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PHP error: "Cannot pass parameter 2 by reference"

I just need help on this PHP error which I do not quite understand:

Fatal error: Cannot pass parameter 2 by reference in /web/stud/openup/inactivatesession.php on line 13

<?php

error_reporting(E_ALL);

include('connect.php');

$createDate = mktime(0,0,0,09,05,date("Y"));
$selectedDate =  date('d-m-Y', ($createDate));

$sql = "UPDATE Session SET Active = ? WHERE DATE_FORMAT(SessionDate,'%Y-%m-%d' ) <= ?";
$update = $mysqli->prepare($sql);
$update->bind_param("is", 0, $selectedDate);  //LINE 13
$update->execute();

?>

What does this error mean? How can this error be fixed?

Solution

  • The error means that the 2nd argument is expected to be a reference to a variable.

    Since you are not handing a variable but an integer of value 0, it generates said error.

    To circumvent this do:

    $a = 0;
$update->bind_param("is", $a, $selectedDate);  //LINE 13

    In case you want to understand what is happening, as opposed to just fixing your Fatal error, read this: http://php.net/manual/en/language.references.pass.php