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Commit 765ff8ca authored by ericrw96's avatar ericrw96
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Add in example code

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CFLAGS=-Wall -Werror -Wmissing-prototypes -g -fPIC
CFILES=list.c list_example.c
default:
$(CC) -o list_example $(CFLAGS) $(CFILES)
README 0 → 100644
This is an example of using the given list implementation
list.c 0 → 100644
#include "list.h"
#include <assert.h>
/* Our doubly linked lists have two header elements: the "head"
just before the first element and the "tail" just after the
last element. The `prev' link of the front header is null, as
is the `next' link of the back header. Their other two links
point toward each other via the interior elements of the list.
An empty list looks like this:
+------+ +------+
<---| head |<--->| tail |--->
+------+ +------+
A list with two elements in it looks like this:
+------+ +-------+ +-------+ +------+
<---| head |<--->| 1 |<--->| 2 |<--->| tail |<--->
+------+ +-------+ +-------+ +------+
The symmetry of this arrangement eliminates lots of special
cases in list processing. For example, take a look at
list_remove(): it takes only two pointer assignments and no
conditionals. That's a lot simpler than the code would be
without header elements.
(Because only one of the pointers in each header element is used,
we could in fact combine them into a single header element
without sacrificing this simplicity. But using two separate
elements allows us to do a little bit of checking on some
operations, which can be valuable.) */
static bool is_sorted (struct list_elem *a, struct list_elem *b,
list_less_func *less, void *aux);
/* Returns true if ELEM is a head, false otherwise. */
static inline bool
is_head (struct list_elem *elem)
{
return elem != NULL && elem->prev == NULL && elem->next != NULL;
}
/* Returns true if ELEM is an interior element,
false otherwise. */
static inline bool
is_interior (struct list_elem *elem)
{
return elem != NULL && elem->prev != NULL && elem->next != NULL;
}
/* Returns true if ELEM is a tail, false otherwise. */
static inline bool
is_tail (struct list_elem *elem)
{
return elem != NULL && elem->prev != NULL && elem->next == NULL;
}
/* Initializes LIST as an empty list. */
void
list_init (struct list *list)
{
assert (list != NULL);
list->head.prev = NULL;
list->head.next = &list->tail;
list->tail.prev = &list->head;
list->tail.next = NULL;
}
/* Returns the beginning of LIST. */
struct list_elem *
list_begin (struct list *list)
{
assert (list != NULL);
return list->head.next;
}
/* Returns the element after ELEM in its list. If ELEM is the
last element in its list, returns the list tail. Results are
undefined if ELEM is itself a list tail. */
struct list_elem *
list_next (struct list_elem *elem)
{
assert (is_head (elem) || is_interior (elem));
return elem->next;
}
/* Returns LIST's tail.
list_end() is often used in iterating through a list from
front to back. See the big comment at the top of list.h for
an example. */
struct list_elem *
list_end (struct list *list)
{
assert (list != NULL);
return &list->tail;
}
/* Returns the LIST's reverse beginning, for iterating through
LIST in reverse order, from back to front. */
struct list_elem *
list_rbegin (struct list *list)
{
assert (list != NULL);
return list->tail.prev;
}
/* Returns the element before ELEM in its list. If ELEM is the
first element in its list, returns the list head. Results are
undefined if ELEM is itself a list head. */
struct list_elem *
list_prev (struct list_elem *elem)
{
assert (is_interior (elem) || is_tail (elem));
return elem->prev;
}
/* Returns LIST's head.
list_rend() is often used in iterating through a list in
reverse order, from back to front. Here's typical usage,
following the example from the top of list.h:
for (e = list_rbegin (&foo_list); e != list_rend (&foo_list);
e = list_prev (e))
{
struct foo *f = list_entry (e, struct foo, elem);
...do something with f...
}
*/
struct list_elem *
list_rend (struct list *list)
{
assert (list != NULL);
return &list->head;
}
/* Return's LIST's head.
list_head() can be used for an alternate style of iterating
through a list, e.g.:
e = list_head (&list);
while ((e = list_next (e)) != list_end (&list))
{
...
