Re: Index Error: output_index < noutputs

Hi Vasil,

just wanted to express my appreciation for the detail of investigation you're doing there.
Thanks!

Marcus

On 27.09.23 19:55, Vasil Velichkov wrote:
> 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
>