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

booleantype at ya dot ru 18-May-2021 07:58


Answer to Manu Manjunath post (#114336).



IMO, pop() works as expected.



There are 2 main groups of methods:



1) pop() & push() are inherited from SplDoublyLinkedList and can be applied to SplStack as well as SplQueue (ie are "faceless"). It isn't about stack or queue; it's just about deleting / adding element to the end of the list;



2) the same situation with shift() & unshift(): it is just about adding an element to the beginning of the list, and doesn't matter, if we use it on SplStack or SplQueue.



So, yes, $q->pop(); will remove *last* element from SplQueue $q.



But enqueue() & dequeue() *are about* SplQueue. FIFO principle is realized by these methods, which were implemented *exactly* for queue purpose:

- enqueue() adds an element to the end of the queue and is alias for "faceless" push() (FI...);

- dequeue() removes element from the beginning of the queue and is alias for "faceless" shift() (...FO).



If you want to delete *next in line* element from *queue*, use dequeue().

If you want to delete *last* element from the list (doesn't matter, if it's queue or stack), use pop().

mostefa dot medjahed dot pro at gmail dot com 01-Mar-2021 07:13


As was said before, the push () and pop () methods on a SplQueue object, its behave like a stack rather than a queue.



Knowing that the enqueue () and dequeue () methods are respectively aliases of push () and shift () methods, we can also use SplQueue :: push () and SplQueue :: shift () for the same purpose as SplQueue :: enqueue and SplQueue :: dequeue.

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().

The SplQueue class

简介

类摘要

Table of Contents

User Contributed Notes