is_nan

(PHP 4 >= 4.2.0, PHP 5, PHP 7)

is_nanFinds whether a value is not a number

Descrierea

is_nan ( float $num ) : bool

Checks whether num is 'not a number', like the result of acos(1.01).

Parametri

num

The value to check

Valorile întoarse

Returns true if num is 'not a number', else false.

Exemple

Example #1 is_nan() example

<?php
// Invalid calculation, will return a 
// NaN value
$nan acos(8);

var_dump($nanis_nan($nan));
?>

Exemplul de mai sus va afișa:

float(NAN)
bool(true)

A se vedea și

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User Contributed Notes 7 notes

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17
darkangel at moveinmod dot net
18 years ago
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.
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5
10basetom
8 years ago
I would use is_numeric() instead of ctype_digit() if you cannot be 100% sure what data type the string will be. Example from the docs:

<?php
$numeric_string
= '42';
$integer        = 42;

ctype_digit($numeric_string);  // true
ctype_digit($integer);         // false (ASCII 42 is the * character)

is_numeric($numeric_string);   // true
is_numeric($integer);          // true
?>
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1
php at darkain dot com
7 years ago
Starting with PHP 7, the string 'NaN' evaluates to the NaN value as well.

Example:
var_dump( (float) 'NaN' );

PHP 5.x and HHVM:
float(0)

PHP 7.0:
float(NAN)
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0
ScorpioT1000
3 years ago
function is_nan2($n) {
    return $n !== $n;
}

is_nan2(NAN); // true
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-4
J.K.
14 years ago
For seeing whether or not something is a number, use ctype_digit().
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-5
php at keith tyler dot com
13 years ago
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.
up
-11
modern dot apocalypse at gmail dot com
12 years ago
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"
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