mirror of https://github.com/mkerrisk/man-pages
185 lines
5.3 KiB
Plaintext
185 lines
5.3 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "INSQUE" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" insque
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.SH NAME
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insque, remque \- insert or remove an element in a queue
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.SH SYNOPSIS
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.LP
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\fB#include <search.h>
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.br
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.sp
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void insque(void *\fP\fIelement\fP\fB, void *\fP\fIpred\fP\fB);
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.br
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void remque(void *\fP\fIelement\fP\fB); \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIinsque\fP() and \fIremque\fP() functions shall manipulate queues
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built from doubly-linked lists. The queue can be
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either circular or linear. An application using \fIinsque\fP() or
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\fIremque\fP() 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
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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
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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
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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.
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.LP
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The \fIinsque\fP() function shall insert the element pointed to by
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\fIelement\fP into a queue immediately after the element
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pointed to by \fIpred\fP.
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.LP
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The \fIremque\fP() function shall remove the element pointed to by
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\fIelement\fP from a queue.
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.LP
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If the queue is to be used as a linear list, invoking \fIinsque\fP(&\fIelement\fP,
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NULL), where \fIelement\fP is the
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initial element of the queue, shall initialize the forward and backward
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pointers of \fIelement\fP to null pointers.
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.LP
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If the queue is to be used as a circular list, the application shall
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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.
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.SH RETURN VALUE
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.LP
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The \fIinsque\fP() and \fIremque\fP() functions do not return a value.
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.SH ERRORS
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.LP
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No errors are defined.
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.SS Creating a Linear Linked List
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.LP
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The following example creates a linear linked list.
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.sp
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.RS
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.nf
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\fB#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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.sp
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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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.sp
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insque (&element1, NULL);
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insque (&element2, &element1);
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\fP
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.fi
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.RE
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.SS Creating a Circular Linked List
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.LP
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The following example creates a circular linked list.
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.sp
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.RS
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.nf
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\fB#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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.sp
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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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.sp
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element1.fwd = &element1;
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element1.bck = &element1;
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.sp
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insque (&element2, &element1);
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\fP
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.fi
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.RE
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.SS Removing an Element
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.LP
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The following example removes the element pointed to by \fIelement1\fP.
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.sp
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.RS
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.nf
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\fB#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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\fP
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.fi
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.RE
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.SH APPLICATION USAGE
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.LP
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The historical implementations of these functions described the arguments
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as being of type \fBstruct qelem *\fP rather than as
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being of type \fBvoid *\fP as defined here. In those implementations,
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\fBstruct qelem\fP was commonly defined in \fI<search.h>\fP as:
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.sp
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.RS
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.nf
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\fBstruct 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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\fP
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.fi
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.RE
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.LP
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Applications using these functions, however, were never able to use
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this structure directly since it provided no room for the
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actual data contained in the elements. Most applications defined structures
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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
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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
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structures with the same name, if they literally used \fBstruct
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qelem\fP as specified.
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.LP
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As described here, the implementations were actually expecting a structure
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type where the first two members were forward and
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backward pointers to structures. With C compilers that didn't provide
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function prototypes, applications used structures as
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specified in the DESCRIPTION above and the compiler did what the application
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expected.
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.LP
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If this method had been carried forward with an ISO\ C standard compiler
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and the historical function prototype, most
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applications would have to be modified to cast pointers to the structures
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actually used to be pointers to \fBstruct qelem\fP to
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avoid compilation warnings. By specifying \fBvoid *\fP as the argument
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type, applications do not need to change (unless they
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specifically referenced \fBstruct qelem\fP and depended on it being
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defined in \fI<search.h>\fP).
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.SH RATIONALE
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.LP
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None.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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The Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<search.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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