编辑用户登录与退出的php代码

在PHP中编辑用户登录和注销功能的基本代码通常涉及以下几个步骤：

**登录（Login.php）**:

<?php
session_start();

// 检查用户是否已经登录
if(isset($_SESSION['username'])) {
    header("Location: dashboard.php"); // 如果已登录，重定向到仪表盘页面
} else {
    if($_SERVER["REQUEST_METHOD"] == "POST") {
        $username = $_POST['username'];
        $password = $_POST['password'];

        // 连接到数据库（这里仅做示例，实际应用需要连接并验证）
        $conn = mysqli_connect("localhost", "db_user", "db_password", "database_name");
        
        $query = "SELECT * FROM users WHERE username = ?";
        $stmt = mysqli_prepare($conn, $query);
        mysqli_stmt_bind_param($stmt, "s", $username);

        mysqli_stmt_execute($stmt);
        mysqli_stmt_store_result($stmt);

        if(mysqli_num_rows($stmt) == 1) {
            $row = mysqli_fetch_assoc($stmt);
            if(password_verify($password, $row['password'])) {
                $_SESSION['username'] = $username;
                header("Location: dashboard.php");
            } else {
                echo "Invalid credentials!";
            }
        } else {
            echo "User not found!";
        }

        mysqli_stmt_close($stmt);
        mysqli_close($conn);
    } else {
        // 显示登录表单
        include 'login_form.html';
    }
}
?>

**注销（Logout.php）**:

<?php
session_start();
session_unset(); // 清除所有会话变量
session_destroy(); // 销毁当前会话

header("Location: login.php"); // 重定向回登录页
exit; // 确保页面不再执行其他代码
?>

**登录表单（login_form.html）**:

<form method="post" action="Login.php">
    <label>Username:</label>
    <input type="text" name="username" required><br>
    <label>Password:</label>
    <input type="password" name="password" required><br>
    <button type="submit">Login</button>
</form>