PHP code sharing for querying different elements in two arrays

<?php
  $a = array(
  "max_allow_dialogs",
  "livechat_server_ip",
  "livechat_service_time",
  "abort_zh_cn",
  "abort_zh_tw",
  "abort_en_usa",
  "welcome_zh_cn",
  "welcome_zh_tw",
  "welcome_en_usa",
  "timeout_zh_cn",
  "timeout_zh_tw",
  "timeout_en_usa",
  "absence_zh_cn",
  "absence_zh_tw",
  "absence_en_usa"
  );
  $b = array(
  "max_allow_dialogs",
  "livechat_server_ip",
  "livechat_service_time",
  "abort_zh_cn",
  "abort_zh_tw",
  "abort_en_usa",
  "welcome_zh_cn",
  "welcome_zh_tw",
  "welcome_en_usa",
  "timeout_zh_cn",
  "timeout_zh_tw",
  "timeout_en_usa",
  );
  $c = array_merge(array_diff($a,$b),array_diff($b,$a));
  print_r($c);
?>

Array
(
  [0] => absence_zh_cn
  [1] => absence_zh_tw
  [2] => absence_en_usa
)