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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |VERSIONS |BUGS |STANDARDS |HISTORY |EXAMPLES |SEE ALSO |COLOPHON | |
STAILQ(3) Library Functions ManualSTAILQ(3)SIMPLEQ_EMPTY, SIMPLEQ_ENTRY, SIMPLEQ_FIRST, SIMPLEQ_FOREACH, SIMPLEQ_HEAD, SIMPLEQ_HEAD_INITIALIZER, SIMPLEQ_INIT, SIMPLEQ_INSERT_AFTER, SIMPLEQ_INSERT_HEAD, SIMPLEQ_INSERT_TAIL, SIMPLEQ_NEXT, SIMPLEQ_REMOVE, SIMPLEQ_REMOVE_HEAD, STAILQ_CONCAT, STAILQ_EMPTY, STAILQ_ENTRY, STAILQ_FIRST, STAILQ_FOREACH, STAILQ_HEAD, STAILQ_HEAD_INITIALIZER, STAILQ_INIT, STAILQ_INSERT_AFTER, STAILQ_INSERT_HEAD, STAILQ_INSERT_TAIL, STAILQ_NEXT, STAILQ_REMOVE, STAILQ_REMOVE_HEAD, - implementation of a singly linked tail queue
Standard C library (libc,-lc)
#include <sys/queue.h>STAILQ_ENTRY(TYPE);STAILQ_HEAD(HEADNAME, TYPE);STAILQ_HEAD STAILQ_HEAD_INITIALIZER(STAILQ_HEADhead);void STAILQ_INIT(STAILQ_HEAD *head);int STAILQ_EMPTY(STAILQ_HEAD *head);void STAILQ_INSERT_HEAD(STAILQ_HEAD *head,struct TYPE *elm, STAILQ_ENTRYNAME);void STAILQ_INSERT_TAIL(STAILQ_HEAD *head,struct TYPE *elm, STAILQ_ENTRYNAME);void STAILQ_INSERT_AFTER(STAILQ_HEAD *head, struct TYPE *listelm,struct TYPE *elm, STAILQ_ENTRYNAME);struct TYPE *STAILQ_FIRST(STAILQ_HEAD *head);struct TYPE *STAILQ_NEXT(struct TYPE *elm, STAILQ_ENTRYNAME);STAILQ_FOREACH(struct TYPE *var, STAILQ_HEAD *head, STAILQ_ENTRYNAME);void STAILQ_REMOVE(STAILQ_HEAD *head, struct TYPE *elm, TYPE,STAILQ_ENTRYNAME);void STAILQ_REMOVE_HEAD(STAILQ_HEAD *head,STAILQ_ENTRYNAME);void STAILQ_CONCAT(STAILQ_HEAD *head1, STAILQ_HEAD *head2);Note: Identical macros prefixed with SIMPLEQ instead of STAILQ exist; see VERSIONS.
These macros define and operate on singly linked tail queues. In the macro definitions,TYPE is the name of a user-defined structure, that must contain a field of typeSTAILQ_ENTRY, namedNAME. The argumentHEADNAME is the name of a user-defined structure that must be declared using the macroSTAILQ_HEAD().Creation A singly linked tail queue is headed by a structure defined by theSTAILQ_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. ASTAILQ_HEAD structure is declared as follows: STAILQ_HEAD(HEADNAME, TYPE) head; wherestruct HEADNAME is the structure to be defined, andstructTYPE 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: struct HEADNAME *headp; (The nameshead andheadp are user selectable.)STAILQ_ENTRY() declares a structure that connects the elements in the tail queue.STAILQ_HEAD_INITIALIZER() evaluates to an initializer for the tail queuehead.STAILQ_INIT() initializes the tail queue referenced byhead.STAILQ_EMPTY() evaluates to true if there are no items on the tail queue.InsertionSTAILQ_INSERT_HEAD() inserts the new elementelm at the head of the tail queue.STAILQ_INSERT_TAIL() inserts the new elementelm at the end of the tail queue.STAILQ_INSERT_AFTER() inserts the new elementelm after the elementlistelm.TraversalSTAILQ_FIRST() returns the first item on the tail queue or NULL if the tail queue is empty.STAILQ_NEXT() returns the next item on the tail queue, or NULL this item is the last.STAILQ_FOREACH() traverses the tail queue referenced byhead in the forward direction, assigning each element in turn tovar.RemovalSTAILQ_REMOVE() removes the elementelm from the tail queue.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 genericSTAILQ_REMOVE() macro.Other featuresSTAILQ_CONCAT() concatenates the tail queue headed byhead2 onto the end of the one headed byhead1 removing all entries from the former.
STAILQ_EMPTY() returns nonzero if the queue is empty, and zero if the queue contains at least one entry.STAILQ_FIRST(), andSTAILQ_NEXT() return a pointer to the first or nextTYPE structure, respectively.STAILQ_HEAD_INITIALIZER() returns an initializer that can be assigned to the queuehead.
Some BSDs provide SIMPLEQ instead of STAILQ. They are identical, but for historical reasons they were named differently on different BSDs. STAILQ originated on FreeBSD, and SIMPLEQ originated on NetBSD. For compatibility reasons, some systems provide both sets of macros. glibc provides both STAILQ and SIMPLEQ, which are identical except for a missing SIMPLEQ equivalent toSTAILQ_CONCAT().
STAILQ_FOREACH() doesn't allowvar to be removed or freed within the loop, as it would interfere with the traversal.STAILQ_FOREACH_SAFE(), which is present on the BSDs but is not present in glibc, fixes this limitation by allowingvar to safely be removed from the list and freed from within the loop without interfering with the traversal.
BSD.
4.4BSD.
#include <stddef.h> #include <stdio.h> #include <stdlib.h> #include <sys/queue.h> 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 (unsigned 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\n", 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); }insque(3),queue(7)
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17STAILQ(3)Pages that refer to this page:queue(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |