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. |  |
NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |STANDARDS |HISTORY |BUGS |EXAMPLES |SEE ALSO |COLOPHON | |
LIST(3) Library Functions ManualLIST(3)LIST_EMPTY, LIST_ENTRY, LIST_FIRST, LIST_FOREACH, LIST_HEAD, LIST_HEAD_INITIALIZER, LIST_INIT, LIST_INSERT_AFTER, LIST_INSERT_BEFORE, LIST_INSERT_HEAD, LIST_NEXT, LIST_REMOVE - implementation of a doubly linked list
Standard C library (libc,-lc)
#include <sys/queue.h>LIST_ENTRY(TYPE);LIST_HEAD(HEADNAME, TYPE);LIST_HEAD LIST_HEAD_INITIALIZER(LIST_HEADhead);void LIST_INIT(LIST_HEAD *head);int LIST_EMPTY(LIST_HEAD *head);void LIST_INSERT_HEAD(LIST_HEAD *head,struct TYPE *elm, LIST_ENTRYNAME);void LIST_INSERT_BEFORE(struct TYPE *listelm,struct TYPE *elm, LIST_ENTRYNAME);void LIST_INSERT_AFTER(struct TYPE *listelm,struct TYPE *elm, LIST_ENTRYNAME);struct TYPE *LIST_FIRST(LIST_HEAD *head);struct TYPE *LIST_NEXT(struct TYPE *elm, LIST_ENTRYNAME);LIST_FOREACH(struct TYPE *var, LIST_HEAD *head, LIST_ENTRYNAME);void LIST_REMOVE(struct TYPE *elm, LIST_ENTRYNAME);
These macros define and operate on doubly linked lists. In the macro definitions,TYPE is the name of a user-defined structure, that must contain a field of typeLIST_ENTRY, namedNAME. The argumentHEADNAME is the name of a user-defined structure that must be declared using the macroLIST_HEAD().Creation A list is headed by a structure defined by theLIST_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. ALIST_HEAD structure is declared as follows: LIST_HEAD(HEADNAME, TYPE) head; wherestruct HEADNAME is the structure to be defined, andstructTYPE 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: struct HEADNAME *headp; (The nameshead andheadp are user selectable.)LIST_ENTRY() declares a structure that connects the elements in the list.LIST_HEAD_INITIALIZER() evaluates to an initializer for the listhead.LIST_INIT() initializes the list referenced byhead.LIST_EMPTY() evaluates to true if there are no elements in the list.InsertionLIST_INSERT_HEAD() inserts the new elementelm at the head of the list.LIST_INSERT_BEFORE() inserts the new elementelm before the elementlistelm.LIST_INSERT_AFTER() inserts the new elementelm after the elementlistelm.TraversalLIST_FIRST() returns the first element in the list, or NULL if the list is empty.LIST_NEXT() returns the next element in the list, or NULL if this is the last.LIST_FOREACH() traverses the list referenced byhead in the forward direction, assigning each element in turn tovar.RemovalLIST_REMOVE() removes the elementelm from the list.
LIST_EMPTY() returns nonzero if the list is empty, and zero if the list contains at least one entry.LIST_FIRST(), andLIST_NEXT() return a pointer to the first or nextTYPE structure, respectively.LIST_HEAD_INITIALIZER() returns an initializer that can be assigned to the listhead.
BSD.
4.4BSD.
LIST_FOREACH() doesn't allowvar to be removed or freed within the loop, as it would interfere with the traversal.LIST_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.
#include <stddef.h> #include <stdio.h> #include <stdlib.h> #include <sys/queue.h> 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\n", 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); }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 2025-05-17LIST(3)Pages that refer to this page:man-pages(7), 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. | |