Doubt about the error "Strict standards: Only variables should be passed by Reference in"

Question

To record some dates in the database in the desired format I am doing so:

 mysqli_stmt_bind_param
    (
        $stmt,
        's',
        date("Y-m-d", strtotime($data))
    );

Or, to catch the present day, simply:

 mysqli_stmt_bind_param
    (
        $stmt,
        's',
        date("Y-m-d")
    );

However, despite recording normally, I get this error (notice right?):

Strict standards: Only variables should be passed by Reference in line "5" // is on the date line...

Is this way of passing the value to the field wrong? What is the correct one? What does this error mean?

Answer 1

Yes it’s wrong, mysqli_stmt_bind_param expects the second(oo) or third(procedural) argument to be at all times a reference that means it must be a variable and not the return of a function/method or value passed right.

The correct is to create a variable before calling mysqli_stmt_bind_param or do date search by database using function now() or equivalent.

$data = date("Y-m-d");
mysqli_stmt_bind_param($stmt, 's', $data);