as not been used, then the error message is sent to the
                file defined by
                    
                    <span>
                        <code class="methodname">set_errfile()</code> or <code class="methodname">set_error_stream()</code>.
                    </span>
                If none of these methods have been used, then the error message is sent to
                standard error.
            </p>
                <p>
                The error message consists of the prefix string