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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)

See Also


User Contributed Notes
is_nan
php at keith tyler dot com
14-Apr-2010 11:46
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.
J.K.
07-Jul-2009 11:44
For seeing whether or not something is a number, use ctype_digit().
darkangel at moveinmod dot net
02-Mar-2006 06:04
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.
Sku
04-Dec-2005 09:29
Hi nez,

better would be:

function isNaN( $var ) {
     return !ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}

ys, Sku
nez [at] NOSPAM gazeta [dot] pl
26-Sep-2005 08:27
Paul, i guess better would be:

function isNaN( $var ) {
     return ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}
Vincent
24-Feb-2005 02:04
Since NaN is not even equal to itself, here is a way to test it:

<?php

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

?>
 

 
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