title: GNU Radio version
body: <p>How do I find out the version of GNU Radio that I have installed?</p>
  
  <p>I would like the use their messaging libraries, but they are available on newer versions of gnuradio only and for some reason I'm getting a compilation error when I try to use the following code:</p>
  
  <pre><code>message_port_register_out(pmt::mp("out_message"));
  </code></pre>
  
  <p>I get the following error on compilation:</p>
  
  <pre><code>error: ‘message_port_register_out’ was not declared in this scope
  </code></pre>
  
  <p>It's supposed to be part of the <code>gr_basic_block</code>, which all blocks inherit from, but it's not compiling.</p>