PHP | AppendIterator key() Function

The AppendIterator::key() function is an inbuilt function in PHP which is used to return the current key.

Syntax:

scalar AppendIterator::key( void )

Parameters: This function does not accept any parameters.

Return Value: This function returns the current key if it is valid or NULL otherwise.

Below programs illustrate the AppendIterator::key() function in PHP:

Program 1:

<?php

// Declare an ArrayIterator
$arr1 = new ArrayIterator(array('G', 'e', 'e', 'k', 's'));

// Create a new AppendIterator
$itr = new AppendIterator;

// Append the ArrayIterator element
$itr->append($arr1);

// Display the result
while ($itr->valid()) {
    echo "ArrayIterator Key: " . $itr->key() .
    "  ArrayIterator Value: " . $itr->current() . "\n";

    $itr->next();
}

?>

Output:

ArrayIterator Key: 0  ArrayIterator Value: G
ArrayIterator Key: 1  ArrayIterator Value: e
ArrayIterator Key: 2  ArrayIterator Value: e
ArrayIterator Key: 3  ArrayIterator Value: k
ArrayIterator Key: 4  ArrayIterator Value: s

Program 2:

<?php

// Declare an ArrayIterator
$arr1 = new ArrayIterator(
    array(
        "a" => "Geeks",
        "b" => "for",
        "c" => "Geeks"
    )
);

$arr2 = new ArrayIterator(
    array(
        "x" => "Computer",
        "y" => "Science",
        "z" => "Portal"
    )
);

// Create a new AppendIterator
$itr = new AppendIterator;
$itr->append($arr1);
$itr->append($arr2);

$itr->rewind();

// Display the result
while ($itr->valid()) {
    echo "ArrayIterator Key: " . $itr->key() .
    "  ArrayIterator Value: " . $itr->current() . "\n";

    $itr->next();
}

?>

Output:

ArrayIterator Key: a  ArrayIterator Value: Geeks
ArrayIterator Key: b  ArrayIterator Value: for
ArrayIterator Key: c  ArrayIterator Value: Geeks
ArrayIterator Key: x  ArrayIterator Value: Computer
ArrayIterator Key: y  ArrayIterator Value: Science
ArrayIterator Key: z  ArrayIterator Value: Portal

Reference: https://www.php.net/manual/en/appenditerator.key.php