php - eregi to pregmatch not working -

how change not alphanumeric? (on google see want alphanumeric)

code :

         /* check if username not alphanumeric */      else if(!preg_match("/^[a-za-z0-9,]+$/", $subuser)){         $form->seterror($field, "* username not alphanumeric");      } 

it keeps saying

* username not alphanumeric 

this old part when had eregi

         /* check if username not alphanumeric */      else if(!eregi("^([0-9a-z])+$", $subuser)){         $form->seterror($field, "* username not alphanumeric");      } 

easist way regex use ^ inside [] character class negate it:

if(preg_match('/[^a-z0-9]/i', $subuser)) {     //contains @ least 1 non alpha-num character. } 

however, php supplies built-in function this: ctype_alnum()

if(!ctype_alnum($subuser)) { .... }