title: What is the difference between &foo::function and foo::function?
body: <p>I am using the gtkmm library on linux to draw a simple menu for my GUI.</p>
  
  <p>In the below code the compiler complained about unable to resolve address</p>
  
  <pre><code>        sigc::mem_fun(*this, AppWindow::hide)));
                                           ^
  appwindow.cpp:15:41: note:   could not resolve address from overloaded function
  </code></pre>
  
  <p>But when I insert the <code>&amp;</code> it compiles fine</p>
  
  <pre><code>m_menu_app.items().push_back(MenuElem("Quit",
      sigc::mem_fun(*this, &amp;AppWindow::hide)));
  </code></pre>
  
  <p>What difference does it make here? Isn't the <code>hide</code> function just an address in the first place?</p>