libslack(link) - linked list module
#include <slack/std.h> #include <slack/link.h> typedef struct slink_t slink_t; typedef struct dlink_t dlink_t; struct slink_t { void *next; }; struct dlink_t { void *next; void *prev; }; int slink_has_next(void *link); void *slink_next(void *link); int dlink_has_next(void *link); void *dlink_next(void *link); int dlink_has_prev(void *link); void *dlink_prev(void *link); void *slink_insert(void *link, void *item); void *dlink_insert(void *link, void *item); void *slink_remove(void *link); void *dlink_remove(void *link); void *slink_freelist_init(void *freelist, size_t nelem, size_t size); void *dlink_freelist_init(void *freelist, size_t nelem, size_t size); void *slink_freelist_attach(void *freelist1, void *freelist2); void *dlink_freelist_attach(void *freelist1, void *freelist2); void *slink_alloc(void **freelist); void *dlink_alloc(void **freelist); void *slink_free(void **freelist, void *item); void *dlink_free(void **freelist, void *item);
This module provides functions for manipulating singly and doubly linked lists. Two abstract types are defined: slink_t, containing a pointer to the next item, and dlink_t, containing pointers to the next and previous items. These functions work with any struct whose first element is an slink_t or a dlink_t struct. There is support for optional growable free lists so items may be dynamically allocated individually or allocated from a free list. Free lists can be arrays of structs or dynamically allocated. When a free list is exhausted, further memory may be attached to the free list to extend it.
int slink_has_next(void *link)
Returns 1
if link
's next
pointer is not null
. Otherwise, returns
0
. On error, returns -1
with errno
set appropriately.
void *slink_next(void *link)
Returns link
's next
pointer. On error, returns null
with errno
set appropriately.
int dlink_has_next(void *link)
Returns 1
if link
's next
pointer is not null
. Otherwise, returns
0
. On error, returns -1
with errno
set appropriately.
void *dlink_next(void *link)
Returns link
's next
pointer. On error, returns null
with errno
set appropriately.
int dlink_has_prev(void *link)
Returns 1
if link
's prev
pointer is not null
. Otherwise, returns
0
. On error, returns -1
with errno
set appropriately.
void *dlink_prev(void *link)
Returns link
's prev
pointer. On error, returns null
with errno
set appropriately.
void *slink_insert(void *link, void *item)
Inserts item
before link
. Returns item
. On error, returns null
with errno
set appropriately. Items may only be inserted at the beginning
of a singly linked list.
void *dlink_insert(void *link, void *item)
Inserts item
before link
. Returns item
. On error, returns null
with errno
set appropriately. Items may be inserted anywhere in a doubly
linked list.
void *slink_remove(void *link)
Removes the first item from the list beginning with link
. On success,
returns link
's next
pointer. On error, returns null
with errno
set appropriately.
void *dlink_remove(void *link)
Removes link
from the list of which it is part. On success, returns
link
's next
pointer. On error, returns null
with errno
set
appropriately.
void *slink_freelist_init(void *freelist, size_t nelem, size_t size)
Initialises an array of nelem
elements each size
bytes for use as a
singly linked free list. On success, returns freelist
. On error, returns
null
with errno
set appropriately.
void *dlink_freelist_init(void *freelist, size_t nelem, size_t size)
Initialises an array of nelem
elements each size
bytes for use as a
doubly linked free list. On success, returns freelist
. On error, returns
null
with errno
set appropriately.
void *slink_freelist_attach(void *freelist1, void *freelist2)
Attaches freelist2
to the end of freelist1
. Both free lists must have
already been initialised with slink_freelist_init(3). Note that it will
not be possible to separate these free lists. On success, returns a pointer
to the beginning of the combined freelist. On error, returns null
with
errno
set appropriately.
