Php empty () error, Fatal error: Can't use function return

The error message "Fatal error: Can't use function return value in write context" is displayed in the empty function today. I think this function has been used for a long time. Why, let's take a look at my analysis process.

Error Message

Fatal error: Can't use function return value in write context in empty. php on line 5

My code is written in this way.

The Code is as follows:	Copy code
$ Str = ""; If (empty (trim ($ str ))){ Echo "empty "; }

Then

Fatal error: Can't use function return value in write context in empty. php on line 5

I went to the official website to check the manual.

Bool empty (mixed $ var)

If var is a non-null or non-zero value, empty () returns FALSE. In other words, "", 0, "0", NULL, FALSE, array (), var $ var; and objects without any attributes will be considered empty, if var is null, TRUE is returned. Empty () is the antonym of (boolean) var except when the variable is not set.

It can be seen that empty can only be used to check the variable value, but cannot be used to check the return value of the function. The correct usage should be

The Code is as follows:	Copy code
$ Var = trim (""); // The result is true because $ var is a null string. If (empty ($ var )){ Echo 'empty '; }

Empty (trim ($ str) is incorrect.