PHP5 in Practice  (U.S.)Elliott III & Jonathan D.Eisenhamer

queue.php

<?php  
// A library to implement queues in PHP via arrays  
// The Initialize function creates a new queue:  
function &queue_initialize() {  
    // In this case, just return a new array  
    $new = array();  
    return $new;  
}  
// The destroy function will get rid of a queue  
function queue_destroy(&$queue) {  
    // Since PHP is nice to us, we can just use unset  
    unset($queue);  
}  
// The enqueue operation adds a new value unto the back of the queue  
function queue_enqueue(&$queue, $value) {  
    // We are just adding a value to the end of the array, so can use the  
    //  [] PHP Shortcut for this.  It's faster than using array_push  
    $queue[] = $value;  
}  
// Dequeue removes the front of the queue and returns it to you  
function queue_dequeue(&$queue) {  
    // Just use array unshift  
    return array_shift($queue);  
}  
// Peek returns a copy of the front of the queue, leaving it in place  
function queue_peek(&$queue) {  
    // Return a copy of the value found in front of queue  
    //  (at the beginning of the array)  
    return $queue[0];  
}  
// Size returns the number of elements in the queue  
function queue_size(&$queue) {  
    // Just using count will give the proper number:  
    return count($queue);  
}  
// Rotate takes the item on the front and sends it to the back of the queue.  
function queue_rotate(&$queue) {  
    // Remove the first item and insert it at the rear.  
    $queue[] = array_shift($queue);  
}  
// Let's use these to create a small queue of data and manipulate it.  
// Start by adding a few words to it:  
$myqueue =& queue_initialize();  
queue_enqueue($myqueue, 'Opal');  
queue_enqueue($myqueue, 'Dolphin');  
queue_enqueue($myqueue, 'Pelican');  
// The queue is: Opal Dolphin Pelican  
// Check the size, it should be 3  
echo '<p>Queue size is: ', queue_size($myqueue), '</p>';  
// Peek at the front of the queue, it should be: Opal  
echo '<p>Front of the queue is: ', queue_peek($myqueue), '</p>';  
// Now rotate the queue, giving us: Dolphin Pelican Opal  
queue_rotate($myqueue);  
// Remove the front element, returning: Dolphin  
echo '<p>Removed the element at the front of the queue: ',  
    queue_dequeue($myqueue), '</p>';  
// Now destroy it, we are done.  
queue_destroy($myqueue);  
?>