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Rearrangement of links and better explanation of variadic macro support.

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Edward Diener
2020-09-19 09:14:26 -04:00
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html> <html>
<head> <head>
<meta content="text/html; charset=windows-1252" http-equiv="content-type"> <meta content="text/html; charset=windows-1252"
http-equiv="content-type">
<title>contents.html</title> <title>contents.html</title>
<link rel="stylesheet" type="text/css" href="styles.css"> <link rel="stylesheet" type="text/css" href="styles.css">
<style> <style>
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</style> </style>
</head> </head>
<body> <body>
<h4><a href="AppendixA-AnIntroductiontoPreprocessorMetaprogramming.html" <h4><a href="index.html" target="_top">Introduction</a></h4>
target="_top">Introduction</a></h4> <h4><a
href="AppendixA-AnIntroductiontoPreprocessorMetaprogramming.html"
target="_top">Basic Intro</a></h4>
<a href="topics.html"> </a>
<h4><a href="topics.html">Topics</a></h4> <h4><a href="topics.html">Topics</a></h4>
<a href="topics.html"> <a href="topics.html"> </a>
</a> <h4><a href="terms.html">Terminology</a></h4>
<h4><a href="topics.html"></a><a href="terms.html">Terminology</a></h4> <a href="terms.html"> </a>
<a href="terms.html"> <h4><a href="data.html">Data Types</a></h4>
</a> <a href="data.html"> </a>
<h4><a href="terms.html"></a><a href="data.html">Data Types</a></h4> <h4><a href="ref.html">Reference</a></h4>
<a href="data.html"> <a href="ref.html"> </a>
</a> <h4><a href="headers.html">Headers</a></h4>
<h4><a href="data.html"></a><a href="ref.html">Reference</a></h4> <a href="headers.html"> </a>
<a href="ref.html"> <h4><a href="examples.html">Examples</a></h4>
</a> <a href="examples.html"> </a>
<h4><a href="ref.html"></a><a href="headers.html">Headers</a></h4> <h4><a href="miscellanea.html">Miscellanea</a></h4>
<a href="headers.html">
</a>
<h4><a href="headers.html"></a><a href="examples.html">Examples</a></h4>
<a href="examples.html">
</a>
<h4><a href="examples.html"></a><a href="miscellanea.html">Miscellanea</a></h4>
<a href="miscellanea.html"> <a href="miscellanea.html">
<!-- <!--
<EFBFBD> Copyright Housemarque Oy 2002<30> Copyright Paul Mensonides 2002 <EFBFBD> Copyright Housemarque Oy 2002<30> Copyright Paul Mensonides 2002

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both C++ and C compilation. It does not depend on any other Boost both C++ and C compilation. It does not depend on any other Boost
libraries and therefore may be used as a standalone library.<br> libraries and therefore may be used as a standalone library.<br>
</div> </div>
<div>The library assumes that the compiler supports variadic macros. <div>The library requires that the compiler supports <a
Since variadic macros are a C99 or C++11 feature the library href="topics/variadic_macros.html">variadic macros</a>. Since
ostensibly requires at least compilation at those C or C++ variadic macros are a C99 or C++11 feature the library ostensibly
standard levels. A number of compilers support variadic macros at requires at least compilation at those C or C++ standard levels. A
a lower level, so it still may be possible using the library at number of compilers support variadic macros at a lower level, so
the C++03 compilation level, as long as strict C++03 compliance is it still may be possible using the library at that compilation
not enforced.<br> level, as long as strict C++98/C++03 compliance is not enforced.<br>
</div> </div>
<div> An excerpt from <i>C++ Template Metaprogramming: Concepts, <div> An excerpt from <i>C++ Template Metaprogramming: Concepts,
Tools, and Techniques from Boost and Beyond</i> by Dave Abrahams Tools, and Techniques from Boost and Beyond</i> by Dave Abrahams

