php - Codeigniter is giving me an error called "Disallowed Key Characters." -

i have input name="exam[a+]". have figured out when called $this->input->post("exam") giving me error called "disallowed key characters". want add + sign in key characters. here code in system file.

function _clean_input_keys($str)     {         if ( ! preg_match("/^[a-z0-9:_\/-]+$/i", $str))         {             exit('disallowed key characters.');         }          // clean utf-8 if supported         if (utf8_enabled === true)         {             $str = $this->uni->clean_string($str);         }          return $str;     } 

how change regular expression add + sign in input. hope have made question clear. if there still confusion please notify me. edit question again. in advance.

use regex allow +:

^[a-z0-9:_\/+-]+$ 

the main point unescaped hyphen must @ end of character class.

here a demo.