ent/entry_type.html#idp51474368-bb"><span class="keyword">operator</span><span class="special">+=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">string_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  <span class="special">}</span><span class="special">;</span>

  <span class="comment">// <a class="link" href="basic_environment.html#boost.process.basic_environmentconstruct-copy-destruct">construc