insque(3) Library Functions Manual insque(3)NAME
insque, remque - Inserts or removes an element in a queue
LIBRARY
Standard C Library (libc.a, libc.so)
SYNOPSIS
#include <search.h>
void insque(
void *element,
void *pred);
void remque(
void *element);
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
insque(), remque(): XPG4-UNIX
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Points to the element in the queue immediately before the element to be inserted. Points to the element to be inserted or deleted.
DESCRIPTION
The insque() and remque() functions manipulate queues built from doubly-linked lists. The queue can be either circular or linear.
An application using these functions must define a structure in which the first two members are pointers to the same type of structure and
any further members are application-specific. The first member of the structure is a forward pointer to the next entry in the queue. The
second member is a backward pointer to the previous entry in the queue. If the queue is linear, it is terminated with null pointers.
The insque() function inserts the element pointed to by element into a queue immediately after the element pointed to by pred.
The remque() function removed the element pointed to by element from a queue.
When using the queue as a linear list, the forward and backward pointers of element can be initialized to null pointers by invoking
insque (&element, NULL);
where element is the initial element of the queue.
When using the queue as a circular list, the application must initialize the forward pointer and the backward pointer of the initial ele-
ment of the queue to the element's own address.
RETURN VALUES
The insque() and remque() functions do not return a value.
RELATED INFORMATION
Standards: standards(5) delim off
insque(3)
Check Out this Related Man Page
INSQUE(3P) POSIX Programmer's Manual INSQUE(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
insque, remque - insert or remove an element in a queue
SYNOPSIS
#include <search.h>
void insque(void *element, void *pred);
void remque(void *element);
DESCRIPTION
The insque() and remque() functions shall manipulate queues built from doubly-linked lists. The queue can be either circular or linear. An
application using insque() or remque() shall ensure it defines a structure in which the first two members of the structure are pointers to
the same type of structure, and any further members are application-specific. The first member of the structure is a forward pointer to
the next entry in the queue. The second member is a backward pointer to the previous entry in the queue. If the queue is linear, the queue
is terminated with null pointers. The names of the structure and of the pointer members are not subject to any special restriction.
The insque() function shall insert the element pointed to by element into a queue immediately after the element pointed to by pred.
The remque() function shall remove the element pointed to by element from a queue.
If the queue is to be used as a linear list, invoking insque(&element, NULL), where element is the initial element of the queue, shall ini-
tialize the forward and backward pointers of element to null pointers.
If the queue is to be used as a circular list, the application shall ensure it initializes the forward pointer and the backward pointer of
the initial element of the queue to the element's own address.
RETURN VALUE
The insque() and remque() functions do not return a value.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
Creating a Linear Linked List
The following example creates a linear linked list.
#include <search.h>
...
struct myque element1;
struct myque element2;
char *data1 = "DATA1";
char *data2 = "DATA2";
...
element1.data = data1;
element2.data = data2;
insque (&element1, NULL);
insque (&element2, &element1);
Creating a Circular Linked List
The following example creates a circular linked list.
#include <search.h>
...
struct myque element1;
struct myque element2;
char *data1 = "DATA1";
char *data2 = "DATA2";
...
element1.data = data1;
element2.data = data2;
element1.fwd = &element1;
element1.bck = &element1;
insque (&element2, &element1);
Removing an Element
The following example removes the element pointed to by element1.
#include <search.h>
...
struct myque element1;
...
remque (&element1);
APPLICATION USAGE
The historical implementations of these functions described the arguments as being of type struct qelem * rather than as being of type void
* as defined here. In those implementations, struct qelem was commonly defined in <search.h> as:
struct qelem {
struct qelem *q_forw;
struct qelem *q_back;
};
Applications using these functions, however, were never able to use this structure directly since it provided no room for the actual data
contained in the elements. Most applications defined structures that contained the two pointers as the initial elements and also provided
space for, or pointers to, the object's data. Applications that used these functions to update more than one type of table also had the
problem of specifying two or more different structures with the same name, if they literally used struct qelem as specified.
As described here, the implementations were actually expecting a structure type where the first two members were forward and backward
pointers to structures. With C compilers that didn't provide function prototypes, applications used structures as specified in the DESCRIP-
TION above and the compiler did what the application expected.
If this method had been carried forward with an ISO C standard compiler and the historical function prototype, most applications would have
to be modified to cast pointers to the structures actually used to be pointers to struct qelem to avoid compilation warnings. By specifying
void * as the argument type, applications do not need to change (unless they specifically referenced struct qelem and depended on it being
defined in <search.h>).
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
The Base Definitions volume of IEEE Std 1003.1-2001, <search.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
online at http://www.opengroup.org/unix/online.html .
IEEE /The Open Group 2003 INSQUE(3P)