Queue/Definition: Difference between revisions
Add Cowgol
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</lang>
=={{header|Cowgol}}==
This code should be put in a file called <code>queue.coh</code>, to be used with the
Cowgol program at [[Queue/Usage]]. The queue is implemented by means of a linked list.
<lang cowgol>include "strings.coh";
include "malloc.coh";
# Define types. The calling code is expected to provide a QueueData type.
record QueueItem is
data: QueueData;
next: [QueueItem];
end record;
record QueueMeta is
head: [QueueItem];
tail: [QueueItem];
end record;
typedef Queue is [QueueMeta];
const Q_NONE := 0 as [QueueItem];
# Allocate and free the queue datastructure.
sub MakeQueue(): (q: Queue) is
q := Alloc(@bytesof QueueMeta) as Queue;
q.head := Q_NONE;
q.tail := Q_NONE;
end sub;
sub FreeQueue(q: Queue) is
var cur := q.head;
while cur != Q_NONE loop
var next := cur.next;
Free(cur as [uint8]);
cur := next;
end loop;
Free(q as [uint8]);
end sub;
# Check if queue is empty.
sub QueueEmpty(q: Queue): (r: uint8) is
r := 0;
if q.head == Q_NONE then
r := 1;
end if;
end sub;
# Enqueue and dequeue data. Cowgol has no exceptions, so the calling code
# should check QueueEmpty first.
sub Enqueue(q: Queue, d: QueueData) is
var item := Alloc(@bytesof QueueItem) as [QueueItem];
item.data := d;
item.next := Q_NONE;
if q.head == Q_NONE then
q.head := item;
else
q.tail.next := item;
end if;
q.tail := item;
end sub;
sub Dequeue(q: Queue): (d: QueueData) is
d := q.head.data;
var cur := q.head;
q.head := q.head.next;
Free(cur as [uint8]);
if q.head == Q_NONE then
q.tail := Q_NONE;
end if;
end sub;</lang>
=={{header|D}}==
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