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PHP SplDoublyLinkedList key() Function

Last Updated : 23 Jun, 2023
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The SplDoublyLinkedList::key() function is an inbuilt function in PHP which is used to return the index of the current node. Syntax: 
mixed SplDoublyLinkedList::key( void )
Parameters: This function does not accepts any parameters. Return Value: It returns the index of current node. Below programs illustrate the SplDoublyLinkedList::key() function in PHP: Program 1: php 
<?php 

// Declare an empty SplDoublyLinkedList
$list = new \SplDoublyLinkedList;

// Use SplDoublyLinkedList::add() function to 
// add elements to the SplDoublyLinkedList
$list->add(0, 30);
$list->add(1, 20);
$list->add(2, 30);
$list->add(3, "Geeks");
$list->add(4, 'G');
$list->rewind();

// Use SplDoublyLinkedList::key() function
// to get the key
var_dump($list->key());

// Use next() function to increment
// the index value
$list->next();

// Use SplDoublyLinkedList::key() function
// to get the key
var_dump($list->key());

?>
Output: 
int(0)
int(1)
Program 2: php 
<?php 

// Declare an empty SplDoublyLinkedList
$list = new \SplDoublyLinkedList();

// Use SplDoublyLinkedList::push() function to 
// add elements to the SplDoublyLinkedList
$list->push(1);
$list->push(2);
$list->push(3);
$list->push(8);
$list->push(5);

$list->rewind();

// Use SplDoublyLinkedList::key() function
// to get the key
var_dump($list->key());

// Use next() function to increment
// the index value
$list->next();
$list->next();
$list->next();

// Use SplDoublyLinkedList::key() function
// to get the key
var_dump($list->key());

?>
Output: 
int(0)
int(3)
Reference: https://www.php.net/manual/en/spldoublylinkedlist.key.php

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