}
*/
struct list_elem *
list_head (struct list *list)
{
assert (list != NULL);
return &list->head;
}
/* Return's LIST's tail. */
struct list_elem *
list_tail (struct list *list)
{
assert (list != NULL);
return &list->tail;
}
/* Inserts ELEM just before BEFORE, which may be either an
interior element or a tail. The latter case is equivalent to
list_push_back(). */
void
list_insert (struct list_elem *before, struct list_elem *elem)
{
assert (is_interior (before) || is_tail (before));
assert (elem != NULL);
elem->prev = before->prev;
elem->next = before;
before->prev->next = elem;
before->prev = elem;
}
/* Removes elements FIRST though LAST (exclusive) from their
current list, then inserts them just before BEFORE, which may
be either an interior element or a tail. */
void
list_splice (struct list_elem *before,
struct list_elem *first, struct list_elem *last)
{
assert (is_interior (before) || is_tail (before));
if (first == last)
return;
last = list_prev (last);
assert (is_interior (first));
assert (is_interior (last));
/* Cleanly remove FIRST...LAST from its current list. */
first->prev->next = last->next;
last->next->prev = first->prev;
/* Splice FIRST...LAST into new list. */
first->prev = before->prev;
last->next = before;
before->prev->next = first;
before->prev = last;
}
/* Inserts ELEM at the beginning of LIST, so that it becomes the
front in LIST. */
void
list_push_front (struct list *list, struct list_elem *elem)
{
list_insert (list_begin (list), elem);
}
/* Inserts ELEM at the end of LIST, so that it becomes the
back in LIST. */
void
list_push_back (struct list *list, struct list_elem *elem)
{
list_insert (list_end (list), elem);
}
/* Removes ELEM from its list and returns the element that
followed it. Undefined behavior if ELEM is not in a list.
It's not safe to treat ELEM as an element in a list after
removing it. In particular, using list_next() or list_prev()
on ELEM after removal yields undefined behavior. This means
that a naive loop to remove the elements in a list will fail:
** DON'T DO THIS **
for (e = list_begin (&list); e != list_end (&list); e = list_next (e))
{
...do something with e...
list_remove (e);
}
** DON'T DO THIS **
Here is one correct way to iterate and remove elements from a
list:
for (e = list_begin (&list); e != list_end (&list); e = list_remove (e))
{
...do something with e...
}
If you need to free() elements of the list then you need to be
more conservative. Here's an alternate strategy that works
even in that case:
while (!list_empty (&list))
{
struct list_elem *e = list_pop_front (&list);
...do something with e...
}
*/
struct list_elem *
list_remove (struct list_elem *elem)
{
assert (is_interior (elem));
elem->prev->next = elem->next;
elem->next->prev = elem->prev;
return elem->next;
}
/* Removes the front element from LIST and returns it.
Undefined behavior if LIST is empty before removal. */
struct list_elem *
list_pop_front (struct list *list)
{
struct list_elem *front = list_front (list);
list_remove (front);
return front;
}
/* Removes the back element from LIST and returns it.
Undefined behavior if LIST is empty before removal. */
struct list_elem *
list_pop_back (struct list *list)
{
struct list_elem *back = list_back (list);
list_remove (back);
return back;
}
/* Returns the front element in LIST.
Undefined behavior if LIST is empty. */
struct list_elem *
list_front (struct list *list)
{
assert (!list_empty (list));
return list->head.next;
}
/* Returns the back element in LIST.
Undefined behavior if LIST is empty. */
struct list_elem *
list_back (struct list *list)
{
assert (!list_empty (list));
return list->tail.prev;
}
/* Returns the number of elements in LIST.
