How to Retrieve the First Key of an Array in PHP with array_key_first()

PHP is a widely used server‑side scripting language, and functions are essential. The array_key_first() function, introduced in PHP 7.3, returns the first key of an array.

Syntax: array_key_first(array $array): mixed The parameter $array is the array to operate on. The function returns the first key name, or NULL if the array is empty.

Example:

$students = array(
    "Tom"   => 18,
    "Jerry" => 19,
    "Alice" => 20
);
$first_key = array_key_first($students);
echo "The first student's name is: " . $first_key;

This code defines an associative array $students where keys are names and values are ages, obtains the first key with array_key_first(), stores it in $first_key, and echoes the result, which will be “Tom”.

Note that array_key_first() is available only in PHP 7.3 and later. For earlier versions you can achieve the same result with array_keys():

$students = array(
    "Tom"   => 18,
    "Jerry" => 19,
    "Alice" => 20
);
$keys = array_keys($students);
$first_key = $keys[0];
echo "The first student's name is: " . $first_key;

This alternative first retrieves all keys with array_keys(), then selects the first element.

Summary

The array_key_first() function, added in PHP 7.3, provides a convenient way to get an array’s first key; on older PHP versions you can use array_keys() and take the first element.