insque(3) - Linux manual page (original) (raw)
insque(3) Library Functions Manual insque(3)
NAME top
insque, remque - insert/remove an item from a queueLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#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**():
_XOPEN_SOURCE >= 500
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCEDESCRIPTION top
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 top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **insque**(), **remque**() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘VERSIONS top
On ancient systems, 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>_.STANDARDS top
POSIX.1-2008.HISTORY top
POSIX.1-2001.BUGS top
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.EXAMPLES top
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 listProgram source
#include <search.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
struct element {
struct element *forward;
struct element *backward;
char *name;
};
static struct element *
new_element(void)
{
struct element *e;
e = malloc(sizeof(*e));
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);
}SEE ALSO top
[queue(7)](../man7/queue.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 insque(3)
Pages that refer to this page:circleq(3), list(3), slist(3), stailq(3), tailq(3), queue(7)