1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Annex: No 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. Boost.ScopeExit 1.1.0"> 8<link rel="up" href="../index.html" title="Chapter 1. Boost.ScopeExit 1.1.0"> 9<link rel="prev" href="alternatives.html" title="Annex: Alternatives"> 10<link rel="next" href="../reference.html" title="Reference"> 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="alternatives.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="../reference.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="scope_exit.no_variadic_macros"></a><a class="link" href="no_variadic_macros.html" title="Annex: No Variadic Macros">Annex: No Variadic Macros</a> 28</h2></div></div></div> 29<p> 30 This section presents an alternative syntax for compilers without variadic 31 macro support. 32 </p> 33<h4> 34<a name="scope_exit.no_variadic_macros.h0"></a> 35 <span class="phrase"><a name="scope_exit.no_variadic_macros.sequence_syntax"></a></span><a class="link" href="no_variadic_macros.html#scope_exit.no_variadic_macros.sequence_syntax">Sequence 36 Syntax</a> 37 </h4> 38<p> 39 Most modern compilers support variadic macros (notably, these include GCC, 40 MSVC, and all C++11 compilers). <a href="#ftn.scope_exit.no_variadic_macros.f0" class="footnote" name="scope_exit.no_variadic_macros.f0"><sup class="footnote">[10]</sup></a> However, in the rare case that programmers need to use this library 41 on a complier without variaidc macros, this library also allows to specify 42 the capture list using a <a href="http://www.boost.org/libs/preprocessor" target="_top">Boost.Preprocessor</a> 43 sequence where tokens are separated by round parenthesis <code class="computeroutput"><span class="special">()</span></code>: 44 </p> 45<pre class="programlisting"><span class="special">(</span><span class="identifier">capture1</span><span class="special">)</span> <span class="special">(</span><span class="identifier">capture2</span><span class="special">)</span> <span class="special">...</span> <span class="comment">// All compilers.</span> 46</pre> 47<p> 48 Instead of the comma-separated list that we have seen so far which requires 49 variadic macros: 50 </p> 51<pre class="programlisting"><span class="identifier">capture1</span><span class="special">,</span> <span class="identifier">capture2</span><span class="special">,</span> <span class="special">...</span> <span class="comment">// Only compilers with variadic macros.</span> 52</pre> 53<p> 54 For example, the following syntax is accepted on all compilers with and without 55 variadic macros (see also <a href="../../../test/world_seq.cpp" target="_top"><code class="literal">world_seq.cpp</code></a> 56 and <a href="../../../test/world.cpp" target="_top"><code class="literal">world.cpp</code></a>): 57 </p> 58<div class="informaltable"><table class="table"> 59<colgroup> 60<col> 61<col> 62</colgroup> 63<thead><tr> 64<th> 65 <p> 66 Boost.Preprocessor Sequence (All Compilers) 67 </p> 68 </th> 69<th> 70 <p> 71 Comma-Separated List (Variadic Macros Only) 72 </p> 73 </th> 74</tr></thead> 75<tbody><tr> 76<td> 77 <p> 78</p> 79<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">void</span> <span class="identifier">world</span><span class="special">::</span><span class="identifier">add_person</span><span class="special">(</span><span class="identifier">person</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span> 80 <span class="keyword">bool</span> <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span> 81 82 <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span> <span class="comment">// (1) direct action</span> 83 <span class="comment">// Following block is executed when the enclosing scope exits.</span> 84 <span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(</span> <span class="special">(&</span><span class="identifier">commit</span><span class="special">)</span> <span class="special">(&</span><span class="identifier">persons_</span><span class="special">)</span> <span class="special">)</span> <span class="special">{</span> 85 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">commit</span><span class="special">)</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span> <span class="comment">// (2) rollback action</span> 86 <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span> 87 88 <span class="comment">// ... // (3) other operations</span> 89 90 <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span> <span class="comment">// (4) disable rollback actions</span> 91<span class="special">}</span> 92</pre> 93<p> 94 </p> 95 </td> 96<td> 97 <p> 98</p> 99<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">void</span> <span class="identifier">world</span><span class="special">::</span><span class="identifier">add_person</span><span class="special">(</span><span class="identifier">person</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span> 100 <span class="keyword">bool</span> <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span> 101 102 <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span> <span class="comment">// (1) direct action</span> 103 <span class="comment">// Following block is executed when the enclosing scope exits.</span> 104 <span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(&</span><span class="identifier">commit</span><span class="special">,</span> <span class="special">&</span><span class="identifier">persons_</span><span class="special">)</span> <span class="special">{</span> 105 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">commit</span><span class="special">)</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span> <span class="comment">// (2) rollback action</span> 106 <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span> 107 108 <span class="comment">// ... // (3) other operations</span> 109 110 <span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span> <span class="comment">// (4) disable rollback actions</span> 111<span class="special">}</span> 112</pre> 113<p> 114 </p> 115 </td> 116</tr></tbody> 117</table></div> 118<p> 119 Note how the same macros accept both syntaxes on compilers with variadic macros 120 and only the <a href="http://www.boost.org/libs/preprocessor" target="_top">Boost.Preprocessor</a> 121 sequence syntax on compilers without variadic macros. Older versions of this 122 library used to only support the <a href="http://www.boost.org/libs/preprocessor" target="_top">Boost.Preprocessor</a> 123 sequence syntax so this syntax is supported also for backward compatibility. 