221 lines
7.7 KiB
HTML
221 lines
7.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>insque</title>
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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<basefont size="3"> <a name="insque"></a> <a name="tag_03_281"></a><!-- insque -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_281_01"></a>NAME</h4>
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<blockquote>insque, remque - insert or remove an element in a queue</blockquote>
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<h4><a name="tag_03_281_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/search.h.html">search.h</a>><br>
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<br>
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void insque(void *</tt><i>element</i><tt>, void *</tt><i>pred</i><tt>);<br>
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void remque(void *</tt><i>element</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_281_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>insque</i>() and <i>remque</i>() functions shall manipulate queues built from doubly-linked lists. The queue can be
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either circular or linear. An application using <i>insque</i>() or <i>remque</i>() shall ensure it defines a structure in which the
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first two members of the structure are pointers to the same type of structure, and any further members are application-specific.
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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
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the previous entry in the queue. If the queue is linear, the queue is terminated with null pointers. The names of the structure and
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of the pointer members are not subject to any special restriction.</p>
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<p>The <i>insque</i>() function shall insert the element pointed to by <i>element</i> into a queue immediately after the element
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pointed to by <i>pred</i>.</p>
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<p>The <i>remque</i>() function shall remove the element pointed to by <i>element</i> from a queue.</p>
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<p>If the queue is to be used as a linear list, invoking <i>insque</i>(&<i>element</i>, NULL), where <i>element</i> is the
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initial element of the queue, shall initialize the forward and backward pointers of <i>element</i> to null pointers.</p>
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<p>If the queue is to be used as a circular list, the application shall ensure it initializes the forward pointer and the backward
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pointer of the initial element of the queue to the element's own address.</p>
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</blockquote>
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<h4><a name="tag_03_281_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>The <i>insque</i>() and <i>remque</i>() functions do not return a value.</p>
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</blockquote>
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<h4><a name="tag_03_281_05"></a>ERRORS</h4>
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<blockquote>
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<p>No errors are defined.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_281_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_281_06_01"></a>Creating a Linear Linked List</h5>
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<p>The following example creates a linear linked list.</p>
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<pre>
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<tt>#include <search.h>
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...
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struct myque element1;
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struct myque element2;
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<br>
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char *data1 = "DATA1";
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char *data2 = "DATA2";
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...
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element1.data = data1;
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element2.data = data2;
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<br>
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insque (&element1, NULL);
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insque (&element2, &element1);
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</tt>
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</pre>
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<h5><a name="tag_03_281_06_02"></a>Creating a Circular Linked List</h5>
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<p>The following example creates a circular linked list.</p>
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<pre>
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<tt>#include <search.h>
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...
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struct myque element1;
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struct myque element2;
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<br>
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char *data1 = "DATA1";
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char *data2 = "DATA2";
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...
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element1.data = data1;
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element2.data = data2;
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<br>
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element1.fwd = &element1;
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element1.bck = &element1;
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<br>
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insque (&element2, &element1);
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</tt>
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</pre>
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<h5><a name="tag_03_281_06_03"></a>Removing an Element</h5>
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<p>The following example removes the element pointed to by <i>element1</i>.</p>
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<pre>
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<tt>#include <search.h>
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...
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struct myque element1;
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...
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remque (&element1);
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_281_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The historical implementations of these functions described the arguments as being of type <b>struct qelem *</b> rather than as
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being of type <b>void *</b> as defined here. In those implementations, <b>struct qelem</b> was commonly defined in <a href=
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"../basedefs/search.h.html"><i><search.h></i></a> as:</p>
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<pre>
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<tt>struct qelem {
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struct qelem *q_forw;
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struct qelem *q_back;
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};
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</tt>
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</pre>
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<p>Applications using these functions, however, were never able to use this structure directly since it provided no room for the
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actual data contained in the elements. Most applications defined structures that contained the two pointers as the initial elements
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and also provided space for, or pointers to, the object's data. Applications that used these functions to update more than one type
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of table also had the problem of specifying two or more different structures with the same name, if they literally used <b>struct
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qelem</b> as specified.</p>
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<p>As described here, the implementations were actually expecting a structure type where the first two members were forward and
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backward pointers to structures. With C compilers that didn't provide function prototypes, applications used structures as
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specified in the DESCRIPTION above and the compiler did what the application expected.</p>
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<p>If this method had been carried forward with an ISO C standard compiler and the historical function prototype, most
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applications would have to be modified to cast pointers to the structures actually used to be pointers to <b>struct qelem</b> to
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avoid compilation warnings. By specifying <b>void *</b> as the argument type, applications do not need to change (unless they
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specifically referenced <b>struct qelem</b> and depended on it being defined in <a href=
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"../basedefs/search.h.html"><i><search.h></i></a>).</p>
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</blockquote>
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<h4><a name="tag_03_281_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_281_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_281_10"></a>SEE ALSO</h4>
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<blockquote>
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<p>The Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/search.h.html"><i><search.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_281_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 4, Version 2.</p>
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</blockquote>
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<h4><a name="tag_03_281_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from X/OPEN UNIX extension to BASE.</p>
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</blockquote>
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<h4><a name="tag_03_281_13"></a>Issue 6</h4>
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<blockquote>
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<p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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