php如何删除cookies

<?php
setcookie ( "cookie_user", "test", time () + 60 * 60 * 24 * 30 );
setcookie ( "cookie_pass", md5 ( "test" ), time () + 60 * 60 * 24 * 30 );
function logout() {
  setcookie ( "cookie_user", "", time () + 60 * 60 * 24 * 30 );
  setcookie ( "cookie_pass", "", time () + 60 * 60 * 24 * 30 );
}
/* http://www.manongjc.com/article/1253.html */
logout ();
echo $_COOKIE [&#39;cookie_user&#39;] . "<br />";
echo "You have successfully logged out.";
?>

<?php
setcookie ( "cookie_user", "test", time () + 60 * 60 * 24 * 30 );
setcookie ( "cookie_pass", md5 ( "test" ), time () + 60 * 60 * 24 * 30 );
function logout() {
  setcookie ( "cookie_user", "test", time () - 100 );
  setcookie ( "cookie_pass", md5 ( "test" ), time () - 100 );
}
logout ();
echo $_COOKIE [&#39;cookie_user&#39;] . "<br />";
echo "You have successfully logged out.";
?>