SIMPLEQ_EMPTY, SIMPLEQ_ENTRY, SIMPLEQ_FIRST, SIMPLEQ_FOREACH, SIMPLEQ_HEAD, SIMPLEQ_HEAD_INITIALIZER,

STAILQ_FOREACH() doesn't allow var to be removed or freed within the loop, as it would interfere with the
       traversal.  STAILQ_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.

       These macros define and operate on singly linked tail queues.

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

   Creation
       A  singly  linked tail queue is headed by a structure defined by the STAILQ_HEAD() macro.  This structure
       contains a pair of pointers, one to the first element in the tail queue and the other to the last element
       in the tail queue.  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 tail queue after an
       existing element, at the head of the tail queue, or  at  the  end  of  the  tail  queue.   A  STAILQ_HEAD
       structure is declared as follows:

           STAILQ_HEAD(HEADNAME, TYPE) head;

       where  structHEADNAME is the structure to be defined, and structTYPE is the type of the elements to be
       linked into the tail queue.  A pointer to the head of the tail queue can later be declared as:

           struct HEADNAME *headp;

       (The names head and headp are user selectable.)

       STAILQ_ENTRY() declares a structure that connects the elements in the tail queue.

       STAILQ_HEAD_INITIALIZER() evaluates to an initializer for the tail queue head.

       STAILQ_INIT() initializes the tail queue referenced by head.

       STAILQ_EMPTY() evaluates to true if there are no items on the tail queue.

   InsertionSTAILQ_INSERT_HEAD() inserts the new element elm at the head of the tail queue.

       STAILQ_INSERT_TAIL() inserts the new element elm at the end of the tail queue.

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

   TraversalSTAILQ_FIRST() returns the first item on the tail queue or NULL if the tail queue is empty.

       STAILQ_NEXT() returns the next item on the tail queue, or NULL this item is the last.

       STAILQ_FOREACH() traverses the tail queue referenced by head in the  forward  direction,  assigning  each
       element in turn to var.

   RemovalSTAILQ_REMOVE() removes the element elm from the tail queue.

       STAILQ_REMOVE_HEAD() removes the element at the head of the tail queue.  For optimum efficiency, elements
       being  removed  from  the head of the tail queue should use this macro explicitly rather than the generic
       STAILQ_REMOVE() macro.

   OtherfeaturesSTAILQ_CONCAT() concatenates the tail queue headed by head2 onto the end  of  the  one  headed  by  head1
       removing all entries from the former.

       #include <stddef.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/queue.h>

       struct entry {
           int data;
           STAILQ_ENTRY(entry) entries;        /* Singly linked tail queue */
       };

       STAILQ_HEAD(stailhead, entry);

       int
       main(void)
       {
           struct entry *n1, *n2, *n3, *np;
           struct stailhead head;                  /* Singly linked tail queue
                                                      head */

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

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

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

           n2 = malloc(sizeof(struct entry));      /* Insert after */
           STAILQ_INSERT_AFTER(&head, n1, n2, entries);

           STAILQ_REMOVE(&head, n2, entry, entries); /* Deletion */
           free(n2);

           n3 = STAILQ_FIRST(&head);
           STAILQ_REMOVE_HEAD(&head, entries);     /* Deletion from the head */
           free(n3);

           n1 = STAILQ_FIRST(&head);
           n1->data = 0;
           for (unsigned int i = 1; i < 5; i++) {
               n1 = malloc(sizeof(struct entry));
               STAILQ_INSERT_HEAD(&head, n1, entries);
               n1->data = i;
           }
                                                   /* Forward traversal */
           STAILQ_FOREACH(np, &head, entries)
               printf("%i\n", np->data);
                                                   /* TailQ deletion */
           n1 = STAILQ_FIRST(&head);
           while (n1 != NULL) {
               n2 = STAILQ_NEXT(n1, entries);
               free(n1);
               n1 = n2;
           }
           STAILQ_INIT(&head);

           exit(EXIT_SUCCESS);
       }

       4.4BSD.

       Standard C library (libc, -lc)

       SIMPLEQ_EMPTY,  SIMPLEQ_ENTRY,  SIMPLEQ_FIRST,  SIMPLEQ_FOREACH,  SIMPLEQ_HEAD, SIMPLEQ_HEAD_INITIALIZER,
       SIMPLEQ_INIT,    SIMPLEQ_INSERT_AFTER,    SIMPLEQ_INSERT_HEAD,     SIMPLEQ_INSERT_TAIL,     SIMPLEQ_NEXT,
       SIMPLEQ_REMOVE,    SIMPLEQ_REMOVE_HEAD,    STAILQ_CONCAT,   STAILQ_EMPTY,   STAILQ_ENTRY,   STAILQ_FIRST,
       STAILQ_FOREACH,     STAILQ_HEAD,     STAILQ_HEAD_INITIALIZER,      STAILQ_INIT,      STAILQ_INSERT_AFTER,
       STAILQ_INSERT_HEAD,  STAILQ_INSERT_TAIL, STAILQ_NEXT, STAILQ_REMOVE, STAILQ_REMOVE_HEAD, - implementation
       of a singly linked tail queue

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

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

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

insque(3), queue(7)

Linux man-pages 6.9.1                              2024-06-16                                          STAILQ(3)

       BSD.

#include<sys/queue.h>STAILQ_ENTRY(TYPE);STAILQ_HEAD(HEADNAME,TYPE);STAILQ_HEADSTAILQ_HEAD_INITIALIZER(STAILQ_HEADhead);voidSTAILQ_INIT(STAILQ_HEAD*head);intSTAILQ_EMPTY(STAILQ_HEAD*head);voidSTAILQ_INSERT_HEAD(STAILQ_HEAD*head,structTYPE*elm,STAILQ_ENTRYNAME);voidSTAILQ_INSERT_TAIL(STAILQ_HEAD*head,structTYPE*elm,STAILQ_ENTRYNAME);voidSTAILQ_INSERT_AFTER(STAILQ_HEAD*head,structTYPE*listelm,structTYPE*elm,STAILQ_ENTRYNAME);structTYPE*STAILQ_FIRST(STAILQ_HEAD*head);structTYPE*STAILQ_NEXT(structTYPE*elm,STAILQ_ENTRYNAME);STAILQ_FOREACH(structTYPE*var,STAILQ_HEAD*head,STAILQ_ENTRYNAME);voidSTAILQ_REMOVE(STAILQ_HEAD*head,structTYPE*elm,TYPE,STAILQ_ENTRYNAME);voidSTAILQ_REMOVE_HEAD(STAILQ_HEAD*head,STAILQ_ENTRYNAME);voidSTAILQ_CONCAT(STAILQ_HEAD*head1,STAILQ_HEAD*head2);Note: Identical macros prefixed with SIMPLEQ instead of STAILQ exist; see VERSIONS.

       Some  BSDs  provide  SIMPLEQ instead of STAILQ.  They are identical, but for historical reasons they were
       named differently on different BSDs.  STAILQ originated on FreeBSD, and  SIMPLEQ  originated  on  NetBSD.
       For  compatibility  reasons,  some  systems  provide both sets of macros.  glibc provides both STAILQ and
       SIMPLEQ, which are identical except for a missing SIMPLEQ equivalent to STAILQ_CONCAT().