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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
INSQUE(3P) POSIX Programmer's Manual INSQUE(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
insque, remque — insert or remove an element in a queue
#include <search.h>
void insque(void *element, void *pred);
void remque(void *element);
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 initialize 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.
The insque() and remque() functions do not return a value.
No errors are defined.
The following sections are informative.
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);
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
DESCRIPTION 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>).
None.
None.
The Base Definitions volume of POSIX.1‐2008, search.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 INSQUE(3P)
Pages that refer to this page: search.h(0p), remque(3p)