Smarty配置

//老师给看看为什么运行了什么都没有，代码都正确啊，而且源码我这里运行的时候也是空白……

<?php

require ('../smarty/Smarty.php');

$smarty = new Smarty();

$smarty->left_delimiter = "{";

$smarty->right_delimiter = "}";

$smarty->template_dir = "tpl";

$smarty->compile_dir = "template_c";

$smarty->cache_dir = "cache";

$smarty->caching = true;

$smarty->cache_lifetime = 120;

$smarty->assign('articletitle','文章标题'); 

$smarty->display("test.tpl");