1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Using variadic macros</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Chapter 1. The Variadic Macro Data Library 1.9"> 8<link rel="up" href="../index.html" title="Chapter 1. The Variadic Macro Data Library 1.9"> 9<link rel="prev" href="vmd_whyhow.html" title="Why and how to use"> 10<link rel="next" href="vmd_vc.html" title="Visual C++ define"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="vmd_whyhow.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="vmd_vc.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="variadic_macro_data.vmd_vmacros"></a><a class="link" href="vmd_vmacros.html" title="Using variadic macros">Using variadic macros</a> 28</h2></div></div></div> 29<p> 30 Variadic macros, as specified by C++11, is a feature taken from the C99 specification. 31 They are macros which take a final parameter denoted as '...' which represents 32 one or more final arguments to the macro as a series of comma-separated tokens. 33 In the macro expansion a special keyword of <code class="computeroutput"><span class="identifier">__VA_ARGS__</span></code> 34 represents the comma-separated tokens. This information when passed to a variadic 35 macro I call 'variadic macro data', which gives its name to this library. The 36 more general term 'variadic data' is used in this documentation to specify 37 data passed to a macro which can contain any number of macro tokens as a single 38 macro parameter, such as is found in Boost PP data types. 39 </p> 40<h4> 41<a name="variadic_macro_data.vmd_vmacros.h0"></a> 42 <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 43 support</a> 44 </h4> 45<p> 46 The Boost PP library has support for variadic macros and uses its own criteria 47 to determine if a particular compiler has that support. Boost PP defines or 48 uses the macro BOOST_PP_VARIADICS to denote whether the compiler being used 49 supports variadic macros. When BOOST_PP_VARIADICS is set to 1 the compiler 50 supports variadic macros, otherwise when BOOST_PP_VARIADICS is set to 0 the 51 compiler does not support variadic macros. If a user of Boost PP sets this 52 value, Boost PP uses the value the end-user sets, otherwise Boost PP defines 53 the value of BOOST_PP_VARIADICS based on its own analysis of the compiler being 54 used. This macro can also be checked to determine if a compiler has support 55 for variadic macros. 56 </p> 57<h4> 58<a name="variadic_macro_data.vmd_vmacros.h1"></a> 59 <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 60 variadic macro support</a> 61 </h4> 62<p> 63 The VMD library automatically determines whether variadic macro support is 64 enabled for a particular compiler by also using the same BOOST_PP_VARIADICS 65 macro from Boost PP. The end-user of VMD can also manually set the macro BOOST_PP_VARIADICS 66 to turn on or off compiler support for variadic macros in the VMD library. 67 When BOOST_PP_VARIADICS is set to 0 variadic macros are not supported in the 68 VMD library, otherwise when BOOST_PP_VARIADICS is set to non-zero they are 69 supported in the VMD library. This same macro can be used to determine if VMD 70 supports variadic macros for a particular compiler. 71 </p> 72<p> 73 Since this library completely depends on variadic macro support, if BOOST_PP_VARIADICS 74 is set to 0, using any of the macros in VMD will lead to a compiler error since 75 the macro will not be defined. However just including any of the header files 76 in VMD, even with no variadic macro support for the compiler, will not lead 77 to any compiler errors. 78 </p> 79</div> 80<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 81<td align="left"></td> 82<td align="right"><div class="copyright-footer">Copyright © 2010-2017 Tropic Software 83 East Inc</div></td> 84</tr></table> 85<hr> 86<div class="spirit-nav"> 87<a accesskey="p" href="vmd_whyhow.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="vmd_vc.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 88</div> 89</body> 90</html> 91
