# is_nan

(PHP 4 >= 4.2.0, PHP 5)

is_nanFinds whether a value is not a number

### Description

bool is_nan ( float \$val )

Checks whether val is 'not a number', like the result of acos(1.01).

### Parameters

val

The value to check

### Return Values

Returns TRUE if val is 'not a number', else FALSE.

### Examples

Example #1 is_nan() example

<?php
// Invalid calculation, will return a
// NaN value
\$nan acos(8);

var_dump(\$nanis_nan(\$nan));
?>

The above example will output:

float(NAN)
bool(true)

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### User Contributed Notes 5 notes

darkangel at moveinmod dot net
8 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.
modern dot apocalypse at gmail dot com
2 years ago
I have decided to do some testing because I am getting unusual results with the is_nan function and here are the results of my tests:

<?php
var_dump
(NAN); // float NAN

var_dump(NAN == NAN); // boolean true
var_dump(NAN === NAN); // boolean true
var_dump(is_nan(NAN)); // boolean true

var_dump(NAN == 12); // boolean true
var_dump(NAN === 12); // boolean false
var_dump(is_nan(12)); // boolean false

var_dump(NAN == 12.4); // boolean true
var_dump(NAN === 12.4); // boolean true
var_dump(is_nan(12.4)); // boolean false

var_dump(NAN == NULL); // boolean true
var_dump(NAN === NULL); // boolean false
var_dump(is_nan(NULL)); // boolean false

var_dump(NAN == 'K<WNPO'); // boolean true
var_dump(NAN === 'K<WNPO'); // boolean false
var_dump(is_nan('K<WNPO')); // null and throws a warning "Warning: is_nan() expects parameter 1 to be double, string given in NANTest.php on line 13"
J.K.
4 years ago
For seeing whether or not something is a number, use ctype_digit().
php at keith tyler dot com
4 years ago
It seems odd to me, but in boolean context, NAN evalutes to true.

<?php
var_dump
(acos(8));
var_dump((bool)acos(8));
?>

Returns:

float(NAN)
bool(true)

Incidentally INF and -INF also evaluate to true.
-3
Vincent
9 years ago
Since NaN is not even equal to itself, here is a way to test it:

<?php

function my_is_nan(\$_) {
return (
\$_ !== \$_);
}

?>