php Note: empty() only checks variables as anything error_PHP tutorial

Today I found a tip when using the empty() function to determine whether a variable is null. Note: empty() only checks variables as anything else will result in a parse error. In other words, the following will not work: empty(trim ($name)). It was wrong, and it took me half a day to find the problem.

When you use empty to check the result returned by a function, the following fatal error will be reported:

Fatal error: Can't use function return value in write context in : .............

For example:

echo empty(yourfunction(xx, oo));

Go to the PHP manual and see the following text where the empty function is described:

Note: empty() only checks variables as anything else will result in a parse error. In other words, the following will not work:empty(trim($name)).

empty() only tests variables, testing anything that is not a variable will result in a parsing error!

Therefore, we cannot use empty to directly detect the value returned by the function. We need to assign the return value of the function to a variable first, and then use empty to detect the variable.

So, we can write it in the following form:

$return= yourfunction(xx, oo);

echo empty(return);