一段完整的php登录函数

这段代码比较完整，带session写入，mysql数据库查询

//escape data and strip tags
function safestrip($string){
	$string = strip_tags($string);
	$string = mysql_real_escape_string($string);
	return $string;
}
 
//function to show any messages
function messages() {
    $message = '';
    if($_SESSION['success'] != '') {
        $message = '<span class="success" id="message">'.$_SESSION['success'].'</span>';
        $_SESSION['success'] = '';
    }
    if($_SESSION['error'] != '') {
        $message = '<span class="error" id="message">'.$_SESSION['error'].'</span>';
        $_SESSION['error'] = '';
    }
    return $message;
}
 
//log user in ---------------------------------------------------
function login($username, $password){
 
  //call safestrip function 
  $user = safestrip($user);
  $pass = safestrip($pass);  
 
  //convert password to md5 
  $pass = md5($pass);
 
   // check if the user id and password combination exist in database
   $sql = mysql_query("SELECT * FROM table WHERE username = '$user' AND password = '$pass'")or die(mysql_error());  
 
   //if match is equal to 1 there is a match 
   if (mysql_num_rows($sql) == 1) {	  
 
	  		   //set session
			   $_SESSION['authorized'] = true;
 
			   // reload the page
			  $_SESSION['success'] = 'Login Successful';
			  header('Location: ./index.php');
			  exit;			
 
 
    } else {
		// login failed save error to a session
  		$_SESSION['error'] = 'Sorry, wrong username or password';
   }
}
 
//usage example
//show any errors
messages();
 
//pass username and password to login function the username and password would be taken from a form
login($username, $password);