求大神给指点下这些代码有什么问题啊，为什么session变量不生效啊
<?php require_once('Connections/yiwuyiwu.php'); ?><br><?php <br />if (!function_exists("GetSQLValueString")) {<br>function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "") <br>{<br> $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;<br><br> $theValue = function_exists("mysql_real_escape_string") ? mysql_real_escape_string($theValue) : mysql_escape_string($theValue);<br><br> switch ($theType) {<br> case "text":<br> $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";<br> break; <br> case "long":<br> case "int":<br> $theValue = ($theValue != "") ? intval($theValue) : "NULL";<br> break;<br> case "double":<br> $theValue = ($theValue != "") ? "'" . doubleval($theValue) . "'" : "NULL";<br> break;<br> case "date":<br> $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";<br> break;<br> case "defined":<br> $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;<br> break;<br> }<br> return $theValue;<br>}<br>}<br><br>mysql_select_db($database_yiwuyiwu, $yiwuyiwu);<br>$query_Recordset1 = "SELECT * FROM `user`";<br>$Recordset1 = mysql_query($query_Recordset1, $yiwuyiwu) or die(mysql_error());<br>$row_Recordset1 = mysql_fetch_assoc($Recordset1);<br>$totalRows_Recordset1 = mysql_num_rows($Recordset1);<br>?><br><?php <br />// *** Validate request to login to this site.<br>if (!isset($_SESSION)) {<br> session_start();<br>}<br>// ***session变量开始了<br>$loginFormAction = $_SERVER['PHP_SELF'];<br>if (isset($_GET['accesscheck'])) {<br> $_SESSION['PrevUrl'] = $_GET['accesscheck'];<br>}<br><br>if (isset($_POST['Username'])) {<br> $loginUsername=$_POST['Username'];<br> $password=(md5($_POST['Password']));<br> $MM_fldUserAuthorization = "enable";<br> $MM_redirectLoginSuccess = "index.php";<br> $MM_redirectLoginFailed = "zhuce.php";<br> $MM_redirecttoReferrer = false;<br> //*** 输入账号和密码，判断转向页面。<br> mysql_select_db($database_yiwuyiwu, $yiwuyiwu);<br> <br> $LoginRS__query=sprintf("SELECT u_id u_name, pass, enable FROM `user` WHERE u_name=%s AND pass=%s",<br> //*** 启用符号是这个“·”<br> GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text")); <br> <br> $LoginRS = mysql_query($LoginRS__query, $yiwuyiwu) or die(mysql_error());<br> $row_LoginRS = mysql_fetch_assoc($LoginRS);<br> $loginFoundUser = mysql_num_rows($LoginRS);<br> <br> <br> if ($loginFoundUser) {<br> <br> $loginStrGroup = mysql_result($LoginRS,0,'enable');<br> <br> //*** 声明三个会话变量并分配值<br> $_SESSION['MM_Username'] = $loginUsername;<br> $_SESSION['MM_UserGroup'] = $loginStrGroup; <br> $_SESSION['u_id']= $row_LoginRS('u_id'); <br><br> if (isset($_SESSION['PrevUrl']) && false) {<br> $MM_redirectLoginSuccess = $_SESSION['PrevUrl']; <br> }<br> header("Location: " . $MM_redirectLoginSuccess );<br> }<br> else {<br> header("Location: ". $MM_redirectLoginFailed );<br> }<br>}<br>?><br>nbsp;html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><br><br><br><meta><br><title></title><br><br><br><br> <h3>登录系统</h3><br> <hr><br><br>
