What are the common pitfalls when upgrading PHP versions on a web server?

Common pitfalls when upgrading PHP versions on a web server include deprecated functions or features that are no longer supported in the new version, changes in syntax or behavior that may break existing code, and compatibility issues with third-party libraries or frameworks. To solve these issues, it is important to thoroughly test the application in a development environment before upgrading, update any deprecated functions or features, and make necessary code changes to ensure compatibility with the new PHP version.

// Example code to update deprecated function to its new equivalent
// Deprecated function: mysql_connect()
// New function: mysqli_connect()

// Deprecated code
$conn = mysql_connect($servername, $username, $password);

// Updated code
$conn = mysqli_connect($servername, $username, $password);