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.
EINVALWhen null pointers are incorrectly passed as arguments to most functions.
ENOSPCWhen 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>