Notice: ... Unknown on line 0 - How to find correct line, it's NOT "line 0"

Question

Edit: added the PDO call.

This is the actual error:

Notice: Object of class PDOStatement could not be converted to int in Unknown on line 0

How can I in general find out which line is the correct line of the error/notice, since it is NOT line 0?

I tried using register_tick_function echoing out file:line, which does not work, because the notice is always outputted at the end of my total output.

I am looking for a general debugging way, since I could not find any error in my class of that object.

// PHP PDO Standard
$db_server = 'mysql:host='.$this->db_host.';dbname='.$this->db_dbase;
try {
  $this->db_connection = new PDO($db_server, $this->db_user, $this->db_pass);
  $pdo_set = $this->db_connection->setAttribute(PDO::ATTR_EMULATE_PREPARES, FALSE);
  $pdo_set = $this->db_connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
  $pdo_set = $this->db_connection->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
  //DebugPrint($pdo_set, '$pdo_set');
} catch (PDOException $e) {
  //print 'Error!: '.$e->getMessage().'<br/>';
  die();
}

Answer 1

Finally, I found my own answer to my very own problem:

// doing PDO-sql, inserting session data, I ran into my problem.
$this->db_connection = new PDO(...);
$sql_query = "INSERT INTO ".$this->session_db_table." (...) VALUES (...)";
$sql_result = $this->db_connection->query($sql_query);

// This is the line (ideally named "0") from the notice:
return $sql_result;

return $sql_result is throwing this notice:

"Notice: Object of class PDOStatement could not be converted to int in Unknown on line 0"

$sql_result is an object; return format expected seems to be boolean.

So I removed this return and the notice is now gone.