使用PHP和Mysql实现基础论坛（功能包括：用户登录注册更改密码以及发表帖子，查看帖子并能够删除帖子）

实现一个基础论坛需要以下步骤：

1. 创建数据库和数据表

在 MySQL 中创建一个数据库和数据表，用于存储用户信息和帖子信息。可以使用 phpMyAdmin 或 MySQL 命令行来创建。

CREATE DATABASE forum_db;
USE forum_db;

CREATE TABLE users (
  id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
  username VARCHAR(30) NOT NULL,
  password VARCHAR(30) NOT NULL
);

CREATE TABLE posts (
  id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
  title VARCHAR(50) NOT NULL,
  content TEXT NOT NULL,
  author VARCHAR(30) NOT NULL,
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
  updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

2. 创建用户登录、注册、更改密码功能

在 PHP 中创建一个用户管理类，用于处理用户的登录、注册和更改密码功能。在类中，可以使用 PDO 来连接 MySQL 数据库，并执行 SQL 查询。

class UserManager {
  private $db;

  function __construct() {
    $dsn = 'mysql:host=localhost;dbname=forum_db';
    $username = 'root';
    $password = '';

    try {
      $this->db = new PDO($dsn, $username, $password);
    } catch (PDOException $e) {
      die('Database connection failed: ' . $e->getMessage());
    }
  }

  function register($username, $password) {
    $stmt = $this->db->prepare('INSERT INTO users (username, password) VALUES (:username, :password)');
    $stmt->bindParam(':username', $username);
    $stmt->bindParam(':password', $password);
    $stmt->execute();
  }

  function login($username, $password) {
    $stmt = $this->db->prepare('SELECT * FROM users WHERE username = :username AND password = :password');
    $stmt->bindParam(':username', $username);
    $stmt->bindParam(':password', $password);
    $stmt->execute();
    $user = $stmt->fetch(PDO::FETCH_ASSOC);
    return $user;
  }

  function changePassword($username, $password) {
    $stmt = $this->db->prepare('UPDATE users SET password = :password WHERE username = :username');
    $stmt->bindParam(':username', $username);
    $stmt->bindParam(':password', $password);
    $stmt->execute();
  }
}

3. 创建帖子发布、查看和删除功能

在 PHP 中创建一个帖子管理类，用于处理帖子的发布、查看和删除功能。在类中，同样可以使用 PDO 来连接 MySQL 数据库，并执行 SQL 查询。

class PostManager {
  private $db;

  function __construct() {
    $dsn = 'mysql:host=localhost;dbname=forum_db';
    $username = 'root';
    $password = '';

    try {
      $this->db = new PDO($dsn, $username, $password);
    } catch (PDOException $e) {
      die('Database connection failed: ' . $e->getMessage());
    }
  }

  function createPost($title, $content, $author) {
    $stmt = $this->db->prepare('INSERT INTO posts (title, content, author) VALUES (:title, :content, :author)');
    $stmt->bindParam(':title', $title);
    $stmt->bindParam(':content', $content);
    $stmt->bindParam(':author', $author);
    $stmt->execute();
  }

  function getPosts() {
    $stmt = $this->db->query('SELECT * FROM posts');
    $posts = $stmt->fetchAll(PDO::FETCH_ASSOC);
    return $posts;
  }

  function deletePost($id) {
    $stmt = $this->db->prepare('DELETE FROM posts WHERE id = :id');
    $stmt->bindParam(':id', $id);
    $stmt->execute();
  }
}

4. 创建前端页面

在 HTML 中创建一个登录、注册、更改密码和帖子管理的前端页面。在页面中，可以使用 PHP 来处理用户输入和输出结果。

<?php
session_start();
require_once 'UserManager.php';
require_once 'PostManager.php';

$userManager = new UserManager();
$postManager = new PostManager();

if (isset($_POST['register'])) {
  $username = $_POST['username'];
  $password = $_POST['password'];
  $userManager->register($username, $password);
}

if (isset($_POST['login'])) {
  $username = $_POST['username'];
  $password = $_POST['password'];
  $user = $userManager->login($username, $password);
  if ($user) {
    $_SESSION['user'] = $user;
  } else {
    echo 'Login failed';
  }
}

if (isset($_POST['change_password'])) {
  $username = $_SESSION['user']['username'];
  $password = $_POST['new_password'];
  $userManager->changePassword($username, $password);
  $_SESSION['user']['password'] = $password;
}

if (isset($_POST['create_post'])) {
  $title = $_POST['title'];
  $content = $_POST['content'];
  $author = $_SESSION['user']['username'];
  $postManager->createPost($title, $content, $author);
}

if (isset($_POST['delete_post'])) {
  $id = $_POST['id'];
  $postManager->deletePost($id);
}

if (isset($_SESSION['user'])) {
  $posts = $postManager->getPosts();
}
?>

<!DOCTYPE html>
<html>
<head>
  <title>Forum</title>
</head>
<body>
  <?php if (isset($_SESSION['user'])): ?>
    <h1>Welcome <?php echo $_SESSION['user']['username']; ?></h1>
    <form method="post">
      <label>New Password:</label>
      <input type="password" name="new_password">
      <input type="submit" name="change_password" value="Change Password">
    </form>
    <form method="post">
      <label>Title:</label>
      <input type="text" name="title">
      <label>Content:</label>
      <textarea name="content"></textarea>
      <input type="submit" name="create_post" value="Create Post">
    </form>
    <table>
      <thead>
        <tr>
          <th>Title</th>
          <th>Content</th>
          <th>Author</th>
          <th>Created At</th>
          <th>Updated At</th>
          <th>Action</th>
        </tr>
      </thead>
      <tbody>
        <?php foreach ($posts as $post): ?>
          <tr>
            <td><?php echo $post['title']; ?></td>
            <td><?php echo $post['content']; ?></td>
            <td><?php echo $post['author']; ?></td>
            <td><?php echo $post['created_at']; ?></td>
            <td><?php echo $post['updated_at']; ?></td>
            <td>
              <form method="post">
                <input type="hidden" name="id" value="<?php echo $post['id']; ?>">
                <input type="submit" name="delete_post" value="Delete">
              </form>
            </td>
          </tr>
        <?php endforeach; ?>
      </tbody>
    </table>
    <form method="post">
      <input type="submit" name="logout" value="Logout">
    </form>
  <?php else: ?>
    <form method="post">
      <label>Username:</label>
      <input type="text" name="username">
      <label>Password:</label>
      <input type="password" name="password">
      <input type="submit" name="login" value="Login">
    </form>
    <form method="post">
      <label>Username:</label>
      <input type="text" name="username">
      <label>Password:</label>
      <input type="password" name="password">
      <input type="submit" name="register" value="Register">
    </form>
  <?php endif; ?>
</body>
</html>