如果要解析空值，请使用preg_match检查值

Question

I want to check a input value with preg_match. So if user insert anything on input field, preg_match check this value else return error. But if have no input value, sql save only empty field.

When I insert anything on input field, preg_match working well but if input value is empty this preg_match stop insert anything on sql.

here is this:

$langu = mysqli_real_escape_string($db, $_POST['langu']);
$relig = mysqli_real_escape_string($db, $_POST['relig']);

if(preg_match("/^([0-9a-zA-Z])+$/i", $langu) || preg_match("/^([0-9a-zA-Z])+$/i", $relig)){
// insert at sql
// If $langu or $relig is empty store empty, but I cannot parsing empty value by preg_match
} else { echo 'error';}

Answer 1

You can check if the string is empty first:

if(
   (!empty($langu) && preg_match("/^([0-9a-zA-Z])+$/i", $langu)) || 
   (!empty($relig) && preg_match("/^([0-9a-zA-Z])+$/i", $relig))
) {

(formatted so you can see conditions)