typo3 hooks

ext_localconf.php:
$GLOBALS ['TYPO3_CONF_VARS']['SC_OPTIONS']['t3lib/class.t3lib_tcemain.php']['pro
cessDatamapClass'][] = 'EXT:mitplugin/class.tx_mitplugin_hook.php:tx_mitplugin_hook';

tx_mitplugin_hook.php:
class tx_mitplugin_hook {
    function processDatamap_postProcessFieldArray ($status, $table, $id, &$fieldArray, &$this) {
    //insert code here
    }
}