. */
           LIST_INSERT_AFTER(n1, n2, entries);

           n3 = malloc(sizeof(struct entry));      /* Insert before. */
           LIST_INSERT_BEFORE(n2, n3, entries);

           i = 0;                                  /* Forward traversal. */
           LIST_FOREACH(np, &head, entries)
               np->data = i++;

           LIST_REMOVE(n2, entries);               /* Deletion. */
           free(n2);
                                                   /* Forward traversal. */
           LIST_FOREACH(np, &head, entries)
               printf("%i\n", np->data);
                                                   /* List Deletion. */
           n1 = LIST_FIRST(&head);
           while (n1 != NULL) {
               n2 = LIST_NEXT(n1, entries);
               free(n1);
               n1 = n2;
           }
           LIST_INIT(&head);

           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

       insque(3), queue(7)

COLOPHON         top

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GNU                              2020-10-19                          LIST(3)

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