title: What's the scope of the "using" declaration in C++?
body: <p>I'm using the 'using' declaration in C++ to add std::string and std::vector to the local namespace (to save typing unnecessary 'std::'s).</p>
  
  <pre><code>using std::string;
  using std::vector;
  
  class Foo { /*...*/ };
  </code></pre>
  
  <p>What is the scope on this declaration?  If I do this in a header, will it inject these 'using' declarations into every cpp file that includes the header?</p>