.\" Copyright (c) 1993 .\" The Regents of the University of California. All rights reserved. .\" and Copyright (c) 2020 by Alejandro Colomar .\" .\" %%%LICENSE_START(BSD_3_CLAUSE_UCB) .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" %%%LICENSE_END .\" .\" .TH LIST 3 2020-12-21 "GNU" "Linux Programmer's Manual" .SH NAME LIST_EMPTY, LIST_ENTRY, LIST_FIRST, LIST_FOREACH, .\"LIST_FOREACH_FROM, .\"LIST_FOREACH_SAFE, .\"LIST_FOREACH_FROM_SAFE, LIST_HEAD, LIST_HEAD_INITIALIZER, LIST_INIT, LIST_INSERT_AFTER, LIST_INSERT_BEFORE, LIST_INSERT_HEAD, LIST_NEXT, .\"LIST_PREV, LIST_REMOVE .\"LIST_SWAP \- implementation of a doubly linked list .SH SYNOPSIS .nf .B #include .PP .BI "int LIST_EMPTY(LIST_HEAD *" head ");" .PP .B LIST_ENTRY(TYPE); .PP .BI "struct TYPE *LIST_FIRST(LIST_HEAD *" head ");" .PP .BI "LIST_FOREACH(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ");" .\".PP .\".BI "LIST_FOREACH_FROM(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ");" .\".PP .\".BI "LIST_FOREACH_FROM_SAFE(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ", struct TYPE *" temp_var ");" .\".PP .\".BI "LIST_FOREACH_SAFE(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ", struct TYPE *" temp_var ");" .PP .B LIST_HEAD(HEADNAME, TYPE); .PP .BI "LIST_HEAD LIST_HEAD_INITIALIZER(LIST_HEAD " head ");" .PP .BI "void LIST_INIT(LIST_HEAD *" head ");" .PP .BI "void LIST_INSERT_AFTER(struct TYPE *" listelm ", struct TYPE *" elm "," .BI " LIST_ENTRY " NAME ");" .PP .BI "void LIST_INSERT_BEFORE(struct TYPE *" listelm ", struct TYPE *" elm "," .BI " LIST_ENTRY " NAME ");" .PP .BI "void LIST_INSERT_HEAD(LIST_HEAD *" head ", struct TYPE *" elm "," .BI " LIST_ENTRY " NAME ");" .PP .BI "struct TYPE *LIST_NEXT(struct TYPE *" elm ", LIST_ENTRY " NAME ");" .\".PP .\".BI "struct TYPE *LIST_PREV(struct TYPE *" elm ", LIST_HEAD *" head ", struct TYPE, LIST_ENTRY " NAME ");" .PP .BI "void LIST_REMOVE(struct TYPE *" elm ", LIST_ENTRY " NAME ");" .\".PP .\".BI "void LIST_SWAP(LIST_HEAD *" head1 ", LIST_HEAD *" head2 ", struct TYPE, LIST_ENTRY " NAME ");" .fi .SH DESCRIPTION These macros define and operate on doubly linked lists. .PP In the macro definitions, .I TYPE is the name of a user-defined structure, that must contain a field of type .IR LIST_ENTRY , named .IR NAME . The argument .IR HEADNAME is the name of a user-defined structure that must be declared using the macro .BR LIST_HEAD (). .PP A list is headed by a structure defined by the .BR LIST_HEAD () macro. This structure contains a single pointer to the first element on the list. The elements are doubly linked so that an arbitrary element can be removed without traversing the list. New elements can be added to the list after an existing element, before an existing element, or at the head of the list. A .I LIST_HEAD structure is declared as follows: .PP .in +4 .EX LIST_HEAD(HEADNAME, TYPE) head; .EE .in .PP where .I struct HEADNAME is the structure to be defined, and .I struct TYPE is the type of the elements to be linked into the list. A pointer to the head of the list can later be declared as: .PP .in +4 .EX struct HEADNAME *headp; .EE .in .PP (The names .I head and .I headp are user selectable.) .PP The macro .BR LIST_HEAD_INITIALIZER () evaluates to an initializer for the list .IR head . .PP The macro .BR LIST_EMPTY () evaluates to true if there are no elements in the list. .PP The macro .BR LIST_ENTRY () declares a structure that connects the elements in the list. .PP The macro .BR LIST_FIRST () returns the first element in the list or NULL if the list is empty. .PP The macro .BR LIST_FOREACH () traverses the list referenced by .I head in the forward direction, assigning each element in turn to .IR var . .\" .PP .