title: clang 3.1 can't see unique_ptr?
body: <p>I've just started playing around with clang and tried to compile the following sample program:</p>
  
  <pre><code>#include &lt;memory&gt;
  #include &lt;iostream&gt;
  
  int main()
  {
      std::unique_ptr&lt;unsigned&gt; u(new unsigned(10));
      std::cout &lt;&lt; *u &lt;&lt; std::endl;
      return 0;
  }
  </code></pre>
  
  <p>When I compile I get the following errors:</p>
  
  <pre><code>$ clang++ helloworld.cpp 
  helloworld.cpp:6:10: error: no member named 'unique_ptr' in namespace 'std'
      std::unique_ptr&lt;unsigned&gt; u(new unsigned(10));
      ~~~~~^
  helloworld.cpp:6:29: error: expected '(' for function-style cast or type construction
      std::unique_ptr&lt;unsigned&gt; u(new unsigned(10));
                      ~~~~~~~~^
  helloworld.cpp:6:31: error: use of undeclared identifier 'u'
      std::unique_ptr&lt;unsigned&gt; u(new unsigned(10));
                                ^
  helloworld.cpp:7:19: error: use of undeclared identifier 'u'
      std::cout &lt;&lt; *u &lt;&lt; std::endl;
                    ^
  4 errors generated.
  </code></pre>
  
  <p>I am using Clang 3.1 on Mac OS X:</p>
  
  <pre><code>$ clang++ --version
  Apple clang version 3.1 (tags/Apple/clang-318.0.61) (based on LLVM 3.1svn)
  Target: x86_64-apple-darwin11.4.0
  Thread model: posix
  </code></pre>
  
  <p>Any ideas why this wouldn't compile?</p>