PHP warning Cannot modify header information - headers already sent by (output started at...
出现这种错误一般是在发送header之前有输出内容
有echo,print, <?php之前有空格,文件为UTF-8 BOM类型之类的。。。
可参看
http://stackoverflow.com/questions/8028957/how-to-fix-headers-already-sent-error-in-php