PHP7.2.24出现Call to undefined function mysqli_connect()错误求助

Hey there! Welcome to Stack Overflow 😊 Let's break down how to fix your error first, then go over some important security improvements for your login code.

错误原因 #

The error Call to undefined function mysqli_connect() means your PHP 7.2 installation on Ubuntu 18.04 doesn't have the mysqli extension installed or enabled. This extension is required to connect to MySQL databases using the mysqli functions.

修复步骤 #

Follow these steps to get the extension set up:

1. Install the mysqli extension for PHP 7.2:

   sudo apt-get update && sudo apt-get install php7.2-mysqli
   

2. Restart Apache to apply the changes:

   sudo systemctl restart apache2
   

3. Verify the extension is enabled:
   Create a file named phpinfo.php in /var/www/html/ with this content:

   <?php phpinfo(); ?>
   

   Access it via your browser (e.g., http://your-server-ip/phpinfo.php) and search for "mysqli"—you should see a section confirming the module is active.

代码安全优化（非常重要！） #

Your current login code has critical security flaws that could let attackers access your database. Here's how to fix them:

• SQL Injection Risk: Never directly insert user input into SQL queries. Use prepared statements instead.
• Redundant Code: You already specified the database in mysqli_connect(), so mysqli_select_db($a,$db); is unnecessary.
• Plaintext Passwords: Storing passwords as plain text is a huge security risk. Always hash passwords with password_hash() when saving them, and verify with password_verify().

优化后的代码示例 #

<?php
$host = "localhost";
$user = "root";
$password = "";
$db = "demo";

// 建立数据库连接并检查错误
$conn = mysqli_connect($host, $user, $password, $db);
if (!$conn) {
    die("数据库连接失败: " . mysqli_connect_error());
}

// 检查POST参数是否存在
if (isset($_POST['username'], $_POST['password'])) {
    $username = $_POST['username'];
    $inputPassword = $_POST['password'];

    // 使用预处理语句防止SQL注入
    $query = "SELECT * FROM demo WHERE User = ? LIMIT 1";
    $stmt = mysqli_prepare($conn, $query);
    mysqli_stmt_bind_param($stmt, "s", $username);
    mysqli_stmt_execute($stmt);
    $result = mysqli_stmt_get_result($stmt);

    if ($userData = mysqli_fetch_assoc($result)) {
        // 验证密码（确保数据库中存储的是password_hash生成的哈希值）
        if (password_verify($inputPassword, $userData['Pass'])) {
            echo "You Have Successfully Logged in";
        } else {
            echo "You Have Entered Incorrect Password";
        }
    } else {
        echo "You Have Entered Incorrect Username or Password";
    }

    // 关闭预处理语句
    mysqli_stmt_close($stmt);
}

// 关闭数据库连接
mysqli_close($conn);
?>

内容的提问来源于stack exchange，提问作者kaiwen_