<html> <head> <title>BOOST_PP_VARIADIC_HAS_OPT</title> <link rel="stylesheet" type="text/css" href="../styles.css"> </head> <body> <div style="margin-left: 0px;"> The <b>BOOST_PP_VARIADIC_HAS_OPT</b> macro determines whether or not the C++20 __VA_OPT__ construct is supported for the compiler's preprocessor being used. Expands to 1 if the __VA_OPT__ construct is supported, otherwise expands to 0. </div> <h4>Usage</h4> <div class="code"> <b>BOOST_PP_VARIADIC_HAS_OPT</b>() <br> </div> <h4>Arguments</h4> <dl> <dt>None<br> </dt> </dl> <h4>Remarks</h4> <div> This macro only returns 1 if the compiler is compiling at its own C++20 level and __VA_OPT__ is supported. It is possible for a compiler to support the __VA_OPT__ construct when not compiling at its own C++20 level, but this macro will return 0 in that case even if __VA_OPT__ is normally supported for that level. The reason for this is that such a compiler may have a compiler switch, enforcing a strict adherence to a particular C++ standard level, which gives a warning or an error if __VA_OPT__ is specified below the C++20 level, and the preprocessor library wants to avoid that happening. Therefore the macro will only test to see whether or not __VA_OPT__ is supported at the C++20 level, while otherwise always returning 0 for all lesser C++ standard levels. </div> <h4>Requirements</h4> <div> <b>Header:</b> <a href="../headers/variadic/has_opt.html"><boost/preprocessor/variadic/has_opt.hpp></a> </div> <h4>Sample Code</h4> <div> <pre> #include <<a href="../headers/variadic/has_opt.html">boost/preprocessor/variadic/has_opt.hpp</a>><br> #if <a href="variadic_has_opt.html">BOOST_PP_VARIADIC_HAS_OPT</a>() // Preprocessor code which uses __VA_OPT__ #else // Preprocessor code which does not use __VA_OPT__ #endif </pre> <br> or within a macro definition<br><br> <pre> #include <boost/preprocessor/control/iif.hpp> #include <<a href="../headers/variadic/has_opt.html">boost/preprocessor/variadic/has_opt.hpp</a>><br> #define USE_OPT(...) BOOST_PP_IIF(<a href="variadic_has_opt.html">BOOST_PP_VARIADIC_HAS_OPT</a>(),MACRO_USING_OPT,MACRO_NOT_USING_OPT)(__VA_ARGS__) #define MACRO_USING_OPT(...) __VA_OPT__( preprocessor tokens ) anything #define MACRO_NOT_USING_OPT(...) anything </pre> </div> <hr size="1"> <div style="margin-left: 0px;"> <i></i><i>� Copyright Edward Diener 2019</i> </div> <div style="margin-left: 0px;"> <p><small>Distributed under the Boost Software License, Version 1.0. (See accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p> </div> </body> </html>