title: Message "error: use of undeclared identifier 'assert'"
body: <p>I had a piece of code that was including some Boost headers. Upon compilation I received errors like</p>
  <pre class="lang-none prettyprint-override"><code>/usr/local/include/boost/smart_ptr/shared_ptr.hpp:1041:9: error: use of undeclared identifier 'assert'
  
          BOOST_ASSERT( deleter_.use_count() &lt;= 1 );
  
          ^
  
  /usr/local/include/boost/assert.hpp:60:29: note: expanded from macro 'BOOST_ASSERT'
  
  # define BOOST_ASSERT(expr) assert(expr)
                                  ^
  </code></pre>
  <p>These errors however only occurred on Windows and macOS.</p>
  <p>Explicitly including either <code>&lt;cassert&gt;</code> or <code>&lt;assert.h&gt;</code> before the Boost headers had no effect.</p>