What is the role of session_id() in verifying the existence of a current session in PHP?

session_id() is a function in PHP that retrieves the current session ID. By using session_id(), we can verify the existence of a current session by checking if the returned session ID is not empty. This can help ensure that the user is logged in and has an active session before proceeding with any sensitive operations.

session_start();

if(!empty(session_id())) {
    // Session exists, perform necessary operations
    echo "Session is active.";
} else {
    // Session does not exist, handle accordingly
    echo "Session is not active.";
}