is_null($x) vs $x == null[复制]

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What's the difference between is_null($var) and ($var === null)?

可能的重复:is_null($var)和($var == null)之间的区别是什么?

PHP has two (that I know of, and three if you count isset()) methods to determine if a value is null: is_null() and === null. I have heard, but not confirmed, that === null is faster, but in a code review someone strongly suggested that I use is_null() instead as it is specifically designed for the null-evaluation purpose. He also started talking about math or something.

PHP有两个(我知道的，如果您计算isset())方法来确定一个值是否为null: is_null()和== null。我已经听说了，但是没有得到确认，== null是更快的，但是在一个代码检查中，有人强烈建议我使用is_null()，因为它是专门为null评估目的而设计的。他也开始谈论数学什么的。

Anyway, the fact that is_null() is apparently slower also leads me to believe that it's doing more than === null does and is probably preferred. Is there any reason to use one or the other? Is one always preferred? What about isset()?

无论如何，is_null()显然是较慢的，这使我相信它所做的事情多于== null，并且可能是首选。有什么理由使用它吗?是一个总是喜欢吗?收取()呢?

As an addendum to possibly not get this question closed, what about isset() vs. is_null()? It seems that all isset() will do is suppress the notice, so unless you actually want a notice for an undefined variable, any reason to use is_null() instead? How about if you know the variable is initialized at the time?

作为可能不关闭这个问题的附录，isset()和is_null()如何?似乎所有的isset()都将会阻止通知，所以除非您实际上想要一个未定义变量的通知，否则使用is_null()的任何理由?如果你知道变量是在时间初始化的?

Finally, is there any mathematical reason to prefer is_null() over === null? Something about null not being comparable?

最后，是否有任何数学上的理由来选择is_null() / == null?关于零的东西没有可比性?

7 个解决方案

#1

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There is absolutely no difference in functionality between is_null and === null.

is_null和== null之间的功能完全没有区别。

The only difference is that is_null is a function and thus

唯一的区别是is_null是一个函数。

is marginally slower (function call overhead)
稍微慢一点(函数调用开销)
can be used as a callback, e.g. array_map('is_null', $array).
可以用作回调，例如array_map('is_null'， $array)。

Personally, I use null === whenever I can, as it is more consistent with false === and true === checks.

就我个人而言，我使用null ===每当我可以，因为它与false ==和true ==检查更一致。

If you want, you can check the code: is_identical_function (===) and php_is_type (is_null) do the same thing for the IS_NULL case.

如果您愿意，您可以检查代码:is_idal_function(===)和php_is_type (is_null)对is_null案例执行相同的操作。

The related isset() language construct checks whether the variable actually exists before doing the null check. So isset($undefinedVar) will not throw a notice.

相关的isset()语言结构检查变量是否在执行null检查之前存在。所以isset($undefinedVar)不会抛出一个通知。

Also note that isset() may sometimes return true even though the value is null - this is the case when it is used on an overloaded object, i.e. if the object defines an offsetExists/__isset method that returns true even if the offset is null (this is actually quite common, because people use array_key_exists in offsetExists/__isset).

还要注意,有时收取()返回true即使值是null -这是一个重载的对象上使用的情况时,即如果该对象定义了一个offsetExists / __isset方法返回true即使抵消为空(这是很常见的,因为人们用array_key_exists offsetExists / __isset)。

#2

As stated by others, there is a time difference between using === and is_null(). Did some quick testing and got these results:

如其他人所述，使用===和is_null()之间存在时间差。做了一些快速测试并得到了这些结果:

<?php

//checking with ===
$a = array();
$time = microtime(true);
for($i=0;$i<10000;$i++) {
    if($a[$i] === null) {
         //do nothing
    }
}
echo 'Testing with === ', microtime(true) - $time, "\n";

//checking with is_null()
$time = microtime(true);
for($i=0;$i<10000;$i++) {
    if(is_null($a[$i])) {
         //do nothing
    }
}
echo 'Testing with is_null() ', microtime(true) - $time;
?>

Gives the results

给出了结果

Testing with === 0.0090668201446533

测试与= = = 0.0090668201446533

Testing with is_null() 0.013684034347534

0.013684034347534测试与is_null()

See the code in action

参见操作中的代码。

#3

They all have their places, though only isset() will avoid undefined variable warnings:

它们都有自己的位置，尽管只有isset()将避免未定义的变量警告:

$ php -a
Interactive shell

php > var_dump(is_null($a));
PHP Notice:  Undefined variable: a in php shell code on line 1
bool(true)
php > var_dump($a === null);
PHP Notice:  Undefined variable: a in php shell code on line 1
bool(true)
php > var_dump(isset($a));
bool(false)
php >

#4

You need isset() if the variable is possibly not defined. It returns false when the variable is not defined or === null (yes, it's that ugly). Only isset() and empty() do not raise an E_NOTICE if the variable or array element does not exist.

如果变量可能没有定义，则需要isset()。当变量未被定义或== null时，它将返回false(是的，它是那么难看)。如果变量或数组元素不存在，则只有isset()和empty()不会引起E_NOTICE。

There is not really a difference between is_null and === null. I think === is much nicer but when you e.g. need to use call_user_func for some dubious reason, you'd have to use is_null.

is_null和== null之间并没有真正的区别。我认为===更好，但是当您需要使用call_user_func时，您必须使用is_null。

#5

=== and is_null is the same.

===和is_null是相同的。

According to this comment is_null is only 250ns slower. I think because a function is slower than an operator.

根据这个注释，is_null的速度只有250ns。因为函数比运算符慢。

#6

I'm not able to say wether it's better to use is_null or === null. But be aware when using isset on arrays.

我不能说使用is_null或== null会更好。但是在使用isset的时候要注意。

$a = array('foo' => null);

var_dump(isset($a['foo'])); // false
var_dump(is_null($a['foo'])); // true
var_dump(array_key_exists('foo', $a)); // true

#7

The PHP documentation has a good discussion and experiments on is_null, === null, isset. Especially read the comment section.

PHP文档在is_null上有很好的讨论和实验，== null, isset。特别是阅读评论部分。

#1

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