PHP key() Function

The key() function is an inbuilt function in PHP which is used to return the index of the element of a given array to which the internal pointer is currently pointing. The current element may be starting or next element which depends on the cursor position. By default cursor position is at zero index i.e, at starting element of the given array.

Syntax:

key($array)

Parameters: This function accepts a single parameter $array. It is the array for which we want to find the current element pointed by the internal pointer.

Return Value: It returns the index of current element of the given array. If the input array is empty then the key() function will return NULL.

Below programs illustrate the key() function in PHP:

Program 1:

<?php

// input array
$arr = array("Ram", "Geeta", "Shita", "Ramu");

// Here key function prints the index of
// current element of the array.
echo "The index of the current element of".
                    " the array is: " . key($arr);

?>

Output:

The index of the current element of the array is: 0

Program 2:

<?php

// input array
$arr=array("Ram", "Geeta", "Shita", "Ramu");

// next function increase the internal pointer
// to point next to the current element.
next($arr);

// Here key function prints the index of
// the current element of the array.
echo "The index of the current element of".
                " the array is: " . key($arr);

?>

Output:

The index of the current element of the array is: 1

Program 3:

<?php

// input array
$arr = array("0", "F", "D", "4");

// using next() function to increment
// internal pointer two times
next($arr);
next($arr);

// Here key function prints the index of
// element of the current array position.
echo "The index of the current element of".
                " the array is: " . key($arr);

?>

Output:

The index of the current element of the array is: 2

Reference:
http://php.net/manual/en/function.key.php