PHP is_nan() Function – Determine If a Value Is Not a Number

is_nan() is a PHP function that checks whether a given float value is not a number (NaN) and returns a boolean.

Signature: bool is_nan(float $val) If the argument is a non‑numeric result such as acos(1.01), the function returns true; otherwise it returns false.

Parameter: $val – the value to be examined.

Return value: true if $val is NaN, false otherwise.

Example:

<?php
// Invalid calculation, will return a NaN value
$nan = acos(8);
var_dump($nan, is_nan($nan));
?>

Output:

float(NAN)
bool(true)