Runs in O(n) in the number of elements. */
size_t
list_size (struct list *list)
{
struct list_elem *e;
size_t cnt = 0;
for (e = list_begin (list); e != list_end (list); e = list_next (e))
cnt++;
return cnt;
}
/* Returns true if LIST is empty, false otherwise. */
bool
list_empty (struct list *list)
{
return list_begin (list) == list_end (list);
}
/* Swaps the `struct list_elem *'s that A and B point to. */
static void
swap (struct list_elem **a, struct list_elem **b)
{
struct list_elem *t = *a;
*a = *b;
*b = t;
}
/* Reverses the order of LIST. */
void
list_reverse (struct list *list)
{
if (!list_empty (list))
{
struct list_elem *e;
for (e = list_begin (list); e != list_end (list); e = e->prev)
swap (&e->prev, &e->next);
swap (&list->head.next, &list->tail.prev);
swap (&list->head.next->prev, &list->tail.prev->next);
}
}
/* Returns true only if the list elements A through B (exclusive)
are in order according to LESS given auxiliary data AUX. */
static bool
is_sorted (struct list_elem *a, struct list_elem *b,
list_less_func *less, void *aux)
{
if (a != b)
while ((a = list_next (a)) != b)
if (less (a, list_prev (a), aux))
return false;
return true;
}
/* Finds a run, starting at A and ending not after B, of list
elements that are in nondecreasing order according to LESS
given auxiliary data AUX. Returns the (exclusive) end of the
run.
A through B (exclusive) must form a non-empty range. */
static struct list_elem *
find_end_of_run (struct list_elem *a, struct list_elem *b,
list_less_func *less, void *aux)
{
assert (a != NULL);
assert (b != NULL);
assert (less != NULL);
assert (a != b);
do
{
a = list_next (a);
}
while (a != b && !less (a, list_prev (a), aux));
return a;
}
/* Merges A0 through A1B0 (exclusive) with A1B0 through B1
(exclusive) to form a combined range also ending at B1
(exclusive). Both input ranges must be nonempty and sorted in
nondecreasing order according to LESS given auxiliary data
AUX. The output range will be sorted the same way. */
static void
inplace_merge (struct list_elem *a0, struct list_elem *a1b0,
struct list_elem *b1,
list_less_func *less, void *aux)
{
assert (a0 != NULL);
assert (a1b0 != NULL);
assert (b1 != NULL);
assert (less != NULL);
assert (is_sorted (a0, a1b0, less, aux));
assert (is_sorted (a1b0, b1, less, aux));
while (a0 != a1b0 && a1b0 != b1)
if (!less (a1b0, a0, aux))
a0 = list_next (a0);
else
{
a1b0 = list_next (a1b0);
list_splice (a0, list_prev (a1b0), a1b0);
}
}
/* Sorts LIST according to LESS given auxiliary data AUX, using a
natural iterative merge sort that runs in O(n lg n) time and
O(1) space in the number of elements in LIST. */
void
list_sort (struct list *list, list_less_func *less, void *aux)
{
size_t output_run_cnt; /* Number of runs output in current pass. */
assert (list != NULL);
assert (less != NULL);
/* Pass over the list repeatedly, merging adjacent runs of
nondecreasing elements, until only one run is left. */
do
{
struct list_elem *a0; /* Start of first run. */
struct list_elem *a1b0; /* End of first run, start of second. */
struct list_elem *b1; /* End of second run. */
output_run_cnt = 0;
for (a0 = list_begin (list); a0 != list_end (list); a0 = b1)
{
/* Each iteration produces one output run. */
output_run_cnt++;
/* Locate two adjacent runs of nondecreasing elements
A0...A1B0 and A1B0...B1. */
a1b0 = find_end_of_run (a0, list_end (list), less, aux);
if (a1b0 == list_end (list))
break;
b1 = find_end_of_run (a1b0, list_end (list), less, aux);
/* Merge the runs. */
inplace_merge (a0, a1b0, b1, less, aux);
}
}
while (output_run_cnt > 1);
assert (is_sorted (list_begin (list), list_end (list), less, aux));
}
/* Inserts ELEM in the proper position in LIST, which must be
sorted according to LESS given auxiliary data AUX.