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</head> </head>
<body> <body>
<h4>Variadic Macros</h4> <h4>Variadic Macros</h4>
<div> Variadic macros are supported by nearly all compilers. This library assumes <div> Variadic macros are supported by nearly all compilers.
the compiler supports variadic macros. Variadic macros are macros of the form: </div> Variadic macros are macros of the form: </div>
<div class="code"> <div class="code">
<pre>#define SOME_MACRO(ZeroOrMoreParameters,...) macro expansion possible specifying __VA_ARGS__</pre> <pre>#define SOME_MACRO(ZeroOrMoreParameters,...) macro expansion possible specifying __VA_ARGS__</pre>
</div> </div>
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</div> </div>
<u> <span style="font-weight: bold;">Preprocessor Library Support<br> <u> <span style="font-weight: bold;">Preprocessor Library Support<br>
</span></u> </span></u>
<div>The library assumes support for variadic macros for all <div>The library requires support for variadic macros for all
compilers using the library.<br> compilers using the library. This usually means that compilation
at the C level is C99 or higher and that compilation at the C++
level is C++11 or higher. Many C++ compilers support variadic
macros at the C++98/C++03 level as long as strict compliance is
not turned on for those compilers at that level. In particular
both the gcc and clang compilers will support variadic macros at
the C++98/C++03 levels as long as strict ANSI compliance is not
turned on at that level. For those compilers this largely means
that the <code>-pedantic</code> or <code>-pedantic-errors</code>
option is not used at the C++98/C++03 level of compilation. Boost
C++ is deprecating compiling Boost libraries at the C++98/C++03
level, so if you must still use this library at that level be
aware of these aforementioned caveats.<br>
<br> <br>
<a name="vmvcquirk"></a>Visual C++'s default preprocessor has a few <a name="vmvcquirk"></a>Visual C++'s default preprocessor has a
quirks related to variadic macros which require the end-user to code few quirks related to variadic macros which require the end-user
slightly differently. When Visual C++'s default preprocessor is being to code slightly differently. When Visual C++'s default
used BOOST_PP_VARIADICS_MSVC is 1, otherwise it is 0. In this way the preprocessor is being used BOOST_PP_VARIADICS_MSVC is 1, otherwise
end-user can test for the presence of Visual C++'s default preprocessor it is 0. In this way the end-user can test for the presence of
and code accordingly.<br> Visual C++'s default preprocessor and code accordingly.<br>
<br> <br>
Support for working with variadic data is largely centered on Support for working with variadic data is largely centered on
being able to convert variadic data to other library data types, being able to convert variadic data to other library data types,
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of the ability of the variadic parameters to encompass a variable of the ability of the variadic parameters to encompass a variable
number of arguments. The library has functionality which can know number of arguments. The library has functionality which can know
the number of variadic arguments passed when invoking a variadic the number of variadic arguments passed when invoking a variadic
macro. This allows the same variadic macro to work macro. This allows the same variadic macro to work with different
with different numbers of parameters, therefore providing more numbers of parameters, therefore providing more than one
than one syntactical equivalent for the same macro name.<br> syntactical equivalent for the same macro name.<br>
<br> <br>
The macros in the library which offer this enhanced functionality The macros in the library which offer this enhanced functionality
are all centered on <i>tuple</i> manipulation. With variadic are all centered on <i>tuple</i> manipulation. With variadic
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<div>An array as a preprocessor data type is a two-element tuple <div>An array as a preprocessor data type is a two-element tuple
where the first element is the array size and the second element where the first element is the array size and the second element
is a tuple which constitutes the array data. Because a tuple knows is a tuple which constitutes the array data. Because a tuple knows
its own size because of compiler support for variadic macros, there is its own size because of compiler support for variadic macros,
no reason to use the array preprocessor data type as opposed to there is no reason to use the array preprocessor data type as
the tuple preprocessor data type; the tuple data type now has all opposed to the tuple preprocessor data type; the tuple data type
of the functionality which the array data type has and is now has all of the functionality which the array data type has and
syntactically easier to use. The preprocessor array data type is is syntactically easier to use. The preprocessor array data type
essentially obsolete for modern C++ compilers.</div> is essentially obsolete for modern C++ compilers.</div>
<u style="font-weight: bold;">Using Variadic Data</u> <u style="font-weight: bold;">Using Variadic Data</u>
<div>Variadic data exists in the form of comma-separated <div>Variadic data exists in the form of comma-separated
preprocessor tokens. This is the case whether the variadic data preprocessor tokens. This is the case whether the variadic data
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to work and may fail.<br> to work and may fail.<br>
</span><br> </span><br>
This occurs because of a preprocessor weakness in a number of This occurs because of a preprocessor weakness in a number of
compilers, currently most notably Visual C++'s default preprocessor. compilers, currently most notably Visual C++'s default
Even passing variadic data as arguments to a non-variadic macro, when preprocessor. Even passing variadic data as arguments to a
it is not represented in the form of&nbsp; __VA_ARGS__, may fail with non-variadic macro, when it is not represented in the form
certain compilers.<br> of&nbsp; __VA_ARGS__, may fail with certain compilers.<br>
<br> <br>
What follows are very simple examples, showing how variadic data What follows are very simple examples, showing how variadic data
can be passed to a non-variadic macro.<br> can be passed to a non-variadic macro.<br>