blocks|key|3137902|text|你要找的是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3137903|if($variable+===+NULL)+{...}|code-block|syntax|javascript|3137904|请注意===。|offset|length|style|CODE|3137905|在使用==时，就像您所做的那样，PHP将NULL、false、空字符串和空数组等同对待。|3137906|entityMap^0|0|0|3|3|0|3|2|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@$I|W|J|X|K|L]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

What you're looking for is:

<pre><code>if($variable === NULL) {...}
</code></pre>

Note the <code>===</code>. 
When use <code>==</code>, as you did, PHP treats NULL, false, 0, the empty string, and empty arrays as equal.

blocks|key|248820|text|这不是的错误，而是的正常行为。这是因为PHP中的==操作符没有检查类型。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|248821|''+==+null+==+0+==+false|code-block|syntax|javascript|248822|如果您还想检查这些值是否具有相同的类型，请改用===。要深入研究这种差异，请阅读official+documentation。|248823|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/language.operators.comparison.php^0|9|R|O|2|0|0|0|1R|N|3|14|M|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|10|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|D]]|E|@$9|16|A|17|1|18]]|F|$]]|$1|N|3|-4|5|6|7|19|8|@]|E|@]|F|$]]]|O|$P|$5|Q|R|S|F|$T|U]]]]

This is not a bug but PHP normal behavior. It happens because the <code>==</code> operator in PHP doesn't check for type. 

<pre><code>'' == null == 0 == false
</code></pre>

If you want also to check if the values have the same type, use <code>===</code> instead. To study in deep this difference, please read the <a href="http://php.net/manual/en/language.operators.comparison.php" rel="noreferrer">official documentation</a>.

blocks|key|2923781|text|检查==与===|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2923782|''+==+NULL将返回true|2923783|0+==+NULL将返回true|2923784|false+==+null将返回true|2923785|where+as|2923786|''+===+NULL将返回false|2923787|0+===+NULL将返回false|2923788|false+===+NULL将返回false|2923789|entityMap^0|2|2|5|3|0|0|A|0|0|9|0|0|D|0|0|0|B|0|0|A|0|0|E|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|19|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|R|3|S|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|U|$]]

check <code>==</code> vs <code>===</code> 

<code>'' == NULL</code> would return true 
<code>0 == NULL</code> would return true 
<code>false == null</code> would return true 

where as

<code>'' === NULL</code> would return false 
<code>0 === NULL</code> would return false 
<code>false === NULL</code> would return false

blocks|key|2923795|text|如下表所示，empty($foo)等同于$foo==null，is_null($foo)具有与$foo===null相同的功能。该表还显示了有关null比较的一些棘手的值。(ϕ表示未初始化的变量。)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2923796|+++++++++empty++++is_null+
+++++++++==null++===null++isset+++array_key_exists
++++++ϕ+%7C+++T+++%7C+++T+++%7C+++F+++%7C+++F+++
+++null+%7C+++T+++%7C+++T+++%7C+++F+++%7C+++T+++
+++++""+%7C+++T+++%7C+++F+++%7C+++T+++%7C+++T+++
+++++[]+%7C+++T+++%7C+++F+++%7C+++T+++%7C+++T
++++++0+%7C+++T+++%7C+++F+++%7C+++T+++%7C+++T++++++
++false+%7C+++T+++%7C+++F+++%7C+++T+++%7C+++T+++
+++true+%7C+++F+++%7C+++F+++%7C+++T+++%7C+++T+++
++++++1+%7C+++F+++%7C+++F+++%7C+++T+++%7C+++T+++
+++++\0+%7C+++F+++%7C+++F+++%7C+++T+++%7C+++T+++|code-block|syntax|javascript|2923797|entityMap^0|6|B|K|A|V|D|1B|B|20|4|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|L|$]]

As is shown in the following table, <code>empty($foo)</code> is equivalent to <code>$foo==null</code> and <code>is_null($foo)</code> has the same function of <code>$foo===null</code>. The table also shows some tricky values regarding the <code>null</code> comparison. (ϕ denotes an uninitialized variables. )
<pre><code> empty is_null 
 ==null ===null isset array_key_exists
 ϕ | T | T | F | F 
 null | T | T | F | T 
 &quot;&quot; | T | F | T | T 
 [] | T | F | T | T
 0 | T | F | T | T 
 false | T | F | T | T 
 true | F | F | T | T 
 1 | F | F | T | T 
 \0 | F | F | T | T 
</code></pre>

blocks|key|3137931|text|如果使用==，php会将空字符串或数组视为null。要区分null和empty，可以使用===或is_null。所以：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3137932|if($a+===+NULL)或if(is_null($a))|3137933|entityMap^0|4|2|L|4|T|4|Y|5|18|3|1C|7|0|0|F|G|F|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|I|$]]

