PHP除开BOM头后出现乱码

PHP去除BOM头后出现乱码
程序用的是Notepad++文本编辑器编写的，当选择格式->以UTF-8格式编码后，中文字符（从数据库读取，存储到$_SESSION中）可以正常显示，但是会出现以下警告

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at E:\wamp\www\biyesheji\login_check.php:1) in E:\wamp\www\biyesheji\login_check.php on line 1

Warning: Cannot modify header information - headers already sent by (output started at E:\wamp\www\biyesheji\login_check.php:1) in E:\wamp\www\biyesheji\login_check.php
Array ( [username] => 张三 [userid] => 2009011105 [role] => 3 )

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去掉BOM头后，警告消失，但是中文字符全部变成乱码

Array ( [username] => 寮犱笁 [userid] => 2009011105 [role] => 3 )
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求解决方法

------解决方案--------------------

header('Content-type: text/html; charset=utf-8');

加一句申明是UTF-8编码，不然浏览器可能会自己去检测