Runs in O(n) average case in the number of elements in LIST. */
void
list_insert_ordered (struct list *list, struct list_elem *elem,
list_less_func *less, void *aux)
{
struct list_elem *e;
assert (list != NULL);
assert (elem != NULL);
assert (less != NULL);
for (e = list_begin (list); e != list_end (list); e = list_next (e))
if (less (elem, e, aux))
break;
return list_insert (e, elem);
}
/* Iterates through LIST and removes all but the first in each
set of adjacent elements that are equal according to LESS
given auxiliary data AUX. If DUPLICATES is non-null, then the
elements from LIST are appended to DUPLICATES. */
void
list_unique (struct list *list, struct list *duplicates,
list_less_func *less, void *aux)
{
struct list_elem *elem, *next;
assert (list != NULL);
assert (less != NULL);
if (list_empty (list))
return;
elem = list_begin (list);
while ((next = list_next (elem)) != list_end (list))
if (!less (elem, next, aux) && !less (next, elem, aux))
{
list_remove (next);
if (duplicates != NULL)
list_push_back (duplicates, next);
}
else
elem = next;
}
/* Returns the element in LIST with the largest value according
to LESS given auxiliary data AUX. If there is more than one
maximum, returns the one that appears earlier in the list. If
the list is empty, returns its tail. */
struct list_elem *
list_max (struct list *list, list_less_func *less, void *aux)
{
struct list_elem *max = list_begin (list);
if (max != list_end (list))
{
struct list_elem *e;
for (e = list_next (max); e != list_end (list); e = list_next (e))
if (less (max, e, aux))
max = e;
}
return max;
}
/* Returns the element in LIST with the smallest value according
to LESS given auxiliary data AUX. If there is more than one
minimum, returns the one that appears earlier in the list. If
the list is empty, returns its tail. */
struct list_elem *
list_min (struct list *list, list_less_func *less, void *aux)
{
struct list_elem *min = list_begin (list);
if (min != list_end (list))
{
struct list_elem *e;
for (e = list_next (min); e != list_end (list); e = list_next (e))
if (less (e, min, aux))
min = e;
}
return min;
}
list.h 0 → 100644
#ifndef __LIST_H
#define __LIST_H
/* This code is taken from the Pintos education OS.
* For copyright information, see www.pintos-os.org */
/* Doubly linked list.
This implementation of a doubly linked list does not require
use of dynamically allocated memory. Instead, each structure
that is a potential list element must embed a struct list_elem
member. All of the list functions operate on these `struct
list_elem's. The list_entry macro allows conversion from a
struct list_elem back to a structure object that contains it.
For example, suppose there is a needed for a list of `struct
foo'. `struct foo' should contain a `struct list_elem'
member, like so:
struct foo
{
struct list_elem elem;
int bar;
...other members...
};
Then a list of `struct foo' can be be declared and initialized
like so:
struct list foo_list;
list_init (&foo_list);
Iteration is a typical situation where it is necessary to
convert from a struct list_elem back to its enclosing
structure. Here's an example using foo_list:
struct list_elem *e;
for (e = list_begin (&foo_list); e != list_end (&foo_list);
e = list_next (e))
{
struct foo *f = list_entry (e, struct foo, elem);
...do something with f...
}
You can find real examples of list usage throughout the
source; for example, malloc.c, palloc.c, and thread.c in the
threads directory all use lists.
The interface for this list is inspired by the list<> template
in the C++ STL. If you're familiar with list<>, you should
find this easy to use. However, it should be emphasized that
these lists do *no* type checking and can't do much other
correctness checking. If you screw up, it will bite you.
Glossary of list terms:
- "front": The first element in a list. Undefined in an
empty list. Returned by list_front().
- "back": The last element in a list. Undefined in an empty
list. Returned by list_back().
- "tail": The element figuratively just after the last
element of a list. Well defined even in an empty list.
Returned by list_end(). Used as the end sentinel for an
iteration from front to back.
- "beginning": In a non-empty list, the front. In an empty
list, the tail. Returned by list_begin(). Used as the
starting point for an iteration from front to back.
- "head": The element figuratively just before the first
element of a list. Well defined even in an empty list.
