title: GTK-WARNING cannot open display on mac
body: <p>I'm following the GTK tutorial and already installed all the dependencies and all is working although when I run my code I get this error:</p>
  
  <pre><code>(process:34571): Gtk-WARNING **: Locale not supported by C library.
      Using the fallback 'C' locale.
  
  (main:34571): Gtk-WARNING **: cannot open display:
  </code></pre>
  
  <p>my main.cpp is:</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;gtk/gtk.h&gt;
  
  int main (int argc, char *argv[]) 
  {
      std::cout &lt;&lt; "hello GTK!!" &lt;&lt; std::endl;
  
      GtkWidget *window;
  
      gtk_init(&amp;argc, &amp;argv);
  
      window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
      gtk_widget_show(window);
  
      gtk_main();
  
      return 0;
  }
  </code></pre>
  
  <p>how can I solve this?</p>