title: Cannot listen on specific port num with localhost address with http_listener(C++ REST SDK)
body: <p>I use C++ REST SDK to build up a HTTP server which is used for receiving requests from postman, but if I code like this:</p>
  
  <pre><code>http_listener listener(L"http://localhost/io");
  listener.open().wait();
  
  listener.support(methods::POST, [](http_request req) {
   });
  </code></pre>
  
  <p>Postman can connect to it with <code>http://localhost/io</code> in POST method,
  But if I code like :</p>
  
  <pre><code>http_listener listener(L"http://localhost:6000/io");
  </code></pre>
  
  <p>Postman cannot connect to it with <code>http://localhost:6000/io</code> and POST method. 
  But if I code like <code>http_listener listener(L"http://localhost/io:6000");</code>
  Postman can connect with it in <code>http://localhost/io:6000</code> with POST method. How could I make <code>http://localhost:6000/io</code> works for my listener ?  Another program I work with always send http request to <code>http://localhost:6000/io</code>, so I need to let my server listen on this address.</p>
  
  <pre><code>http_listener listener(L"http://localhost:6000"); //doesn't work, too.
  </code></pre>
  
  <p>But when I change 6000 to any other port num,like 7000 or 8000, like <code>http_listener listener(L"http://localhost:7000")</code> or <code>http_listener listener(L"http://localhost:7000/io")</code> it works for me. I use <code>netstat -a -b</code> to check whether 6000 has been occupied by another program, but 6000 is free.</p>