/*
bool setcookie ( string $name [, string $value = "" [, int $expire = 0
[, string $path = ""
[, string $domain = ""
[, bool $secure = false
[, bool $httponly = false ]]]]]] )
*/
setcookie($cookie_name, null, -1);
if (!isset($_COOKIE[$cookie_name]))
echo "Cookie named 'user_name' is not set";
/*
run:
Cookie named 'user_name' is not set
*/