Hi Elmore, On 27/09/2023 03.17, Elmore Family wrote: > I am using a gnu radio flowgraph to attempt to select the appropriate > Selector Block output as explained below. The following error occurs when I > run the flowgraph: Index Error: output_index must be < noutputs.
> I forgot to include the version: 3.9.4.0. Lets try analyzing the source code where this error is thrown. $ git checkout v3.9.4.0 $ grep "output_index must be < noutputs" . -R ./gr-blocks/lib/selector_impl.cc: throw std::out_of_range("output_index must be < noutputs"); https://github.com/gnuradio/gnuradio/blob/v3.9.4.0/gr-blocks/lib/selector_impl.cc#L66-L73 66 void selector_impl::set_output_index(unsigned int output_index) 67 { 68 gr::thread::scoped_lock l(d_mutex); 69 if (output_index < d_num_outputs) 70 d_output_index = output_index; 71 else 72 throw std::out_of_range("output_index must be < noutputs"); 73 } The code is pretty simple, the only possible case is the value of output_index variable to be greater or equal to d_num_outputs variable. You are calling set_output_index with 1 so d_num_outputs must be either 0 or 1. Now let's check where d_num_outputs gets its value. $ grep -n d_num_outputs ./gr-blocks/lib/selector_impl.cc 40: d_num_outputs(0) 69: if (output_index < d_num_outputs) 100: if (new_port < d_num_outputs) 138: d_num_outputs = (unsigned int)noutputs; It is initialized to 0 in the constructor on line 40 and get assigned in selector_impl::check_topology function on line 138. https://github.com/gnuradio/gnuradio/blob/v3.9.4.0/gr-blocks/lib/selector_impl.cc#L134-L145 So it looks that you are calling set set_output_index(1) before check_topology() has been called, before the flowgraph is started. Looks like you need to start the flowgraph first and then call set_output_index(1) Hope this helps. Regards, Vasil