mirror of https://github.com/mkerrisk/man-pages
350 lines
9.1 KiB
Groff
350 lines
9.1 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\" and Copyright (c) 2020 by Alejandro Colomar <colomar.6.4.3@gmail.com>
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.\"
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.\" %%%LICENSE_START(BSD_3_CLAUSE_UCB)
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\" %%%LICENSE_END
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.\"
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.\"
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.TH LIST 3 2020-12-21 "GNU" "Linux Programmer's Manual"
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.SH NAME
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LIST_EMPTY,
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LIST_ENTRY,
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LIST_FIRST,
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LIST_FOREACH,
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.\"LIST_FOREACH_FROM,
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.\"LIST_FOREACH_SAFE,
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.\"LIST_FOREACH_FROM_SAFE,
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LIST_HEAD,
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LIST_HEAD_INITIALIZER,
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LIST_INIT,
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LIST_INSERT_AFTER,
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LIST_INSERT_BEFORE,
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LIST_INSERT_HEAD,
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LIST_NEXT,
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.\"LIST_PREV,
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LIST_REMOVE
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.\"LIST_SWAP
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\- implementation of a doubly linked list
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.SH SYNOPSIS
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.nf
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.B #include <sys/queue.h>
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.PP
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.BI "int LIST_EMPTY(LIST_HEAD *" head ");"
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.PP
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.B LIST_ENTRY(TYPE);
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.PP
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.BI "struct TYPE *LIST_FIRST(LIST_HEAD *" head ");"
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.PP
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.BI "LIST_FOREACH(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ");"
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.\".PP
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.\".BI "LIST_FOREACH_FROM(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ");"
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.\".PP
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.\".BI "LIST_FOREACH_FROM_SAFE(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ", struct TYPE *" temp_var ");"
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.\".PP
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.\".BI "LIST_FOREACH_SAFE(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ", struct TYPE *" temp_var ");"
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.PP
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.B LIST_HEAD(HEADNAME, TYPE);
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.PP
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.BI "LIST_HEAD LIST_HEAD_INITIALIZER(LIST_HEAD " head ");"
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.PP
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.BI "void LIST_INIT(LIST_HEAD *" head ");"
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.PP
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.BI "void LIST_INSERT_AFTER(struct TYPE *" listelm ", struct TYPE *" elm ","
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.BI " LIST_ENTRY " NAME ");"
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.PP
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.BI "void LIST_INSERT_BEFORE(struct TYPE *" listelm ", struct TYPE *" elm ","
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.BI " LIST_ENTRY " NAME ");"
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.PP
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.BI "void LIST_INSERT_HEAD(LIST_HEAD *" head ", struct TYPE *" elm ","
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.BI " LIST_ENTRY " NAME ");"
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.PP
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.BI "struct TYPE *LIST_NEXT(struct TYPE *" elm ", LIST_ENTRY " NAME ");"
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.\".PP
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.\".BI "struct TYPE *LIST_PREV(struct TYPE *" elm ", LIST_HEAD *" head ", struct TYPE, LIST_ENTRY " NAME ");"
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.PP
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.BI "void LIST_REMOVE(struct TYPE *" elm ", LIST_ENTRY " NAME ");"
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.\".PP
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.\".BI "void LIST_SWAP(LIST_HEAD *" head1 ", LIST_HEAD *" head2 ", struct TYPE, LIST_ENTRY " NAME ");"
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.fi
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.SH DESCRIPTION
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These macros define and operate on doubly linked lists.
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.PP
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In the macro definitions,
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.I TYPE
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is the name of a user-defined structure,
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that must contain a field of type
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.IR LIST_ENTRY ,
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named
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.IR NAME .
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The argument
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.IR HEADNAME
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is the name of a user-defined structure that must be declared
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using the macro
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.BR LIST_HEAD ().
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.PP
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A list is headed by a structure defined by the
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.BR LIST_HEAD ()
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macro.
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This structure contains a single pointer to the first element
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on the list.
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The elements are doubly linked so that an arbitrary element can be
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removed without traversing the list.
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New elements can be added to the list after an existing element,
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before an existing element, or at the head of the list.
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A
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.I LIST_HEAD
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structure is declared as follows:
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.PP
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.in +4
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.EX
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LIST_HEAD(HEADNAME, TYPE) head;
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.EE
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.in
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.PP
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where
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.I struct HEADNAME
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is the structure to be defined, and
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.I struct TYPE
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is the type of the elements to be linked into the list.
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A pointer to the head of the list can later be declared as:
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.PP
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.in +4
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.EX
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struct HEADNAME *headp;
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.EE
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.in
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.PP
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(The names
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.I head
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and
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.I headp
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are user selectable.)
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.PP
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The macro
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.BR LIST_HEAD_INITIALIZER ()
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evaluates to an initializer for the list
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.IR head .
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.PP
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The macro
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.BR LIST_EMPTY ()
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evaluates to true if there are no elements in the list.
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.PP
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The macro
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.BR LIST_ENTRY ()
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declares a structure that connects the elements in
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the list.
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.PP
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The macro
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.BR LIST_FIRST ()
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returns the first element in the list or NULL if the list
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is empty.