124 However, in the current version of this library and on compilers with variadic 125 macros, the comma-separated syntax is preferred because it is more readable. 126 </p> 127<p> 128 Finally, an empty capture list is always specified using <code class="computeroutput"><span class="keyword">void</span></code> 129 on compilers with and without variaidc macros (see also <a href="../../../test/world_void.cpp" target="_top"><code class="literal">world_void.cpp</code></a>): 130 </p> 131<p> 132</p> 133<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">world_t</span> <span class="special">{</span> 134 <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">person</span><span class="special">></span> <span class="identifier">persons</span><span class="special">;</span> 135 <span class="keyword">bool</span> <span class="identifier">commit</span><span class="special">;</span> 136<span class="special">}</span> <span class="identifier">world</span><span class="special">;</span> <span class="comment">// Global variable.</span> 137 138<span class="keyword">void</span> <span class="identifier">add_person</span><span class="special">(</span><span class="identifier">person</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a_person</span><span class="special">)</span> <span class="special">{</span> 139 <span class="identifier">world</span><span class="special">.</span><span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">false</span><span class="special">;</span> 140 <span class="identifier">world</span><span class="special">.</span><span class="identifier">persons</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">a_person</span><span class="special">);</span> 141 142 <span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// No captures.</span> 143 <span class="keyword">if</span><span class="special">(!</span><span class="identifier">world</span><span class="special">.</span><span class="identifier">commit</span><span class="special">)</span> <span class="identifier">world</span><span class="special">.</span><span class="identifier">persons</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span> 144 <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span> 145 146 <span class="comment">// ...</span> 147 148 <span class="identifier">world</span><span class="special">.</span><span class="identifier">commit</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">;</span> 149<span class="special">}</span> 150</pre> 151<p> 152 </p> 153<h4> 154<a name="scope_exit.no_variadic_macros.h1"></a> 155 <span class="phrase"><a name="scope_exit.no_variadic_macros.examples"></a></span><a class="link" href="no_variadic_macros.html#scope_exit.no_variadic_macros.examples">Examples</a> 156 </h4> 157<p> 158 For reference, the following is a list of most of the examples presented in 159 this documentation reprogrammed using the <a href="http://www.boost.org/libs/preprocessor" target="_top">Boost.Preprocessor</a> 160 sequence syntax instead of comma-separated lists (in alphabetic order): 161 </p> 162<div class="informaltable"><table class="table"> 163<colgroup><col></colgroup> 164<thead><tr><th> 165 <p> 166 Files 167 </p> 168 </th></tr></thead> 169<tbody> 170<tr><td> 171 <p> 172 <a href="../../../test/same_line_seq.cpp" target="_top"><code class="literal">same_line_seq.cpp</code></a> 173 </p> 174 </td></tr> 175<tr><td> 176 <p> 177 <a href="../../../example/scope_guard_seq.cpp" target="_top"><code class="literal">scope_guard_seq.cpp</code></a> 178 </p> 179 </td></tr> 180<tr><td> 181 <p> 182 <a href="../../../example/try_catch_seq.cpp" target="_top"><code class="literal">try_catch_seq.cpp</code></a> 183 </p> 184 </td></tr> 185<tr><td> 186 <p> 187 <a href="../../../test/world_checkpoint_all_seq.cpp" target="_top"><code class="literal">world_checkpoint_all_seq.cpp</code></a> 188 </p> 189 </td></tr> 190<tr><td> 191 <p> 192 <a href="../../../test/world_checkpoint_seq.cpp" target="_top"><code class="literal">world_checkpoint_seq.cpp</code></a> 193 </p> 194 </td></tr> 195<tr><td> 196 <p> 197 <a href="../../../test/world_this_seq.cpp" target="_top"><code class="literal">world_this_seq.cpp</code></a> 198 </p> 199 </td></tr> 200<tr><td> 201 <p> 202 <a href="../../../test/world_tpl_seq.cpp" target="_top"><code class="literal">world_tpl_seq.cpp</code></a> 203 </p> 204 </td></tr> 205</tbody> 206</table></div> 207<div class="footnotes"> 208<br><hr style="width:100; text-align:left;margin-left: 0"> 209<div id="ftn.scope_exit.no_variadic_macros.f0" class="footnote"><p><a href="#scope_exit.no_variadic_macros.f0" class="para"><sup class="para">[10] </sup></a> 210 A C++ compiler does not support variadic macros if the <a href="http://www.boost.org/libs/config" target="_top">Boost.Config</a> 211 macro <code class="computeroutput"><span class="identifier">BOOST_NO_CXX11_VARIADIC_MACROS</span></code> 212 is defined for that compiler. 213 </p></div> 214</div> 215</div> 216<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 217<td align="left"></td> 218<td align="right"><div class="copyright-footer">Copyright © 2006-2012 Alexander Nasonov, Lorenzo Caminiti<p> 219 Distributed under the Boost Software License, Version 1.0 (see accompanying 220 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>) 221 </p> 222</div></td> 223</tr></table> 224<hr> 225<div class="spirit-nav"> 226<a accesskey="p" href="alternatives.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="../reference.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 227</div> 228</body> 229</html> 230
