PHP 8.4.0 RC4 available for testing

    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)

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    User Contributed Notes 4 notes

    up
    25
    darkangel at moveinmod dot net
    18 years ago
    nan/"not a number" is not meant to see if the data type is numeric/textual/etc..

    NaN is actually a set of values which can be stored in floating-point variables, but dont actually evaluate to a proper floating point number.

    The floating point system has three sections: 1 bit for the sign (+/-), an 8 bit exponent, and a 23 bit fractional part.
    There are rules governing which combinations of values can be placed into each section, and some values are reserved for numbers such as infinity. This leads to certain combinations being invalid, or in other words, not a number.
    up
    14
    10basetom
    9 years ago
    I would use is_numeric() instead of ctype_digit() if you cannot be 100% sure what data type the string will be. Example from the docs:

    <?php
    $numeric_string     = '42';
    $integer = 42;

    ctype_digit($numeric_string); // true
    ctype_digit($integer); // false (ASCII 42 is the * character)

    is_numeric($numeric_string); // true
    is_numeric($integer); // true
    ?>
    up
    2
    ScorpioT1000
    4 years ago
    function is_nan2($n) {
    return $n !== $n;
    }

    is_nan2(NAN); // true
    up
    1
    php at darkain dot com
    8 years ago
    Starting with PHP 7, the string 'NaN' evaluates to the NaN value as well.

    Example:
    var_dump( (float) 'NaN' );

    PHP 5.x and HHVM:
    float(0)

    PHP 7.0:
    float(NAN)
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