I moved the Selector code (i.e. set_wave_select(wave_select)) into the
portion of my code which runs after the flowgraph is running. I still get
the same error.
Jim
-----Original Message-----
From: Vasil Velichkov
Sent: Wednesday, September 27, 2023 1:55 PM
To: Elmore Family
Cc: discuss-gnuradio@gnu.org
Subject: Re: Index Error: output_index < noutputs
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
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