.\" 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 2020-10-21 "GNU" "Linux Programmer's Manual" .SH NAME .Nm TAILQ_CONCAT , .Nm TAILQ_EMPTY , .Nm TAILQ_ENTRY , .Nm TAILQ_FIRST , .Nm TAILQ_FOREACH , .\" .Nm TAILQ_FOREACH_FROM , .\" .Nm TAILQ_FOREACH_FROM_SAFE , .Nm TAILQ_FOREACH_REVERSE , .\" .Nm TAILQ_FOREACH_REVERSE_FROM , .\" .Nm TAILQ_FOREACH_REVERSE_FROM_SAFE , .\" .Nm TAILQ_FOREACH_REVERSE_SAFE , .\" .Nm TAILQ_FOREACH_SAFE , .Nm TAILQ_HEAD , .Nm TAILQ_HEAD_INITIALIZER , .Nm TAILQ_INIT , .Nm TAILQ_INSERT_AFTER , .Nm TAILQ_INSERT_BEFORE , .Nm TAILQ_INSERT_HEAD , .Nm TAILQ_INSERT_TAIL , .Nm TAILQ_LAST , .Nm TAILQ_NEXT , .Nm TAILQ_PREV , .Nm TAILQ_REMOVE .\" .Nm TAILQ_SWAP .SH SYNOPSIS .In sys/queue.h .\" .Fn TAILQ_CONCAT "TAILQ_HEAD *head1" "TAILQ_HEAD *head2" "TAILQ_ENTRY NAME" .Fn TAILQ_EMPTY "TAILQ_HEAD *head" .Fn TAILQ_ENTRY "TYPE" .Fn TAILQ_FIRST "TAILQ_HEAD *head" .Fn TAILQ_FOREACH "TYPE *var" "TAILQ_HEAD *head" "TAILQ_ENTRY NAME" .\" .Fn TAILQ_FOREACH_FROM "TYPE *var" "TAILQ_HEAD *head" "TAILQ_ENTRY NAME" .\" .Fn TAILQ_FOREACH_FROM_SAFE "TYPE *var" "TAILQ_HEAD *head" "TAILQ_ENTRY NAME" "TYPE *temp_var" .Fn TAILQ_FOREACH_REVERSE "TYPE *var" "TAILQ_HEAD *head" "HEADNAME" "TAILQ_ENTRY NAME" .\" .Fn TAILQ_FOREACH_REVERSE_FROM "TYPE *var" "TAILQ_HEAD *head" "HEADNAME" "TAILQ_ENTRY NAME" .\" .Fn TAILQ_FOREACH_REVERSE_FROM_SAFE "TYPE *var" "TAILQ_HEAD *head" "HEADNAME" "TAILQ_ENTRY NAME" "TYPE *temp_var" .\" .Fn TAILQ_FOREACH_REVERSE_SAFE "TYPE *var" "TAILQ_HEAD *head" "HEADNAME" "TAILQ_ENTRY NAME" "TYPE *temp_var" .\" .Fn TAILQ_FOREACH_SAFE "TYPE *var" "TAILQ_HEAD *head" "TAILQ_ENTRY NAME" "TYPE *temp_var" .Fn TAILQ_HEAD "HEADNAME" "TYPE" .Fn TAILQ_HEAD_INITIALIZER "TAILQ_HEAD head" .Fn TAILQ_INIT "TAILQ_HEAD *head" .Fn TAILQ_INSERT_AFTER "TAILQ_HEAD *head" "TYPE *listelm" "TYPE *elm" "TAILQ_ENTRY NAME" .Fn TAILQ_INSERT_BEFORE "TYPE *listelm" "TYPE *elm" "TAILQ_ENTRY NAME" .Fn TAILQ_INSERT_HEAD "TAILQ_HEAD *head" "TYPE *elm" "TAILQ_ENTRY NAME" .Fn TAILQ_INSERT_TAIL "TAILQ_HEAD *head" "TYPE *elm" "TAILQ_ENTRY NAME" .Fn TAILQ_LAST "TAILQ_HEAD *head" "HEADNAME" .Fn TAILQ_NEXT "TYPE *elm" "TAILQ_ENTRY NAME" .Fn TAILQ_PREV "TYPE *elm" "HEADNAME" "TAILQ_ENTRY NAME" .Fn TAILQ_REMOVE "TAILQ_HEAD *head" "TYPE *elm" "TAILQ_ENTRY NAME" .\" .Fn TAILQ_SWAP "TAILQ_HEAD *head1" "TAILQ_HEAD *head2" "TYPE" "TAILQ_ENTRY NAME" .\" .SH DESCRIPTION .Pp In the macro definitions, .Fa TYPE is the name of a user defined structure, that must contain a field of type .Li SLIST_ENTRY , .Li STAILQ_ENTRY , .Li LIST_ENTRY , .Li TAILQ_ENTRY , or .Li CIRCLEQ_ENTRY , named .Fa NAME . The argument .Fa HEADNAME is the name of a user defined structure that must be declared using the macros .Li SLIST_HEAD , .Li STAILQ_HEAD , .Li LIST_HEAD , .Li TAILQ_HEAD , or .Li CIRCLEQ_HEAD . See the examples below for further explanation of how these macros are used. .Ss Tail queues A tail queue is headed by a structure defined by the .Nm 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 .Fa TAILQ_HEAD structure is declared as follows: .Bd -literal -offset indent TAILQ_HEAD(HEADNAME, TYPE) head; .Ed .Pp where .Li HEADNAME is the name of the structure to be defined, and .Li 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: .Bd -literal -offset indent struct HEADNAME *headp; .Ed .Pp (The names .Li head and .Li headp are user selectable.) .Pp The macro .Nm TAILQ_HEAD_INITIALIZER evaluates to an initializer for the tail queue .Fa head . .Pp The macro .Nm TAILQ_CONCAT concatenates the tail queue headed by .Fa head2 onto the end of the one headed by .Fa head1 removing all entries from the former. .Pp The macro .Nm TAILQ_EMPTY evaluates to true if there are no items on the tail queue. .Pp The macro .Nm TAILQ_ENTRY declares a structure that connects the elements in the tail queue. .Pp The macro .Nm TAILQ_FIRST returns the first item on the tail queue or NULL if the tail queue is empty. .Pp The macro .Nm TAILQ_FOREACH traverses the tail queue referenced by .Fa head in the forward direction, assigning each element in turn to .Fa var . .Fa var is set to .Dv NULL if the loop completes normally, or if there were no elements. .