.\" 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 STAILQ 3 2020-10-21 "GNU" "Linux Programmer's Manual" .SH NAME STAILQ_CONCAT, STAILQ_EMPTY, STAILQ_ENTRY, STAILQ_FIRST, STAILQ_FOREACH, .\"STAILQ_FOREACH_FROM, .\"STAILQ_FOREACH_FROM_SAFE, .\"STAILQ_FOREACH_SAFE, STAILQ_HEAD, STAILQ_HEAD_INITIALIZER, STAILQ_INIT, STAILQ_INSERT_AFTER, STAILQ_INSERT_HEAD, STAILQ_INSERT_TAIL, .\"STAILQ_LAST, STAILQ_NEXT, STAILQ_REMOVE, .\"STAILQ_REMOVE_AFTER, STAILQ_REMOVE_HEAD, .\"STAILQ_SWAP \- implementation of a singly linked tail queue .SH SYNOPSIS .nf .B #include .PP .BI "void STAILQ_CONCAT(STAILQ_HEAD *" head1 ", STAILQ_HEAD *" head2 ");" .PP .BI "int STAILQ_EMPTY(STAILQ_HEAD *" head ");" .PP .B STAILQ_ENTRY(TYPE); .PP .BI "struct TYPE *STAILQ_FIRST(STAILQ_HEAD *" head ");" .PP .BI "STAILQ_FOREACH(struct TYPE *" var ", STAILQ_HEAD *" head ", STAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "STAILQ_FOREACH_FROM(struct TYPE *" var ", STAILQ_HEAD *" head ", STAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "STAILQ_FOREACH_FROM_SAFE(struct TYPE *" var ", STAILQ_HEAD *" head ", STAILQ_ENTRY " NAME ", struct TYPE *" temp_var ");" .\" .PP .\" .BI "STAILQ_FOREACH_SAFE(struct TYPE *" var ", STAILQ_HEAD *" head ", STAILQ_ENTRY " NAME ", struct TYPE *" temp_var ");" .PP .B STAILQ_HEAD(HEADNAME, TYPE); .PP .BI "STAILQ_HEAD STAILQ_HEAD_INITIALIZER(STAILQ_HEAD " head ");" .PP .BI "void STAILQ_INIT(STAILQ_HEAD *" head ");" .PP .BI "void STAILQ_INSERT_AFTER(STAILQ_HEAD *" head ", struct TYPE *" listelm "," .BI " struct TYPE *" elm ", STAILQ_ENTRY " NAME ");" .PP .BI "void STAILQ_INSERT_HEAD(STAILQ_HEAD *" head ", struct TYPE *" elm "," .BI " STAILQ_ENTRY " NAME ");" .PP .BI "void STAILQ_INSERT_TAIL(STAILQ_HEAD *" head ", struct TYPE *" elm "," .BI " STAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "struct TYPE *STAILQ_LAST(STAILQ_HEAD *" head ", struct TYPE *" elm ", STAILQ_ENTRY " NAME ");" .PP .BI "struct TYPE *STAILQ_NEXT(struct TYPE *" elm ", STAILQ_ENTRY " NAME ");" .PP .BI "void STAILQ_REMOVE(STAILQ_HEAD *" head ", struct TYPE *" elm ", TYPE," .BI " STAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "void STAILQ_REMOVE_AFTER(STAILQ_HEAD *" head ", struct TYPE *" elm "," .\" .BI " STAILQ_ENTRY " NAME ");" .PP .BI "void STAILQ_REMOVE_HEAD(STAILQ_HEAD *" head ", STAILQ_ENTRY " NAME ");" .\" .PP .\" .BI "void STAILQ_SWAP(STAILQ_HEAD *" head1 ", STAILQ_HEAD *" head2 "," .\" .BI " STAILQ_ENTRY " NAME ");" .fi .SH DESCRIPTION These macros define and operate on singly 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 STAILQ_ENTRY , named .IR NAME . The argument .I HEADNAME is the name of a user-defined structure that must be declared using the macro .BR STAILQ_HEAD (). .PP A singly linked tail queue is headed by a structure defined by the .BR STAILQ_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 singly linked for minimum space and pointer manipulation overhead at the expense of O(n) removal for arbitrary elements. New elements can be added to the tail queue after an existing element, at the head of the tail queue, or at the end of the tail queue. A .I STAILQ_HEAD structure is declared as follows: .PP .in +4 .EX STAILQ_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 STAILQ_HEAD_INITIALIZER () evaluates to an initializer for the tail queue .IR head . .PP The macro .BR STAILQ_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 STAILQ_EMPTY () evaluates to true if there are no items on the tail queue. .PP The macro .BR STAILQ_ENTRY () declares a structure that connects the elements in the tail queue. .PP The macro .BR STAILQ_FIRST () returns the first item on the tail queue or NULL if the tail queue is empty. .PP The macro .BR STAILQ_FOREACH () traverses the tail queue referenced by .I head in the forward direction, assigning each element in turn to .IR var . .\" .PP .