forked from boostorg/preprocessor
Add a topic on "emptiness"
This commit is contained in:
Edward Diener
@ -15,6 +15,7 @@
|
|||||||
<li><a href="topics/file_iteration.html">file iteration</a></li>
|
<li><a href="topics/file_iteration.html">file iteration</a></li>
|
||||||
<li><a href="topics/evaluated_slots.html">evaluated slots</a></li>
|
<li><a href="topics/evaluated_slots.html">evaluated slots</a></li>
|
||||||
<li><a href="topics/variadic_macros.html">variadic macros</a></li>
|
<li><a href="topics/variadic_macros.html">variadic macros</a></li>
|
||||||
|
<li><a href="topics/emptiness.html">emptiness</a></li>
|
||||||
</ul>
|
</ul>
|
||||||
<!--
|
<!--
|
||||||
<EFBFBD> Copyright Housemarque Oy 2002
|
<EFBFBD> Copyright Housemarque Oy 2002
|
||||||
|
|||||||
97
doc/topics/emptiness.html
Normal file
97
doc/topics/emptiness.html
Normal file
@ -0,0 +1,97 @@
|
|||||||
|
<html>
|
||||||
|
<head>
|
||||||
|
<meta content="text/html; charset=windows-1252" http-equiv="content-type">
|
||||||
|
<title>emptiness.html</title>
|
||||||
|
<link rel="stylesheet" type="text/css" href="../styles.css">
|
||||||
|
<style>
|
||||||
|
u { font-weight: normal; text-decoration: none; }
|
||||||
|
</style>
|
||||||
|
</head>
|
||||||
|
<body>
|
||||||
|
<h4>Variadic Macros</h4>
|
||||||
|
<div> Variadic macros are supported by a number of compilers. They are
|
||||||
|
macros of the form: </div>
|
||||||
|
<div class="code">
|
||||||
|
<pre>#define SOME_MACRO(ZeroOrMoreParameters,...) macro expansion possible specifying __VA_ARGS__</pre>
|
||||||
|
</div>
|
||||||
|
<div> The '...' in the parameter list represents the variadic data when the
|
||||||
|
macro is invoked and the __VA_ARGS__ in the expansion represents the
|
||||||
|
variadic data in the expansion of the macro. Variadic data is of the form
|
||||||
|
of 1 or more preprocessor tokens separated by commas.<br>
|
||||||
|
<br>
|
||||||
|
The '...' must be the last parameter in the macro definition and there may
|
||||||
|
be 0 or more non-variadic parameters preceding it.<br>
|
||||||
|
<br>
|
||||||
|
In the expansion of the macro __VA_ARGS__ may be specified 0 or more times
|
||||||
|
to represent the variadic data. The variadic data in the expansion is a
|
||||||
|
comma separated list of preprocessor tokens representing the variadic data
|
||||||
|
which the invoker of the macro enters as the last arguments to the macro.<br>
|
||||||
|
</div>
|
||||||
|
<h4>Example<u> - Creating and invoking a variadic macro.</u></h4>
|
||||||
|
<div class="code">
|
||||||
|
<pre>#define INITIALIZE_INT_ARRAY(array_name,...) \ <br> static int array_name[] = { __VA_ARGS__ }; \ <br> /**/<br><br> INITIALIZE_INT_ARRAY(myname,45,789,33510,9346,2)</pre>
|
||||||
|
</div>
|
||||||
|
<u> <span style="font-weight: bold;">Preprocessor
|
||||||
|
Library Support<br>
|
||||||
|
</span></u>
|
||||||
|
<div>The library offers support for variadic macros for those
|
||||||
|
compilers
|
||||||
|
which support the feature. The library can automatically detect whether
|
||||||
|
a compiler supports variadic macros and sets the macro
|
||||||
|
BOOST_PP_VARIADICS accordingly to 1 if the compiler supports variadic
|
||||||
|
macros or 0 if the compiler does not support variadic macros.<br>
|
||||||
|
<br>
|
||||||
|
The end-user can #define BOOST_PP_VARIADICS to 1 or 0 himself in a
|
||||||
|
translation unit, before including any preprocessor header files, to
|
||||||
|
prevent the library from attempting to detect whether the compiler
|
||||||
|
supports variadic macros. This has the effect of manually turning on or
|
||||||
|
off variadic macro support in the library. Of course if one manually
|
||||||
|
turns on variadic macro support in the library, and one's compiler does
|
||||||
|
not support variadic macros, functionality in the library which uses
|
||||||
|
variadic macros will fail with error messages from the compiler.<br>
|
||||||
|
<br>
|
||||||
|
When BOOST_PP_VARIADICS is 1, the library offers some extended
|
||||||
|
functionality
|
||||||
|
by using variadic macros, and also offers extended support for working
|
||||||
|
with variadic data.<br><br>
|
||||||
|
<a name="vmvcquirk"></a>Visual C++ has a
|
||||||
|
few quirks related to variadic macros which require the end-user to code
|
||||||
|
slightly differently. When BOOST_PP_VARIADICS is 1 and Visual C++ is the
|
||||||
|
compiler BOOST_PP_VARIADICS_MSVC is 1, else when BOOST_PP_VARIADICS is 1
|
||||||
|
and Visual C++ is not the compiler BOOST_PP_VARIADICS_MSVC is 0. When
|
||||||
|
BOOST_PP_VARIADICS is 0 then BOOST_PP_VARIADICS_MSVC is not defined.
|
||||||
|
In this way the end-user, when using variadic macros, can test for the
|
||||||
|
presence of Visual C++ as the compiler and code accordingly.<br>
|
||||||
|
<br>
|
||||||
|
Support for working with variadic
|
||||||
|
data is largely centered on being able to convert variadic data to
|
||||||
|
other library data types, since the
|
||||||
|
functionality for working with those Boost preprocessor library data
|
||||||
|
types is much greater than that for working with variadic data directly.<br>
|
||||||
|
</div>
|
||||||
|
<b>See</b> <b>Also</b><br>
|
||||||
|
<ul>
|
||||||
|
<li><a href="../ref/variadics.html">BOOST_PP_VARIADICS</a></li>
|
||||||
|
<li><a href="../headers/tuple.html">Tuple Macros</a><br>
|
||||||
|
</li>
|
||||||
|
<li><a href="../headers/variadic.html">Variadic
|
||||||
|
Macros<br>
|
||||||
|
</a></li>
|
||||||
|
<li><a href="../ref/array_enum.html">BOOST_PP_ARRAY_ENUM</a></li>
|
||||||
|
<li><a href="../ref/list_enum_r.html">BOOST_PP_LIST_ENUM</a></li>
|
||||||
|
<li><a href="../ref/seq_enum.html">BOOST_PP_SEQ_ENUM</a></li>
|
||||||
|
<li><a href="../ref/tuple_enum.html">BOOST_PP_TUPLE_ENUM</a></li>
|
||||||
|
<li><a href="../ref/overload.html">BOOST_PP_OVERLOAD</a></li>
|
||||||
|
</ul>
|
||||||
|
<hr size="1">
|
||||||
|
<div style="margin-left: 0px;"> <i><EFBFBD> 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>
|
||||||
Reference in New Issue
Block a user