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

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