Boost C++ Libraries: Ticket #12121: Duplicate conflicting forward declaration of basic_string_ref https://svn.boost.org/trac10/ticket/12121 <p> In Boost 1.61 Beta 1, a new error means to much forward declaration of basic_string_ref. </p> <p> boost/log/utility/formatting_ostream.hpp:39:76: error: redefinition of default argument for 'class traits' </p> <blockquote> <p> template&lt;typename charT, typename traits = std::char_traits&lt;charT&gt; &gt; class basic_string_ref; </p> </blockquote> <p> Its also declared in boost/utility/string_ref_fwd.hpp and boost/utility/string_ref.hpp </p> <p> Removing the fwd declaration in formatting_ostream.hpp:39 and all is working. </p> <p> Boost 1.61.0 beta gcc 5.3.0 (x86_64-win32-seh-rev0, Built by MinGW-W64 project) </p> en-us Boost C++ Libraries /htdocs/site/boost.png https://svn.boost.org/trac10/ticket/12121 Trac 1.4.3 Andrey Semashev Tue, 12 Apr 2016 08:17:25 GMT status changed; resolution set https://svn.boost.org/trac10/ticket/12121#comment:1 https://svn.boost.org/trac10/ticket/12121#comment:1 <ul> <li><strong>status</strong> <span class="trac-field-old">new</span> → <span class="trac-field-new">closed</span> </li> <li><strong>resolution</strong> → <span class="trac-field-new">fixed</span> </li> </ul> <p> Should be fixed in <a class="ext-link" href="https://github.com/boostorg/log/commit/768ac379dbd1da098b9e36c50f641bd3af338e30"><span class="icon">​</span>https://github.com/boostorg/log/commit/768ac379dbd1da098b9e36c50f641bd3af338e30</a>. Thanks. </p> Ticket