php determines whether it is null

php determines whether a variable is NULL

There are many ways to determine whether a variable is NULL in PHP:

is_null or isset

Both functions can determine whether a variable is NULL. They have the same recognition of empty strings, 0, and false. That is is_null=! isset(). But isset is a grammatical structure and is_null is a function. In terms of performance, the grammatical structure is relatively better. Therefore, many places recommend using isset instead of is_null.

== or ===

In some cases, it is recommended to use isset to determine whether a variable is NULL. But semantically speaking, "whether a variable has been explicitly initialized" and "whether it is NULL" are different concepts. In some scenarios, it is inappropriate to use isset, such as checking whether the return value of a function is NULL. At this time, you can use "==" and "====" to determine whether they are NULL.

For "==" and "===", they are directly different

For "==", it recognizes the empty string, 0, false are all NULL. For "===", only if a variable is really NULL, it represents NULL. In addition, the performance of "===" is basically similar to "isset", or even better.

So to sum up the above, the best way to judge whether a variable is NULL is to use "===" directly, so that you don't have to hesitate between is_null and isset. In fact, the above conclusion is also consistent with False's judgment.

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