PHP 中 NULL 和 null 的区别
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Difference between NULL and null in PHP
提问by cmcculloh
Is there a difference between NULLand nullin PHP? Sometimes they seem to be interchangeable and sometimes not.
PHP 中的NULL和有区别null吗？有时它们似乎可以互换，有时则不能。
edit: for some reason when I read the documentation linked to in the answer (before posting this question) I read it as "case sensitive" instead of "case insensitive" which was the whole reason I posted this question in the first place...
编辑：出于某种原因，当我阅读答案中链接的文档时（在发布此问题之前），我将其阅读为“区分大小写”而不是“不区分大小写”，这是我首先发布此问题的全部原因。 .
回答by mbillard
Null is case insensitive.
Null 不区分大小写。
From the documentation:
从文档：
There is only one value of type null, and that is the case-insensitivekeyword NULL.
只有一个 null 类型的值，那就是不区分大小写的关键字 NULL。
回答by SolidSnake
There is no difference. Same type just its a case insensitivekeyword. Same as True/Falseetc...
没有区别。相同类型只是不区分大小写的关键字。与True/False等相同...
回答by David Hahn
well there is a technical difference, just not what you're thinking (think: where does it appear in the dictionary): the ASCII value for lowercase null appears after the upper case. Try:
好吧，存在技术差异，而不是您的想法（想想：它出现在字典中的哪个位置）：小写 null 的 ASCII 值出现在大写之后。尝试：
$a = NULL;
$b = null;
if($a < $b){
print 'first num appears earlier in the dictionary than second num';
}
else {
print'the right num appears in the dictionary before the left num ';
}
** actually there is no ASCII value for lower case null while upper case NULL is 0. lowercase null would be evaluated as a string value which would be greater than 0. The difference between all upper and lower case ASCII values is 32, except here where an entire string value is considered.
** 实际上没有小写空值的 ASCII 值，而大写空值是 0。小写空值将被评估为一个大于 0 的字符串值。所有大写和小写 ASCII 值之间的差异是 32，除了这里其中考虑了整个字符串值。
