php man page for session_unset

SESSION_UNSET(3)							 1							  SESSION_UNSET(3)

session_unset - Free all session variables

SYNOPSIS
       void session_unset (void  )

DESCRIPTION
	The session_unset(3) function frees all session variables currently registered.

RETURN VALUES
	No value is returned.

NOTES
       Note

	       If  $_SESSION  (or  $HTTP_SESSION_VARS  for  PHP 4.0.6 or less) is used, use unset(3) to unregister a session variable, i.e.  unset
	      ($_SESSION['varname']);.

       Caution

	       Do NOT unset the whole $_SESSION with unset($_SESSION) as this will disable the registering of session variables through the $_SES-
	      SION superglobal.

PHP Documentation Group 													  SESSION_UNSET(3)