PHP - Manual: is_nan

2024-12-22

lcg_value »

« is_infinite

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

add a note

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"

add a note

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

有任何技术问题请点击这里网站运营推广招聘

IT PHP 编程语言 Linux 开发编程科技 Elasticsearch HTML/CSS/XML 网络数据库 JAVA 面试 NoSQL C/C++ Golang Git 算法操作系统正则表达式 Redis 互联网 MySql JavaScript 运维软件国际架构设计 Mac OS TCP/IP Excel Vim Windows Socket Oracle VR MongoDB Python 运营 MemCache 商业硬件电子娱乐设计 nginx 摄影游戏 WordPress HTTP 团建数码电器

php7 安装fileinfo扩展 preg_split — 通过一个正则表达式分隔字符串 php位值,解决 PHP 中 usort 在值相同时改变原始位置的问题 [PHP] inet_pton/inet_ntop IP地址转换函数 [鸟哥]PHP_INT_MIN 和 -9223372036854775808 PHP 8.1 ADORecordSet对象 adodb手册 opcache预加载 Composer的Packagist资源 array_multisort() 多字段排序 mysql面试题 PHPMailer设置utf8 PHPMailer字符集CharSet PHP json解析（json_decode）页面工具 [原创]诡异的php-fpm超时问题 php中几种注释规范纯php实现DES以及TripleDES加密算法 php扩展开发 PHP获取指定函数定义在哪个文件中及行号 php上周一、本周一、下周一日期

略微加速

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