is_nan

(PHP 4 >= 4.2.0, PHP 5)

is_nan — 値が数値でないかどうかを判定する

説明

bool is_nan ( float $val )

val が '非数値 (not a number)' であるかどうかを調べます。たとえば acos(1.01) の結果などがこれにあたります。

パラメータ

val: 調べる値。

返り値

val が '非数値 (not a number)' の場合に TRUE、そうでない場合に FALSE を返します。

例

例1 is_nan() の例


<?php
// 無効な計算なので、
// NaN 値を返します
$nan = acos(8);

var_dump($nan, is_nan($nan));
?>

上の例の出力は以下となります。

float(NAN)
bool(true)

参考

is_finite() - 値が有限の数値であるかどうかを判定する
is_infinite() - 値が無限大であるかどうかを判定する

lcg_value

is_infinite

[edit] Last updated: Fri, 25 May 2012

add a note User Contributed Notes is_nan

modern dot apocalypse at gmail dot com 15-Mar-2012 10:14


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"

php at keith tyler dot com 14-Apr-2010 04:46


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 04:44


For seeing whether or not something is a number, use ctype_digit().

darkangel at moveinmod dot net 01-Mar-2006 10:04


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 01:29


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 01:27


Paul, i guess better would be:



function isNaN( $var ) {

     return ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);

}

Vincent 23-Feb-2005 06:04


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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