\" The macro .\" .BR LIST_FOREACH_FROM () .\" behaves identically to .\" .BR LIST_FOREACH () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found LIST element and begins the loop at .\" .I var .\" instead of the first element in the LIST referenced by .\" .IR head . .\" .PP .\" The macro .\" .BR LIST_FOREACH_SAFE () .\" traverses the list referenced by .\" .I head .\" in the forward direction, assigning each element in turn to .\" .IR var . .\" However, unlike .\" .BR LIST_FOREACH () .\" here it is permitted to both remove .\" .I var .\" as well as free it from within the loop safely without interfering with the .\" traversal. .\" .PP .\" The macro .\" .BR LIST_FOREACH_FROM_SAFE () .\" behaves identically to .\" .BR LIST_FOREACH_SAFE () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found LIST element and begins the loop at .\" .I var .\" instead of the first element in the LIST referenced by .\" .IR head . .PP The macro .BR LIST_INIT () initializes the list referenced by .IR head . .PP The macro .BR LIST_INSERT_HEAD () inserts the new element .I elm at the head of the list. .PP The macro .BR LIST_INSERT_AFTER () inserts the new element .I elm after the element .IR listelm . .PP The macro .BR LIST_INSERT_BEFORE () inserts the new element .I elm before the element .IR listelm . .PP The macro .BR LIST_NEXT () returns the next element in the list, or NULL if this is the last. .\" .PP .\" The macro .\" .BR LIST_PREV () .\" returns the previous element in the list, or NULL if this is the first. .\" List .\" .I head .\" must contain element .\" .IR elm . .PP The macro .BR LIST_REMOVE () removes the element .I elm from the list. .\" .PP .\" The macro .\" .BR LIST_SWAP () .\" swaps the contents of .\" .I head1 .\" and .\" .IR head2 . .SH RETURN VALUE .BR LIST_EMPTY () returns nonzero if the list is empty, and zero if the list contains at least one entry. .PP .BR LIST_FIRST (), and .BR LIST_NEXT () return a pointer to the first or next .I TYPE structure, respectively. .PP .BR LIST_HEAD_INITIALIZER () returns an initializer that can be assigned to the list .IR head . .SH CONFORMING TO Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008. Present on the BSDs (LIST macros first appeared in 4.4BSD). .SH BUGS The macro .BR LIST_FOREACH () doesn't allow .I var to be removed or freed within the loop, as it would interfere with the traversal. The macro .BR LIST_FOREACH_SAFE (), which is present on the BSDs but is not present in glibc, fixes this limitation by allowing .I var to safely be removed from the list and freed from within the loop without interfering with the traversal. .SH EXAMPLES .EX #include #include #include #include struct entry { int data; LIST_ENTRY(entry) entries; /* List. */ }; LIST_HEAD(listhead, entry); int main(void) { struct entry *n1, *n2, *n3, *np; struct listhead head; /* List head. */ int i; LIST_INIT(&head); /* Initialize the list. */ n1 = malloc(sizeof(struct entry)); /* Insert at the head. */ LIST_INSERT_HEAD(&head, n1, entries); n2 = malloc(sizeof(struct entry)); /* Insert after. */ LIST_INSERT_AFTER(n1, n2, entries); n3 = malloc(sizeof(struct entry)); /* Insert before. */ LIST_INSERT_BEFORE(n2, n3, entries); i = 0; /* Forward traversal. */ LIST_FOREACH(np, &head, entries) np->data = i++; LIST_REMOVE(n2, entries); /* Deletion. */ free(n2); /* Forward traversal. */ LIST_FOREACH(np, &head, entries) printf("%i\en", np->data); /* List Deletion. */ n1 = LIST_FIRST(&head); while (n1 != NULL) { n2 = LIST_NEXT(n1, entries); free(n1); n1 = n2; } LIST_INIT(&head); exit(EXIT_SUCCESS); } .EE .SH SEE ALSO .BR insque (3), .BR queue (7) .SH COLOPHON This page is part of release 5.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.