PHP implements verification email to activate new user login function after registration

CREATE TABLE IF NOT EXISTS `t_user` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `username` varchar(30) NOT NULL COMMENT '用户名',
 `password` varchar(32) NOT NULL COMMENT '密码',
 `email` varchar(30) NOT NULL COMMENT '邮箱',
 `token` varchar(50) NOT NULL COMMENT '帐号激活码',
 `token_exptime` int(10) NOT NULL COMMENT '激活码有效期',
 `status` tinyint(1) NOT NULL DEFAULT '0' COMMENT '状态,0-未激活,1-已激活',
 `regtime` int(10) NOT NULL COMMENT '注册时间',
 PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

<form id="reg" action="register.php" method="post">
  <p>用户名：<input type="text" class="input" name="username" id="user"></p>
  <p>密 码：<input type="password" class="input" name="password" id="pass"></p>
  <p>E-mail：<input type="text" class="input" name="email" id="email"></p>
  <p><input type="submit" class="btn" value="提交注册"></p>
</form>

include_once("connect.php");//连接数据库
include_once("smtp.class.php");//邮件发送类

$username = stripslashes(trim($_POST['username']));
$query = mysql_query("select id from t_user where username='$username'");
$num = mysql_num_rows($query);
if($num==1){
  echo '用户名已存在，请换个其他的用户名';
  exit;
}

$password = md5(trim($_POST['password'])); //加密密码
$email = trim($_POST['email']); //邮箱
$regtime = time();
$token = md5($username.$password.$regtime); //创建用于激活识别码
$token_exptime = time()+60*60*24;//过期时间为24小时后
$sql = "insert into `t_user` (`username`,`password`,`email`,`token`,`token_exptime`,`regtime`)
values ('$username','$password','$email','$token','$token_exptime','$regtime')";
mysql_query($sql);

if (mysql_insert_id()) {//写入成功，发邮件
  include_once("smtp.class.php");
  $smtpserver = "smtp.163.com"; //SMTP服务器
  $smtpserverport = 25; //SMTP服务器端口
  $smtpusermail = "hjl416148489_4@163.com"; //SMTP服务器的用户邮箱
  $smtpuser = "hjl416148489_4@163.com"; //SMTP服务器的用户帐号
  $smtppass = "hjl7233163"; //SMTP服务器的用户密码
  $smtp = new Smtp($smtpserver, $smtpserverport, true, $smtpuser, $smtppass); //这里面的一个true是表示使用身份验证,否则不使用身份验证.
  $emailtype = "HTML"; //信件类型，文本:text；网页：HTML
  $smtpemailto = $email;
  $smtpemailfrom = $smtpusermail;
  $emailsubject = "用户帐号激活";
  $emailbody = "亲爱的" . $username . "：<br/>感谢您在我站注册了新帐号。<br/>请点击链接激活您的帐号。<br/><a href=&#39;http://www.jb51.net/demo/active.php?verify=" . $token . "&#39; target=&#39;_blank&#39;>http://www.jb51.net/demo/active.php?verify=" . $token . "</a><br/>如果以上链接无法点击，请将它复制到你的浏览器地址栏中进入访问，该链接24小时内有效。<br/>如果此次激活请求非你本人所发，请忽略本邮件。<br/><p style=&#39;text-align:right&#39;>-------- 脚本之家http://www.jb51.net敬上</p>";
  $rs = $smtp->sendmail($smtpemailto, $smtpemailfrom, $emailsubject, $emailbody, $emailtype);
  if ($rs == 1) {
    $msg = &#39;恭喜您，注册成功！<br/>请登录到您的邮箱及时激活您的帐号！&#39;;
  } else {
    $msg = $rs;
  }
  echo $msg;
}

include_once("connect.php");//连接数据库
$verify = stripslashes(trim($_GET['verify']));
$nowtime = time();
$query = mysql_query("select id,token_exptime from t_user where status='0' and
`token`='$verify'");
$row = mysql_fetch_array($query);
if($row){
  if($nowtime>$row['token_exptime']){ //24hour
    $msg = '您的激活有效期已过，请登录您的帐号重新发送激活邮件.';
  }else{
    mysql_query("update t_user set status=1 where id=".$row['id']);
    if(mysql_affected_rows($link)!=1) die(0);
    $msg = '激活成功！';
  }
}else{
  $msg = 'error.';
}
echo $msg;