void *dlink_freelist_attach(void *freelist1, void *freelist2)
Attaches freelist2
to the end of freelist1
. Both free lists must have
already been initialised with dlink_freelist_init(3). Note that it will
not be possible to separate these free lists. On success, returns a pointer
to the beginning of the combined freelist. On error, returns null
with
errno
set appropriately.
void *slink_alloc(void **freelist)
Allocates an item from *freelist
and updates *freelist
to point to the
next free item. *freelist
must be a singly linked freelist initialised
with slink_freelist_init(3). On success, returns the allocated item. On
error, returns null
with errno
set appropriately.
void *dlink_alloc(void **freelist)
Allocates an item from *freelist
and updates *freelist
to point to the
next free item. *freelist
must be a doubly linked freelist initialised
with dlink_freelist_init(3). On success, returns the allocated item. On
error, returns null
with errno
set appropriately.
void *slink_free(void **freelist, void *item)
Inserts item
into *freelist
and updates *freelist
to point to
item. *freelist
must be a singly linked freelist initialised with
slink_freelist_init(3). On success, returns the resulting free list. On
error, returns null
with errno
set appropriately.
void *dlink_free(void **freelist, void *item)
Inserts item
into *freelist
and updates *freelist
to point to
item
. *freelist
must be a doubly linked freelist initialised with
dlink_freelist_init(3). On success, returns the resulting free list. On
error, returns null
with errno
set appropriately.
The following errors are returned by these functions.
EINVAL
When null
pointers are incorrectly passed as arguments to most functions.
ENOSPC
When slink_alloc(3) or dlink_alloc(3) is called and the free list is exhausted.
Unsafe
This module declares abstract types. They must be used as part of larger data structures. It is assumed that the surrounding data structure and its functions will provide any locking that is required.
A singly linked example that reads pairs of numbers from stdin (attaching more space to the list as necessary), iterates over the items and then deletes them:
#include <slack/std.h> #include <slack/link.h> typedef struct spoint_t spoint_t; struct spoint_t { slink_t link; int x; int y; }; #define SLIST_SIZE 10 #define MAX_ADDITIONS 100 spoint_t sfreespace[SLIST_SIZE]; spoint_t *sfreelist = sfreespace; spoint_t *spoints = NULL; spoint_t *additional[MAX_ADDITIONS]; int added = 0; int main(int ac, char **av) { spoint_t *item, *morespace; int x, y, i; // Initialize the singly-linked list of points if (slink_freelist_init(sfreespace, SLIST_SIZE, sizeof(spoint_t)) != sfreespace) return EXIT_FAILURE; // Read coordinates from stdin and populate the list while (scanf("%d %d", &x, &y) == 2) { // Add more space to the list when it runs out if (!(item = slink_alloc((void **)&sfreelist))) { if (added == MAX_ADDITIONS) return EXIT_FAILURE; // or extend additional if (!(morespace = malloc(SLIST_SIZE * sizeof(spoint_t)))) return EXIT_FAILURE; additional[added++] = morespace; // remember to free this if (slink_freelist_init(morespace, SLIST_SIZE, sizeof(spoint_t)) != morespace) return EXIT_FAILURE; if (!(sfreelist = slink_freelist_attach(sfreelist, morespace))) return EXIT_FAILURE; if (!(item = slink_alloc((void **)&sfreelist))) return EXIT_FAILURE; } // Initialize the item item->x = x; item->y = y; // Insert it into the list if (!(spoints = slink_insert(spoints, item))) return EXIT_FAILURE; } // Iterate over the list with slink_next() for (item = spoints; item; item = slink_next(item)) printf("%d %d\n", item->x, item->y); // Iterate over the list with slink_has_next() for (item = spoints; slink_has_next(item) == 1; item = slink_next(item)) { spoint_t *next = slink_next(item); printf("%d %d -> %d %d\n", item->x, item->y, next->x, next->y); } if (item) printf("%d %d !\n", item->x, item->y); // Remove the items (printing them out) while (spoints) { spoints = slink_remove(item = spoints); printf("%d %d\n", item->x, item->y); slink_free((void **)&sfreelist, item); } // Deallocate any attached freelists for (i = 0; i < added; ++i) free(additional[i]); return EXIT_SUCCESS; }