\" .Pp .\" The macro .\" .Nm TAILQ_FOREACH_FROM .\" behaves identically to .\" .Nm TAILQ_FOREACH .\" when .\" .Fa var .\" is NULL, else it treats .\" .Fa var .\" as a previously found TAILQ element and begins the loop at .\" .Fa var .\" instead of the first element in the TAILQ referenced by .\" .Fa head . .Pp The macro .Nm TAILQ_FOREACH_REVERSE traverses the tail queue referenced by .Fa head in the reverse direction, assigning each element in turn to .Fa var . .\" .Pp .\" The macro .\" .Nm TAILQ_FOREACH_REVERSE_FROM .\" behaves identically to .\" .Nm TAILQ_FOREACH_REVERSE .\" when .\" .Fa var .\" is NULL, else it treats .\" .Fa var .\" as a previously found TAILQ element and begins the reverse loop at .\" .Fa var .\" instead of the last element in the TAILQ referenced by .\" .Fa head . .\" .Pp .\" The macros .\" .Nm TAILQ_FOREACH_SAFE .\" and .\" .Nm TAILQ_FOREACH_REVERSE_SAFE .\" traverse the list referenced by .\" .Fa head .\" in the forward or reverse direction respectively, .\" assigning each element in turn to .\" .Fa var . .\" However, unlike their unsafe counterparts, .\" .Nm TAILQ_FOREACH .\" and .\" .Nm TAILQ_FOREACH_REVERSE .\" permit to both remove .\" .Fa var .\" as well as free it from within the loop safely without interfering with the .\" traversal. .\" .Pp .\" The macro .\" .Nm TAILQ_FOREACH_FROM_SAFE .\" behaves identically to .\" .Nm TAILQ_FOREACH_SAFE .\" when .\" .Fa var .\" is NULL, else it treats .\" .Fa var .\" as a previously found TAILQ element and begins the loop at .\" .Fa var .\" instead of the first element in the TAILQ referenced by .\" .Fa head . .\" .Pp .\" The macro .\" .Nm TAILQ_FOREACH_REVERSE_FROM_SAFE .\" behaves identically to .\" .Nm TAILQ_FOREACH_REVERSE_SAFE .\" when .\" .Fa var .\" is NULL, else it treats .\" .Fa var .\" as a previously found TAILQ element and begins the reverse loop at .\" .Fa var .\" instead of the last element in the TAILQ referenced by .\" .Fa head . .Pp The macro .Nm TAILQ_INIT initializes the tail queue referenced by .Fa head . .Pp The macro .Nm TAILQ_INSERT_HEAD inserts the new element .Fa elm at the head of the tail queue. .Pp The macro .Nm TAILQ_INSERT_TAIL inserts the new element .Fa elm at the end of the tail queue. .Pp The macro .Nm TAILQ_INSERT_AFTER inserts the new element .Fa elm after the element .Fa listelm . .Pp The macro .Nm TAILQ_INSERT_BEFORE inserts the new element .Fa elm before the element .Fa listelm . .Pp The macro .Nm TAILQ_LAST returns the last item on the tail queue. If the tail queue is empty the return value is .Dv NULL . .Pp The macro .Nm TAILQ_NEXT returns the next item on the tail queue, or NULL if this item is the last. .Pp The macro .Nm TAILQ_PREV returns the previous item on the tail queue, or NULL if this item is the first. .Pp The macro .Nm TAILQ_REMOVE removes the element .Fa elm from the tail queue. .\" .Pp .\" The macro .\" .Nm TAILQ_SWAP .\" swaps the contents of .\" .Fa head1 .\" and .\" .Fa head2 . .Pp See the EXAMPLES section below for an example program using a tail queue. .SH RETURN VALUE .SH CONFORMING TO .SH BUGS .SH EXAMPLES .SH SEE ALSO