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Класс SplQueue

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

Введение

Класс SplQueue предоставляет основные функциональные возможности очереди, реализованные с использованием двусвязного списка.

Обзор классов

class SplQueue extends SplDoublyLinkedList implements Iterator, ArrayAccess, Countable {
/* Методы */
public __construct()
public dequeue(): mixed
public enqueue(mixed $value): void
public setIteratorMode(int $mode): void
/* Наследуемые методы */
public SplDoublyLinkedList::add(int $index, mixed $value): void
public SplDoublyLinkedList::offsetExists(int $index): bool
public SplDoublyLinkedList::offsetSet(?int $index, mixed $value): void
public SplDoublyLinkedList::offsetUnset(int $index): void
public SplDoublyLinkedList::push(mixed $value): void
public SplDoublyLinkedList::unserialize(string $data): void
public SplDoublyLinkedList::unshift(mixed $value): void
}

Содержание

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User Contributed Notes 6 notes

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43
Manu Manjunath
7 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().
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1
mostefa dot medjahed dot pro at gmail dot com
8 months 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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3
MrStonedOne
6 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;
        }
    }
}
?>
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1
lincoln dot du dot j at gmail dot com
4 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
        )

)
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1
Stingus
5 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
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1
booleantype at ya dot ru
6 months 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().
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