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