Ensure that only one user is logged in to the PHP system

Title: Ensure that only one user is logged in to the PHP system, specific code examples are needed

When developing a website or application, sometimes it is necessary to ensure that the system only allows one user to log in , to ensure data security and prevent confusion caused by multiple people logging in at the same time. In PHP, this function can be achieved by setting session. Below I will introduce how to use PHP code to ensure that only one user is logged in to the system.

First, after the user successfully logs in, we need to store the user's unique identifier in the session. In this way we can determine whether a user has logged in on other pages. The following is a code example of a simple login page:

<?php
session_start();

// 模拟用户登录，获取用户唯一标识，这里假设用户ID为1
$userId = 1;

// 将用户ID存储在session中
$_SESSION['userId'] = $userId;

// 跳转到其他页面
header("Location: dashboard.php");
?>

In other pages that need to ensure that only one user is logged in, we can check whether the user ID has been stored in the session. If it already exists, it means there is already a user. After logging in, you can take appropriate measures, such as forcing the current user to log out or preventing other users from logging in. The following is a simple code example to determine whether the user is logged in:

<?php
session_start();

// 检查session中是否存储了用户ID
if(isset($_SESSION['userId'])) {
    // 已有用户登录，可以进行相应操作，比如强制退出当前用户
    // unset($_SESSION['userId']);
    // header("Location: login.php");
    
    // 或者阻止其他用户登录
    die("只允许一个用户登录！");
} else {
    // 没有用户登录，可以正常执行页面逻辑
}
?>

Through the above code example, we can implement the function of ensuring that only one user is logged in in the PHP system. When a user logs in, we store the user ID in the session and determine whether the session already has a user ID in other pages, thereby ensuring that only one user can log in to the system. This effectively enhances the security and stability of the system.

The above is the detailed content of Ensure that only one user is logged in to the PHP system. For more information, please follow other related articles on the PHP Chinese website!