CREATE TABLE `user` (
  `uid` mediumint(8) unsigned NOT NULL auto_increment,
  `username` char(15) NOT NULL default '',
  `password` char(32) NOT NULL default '',
  `email` varchar(40) NOT NULL default '',
  `regdate` int(10) unsigned NOT NULL default '0',
  PRIMARY KEY  (`uid`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

<fieldset>
<legend>用户注册</legend>
<form name="RegForm" method="post" action="reg.php" onSubmit="return InputCheck(this)">
<p>
<label for="username" class="label">用户名:</label>
<input id="username" name="username" type="text" class="input" />
<span>(必填，3-15字符长度，支持汉字、字母、数字及_)</span>
<p/>
<p>
<label for="password" class="label">密 码:</label>
<input id="password" name="password" type="password" class="input" />
<span>(必填，不得少于6位)</span>
<p/>
<p>
<label for="repass" class="label">重复密码:</label>
<input id="repass" name="repass" type="password" class="input" />
<p/>
<p>
<label for="email" class="label">电子邮箱:</label>
<input id="email" name="email" type="text" class="input" />
<span>(必填)</span>
<p/>
<p>
<input type="submit" name="submit" value="  提交注册  " class="left" />
</p>
</form>
</fieldset>

<style type="text/css">
    html{font-size:12px;}
    fieldset{width:520px; margin: 0 auto;}
    legend{font-weight:bold; font-size:14px;}
    label{float:left; width:70px; margin-left:10px;}
    .left{margin-left:80px;}
    .input{width:150px;}
    span{color: #666666;}
</style>

<script language=JavaScript>
<!--

function InputCheck(RegForm)
{
  if (RegForm.username.value == "")
  {
    alert("用户名不可为空!");
    RegForm.username.focus();
    return (false);
  }
  if (RegForm.password.value == "")
  {
    alert("必须设定登录密码!");
    RegForm.password.focus();
    return (false);
  }
  if (RegForm.repass.value != RegForm.password.value)
  {
    alert("两次密码不一致!");
    RegForm.repass.focus();
    return (false);
  }
  if (RegForm.email.value == "")
  {
    alert("电子邮箱不可为空!");
    RegForm.email.focus();
    return (false);
  }
}

//-->
</script>

<?php
$conn = @mysql_connect("localhost","root","123456");
if (!$conn){
    die("连接数据库失败：" . mysql_error());
}
mysql_select_db("test", $conn);
//字符转换，读库
mysql_query("set character set 'gbk'");
//写库
mysql_query("set names 'gbk'");
?>

if(!isset($_POST['submit'])){
    exit('非法访问!');
}
$username = $_POST['username'];
$password = $_POST['password'];
$email = $_POST['email'];
//注册信息判断
if(!preg_match('/^[\w\x80-\xff]{3,15}$/', $username)){
    exit('错误：用户名不符合规定。<a href="javascript:history.back(-1);">返回</a>');
}
if(strlen($password) < 6){
    exit('错误：密码长度不符合规定。<a href="javascript:history.back(-1);">返回</a>');
}
if(!preg_match('/^w+([-+.]w+)*@w+([-.]w+)*.w+([-.]w+)*$/', $email)){
    exit('错误：电子邮箱格式错误。<a href="javascript:history.back(-1);">返回</a>');
}

//包含数据库连接文件
include('conn.php');
//检测用户名是否已经存在
$check_query = mysql_query("select uid from user where username='$username' limit 1");
if(mysql_fetch_array($check_query)){
    echo '错误：用户名 ',$username,' 已存在。<a href="javascript:history.back(-1);">返回</a>';
    exit;
}
//写入数据
$password = MD5($password);
$regdate = time();
$sql = "INSERT INTO user(username,password,email,regdate)VALUES('$username','$password','$email',
$regdate)";
if(mysql_query($sql,$conn)){
    exit('用户注册成功！点击此处 <a href="login.html">登录</a>');
} else {
    echo '抱歉！添加数据失败：',mysql_error(),'<br />';
    echo '点击此处 <a href="javascript:history.back(-1);">返回</a> 重试';
}

<fieldset>
<legend>用户登录</legend>
<form name="LoginForm" method="post" action="login.php" onSubmit="return InputCheck(this)">
<p>
<label for="username" class="label">用户名:</label>
<input id="username" name="username" type="text" class="input" />
<p/>
<p>
<label for="password" class="label">密 码:</label>
<input id="password" name="password" type="password" class="input" />
<p/>
<p>
<input type="submit" name="submit" value="  确 定  " class="left" />
</p>
</form>
</fieldset>

if(!isset($_POST['submit'])){
    exit('非法访问!');
}
$username = htmlspecialchars($_POST['username']);
$password = MD5($_POST['password']);

//包含数据库连接文件
include('conn.php');
//检测用户名及密码是否正确
$check_query = mysql_query("select uid from user where username='$username' and password='$password' limit 1");
if($result = mysql_fetch_array($check_query)){
    //登录成功
    $_SESSION['username'] = $username;
    $_SESSION['userid'] = $result['uid'];
    echo $username,' 欢迎你！进入 <a href="my.php">用户中心</a><br />';
    echo '点击此处 <a href="login.php?action=logout">注销</a> 登录！<br />';
    exit;
} else {
    exit('登录失败！点击此处 <a href="javascript:history.back(-1);">返回</a> 重试');
}

session_start();

//注销登录
if($_GET['action'] == "logout"){
    unset($_SESSION['userid']);
    unset($_SESSION['username']);
    echo '注销登录成功！点击此处 <a href="login.html">登录</a>';
    exit;
}

<?php
session_start();

//检测是否登录，若没登录则转向登录界面
if(!isset($_SESSION['userid'])){
    header("Location:login.html");
    exit();
}
//包含数据库连接文件
include('conn.php');
$userid = $_SESSION['userid'];
$username = $_SESSION['username'];
$user_query = mysql_query("select * from user where uid=$userid limit 1");
$row = mysql_fetch_array($user_query);
echo '用户信息：<br />';
echo '用户ID：',$userid,'<br />';
echo '用户名：',$username,'<br />';
echo '邮箱：',$row<'email'>,'<br />';
echo '注册日期：',date("Y-m-d", $row['regdate']),'<br />';
echo '<a href="login.php?action=logout">注销</a> 登录<br />';
?>