is_nan

(PHP 4 >= 4.2.0, PHP 5)

is_nan — 값이 수가 아닌지 확인합니다

설명

bool is_nan ( float $val )

val이 '숫자가 아닌'지 확인합니다. acos(1.01)의 결과 등은 숫자가 아닙니다.

인수

val: 확인할 값

반환값

val이 '숫자가 아닐' 경우 TRUE, 아니면 FALSE를 반환합니다.

예제

Example #1 is_nan() 예제


// NaN을 반환하는
// 잘못된 계산
$nan = acos(8);

var_dump($nan, is_nan($nan));
?>

위 예제의 출력:

float(NaN)
bool(true)

참고

in_finite()
in_infinite()

lcg_value

is_infinite

[edit] Last updated: Sat, 07 Jan 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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