Text String Validation

[Glese]

I do want to validate a password input field to only allow numbers and letters without special character and spaces, and I also do want the same for the name input field.

 

Since the old fashioned ways are deprecated. How would one approach to solve this issue the new way?

[canabatz]

function safe($value){ 
   return mysql_real_escape_string($value); 
   }

if($_POST['submit'])
{
$username1=safe($_POST['username']);
$password=safe($_POST['password']);
.......more code here

[QuickOldCar]

http://php.net/manual/en/function.ctype-alnum.php