SIMPLE SOLUTIONS

INSQUE(3) - man page online | library functions

Insert/remove an item from a queue.

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2015-08-08
INSQUE(3)                           Linux Programmer's Manual                           INSQUE(3)

NAME insque, remque - insert/remove an item from a queue
SYNOPSIS #include <search.h> void insque(void *elem, void *prev); void remque(void *elem); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): insque(), remque(): _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
DESCRIPTION The insque() and remque() functions manipulate doubly-linked lists. Each element in the list is a structure of which the first two elements are a forward and a backward pointer. The linked list may be linear (i.e., NULL forward pointer at the end of the list and NULL backward pointer at the start of the list) or circular. The insque() function inserts the element pointed to by elem immediately after the element pointed to by prev. If the list is linear, then the call insque(elem, NULL) can be used to insert the initial list element, and the call sets the forward and backward pointers of elem to NULL. If the list is circular, the caller should ensure that the forward and backward pointers of the first element are initialized to point to that element, and the prev argument of the insque() call should also point to the element. The remque() function removes the element pointed to by elem from the doubly-linked list.
ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌───────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├───────────────────┼───────────────┼─────────┤ │insque(), remque() │ Thread safety │ MT-Safe │ └───────────────────┴───────────────┴─────────┘
CONFORMING TO POSIX.1-2001, POSIX.1-2008.
NOTES Traditionally (e.g., SunOS, Linux libc4 and libc5), the arguments of these functions were of type struct qelem *, defined as: struct qelem { struct qelem *q_forw; struct qelem *q_back; char q_data[1]; }; This is still what you will get if _GNU_SOURCE is defined before including <search.h>. The location of the prototypes for these functions differs among several versions of UNIX. The above is the POSIX version. Some systems place them in <string.h>.
BUGS In glibc 2.4 and earlier, it was not possible to specify prev as NULL. Consequently, to build a linear list, the caller had to build a list using an initial call that contained the first two elements of the list, with the forward and backward pointers in each element suitably initialized.
EXAMPLE The program below demonstrates the use of insque(). Here is an example run of the pro‐ gram: $ ./a.out -c a b c Traversing completed list: a b c That was a circular list Program source #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <search.h> struct element { struct element *forward; struct element *backward; char *name; }; static struct element * new_element(void) { struct element *e; e = malloc(sizeof(struct element)); if (e == NULL) { fprintf(stderr, "malloc() failed\n"); exit(EXIT_FAILURE); } return e; } int main(int argc, char *argv[]) { struct element *first, *elem, *prev; int circular, opt, errfnd; /* The "-c" command-line option can be used to specify that the list is circular */ errfnd = 0; circular = 0; while ((opt = getopt(argc, argv, "c")) != -1) { switch (opt) { case 'c': circular = 1; break; default: errfnd = 1; break; } } if (errfnd || optind >= argc) { fprintf(stderr, "Usage: %s [-c] string...\n", argv[0]); exit(EXIT_FAILURE); } /* Create first element and place it in the linked list */ elem = new_element(); first = elem; elem->name = argv[optind]; if (circular) { elem->forward = elem; elem->backward = elem; insque(elem, elem); } else { insque(elem, NULL); } /* Add remaining command-line arguments as list elements */ while (++optind < argc) { prev = elem; elem = new_element(); elem->name = argv[optind]; insque(elem, prev); } /* Traverse the list from the start, printing element names */ printf("Traversing completed list:\n"); elem = first; do { printf(" %s\n", elem->name); elem = elem->forward; } while (elem != NULL && elem != first); if (elem == first) printf("That was a circular list\n"); exit(EXIT_SUCCESS); }
COLOPHON This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.
2015-08-08 INSQUE(3)
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refer to attributes(7) | feature_test_macros(7)