Returned by list_rend(). Used as the end sentinel for an
iteration from back to front.
- "reverse beginning": In a non-empty list, the back. In an
empty list, the head. Returned by list_rbegin(). Used as
the starting point for an iteration from back to front.
- "interior element": An element that is not the head or
tail, that is, a real list element. An empty list does
not have any interior elements.
*/
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
/* List element. */
struct list_elem
{
struct list_elem *prev; /* Previous list element. */
struct list_elem *next; /* Next list element. */
};
/* List. */
struct list
{
struct list_elem head; /* List head. */
struct list_elem tail; /* List tail. */
};
/* Converts pointer to list element LIST_ELEM into a pointer to
the structure that LIST_ELEM is embedded inside. Supply the
name of the outer structure STRUCT and the member name MEMBER
of the list element. See the big comment at the top of the
file for an example. */
#define list_entry(LIST_ELEM, STRUCT, MEMBER) \
((STRUCT *) ((uint8_t *) &(LIST_ELEM)->next \
- offsetof (STRUCT, MEMBER.next)))
void list_init (struct list *);
/* List traversal. */
struct list_elem *list_begin (struct list *);
struct list_elem *list_next (struct list_elem *);
struct list_elem *list_end (struct list *);
struct list_elem *list_rbegin (struct list *);
struct list_elem *list_prev (struct list_elem *);
struct list_elem *list_rend (struct list *);
struct list_elem *list_head (struct list *);
struct list_elem *list_tail (struct list *);
/* List insertion. */
void list_insert (struct list_elem *, struct list_elem *);
void list_splice (struct list_elem *before,
struct list_elem *first, struct list_elem *last);
void list_push_front (struct list *, struct list_elem *);
void list_push_back (struct list *, struct list_elem *);
/* List removal. */
struct list_elem *list_remove (struct list_elem *);
struct list_elem *list_pop_front (struct list *);
struct list_elem *list_pop_back (struct list *);
/* List elements. */
struct list_elem *list_front (struct list *);
struct list_elem *list_back (struct list *);
/* List properties. */
size_t list_size (struct list *);
bool list_empty (struct list *);
/* Miscellaneous. */
void list_reverse (struct list *);
/* Compares the value of two list elements A and B, given
auxiliary data AUX. Returns true if A is less than B, or
false if A is greater than or equal to B. */
typedef bool list_less_func (const struct list_elem *a,
const struct list_elem *b,
void *aux);
/* Operations on lists with ordered elements. */
void list_sort (struct list *,
list_less_func *, void *aux);
void list_insert_ordered (struct list *, struct list_elem *,
list_less_func *, void *aux);
void list_unique (struct list *, struct list *duplicates,
list_less_func *, void *aux);
/* Max and min. */
struct list_elem *list_max (struct list *, list_less_func *, void *aux);
struct list_elem *list_min (struct list *, list_less_func *, void *aux);
#endif /* list.h */
#include "list.h"
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
struct Name {
char name [400];
struct list_elem elem;
};
struct Name* make_name(char * name);
void print_list(struct list * l);
// would have to add more checking if it was not a dummy example
struct Name* make_name(char * name){
struct Name * n = malloc(sizeof(struct Name));
strcpy(n->name,name);
return n;
}
// pass a pointer to be safe, although do not have to if you are making no modifications
void print_list(struct list* l){
struct list_elem * e;
printf("Printing a list of size %d\n", (int)list_size(l));
for(e = list_begin(l); e != list_end(l); e = list_next(e)){
struct Name * name = list_entry(e, struct Name, elem);
printf("There is an element with a name of %s\n", name->name);
}
printf("The list was printed\n\n");
}
int main(){
struct list example_list;
// must initialize the list
list_init(&example_list);
print_list(&example_list);
struct Name* one = make_name("Eric Williamson");
list_push_back(&example_list,&one->elem);
print_list(&example_list);
list_push_front(&example_list,&make_name("Harrison Fang")->elem);
print_list(&example_list);
list_pop_front(&example_list);
print_list(&example_list);
return 0;
}
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