$_SERVER['SERVER_NAME'] in read-only.

Hello, I am using the variable $_SERVER['SERVER_NAME'] inside a function, for example: function check_servname() { global $server ; if($_SERVER['SERVER_NAME'] != $server) {

     echo "NOT OK, NOT GOOD SERVER NAME" ;
     exit ;

} } But we can modify the value of $_SERVER['SERVER_NAME'] before calling the function check_servname(). And I am looking for a the right server name not for a server name which may have been changed before calling check_servername: $_SERVER['SERVER_NAME'] = "www.google.com" ; //before calling check_servname and $_SERVER['SERVER_NAME'] will be "www.google.com" inside the function even the server name is not "www.google.com". Is there any way to get the server name with a variable which would be read-only ? Thanks, Vincent.