The SplQueue class

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

Einführung

The SplQueue class provides the main functionalities of a queue implemented using a doubly linked list by setting the iterator mode to SplDoublyLinkedList::IT_MODE_FIFO.

Klassenbeschreibung

class SplQueue extends SplDoublyLinkedList {

/* Geerbte Konstanten */

public const int SplDoublyLinkedList::IT_MODE_LIFO;

public const int SplDoublyLinkedList::IT_MODE_FIFO;

public const int SplDoublyLinkedList::IT_MODE_DELETE;

public const int SplDoublyLinkedList::IT_MODE_KEEP;

/* Methoden */

public dequeue(): mixed

public enqueue(mixed $value): void

/* Geerbte Methoden */

public SplDoublyLinkedList::add(int $index, mixed $value): void

public SplDoublyLinkedList::bottom(): mixed

public SplDoublyLinkedList::count(): int

public SplDoublyLinkedList::current(): mixed

public SplDoublyLinkedList::getIteratorMode(): int

public SplDoublyLinkedList::isEmpty(): bool

public SplDoublyLinkedList::key(): int

public SplDoublyLinkedList::next(): void

public SplDoublyLinkedList::offsetExists(int $index): bool

public SplDoublyLinkedList::offsetGet(int $index): mixed

public SplDoublyLinkedList::offsetSet(?int $index, mixed $value): void

public SplDoublyLinkedList::offsetUnset(int $index): void

public SplDoublyLinkedList::pop(): mixed

public SplDoublyLinkedList::prev(): void

public SplDoublyLinkedList::push(mixed $value): void

public SplDoublyLinkedList::rewind(): void

public SplDoublyLinkedList::serialize(): string

public SplDoublyLinkedList::setIteratorMode(int $mode): int

public SplDoublyLinkedList::shift(): mixed

public SplDoublyLinkedList::top(): mixed

public SplDoublyLinkedList::unserialize(string $data): void

public SplDoublyLinkedList::unshift(mixed $value): void

public SplDoublyLinkedList::valid(): bool

}

Beispiele

Beispiel #1 SplQueue example

<?php
$q = new SplQueue();
$q[] = 1;
$q[] = 2;
$q[] = 3;
foreach ($q as $elem)  {
 echo $elem."\n";
}
?>

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

1
2
3

Beispiel #2 Efficiently handling tasks with SplQueue

<?php
$q = new SplQueue();
$q->setIteratorMode(SplQueue::IT_MODE_DELETE);
// ... enqueue some tasks on the queue ...
// process them
foreach ($q as $task) {
    // ... process $task ...
    // add new tasks on the queue
    $q[] = $newTask;
    // ...
}
?>

Inhaltsverzeichnis

SplQueue::dequeue — Dequeues a node from the queue
SplQueue::enqueue — Adds an element to the queue

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User Contributed Notes 6 notes

down

Manu Manjunath ¶

10 years ago

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().

down

MrStonedOne ¶

9 years ago

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;

        }

    }

}

?>

down

lincoln dot du dot j at gmail dot com ¶

7 years ago

<?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
        )

)

down

booleantype at ya dot ru ¶

3 years ago

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().

down

Stingus ¶

8 years ago

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

down

-2

mostefa dot medjahed dot pro at gmail dot com ¶

3 years ago

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.

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