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SplQueue::__construct — Constructs a new queue implemented using a doubly linked list
SplQueue::dequeue — Dequeues a node from the queue
SplQueue::enqueue — Adds an element to the queue
SplQueue::setIteratorMode — Sets the mode of iteration

User Contributed Notes

lincoln dot du dot j at gmail dot com 12-Jul-2017 07:07


<?php

  

$queue = new SplQueue();

$queue->enqueue('A');

$queue->enqueue('B');

$queue->enqueue('C');



$queue->rewind();

while($queue->valid()){

    echo $queue->current(),"\n";

    $queue->next();

}



print_r($queue);

$queue->dequeue(); //remove first one

print_r($queue);



?>

Output



A

B

C

SplQueue Object

(

    [flags:SplDoublyLinkedList:private] => 4

    [dllist:SplDoublyLinkedList:private] => Array

        (

            [0] => A

            [1] => B

            [2] => C

        )



)

SplQueue Object

(

    [flags:SplDoublyLinkedList:private] => 4

    [dllist:SplDoublyLinkedList:private] => Array

        (

            [0] => B

            [1] => C

        )



)

Stingus 23-Sep-2016 10:16


Take care that SplQueue::valid() is not returning true if the queue has nodes. Use isEmpty() instead:



$queue = new SplQueue();

$queue->enqueue('A');

$queue->enqueue('B');

$queue->enqueue('C');

var_dump($queue->valid()); // false

var_dump(!$queue->isEmpty()); // true

MrStonedOne 31-Dec-2014 04:49


You can use shift/unshift and push/pop to dequeue/undequeue and queue/unqueue respectively. Really handy for those applications that use sockets where you might not know you can't send data until you attempt to.





for example, this is a function for an application that will un-dequeue the remainder of the data if socket_write indicated it did not write the entire contents of the provided data.





<?php


function processSendQueue($socket, $sendQueue) {


    while (!$sendQueue->isEmpty()) {


                            //shift() is the same as dequeue()


        $senditem = $sendQueue->shift();





        //returns the number of bytes written.


        $rtn = socket_write($socket, $senditem);


        if ($rtn === false) {


            $sendQueue->unshift($senditem);


            throw new exception("send error: " . socket_last_error($socket));


            return;


        }


        if ($rtn < strlen($senditem) {


            $sendQueue->unshift(substr($senditem, $rtn);


            break;


        }


    }


}


?>

Manu Manjunath 10-Feb-2014 10:56


SplQueue inherits from SplDoublyLinkedList. So, objects of SplQueue support methods push() and pop(). But please be advised that if you use push() and pop() methods on a SplQueue object, it behaves like a stack rather than a queue.



For example:



$q = new SplQueue();

$q->push(1);

$q->push(2);

$q->push(3);

$q->pop();

print_r($q);



Above code returns:



SplQueue Object

(

    [flags:SplDoublyLinkedList:private] => 4

    [dllist:SplDoublyLinkedList:private] => Array

        (

            [0] => 1

            [1] => 2

        )

)



Note that 3 got popped and *not* 1.



So, please make sure that you use only enqueue() and dequeue() methods on a SplQueue object and *not* push() and pop().

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