>std::list&lt;int&gt;</code> is actually defined as
  <code class="classname">std::__cxx11::list&lt;int&gt;</code>. Because the symbols
  for the new implementations have different names the definitions for both
  versions can be present in the same library.
</p><p> The <span class="symbol">_GLIBCXX_USE_CXX11_ABI</span> macro (see
  <a class="xref" href="using_macros.html" title="Macros">Macros</a>) controls whether
  the declarations in the library headers use the old or new ABI.
  So the decision of which