NAME¶

TAILQ_CONCAT, TAILQ_EMPTY, TAILQ_ENTRY, TAILQ_FIRST, TAILQ_FOREACH, TAILQ_FOREACH_REVERSE, TAILQ_HEAD, TAILQ_HEAD_INITIALIZER, TAILQ_INIT, TAILQ_INSERT_AFTER, TAILQ_INSERT_BEFORE, TAILQ_INSERT_HEAD, TAILQ_INSERT_TAIL, TAILQ_LAST, TAILQ_NEXT, TAILQ_PREV, TAILQ_REMOVE - implementation of a doubly linked tail queue

LIBRARY¶

Standard C library (libc, -lc)

SYNOPSIS¶

#include <sys/queue.h>

TAILQ_ENTRY(TYPE);

TAILQ_HEAD(HEADNAME, TYPE);
TAILQ_HEAD TAILQ_HEAD_INITIALIZER(TAILQ_HEAD head);
void TAILQ_INIT(TAILQ_HEAD *head);

int TAILQ_EMPTY(TAILQ_HEAD *head);

void TAILQ_INSERT_HEAD(TAILQ_HEAD *head,
                         struct TYPE *elm, TAILQ_ENTRY NAME);
void TAILQ_INSERT_TAIL(TAILQ_HEAD *head,
                         struct TYPE *elm, TAILQ_ENTRY NAME);
void TAILQ_INSERT_BEFORE(struct TYPE *listelm,
                         struct TYPE *elm, TAILQ_ENTRY NAME);
void TAILQ_INSERT_AFTER(TAILQ_HEAD *head, struct TYPE *listelm,
                         struct TYPE *elm, TAILQ_ENTRY NAME);

struct TYPE *TAILQ_FIRST(TAILQ_HEAD *head);
struct TYPE *TAILQ_LAST(TAILQ_HEAD *head, HEADNAME);
struct TYPE *TAILQ_PREV(struct TYPE *elm, HEADNAME, TAILQ_ENTRY NAME);
struct TYPE *TAILQ_NEXT(struct TYPE *elm, TAILQ_ENTRY NAME);

TAILQ_FOREACH(struct TYPE *var, TAILQ_HEAD *head,
                         TAILQ_ENTRY NAME);
TAILQ_FOREACH_REVERSE(struct TYPE *var, TAILQ_HEAD *head, HEADNAME,
                         TAILQ_ENTRY NAME);

void TAILQ_REMOVE(TAILQ_HEAD *head, struct TYPE *elm,
                         TAILQ_ENTRY NAME);

void TAILQ_CONCAT(TAILQ_HEAD *head1, TAILQ_HEAD *head2,
                         TAILQ_ENTRY NAME);

DESCRIPTION¶

These macros define and operate on doubly linked tail queues.

In the macro definitions, TYPE is the name of a user defined structure, that must contain a field of type TAILQ_ENTRY, named NAME. The argument HEADNAME is the name of a user defined structure that must be declared using the macro TAILQ_HEAD().

TAILQ_HEAD(HEADNAME, TYPE) head;

struct HEADNAME *headp;

RETURN VALUE¶

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

TAILQ_FIRST(), TAILQ_LAST(), TAILQ_PREV(), and TAILQ_NEXT() return a pointer to the first, last, previous, or next TYPE structure, respectively.

TAILQ_HEAD_INITIALIZER() returns an initializer that can be assigned to the queue head.

STANDARDS¶

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

BUGS¶

TAILQ_FOREACH() and TAILQ_FOREACH_REVERSE() don't allow var to be removed or freed within the loop, as it would interfere with the traversal. TAILQ_FOREACH_SAFE() and TAILQ_FOREACH_REVERSE_SAFE(), which are present on the BSDs but are not present in glibc, fix 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;


    TAILQ_ENTRY(entry) entries;             /* Tail queue */
};
TAILQ_HEAD(tailhead, entry);
int
main(void)
{


    struct entry *n1, *n2, *n3, *np;


    struct tailhead head;                   /* Tail queue head */


    int i;


    TAILQ_INIT(&head);                      /* Initialize the queue */


    n1 = malloc(sizeof(struct entry));      /* Insert at the head */


    TAILQ_INSERT_HEAD(&head, n1, entries);


    n1 = malloc(sizeof(struct entry));      /* Insert at the tail */


    TAILQ_INSERT_TAIL(&head, n1, entries);


    n2 = malloc(sizeof(struct entry));      /* Insert after */


    TAILQ_INSERT_AFTER(&head, n1, n2, entries);


    n3 = malloc(sizeof(struct entry));      /* Insert before */


    TAILQ_INSERT_BEFORE(n2, n3, entries);


    TAILQ_REMOVE(&head, n2, entries);       /* Deletion */


    free(n2);


                                            /* Forward traversal */


    i = 0;


    TAILQ_FOREACH(np, &head, entries)


        np->data = i++;


                                            /* Reverse traversal */


    TAILQ_FOREACH_REVERSE(np, &head, tailhead, entries)


        printf("%i\n", np->data);


                                            /* TailQ deletion */


    n1 = TAILQ_FIRST(&head);


    while (n1 != NULL) {


        n2 = TAILQ_NEXT(n1, entries);


        free(n1);


        n1 = n2;


    }


    TAILQ_INIT(&head);


    exit(EXIT_SUCCESS);
}

SEE ALSO¶

insque(3), queue(7)