Name
insque, remque — insert/remove an item from a queue
Synopsis
#include <search.h>
void
insque( |
void *elem, |
void *prev); |
void
remque( |
void *elem); |
![[Note]](../stylesheet/note.png) |
Note | ||||
|---|---|---|---|---|---|
|
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 |
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 4.07 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
https://www.kernel.org/doc/man−pages/.
|
peter memishian -- meemgnu.ai.mit.edu $Id: insque.3,v 1.2 1996/10/30 21:03:39 meem Exp meem $ and Copyright (c) 2010, Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END References consulted: Linux libc source code (5.4.7) Solaris 2.x, OSF/1, and HP-UX manpages Curry's "UNIX Systems Programming for SVR4" (O'Reilly & Associates 1996) Changed to POSIX, 2003-08-11, aeb+wh mtk, 2010-09-09: Noted glibc 2.4 bug, added info on circular lists, added example program |