How to update post meta with xml data

Question

I am trying to get this to work, but it doesn't. What is wrong?

$tutorgeocodesrc = "http://where.yahooapis.com/geocode?location=" . urlencode($tutoraddressfull) . "&appid=...";
$tutorgeocode    = simplexml_load_file($tutorgeocodesrc);
$tutorlat        = $tutorgeocode->Result[0]->latitude;
$tutorlng        = $tutorgeocode->Result[0]->longitude;
foreach($tutorgeocode->Result[0]->latitude as $child) 
{
    update_post_meta($user_id, 'tutorcords', $tutorlat);
}

Answer 1

On which hook of WP init this code part?

$user_id - why and from how is this var value? update_post_meta() will use the post ID, see Codex.