function checkUserIsOnline($userid){
		$online = false;
		$res = $GLOBALS['TYPO3_DB']->sql_query('SELECT DISTINCT ses_userid, username, name
				FROM fe_sessions LEFT JOIN fe_users ON (ses_userid=uid)
				WHERE ses_tstamp+3600 > unix_timestamp() OR is_online+3600 > unix_timestamp() and ses_userid='.$userid);
		while(false!==($row=$GLOBALS['TYPO3_DB']->sql_fetch_assoc($res))){
			if($row['ses_userid']==$userid)$online=true;
		}
		return $online;
	}

$TYPO3_CONF_VARS[‘SYS’][‘sqlDebug’] = ‘2’;    //  Modified or inserted by TYPO3 Install Tool.

Extenstion: cc_debug 让显示效果更好点 (continue reading…)

Using sessions
Sessions are a mechanism to carry user data (parameters) along the web site visit without having to post them over and over again. The data is available as long as the session is valid, usually until all browser windows are closed.

Since TYPO3 instantiates a session automatically, you can use this existing session to read/write data into it. However, you must first understand that sessions in frontend and backend are handled differently.

The routine on the other hand is always the same.

Recover your data from the session
Add values (possibly into an array that holds all the session data)
Save your data to the session (continue reading…)