php php是空的还是空的？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/8236354/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
php is null or empty?
提问by Erin Tucker
I have a question regarding NULLin PHP:
我有一个关于NULLPHP的问题：
$a = '';
if($a == NULL) {
echo 'is null';
}
Why do I see is nullwhen $ais an empty string? Is that a bug?
为什么我看到的是$a空字符串时为空？这是一个错误吗？
回答by Godwin
What you're looking for is:
你要找的是：
if($variable === NULL) {...}
Note the ===.
When use ==, as you did, PHP treats NULL, false, 0, the emptystring, and emptyarrays as equal.
请注意===.
使用时==，正如您所做的那样，PHP 将NULL、false、0、空字符串和空数组视为相等。
回答by PHPst
As is shown in the following table, empty($foo)is equivalent to $foo==nulland is_null($foo)has the same function of $foo===null. The table also shows some tricky values regarding the nullcomparison. (? denotes an uninitialized variables. )
如下表所示，empty($foo)相当于$foo==null并is_null($foo)具有相同的功能$foo===null。该表还显示了一些有关null比较的棘手值。(? 表示一个未初始化的变量。)
empty is_null
==null ===null isset array_key_exists
? | T | T | F | F
null | T | T | F | T
"" | T | F | T | T
[] | T | F | T | T
0 | T | F | T | T
false | T | F | T | T
true | F | F | T | T
1 | F | F | T | T
TRUE FALSE 1 0 -1 "1" "0" "-1" NULL array() "php" ""
[...]
"" FALSE TRUE FALSE TRUE FALSE FALSE FALSE FALSE TRUE FALSE FALSE TRUE
| F | F | T | T
I never use empty()and is_null()functions. Using simple comparison is less ambiguous, faster and cleaner.Particularly there will be less curly brackets to match.
我从不使用empty()和is_null()函数。使用简单的比较可以减少歧义、更快、更清晰。特别是匹配的大括号会更少。
e.g if($x==null || $y==null)vs if(is_null($x) || is_null($y))
例如if($x==null || $y==null)vsif(is_null($x) || is_null($y))
回答by jancha
check ==vs ===
检查==与===
'' == NULLwould return true0 == NULLwould return truefalse == nullwould return true
'' == NULL会返回true0 == NULL会返回truefalse == null会返回true
where as
然而
'' === NULLwould return false0 === NULLwould return falsefalse === NULLwould return false
'' === NULL会返回假0 === NULL会返回假false === NULL会返回假
回答by Felix Kling
No it's not a bug. Have a look at the Loose comparisons with ==table(second table), which shows the result of comparing each value in the first column with the values in the other columns:
不，这不是错误。查看与 ==表（第二个表）的松散比较，它显示了将第一列中的每个值与其他列中的值进行比较的结果：
'' == null == 0 == false
There you can see that an empty string ""compared with false, 0, NULLor ""will yield true.
在那里，你可以看到一个空字符串""相比false，0，NULL或""将产生真实的。
You might want to use is_null[docs]instead, or strict comparison (third table).
您可能想改用is_null[docs]或严格比较（第三个表）。
回答by Aurelio De Rosa
This is nota bug but PHP normal behavior. It happens because the ==operator in PHP doesn't check for type.
这不是错误而是 PHP 的正常行为。这是因为==PHP 中的运算符不检查类型。
$a = '';
if(empty($a)) {
echo 'is empty';
}
If you want also to check if the values have the same type, use ===instead. To study in deep this difference, please read the official documentation.
如果您还想检查值是否具有相同的类型，请===改用。要深入研究这种差异，请阅读官方文档。
回答by dayuloli
If you use ==, php treats an empty string or array as null. To make the distinction between nulland empty, either use ===or is_null. So:
如果使用==，php 会将空字符串或数组视为null。要区分null和empty，请使用===或is_null。所以：
if($a === NULL)or if(is_null($a))
if($a === NULL)或者 if(is_null($a))
回答by Foued MOUSSI
PHP 7 isset() vs empty() vs is_null()
PHP 7 isset() vs empty() vs is_null()
回答by ewizard
Use empty- http://php.net/manual/en/function.empty.php.
使用empty- http://php.net/manual/en/function.empty.php。
Example:
例子：
##代码##