.\" 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 TAILQ 3 2020-12-21 "GNU" "Linux Programmer's Manual" .SH NAME TAILQ_CONCAT, TAILQ_EMPTY, TAILQ_ENTRY, TAILQ_FIRST, TAILQ_FOREACH, .\"TAILQ_FOREACH_FROM, .\"TAILQ_FOREACH_FROM_SAFE, TAILQ_FOREACH_REVERSE, .\"TAILQ_FOREACH_REVERSE_FROM, .\"TAILQ_FOREACH_REVERSE_FROM_SAFE, .\"TAILQ_FOREACH_REVERSE_SAFE, .\"TAILQ_FOREACH_SAFE, TAILQ_HEAD, TAILQ_HEAD_INITIALIZER, TAILQ_INIT, TAILQ_INSERT_AFTER, TAILQ_INSERT_BEFORE, TAILQ_INSERT_HEAD, TAILQ_INSERT_TAIL, TAILQ_LAST, TAILQ_NEXT, TAILQ_PREV, TAILQ_REMOVE .\"TAILQ_SWAP \- implementation of a doubly linked tail queue .SH SYNOPSIS .nf .B #include .PP .BI "void TAILQ_CONCAT(TAILQ_HEAD *" head1 ", TAILQ_HEAD *" head2 "," .BI " TAILQ_ENTRY " NAME ");" .PP .BI "int TAILQ_EMPTY(TAILQ_HEAD *" head ");" .PP .B TAILQ_ENTRY(TYPE); .PP .BI "struct TYPE *TAILQ_FIRST(TAILQ_HEAD *" head ");" .PP .BI "TAILQ_FOREACH(struct TYPE *" var ", TAILQ_HEAD *" head ", TAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "TAILQ_FOREACH_FROM(struct TYPE *" var ", TAILQ_HEAD *" head ", TAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "TAILQ_FOREACH_FROM_SAFE(struct TYPE *" var ", TAILQ_HEAD *" head ", TAILQ_ENTRY " NAME ", struct TYPE *" temp_var ");" .PP .BI "TAILQ_FOREACH_REVERSE(struct TYPE *" var ", TAILQ_HEAD *" head ", HEADNAME," .BI " TAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "TAILQ_FOREACH_REVERSE_FROM(struct TYPE *" var ", TAILQ_HEAD *" head ", HEADNAME, TAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "TAILQ_FOREACH_REVERSE_FROM_SAFE(struct TYPE *" var ", TAILQ_HEAD *" head ", HEADNAME, TAILQ_ENTRY " NAME ", struct TYPE *" temp_var ");" .\" .PP .\" .BI "TAILQ_FOREACH_REVERSE_SAFE(struct TYPE *" var ", TAILQ_HEAD *" head ", HEADNAME, TAILQ_ENTRY " NAME ", TYPE *" temp_var ");" .\" .PP .\" .BI "TAILQ_FOREACH_SAFE(struct TYPE *" var ", TAILQ_HEAD *" head ", TAILQ_ENTRY " NAME ", struct TYPE *" temp_var ");" .PP .B TAILQ_HEAD(HEADNAME, TYPE); .PP .BI "TAILQ_HEAD TAILQ_HEAD_INITIALIZER(TAILQ_HEAD " head ");" .PP .BI "void TAILQ_INIT(TAILQ_HEAD *" head ");" .PP .BI "void TAILQ_INSERT_AFTER(TAILQ_HEAD *" head ", struct TYPE *" listelm "," .BI " struct TYPE *" elm ", TAILQ_ENTRY " NAME ");" .PP .BI "void TAILQ_INSERT_BEFORE(struct TYPE *" listelm ", struct TYPE *" elm "," .BI " TAILQ_ENTRY " NAME ");" .PP .BI "void TAILQ_INSERT_HEAD(TAILQ_HEAD *" head ", struct TYPE *" elm "," .BI " TAILQ_ENTRY " NAME ");" .PP .BI "void TAILQ_INSERT_TAIL(TAILQ_HEAD *" head ", struct TYPE *" elm "," .BI " TAILQ_ENTRY " NAME ");" .PP .BI "struct TYPE *TAILQ_LAST(TAILQ_HEAD *" head ", HEADNAME);" .PP .BI "struct TYPE *TAILQ_NEXT(struct TYPE *" elm ", TAILQ_ENTRY " NAME ");" .PP .BI "struct TYPE *TAILQ_PREV(struct TYPE *" elm ", HEADNAME, TAILQ_ENTRY " NAME ");" .PP .BI "void TAILQ_REMOVE(TAILQ_HEAD *" head ", struct TYPE *" elm ", TAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "void TAILQ_SWAP(TAILQ_HEAD *" head1 ", TAILQ_HEAD *" head2 ", TYPE, TAILQ_ENTRY " NAME ");" .fi .SH DESCRIPTION These macros define and operate on doubly linked tail queues. .PP In the macro definitions, .I TYPE is the name of a user defined structure, that must contain a field of type .IR TAILQ_ENTRY , named .IR NAME . The argument .I HEADNAME is the name of a user defined structure that must be declared using the macro .BR TAILQ_HEAD (). .PP A tail queue is headed by a structure defined by the .BR TAILQ_HEAD () macro. This structure contains a pair of pointers, one to the first element in the tail queue and the other to the last element in the tail queue. The elements are doubly linked so that an arbitrary element can be removed without traversing the tail queue. New elements can be added to the tail queue after an existing element, before an existing element, at the head of the tail queue, or at the end of the tail queue. A .I TAILQ_HEAD structure is declared as follows: .PP .in +4 .EX TAILQ_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 tail queue. A pointer to the head of the tail queue 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 TAILQ_HEAD_INITIALIZER () evaluates to an initializer for the tail queue .IR head . .PP The macro .BR TAILQ_CONCAT () concatenates the tail queue headed by .I head2 onto the end of the one headed by .I head1 removing all entries from the former. .PP The macro .BR TAILQ_EMPTY () evaluates to true if there are no items on the tail queue. .PP The macro .BR TAILQ_ENTRY () declares a structure that connects the elements in the tail queue. .PP The macro .BR TAILQ_FIRST () returns the first item on the tail queue or NULL if the tail queue is empty. .PP The macro .BR TAILQ_FOREACH () traverses the tail queue referenced by .I head in the forward direction, assigning each element in turn to .IR var . .I var is set to NULL if the loop completes normally, or if there were no elements. .\" .PP .\" The macro .\" .BR TAILQ_FOREACH_FROM () .\" behaves identically to .\" .BR TAILQ_FOREACH () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found TAILQ element and begins the loop at .\" .I var .\" instead of the first element in the TAILQ referenced by .\" .IR head . .PP The macro .BR TAILQ_FOREACH_REVERSE () traverses the tail queue referenced by .I head in the reverse direction, assigning each element in turn to .IR var . .\" .PP .\" The macro .\" .BR TAILQ_FOREACH_REVERSE_FROM () .\" behaves identically to .\" .BR TAILQ_FOREACH_REVERSE () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found TAILQ element and begins the reverse loop at .\" .I var .\" instead of the last element in the TAILQ referenced by .\" .IR head . .\" .PP .\" The macros .\" .BR TAILQ_FOREACH_SAFE () .\" and .\" .BR TAILQ_FOREACH_REVERSE_SAFE () .\" traverse the list referenced by .\" .I head .\" in the forward or reverse direction respectively, .\" assigning each element in turn to .\" .IR var . .\" However, unlike their unsafe counterparts, .\" .BR TAILQ_FOREACH () .\" and .\" .BR TAILQ_FOREACH_REVERSE () .\" permit to both remove .\" .I var .\" as well as free it from within the loop safely without interfering with the .\" traversal. .\" .PP .\" The macro .\" .BR TAILQ_FOREACH_FROM_SAFE () .\" behaves identically to .\" .BR TAILQ_FOREACH_SAFE () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found TAILQ element and begins the loop at .\" .I var .\" instead of the first element in the TAILQ referenced by .\" .IR head . .\" .PP .\" The macro .\" .BR TAILQ_FOREACH_REVERSE_FROM_SAFE () .