md5（）函数中的PHP显示错误[关闭]

I tried to assign a salt to md5() function along with the password parameter. But PHP is displaying an error message when the code is executed.

An error message Strict standards: Only variables should be passed by reference is displayed when I try to execute the following code. I tried to assign the reference to a variable and pass it to the md5() function. But still PHP is displaying the same error message.

    global $Database;
    if ($stmt = $Database -> prepare("SELECT * FROM users WHERE username = ? and password = ?")) {
        $salt = $this->salt;
        $stmt -> bind_param("ss", $user, md5($pass . $salt));
        $stmt -> execute();
        $stmt -> store_result();

        if ($stmt -> num_rows > 0) {
            $stmt -> close();
            return TRUE;
        } else {
            $stmt -> close();
            return FALSE;
        }
    } else {
        die("ERROR: Could not prepare MySQLI statement");
    }

bind_param's params need references to variables. You cannot use md5() directly, you'll need to assign it to a variable first:

md5pass = md5($pass . $salt);

Then, use it:

$stmt -> bind_param("ss", $user, $md5pass);

Tip: Please don't use md5() for hashing passwords. You can use crypt() with blowfish algorithm as it is much more secure.