PHP ʖ²ἯTH º󍋼/A function_exists Description if (function_exists('imap_open')) {echo "IMAP functions are available. br \n";} else {echo "IMAP functions are not available. br \n";} º󍋼/A ưµ㼯A func_num_args ɏһ¼¶ get_defined_functions