error Strict Standards:Error Only variables should be used by reference in C:\\wamp64\\www\\Exercise Files\\CRUD\\crud-mysqli.php on line 545

Question

On a lynda.com tutorial I am getting this error :

error Strict standards:Error Only variables should be passed by reference in C:\\wamp64\\www\\Exercise Files\\CRUD\\crud-mysqli.php on line 545

I can't see in the code where anything is passed by reference.
I understand the @ operater is an error operator and I think this is causing the error

function insert_album_sql( $album )
{
global $CRUD;
$dbh = $CRUD['dbh'];

$query = '
    INSERT INTO album
        ( title, artist, label, released )
        VALUES ( ?, ?, ?, ? )
';

$sth = $dbh->prepare($query);
if($sth) {
    $sth->bind_param("ssss", @$album['title'], @$album['artist'],   @$album['label'], @$album['released'] );
    $sth->execute();
} else {
    error("insert_album_sql: insert prepare returned no statement handle");    
}

// check for errors
$err = $sth->error;
if($err) error( $err );

return($dbh->insert_id);
}

Answer 1

My educated guess is that line 545 is this:

$sth->bind_param("ssss", @$album['title'], @$album['artist'],   @$album['label'], @$album['released'] );

You have a better chance to determine it for sure than any of us, though, since any decent editor should have a way to either display line numbers or browse to a line by number.

From the bind_param() manual page :

Binds variables to a prepared statement as parameters

That means that the function doesn't read the value. Instead, it keeps a reference to the original variable to read it later. If don't provide a raw variable, it cannot work.

(Disclaimer: I haven't really tested whether @ in particular actually prevents bind_param() from working because I don't know all PHP internals by heart.)

Solution: get rid of @ entirely. You don't want to hide error messages because coding blindly it's neither productive nor fun.

A tutorial that uses a global variable to pass the database connection to the function and abuses @ that way is not a reliable source of knowledge to begin with so it's just possible that such strict standards violation is there in the first place.