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<title>Annex: No Variadic Macros</title>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_localfunction.no_variadic_macros"></a><a class="link" href="no_variadic_macros.html" title="Annex: No Variadic Macros">Annex: No Variadic
Macros</a>
</h2></div></div></div>
<p>
This section illustrates an alternative syntax for compilers without variadic
macro support.
</p>
<h4>
<a name="boost_localfunction.no_variadic_macros.h0"></a>
<span class="phrase"><a name="boost_localfunction.no_variadic_macros.sequence_syntax"></a></span><a class="link" href="no_variadic_macros.html#boost_localfunction.no_variadic_macros.sequence_syntax">Sequence Syntax</a>
</h4>
<p>
Most modern compilers support <a href="http://en.wikipedia.org/wiki/Variadic_macro" target="_top">variaid
macros</a> (notably, these include GCC, MSVC, and all <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a>
compilers). However, in the rare case that programmers need to use this library
on a compiler without variadic macros, this library also allows to specify
its macro parameters using a <a href="http://www.boost.org/libs/preprocessor" target="_top">Boost.Preprocessor</a>
sequence where tokens are separated by round parenthesis <code class="computeroutput"><span class="special">()</span></code>:
</p>
<pre class="programlisting"><span class="special">(</span><span class="identifier">token1</span><span class="special">)</span> <span class="special">(</span><span class="identifier">token2</span><span class="special">)</span> <span class="special">...</span> <span class="comment">// All compilers.</span>
</pre>
<p>
Instead of the comma-separated list that we have seen so far which requires
variadic macros:
</p>
<pre class="programlisting"><span class="identifier">token1</span><span class="special">,</span> <span class="identifier">token2</span><span class="special">,</span> <span class="special">...</span> <span class="comment">// Only compilers with varidic macros.</span>
</pre>
<p>
For example, the following syntax is accepted on all compilers with and without
variadic macros (see also <a href="../../../test/add_seq.cpp" target="_top"><code class="literal">add_seq.cpp</code></a>):
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span>
<span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span>
<span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">)</span> <span class="special">(</span><span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">)</span> <span class="special">(</span><span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">)</span> <span class="special">{</span>
<span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span>
<span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span>
<span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
<span class="keyword">int</span> <span class="identifier">nums</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span><span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">add</span><span class="special">);</span>
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">sum</span> <span class="special">==</span> <span class="number">60</span><span class="special">);</span>
<span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
However, on compilers with variadic macros the comma-separated syntax we have
seen so far is preferred because more readable (see also <a href="../../../test/add.cpp" target="_top"><code class="literal">add.cpp</code></a>):
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Some local scope.</span>
<span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> <span class="comment">// Variables in scope to bind.</span>
<span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">,</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">{</span>
<span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span>
<span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span>
<span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// Call the local function.</span>
<span class="keyword">int</span> <span class="identifier">nums</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span><span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">add</span><span class="special">);</span> <span class="comment">// Pass it to an algorithm.</span>
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">sum</span> <span class="special">==</span> <span class="number">60</span><span class="special">);</span> <span class="comment">// Assert final summation value.</span>
<span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
Note that the same macros accept both syntaxes on compilers with variadic macros
and only the sequence syntax on compilers without variadic macros. Finally,
an empty local function parameter list is always specified using <code class="computeroutput"><span class="keyword">void</span></code> on compilers with and without variadic
macros:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// No parameter.</span>
<span class="keyword">return</span> <span class="number">10</span><span class="special">;</span>
<span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">ten</span><span class="special">)</span>
<span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">ten</span><span class="special">()</span> <span class="special">==</span> <span class="number">10</span><span class="special">);</span>
</pre>
<p>
</p>
<h4>
<a name="boost_localfunction.no_variadic_macros.h1"></a>
<span class="phrase"><a name="boost_localfunction.no_variadic_macros.examples"></a></span><a class="link" href="no_variadic_macros.html#boost_localfunction.no_variadic_macros.examples">Examples</a>
</h4>
<p>
For reference, the following is a list of most of the examples presented in
this documentation reprogrammed using the sequence syntax instead of the comma-separated
syntax (in alphabetic order):
</p>
<div class="informaltable"><table class="table">
<colgroup><col></colgroup>
<thead><tr><th>
<p>
Files
</p>
</th></tr></thead>
<tbody>
<tr><td>
<p>
<a href="../../../test/add_classifiers_seq.cpp" target="_top"><code class="literal">add_classifiers_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/add_default_seq.cpp" target="_top"><code class="literal">add_default_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/add_except_seq.cpp" target="_top"><code class="literal">add_except_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/add_inline_seq.cpp" target="_top"><code class="literal">add_inline_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/add_params_only_seq.cpp" target="_top"><code class="literal">add_params_only_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/add_template_seq.cpp" target="_top"><code class="literal">add_template_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/add_this_seq.cpp" target="_top"><code class="literal">add_this_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/add_typed_seq.cpp" target="_top"><code class="literal">add_typed_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/add_with_default_seq.cpp" target="_top"><code class="literal">add_with_default_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/all_decl_seq.cpp" target="_top"><code class="literal">all_decl_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/factorial_seq.cpp" target="_top"><code class="literal">factorial_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/macro_commas_seq.cpp" target="_top"><code class="literal">macro_commas_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/nesting_seq.cpp" target="_top"><code class="literal">nesting_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/overload_seq.cpp" target="_top"><code class="literal">overload_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/return_assign_seq.cpp" target="_top"><code class="literal">return_assign_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/return_derivative_seq.cpp" target="_top"><code class="literal">return_derivative_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/return_inc_seq.cpp" target="_top"><code class="literal">return_inc_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/return_setget_seq.cpp" target="_top"><code class="literal">return_setget_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/return_this_seq.cpp" target="_top"><code class="literal">return_this_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/same_line_seq.cpp" target="_top"><code class="literal">same_line_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/transform_seq.cpp" target="_top"><code class="literal">transform_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/typeof_seq.cpp" target="_top"><code class="literal">typeof_seq.cpp</code></a>
</p>
</td></tr>
<tr><td>
<p>
<a href="../../../test/typeof_template_seq.cpp" target="_top"><code class="literal">typeof_template_seq.cpp</code></a>
</p>
</td></tr>
</tbody>
</table></div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2009-2012 Lorenzo
Caminiti<p>
Distributed under the Boost Software License, Version 1.0 (see accompanying
file LICENSE_1_0.txt or a copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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