Math 函数
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is_nan

(PHP 4 >= 4.2.0, PHP 5)

is_nan — 判断是否为合法数值

说明

bool is_nan ( float $val )

如果 val 为“非数值”，例如 acos(1.01) 的结果，则返回 TRUE。

参见 is_finite() 和 is_infinite()。

Math 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 判断是否为合法数值

用户评论:

modern dot apocalypse at gmail dot com (15-Mar-2012 06:14)

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 (15-Apr-2010 12:46)

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. (08-Jul-2009 12:44)

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 09:27)

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

?>