is_infinite
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.
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)
add a note
User Contributed Notes
is_nan
php at keith tyler dot com
14-Apr-2010 04:46
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 ($_ !== $_);
}
?>