title: Is begin() == end() for any empty() vector?
body: <p>I have long assumed that for any empty <code>std::vector</code> <em>V</em>, <code>V.begin() == V.end()</code>. Yet I see nothing in the C++ specification that states this to <em>always</em> be true. Is it necessarily true or does it just happen to be true on most implementations?</p>