DevConf 2015

# is_nan

(PHP 4 >= 4.2.0, PHP 5)

is_nanFinds whether a value is not a number

### Description

bool is_nan ( float `\$val` )

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

### Parameters

`val`

The value to check

### Return Values

Returns `TRUE` if `val` is 'not a number', else `FALSE`.

### Examples

Example #1 is_nan() example

``` <?php// Invalid calculation, will return a // NaN value\$nan = acos(8);var_dump(\$nan, is_nan(\$nan));?> ```

The above example will output:

```float(NAN)
bool(true)
```

### User Contributed Notes 6 notes

11
darkangel at moveinmod dot net
9 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. ```
modern dot apocalypse at gmail dot com
3 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:<?phpvar_dump(NAN); // float NANvar_dump(NAN == NAN); // boolean truevar_dump(NAN === NAN); // boolean truevar_dump(is_nan(NAN)); // boolean truevar_dump(NAN == 12); // boolean truevar_dump(NAN === 12); // boolean falsevar_dump(is_nan(12)); // boolean falsevar_dump(NAN == 12.4); // boolean truevar_dump(NAN === 12.4); // boolean truevar_dump(is_nan(12.4)); // boolean falsevar_dump(NAN == NULL); // boolean truevar_dump(NAN === NULL); // boolean falsevar_dump(is_nan(NULL)); // boolean falsevar_dump(NAN == 'K<WNPO'); // boolean truevar_dump(NAN === 'K<WNPO'); // boolean falsevar_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" ```
J.K.
5 years ago
``` For seeing whether or not something is a number, use ctype_digit(). ```
10basetom
7 days 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);  // truectype_digit(\$integer);         // false (ASCII 42 is the * character)is_numeric(\$numeric_string);   // trueis_numeric(\$integer);          // true?> ```
-3
php at keith tyler dot com
5 years ago
``` It seems odd to me, but in boolean context, NAN evalutes to true. <?phpvar_dump(acos(8));var_dump((bool)acos(8));?>Returns:float(NAN)bool(true)Incidentally INF and -INF also evaluate to true. ```
-10
Vincent
10 years ago
``` Since NaN is not even equal to itself, here is a way to test it:<?phpfunction my_is_nan(\$_) {return (\$_ !== \$_);}?> ```