将对象作为参数传递给函数不工作[关闭]

Question

This seems extremely easy but for the life of me can't figure out why this is not working. I am trying to simply pass an object into a function but I get this error:

Catchable fatal error: Argument 3 passed to write_query() must be an instance of mysqli, null given, called in C:\xampp\htdocs\CSP\login\login.php on line 28 and defined in C:\xampp\htdocs\CSP\php_scripts\login_script.php on line 40

These are my functions definitions:

function conn_database()
    {
        if (!empty($_POST['userid']) && !empty($_POST['password']))
        {
            $conn = new mysqli('localhost', 'root', '', 'csp');

            if (mysqli_connect_errno()) 
            {
                echo 'Connection to database failed:'.mysqli_connect_error();
                exit();
            }
            return $conn;
        }

    }


function write_query($userid, $password, mysqli $conn)
    {
        $query = 'select * from authorized_users '
        ."where userid= '$userid'"
        ."and password_id='$password'";
        $result = $conn->query($query);
        return $result;
    }

I am calling them like this:

$conn = conn_database();
$result = write_query($userid, $password, $conn);

I'm type hinting in the definition of the write_query() but from what I understand from the error, my third argument is not considered an instance of mysqli. (I am aware I should be salting the password and all, I'm just trying to get this to work first). Any suggestions would be appreciated

Answer 1

Your third paramater is not an instance of mysqli. It is null. This is because your get_connection function is not returning anything.

Why are you checking for this:

if (!empty($_POST['userid']) && !empty($_POST['password']))

This means you code will only try and connect to the SQL server if you provide it with post data for userid and password only. If this is the behaviour you want, you should put the if statement outside the function, something like this:

if (!empty($_POST['userid']) && !empty($_POST['password']))
  $conn = conn_database();
  $result = write_query($userid, $password, $conn);
}

although it seems that userid and password aren't set, regardless. Make sure to check the name attribute on your inputs and do a var_dump($_POST) to see whats being posted to your script.