Session和Cookie的使用

//判断数组中某下标变量是否存在，存在则返回其值，否则返回空
function checkvar($index,$arr)
{
  $result = "";

  //判断SESSION
  if($arr == "s")
  {
    if(isset($_SESSION[$index]))
      $result = $_SESSION[$index];
  }

  //判断COOKIE
  if($arr == "c")
  {
    if(isset($_COOKIE[$index]))
      $result = $_COOKIE[$index];
  }

  //判断POST
  if($arr == "p")
  {
    if(isset($_POST[$index]))
      $result = $_POST[$index];
  }

  //判断GET
  if($arr == "g")
  {
    if(isset($_GET[$index]))
      $result = $_GET[$index];
  }

  return $result;
}

if(!empty($_SESSION['sess_u']))
  $u = $_SESSION['sess_u'];
elseif(!empty($_COOKIE['cook_u']))
  $u = $_COOKIE['cook_u'];
else
  $u = "";

if(!empty($_SESSION['sess_p']))
  $p = $_SESSION['sess_p'];
elseif(!empty($_COOKIE['cook_p']))
  $p = $_COOKIE['cook_p'];
else
  $p = "";

if($u!="")
{
  $query = "select * from `user` where `name`='$u' and `mdpsw`='$p'";
  $res = mysql_query($query);
  if(mysql_num_rows($res)!=1)
  {
    echo "用户名/密码错误！";
    mysql_close();
    exit();    
  }
  ...
}

session_start();
session_register("sess_u","sess_p");
$_SESSION['sess_u'] = $username;
$_SESSION['sess_p'] = $mdpass;	
setcookie("cook_u",$username,time()+$cookietime);
setcookie("cook_p",$mdpass,time()+$cookietime);

参见Session为空的问题