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_BEFORE, LIST_INSERT_HEAD, LIST_NEXT, LIST_REMOVE -
       implementation of a doubly linked list

SYNOPSIS         top

       #include <sys/queue.h>

       LIST_ENTRY(TYPE);

       LIST_HEAD(HEADNAME, TYPE);
       LIST_HEAD LIST_HEAD_INITIALIZER(LIST_HEAD head);
       void LIST_INIT(LIST_HEAD *head);

       int LIST_EMPTY(LIST_HEAD *head);

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

       struct TYPE *LIST_FIRST(LIST_HEAD *head);
       struct TYPE *LIST_NEXT(struct TYPE *elm, LIST_ENTRY NAME);

       LIST_FOREACH(struct TYPE *var, LIST_HEAD *head, 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().

   Creation
       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.)

       LIST_ENTRY() declares a structure that connects the elements in
       the list.

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

       LIST_INIT() initializes the list referenced by head.

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

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

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

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

   Traversal
       LIST_FIRST() returns the first element in the list, or NULL if
       the list is empty.

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

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

   Removal
       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

       LIST_FOREACH() doesn't allow var to be removed or freed within
       the loop, as it would interfere with the traversal.
       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                            2021-03-22                        LIST(3)

Pages that refer to this page: man-pages(7)queue(7)