PHP determines whether the value is empty

I recently learned PHP, and I have some doubts about judging whether it is empty, and I would like to share the records with you.

empty

If variable is a non-empty or non-zero value, empty() returns FALSE. In other words, "", 0, "0", NULL, FALSE, array(), var $var, undefined; and objects without any attributes will be considered empty. If var is empty, TRUE will be returned. . (Recommended learning: PHP Programming from Beginner to Master)

If e is undefined or the value is NULLL, e is undefined or the value is NULLL, e=NULL, it must be empty , that is, empty($e)=true;

If e is int type, e is int type, e=0, relative to the number, 0 represents zero, that is, empty($e)=true;

If e is string type, e is string type, e="", relative to string, "" means empty, that is, empty($e)=true;

If e is string type, e is string type, e="0", relative to string, "0" means zero, that is, empty($e)=true;

If e is bool Type, e is bool type, e=false, relative to true, false means empty, that is, empty($e)=true;

If e is array type, e is array type, a=array( ), relative to an array, data without elements is empty, that is, empty($e)=true;

isset

If the variable exists (non-NULL) Returns TRUE, otherwise returns FALSE (including undefined). The variable value is set to: null, and the return value is also false; after unsetting a variable, the variable is canceled. Note that isset handles NULL value variables specially.

is_null

Check whether the incoming value [value, variable, expression] is null. Only one variable is defined and its value is null. Returns TRUE. Others return FALSE [An error will occur after undefined variables are passed in! 】

In some cases, it is recommended to use isset to determine whether a variable is NULL.

But semantically speaking, "whether a variable has been displayed initialized" and "whether it is NULL" are different concepts. It is inappropriate to use isset in some scenarios, such as checking a function. Whether the return value is NULL.

You can use "==" and "===" at this time to determine whether they are NULL.

As for "==" and "===", their direct difference is still very big. For "==", it recognizes the empty string, and 0 and false are both NULL. For "===", it represents NULL only if a variable is really NULL.

In addition, compared to "isset", the performance of "===" is basically similar, 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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