PHP - Manual: is_nan

2024-11-15

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is_nan

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

is_nan — 判断是否为合法数值

说明

is_nan(float $val): bool

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

参数

val: 要检查的值

返回值

如果 val 不是一个数字（not a number）返回 true，否则返回 false。

范例

示例 #1 is_nan() 例子


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

var_dump($nan, is_nan($nan));
?>

以上例程会输出：

float(NAN)
bool(true)

参见

is_finite() - 判断是否为有限值
is_infinite() - 判断是否为无限值

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User Contributed Notes 7 notes

down

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.

down

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

is_numeric($numeric_string);   // true
is_numeric($integer);          // true
?>

down

ScorpioT1000 ¶

2 years ago


function is_nan2($n) {
    return $n !== $n;
}

is_nan2(NAN); // true

down

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)

down

-6

J.K. ¶

12 years ago


For seeing whether or not something is a number, use ctype_digit().

down

-7

php at keith tyler dot com ¶

12 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.

down

-12

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:

<?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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官方地址：https://www.php.net/manual/en/function.is-nan.php

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PHP官方手册 - 互联网笔记

is_nan

说明

参数

返回值

范例

参见

User Contributed Notes 7 notes