PHP programming ensures only one user logs in

Title: PHP programming to ensure that only one user can log in

In web development, it is a very important security measure to ensure that users can only log in with one account at the same time. . PHP, as a popular back-end programming language, provides a variety of ways to achieve this function. This article will introduce how to use PHP programming to ensure that only one user logs in, and achieve this through specific code examples.

1. Use Session to control user login status

First, we can use PHP's Session mechanism to control user login status. When a user successfully logs in, we store their username in the Session. When the user accesses the page that requires login, we first check whether the login user's information exists in the Session. If it does not exist, we will jump to the login page.

session_start();

if(isset($_SESSION['username'])){
    // 用户已经登陆，允许访问
} else {
    // 用户未登陆，跳转至登陆页面
    header("Location: login.php");
    exit();
}

2. Restrict multiple logins with the same username

In order to ensure that only one user can log in, we need to check whether there is an existing user when logging in. There is a user logged in. If so, the previously logged in user will be kicked out.

session_start();

if(isset($_SESSION['username'])){
    // 已经有用户登陆，执行踢出操作
    session_unset();
}

// 根据用户输入的用户名和密码进行登陆
$username = $_POST['username'];
$password = $_POST['password'];

// 验证用户名和密码的逻辑省略

// 登陆成功后将用户名存储在Session中
$_SESSION['username'] = $username;

3. Use database to record login status

In addition to Session, we can also record login status in the database so that it can be used in multiple Login status is shared between server instances.

// 假设我们有一张user表来存储用户信息，包括用户名和已登陆状态字段
// 字段名称假设为username和logged_in

// 登陆时更新用户的登陆状态
$username = $_POST['username'];

// 更新用户的已登陆状态为1
// 其他用户的登陆状态设置为0
$sql = "UPDATE user SET logged_in = 0";
$result = mysqli_query($conn, $sql);

$sql = "UPDATE user SET logged_in = 1 WHERE username = '$username'";
$result = mysqli_query($conn, $sql);

In summary, using the Session mechanism combined with the database to record login status can effectively ensure that only one user is allowed to log in at the same time. Through the above sample code, we can implement this function in PHP programming to improve the security and user experience of the website.

The above is the detailed content of PHP programming ensures only one user logs in. For more information, please follow other related articles on the PHP Chinese website!