NAME

       insque, remque - insert/remove an item from a queue

SYNOPSIS

       #include <search.h>

       void insque(void *elem, void *prev);

       void remque(void *elem);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       insque(), remque():
           _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION

       The  insque()  and  remque()  functions  manipulate  doubly-linked  lists.  Each element in the list is a
       structure of which the first two elements are a forward and a backward pointer.  The linked list  may  be
       linear  (i.e.,  NULL forward pointer at the end of the list and NULL backward pointer at the start of the
       list) or circular.

       The insque() function inserts the element pointed to by elem immediately after the element pointed to  by
       prev.

       If  the  list is linear, then the call insque(elem, NULL) can be used to insert the initial list element,
       and the call sets the forward and backward pointers of elem to NULL.

       If the list is circular, the caller should ensure that the forward and backward  pointers  of  the  first
       element  are initialized to point to that element, and the prev argument of the insque() call should also
       point to the element.

       The remque() function removes the element pointed to by elem from the doubly-linked list.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────────────┬───────────────┬─────────┐
       │Interface          │ Attribute     │ Value   │
       ├───────────────────┼───────────────┼─────────┤
       │insque(), remque() │ Thread safety │ MT-Safe │
       └───────────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

       Traditionally (e.g., SunOS, Linux libc4 and libc5), the arguments of these functions were of type  struct
       qelem *, defined as:

           struct qelem {
               struct qelem *q_forw;
               struct qelem *q_back;
               char          q_data[1];
           };

       This is still what you will get if _GNU_SOURCE is defined before including <search.h>.

       The  location of the prototypes for these functions differs among several versions of UNIX.  The above is
       the POSIX version.  Some systems place them in <string.h>.

BUGS

       In glibc 2.4 and earlier, it was not possible to specify prev as NULL.  Consequently, to build  a  linear
       list,  the  caller had to build a list using an initial call that contained the first two elements of the
       list, with the forward and backward pointers in each element suitably initialized.

EXAMPLE

       The program below demonstrates the use of insque().  Here is an example run of the program:

           $ ./a.out -c a b c
           Traversing completed list:
               a
               b
               c
           That was a circular list

   Program source

       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <search.h>

       struct element {
           struct element *forward;
           struct element *backward;
           char *name;
       };

       static struct element *
       new_element(void)
       {
           struct element *e;

           e = malloc(sizeof(struct element));
           if (e == NULL) {
               fprintf(stderr, "malloc() failed\n");
               exit(EXIT_FAILURE);
           }

           return e;
       }

       int
       main(int argc, char *argv[])
       {
           struct element *first, *elem, *prev;
           int circular, opt, errfnd;

           /* The "-c" command-line option can be used to specify that the
              list is circular */

           errfnd = 0;
           circular = 0;
           while ((opt = getopt(argc, argv, "c")) != -1) {
               switch (opt) {
               case 'c':
                   circular = 1;
                   break;
               default:
                   errfnd = 1;
                   break;
               }
           }

           if (errfnd || optind >= argc) {
               fprintf(stderr,  "Usage: %s [-c] string...\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           /* Create first element and place it in the linked list */

           elem = new_element();
           first = elem;

           elem->name = argv[optind];

           if (circular) {
               elem->forward = elem;
               elem->backward = elem;
               insque(elem, elem);
           } else {
               insque(elem, NULL);
           }

           /* Add remaining command-line arguments as list elements */

           while (++optind < argc) {
               prev = elem;

               elem = new_element();
               elem->name = argv[optind];
               insque(elem, prev);
           }

           /* Traverse the list from the start, printing element names */

           printf("Traversing completed list:\n");
           elem = first;
           do {
               printf("    %s\n", elem->name);
               elem = elem->forward;
           } while (elem != NULL && elem != first);

           if (elem == first)
               printf("That was a circular list\n");

           exit(EXIT_SUCCESS);
       }

COLOPHON

       This page is part of release 4.04 of  the  Linux  man-pages  project.   A  description  of  the  project,
       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       http://www.kernel.org/doc/man-pages/.

                                                   2015-08-08                                          INSQUE(3)