A doubly linked example that reads pairs of numbers from stdin (attaching more space to the list as necessary), iterates over the items and then deletes them:
#include <slack/std.h> #include <slack/link.h> typedef struct dpoint_t dpoint_t; struct dpoint_t { dlink_t link; int x; int y; }; #define DLIST_SIZE 10 #define MAX_ADDITIONS 100 dpoint_t dfreespace[DLIST_SIZE]; dpoint_t *dfreelist = dfreespace; dpoint_t *dpoints = NULL; dpoint_t *additional[MAX_ADDITIONS]; int added = 0; int main(int ac, char **av) { dpoint_t *item, *morespace; dpoint_t *last; int x, y, i; // Initialize the doubly-linked list of points if (dlink_freelist_init(dfreespace, DLIST_SIZE, sizeof(dpoint_t)) != dfreespace) return EXIT_FAILURE; // Read coordinates from stdin and populate the list while (scanf("%d %d", &x, &y) == 2) { // Add more space to the list when it runs out if (!(item = dlink_alloc((void **)&dfreelist))) { if (added == MAX_ADDITIONS) return EXIT_FAILURE; // or extend additional if (!(morespace = malloc(DLIST_SIZE * sizeof(dpoint_t)))) return EXIT_FAILURE; additional[added++] = morespace; // remember to free this if (dlink_freelist_init(morespace, DLIST_SIZE, sizeof(dpoint_t)) != morespace) return EXIT_FAILURE; if (!(dfreelist = dlink_freelist_attach(dfreelist, morespace))) return EXIT_FAILURE; if (!(item = dlink_alloc((void **)&dfreelist))) return EXIT_FAILURE; } // Initialize the item item->x = x; item->y = y; // Insert it into the list if (!(dpoints = dlink_insert(dpoints, item))) return EXIT_FAILURE; } // Iterate over the list with dlink_next() for (item = dpoints; item; item = dlink_next(item)) { dpoint_t *prev = dlink_prev(item); dpoint_t *next = dlink_next(item); if (prev && next) printf("%d %d -> %d %d -> %d %d\n", prev->x, prev->y, item->x, item->y, next->x, next->y); else if (prev) printf("%d %d -> %d %d -> end\n", prev->x, prev->y, item->x, item->y); else if (next) printf("start -> %d %d -> %d %d\n", item->x, item->y, next->x, next->y); } // Iterate backwards with dlink_has_next() and dlink_prev() for (item = dpoints; dlink_has_next(item) == 1; item = dlink_next(item)) {} for (; item; item = dlink_prev(item)) { dpoint_t *prev = dlink_prev(item); dpoint_t *next = dlink_next(item); if (prev && next) printf("%d %d -> %d %d -> %d %d\n", prev->x, prev->y, item->x, item->y, next->x, next->y); else if (prev) printf("%d %d -> %d %d -> end\n", prev->x, prev->y, item->x, item->y); else if (next) printf("start -> %d %d -> %d %d\n", item->x, item->y, next->x, next->y); } // Remove the items (printing them out) while (dpoints) { dpoints = dlink_remove(item = dpoints); printf("%d %d\n", item->x, item->y); dlink_free((void **)&dfreelist, item); } // Deallocate any attached freelists for (i = 0; i < added; ++i) free(additional[i]); return EXIT_SUCCESS; }
These functions only work on structs where the next
and prev
pointers
at the first elements. To fix this would require adding an offset
parameter to each function to tell it where the next
and prev
pointers
were within the item. It's probably not worth it.
Attached free lists can't be detached. To change this would require more code and more metadata. Again, it's probably not worth it.
libslack(3), list(3), map(3), mem(3), locker(3)
20100612 raf <raf@raf.org>