# is_nan

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

is_nan値が非数かどうかを判定する

### 説明

is_nan(float `\$num`): bool

`num` 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。

`num`

### 戻り値

`num` 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

``` <?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));?> ```

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

### 参考

• is_finite() - 値が有限の数値であるかどうかを判定する
• is_infinite() - 値が無限大であるかどうかを判定する

### User Contributed Notes 7 notes

17
darkangel at moveinmod dot net
16 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. ```
10basetom
7 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);  // truectype_digit(\$integer);         // false (ASCII 42 is the * character)is_numeric(\$numeric_string);   // trueis_numeric(\$integer);          // true?> ```
php at darkain dot com
6 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) ```
ScorpioT1000
2 years ago
``` function is_nan2(\$n) {    return \$n !== \$n;}is_nan2(NAN); // true ```
-4
J.K.
12 years ago
``` For seeing whether or not something is a number, use ctype_digit(). ```
-5
php at keith tyler dot com
12 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. ```
-11
modern dot apocalypse at gmail dot com
10 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" ```