目录

一、登录功能

二、登出功能

一、登录功能

<?php
session_start();
if(isset($_POST['username']) && isset($_POST['password'])){
            $username=$_POST['username'];
            $password=$_POST['password'];
            $sql="SELECT * FROM user_form WHERE username='{$username}' AND password='{$password}'";
            $res=mysqli_query($link,$sql);
            $row = mysqli_fetch_assoc($res);
            
            if(!$row){
                $url = 'login.php';
                echo '<script>alert("用户名或密码输入错误！");location.href="'.$url.'"</script>';
                
            }else{
                $_SESSION['userid']=$row['userid'];
                $_SESSION['username']=$row['username'];
                $url = 'index.php';
                echo '<script>alert("登录成功。用户ID:'.$_SESSION['userid'].'！");location.href="'.$url.'"</script>';
            }
      
        }
        
?>

二、登出功能

<a href="index.php?logout=<?php echo $uid; ?>" onclick="return confirm('确定要退出吗?');">
    <i class="fas fa-window-close" id="signout" style="display: <?php if(isset($uid)){ echo 'inline-block';}else{ echo 'none';}?> ;"></i>
</a>

<?php

    // 连接数据库
    include 'config.php';
    $uid = $_SESSION['userid'];

    mysqli_set_charset($link,"utf8");
    mysqli_select_db($link,"travel");

    if(isset($uid)){
        
        $sql="SELECT * FROM user_form WHERE userid={$uid}";
        $res=mysqli_query($link,$sql);
        $row = mysqli_fetch_assoc($res);
        if(!$row){
            echo '<script>alert("网站有些问题，请咨询管理员/(ㄒoㄒ)/~~")</script>';
        }
        
    }
    
    if(isset($_GET['logout'])){
        unset($uid);
        session_destroy();
        header('location:login.php');
    }

    // 数据取出来之后，关闭数据库
    mysqli_close($link);
    
?>

isset -- 检测变量是否设置

使用 unset() 释放了一个变量之后，它将不再是 isset()