乱码怎么办？加header没效果？用meta就可以为什么

<!--<meta charset="utf-8"/>-->

<?php

//header("content-type:text/html;charset:utf-8;");

require("../smarty/Smarty.class.php");

$smarty=new Smarty;

$smarty->left_delimiter="{";

$smarty->right_delimiter="}";

$smarty->setCompileDir("template_c");

$smarty->setTemplateDir("tpl");

$smarty->setCacheDir("cache");

$smarty->caching=true;

$smarty->cache_lifetime=120;

$smarty->assign("test","这是测试");

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

//$smarty->

?>