If you use <code>==</code>, php treats an empty string or array as <code>null</code>. To make the distinction between <code>null</code> and <code>empty</code>, either use <code>===</code> or <code>is_null</code>. So:

<code>if($a === NULL)</code> or <code>if(is_null($a))</code>

blocks|key|247172|text|使用empty+-+http://php.net/manual/en/function.empty.php。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|247173|示例：|247174|$a+=+'';
if(empty($a))+{
++++echo+'is+empty';
}|code-block|syntax|javascript|247175|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/function.empty.php^0|2|5|A|17|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Use <code>empty</code> - <a href="http://php.net/manual/en/function.empty.php" rel="nofollow noreferrer">http://php.net/manual/en/function.empty.php</a>.

Example:

<pre><code>$a = '';
if(empty($a)) {
 echo 'is empty';
}
</code></pre>

blocks|key|245164|text|PHP7+isset()+vs+empty()+vs+is_null()|type|unstyled|depth|inlineStyleRanges|entityRanges|data|245165|​|245166|📷|atomic|offset|length|245167|245168|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/76055a977db344839db2d6a98abcbd2e.png|imageAlt^0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@$G|V|H|W|1|X]]|A|$]]|$1|I|3|C|5|6|7|Y|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q|R|-4]]]]

PHP 7 isset() vs empty() vs is_null() 

<a href="https://i.stack.imgur.com/DW4Rb.png" rel="noreferrer"><img src="https://i.stack.imgur.com/DW4Rb.png" alt="enter image description here"></a>

blocks|key|2923866|text|另外，如果有人正在处理&nbsp;，这在处理&nbsp;时也可以。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2923867|先用str_replace()替换，再用empty()检查|2923868|empty(str_replace("&nbsp;"+,""+,+$YOUR_DATA))+?+$YOUR_DATA+=+'--'+:+$YOUR_DATA;|code-block|syntax|javascript|2923869|entityMap^0|B|6|M|6|0|2|D|K|7|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|N|$]]

Just to addon if someone is dealing with <code>&amp;nbsp;</code>, this would work if dealing with <code>&amp;nbsp;</code>.
Replace it with <code>str_replace()</code> first and check it with <code>empty()</code>
<pre><code>empty(str_replace(&quot;&amp;nbsp;&quot; ,&quot;&quot; , $YOUR_DATA)) ? $YOUR_DATA = '--' : $YOUR_DATA;
</code></pre>

blocks|key|247196|text|NULL表示没有值的变量。要检查变量是否为NULL，可以使用is_null($var)或与NULL的比较(===)。但是，如果未定义变量，这两种方法都会生成警告。类似于isset($var)和empty($var)，可以作为函数使用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|247197|var_dump(is_null($var));+//+true
var_dump($var+===+null);+//+true
var_dump(empty($var));+//+true|code-block|syntax|javascript|247198|在How+to+check+if+a+variable+is+NULL+in+PHP?中阅读更多内容|247199|entityMap|0|LINK|mutability|MUTABLE|url|https://stackhowto.com/how-to-check-if-a-variable-is-null-in-php/^0|0|4|19|4|U|D|1H|3|2C|B|2O|B|0|0|1|16|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|D]|$9|12|A|13|B|D]|$9|14|A|15|B|D]|$9|16|A|17|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|18|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|19|8|@]|E|@$9|1A|A|1B|1|1C]]|F|$]]|$1|N|3|-4|5|6|7|1D|8|@]|E|@]|F|$]]]|O|$P|$5|Q|R|S|F|$T|U]]]]

NULL stands for a variable without value. To check if a variable is NULL you can either use <code>is_null($var)</code> or the comparison (<code>===</code>) with NULL. Both ways, however, generate a warning if the variable is not defined. Similar to <code>isset($var)</code> and <code>empty($var)</code>, which can be used as functions.
<pre><code>var_dump(is_null($var)); // true
var_dump($var === null); // true
var_dump(empty($var)); // true
</code></pre>
Read more in <a href="https://stackhowto.com/how-to-check-if-a-variable-is-null-in-php/" rel="nofollow noreferrer">How to check if a variable is NULL in PHP?</a>

I have a question regarding <code>NULL</code> in PHP:

<pre><code> $a = '';
 if($a == NULL) {
 echo 'is null';
 }
</code></pre>

Why do I see is null when <code>$a</code> is an empty string? Is that a bug?

php is null when empty?

我有一个关于PHP中的NULL的问题：  $a = '';  if($a == NULL) {      echo 'is null';  }当$a为空字符串时，为什么我看到is null？那是个bug吗？

问php为空时是否为空？
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问php为空时是否为空？EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问php为空时是否为空？
EN