.\" Copyright (c) 1993 .\" The Regents of the University of California. All rights reserved. .\" and Copyright (c) 2020 by Alejandro Colomar .\" .\" SPDX-License-Identifier: BSD-3-Clause .\" .\" .TH LIST 3 2023-03-30 "Linux man-pages 6.04" .SH NAME LIST_EMPTY, LIST_ENTRY, LIST_FIRST, LIST_FOREACH, .\"LIST_FOREACH_FROM, .\"LIST_FOREACH_SAFE, .\"LIST_FOREACH_FROM_SAFE, LIST_HEAD, LIST_HEAD_INITIALIZER, LIST_INIT, LIST_INSERT_AFTER, LIST_INSERT_BEFORE, LIST_INSERT_HEAD, LIST_NEXT, .\"LIST_PREV, LIST_REMOVE .\"LIST_SWAP \- implementation of a doubly linked list .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .B #include .PP .B LIST_ENTRY(TYPE); .PP .B LIST_HEAD(HEADNAME, TYPE); .BI "LIST_HEAD LIST_HEAD_INITIALIZER(LIST_HEAD " head ); .BI "void LIST_INIT(LIST_HEAD *" head ); .PP .BI "int LIST_EMPTY(LIST_HEAD *" head ); .PP .BI "void LIST_INSERT_HEAD(LIST_HEAD *" head , .BI " struct TYPE *" elm ", LIST_ENTRY " NAME ); .BI "void LIST_INSERT_BEFORE(struct TYPE *" listelm , .BI " struct TYPE *" elm ", LIST_ENTRY " NAME ); .BI "void LIST_INSERT_AFTER(struct TYPE *" listelm , .BI " struct TYPE *" elm ", LIST_ENTRY " NAME ); .PP .BI "struct TYPE *LIST_FIRST(LIST_HEAD *" head ); .\" .BI "struct TYPE *LIST_PREV(struct TYPE *" elm ", LIST_HEAD *" head , .\" .BI " struct TYPE, LIST_ENTRY " NAME ); .BI "struct TYPE *LIST_NEXT(struct TYPE *" elm ", LIST_ENTRY " NAME ); .PP .BI "LIST_FOREACH(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ); .\" .BI "LIST_FOREACH_FROM(struct TYPE *" var ", LIST_HEAD *" head ", LIST_ENTRY " NAME ); .\" .PP .\" .BI "LIST_FOREACH_SAFE(struct TYPE *" var ", LIST_HEAD *" head , .\" .BI " LIST_ENTRY " NAME ", struct TYPE *" temp_var ); .\" .BI "LIST_FOREACH_FROM_SAFE(struct TYPE *" var ", LIST_HEAD *" head , .\" .BI " LIST_ENTRY " NAME ", struct TYPE *" temp_var ); .PP .BI "void LIST_REMOVE(struct TYPE *" elm ", LIST_ENTRY " NAME ); .\" .PP .\" .BI "void LIST_SWAP(LIST_HEAD *" head1 ", LIST_HEAD *" head2 , .\" .BI " struct TYPE, LIST_ENTRY " NAME ); .fi .SH DESCRIPTION These macros define and operate on doubly linked lists. .PP In the macro definitions, .I TYPE is the name of a user-defined structure, that must contain a field of type .IR LIST_ENTRY , named .IR NAME . The argument .I HEADNAME is the name of a user-defined structure that must be declared using the macro .BR LIST_HEAD (). .SS Creation A list is headed by a structure defined by the .BR LIST_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. A .I LIST_HEAD structure is declared as follows: .PP .in +4 .EX LIST_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 list. A pointer to the head of the list 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 .BR LIST_ENTRY () declares a structure that connects the elements in the list. .PP .BR LIST_HEAD_INITIALIZER () evaluates to an initializer for the list .IR head . .PP .BR LIST_INIT () initializes the list referenced by .IR head . .PP .BR LIST_EMPTY () evaluates to true if there are no elements in the list. .SS Insertion .BR LIST_INSERT_HEAD () inserts the new element .I elm at the head of the list. .PP .BR LIST_INSERT_BEFORE () inserts the new element .I elm before the element .IR listelm . .PP .BR LIST_INSERT_AFTER () inserts the new element .I elm after the element .IR listelm . .SS Traversal .BR LIST_FIRST () returns the first element in the list, or NULL if the list is empty. .\" .PP .\" .BR LIST_PREV () .\" returns the previous element in the list, or NULL if this is the first. .\" List .\" .I head .\" must contain element .\" .IR elm . .PP .BR LIST_NEXT () returns the next element in the list, or NULL if this is the last. .PP .BR LIST_FOREACH () traverses the list referenced by .I head in the forward direction, assigning each element in turn to .IR var . .\" .PP .\" .BR LIST_FOREACH_FROM () .\" behaves identically to .\" .BR LIST_FOREACH () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found LIST element and begins the loop at .\" .I var .\" instead of the first element in the LIST referenced by .\" .IR head . .\" .PP .\" .BR LIST_FOREACH_SAFE () .\" traverses the list referenced by .\" .I head .\" in the forward direction, assigning each element in turn to .\" .IR var . .\" However, unlike .\" .BR LIST_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 .\" .BR LIST_FOREACH_FROM_SAFE () .\" behaves identically to .\" .BR LIST_FOREACH_SAFE () .\" when .\" .I var .\" is NULL, else it treats .\" .I var .\" as a previously found LIST element and begins the loop at .\" .I var .\" instead of the first element in the LIST referenced by .\" .IR head . .SS Removal .BR LIST_REMOVE () removes the element .I elm from the list. .\" .SS Other features .\" .BR LIST_SWAP () .\" swaps the contents of .\" .I head1 .\" and .\" .IR head2 . .SH RETURN VALUE .BR LIST_EMPTY () returns nonzero if the list is empty, and zero if the list contains at least one entry. .PP .BR LIST_FIRST (), and .BR LIST_NEXT () return a pointer to the first or next .I TYPE structure, respectively. .PP .BR LIST_HEAD_INITIALIZER () returns an initializer that can be assigned to the list .IR head . .SH STANDARDS BSD. .SH HISTORY 4.4BSD. .SH BUGS .BR LIST_FOREACH () doesn't allow .I var to be removed or freed within the loop, as it would interfere with the traversal. .BR LIST_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 .\" SRC BEGIN (list.c) .EX #include #include #include #include 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\en", 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); } .EE .\" SRC END .SH SEE ALSO .BR insque (3), .BR queue (7)