錯誤提示:SAE_Warning: Cannot modify header information - headers already sent by (output started at /data1/www/htdocs/345/leank/1/bbs/login.php:15) in bbs/login.php on line 9SAE_Warning: Cannot modify header information - headers already sent by (output started at /data1/www/htdocs/345/leank/1/bbs/login.php:15) in bbs/login.php on line 10SAE_Warning: Cannot modify header information - headers already sent by (output started at /data1/www/htdocs/345/leank/1/bbs/login.php:15) in bbs/login.php on line 28SAE_Warning: Cannot modify header information - headers already sent by (output started at /data1/www/htdocs/345/leank/1/bbs/login.php:15) in bbs/login.php on line 29大致的代碼:<?php/* * 未完成內容 : 添加判斷的url中log?= "" 的if語句,來判斷用戶是登陸還是退出 *添加一個判斷是否已經登陸的if語句 * */include("conn.php");function clearcookies(){    setCookie('username','',time()-3600);    setCookie('logset','',time()-3600); }?>   <?php     if ($_POST['loginsubmit'])  //檢查是否提交     {        clearcookies();        $sql = "SELECT * FROM user WHERE username = '$_POST[username]'";        $query = mysql_query($sql);        $userinfo = mysql_fetch_array($query);        if ($_POST[password] != "" & $_POST[username] != "") //檢查用戶名密碼是否填寫         {            if ($userinfo['password'] == $_POST['password'] ) //在SQL中檢查用戶名密碼是否正確             {                $username = $_POST[username];                                 setcookie('username','$username',time()+31536000,'/');                setcookie('logset','ok',time()+31536000,'/');                echo "<meta http-equiv=refresh content=0;url=index.php?foo=$_POST[username]>";             }            else             {                echo "登錄失敗!";                echo "請檢查您的用戶名或密碼是否都填寫正確";             }         }        else         {            echo "登錄失敗!";            echo "請檢查您的用戶名或密碼是否為空";         }     }  ?>處錯誤的大致是這個位置:setcookie('username','$username',time()+31536000,'/');setcookie('logset','ok',time()+31536000,'/');