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Updated for VC++ quirks and overload code example.

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Edward Diener
2016-04-11 14:24:38 -04:00
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<html> <html>
<head> <head>
<meta content="text/html; charset=windows-1252" http-equiv="content-type">
<title>BOOST_PP_OVERLOAD</title> <title>BOOST_PP_OVERLOAD</title>
<link rel="stylesheet" type="text/css" href="../styles.css"> <link rel="stylesheet" type="text/css" href="../styles.css">
</head> </head>
<body> <body>
<div style="margin-left: 0px;"> The <b>BOOST_PP_OVERLOAD</b> variadic macro expands to the name of a non-variadic macro having a given number of parameters.<br> <div style="margin-left: 0px;"> The <b>BOOST_PP_OVERLOAD</b> variadic
macro expands to the name of a non-variadic macro having a given number of
parameters.<br>
</div> </div>
<h4>Usage</h4> <h4>Usage</h4>
<div class="code"> <b>BOOST_PP_OVERLOAD</b>(<i>prefix</i>,...) <a href="../topics/variadic_macros.html#VNotation" target="_self"><sup>(v)</sup></a><br> <div class="code"> <b>BOOST_PP_OVERLOAD</b>(<i>prefix</i>,...) <a href="../topics/variadic_macros.html#VNotation"
target="_self"><sup>(v)</sup></a><br>
</div> </div>
<h4>Arguments</h4> <h4>Arguments</h4>
<dl> <dl>
<dt>prefix<br> <dt>prefix<br>
</dt><dd> </dt>
The prefix of the non-variadic macro name. <dd> The prefix of the non-variadic macro name. </dd>
</dd><dt>...<br> <dt>...<br>
</dt><dd><i> </dt>
Variadic data</i>. The number of variadic data <dd><i> Variadic data</i>. The number of variadic data
elements, as determined by BOOST_PP_VARIADIC_SIZE, is appended to the elements, as determined by BOOST_PP_VARIADIC_SIZE, is appended to the
prefix to form the output non-variadic macro name.<br> prefix to form the output non-variadic macro name.<br>
</dd> </dd>
</dl> </dl>
<h4>Remarks</h4> <h4>Remarks</h4>
<div> This macro creates a macro name which depends on the number of elements of variadic data. It should be used in the form of <br> <div> This macro creates a macro name which depends on the number of
elements of variadic data. It should be used in the form of <br>
BOOST_PP_OVERLOAD(MACRO_NAME_,__VA_ARGS__)(__VA_ARGS__) in order to BOOST_PP_OVERLOAD(MACRO_NAME_,__VA_ARGS__)(__VA_ARGS__) in order to
call a non-variadic macro taking a given number of variadic data call a non-variadic macro taking a given number of variadic data
elements as non-variadic arguments. In this way one can invoke a elements as non-variadic arguments. In this way one can invoke a
variadic macro with a variable number of parameters which calls one of variadic macro with a variable number of parameters which calls one of
a series of non-variadic macros doing very similar things. a series of non-variadic macros doing very similar things.
</div><b>Requirements</b> </div>
<b>Requirements</b>
<div> <b>Header:</b> &nbsp;<a href="../headers/facilities/overload.html">&lt;boost/preprocessor/facilities/overload.hpp&gt;</a> <div> <b>Header:</b> &nbsp;<a href="../headers/facilities/overload.html">&lt;boost/preprocessor/facilities/overload.hpp&gt;</a>
</div> </div>
<h4>Sample Code</h4> <h4>Sample Code</h4>
<div> <div>
<pre>#include &lt;<a href="../headers/facilities/overload.html">boost/preprocessor/facilities/overload.hpp</a>&gt;<br>#include &lt;<a href="../headers/cat.html">boost/preprocessor/cat.hpp</a>&gt;<br>#include &lt;<a href="../headers/facilities/empty.html">boost/preprocessor/facilities/empty.hpp</a>&gt;<br>#include &lt;<a href="../headers/arithmetic/add.html">boost/preprocessor/arithmetic/add.hpp</a>&gt;<br><br>#define MACRO_1(number) MACRO_2(number,10)<br>#define MACRO_2(number1,number2) <a href="add.html">BOOST_PP_ADD</a>(number1,number2)<br><br>#define MACRO_ADD_NUMBERS(...) <a href="overload.html">BOOST_PP_OVERLOAD</a>(MACRO_,__VA_ARGS__)(__VA_ARGS__)<br><br>// or for Visual C++<br><br>#define MACRO_ADD_NUMBERS(...) \<br> <a href="cat.html">BOOST_PP_CAT</a>(<a href="overload.html">BOOST_PP_OVERLOAD</a>(MACRO_,__VA_ARGS__)(__VA_ARGS__),<a href="empty.html">BOOST_PP_EMPTY</a>())<br><br>MACRO_ADD_NUMBERS(5) // output is 15<br>MACRO_ADD_NUMBERS(3,6) // output is 9<br></pre> <pre>#include &lt;<a href="../headers/facilities/overload.html">boost/preprocessor/facilities/overload.hpp</a>&gt;<br>#include <<a
href="../headers/cat.html">boost/preprocessor/cat.hpp</a>><br>#include <<a href="../headers/facilities/empty.html">boost/preprocessor/facilities/empty.hpp</a>><br>#include <<a
href="../headers/arithmetic/add.html">boost/preprocessor/arithmetic/add.hpp</a>><br><br>#define MACRO_1(number) MACRO_2(number,10)<br>#define MACRO_2(number1,number2) <a
href="add.html">BOOST_PP_ADD</a>(number1,number2)<br><br>#if !BOOST_PP_VARIADICS_MSVC<br><br>#define MACRO_ADD_NUMBERS(...) <a
href="overload.html">BOOST_PP_OVERLOAD</a>(MACRO_,__VA_ARGS__)(__VA_ARGS__)<br><br>#else<br><br>// or for Visual C++<br><br>#define MACRO_ADD_NUMBERS(...) \<br> <a
href="cat.html">BOOST_PP_CAT</a>(<a href="overload.html">BOOST_PP_OVERLOAD</a>(MACRO_,__VA_ARGS__)(__VA_ARGS__),<a
