为什么这个表达式返回错误，我该如何解决？ [重复]

This code:

if(!empty(trim($_POST['post']))){ }

return this error:

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

How can I resolve and avoid to do 2 checks ( trim and then empty ) ?

I want to check if POST is not only a blank space.

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In the documentation it actually explains this problem specifically, then gives you an alternate solution. You can use

trim($name) == false.

if (trim($_POST['post'])) {

Is functionally equivalent to what you appear to be trying to do. There's no need to call !empty

you cant use functions inside isset , empty statements. just assign the result of trim to a variable.

$r = trim($_POST['blop']);

if(!empty($r))....

edit: Prior to PHP 5.5

if (trim($_POST['post']) !== "") {
    // this is the same
}

In PHP, functions isset() and empty() are ment to test variables.

That means this

if(empty("someText")) { ... }

or this

if(isset(somefunction(args))) { ... }

doesn't make any sence, since result of a function is always defined, e.t.c.

These functions serve to tell wether a variable is defined or not, so argument must me a variable, or array with index, then it checks the index (works on objects too), like

if(!empty($_POST["mydata"])) {
    //do something
} else {
    echo "Wrong input";
}