!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="用戶名" name="username">br>br>
  input type="password" placeholder="密碼" name="password">br>br>
  input type="text" placeholder="驗證碼" name="verifycode" class="captcha">br>br>
  img id="captcha_img" src="captcha.php?r=?php echo rand();?>" alt="驗證碼">
  label>a href="javascript:void(0)" rel="external nofollow" onclick="document.getElementById('captcha_img').src='captcha.php?r='+Math.random()">換一個/a> /label>br>
  label>input type="checkbox" name="autologin[]" value="1"/>自動登錄/label>br>
  button type="submit">登錄/button>
/form>
/body>
/html>

?php
header("Content-type:text/html;charset=UTF-8");
require "mysql.php";      //導入mysql.php訪問數據庫
session_start();        //開啟會話一獲取到服務器端驗證碼
$username=$_POST['username'];
$password=$_POST['password'];
$autologin=isset($_POST['autologin'])?1:0;   //獲取是否選擇了自動登錄
$verifycode=$_POST['verifycode'];
$code=$_SESSION['code'];    //獲取服務器生成的驗證碼
/*
 * 首先進行判空操作，通過后進行驗證碼驗證，通過后再進行數據庫驗證。
 * 手機號碼和郵箱驗證可根據需要自行添加
 * */
if(checkEmpty($username,$password,$verifycode)){
  if(checkVerifycode($verifycode,$code)){
    if(checkUser($username,$password)){
      $_SESSION['username']=$username; //保存此時登錄成功的用戶名
      if($autologin==1){        //如果用戶勾選了自動登錄就把用戶名和加了密的密碼放到cookie里面
        setcookie("username",$username,time()+3600*24*3);  //有效期設置為3天
        setcookie("password",md5($password),time()+3600*24*3);
      }
      else{
        setcookie("username","",time()-1);  //如果沒有選擇自動登錄就清空cookie
        setcookie("password","",time()-1);
      }
      header("location: index.php ");      //全部驗證都通過之后跳轉到首頁
    }
  }
}
//方法：判斷是否為空
function checkEmpty($username,$password,$verifycode){
  if($username==null||$password==null){
    echo 'html>head>Script Language="JavaScript">alert("用戶名或密碼為空");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
  }
  else{
    if($verifycode==null){
      echo 'html>head>Script Language="JavaScript">alert("驗證碼為空");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
    }
    else{
      return true;
    }
  }
}
//方法：檢查驗證碼是否正確
function checkVerifycode($verifycode,$code){
  if($verifycode==$code){
    return true;
  }
  else{
    echo 'html>head>Script Language="JavaScript">alert("驗證碼錯誤");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
  }
}
//方法：查詢用戶是否在數據庫中
function checkUser($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("用戶不存在");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
  }
  $conn->close();
}
//方法：手機格式驗證
function checkPhoneNum($phonenumber){
  $preg="/^1[34578]{1}\d{9}$/";
  if(preg_match($preg,$phonenumber)){
    return ture; //驗證通過
  }else{
    echo 'html>head>Script Language="JavaScript">alert("手機號碼格式有誤");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";//手機號碼格式不對
  }
}
//方法：郵箱格式驗證
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郵箱格式有誤");/Script>/head>/html>' . "meta http-equiv=\"refresh\" content=\"0;url=login.html\">";
  }
}

?php
//退出登錄并跳轉到登錄頁面
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($_SESSION['username']))
    echo "登錄成功，歡迎您".$_SESSION['username']."a href='logout.php'>退出登錄/a>";
  else
    echo "你還沒有登錄，a href='login.html'>請登錄/a>";
}
else
  echo "登錄成功，歡迎您：".$_COOKIE['username']."a href='logout.php'>退出登錄/a>";