php登录怎么写_php用户登录系统完整实现代码

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) UNIQUE NOT NULL,
    password VARCHAR(255) NOT NULL
);

<?php
$host = 'localhost';
$db   = 'your_database_name';
$user = 'your_db_user';
$pass = 'your_db_password';
<p>try {
$pdo = new PDO("mysql:host=$host;dbname=$db;charset=utf8", $user, $pass);
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (PDOException $e) {
die("数据库连接失败: " . $e->getMessage());
}
?></p>

<?php
require 'config.php';
<p>if ($_SERVER['REQUEST_METHOD'] == 'POST') {
$username = trim($_POST['username']);
$password = $_POST['password'];</p><pre class='brush:php;toolbar:false;'>if (empty($username) || empty($password)) {
    $error = "请填写所有字段";
} elseif (strlen($password) < 6) {
    $error = "密码至少6位";
} else {
    $stmt = $pdo->prepare("SELECT id FROM users WHERE username = ?");
    $stmt->execute([$username]);

    if ($stmt->rowCount() > 0) {
        $error = "用户名已存在";
    } else {
        $hashed = password_hash($password, PASSWORD_DEFAULT);
        $stmt = $pdo->prepare("INSERT INTO users (username, password) VALUES (?, ?)");
        $stmt->execute([$username, $hashed]);
        header("Location: login.php?registered=1");
        exit;
    }
}

<?php
session_start();
require 'config.php';
<p>if ($_SERVER['REQUEST_METHOD'] == 'POST') {
$username = trim($_POST['username']);
$password = $_POST['password'];</p><pre class='brush:php;toolbar:false;'>$stmt = $pdo->prepare("SELECT id, password FROM users WHERE username = ?");
$stmt->execute([$username]);
$user = $stmt->fetch();

if ($user && password_verify($password, $user['password'])) {
    $_SESSION['user_id'] = $user['id'];
    $_SESSION['username'] = $username;
    header("Location: dashboard.php");
    exit;
} else {
    $error = "用户名或密码错误";
}

<?php
session_start();
if (!isset($_SESSION['user_id'])) {
    header("Location: login.php");
    exit;
}
?>
<p><h2>欢迎，<?= htmlspecialchars($_SESSION['username']) ?>!</h2>
<p>这是你的个人面板。</p>
<a href="logout.php">登出</a></p>

<?php
session_start();
session_destroy();
header("Location: login.php");
exit;
?>