SLIST_EMPTY, SLIST_ENTRY, SLIST_FIRST, SLIST_FOREACH, SLIST_HEAD, SLIST_HEAD_INITIALIZER, SLIST_INIT,

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

       These macros define and operate on singly 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  argument  HEADNAME is the name of a user-defined structure that must be
       declared using the macro SLIST_HEAD().

   Creation
       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 structHEADNAME is the structure to be defined, and structTYPE 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.)

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

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

       SLIST_INIT() initializes the list referenced by head.

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

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

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

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

       SLIST_NEXT() returns the next element in the list.

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

   RemovalSLIST_REMOVE() removes the element elm from the list.

       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().

       #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 (unsigned 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);
       }

       4.4BSD.

       Standard C library (libc, -lc)

       SLIST_EMPTY,  SLIST_ENTRY,  SLIST_FIRST,  SLIST_FOREACH,  SLIST_HEAD, SLIST_HEAD_INITIALIZER, SLIST_INIT,
       SLIST_INSERT_AFTER, SLIST_INSERT_HEAD, SLIST_NEXT, SLIST_REMOVE, SLIST_REMOVE_HEAD - implementation of  a
       singly linked list

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.

insque(3), queue(7)

Linux man-pages 6.9.1                              2024-06-15                                           SLIST(3)

       BSD.

#include<sys/queue.h>SLIST_ENTRY(TYPE);SLIST_HEAD(HEADNAME,TYPE);SLIST_HEADSLIST_HEAD_INITIALIZER(SLIST_HEADhead);voidSLIST_INIT(SLIST_HEAD*head);intSLIST_EMPTY(SLIST_HEAD*head);voidSLIST_INSERT_HEAD(SLIST_HEAD*head,structTYPE*elm,SLIST_ENTRYNAME);voidSLIST_INSERT_AFTER(structTYPE*listelm,structTYPE*elm,SLIST_ENTRYNAME);structTYPE*SLIST_FIRST(SLIST_HEAD*head);structTYPE*SLIST_NEXT(structTYPE*elm,SLIST_ENTRYNAME);SLIST_FOREACH(structTYPE*var,SLIST_HEAD*head,SLIST_ENTRYNAME);voidSLIST_REMOVE(SLIST_HEAD*head,structTYPE*elm,SLIST_ENTRYNAME);voidSLIST_REMOVE_HEAD(SLIST_HEAD*head,SLIST_ENTRYNAME);