What are the potential issues when upgrading PHP versions, as seen in the provided code example?

When upgrading PHP versions, one potential issue is deprecated functions or features that are no longer supported in the new version. To solve this, you need to update your code to use the recommended alternatives for the deprecated functions or features. Additionally, you may encounter changes in syntax or behavior that require adjustments in your code. 

// Before PHP 7.0, the PHP MySQL extension was deprecated and removed in PHP 7.0
// To fix this, update your code to use the MySQLi or PDO extension instead

// Deprecated MySQL extension
$link = mysql_connect('localhost', 'user', 'password');

// Updated MySQLi extension
$link = mysqli_connect('localhost', 'user', 'password');

// Updated PDO extension
$dsn = 'mysql:host=localhost;dbname=mydatabase';
$username = 'user';
$password = 'password';
$pdo = new PDO($dsn, $username, $password);

Keywords

backward compatibility deprecated functions syntax errors security vulnerabilities performance degradation

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