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is_nan

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

is_nan — Checks whether a float is NAN

Description

is_nan(float $num): bool

Returns whether the given num is NAN (Not A Number).

NAN is returned from mathematical operations that are undefined, for example when passing parameters outside of function’s input domain. The square root (sqrt()) is only defined for positive numbers, passing a negative number will result in NAN. Other examples of operations returning NAN are dividing INF by INF and any operation involving an existing NAN value.

Note:

Despite its name of Not A Number, NAN is a valid value of type float.

Caution

NAN does not compare equal to NAN. To check whether a float is NAN, is_nan() must be used. Checking $float === NAN will not work.

Parameters

num

The float to check

Return Values

true if num is NAN, else false.

Examples

Example #1 is_nan() example

<?php
$nan = sqrt(-1);

var_dump($nan, is_nan($nan));
?>

The above example will output:

float(NAN)
bool(true)

See Also