href="empty.html">BOOST_PP_EMPTY</a>())<br><br>#endif<br><br>MACRO_ADD_NUMBERS(5) // output is 15<br>MACRO_ADD_NUMBERS(3,6) // output is 9</pre>
</div> </div>
<hr size="1"> <hr size="1">
<div style="margin-left: 0px;"> <i></i><i><EFBFBD> Copyright Edward Diener 2011,2013</i> </div> <div style="margin-left: 0px;"> <i></i><i><EFBFBD> Copyright Edward Diener 2011,2013,2016</i> </div>
<div style="margin-left: 0px;"> <div style="margin-left: 0px;">
<p><small>Distributed under the Boost Software License, Version 1.0. <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> (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> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
</div> </div>
</body>
</html> </body></html>

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<html> <html>
<head> <head>
<meta content="text/html; charset=windows-1252" http-equiv="content-type">
<title>variadic_macros.html</title> <title>variadic_macros.html</title>
<link rel="stylesheet" type="text/css" href="../styles.css"> <link rel="stylesheet" type="text/css" href="../styles.css">
<style> <style>
@ -8,27 +9,23 @@
</head> </head>
<body> <body>
<h4>Variadic Macros</h4> <h4>Variadic Macros</h4>
<div> Variadic macros are supported by a number of compilers. <div> Variadic macros are supported by a number of compilers. They are
They are macros of the form: </div>
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>
<div> The '...' in the parameter list represents the variadic <div> The '...' in the parameter list represents the variadic data when the
data when the macro is invoked and the __VA_ARGS__ in the expansion macro is invoked and the __VA_ARGS__ in the expansion represents the
represents the variadic data in the expansion of the macro. Variadic variadic data in the expansion of the macro. Variadic data is of the form
data is of the form of 1 or more preprocessor tokens separated by of 1 or more preprocessor tokens separated by commas.<br>
commas.<br>
<br> <br>
The '...' must be the last parameter in the macro definition and there The '...' must be the last parameter in the macro definition and there may
may be 0 or more non-variadic parameters preceding it.<br> be 0 or more non-variadic parameters preceding it.<br>
<br> <br>
In the expansion of the macro __VA_ARGS__ may be specified 0 or more In the expansion of the macro __VA_ARGS__ may be specified 0 or more times
times to represent the variadic data. The variadic data in the to represent the variadic data. The variadic data in the expansion is a
expansion is a comma separated list of preprocessor tokens representing comma separated list of preprocessor tokens representing the variadic data
the variadic data which the invoker of the macro enters as the last which the invoker of the macro enters as the last arguments to the macro.<br>
arguments to the macro.<br>
</div> </div>
<h4>Example<u> - Creating and invoking a variadic macro.</u></h4> <h4>Example<u> - Creating and invoking a variadic macro.</u></h4>
<div class="code"> <div class="code">
@ -56,7 +53,15 @@
When BOOST_PP_VARIADICS is 1, the library offers some extended When BOOST_PP_VARIADICS is 1, the library offers some extended
functionality functionality
by using variadic macros, and also offers extended support for working by using variadic macros, and also offers extended support for working
with variadic data.<br> 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> <br>
Support for working with variadic Support for working with variadic
data is largely centered on being able to convert variadic data to data is largely centered on being able to convert variadic data to
@ -178,7 +183,7 @@
of compilers, currently most notably Visual C++. Even passing variadic of compilers, currently most notably Visual C++. Even passing variadic
data as arguments to a non-variadic macro, when it is not represented data as arguments to a non-variadic macro, when it is not represented
in in
the form of&nbsp; __VA_ARGS__, may fail with certain compilers.<br> the form of<EFBFBD> __VA_ARGS__, may fail with certain compilers.<br>
<br> <br>
What follows are very simple examples, showing how variadic data can be What follows are very simple examples, showing how variadic data can be
passed to a non-variadic macro.<br> passed to a non-variadic macro.<br>
@ -245,12 +250,13 @@ style="font-weight: bold;"><span style="font-family: monospace;"></span></span>i
<hr size="1"> <hr size="1">
<div style="margin-left: 0px;"> <i><EFBFBD> Copyright <div style="margin-left: 0px;"> <i><EFBFBD> Copyright
Edward Diener Edward Diener
2011,2013</i> </div> 2011,2013,2016</i> </div>
<div style="margin-left: 0px;"> <div style="margin-left: 0px;">
<p><small>Distributed under the Boost Software License, <p><small>Distributed under the Boost Software License,
Version 1.0. Version 1.0.
(See accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> (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> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
</div> </div>
</body>
</html>
</body></html>