\" behaves identically to .\" .BR TAILQ_FOREACH_REVERSE_SAFE () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found TAILQ element and begins the reverse loop at .\" .I var .\" instead of the last element in the TAILQ referenced by .\" .IR head . .PP The macro .BR TAILQ_INIT () initializes the tail queue referenced by .IR head . .PP The macro .BR TAILQ_INSERT_HEAD () inserts the new element .I elm at the head of the tail queue. .PP The macro .BR TAILQ_INSERT_TAIL () inserts the new element .I elm at the end of the tail queue. .PP The macro .BR TAILQ_INSERT_AFTER () inserts the new element .I elm after the element .IR listelm . .PP The macro .BR TAILQ_INSERT_BEFORE () inserts the new element .I elm before the element .IR listelm . .PP The macro .BR TAILQ_LAST () returns the last item on the tail queue. If the tail queue is empty the return value is NULL. .PP The macro .BR TAILQ_NEXT () returns the next item on the tail queue, or NULL if this item is the last. .PP The macro .BR TAILQ_PREV () returns the previous item on the tail queue, or NULL if this item is the first. .PP The macro .BR TAILQ_REMOVE () removes the element .I elm from the tail queue. .\" .PP .\" The macro .\" .BR TAILQ_SWAP () .\" swaps the contents of .\" .I head1 .\" and .\" .IR head2 . .SH RETURN VALUE .BR TAILQ_EMPTY () returns nonzero if the queue is empty, and zero if the queue contains at least one entry. .PP .BR TAILQ_FIRST (), .BR TAILQ_LAST (), .BR TAILQ_NEXT (), and .BR TAILQ_PREV () return a pointer to the first, last, next or previous .I TYPE structure, respectively. .PP .BR TAILQ_HEAD_INITIALIZER () returns an initializer that can be assigned to the queue .IR head . .SH CONFORMING TO Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008. Present on the BSDs. (TAILQ functions first appeared in 4.4BSD). .SH BUGS The macros .BR TAILQ_FOREACH () and .BR TAILQ_FOREACH_REVERSE () don't allow .I var to be removed or freed within the loop, as it would interfere with the traversal. The macros .BR TAILQ_FOREACH_SAFE () and .BR TAILQ_FOREACH_REVERSE_SAFE (), which are present on the BSDs but are not present in glibc, fix 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; TAILQ_ENTRY(entry) entries; /* Tail queue. */ }; TAILQ_HEAD(tailhead, entry); int main(void) { struct entry *n1, *n2, *n3, *np; struct tailhead head; /* Tail queue head. */ int i; TAILQ_INIT(&head); /* Initialize the queue. */ n1 = malloc(sizeof(struct entry)); /* Insert at the head. */ TAILQ_INSERT_HEAD(&head, n1, entries); n1 = malloc(sizeof(struct entry)); /* Insert at the tail. */ TAILQ_INSERT_TAIL(&head, n1, entries); n2 = malloc(sizeof(struct entry)); /* Insert after. */ TAILQ_INSERT_AFTER(&head, n1, n2, entries); n3 = malloc(sizeof(struct entry)); /* Insert before. */ TAILQ_INSERT_BEFORE(n2, n3, entries); TAILQ_REMOVE(&head, n2, entries); /* Deletion. */ free(n2); /* Forward traversal. */ i = 0; TAILQ_FOREACH(np, &head, entries) np->data = i++; /* Reverse traversal. */ TAILQ_FOREACH_REVERSE(np, &head, tailhead, entries) printf("%i\en", np->data); /* TailQ Deletion. */ n1 = TAILQ_FIRST(&head); while (n1 != NULL) { n2 = TAILQ_NEXT(n1, entries); free(n1); n1 = n2; } TAILQ_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/.