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<title>Using variadic macros</title>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="variadic_macro_data.vmd_vmacros"></a><a class="link" href="vmd_vmacros.html" title="Using variadic macros">Using variadic macros</a>
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</h2></div></div></div>
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<p>
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Variadic macros, as specified by C++11, is a feature taken from the C99 specification.
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They are macros which take a final parameter denoted as '...' which represents
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one or more final arguments to the macro as a series of comma-separated tokens.
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In the macro expansion a special keyword of '__VA_ARGS__' represents the comma-separated
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tokens. This information when passed to a variadic macro I call 'variadic macro
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data', which gives its name to this library. The more general term 'variadic
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data' is used in this documentation to specify data passed to a macro which
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can contain any number of macro tokens as a single macro parameter, such as
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is found in Boost PP data types.
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</p>
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<h4>
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<a name="variadic_macro_data.vmd_vmacros.h0"></a>
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<span class="phrase"><a name="variadic_macro_data.vmd_vmacros.boost_support"></a></span><a class="link" href="vmd_vmacros.html#variadic_macro_data.vmd_vmacros.boost_support">Boost
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support</a>
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</h4>
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<p>
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The Boost PP library has support for variadic macros and uses its own criteria
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to determine if a particular compiler has that support. Boost PP defines or
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uses the macro BOOST_PP_VARIADICS to denote whether the compiler being used
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supports variadic macros. When BOOST_PP_VARIADICS is set to 1 the compiler
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supports variadic macros, otherwise when BOOST_PP_VARIADICS is set to 0 the
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compiler does not support variadic macros. If a user of Boost PP sets this
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value, Boost PP uses the value the end-user sets, otherwise Boost PP defines
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the value of BOOST_PP_VARIADICS based on its own analysis of the compiler being
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used. This macro can also be checked to determine if a compiler has support
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for variadic macros.
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</p>
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<h4>
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<a name="variadic_macro_data.vmd_vmacros.h1"></a>
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<span class="phrase"><a name="variadic_macro_data.vmd_vmacros.determining_variadic_macro_suppo"></a></span><a class="link" href="vmd_vmacros.html#variadic_macro_data.vmd_vmacros.determining_variadic_macro_suppo">Determining
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variadic macro support</a>
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</h4>
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<p>
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The VMD library automatically determines whether variadic macro support is
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enabled for a particular compiler by also using the same BOOST_PP_VARIADICS
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macro from Boost PP. The end-user of VMD can also manually set the macro BOOST_PP_VARIADICS
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to turn on or off compiler support for variadic macros in the VMD library.
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When BOOST_PP_VARIADICS is set to 0 variadic macros are not supported in the
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VMD library, otherwise when BOOST_PP_VARIADICS is set to non-zero they are
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supported in the VMD library. This same macro can be used to determine if VMD
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supports variadic macros for a particular compiler.
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</p>
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<p>
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Since this library depends on variadic macro support, if BOOST_PP_VARIADICS
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is set to 0, using any of the macros in VMD will lead to a compiler error since
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the macro will not be defined. However just including any of the header files
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in VMD, even with no variadic macro support for the compiler, will not lead
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to any compiler errors.
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</p>
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<td align="right"><div class="copyright-footer">Copyright © 2010-2017 Tropic Software
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East Inc</div></td>
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