title: Xcode cannot find 'std' namespace
body: <p>I have the following code</p>
  
  <pre><code>#ifndef TPSO1_thread_h
  #define TPSO1_thread_h
  
  #define _XOPEN_SOURCE
  
  #include &lt;ucontext.h&gt;
  
  struct Thread_Greater;
  
  class Thread {
      ...
  
      friend struct Thread_Greater;
      friend class Scheduler;
  };
  
  
  struct Thread_Greater : public std::binary_function &lt;Thread,Thread,bool&gt; {
      ...
  };
  
  #endif
  </code></pre>
  
  <p>in a .h file. Problem is, when I try to compile it in xcode it says</p>
  
  <pre><code>#Error: use of undeclared identifier 'std'
  </code></pre>
  
  <p>In the line </p>
  
  <pre><code>struct Thread_Greater : public std::binary_function &lt;Thread,Thread,bool&gt; {
  </code></pre>
  
  <p>Is there any include that I am missing?</p>