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								//######################定义函数checkuser()##########################
				function checkuser(){
				global $user_name,$user_card,$user_pass,$user_repass,$user_email,$user_ques,$user_answ;
				global $hostname,$dbuser,$dbname,$dbpassword,$book_table,$send_table,$user_table;
				if(empty($user_name)){echo "用户名不能为空。";
				echo "点此返回";
				exit;}
				if(empty($user_card)){
				echo "请输入你的借阅证号";
				exit;
				}
				if(strlen($user_card)'8'){
					echo"你输入的借阅证号码位数不对。";
					echo "点此返回";
				exit;
				}
				if(empty($user_pass)){
				  echo "你的密码呢？";
					echo "点此返回";
					exit;
				}
				if(empty($user_repass)||(strcmp($user_pass,$user_repass))){
					echo "你的确认密码有误";
					echo "点此返回";
					exit;
				}
				if(empty($user_email)){
				  echo "你的E-MAIL不能为空。";
				  echo "点此返回";
				    exit;
					}
					if(!eregi("^[_\.0-9a-z-]+@([0-9a-z][0-9a-z-]+\.)+[a-z]{2,3}$",$user_email)){
					echo "你的E-MAIL格式不对。";
					echo "点此返回";
				    exit;
					}
				//$db=mysql_connect($hostname,$dbuser,$dbpassword) or die("数据库连接错误！");
				  $db=mysql_connect($hostname,$dbuser);
				  mysql_select_db($dbname,$db);
				$sql="select*from $user_table where user_name='".$user_name."'";
				$result=mysql_query($sql,$db);
				if(mysql_fetch_object($result))
				{
				    echo"已经有相同的名字存在，请重新填写";
					exit;
				}
				$query=mysql_query("insert into $user_table values('','$user_name','$user_card','$user_pass','$user_email','$user_ques','$user_answ')") or die("数据表连接错误。");
				   if($query){
				    echo $user_name.",感谢你的注册，如果此页面没有自动返回，请点击此处返回登录";
					echo "";
				 }
				 }
				?>