!DOCTYPE html>
html lang="en">
head>
  meta charset="UTF-8">
  title>Title/title>
/head>
body>
form method="post" action="doLogin.php">
  input type="text" placeholder="用户名" name="username">br>br>
  input type="password" placeholder="密码" name="password">br>br>
  input type="text" placeholder="验证码" name="verifycode" class="captcha">br>br>
  img id="captcha_img" src="captcha.php?r=?php echo rand();?>" alt="验证码">
  label>a href="javascript:void(0)" rel="external nofollow" onclick="document.getElementById('captcha_img').src='captcha.php?r='+Math.random()">换一个/a> /label>br>
  label>input type="checkbox" name="autologin[]" value="1"/>自动登录/label>br>
  button type="submit">登录/button>
/form>
/body>
/html>

?php
header("Content-type:text/html;charset=UTF-8");
require "mysql.php";      //导入mysql.php访问数据库
session_start();        //开启会话一获取到服务器端验证码
$username=$_POST['username'];
$password=$_POST['password'];
$autologin=isset($_POST['autologin'])?1:0;   //获取是否选择了自动登录
$verifycode=$_POST['verifycode'];
$code=$_SESSION['code'];    //获取服务器生成的验证码
/*
 * 首先进行判空操作，通过后进行验证码验证，通过后再进行数据库验证。
 * 手机号码和邮箱验证可根据需要自行添加
 * */
if(checkEmpty($username,$password,$verifycode)){
  if(checkVerifycode($verifycode,$code)){
    if(checkUser($username,$password)){
      $_SESSION['username']=$username; //保存此时登录成功的用户名
      if($autologin==1){        //如果用户勾选了自动登录就把用户名和加了密的密码放到cookie里面
        setcookie("username",$username,time()+3600*24*3);  //有效期设置为3天
        setcookie("password",md5($password),time()+3600*24*3);
      }
      else{
        setcookie("username","",time()-1);  //如果没有选择自动登录就清空cookie
        setcookie("password","",time()-1);
      }
      header("location: index.php ");      //全部验证都通过之后跳转到首页
    }
  }
}
//方法：判断是否为空
function checkEmpty($username,$password,$verifycode){
  if($username==null||$password==null){
    echo 'html>head>Script Language="JavaScript">alert("用户名或密码为空");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
  }
  else{
    if($verifycode==null){
      echo 'html>head>Script Language="JavaScript">alert("验证码为空");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
    }
    else{
      return true;
    }
  }
}
//方法：检查验证码是否正确
function checkVerifycode($verifycode,$code){
  if($verifycode==$code){
    return true;
  }
  else{
    echo 'html>head>Script Language="JavaScript">alert("验证码错误");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
  }
}
//方法：查询用户是否在数据库中
function checkUser($username,$password){
  $conn=new Mysql();
  $sql="select * from user where name='{$username}' and password='{$password}';";
  $result=$conn->sql($sql);
  if($result){
    return true;
  }
  else{
    echo 'html>head>Script Language="JavaScript">alert("用户不存在");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
  }
  $conn->close();
}
//方法：手机格式验证
function checkPhoneNum($phonenumber){
  $preg="/^1[34578]{1}\d{9}$/";
  if(preg_match($preg,$phonenumber)){
    return ture; //验证通过
  }else{
    echo 'html>head>Script Language="JavaScript">alert("手机号码格式有误");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";//手机号码格式不对
  }
}
//方法：邮箱格式验证
function checkEmail($email){
  $preg = '/^(\w{1,25})@(\w{1,16})(\.(\w{1,4})){1,3}$/';
  if(preg_match($preg, $email)){
    return true;
  }else{
    echo 'html>head>Script Language="JavaScript">alert("y邮箱格式有误");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
  }
}

?php
//退出登录并跳转到登录页面
unset($_SESSION['username']);
setcookie("username","",time()-1);  //清空cookie
setcookie("password","",time()-1);
header("location: login.html ");

?php
session_start();
if(empty($_COOKIE['username'])empty($_COOKIE['password'])){
  if(isset($_SESSION['username']))
    echo "登录成功，欢迎您".$_SESSION['username']."a href='logout.php'>退出登录/a>";
  else
    echo "你还没有登录，a href='login.html'>请登录/a>";
}
else
  echo "登录成功，欢迎您：".$_COOKIE['username']."a href='logout.php'>退出登录/a>";