\" The macro .\" .BR STAILQ_FOREACH_FROM () .\" behaves identically to .\" .BR STAILQ_FOREACH () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found STAILQ element and begins the loop at .\" .I var .\" instead of the first element in the STAILQ referenced by .\" .IR head . .\" .PP .\" The macro .\" .BR STAILQ_FOREACH_SAFE () .\" traverses the tail queue referenced by .\" .I head .\" in the forward direction, assigning each element .\" in turn to .\" .IR var . .\" However, unlike .\" .BR STAILQ_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 STAILQ_FOREACH_FROM_SAFE () .\" behaves identically to .\" .BR STAILQ_FOREACH_SAFE () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found STAILQ element and begins the loop at .\" .I var .\" instead of the first element in the STAILQ referenced by .\" .IR head . .PP The macro .BR STAILQ_INIT () initializes the tail queue referenced by .IR head . .PP The macro .BR STAILQ_INSERT_HEAD () inserts the new element .I elm at the head of the tail queue. .PP The macro .BR STAILQ_INSERT_TAIL () inserts the new element .I elm at the end of the tail queue. .PP The macro .BR STAILQ_INSERT_AFTER () inserts the new element .I elm after the element .IR listelm . .\" .PP .\" The macro .\" .BR STAILQ_LAST () .\" returns the last item on the tail queue. .\" If the tail queue is empty the return value is NULL . .PP The macro .BR STAILQ_NEXT () returns the next item on the tail queue, or NULL this item is the last. .\" .PP .\" The macro .\" .BR STAILQ_REMOVE_AFTER () .\" removes the element after .\" .I elm .\" from the tail queue. .\" Unlike .\" .BR STAILQ_REMOVE (), .\" this macro does not traverse the entire tail queue. .PP The macro .BR STAILQ_REMOVE_HEAD () removes the element at the head of the tail queue. For optimum efficiency, elements being removed from the head of the tail queue should use this macro explicitly rather than the generic .BR STAILQ_REMOVE () macro. .PP The macro .BR STAILQ_REMOVE () removes the element .I elm from the tail queue. .\" .PP .\" The macro .\" .BR STAILQ_SWAP () .\" swaps the contents of .\" .I head1 .\" and .\" .IR head2 . .SH RETURN VALUE .BR STAILQ_EMPTY () returns nonzero if the queue is empty, and zero if the queue contains at least one entry. .PP .BR STAILQ_FIRST (), and .BR STAILQ_NEXT () return a pointer to the first or next .I TYPE structure, respectively. .PP .BR STAILQ_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 (STAILQ macros first appeared in 4.4BSD). .SH BUGS The macro .BR STAILQ_FOREACH () doesn't allow .I var to be removed or freed within the loop, as it would interfere with the traversal. The macro .BR STAILQ_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; STAILQ_ENTRY(entry) entries; /* Singly linked tail queue. */ }; STAILQ_HEAD(stailhead, entry); int main(void) { struct entry *n1, *n2, *n3, *np; struct stailhead head; /* Singly linked tail queue head. */ STAILQ_INIT(&head); /* Initialize the queue. */ n1 = malloc(sizeof(struct entry)); /* Insert at the head. */ STAILQ_INSERT_HEAD(&head, n1, entries); n1 = malloc(sizeof(struct entry)); /* Insert at the tail. */ STAILQ_INSERT_TAIL(&head, n1, entries); n2 = malloc(sizeof(struct entry)); /* Insert after. */ STAILQ_INSERT_AFTER(&head, n1, n2, entries); STAILQ_REMOVE(&head, n2, entry, entries);/* Deletion. */ free(n2); n3 = STAILQ_FIRST(&head); STAILQ_REMOVE_HEAD(&head, entries); /* Deletion from the head. */ free(n3); n1 = STAILQ_FIRST(&head); n1->data = 0; for (int i = 1; i < 5; i++) { n1 = malloc(sizeof(struct entry)); STAILQ_INSERT_HEAD(&head, n1, entries); n1->data = i; } /* Forward traversal. */ STAILQ_FOREACH(np, &head, entries) printf("%i\en", np->data); /* TailQ Deletion. */ n1 = STAILQ_FIRST(&head); while (n1 != NULL) { n2 = STAILQ_NEXT(n1, entries); free(n1); n1 = n2; } STAILQ_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/.