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.PP
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The macro
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.BR LIST_FOREACH ()
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traverses the list referenced by
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.I head
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in the forward direction, assigning each element in turn to
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.IR var .
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.\" .PP
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.\" The macro
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.\" .BR LIST_FOREACH_FROM ()
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.\" behaves identically to
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.\" .BR LIST_FOREACH ()
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.\" when
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.\" .I var
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.\" is NULL, else it treats
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.\" .I var
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.\" as a previously found LIST element and begins the loop at
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.\" .I var
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.\" instead of the first element in the LIST referenced by
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.\" .IR head .
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.\" .PP
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.\" The macro
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.\" .BR LIST_FOREACH_SAFE ()
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.\" traverses the list referenced by
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.\" .I head
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.\" in the forward direction, assigning each element in turn to
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.\" .IR var .
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.\" However, unlike
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.\" .BR LIST_FOREACH ()
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.\" here it is permitted to both remove
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.\" .I var
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.\" as well as free it from within the loop safely without interfering with the
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.\" traversal.
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.\" .PP
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.\" The macro
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.\" .BR LIST_FOREACH_FROM_SAFE ()
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.\" behaves identically to
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.\" .BR LIST_FOREACH_SAFE ()
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.\" when
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.\" .I var
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.\" is NULL, else it treats
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.\" .I var
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.\" as a previously found LIST element and begins the loop at
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.\" .I var
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.\" instead of the first element in the LIST referenced by
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.\" .IR head .
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.PP
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The macro
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.BR LIST_INIT ()
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initializes the list referenced by
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.IR head .
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.PP
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The macro
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.BR LIST_INSERT_HEAD ()
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inserts the new element
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.I elm
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at the head of the list.
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.PP
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The macro
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.BR LIST_INSERT_AFTER ()
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inserts the new element
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.I elm
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after the element
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.IR listelm .
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.PP
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The macro
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.BR LIST_INSERT_BEFORE ()
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inserts the new element
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.I elm
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before the element
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.IR listelm .
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.PP
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The macro
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.BR LIST_NEXT ()
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returns the next element in the list, or NULL if this is the last.
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.\" .PP
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.\" The macro
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.\" .BR LIST_PREV ()
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.\" returns the previous element in the list, or NULL if this is the first.
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.\" List
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.\" .I head
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.\" must contain element
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.\" .IR elm .
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.PP
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The macro
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.BR LIST_REMOVE ()
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removes the element
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.I elm
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from the list.
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.\" .PP
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.\" The macro
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.\" .BR LIST_SWAP ()
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.\" swaps the contents of
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.\" .I head1
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.\" and
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.\" .IR head2 .
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.SH RETURN VALUE
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.BR LIST_EMPTY ()
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returns nonzero if the list is empty,
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and zero if the list contains at least one entry.
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.PP
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.BR LIST_FIRST (),
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and
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.BR LIST_NEXT ()
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return a pointer to the first or next
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.I TYPE
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structure, respectively.
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.PP
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.BR LIST_HEAD_INITIALIZER ()
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returns an initializer that can be assigned to the list
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.IR head .
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.SH CONFORMING TO
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Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008.
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Present on the BSDs
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(LIST macros first appeared in 4.4BSD).
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.SH BUGS
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The macro
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.BR LIST_FOREACH ()
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doesn't allow
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.I var
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to be removed or freed within the loop,
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as it would interfere with the traversal.
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The macro
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.BR LIST_FOREACH_SAFE (),
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which is present on the BSDs but is not present in glibc,
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fixes this limitation by allowing
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.I var
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to safely be removed from the list and freed from within the loop
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without interfering with the traversal.
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.SH EXAMPLES
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.EX
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#include <stddef.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/queue.h>
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struct entry {
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int data;
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LIST_ENTRY(entry) entries; /* List. */
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};
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LIST_HEAD(listhead, entry);
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int
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main(void)
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{
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struct entry *n1, *n2, *n3, *np;
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struct listhead head; /* List head. */
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int i;
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LIST_INIT(&head); /* Initialize the list. */
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n1 = malloc(sizeof(struct entry)); /* Insert at the head. */
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LIST_INSERT_HEAD(&head, n1, entries);
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n2 = malloc(sizeof(struct entry)); /* Insert after. */
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LIST_INSERT_AFTER(n1, n2, entries);
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n3 = malloc(sizeof(struct entry)); /* Insert before. */
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LIST_INSERT_BEFORE(n2, n3, entries);
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i = 0; /* Forward traversal. */
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LIST_FOREACH(np, &head, entries)
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np->data = i++;
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LIST_REMOVE(n2, entries); /* Deletion. */
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free(n2);
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/* Forward traversal. */
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LIST_FOREACH(np, &head, entries)
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printf("%i\en", np->data);
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/* List Deletion. */
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n1 = LIST_FIRST(&head);
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while (n1 != NULL) {
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n2 = LIST_NEXT(n1, entries);
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free(n1);
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n1 = n2;
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}
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LIST_INIT(&head);
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exit(EXIT_SUCCESS);
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}
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.EE
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.SH SEE ALSO
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.BR insque (3),
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.BR queue (7)
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