How to allow underscore and dash with ctype_alnum()?

Question

How can I add the exception of _ and - as valid characters when using ctype_alnum() ?

I have the following code:

if ( ctype_alnum ($username) ) {

  return TRUE;

} elseif (!ctype_alnum  ($username)) {
    
  $this->form_validation->set_message(
    '_check_username',
    'Invalid username! Alphanumerics only.'
  );

  return FALSE;
}

Answer 1

Since ctype_alnum only validates alpha numeric character, Try this:

$sUser = 'my_username01';
$aValid = array('-', '_');

if(!ctype_alnum(str_replace($aValid, '', $sUser))) {
    echo 'Your username is not properly formatted.';
} 

Answer 2

Use preg_match instead, maybe?

if(preg_match("/^[a-zA-Z0-9_\-]+$/", $username)) {
    return true;
} else {
    $this->form_validation->set_message('_check_username', 'Invalid username! Alphanumerics only.');
}

Answer 3

Here is how to use ctype_alnum AND have exceptions, in this case I also allow hyphens ( OR statement).

$oldString = $input_code;
$newString = '';
$strLen = mb_strlen($oldString);
for ($x = 0; $x < $strLen; $x++) 
   {
     $singleChar = mb_substr($oldString, $x, 1);
     if (ctype_alnum($singleChar) OR ($singleChar == '-'))
        {
          $newString = $newString . $singleChar;
        }
   }
$input_code = strtoupper($newString);