如何用php实现用户注册

<form action="register.php" method="post">
  <label for="username">用户名：</label>
  <input type="text" name="username" id="username">

  <label for="email">邮箱：</label>
  <input type="email" name="email" id="email">

  <label for="password">密码：</label>
  <input type="password" name="password" id="password">

  <input type="submit" value="注册">
</form>

<?php
// 接收表单数据
$username = $_POST['username'];
$email = $_POST['email'];
$password = $_POST['password'];

// 验证数据合法性
if (empty($username) || empty($email) || empty($password)) {
  echo '请填写所有字段。';
  exit;
}

// 验证邮箱格式
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
  echo '邮箱地址无效。';
  exit;
}

// 连接数据库
$conn = new mysqli('localhost', 'root', '', 'database');

// 检查用户名是否已存在
$stmt = $conn->prepare('SELECT COUNT(*) FROM users WHERE username = ?');
$stmt->bind_param('s', $username);
$stmt->execute();
$result = $stmt->get_result();
$count = $result->fetch_row()[0];
$stmt->close();

// 如果用户名已存在，返回错误信息
if ($count > 0) {
  echo '用户名已存在。';
  exit;
}

// 检查邮箱是否已存在
$stmt = $conn->prepare('SELECT COUNT(*) FROM users WHERE email = ?');
$stmt->bind_param('s', $email);
$stmt->execute();
$result = $stmt->get_result();
$count = $result->fetch_row()[0];
$stmt->close();

// 如果邮箱已存在，返回错误信息
if ($count > 0) {
  echo '邮箱地址已存在。';
  exit;
}

// 哈希密码
$hashedPassword = password_hash($password, PASSWORD_DEFAULT);

// 插入新用户到数据库
$stmt = $conn->prepare('INSERT INTO users (username, email, password) VALUES (?, ?, ?)');
$stmt->bind_param('sss', $username, $email, $hashedPassword);
$stmt->execute();
$stmt->close();

// 注册成功，重定向到登录页面
header('Location: login.php');
?>