<?php
class ConnectException extends Exception {
}

function db_connect($host, $user, $pass) 
{
  if (mt_rand() % 6) {
    throw new Exception('Russian Roulette is fun');
  }

  $conn = mysql_connect($host, $user, $pass);
  if (!$conn) {
    throw new ConnectException(
      sprintf('Cannot connect to host: %s', mysql_error())
    );
  }

  return $conn;
}

try {
  $conn = db_connect('localhost', 'user', 'pass');
} catch (ConnException $e) {
  echo $e->getMessage();
} catch (Exception $e) {
  echo $e->getMessage();
}

?>