PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

INSQUE(3P)                POSIX Programmer's Manual               INSQUE(3P)

PROLOG         top

       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.

NAME         top

       insque, remque — insert or remove an element in a queue

SYNOPSIS         top

       #include <search.h>

       void insque(void *element, void *pred);
       void remque(void *element);

DESCRIPTION         top

       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.

RETURN VALUE         top

       The insque() and remque() functions do not return a value.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

   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         top

       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>).

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       The Base Definitions volume of POSIX.1‐2008, search.h(0p)

COPYRIGHT         top

       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)